US20140088159A1

US20140088159A1 - Enzyme and receptor modulation

Info

Publication number: US20140088159A1
Application number: US14/091,522
Authority: US
Inventors: Alan Hastings Drummond; Alan Hornsby Davidson; David Festus Charles Moffat; Alastair David Graham Donald; Stephen John Davies
Original assignee: Chroma Therapeutics Ltd
Current assignee: GlaxoSmithKline Intellectual Property Development Ltd
Priority date: 2008-02-29
Filing date: 2013-11-27
Publication date: 2014-03-27
Also published as: JP2011513289A; US20160151509A1; US9636409B2; WO2009106848A2; EA201001390A1; IL207537A0; ZA201006071B; AU2009219926B2; US20100317865A1; WO2009106848A3; EA019838B1; CA2934402A1; GB0803747D0; CN101959534B; AU2009219926A1; EP2252328A2; MX2010009341A; BRPI0908893A2; IL207537A; KR20100126762A

Abstract

Covalent conjugates of an α,α-disubstituted glycine ester and a modulator of the activity of a target intracellular enzyme or receptor, wherein the ester group of the conjugate is hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid and the α,α-disubstituted glycine ester is conjugated to the modulator at a position remote from the binding interface between the inhibitor and the target enzyme or receptor pass into cells and the active acid hydrolysis product accumulates within the cells.

Description

This invention relates to a general method of increasing or prolonging the activity of a compound which modulates the activity of an intracellular enzyme or receptor by the covalent conjugation of an α,α-disubstituted glycine ester motif to the modulator. The invention also relates to modulators to which an α,α-disubstituted glycine ester motif has been covalently conjugated, and to a method for the identification of such conjugates having superior properties relative to the parent non-conjugated modulator. The invention further relates to the use of modulators containing α,α-disubstituted glycine ester motifs that allow the selective accumulation of amino acid conjugates inside cells of the monocyte-macrophage lineage.

BACKGROUND TO THE INVENTION

Many intracellular enzymes and receptors are targets for pharmaceutically useful drugs which modulate their activities by binding to their active sites. Examples appear in Table 1 below. To reach the target enzymes and receptors, modulator compounds must of course cross the cell membrane from plasma/extracellular fluid. In general, charge neutral modulators cross the cell membrane more easily than charged species. A dynamic equilibrium is then set up whereby the modulator equilibrates between plasma and cell interior. As a result of the equilibrium, the intracellular residence times and concentrations of many modulators of intracellular enzymes and receptors are often very low, especially in cases where the modulator is rapidly cleared from the plasma. The potencies of the modulators are therefore poor despite their high binding affinities for the target enzyme or receptor.
Our International Patent Application WO 2006/117567 discloses a method for increasing the intracellular concentration of a given modulator of an intracellular enzyme or receptor by conjugating thereto an α-amino acid ester motif which is hydrolysed by one or more of the intracellular carboxylesterases hCE-1, hCE-2 and hCE-3. This results in increased potency by prolonging the residency of the modulator inside the cell, and leads to improved pharmacokinetic and pharmacodynamic properties. More consistent exposure and reduced dosing frequencies can be achieved. A further benefit is obtained when the α-amino acid ester motif is conjugated to the modulator such that the drug is targeted to the specific target cells responsible for its therapeutic action, reducing systemic exposure and hence side effects.
The α-amino acid ester conjugates disclosed in International Patent Application WO 2006/117567 are all mono-substituted on the α-carbon. That publication does not suggest that α,α-disubstituted glycine ester conjugates can be hydrolysed by intracellular carboxylesterases. In fact, it appears that the ability of the intracellular carboxyl esterases, principally hCE-1, hCE-2 and hCE-3, to hydrolyse α,α-disubstituted glycine ester has not previously been investigated.

BRIEF DESCRIPTION OF THE INVENTION

This invention is based on the novel finding that conjugates of α,α-disubstituted glycine esters can be hydrolysed by intracellular carboxyl esterases, and thus the methods and benefits described in WO 2006/117567 can also be obtained with such conjugates. Such benefits include intracellular accumulation of the acid hydrolysis product, and in some cases selective accumulation in cells of a particular type. As in the case of WO 2006/117567, the present invention takes advantage of the fact that lipophilic (low polarity or charge neutral) molecules pass through the cell membrane and enter cells relatively easily, and hydrophilic (higher polarity, charged) molecules do not. Hence, if a lipophilic motif is attached to a given modulator, allowing the modulator to enter the cell, and if that motif is converted in the cell to one of higher polarity, it is to be expected that the modulator with the higher polarity motif attached would accumulate within the cell. Providing such a motif is attached to the modulator in a way which does not alter its binding mode with the target enzyme or receptor, the accumulation of modulator with the higher polarity motif attached is therefore expected to result in prolonged and/or increased activity.
As in the case of WO 2006/117567, the present invention makes use of the fact that there are carboxylesterase enzymes within cells, which may be utilised to hydrolyse an α,α-disubstituted glycine ester motif attached to a given modulator to the parent acid. Therefore, a modulator may be administered as a covalent conjugate with an α,α-disubstituted glycine ester, in which form it readily enters the cell where it is hydrolysed efficiently by one or more intracellular carboxylesterases, and the resultant α,α-disubstituted glycine-modulator conjugate accumulates within the cell, increasing overall potency and/or active residence time. It has also been found that by modification of the α,α-disubstituted glycine ester motif or the way in which it is conjugated, modulators can be targeted to monocytes and macrophages. Herein, unless “monocyte” or “monocytes” is specified, the term macrophage or macrophages will be used to denote macrophages (including tumour associated macrophages) and/or monocytes.

DETAILED DESCRIPTION OF THE INVENTION

Hence in one broad aspect the present invention provides a covalent conjugate of an α,α-disubstituted glycine ester and a modulator of the activity of a target intracellular enzyme or receptor, wherein: the ester group of the conjugate is hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid; and the α,α-disubstituted glycine ester is covalently attached to the modulator at a position remote from the binding interface between the modulator and the target enzyme or receptor, and/or is conjugated to the modulator such that the binding mode of the conjugated modulator and the said corresponding acid to the target enzyme or receptor is the same as that of the unconjugated modulator.
Looked at in another way, the invention provides a method of increasing or prolonging the intracellular potency and/or residence time of a modulator of the activity of a target intracellular enzyme or receptor comprising structural modification of the modulator by covalent attachment thereto of an α,α-disubstituted glycine ester at a position remote from the binding interface between the modulator and the target enzyme or receptor, and/or such that the binding mode of the conjugated modulator and the said corresponding acid to the target enzyme or receptor is the same as that of the unconjugated modulator, the ester group of the conjugate being hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid.
By covalently attaching the α,α-disubstituted glycine ester part to the modulator such that the binding mode of the modulator to the target enzyme or receptor is preserved, both the ester conjugate and the corresponding acidic α,α-disubstituted glycine conjugate retain the modulator activity of the parent unconjugated modulator. The absolute enzyme inhibitory potencies or the receptor agonist or antagonist potencies of the ester and acid conjugates need not necessarily be as high as the corresponding potencies of the unconjugated modulator, since intracellular hydrolysis of the ester conjugate to the acid conjugate results in an accumulation of the latter within the cell, and the resultant concentration of the acid conjugate within the cell is higher than that achievable with the unconjugated modulator, thereby compensating for any intrinsically lower potency of the former relative to the latter. It will therefore be apparent that the conjugation strategy of the present invention differs from the traditional “pro-drug” approach. In the traditional “prodrug” approach, the parent modulator would be modified by conversion to a derivative which is processed in vivo to release the original modulator, and it is the release of the original modulator which is responsible for the ultimate activity. In the present strategy, the original modulator is modified so that the eventual activity is the combined result of intracellular activity due to the α,α-disubstituted glycine conjugate of the modulator, and the accumulating α,α-disubstituted glycine conjugate of the modulator. The active species is a conjugate, not the original unconjugated modulator.
As stated, the invention is concerned with modification of modulators of intracellular enzymes or receptors. Although the principle of the invention is of general application, not restricted by the chemical identity of the modulator or the identity of the target enzyme or receptor, it is strongly preferred that the modulator be one that exerts its effect by reversible binding to the target enzyme or receptor, as opposed to those whose effect is due to covalent binding to the target enzyme or receptor.
Since for practical utility the carboxylesterase-hydrolysed conjugate is required to retain the intracellular binding activity of the parent modulator with its target enzyme or receptor, attachment of the ester motif must take account of that requirement, which will be fulfilled if the carboxylesterase-hydrolysable α,α-disubstituted glycine ester motif is attached to the modulator such that the binding mode of the corresponding carboxylesterase hydrolysis product (ie the corresponding acid) to the target is essentially the same as the unconjugated modulator. In general this is achieved by covalent attachment of the carboxylesterase ester motif to the modulator at a position remote from the binding interface between the modulator and the target enzyme or receptor. In this way, the motif is arranged to extend into solvent, rather than potentially interfering with the binding mode.
In addition, the α,α-disubstituted glycine ester motif obviously must be a substrate for the carboxylesterase if the former is to be hydrolysed by the latter within the cell. The ability of intracellular carboxylesterases appears not to depend on very strict structural requirements of the α,α-disubstituted glycine ester substrate. Hence most modes of covalent conjugation of the α,α-disubstituted glycine ester motif to a modulator will allow hydrolysis. Attachment by a flexible linker chain will usually be how this is achieved.
It will be appreciated that any chemical modification of a drug may subtly alter its binding geometry, and the chemistry strategy for linkage of the α,α-disubstituted glycine ester carboxylesterase motif may introduce additional binding interactions with the target, or may substitute for one or more such interactions. Hence the requirement that the hydrolysed conjugate's binding mode to the target is the same as the unconjugated modulator is to be interpreted as requiring that there is no significant perturbation of the binding mode, in other words that the binding mode is essentially the same as that of the unconjugated modulator. When the requirement is met, the main binding characteristics of the parent modulator are retained, and the modified and unmodified modulators have an overall common set of binding characteristics. The “same binding mode” and “remote attachment” viewpoints are similar because, as stated above, the usual way of achieving the “same binding mode” requirement is to attach the carboxylesterase motif at a point in the modulator molecule which is remote from the binding interface between the inhibitor and the target enzyme or receptor. However, it should be noted that these requirements do not imply that the conjugate and/or its corresponding acid must have the same in vitro or in vivo modulatory potency as the parent modulator. In general, however, it is preferred that the esterase-hydrolysed carboxylic acid has a potency in an in vitro enzyme- or receptor-binding assay no less than one tenth of the potency of the parent modulator in that assay, and that the ester has a potency in a cellular activity assay at least as high as that of the parent modulator in the same assay. Although traditional medicinal chemistry methods of mapping structure-activity relationships are perfectly capable of identifying an attachment strategy to meet the foregoing “same binding mode” and “remote attachment” requirements, modern techniques such as NMR and X-ray crystallography have advanced to the point where it is very common for the binding mode of a known modulator of an enzyme or receptor to be known, or determinable. Such information is in the vast majority of cases in the public domain, or can be modelled using computer based modelling methods, such as ligand docking and homology modelling, based on the known binding modes of structurally similar modulators, or the known structure of the active site of the target enzyme or receptor. With knowledge of the binding mode of the modulator obtained by these techniques, a suitable location for attachment of the carboxylesterase ester motif may be identified, usually (as stated above) at a point on the modulator which is remote from the binding interface between the inhibitor and the target enzyme or receptor.
Intracellular carboxylesterase enzymes capable of hydrolysing the ester group of the conjugated alpha amino acid to the corresponding acid include the three known human carboxylesterase (“hCE”) enzyme isotypes hCE-1 (also known as CES-1), hCE-2 (also known as CES-2) and hCE-3 (Drug Disc. Today 2005, 10, 313-325). Although these are considered to be the main enzymes other carboxylesterase enzymes such as biphenylhydrolase (BPH) may also have a role in hydrolysing the conjugates.
The broken cell assay described below is a simple method of confirming that a given conjugate of modulator and α,α-disubstituted glycine ester, or a given α,α-disubstituted glycine ester to be assessed as a possible carboxylesterase ester motif, is hydrolysed as required. These enzymes can also be readily expressed using recombinant techniques, and the recombinant enzymes may be used to determine or confirm that hydrolysis occurs.
It is a feature of the invention that the desired conjugate retains the covalently linked α,α-disubstituted glycine acid motif when hydrolysed by the carboxylesterase(s) within the cell, since it is the polar carboxyl group of that motif which prevents or reduces clearance of the hydrolysed conjugate from the cell, and thereby contributes to its accumulation within the cell. Indeed, the cellular potency of the modified modulator is predominantly due to the accumulation of the acid and its modulation of the activity of the target (although the unhydrolysed ester also exerts its activity on the target for so long as it remains unhydrolysed). Since cells in general contain several types of peptidase enzymes, it is preferable that the conjugate, or more especially the hydrolysed conjugate (the corresponding acid), is not a substrate for such peptidases. In particular, it is strongly preferred that the α,α-disubstituted glycine ester group should not be the C-terminal element of a dipeptide motif in the conjugate. However, apart from that limitation on the mode of covalent attachment, the α,α-disubstituted glycine ester group may be covalently attached to the modulator via its amino group or via its one of the α-substituents. In some cases the modulator will have a convenient point of attachment for the carboxylesterase ester motif, and in other cases a synthetic strategy will have to be devised for its attachment.
It has been found that cells that only express the carboxylesterases hCE-2, and/or hCE-3 and recombinant forms of these enzymes will only hydrolyse α,α-disubstituted glycine esters to their resultant acids if the amino nitrogen of the α,α-disubstituted glycine ester is either unsubstituted or is directly linked to a carbonyl group (ie the amino group forms part of an amide motif), whereas cells containing hCE-1 (ie macrophages), or recombinant hCE-1, can hydrolyse α,α-disubstituted glycine esters with a wide range of groups on the nitrogen. This selectivity requirement of hCE-2 and hCE-3 can be turned to advantage where it is required that the modulator should target enzymes or receptors in certain cell types only. The relative amounts of these three carboxylesterase enzymes vary between cell types (see FIG. 1 of WO 2006/117567 and database at http:/symatlas.gnf.org/SymAtlas (note that in this database hCE3/CES3 is referred to by the symbol FLJ21736)). If the modulator is intended to act only in cell types where hCE-1 is found, attachment of the α,α-disubstituted glycine ester carboxylesterase ester motif in such a way that the amino group is not directly attached to a carbonyl, results in the hydrolysed modulator conjugate accumulating preferentially in cells with effective concentrations of hCE-1. Stated in another way, specific accumulation of the acid derived from the modulator conjugate in hCE-1 expressing cells can be achieved by linking the amino acid ester motif to the modulator in such a way that the nitrogen atom of the amino acid ester is not linked directly to a carbonyl, or is left unsubstituted.
Macrophages are known to play a key role in inflammatory disorders through the release of cytokines in particular TNFα and IL-1 (van Roon et al Arthritis and Rheumatism, 2003, 1229-1238). In rheumatoid arthritis they are major contributors to joint inflammation and joint destruction (Conell in N. Eng J. Med. 2004, 350, 2591-2602). Macrophages are also involved in tumour growth and development (Naldini and Carraro in Curr Drug Targets Inflamm Allergy, 2005, 3-8). Hence agents that selectively target macrophage cells could be of value in the treatment of cancer, inflammation and autoimmune disease. Targeting specific cell types would be expected to lead to reduced side-effects. The present invention enables a method of targeting modulators to macrophages, which is based on the above observation that the way in which the α,α-disubstituted glycine ester carboxylesterase ester motif is linked to the modulator determines whether it is hydrolysed by specific carboxylesterases, and hence whether or not the resultant acid accumulates in different cell types.
Specifically, as disclosed in WO 2006/117567, it has been found that macrophages contain the human carboxylesterase hCE-1 whereas other cell types do not. In the conjugates of the invention, when the nitrogen of the ester motif is substituted but not directly bonded to a carbonyl group moiety the ester will only be hydrolysed by hCE-1 and hence the esterase-hydrolysed modulator conjugates will only accumulate in macrophages.
Furthermore, the α,α-disubstituted glycine conjugates of the invention are in general more potent in cells containing the carboxylesterase HCE-1 (ie macrophages) than in cells which only contain the carboxylesterases HCE-2 and HCE-3.
Also, it has been found that conjugates of the invention in which the α,α-disubstituted glycine ester motif is linked to the modulator via one of the α substituents of the α,α-disubstituted glycine ester are in general more potent in cells containing the carboxylesterase HCE-1 (ie macrophages) than in cells which only contain the carboxylesterases HCE-2 and HCE-3. The active hydrolysed acid conjugate therefore accumulates non-selectively in the case of such (generally) C-linked ester conjugates.

TERMINOLOGY

As used herein, the term “α,α-disubstituted glycine” or “α,α-disubstituted glycine acid” means a compound of formula H₂N—C(R₂R₃)—COOH, wherein R₂and R₃represent the α-substituents (which of course are not hydrogen), and an “α,α-disubstituted glycine ester is such a compound wherein the carboxylic acid group is esterified. The term “ester” or “esterified carboxyl group” means a group R₉O(C═O)— in which R₉is the group characterising the ester, notionally derived from the alcohol R₉OH.
As used herein, the term “(C_a-C_b)alkyl” wherein a and b are integers refers to a straight or branched chain alkyl radical having from a to b carbon atoms. Thus when a is 1 and b is 6, for example, the term includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and n-hexyl.
As used herein the term “divalent (C_a-C_b)alkylene radical” wherein a and b are integers refers to a saturated hydrocarbon chain having from a to b carbon atoms and two unsatisfied valences.
As used herein the term “(C_a-C_b)alkenyl” wherein a and b are integers refers to a straight or branched chain alkenyl moiety having from a to b carbon atoms having at least one double bond of either E or Z stereochemistry where applicable. The term includes, for example, vinyl, allyl, 1- and 2-butenyl and 2-methyl-2-propenyl.
As used herein the term “divalent (C_a-C_b)alkenylene radical” means a hydrocarbon chain having from a to b carbon atoms, at least one double bond, and two unsatisfied valences.
As used herein the term “(C_a-C_b)alkynyl” wherein a and b are integers refers to straight chain or branched chain hydrocarbon groups having from two to six carbon atoms and having in addition one triple bond. This term would include for example, ethynyl, 1-propynyl, 1- and 2-butynyl, 2-methyl-2-propynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl and 5-hexynyl.
As used herein the term “divalent (C_a-C_b)alkynylene radical” wherein a and b are integers refers to a divalent hydrocarbon chain having from 2 to 6 carbon atoms, and at least one triple bond.
As used herein the term “carbocyclic” refers to a mono-, bridged mono-, bi- or tricyclic radical having up to 16 ring atoms, all of which are carbon, and includes aryl and cycloalkyl.
As used herein the term “cycloalkyl” refers to a monocyclic saturated carbocyclic radical having from 3-8 carbon atoms and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and norbornyl.
As used herein the unqualified term “aryl” refers to a mono-, bridged mono-, bi- or tri-cyclic carbocyclic aromatic radical, and includes radicals having two monocyclic carbocyclic aromatic rings which are directly linked by a covalent bond. Illustrative of such radicals are phenyl, biphenyl and napthyl.
As used herein the unqualified term “heteroaryl” refers to a mono-, bridged mono-, bi- or tri-cyclic aromatic radical containing one or more heteroatoms selected from S, N and O, and includes radicals having two such monocyclic rings, or one such monocyclic ring and one monocyclic aryl ring, which are directly linked by a covalent bond. Illustrative of such radicals are thienyl, benzthienyl, furyl, benzfuryl, pyrrolyl, imidazolyl, benzimidazolyl, thiazolyl, benzthiazolyl, isothiazolyl, benzisothiazolyl, pyrazolyl, oxazolyl, benzoxazolyl, isoxazolyl, benzisoxazolyl, isothiazolyl, triazolyl, benztriazolyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, indolyl and indazolyl.
As used herein the unqualified term “heterocyclyl” or “heterocyclic” includes “heteroaryl” as defined above, and in its non-aromatic meaning relates to a mono-, bridged mono-, bi- or tri-cyclic non-aromatic radical containing one or more heteroatoms selected from S, N and O, and to groups consisting of a monocyclic non-aromatic radical containing one or more such heteroatoms which is covalently linked to another such radical or to a monocyclic carbocyclic radical. Illustrative of such radicals are pyrrolyl, furanyl, thienyl, piperidinyl, imidazolyl, oxazolyl, isoxazolyl, thiazolyl, thiadiazolyl, pyrazolyl, pyridinyl, pyrrolidinyl, pyrimidinyl, morpholinyl, piperazinyl, indolyl, morpholinyl, benzfuranyl, pyranyl, isoxazolyl, benzimidazolyl, methylenedioxyphenyl, ethylenedioxyphenyl, maleimido and succinimido groups.
Unless otherwise specified in the context in which it occurs, the term “optionally substituted” as applied to any moiety herein means such moiety may be substituted with up to four compatible substituents, each of which independently may be, for example, (C₁-C₆)alkyl, (C₁-C₆)alkoxy, hydroxy, hydroxy(C₁-C₆)alkyl, mercapto, mercapto(C₁-C₆)alkyl, (C₁-C₆)alkylthio, phenyl, halo (including fluoro, bromo and chloro), trifluoromethyl, trifluoromethoxy, nitro, nitrile (—CN), oxo, —COOH, —COOR^A, —COR^A, —SO₂R^A, —CONH₂, —SO₂NH₂, —CONHR^A, —SO₂NHR^A, —CONR^AR^B, —SO₂NR^AR^B, —NH₂, —NHR^A, —NR^AR^B, —OCONH₂, —OCONHR^A, —OCONR^AR^B, —NHCOR^A, —NHCOOR^A, —NR^BCOOR^A, —NHSO₂OR^A, —NR^BSO₂OH, —NR^BSO₂OR^A, —NHCONH₂, —NR^ACONH₂, —NHCONHR^B, —NR^ACONHR^B, —NHCONR^AR^B, or —NR^ACONR^AR^Bwherein R^Aand R^Bare independently a (C₁-C₆)alkyl, (C₃-C₆) cycloalkyl, phenyl or monocyclic heteroaryl having 5 or 6 ring atoms, or R^Aand R^Bwhen attached to the same nitrogen atom form a cyclic amino group (for example morpholino, piperidinyl, piperazinyl, or tetrahydropyrrolyl). An “optional substituent” may be one of the foregoing substituent groups.
The term “side chain of a natural or non-natural alpha-amino acid” refers to the group R¹in a natural or non-natural amino acid of formula NH₂—CH(R¹)—COOH, other than glycine, in which R¹is hydrogen.
Examples of side chains of natural alpha amino acids include those of alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, histidine, 5-hydroxylysine, 4-hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, α-aminoadipic acid, α-amino-n-butyric acid, 3,4-dihydroxyphenylalanine, homoserine, α-methylserine, ornithine, pipecolic acid, and thyroxine.
Natural alpha-amino acids which contain functional substituents, for example amino, carboxyl, hydroxy, mercapto, guanidyl, imidazolyl, or indolyl groups in their characteristic side chains include arginine, lysine, glutamic acid, aspartic acid, tryptophan, histidine, serine, threonine, tyrosine, and cysteine. When one or both of the α-substituents in the α,α-disubstituted glycine ester motif in the compounds of the invention is one of those side chains, the functional substituent may optionally be protected.
The term “protected” when used in relation to a functional substituent in a side chain of a natural alpha-amino acid means a derivative of such a substituent which is substantially non-functional. For example, carboxyl groups may be esterified (for example as a C₁-C₆alkyl ester), amino groups may be converted to amides (for example as a NHCOC₁-C₆alkyl amide) or carbamates (for example as an NHC(═O)OC₁-C₆alkyl or NHC(═O)OCH₂Ph carbamate), hydroxyl groups may be converted to ethers (for example an OC₁-C₆alkyl or a O(C₁-C₆alkyl)phenyl ether) or esters (for example a OC(═O)C₁-C₆alkyl ester) and thiol groups may be converted to thioethers (for example a tert-butyl or benzyl thioether) or thioesters (for example a SC(═O)C₁-C₆alkyl thioester).
There are many possible ester groups which may in principle be present in the α,α-disubstituted glycine ester carboxylesterase ester motif for attachment to the modulator. Likewise, there are many α,α-disubstituted glycines, differing in the α-substituents R₂and R₃, which may be used as esters in the carboxylesterase ester motif. Some α,α-disubstituted glycine esters are rapidly hydrolysed by one or more of the hCE-1, -2 and -3 isotypes or cells containing these enzymes, while others are more slowly hydrolysed, or hydrolysed only to a very small extent. In general, if the carboxylesterase hydrolyses the free α,α-disubstituted glycine ester to the parent acid it will, subject to the N-carbonyl dependence of hCE-2 and hCE-3 discussed above, also hydrolyse the ester motif when covalently conjugated to the modulator.
Hence, the broken cell assay and/or the isolated carboxylesterase assay described herein provide a straightforward, quick and simple first screen for esters which have the required hydrolysis profile. Ester motifs selected in that way may then be re-assayed in the same carboxylesterase assay when conjugated to the modulator via the chosen conjugation chemistry, to confirm that it is still a carboxylesterase substrate in that background.

The Ester Group

As mentioned, intracellular carboxylesterase enzymes capable of hydrolysing the ester group of a compound of the invention to the corresponding acid include the three known human enzyme isotypes hCE-1, hCE-2 and hCE-3. Although these are considered to be the main enzymes, other enzymes such as biphenylhydrolase (BPH) may also have a role in hydrolysing the ester. In general, if the carboxylesterase hydrolyses the free amino acid ester to the parent acid it will also hydrolyse the ester motif when covalently conjugated to the inhibitor. Hence, the broken cell assay and/or the isolated carboxylesterase assay described herein provide a straightforward, quick, and simple first screen, for esters which have the required hydrolysis profile. Ester motifs selected in that way may then be re-assayed in the same carboxylesterase assay when conjugated to the inhibitor via the chosen conjugation chemistry, to confirm that it is still a carboxylesterase substrate in that background.
Subject, to the requirement that they be hydrolysable by intracellular carboxylesterase enzymes, examples of particular ester groups in the α,α-disubstituted glycine ester carboxylesterase ester motif include those of formula —(C═O)OR₁₄wherein R₁₄is R₈R₉R₁₀C— wherein

- (i) R₈is hydrogen or optionally substituted (C₁-C₃)alkyl-(Z¹)_a-[(C₁-C₃)alkyl]_b— or (C₂-C₃)alkenyl-(Z¹)_a—[(C₁-C₃)alkyl]_b— wherein a and b are independently 0 or 1 and Z¹is —O—, —S—, or —NR₁₁— wherein R₁₁is hydrogen or (C₁-C₃)alkyl; and R₉and R₁₀are independently hydrogen or (C₁-C₃)alkyl-;
- (ii) R₈is hydrogen or optionally substituted R₁₂R₁₃N—(C₁-C₃)alkyl- wherein R₁₂is hydrogen or (C₁-C₃)alkyl and R₁₃is hydrogen or (C₁-C₃)alkyl; or R₁₂and R₁₃together with the nitrogen to which they are attached form an optionally substituted monocyclic heterocyclic ring of 5- or 6-ring atoms or bicyclic heterocyclic ring system of 8 to 10 ring atoms, and R₉and R₁₀are independently hydrogen or (C₁-C₃)alkyl-; or
- (iii) R₈and R₉taken together with the carbon to which they are attached form an optionally substituted monocyclic or bridged monocyclic carbocyclic ring of from 3 to 7 ring atoms or bicyclic or bridged monocyclic carbocyclic ring system of 8 to 10 ring atoms, and R₁₀is hydrogen.

In cases (i), (ii) and (iii) above, “alkyl” includes fluoroalkyl.
Within these classes (i), (ii) and (iii), R₁₀is often hydrogen. Specific examples of R₁₄include methyl, trifluoromethyl, ethyl, n- or iso-propyl, n-, sec- or tert-butyl, cyclohexyl, norbornyl, allyl, phenyl, benzyl, 2-, 3- or 4-pyridylmethyl, N-methylpiperidin-4-yl, tetrahydrofuran-3-yl or methoxyethyl. Currently preferred is where R₁₄is cyclopentyl.

α-Substituents

Examples of α-substituents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator may be regarded as selected from the side chains of a natural or non-natural alpha-amino acid, and in such side chains any functional groups may be protected.
For example, α-substituents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator include phenyl and groups of formula —CR_aR_bR_cin which:

- each of R_a, R_band R_cis independently hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, (C₃-C₈)cycloalkyl; or
- R_cis hydrogen and R_aand R_bare independently phenyl or heteroaryl such as pyridyl; or

R_cis hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or (C₃-C₈)cycloalkyl, and R_aand R_btogether with the carbon atom to which they are attached form a 3 to 8 membered cycloalkyl or a 5- to 6-membered heterocyclic ring; or

- R_a, R_band R_ctogether with the carbon atom to which they are attached form a tricyclic ring (for example adamantyl); or

R_aand R_bare each independently (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or a group as defined for R_cbelow other than hydrogen, or R_aand R_btogether with the carbon atom to which they are attached form a cycloalkyl or heterocyclic ring, and R_cis hydrogen, —OH, —SH, halogen, —CN, —CO₂H, (C₁-C₄)perfluoroalkyl, —CH₂OH, —O(C₁-C₆)alkyl, —O(C₂-C₆)alkenyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —S(C₂-C₆)alkenyl, —SO(C₂-C₆)alkenyl, —SO₂(C₂-C₆)alkenyl or a group -Q-W wherein Q represents a bond or —O—, —S—, —SO— or —SO₂— and W represents a phenyl, phenylalkyl, (C₃-C₈)cycloalkyl, (C₃-C₈)cycloalkylalkyl, (C₄-C₈)cycloalkenyl, (C₄-C₈)cycloalkenylalkyl, heteroaryl or heteroarylalkyl group, which group W may optionally be substituted by one or more substituents independently selected from, hydroxyl, halogen, —CN, —CONH₂, —CONH(C₁-C₆)alkyl, —CONH(C₁-C₆alkyl)₂, —CHO, —CH₂OH, (C₁-C₄)perfluoroalkyl, —O(C₁-C₆)alkyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —NO₂, —NH₂, —NH(C₁-C₆)alkyl, —N((C₁-C₆)alkyl)₂, —NHCO(C₁-C₆)alkyl, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, (C₃-C₈)cycloalkyl, (C₄-C₈)cycloalkenyl, phenyl or benzyl.
Alternatively, the α-substituents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator, taken together with the α-carbon itself, may form a 3-6 membered saturated cycloalkyl ring, such as a cyclopropyl, cyclopentyl or cyclohexyl ring or heterocyclyl ring such as a piperidin-4-yl ring.
In some cases, at least one of the α-substitutents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator is a C₁-C₆alkyl substituent, for example methyl, ethyl, or n- or iso-propyl.
In some embodiments, one of the α-substitutents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator is a C₁-C₆alkyl substituent, for example methyl, ethyl, or n- or iso-propyl, and the other is selected from the group consisting of methyl, ethyl, n- and iso-propyl, n-, sec- and tert-butyl, phenyl, benzyl, thienyl, cyclohexyl, and cyclohexylmethyl.
Currently preferred are cases where one of R₂and R₃is methyl. and the other is methyl, ethyl, or n- or iso-propyl; or where R₂and R₃taken together with the carbon to which they are attached form a cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl ring. In a particular case, the α-substitutents R₂and R₃of the α,α-disubstituted glycine ester conjugated to the modulator are each methyl.

Conjugation

As stated above, the α,α-disubstituted glycine ester may be conjugated to the modulator via its amino group, or via one of the α-substituents. A linker radical may be present between the carboxylesterase ester motif and the modulator. The structure of the radical linking the carboxylesterase ester motif to the rest of the modulator obviously depends on the particular chemistry strategy chosen for such linkage. Clearly the chemistry strategy for that coupling may vary widely, and thus many linkage structures are possible. The precise combination of variables making up the linking chemistry between the amino acid ester motif and the rest of the molecule will often be irrelevant to the primary binding mode of the compound as a whole. On the other hand, that linkage chemistry may in some cases pick up additional binding interactions with the enzyme, thereby enhancing binding.
It should also be noted that the benefits of the α,α-disubstituted glycine ester motif described above (facile entry into the cell, carboxylesterase hydrolysis within the cell, and accumulation within the cell of active carboxylic acid hydrolysis product) are best achieved when the linkage between the amino acid ester motif and the rest of the molecule is not a substrate for peptidase activity within the cell, which might result in cleavage of the amino acid from the molecule. Of course, stability to intracellular peptidases is easily tested by incubating the compound with disrupted cell contents, and analysing for any such cleavage.
For example, the α,α-disubstituted glycine ester (formula H₂N—C(R₂R₃)—COOH) may be conjugated to the modulator as
(a) a radical of formula —(CH₂)_z—X¹-L¹-Y—NH—C(R₂)(R₃)—R₁or
(b) a radical of formula —(CH₂)_z—Y-L¹-R₃—C(R₂)(NH₂)(R₁), wherein:

- R₁is the carboxylesterase-hydrolysable ester group;
- R₂and R₃are the α-substituents of the α,α-disubstituted glycine;
- R₂is the side chain of a natural or non-natural alpha amino acid;
- Y is a bond, —C(═O)—, —S(═O)₂—, —C(═O)O—, —C(═O)NR₃—, —C(═S)—NR₄, —C(═NH)—NR₄or —S(═O)₂NR₄— wherein R₄is hydrogen or optionally substituted C₁-C₆alkyl;
- Y¹is a bond, —C(═O)—, —S(═O)₂—, —C(═O)O—, —OC(═O)—, —C(═O)NR₅—, —NR₅(C═O)—, —S(═O)₂NR₅—, —NR₅S(═O)₂—, or —NR₆(C═O)NR₅—, wherein R₅and R6 are independently hydrogen or optionally substituted (C₁-C₆)alkyl,
- L¹is a divalent radical of formula -(Alk¹)_m(Q)_n(Alk²)_p- wherein
  - m, n and p are independently 0 or 1,
  - Q is (i) an optionally substituted divalent mono- or bicyclic, carbocyclic or heterocyclic radical having 5-0.13 ring members, or (ii), in the case where p is 0, a divalent radical of formula -Q¹-X²— wherein X²is —O—, —S— or NR^A— wherein R^Ais hydrogen or optionally substituted C₁-C₃alkyl, and Q¹is an optionally substituted divalent mono- or bicyclic carbocyclic or heterocyclic radical having 5-13 ring members,
  - Alk¹and Alk²independently represent optionally substituted divalent C₃-C₇cycloalkyl radicals, or optionally substituted straight or branched, C₁-C₆alkylene, C₂-C₆alkenylene, or C₂-C₃alkynylene radicals which may optionally contain or terminate in an ether (—O—), thioether (—S—) or amino (—NR^A—) link wherein R^Ais hydrogen or optionally substituted C₁-C₃alkyl;
- X¹is a bond, —C(═O)—; or —S(═O)₂—; —NR₇C(═O)—, —C(═O)NR₇—, —NR₇C(═O)—NR₈—, —NR₇S(═O)₂—, or —S(═O)₂NR₇— wherein R₇and R₈are independently hydrogen or optionally substituted C₁-C₆alkyl; and
- z is 0 or 1.

Taking the variables present in the linkage radical in turn:

- z may be 0 or 1, so that a methylene radical linked to the modulator is optional.
- specific preferred examples of Y include a bond, —(C═O)—, —(C═O)NH—, and —(C═O)O—. However, for hCE-1 specificity when the alpha amino acid ester is conjugated to the inhibitor as a radical of formula (IA), Y should be a bond.
- In the radical L, examples of Alk¹and Alk²radicals, when present, include —CH₂—, —CH₂CH₂— —CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂—, —CH═CH—,
- CH═CHCH₂—, —CH₂CH═CH—, CH₂CH═CHCH₂—, —C≡C—, —C≡CCH₂—, CH₂C≡C—, and CH₂C≡CCH₂. Additional examples of Alk¹and Alk²include —CH₂W—, —CH₂CH₂W— —CH₂CH₂WCH₂—, —CH₂CH₂WCH(CH₃)—, —CH₂WCH₂CH₂—, —CH₂WCH₂CH₂WCH₂—, and —WCH₂CH₂— where W is —O—, —S—, —NH—, —N(CH₃)—, or —CH₂CH₂N(CH₂CH₂OH)CH₂—. Further examples of Alk¹and Alk²include divalent cyclopropyl, cyclopentyl and cyclohexyl radicals.
- In L¹, when n is 0, the radical is a hydrocarbon chain (optionally substituted and perhaps having an ether, thioether or amino linkage). Presently it is preferred that there be no optional substituents in L¹. When both m and p are 0, L¹is a divalent mono- or bicyclic carbocyclic or heterocyclic radical with 5-13 ring atoms (optionally substituted). When n is 1 and at least one of m and p is 1, L¹is a divalent radical including a hydrocarbon chain or chains and a mono- or bicyclic carbocyclic or heterocyclic radical with -13 ring atoms (optionally substituted). When present, Q may be, for example, a divalent phenyl, naphthyl, cyclopropyl, cyclopentyl, or cyclohexyl radical, or a mono-, or bi-cyclic heterocyclic radical having 5 to 13 ring members, such as piperidinyl, piperazinyl, indolyl, pyridyl, thienyl, or pyrrolyl radical, but 1,4-phenylene is presently preferred.
- Specifically, in some embodiments of the invention, m and p may be 0 with n being 1. In other embodiments, n and p may be 0 with m being 1. In further embodiments, m, n and p may be all 0. In still further embodiments m may be 0, n may be 1 with Q being a monocyclic heterocyclic radical, and p may be 0 or 1. Alk¹and Alk², when present, may be selected from —CH₂—, —CH₂CH₂—, and —CH₂CH₂CH₂— and Q may be 1,4-phenylene.

Modulators of Intracellular Enzymes and Receptors

The principles of this invention can be applied to modulators of a wide range of intracellular targets which are implicated in a wide range of diseases. As discussed, the binding modes of known modulators to their targets are generally known soon after the modulators themselves become known. In addition, modern techniques such as X-ray crystallography and NMR are capable of revealing such binding topologies and geometries, as are traditional medicinal chemistry methods of characterising structure-activity relationships. With such knowledge, it is straightforward to identify where in the structure of a given modulator an carboxylesterase ester motif could be attached without disrupting the binding of the modulator to the enzyme or receptor by use of structural data. For example, Table 1 lists some intracellular enzyme or receptor targets where there is published crystal structural data.

TABLE 1

Target	Crystal Structure reference	Target Disease

CD45	Nam et al., J Exp Med 201, 441	Autoimmune disease
	(2005)
Lck	Zhu et al., Structure 7, 651 (1999)	Inflammation
ZAP-70	Jin et al., J Biol Chem 279, 42818	Autoimmune disease
	(2004)
PDE4	Huai et al., Biochemistry 42,	Inflammation
	13220 (2003)
PDE3	Scapin et al., Biochemistry 43,	Asthma
	6091 (2004)
IMPDH	Intchak et al., Cell 85, 921 (1996)	Psoriasis
p38 MAPK	Wang et al., Structure 6, 1117	Inflammation
	(1998)
COX2	Kiefer et al., J Biol Chem 278,	Inflammation
	45763, (2003)
Adenosine Kinase	Schumacher et al., J Mol Biol 298,	Inflammation
	875 (2000)
PLA2	Chandra et al., Biochemistry B	Psoriasis
	10914 (2002)
PLC	Essen et al., Biochemistry 36,	Rheumatoid arthritis
	1704, (1997)
PLD	Leiros et al., J Mol Biol 339, 805	Inflammation
	(2004)
iNOS	Rosenfeld et al., Biochemistry 41,	Inflammation
	13915 (2002)
LTA4 hydrolase	Rudberg et al., J Biol Chem 279,	Inflammation
	27376 (2004)
ICE	Okamato et al., Chem Pharm Bull	Rheumatoid arthritis
	47, 11 (1999)
GSK3β	Bertrand et al., J Mol Biol 333, 393	Rheumatoid arthritis
	(2003)
PKC	Xu et al., JBC 279, 50401 (2004)	Inflammation
PARP	Ruf et al., PNAS (USA) 93, 7481	Proliferative
	(1996)	disorders
MetAP2	Sheppard et al Bioorg Med Chem	Rheumatoid arthritis
	Lett 14, 865 (2004)
Corticosteroid receptor	Bledsoe et al., Cell 110, 93 (2002)	Inflammation
PI3K	Walker et al., Mol Cell Biol 6, 909	Proliferative
	(2000)	disorders
Raf	Wan et al., Cell 116, 855 (2004)	Proliferative
		disorders
AKT/PKB	Yang et al., Nat Struct Biol 9, 940	Proliferative
	(2002)	disorders
HDAC	Finnin et al., Nature 401, 188	Proliferative
	(1999)	disorders
c-Abl	Nagar et al., Cancer Res 62, 4236	Proliferative
	(2002)	disorders
IGF-1R	Munshi et al., Acta Crystallogr	Proliferative
	Sect D 59, 1725 (2003)	disorders
Thymidylate	Stout et al., Structure 6, 839	Proliferative
Synthetase	(1998)	disorders
Glycinamide	Klein et al., J Mol Biol 249, 153	Proliferative
Ribonucleotide	(1995)	disorders
Formyltransferase
Purine Nucleoside	Koelner et al., J Mol Biol 280, 153	Proliferative
Phosphorylase	(1998)	disorders
Estrone Sulphatase	Hernandez-Guzman et al., J Biol	Proliferative
	Chem 278, 22989 (2003)	disorders
EGF-RTK	Stamos et al., J Biol Chem 277,	Proliferative
	46265 (2002)	disorders
Src kinase	Lamers et al., J Mol Biol 285, 713	Proliferative
	(1999)	disorders
VEGFR2	McTigue et al., Structure 7, 319	Proliferative
	(19999)	disorders
Superoxide Dismutase	Hough et al., J Mol Biol 287, 579	Proliferative
	(1999)	disorders
Ornithine	Almrud et al., J Mol Biol 295, 7	Proliferative
Decarboxylase	(2000)	disorders
Topoisomerase II	Classen et al., PNAS (USA) 100,	Proliferative
	10629 (2003)	disorders
Topoisomerase I	Stoker et al., PNAS (USA), 99,	Proliferative
	15387 (2002)	disorders
Androgen Receptor	Matias et al., J Biol Chem 275,	Proliferative
	26164 (2000)	disorders
JNK	Heo et al., EMBO J 23, 2185	Proliferative
	(2004)	disorders
Farnesyl Transferase	Curtin et al., Bioorg Med Chem	Proliferative
	Lett 13, 1367 (2003)	disorders
CDK	Davis et al., Science 291, 134	Proliferative
	(2001)	disorders
Dihydrofolate	Gargaro et al., J Mol Biol 277, 119	Proliferative
Reductase	(1998)	disorders
Flt3	Griffith et al., Mol Cell 13, 169	Proliferative
	(2004)	disorders
Carbonic Anhydrase	Stams et al., Protein Sci 7, 556	Proliferative
	(1998)	disorders
Thymidine	Norman et al., Structure 12, 75	Proliferative
Phosphorylase	(2004)	disorders
Dihydropyrimidine	Dobritzsch et al., JBC 277, 13155,	Proliferative
Dehydrogenase	(2002)	disorders
Mannosidase α	Van den Eisen et al., EMBO J 20,	Proliferative
	3008 (2001)	disorders
Peptidyl-prolyl	Ranganathan et al., Cell 89, 875	Proliferative
isomerase (Pin1)	(1997)	disorders
Retinoid X Receptor	Egea et al., EMBO J 19, 2592	Proliferative
	(2000)	disorders
β-Glucuronidase	Jain et al., Nat Struct Biol 3, 375	Proliferative
	(1996)	disorders
Glutathione	Oakley et al., J Mol Biol 291, 913	Proliferative
Transferase	(1999)	disorders
hsp90	Jez et al., Chem Biol 10, 361	Proliferative
	(2003)	disorders
IMPDH	intchak et al., Cell 85, 921 (1996)	Proliferative
		disorders
Phospholipase A2	Chandra et al., Biochemistry 41,	Proliferative
	10914 (2002)	disorders
Phospholipase C	Essen et al., Biochemistry 36,	Proliferative
	1704, (1997)	disorders
Phospholipase D	Leiros et al., J Mol Biol 339, 805	Proliferative
	(2004)	disorders
MetAP2	Sheppard et al. Bioorg Med Chem	Proliferative
	Lett 14, 865 (2004)	disorders
PTP-1B	Andersen et al., J Biol Chem 275,	Proliferative
	7101 (2000)	disorders
Aurora Kinase	Fancelli et al., in press	Proliferative
		disorders
PDK-1	Komander et al., Biochem J 375,	Proliferative
	255 (2003)	disorders
HMGCoA reductase	Istvan and Deisenhofer Science	Atheriosclerosis
	292, 1160 (2001)
Oxidosqualene	Lenhart et al., Chem Biol 9, 639	Hypercholesterolaemia
cyclase	(2002)
Pyruvate	Mattevi et al., Science 255, 1544	Cardiovascular
dehydrogenase	(1992)	disease
stimulator
Adenylate cyclase	Zhang et al., Nature 386, 247	Cardiovascular
	(1997)	disease
PPARγ agonist	Ebdurp et al., J Med Chem 46,	Diabetes
	1306 (2003)
Alcohol	Bahnson et al., PNAS USA 94,	Alcohol poisoning
dehydrogenase	12797 (1997)
Hormone sensitive	Wei et al., Nat Struct Biol 6, 340	Insulin resistant
lipase	(1999)	diabetes
Adenosine kinase	Mathews et al., Biochemistry 37,	Epilepsy
	15607 (1998)
Aldose reductase	Urzhmsee al., Structure 5, 601	Diabetes
	(1997)
Vitamin D3 receptor	Tocchini-Valentini et al., PNAS	Osteoporosis
	USA 98, 5491 (2001)
Protein tyrosine	Andersen et al., J Biol Chem 275,	Diabetes
phosphatase	7101 (2000)
HIV Protease	Louis et al., Biochemistry 37, 2105	HIV
	(1998)
HCV Polymerase	Bressanelli et al., PNAS USA 96,	Hepatitis C
	13034 (1999)
Neuraminidase	Taylor et al., J Med Chem 41, 798	Influenza
	(1998)
Reverse Transcriptase	Das et al., J Mol Biol 264, 1085	HIV
	(1996)
CMV Protease	Khayat et al., Biochemistry 42,	CMV infection
	885 (2003)
Thymidine Kinase	Champness et al., Proteins 32,	Herpes infections
	350 (1998)
HIV Integrase	Molteni et al., Acta Crystallogr	HIV
	Sect D 57, 536 (2001)

For the purpose of illustration, reference is made to known inhibitors of 5 of the above intracellular targets, whose binding mode to the target is known. These examples illustrate how such structural data can be used to determine the appropriate positions for the attachment of the α,α-disubstituted glycine carboxylesterase ester motif. Schematics of the active sites are shown together with representative inhibitors. In general, positions remote from the binding interface between modulator and target, and therefore pointing away from the enzyme binding interface into solvent are suitable places for attachment of the carboxylesterase ester motif and these are indicated in the diagrams.
A similar approach can also be used for the other examples identified in Table 1. The method of the invention, for increasing cellular potency and/or intracellular residence time of a modulator of the activity of a target intracellular enzyme or receptor, may involve several steps:

Step 1:

Identify a position or positions on one or a plurality of modulator molecules sharing the same binding mode for the target enzyme or receptor, remote from the binding interface between the modulators and the target enzyme or receptor.
Usually such positions are identified from the X-ray co-crystal structure (or structure derived by nmr) of the target enzyme or receptor with a known modulator (or a close structural analogue thereof) bound to the enzyme or receptor, by inspection of the structure. Alternatively the X-ray crystal structure of the target enzyme or receptor with the modulator docked into the active site of the enzyme or receptor is modelled by computer graphics methods, and the model is inspected The presumption is that structural modification of the modulator at positions remote from the binding interface is unlikely to interfere significantly with the binding of the modulator to the active site of the enzyme or receptor. Suitable positions will normally appear from the co-crystal structure or docked model to be orientated towards solvent.

Step 2:

Covalently modify the modulator(s) by attachment of an α,α-disubstituted glycine ester radical, or a range of different α,α-disubstituted glycine ester radicals at one or more of the positions identified in Step 1.
Attachment of α,α-disubstituted glycine ester radicals (ie the potential carboxylesterase motifs) may be via an existing covalent coupling functionality on the modulator(s), or via a suitable functionality specifically introduced for that purpose. The carboxylesterase motifs may be spaced from the main molecular bulk by a spacer or linker element, to position the motif deeper into solvent and thereby reduce still further any small effect of the motif on the binding mode of the modulator and/or to ensure that the motif is accessible to the carboxylesterase by reducing steric interference that may result from the main molecular bulk of the modulator.
Performance of Step 2 results in the preparation of one or, more usually, a small library of candidate modulators, each covalently modified relative to its parent inhibitor by the introduction of a variety of α,α-disubstituted glycine ester radicals, at one pr more points of attachment identified in Step 1.

Step 3:

Test the α,α-disubstituted glycine ester-conjugated modulator(s) prepared in step 2 to determine their activity against the target enzyme or receptor.
As is normal in medicinal chemistry, the carboxylesterase motif version(s) of the parent modulator(s), prepared as a result of performing Steps 1 and 2, are preferably tested in assays appropriate to determine whether the expected retention of modulator activity has in fact been retained, and to what degree and with what potency profile. In accordance with the underlying purpose of the invention, which is to cause the accumulation of modulator activity in cells, suitable assays will normally include assays in cell lines to assess degree of cellular activity, and potency profile, of the modified modulators. Other assays which may be employed in Step 3 include in vitro enzyme or receptor modulation assays to determine the intrinsic activity of the modified modulator and its putative carboxylesterase hydrolysis product; assays to determine the rate of conversion of the modified modulators to the corresponding carboxylic acid by carboxylesterases; and assays to determine the rate and or level of accumulation of the carboxylesterase hydrolysis product (the carboxylic acid) in cells. In such assays, both monocytic and non-monocytic cells, and/or a panel of isolated carboxylesterases, can be used in order to identify compounds that show cell selectivity.
If necessary or desirable, step 3 may be repeated with a different set of candidate alpha amino acid ester-conjugated versions of the parent modulator.

Step 4:

From data acquired in Step 3, select one or more of the tested α,α-disubstituted glycine ester-conjugated versions of the parent modulator(s) which cause modulation of enzyme or receptor activity inside cells, are converted to and accumulate as the corresponding carboxylic acid inside cells, and which show increased or prolonged cellular potency.
The above described Steps 1-4 represent a general algorithm for the implementation of the principles of the present invention.

Synthesis

There are multiple synthetic strategies for the synthesis of the compounds with which the present invention is concerned, but all rely on known chemistry, known to the synthetic organic chemist. Thus, compounds according to formula (I) can be synthesised according to procedures described in the standard literature and are well-known to those skilled in the art. Typical literature sources are “Advanced organic chemistry”, 4^thEdition (Wiley), J March, “Comprehensive Organic Transformation”, 2^ndEdition (Wiley), R. C. Larock, “Handbook of Heterocyclic Chemistry”, 2^ndEdition (Pergamon), A. R. Katritzky), review articles such as found in “Synthesis”, “Acc. Chem. Res.”, “Chem. Rev”, or primary literature sources identified by standard literature searches online or from secondary sources such as “Chemical Abstracts” or “Beilstein”.
The compounds of the invention may be prepared by a number of processes generally described below and more specifically in the Examples hereinafter. In the reactions described below, it may be necessary to protect reactive functional groups, for example hydroxyl, amino and carboxy groups, where these are desired in the final product, to avoid their unwanted participation in the reactions [see for example Greene, T. W., “Protecting Groups in Organic Synthesis”, John Wiley and Sons, 1999]. Conventional protecting groups may be used in conjunction with standard practice. In some instances deprotection may be the final step in the synthesis of a compound of general formula (I), and the processes according to the invention described herein after are understood to extend to such removal of protecting groups.
The compounds of the invention may be prepared according to the following Examples. All temperatures are in ° C. The following abbreviations are used
EtOAc=ethyl acetate
MeCN=acetonitrile
MeOH=methanol
Boc=tert-butoxycarbonyl
CDI=1,1′-carbonyl diimidazole
DCM=dichloromethane
DBU=1,8-Diazabicyclo[5.4.0]undec-7-ene
DMAP=dimethylaminopyridine
DMF=dimethylformamide
DMSO=dimethyl sulfoxide
THF=tetrahydrofuran
HCl=hydrochloric acid
NaHCO₃=sodium hydrogen carbonate
TBDMSCl=tert-butyldimethylchlorosilane

NBS=N-bromosuccinimide

NMM=N-methyl morpholine
NH₄Cl=ammonium chloride
KHMDS=potassium bis(trimethylsilyl)amide
Pd/C=palladium on carbon
MgSO₄=magnesium sulfate
EDC=N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride
Et₂O=diethyl ether
NaBH(OAc)₃=sodium triacetoxyborohydride
HOBt=1-hydroxybenzotriazole
TFA=trifluoroacetic acid
TLC=thin layer chromatography
mL=milliliter(s)
g=gram(s)
mg=milligram(s)
mol=moles
mmol=millimole(s)
LCMS=high performance liquid chromatography/mass spectrometry
NMR=nuclear magnetic resonance
RT=room temperature
Commercially available reagents and solvents (HPLC grade) were used without further purification. Solvents were removed using a Buchi rotary evaporator or a VirTis Benchtop SLC Freeze-dryer. Microwave irradiation was carried out using a Biotage Initiator™ Eight microwave synthesizer. Purification of compounds by flash chromatography column was performed using silica gel, particle size 40-63 μm (230-400 mesh) obtained from Fluorochem. Purification of compounds by preparative HPLC was performed on Gilson systems using reverse phase Axia™ prep Luna C18 columns (10 μm, 100×21.2 mm), gradient 0-100% B (A=water+0.05% TFA, B acetonitrile) over 10 min, flow=25 mL/min, UV detection at 254 nm.
¹H NMR spectra were recorded on a Bruker 300 MHz AV spectrometer in deuterated solvents. Chemical shifts δ are in parts per million. Thin-layer chromatography (TLC) analysis was performed with Kieselgel 60 F₂₅₄(Merck) plates and visualized using UV light.
Analytical HPLC/MS was performed on an Agilent HP1100 LC system using reverse phase Luna C18 columns (3 μm, 50×4.6 mm), gradient 5-95% B (A=water+0.1% Formic acid, B=acetonitrile+0.1% Formic acid) over 2.25 min, flow=2.25 mL/min. UV spectra were recorded at 220 and 254 nm using a G1315B DAD detector. Mass spectra were obtained over the range m/z 150 to 800 on a LC/MSD SL G1956B detector. Data were integrated and reported using ChemStation and ChemStation Data Browser softwares.

Examples 1-6

The compounds 6-amino-5-(2,4-difluoro-benzoyl-1-phenyl-1H-pyridin-2-one (Compound I) and 6-amino-5-(2,4-difluoro-benzoyl-1-(2,5-difluorophenyl-1H-pyridin-2-one (Compound II):
are known inhibitors of the intracellular enzyme p38 MAP kinase (WO 03/076405). Examples 1, 3 and 5 below relate to the covalent conjugation of esterase motifs with di-substitution at the alpha carbon of the amino acid ester to these compounds, in a position remote from the binding interface between the inhibitor and the target enzyme (see the comments above concerning the binding mode of a model p38 MAP kinase inhibitor). Examples 2, 4 and 6 below relate to the carboxylic acid esterase hydrolysis products of Examples 1, 3 and 5 respectively.

Synthesis of Examples 1-6

Intermediate 1

4-Chlorophenyl 3-(2,4-difluorophenyl)-3-oxopropanimidothioate

Intermediate 1 can be prepared using experimental procedures described in WO 2003076405.

Intermediate 2

{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)yl]-phenyl}acetaldehyde

{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)yl]-phenyl}acetaldehyde was synthesised using the route shown in Scheme 1 below.

Stage 1—2-(4-{[3-(2,4-Difluorophenyl)-3-oxopropanimidoyl]amino}phenyl)ethyl acetate

4-Chlorophenyl 3-(2,4-difluorophenyl)-3-oxopropanimidothioate (Intermediate 1) (69.7 g, 192 mmol) was suspended in glacial acetic acid (700 mL) and 2-(4-aminophenyl)ethanol (27.71 g, 202 mmol, 1.05 eq) was added. The mixture was heated at 80° C. for 2.5 hours before being allowed to cool to room temperature and concentrated under reduced pressure. The residue was triturated with Et₂O (500 mL) and washed with Et₂O (2×250 mL) to give a white solid, which was suspended in saturated NaHCO₃(700 mL) and stirred vigorously for 30 minutes. Filtration and washing with water afforded a beige solid which was dried under reduced pressure to give the title compound (64.12 g, 92% yield).
LC/MS: m/z 361 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 7.79-7.71 (1H, m), 7.45-7.07 (6H, m), 5.26 (1H, s), 4.21 (2H, t, J=6.8 Hz), 2.89 (2H, t, J=6.5 Hz), 2.00 (3H, s).

Stage 2—2-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl acetate

CDI (43.26 g, 267 mmol, 1.5 eq) was dissolved in anhydrous THF (1 l) under an atmosphere of nitrogen and cooled to 0° C. Propiolic acid (16.43 mL, 267 mmol, 1.5 eq) was added dropwise and the mixture allowed to warm to room temperature and stirred for 1 hr. A suspension of 2-(4-{[3-(2,4-difluorophenyl)-3-oxopropanimidoyl]-amino}phenyl)ethyl acetate (64.12 g, 178 mmol) in anhydrous THF (500 mL) was added and the mixture heated at 80° C. for 6 hours before being left to stir at room temperature overnight. The resulting precipitate was collected by filtration, washed with Et₂O and dried under reduced pressure to give the title compound as a pale yellow solid (39.56 g). The filtrate was concentrated under reduced pressure to give a brown oil that was triturated with EtOAc (500 mL), providing a second batch of product by filtration (7.21 g). The two batches were combined to afford the title compound as a yellow solid (46.77 g, 64% yield).
LC/MS: m/z 413 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 7.55-7.37 (4H, m), 7.3-7.20 (4H, m), 5.72 (1H, d, J=9.6 Hz), 4.30 (2H, t, J=6.9 Hz), 3.01 (2H, t, J=6.9 Hz), 2.04 (3H, s).

Stage 3—6-Amino-5-(2,4-difluorobenzoyl)-1-[4-(2-hydroxyethyl)phenyl]pyridin-2(1H)-one

2-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl acetate (46.77 g, 113 mmol) was suspended in 6N aqueous HCl (500 mL) and heated at reflux for 2 hours. A precipitate formed upon cooling to room temperature which was collected by filtration, suspended in saturated aqueous NaHCO₃(1000 mL) and stirred vigorously for 30 minutes. Filtration, washing with water (2×500 mL) and drying under reduced pressure afforded the title compound as an off-white solid (40.11 g, 96% yield).
LC/MS: m/z 371 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 7.55-7.37 (4H, m), 7.31-7.20 (4H, m), 5.71 (1H, d, J=9.9 Hz), 4.69 (1H, t, J=5.3 Hz), 3.71 (2H, m), 2.84 (2H, d, J=6.9 Hz).

Stage 4-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}-acetaldehyde

To a suspension of 6-amino-5-(2,4-difluorobenzoyl)-1-[4-(2-hydroxyethyl)phenyl]-pyridin-2(1H)-one (15.00 g, 40.5 mmol) in anhydrous DCM (750 mL) at 0° C. was added Dess-Martin Periodinane (20.62 g, 48.6 mmol, 1.2 eq) in portions. The mixture was allowed to warm to room temperature and stirred for 3 hours, before being poured into saturated aqueous NaHCO₃(400 mL) and saturated aqueous Na₂S₂O₃(400 mL) and stirred vigorously for 30 minutes. The aqueous layer was separated and extracted with DCM (2×500 mL), and the organic extracts combined and dried over MgSO₄. Filtration and concentration under reduced pressure afforded the title compound as a crude pale yellow solid that was used without further purification (15.13 g).
LC/MS: m/z 369 [M+H]⁺.

Intermediate 3

Cyclopentyl 2-methylalaninate hydrochloride

Intermediate 3 was synthesised using the route shown in Scheme 2 below.

Stage 1—Cyclopentyl N-(tert-butoxycarbonyl)-2-methylalaninate

To a solution of N-(tert-butoxycarbonyl)-2-methylalanine (1.00 g, 4.92 mmol) in DCM (10 mL) at 0° C. was added cyclopentanol (0.83 mL, 9.84 mmol), EDCI (1.06 g, 5.42 mmol) and finally DMAP (60 mg, 0.49 mmol). The reaction mixture was warmed to RT and stirred for 18 hours The DCM was removed in vacuo to give a clear oil. The crude residue was dissolved in EtOAc (100 mL) and washed with water, 1M NaHCO₃and brine. The organic phase was dried (MgSO₄) and concentrated in vacuo. The crude extract was purified by column chromatography (10% EtOAc in heptane) to yield the desired product as a clear oil (0.254 g, 20% yield).
¹H NMR (300 MHz, CDCl₃) δ: 5.25-5.17 (1H, m), 5.04 (1H, br s), 1.93-1.54 (8H, m), 1.49 (6H, s), 1.45 (9H, s).

Stage 2—Cyclopentyl 2-methylalaninate hydrochloride (Intermediate 3)

Cyclopentyl N-(tert-butoxycarbonyl)-2-methylalaninate (0.254 g, 0.93 mmol) was dissolved in THF (5 mL) and treated with 4M HCl/dioxane (2 mL) and the reaction mixture was stirred at RT for 24 hours. The crude mixture was concentrated under reduced pressure and triturated with Et₂O to give a white precipitate. This was further washed with Et₂O to give the desired product as a white powder (0.16 g, 82% yield).
¹H NMR (300 MHz, DMSO-d₆) δ: 8.58 (3H, br s), 5.21-5.14 (1H, m), 1.93-1.78 (2H, m), 1.74-1.53 (6H, m), 1.45 (6H, s).

Intermediate 4

tert-Butyl 2-methylalaninate

Intermediate 4 was synthesised using the route shown in Scheme 3 below.

Stage 1—tert-Butyl N-[(benzyloxy)carbonyl]-2-methylalaninate

To a solution of N-[(benzyloxy)carbonyl]-2-methylalanine (1 g, 4.21 mmol) in DCM (10 mL anhydrous) and cyclohexane (10 mL) at 0° C. under nitrogen was added boron trifluoride diethyl etherate (7.7 ul, catalytic). tert-Butyl 2,2,2-trichloroacetimidate (1.51 mL, 8.43 mmol) in cyclohexane (10 mL) was then added slowly over 30 minutes before allowing to warm to RT. Reaction was allowed to stir at RT for 16 hours. To the crude reaction mixture was added 190 mg of NaHCO₃and the reaction filtered. The mother liquors were concentrated in vacuo. The crude extract was purified by column chromatography (10% EtOAc in heptane) to yield the desired product (0.863 g, 70% yield).
¹H NMR (300 MHz, CDCl₃) δ: 7.39-7.31 (5H, m), 5.46 (1H, br s), 5.10 (2H, s), 1.54 (6H, s), 1.45 (9H, s).

Stage 2—tert-butyl 2-methylalaninate (Intermediate 4)

To a solution of tert-Butyl N-[(benzyloxy)carbonyl]-2-methylalaninate (0.863 mg, 2.90 mmol) in EtOAc (20 mL) was added 100 mg of Pd/C catalyst. The mixture was evacuated and stirred under an atmosphere of hydrogen for 18 hours, filtered (Celite), washed with EtOAc and concentrated in vacuo. The product was isolated as a yellow oil (0.45 mg, 96%) which contained traces of EtOAc. The product is believed to be volatile so caution is needed during evaporation in vacuo.
¹H NMR (300 MHz, CDCl₃) δ: 1.48 (9H, s), 1.32 (6H, s).

Intermediate 5

Cyclopentyl 1-aminocyclopentanecarboxylate

Intermediate 5 was synthesised using the route shown in Scheme 4 below.

Stage 1—Cyclopentyl 1-aminocyclopentanecarboxylate

To a solution of 1-aminocyclopentanecarboxylic acid (2.58 g, 19.97 mmol) in cyclopentanol (20 mL), was added concentrated sulfuric acid (2.15 g, 21.97 mmol) and the mixture stirred overnight at 70° C. The reaction was allowed to cool to RT and the cyclopentanol removed under reduced pressure. The residue was dissolved in EtOAc (30 mL) and washed with sat. NaHCO₃(30 mL) and water (3×20 mL) then dried (MgSO₄), filtered and concentrated in vacuo to leave a dark yellow oil.
Purification by column chromatography (15% 1.2M NH₃/MeOH in EtOAc) afforded the desired product (1.97 g, 50% yield).
¹H NMR (300 MHz, CDCl₃) δ: 5.21-5.17 (1H, m), 2.15-1.90 (2H, m), 1.85-1.57 (14H, m).

Intermediate 6

tert-Butyl 1-aminocyclopentanecarboxylate

Intermediate 6 was synthesised using the route shown in Scheme 5 below.

Stage 1 —1-{[(Benzyloxy)carbonyl]amino}cyclopentanecarboxylic acid

To a solution of 1-aminocyclopentanecarboxylic acid (3.0 g, 23.2 mmol) in 1:1 dioxane/water (60 mL), was slowly added Na₂CO₃(12.3 g, 116 mmol) followed by benzyl chloroformate (3.6 mL, 25.5 mmol) and the mixture stirred overnight at RT. The reaction mixture was carefully acidified to pH=2 with 1M HCl then extracted with EtOAc (3×30 mL). The combined organic extracts were washed with brine (30 mL), dried (MgSO₄), filtered and concentrated in vacuo to leave a pale yellow oil. LCMS and NMR showed the crude product to be a mixture of desired product and corresponding benzyl ester. The crude product was dissolved in 1:1 THF/water (60 mL) and treated with lithium hydroxide (2.67 g, 116 mmol). The mixture was stirred at RT overnight then washed with Et₂O (3×30 mL), acidified to pH=2 and extracted with EtOAc (3×30 mL). The combined organic extracts were washed with brine (30 mL), dried (MgSO₄), filtered and concentrated under reduced pressure to afford the title compound (4.76 g, 78%). LCMS: m/z 264 [M+H]⁺.

Stage 2—tert-Butyl 1-{[(benzyloxy)carbonyl]amino}cyclopentanecarboxylate

tert-Butyl 1-{[(benzyloxy)carbonyl]amino}cyclopentanecarboxylate was prepared in a similar fashion to Stage 1 (Scheme 3) of Intermediate 4.
LC/MS: m/z 320 [M+H]⁺.

Stage 3—tert-Butyl 1-aminocyclopentanecarboxylate

tert-Butyl 1-aminocyclopentanecarboxylate was prepared in a similar fashion to Stage 2 (Scheme 3) of Intermediate 4.
¹H NMR (300 MHz, CDCl₃) δ: 2.08-2.02 (2H, m), 1.87-1.72 (4H, m), 1.64-1.58 (2H, m), 1.47 (9H, s).

Example 1

Cyclopentyl N-(2-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1 (2H)-yl]phenyl}ethyl)-2-methylalaninate

In this example compound of the invention, a dimethyl glycine cyclopentyl ester motif is covalently conjugated to the parent p38 MAP kinase inhibitor via the amino group of the dimethyl glycine cyclopentyl ester and through a —CH₂CH₂— linker radical.
The compound was synthesised using Intermediate 2 and Intermediate 3 as described below.
To a solution of Intermediate 2 (189 mg, 0514 mmol) in anhydrous THF (4 mL) were added cyclopentyl 2-methylalaninate hydrochloride (Intermediate 3) (160 mg, 0.77 mmol, 1.5 eq) and NaBH(OAc)₃(326 mg, 1.54 mmol, 3 eq). The mixture was stirred at room temperature for 16 hours, and then quenched with water (20 mL). The aqueous layer was extracted with EtOAc (3×20 mL), and the combined organic extracts washed with brine (40 mL), dried over MgSO₄, filtered and concentrated under reduced pressure. The residue was purified by preparative HPLC to provide the title compound (130 mg, 48% yield).
LC/MS: m/z 524 [M+H]⁺. ¹H NMR (300 MHz, CDCl₃) δ: 10.43 (1H, br s), 7.51-7.34 (4H, m), 7.28-7.26 (2H, m), 7.04-6.90 (2H, m), 5.93 (1H, d, J=9.6 Hz), 5.20-5.10 (1H, m), 2.93-2.75 (4H, m), 1.95-1.55 (8H, m), 1.31 (6H, s).

Example 2

N-(2-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl)-2-methylalanine

This Example relates to the carboxylic acid hydrolysis product of the compound of Example 1.
The compound was synthesised using Intermediate 2 and Intermediate 4 as described below in Scheme 6.

Stage 1—tert-Butyl N-(2-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl)-2-methylalaninate

To a solution of Intermediate 2 (180 mg, 0.489 mmol) in THF (3 mL) was added tert-butyl 2-methylalaninate (Intermediate 4) (117 mg, 0.73 mmol), stirred for 30 minutes, and then NaBH(OAc)₃(310 mg, 1.467 mmol). The reaction was stirred for 24 hours, diluted with EtOAc and the organic washed with sat NaHCO₃, brine, dried (MgSO₄) and concentrated in vacuo. The residue was purified by preparative HPLC to provide the title compound (120 mg, 48% yield).
LC/MS: m/z 512 [M+H]⁺. ¹H NMR (300 MHz, CDCl₃) δ: 10.41 (1H, br s), 7.51-7.34 (4H, m), 7.28-7.26 (2H, m), 7.05-6.90 (2H, m), 5.93 (1H, d, J=9.9 Hz), 5.15 (1H, br s), 2.93-2.78 (4H, m), 1.46 (9H, s), 1.29 (6H, s).

Stage 2—N-(2-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl)-2-methylalanine

To a solution of tert-Butyl N-(2-{4-[(6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl)-2-methylalaninate (100 mg, 0.19 mmol) in DCM (3 mL) was added trifluoroacetic acid (3 mL). The mixture was stirred at room temperature for 16 hours and concentrated under reduced pressure. The residue was triturated with Et₂O, collected by filtration and dried under reduced pressure to afford the title compound as an off-white solid (50 mg, 56% yield).
LC/MS: m/z 456 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 10.05 (1H, br s), 7.60-7.15 (9H, m), 6.95 (1H, br s), 5.72 (1H, d, J=9.6 Hz), 3.15-2.95 (4H, m), 1.33 (6H, br s).

Example 3

Cyclopentyl 1-[(2-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]phenyl}ethyl)amino]cyclopentanecarboxylate

Example 3 was synthesised using Intermediate 2 and Intermediate 5 in a similar manner to Example 1
LC/MS: m/z 550 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 7.55-7.34 (6H, m), 7.29-7.21 (2H, m), 5.72 (1H, d, J=9.8 Hz), 5.27-5.21 (1H, m), 3.31-3.20 (2H, m), 3.10-3.00 (2H, m), 2.22-2.12 (2H, m), 2.08-1.98 (2H, m), 1.90-1.58 (12H, m)

Example 4

1-[(2-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1 (2H)-yl]phenyl}ethyl)amino]cyclopentanecarboxylic acid

Example 4 was synthesized using Intermediate 2 and Intermediate 6 in a similar manner to Example 2.
LCMS: m/z 482 [M+H]⁺. ¹H NMR (300 MHz, DMSO-d₆) δ: 7.52-7.37 (4H, m), 7.31-7.20 (4H, m), 5.71 (1H, d, J=10.0 Hz), 3.08-2.93 (4H, m), 2.10-1.99 (2H, m), 1.78-1.68 (6H, m).

Example 5

Cyclopentyl 5-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-2-methylnorvalinate

¹H NMR (300 MHz, DMSO-d₆) 10.14 (1H, br s), 8.06 (3H, br s), 7.57 (1H, dd, J=8.5, 15.1 Hz), 7.42 (1H, td, J=2.3, 10.0 Hz),), 7.34 (1H, dd, J=2.5, 9.8 Hz), 7.24 (1H, td, J=2.3, 8.5 Hz), 7.03 (2H, d, J=10.2 Hz) 5.74 (1H, d, J=9.8 Hz), 5.23-5.19 (1H, m), 4.13-4.07 (2H, m), 1.97-1.83 (5H, m), 1.70-1.57 (7H, m), 1.45 (3H, s). LCMS purity 95%, m/z 576 [M+H]⁺.
Example 5 was synthesised by the route shown in Scheme 7.

Step 1: 5-Benzyl 1-cyclopentyl N-(tert-butoxycarbonyl)-L-glutamate

To a solution of (2S)-5-(benzyloxy)-2-[(tert-butoxycarbonyl)amino]-5-oxopentanoic acid (10 g, 30 mmol) in DCM (100 mL) was added cyclopentanol (30 mL, 33 mmol), EDC (6.25 g, 33 mmol) and DMAP (362 mg, 3 mmol). The reaction was allowed to stir for 20 hours for complete reaction. The reaction was diluted with DCM, washed with 1M HCl, sat NaHCO₃, brine, dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography (20% EtOAc/Heptane) to provide the title compound as a white solid (8.48 g, 71% yield). m/z 406 [M÷H]⁺.

Step 2: 5-Benzyl 1-cyclopentyl N,N-bis(tert-butoxycarbonyl)-L-glutamate

To a solution of 5-benzyl 1-cyclopentyl N-(tert-butoxycarbonyl)-L-glutamate (8.48 g, 21 mmol) in acetonitrile (100 mL) was added di-tert-butyl dicarbonate (13.69 g, 63 mmol) and DMAP (255 mg, 2.1 mmol). The reaction was heated to 50° C. and stirred overnight before being allowed to cool to room temperature and concentrated under reduced pressure. The crude residue was dissolved in EtOAc and washed with 1M HCl, sat NaHCO₃, and brine. The organic layer was dried over magnesium sulfate and concentrated in vacuo to give a brown oil. Purification by column chromatography (10-20% EtOAc/Heptane) provided the title compound as a colourless oil (10.16 g, 96% yield). m/z 506 [M÷H]⁺.

Step 3: (4S)-4-[Bis(tert-butoxycarbonyl)amino]-5-(cyclopentyloxy)-5-oxopentanoic acid

To a solution of 5-benzyl 1-cyclopentyl N,N-bis(tert-butoxycarbonyl)-L-glutamate (10.16 g, 20.1 mmol) in EtOAc (200 mL) was added Pd/C (1 g). The mixture was stirred under an atmosphere of H₂for 19 hours, filtered through Celite and concentrated in vacuo to provide the title compound as a pale yellow oil (8.28 g, 99% yield). m/z 416 [M+H]⁺.

Step 4: Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-hydroxy-L-norvalinate

(4S)-4-[Bis(tert-butoxycarbonyl)amino]-5-(cyclopentyloxy)-5-oxopentanoic acid (8.28 g, 20 mmol) was dissolved in THF (80 mL) and cooled in an ice bath. NMM (3.3 mL, 30 mmol) was added followed by dropwise addition of isobutylchloroformate (3.6 mL, 28 mmol). The reaction was stirred at 0° C. for 1.5 hours before the reaction was filtered and the precipitate washed with THF. The mother liquors were cooled again to 0° C. and NaBH₄(1.51 g, 40 mmol) added portionwise, stirring for 3 hours. The reaction mixture was quenched with water (80 mL) and extracted with EtOAc (3×100 mL). The combined organic extracts were washed with brine, dried (MgSO₄) and concentrated in vacuo to give a yellow oil. Purification by column chromatography (40% EtOAc/Heptane) provided the title compound as a colourless oil (4.34 g, 54% yield). m/z 402 [M+H]⁺.

Step 5: Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-{[tert-butyl(dimethyl)silyl]oxy}-L-norvalinate

Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-hydroxy-L-norvalinate (4.34 g, 10.8 mmol) was dissolved in acetonitrile (45 mL) and cooled in an ice bath. DBU (1.7 mL, 11.3 mmol) was added followed by TBDMSCI (1.71 g, 11.3 mmol). The reaction was allowed to stir overnight at room temperature and then concentrated in vacuo. The crude residue was dissolved in EtOAc and washed with 1M HCl, sat NaHCO₃, and brine. The organic layer was dried over magnesium sulfate and concentrated in vacuo to give a yellow oil. Purification by column chromatography (20% EtOAc/Heptane) provided the title compound as a colourless oil (3.82 g, 69% yield). m/z 516 [M+H]⁺.

Step 6: Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-{[tert-butyl(dimethyl)silyl]oxy}-2-methylnorvalinate

To a solution of cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-{[tert-butyl(dimethyl)silyl]oxy}-L-norvalinate (3.82 g, 7.4 mmol) in THF (50 mL) at −78° C. under a N₂atmosphere was added 0.91M KHMDS in THF (16.3 mL, 14.8 mmol). The reaction mixture was stirred at −78° C. for 1 hour before addition of methyl iodide (0.92 mL, 14.8 mmol). The reaction was allowed to warm to room temperature and stirred overnight. The reaction mixture was quenched with sat NH₄Cl and the aqueous layer extracted with EtOAc (2×50 mL). The combined organic extracts were washed with brine, dried (MgSO₄) and concentrated in vacuo to give a yellow oil which was used without further purification (3.50 g, 89% yield). m/z 530 [M+H]⁺.

Step 7: Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-hydroxy-2-methylnorvalinate

Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-{[tert-butyl(dimethyl)silyl]oxy}-2-methylnorvalinate was dissolved in acetic acid (45 mL), THF (15 mL) and water (15 mL). The reaction was allowed to stir at 30° C. for 20 hours for complete reaction. The reaction mixture was then diluted with EtOAc and washed with sat NaHCO₃and brine. The organic layer was dried over magnesium sulfate and concentrated in vacuo to give a thick yellow oil which was taken forward without further purification (3.08 g). m/z 416 [M+H]⁺.

Step 8: Cyclopentyl 5-bromo-N,N-bis(tert-butoxycarbonyl)-2-methylnorvalinate

NBS (3.95 g, 22.2 mmol) was suspended in DCM (30 mL) and triphenylphosphine added (5.44 g, 20.7 mmol). The reaction was stirred for 5 minutes before the addition of pyridine (0.94 mL, 8.9 mmol). Cyclopentyl N,N-bis(tert-butoxycarbonyl)-5-hydroxy-2-methylnorvalinate (3.08 g, 7.4 mmol) was then added as a solution in DCM (30 mL) and stirred overnight at room temperature. The reaction mixture was concentrated in vacuo to give a brown oil which was purified by column chromatography (15% EtOAc/Heptane) to provide the title compound as a colourless oil (1.05 g, 30% yield over two steps). m/z 479 [M+H]⁺.

Step 9: Cyclopentyl 5-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-N,N-bis(tert-butoxycarbonyl)-2-methylnorvalinate

6-Amino-5-(2,4-difluorobenzoyl)-1-(2,6-difluoro-4-hydroxyphenyl)pyridin-2(1H)-one [Example 51 WO 03076405] (500 mg, 1.32 mmol) and cyclopentyl 5-bromo-N,N-bis(tert-butoxycarbonyl)-2-methylnorvalinate (696 mg, 1.45 mmol) were mixed together in DMF (10 mL). Potassium carbonate (365 mg, 2.64 mmol) and sodium iodide (396 mg, 2.64 mmol) were then added, stirring at 40° C. overnight. The reaction mixture was then diluted with EtOAc (50 mL) and washed with water and brine. The organic layer was dried over magnesium sulfate and concentrated in vacuo to give a yellow solid which was purified by column chromatography (30-40% EtOAc/Heptane) to provide the title compound as a white solid (604 mg, 59% yield). m/z 776 [M+H]⁺.

Step 10: Cyclopentyl 5-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-2-methylnorvalinate

Cyclopentyl 5-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-N,N-bis(tert-butoxycarbonyl)-2-methylnorvalinate (604 mg) was dissolved in TFA (10 mL) and DCM (10 mL). The reaction was stirred at room temperature overnight. The reaction mixture was concentrated in vacuo to give a brown oil. The crude residue was then diluted with EtOAc (50 mL) and washed with sat NaHCO₃, water and brine. The organic layer was dried over magnesium sulfate and concentrated in vacuo to give a pale yellow solid Example 5 (387 mg, 46% yield).

Example 6

5-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-2-methylnorvaline

¹H NMR (300 MHz, DMSO-d₅) 10.16 (1H, br s), 8.17 (3H, br s), 7.63-7.51 (1H, m), 7.47-7.18 (3H, m), 7.14-6.99 (2H, m), 6.23 (1H, d, J=9.6 Hz), 4.10 (2H, br s), 1.96-1.63 (4H, m), 1.41 (3H, s). LCMS purity 95%, m/z 508 [M+H]⁺.
Example 6 was synthesised by the route shown in Scheme 8.

Step 1: 5-Benzyl 1-tert-butyl N-(tert-butoxycarbonyl)-L-glutamate

To a solution of N-α-tert-butyloxycarbonyl-L-glutamic acid-α-tert-butyl ester (5 g, 16.5 mmol) in DCM (50 mL) was added benzyl alcohol (3.4 mL, 33 mmol), EDC (3.48 g, 18 mmol) and DMAP (201 mg, 1.6 mmol). The reaction was allowed to stir for 20 hours for complete reaction. The reaction was diluted with DCM, washed with 1M HCl, sat NaHCO₃, brine, dried (MgSO₄) and concentrated in vacuo. The residue was purified by column chromatography (20% EtOAc/Heptane) to provide the title compound as a colourless oil (5.98 g, 92% yield). m/z 416 [M+Na]⁺.
Steps 2-9 follows the same methodology as described in Example 5 (Scheme 7).

Step 10: 5-{4-[6-Amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-2-methylnorvaline

tert-Butyl 5-{4-[6-amino-5-(2,4-difluorobenzoyl)-2-oxopyridin-1(2H)-yl]-3,5-difluorophenoxy}-N,N-bis(tert-butoxycarbonyl)-2-methylnorvalinate (70 mg) was dissolved in TFA (2 mL) and DCM (2 mL). The reaction was stirred at room temperature overnight. The reaction mixture was concentrated in vacuo to give a pink oil. The crude residue was then triturated with diethyl ether to give an off-white solid (23 mg, 40% yield) which was filtered off and dried under vacuum to give Example 6 as a TEA salt.

Compound IV (N-Hydroxy-3-phenyl-propionamide)

Compound IV was prepared as shown in Scheme 9 below

N-(1-Isobutoxyethoxy)-3-phenylpropionamide

N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) (151 mg) and 4-Dimethylaminopyridine (catalytic) were added to a stirred solution of hydrocinnamic acid (100 mg), protected hydroxylamine (WO2008/040934) (136 μL) and dichloromethane (5 mL) at RT under a nitrogen atmosphere. The reaction was stirred for 2 hours and then poured into water (50 mL). This was extracted with dichloromethane (2×50 mL). The combined organic layers were dried over sodium sulfate and solvent removed in vacuo. The residue was purified by column chromatography using an eluent of 0 to 100% ethyl acetate in heptanes, reached via a gradient to give the product as a colourless oil (58 mg).

Compound IV

N-Hydroxy-3-phenylpropionamide

N-(1-Isobutoxyethoxy)-3-phenylpropionamide (58 mg) was dissolved in DCM (2 mL) and MeOH (0.5 mL) and stirred at RT under a nitrogen atmosphere. 4M HCl in dioxane (275 μL) was added to the solution and the reaction stirred for 2 hours. Solvent was then removed in vacuo and the residue purified by HPLC to give the product as a pink solid (9 mg).
m/z 166 [M+H]⁺. NMR (300 MHz, DMSO-d₆) 10.37 (1H, bs), 7.21 (5H, m), 2.81 (2H, t, J=7.5 Hz), 2.61 (1H, m), 2.58 (2H, t, J=7.5 Hz).

Synthesis of Examples 7, 8, 9 and 10

The above compounds were synthesised using the intermediates and methods described below.

Intermediates

Intermediate 7

(2E)-3-(5-Formylpyridin-2-yl)-N-(1-isobutoxyethoxy) acrylamide

Intermediate 7 was prepared by methods described in WO2008/040934.

Intermediate 8

3-(4-formylphenyl)-N-(1-isobutoxyethoxy)propanamide

Intermediate 8 was prepared by methods described in WO2008/040934.

Intermediate 9

Cyclopentyl 1-aminocyclohexanecarboxylate

To 1-aminocyclohexanecarboxylic acid (4.2 g, 29 mmol) in cyclohexane (250 mL) was added cyclopentanol (50 mL) and para-toluenesulphonic acid (5.89 g) and the resulting suspension heated at reflux in a Dean-Stark apparatus for 72 hours. On cooling to room temperature the resulting white solid was collected by filtration and washed with cyclohexane (2×100 mL) and dried under reduced pressure to give the title compound (4.1 g) as a colourless solid. m/z 212.3 [M+H]⁺.

Intermediate 10

Cyclopentyl 2-methyl-D,L-leucinate

A solution of (R,S)-α-methylleucine (500 mg, 3.44 mmol) in cyclopentanol (1 mL) and conc. H₂SO₄(0.36 mL) was heated at 80° C. for 28 hours. The reaction was concentrated under reduced pressure and the residue partitioned between saturated NaHCO₃(aq) (20 mL) and dichloromethane (20 mL). The organic layer was dried (MgSO₄) and evaporated to give the desired material (650 mg) as a light brown oil which was used without further purification. m/z 214.3 [M+H]⁺.

EXAMPLES

Example 7

Cyclopentyl 1-({-[3-(hydroxyamino)-3-oxopropyl]benzyl}amino)cyclopentanecarboxylate

To a solution of Intermediate 8 (208 mg, 0.68 mmol) and Intermediate 5 (184 mg, 0.68 mmol) in dichloromethane (20 mL) was added sodium triacetoxyborohydride (430 mg, 2.04 mmol) and acetic acid (474). The resulting solution was stirred at room temperature for 5 hours and then quenched with saturated NH₄Cl. The reaction was extracted with dichloromethane (2×50 mL) and the combined organic layers were dried (MgSO₄) and concentrated in vacuo. The resulting residue was dissolved in 4M HCl in dioxane (1 mL) and stirred at room temperature for 1 hour. The reaction was quenched with NaHCO₃and extracted with ethyl acetate (2×150 mL). The combined organic layers were dried (MgSO₄) and evaporated. The residue was purified by HPLC to give the title compound (80 mg) as a colourless solid. m/z 375 [M+H]⁺. ¹H NMR (300 MHz, MeOD), 7.46 (2H, d J=7.9 Hz), 7.36 (2H, d J=8.1 Hz), 5.40 (1H, m), 4.18 (2H, s), 2.98 (2H, t, J=7.2 Hz), 2.38 (4H, m), 2.08-1.52 (14H, m).

Example 8

1-({4-[3-(Hydroxyamino)-3-oxopropyl]benzyl}amino)cyclo pentanecarboxylic acid

Cyclopentyl 1-({4-[3-(hydroxyamino)-3-oxopropyl]benzyl}amino)cyclopentanecarboxylate (Example 7)(40 mg) was stirred with lithium hydroxide (40 mg, 15 mmol) in THF (1 mL) and water (1 mL) at 45° C. for 36 hours. The reaction was concentrated under reduced pressure and the resulting residue purified by Gilson preparative HPLC. The purified carboxylic acid derivative was stirred in dichloromethane:TFA (1 mL, 1:1 v/v) for 1 h at room temperature and the reaction concentrated under reduced pressure. The title compound (3 mg) was isolated as a colourless solid.
¹H NMR (300 MHz, MeOD), 7.47 (2H, d J=7.9 Hz), 7.36 (2H, d J=8.1 Hz), 4.18 (2H, s), 3.01-2.95 (2H, t J=7.5 Hz), 2.38 (4H, m), 1.97-1.59 (6H, m)

Example 9

Cyclopentyl N-{4-[3-(hydroxyamino)-3-oxopropyl]benzyl}-2-methyl-D,L-leucinate

This was in a similar manner to Example 7 using Intermediate 8 (209 mg, 0.68 mmol) and Intermediate 10 (146 mg, 0.61 mmol) which gave the title compound (200 mg) as a colourless solid. m/z 391.51 [M+H]⁺.
¹H NMR (300 MHz, MeOD) 7.44 (2H, d J=8.1 Hz), 7.35 (2H, d J=8.1 Hz), 5.38-5.33 (1H, m), 4.21 (1H, d J=12.8 Hz), 4.06 (1H, d, J=12.8 Hz), 2.98 (2H, t J=7.6 Hz), 2.41 (2H, t J=7.6 Hz), 2.04-1.72 (11H, m), 1.68 (31-1, s), 0.99 (6H, t J=7.6 Hz).
The following example was made in a similar manner to the title compound of Example 8 using Example 9.

Example 10

N-{4-[3-(Hydroxyamino)-3-oxopropyl]benzyl}-2-methyl-D,L-leucine

m/z 323 [M+H]⁺. ¹H NMR (300 MHz, MeOD), 7.44 (2H, d J=8.1 Hz), 7.35 (2H, d J=8.1 Hz), 4.20 (1H, d J=12.4 Hz), 4.09 (1H, dJ=12.6 Hz), 2.97 (2H, t J=7.3 Hz), 2.41 (2H, t J=7.7 Hz), 2.01-1.87 (3H, m), 1.76 (3H, s), 1.01 (6H, t J=6.3 Hz).

Example 11

Cyclopentyl 1-[({6-[(1E)-3-(hydroxyamino)-3-oxoprop-1-en-1-yl]pyridin-3-yl}methyl)amino]cyclohexanecarboxylate

To a solution of Intermediate 7 (386 mg, 1.83 mmol) and Intermediate 9 (902 mg, 3.02 mmol) in THF (20 mL) was added powdered molecular sieves 4 Å (100 mg) and the resulting mixture was heated at reflux temperature for 12 hours. On cooling to room temperature, sodium borohydride (317 mg, 85 mmol) was added and stirring was continued for 20 minutes. The reaction was quenched with saturated NH₄Cl (50 mL), and then extracted with dichloromethane (3×100 mL). The combined organic layers were dried (MgSO₄), concentrated in vacuo and the resulting residue subjected to column chromatography [silica gel, 5% methanol in DCM]. The purified material was dissolved in dichloromethane (20 mL) to which was added 4M HCl in dioxane and the resulting solution was stirred at room temperature for 1 hour. The reaction was quenched with NaHCO₃and extracted with ethyl acetate (2×150 mL). The combined organic layers were dried (MgSO₄) and evaporated. The residue was purified by HPLC to give the title compound (80 mg) as a colourless solid, m/z 388.25 (M+H)⁺. ¹H NMR (300 MHz, d₆-DMSO) 10.95 (1H, br s), 9.43 (1H, br s), 8.65 (1H, d, J=1.7 Hz), 7.92 (1H, dd, J=2.0, 8.0), 7.67 (1H, d, J=8.0 Hz), 7.50 (1H, d, J=15.4 Hz), 6.98 (1H, d, J=15.4 Hz), 5.23 (1H, t, J=5.3 Hz), 4.16 (2H, br s), 2.15-2.30 (2H, m), 1.16-1.96 (16H, m).

Biological Activity

Histone Deacetylase Activity The ability of compounds to inhibit histone deacetylase activities was measured using the commercially available HDAC fluorescent activity assay from Biomol. In brief, the Fluor de Lys™substrate, a lysine with an epsilon-amino acetylation, is incubated with the source of histone deacetylase activity (HeLa nuclear extract) in the presence or absence of inhibitor. Deacetylation of the substrate sensitises the substrate to Fluor de Lys™developer, which generates a fluorophore. Thus, incubation of the substrate with a source of HDAC activity results in an increase in signal that is diminished in the presence of an HDAC inhibitor.
Data are expressed as a percentage of the control, measured in the absence of inhibitor, with background signal being subtracted from all samples, as follows:
% activity=[(S ⁱ −B)/(S ^o −B)]×100
where Sⁱis the signal in the presence of substrate, enzyme and inhibitor, S^ois the signal in the presence of substrate, enzyme and the vehicle in which the inhibitor is dissolved, and B is the background signal measured in the absence of enzyme.
IC₅₀values were determined by non-linear regression analysis, after fitting the results of eight data points to the equation for sigmoidal dose response with variable slope (% activity against log concentration of Compound), using Graphpad Prism software.
Histone deacetylase activity from crude nuclear extract derived from HeLa cells was used for screening. The preparation, purchased from 4C (Seneffe, Belgium), was prepared from HeLa cells harvested whilst in exponential growth phase. The nuclear extract was prepared according to the methodology described by J. D. Dignam, Nucl. Acid. Res., 1983, 11, 1475-1489, snap frozen in liquid nitrogen and stored at −80° C. The final buffer composition was 20 mM Hepes, 100 mM KCl, 0.2 mM EDTA, 0.5 mM DTT, 0.2 mM PMSF and 20% (v/v) glycerol.

U937 and HUT Cell Inhibition Assay

Cancer cell lines (U937 and HUT) growing in log phase were harvested and seeded at 1000-2000 cells/well (100 μl final volume) into 96-well tissue culture plates. Following 24 hours of growth cells were treated with compound. Plates were then re-incubated for a further 72-96 hours before a WST-1 cell viability assay was conducted according to the suppliers (Roche Applied Science) instructions.
Data were expressed as a percentage inhibition of the control, measured in the absence of inhibitor, as follows:
% inhibition=100−[(S ⁱ /S ^o)×100]
where Sⁱis the signal in the presence of inhibitor and S^ois the signal in the presence of DMSO.
Dose response curves were generated from 8 concentrations (top final concentration 10 μM, with 3-fold dilutions), using 6 replicates.
IC₅₀values were determined by non-linear regression analysis, after fitting the results to the equation for sigmoidal dose response with variable slope (% activity against log concentration of compound), using Graphpad Prism software.

p38 MAP Kinase Enzyme Assay

The ability of compounds to inhibit p38 MAPα Kinase activity was measured in an assay performed by Upstate (Dundee UK). In a final reaction volume of 25 μL, p38 MAP Kinase α (5-10 mU) is incubated with 25 mM Tris pH 7.5, 0.02 mM EGTA, 0.33 mg/mL myelin basic protein, 10 mM Mg Acetate and [γ-³³P-ATP] (specific activity approx. 500 cpm/pmol, concentration as required). The reaction is initiated by the addition of the MgATP mix. After incubation for 40 minutes at room temperature, the reaction is stopped by the addition of 5 μL of a 3% phosphoric acid solution. 10 μL of the reaction is then spotted onto a P30 filtermat and washed three times for 5 minutes in 75 mM phosphoric acid and once in methanol prior to drying and scintillation counting.
Duplicate data points are generated from a 1/3 log dilution series of a stock solution in DMSO. Nine dilutions steps are made from a top concentration of 10 μM, and a ‘no compound’ blank is included. The standard radiometric filter-binding assay is performed at an ATP concentration at, or close to, the Km. Data from scintillation counts are collected and subjected to free-fit analysis by Prism software. From the curve generated, the concentration giving 50% inhibition is determined and reported.

p38 MAP Kinase Cellular Assay: Inhibition of Phosphorylation of MAPKAP2

U937 or HUT78 cells were plated in RPMI 1640, and were incubated at 37° C., 5% CO₂for 18 hours. 10 mM stocks of compounds were diluted media/0.1% DMSO to give a log or semi-log dilution series. The wells for ‘no treatment’ and ‘anisomycin’ were treated with 0.1% DMSO only. The cells were incubated at 37° C., 5% CO₂for a further 4 hours. Anisomycin was added to all wells except ‘no treatment’ at a final concentration of 10 μM. The cells were incubated at 37° C., 5% CO₂for 30 minutes before harvest. Plates were stood on ice whilst harvesting, and all following steps were carried out at 4° C. The cells were pelleted at 1000 rpm for 10 minutes at 4° C., the media aspirated, and the pellet washed with cold PBS. The pellets were lysed in 120 μl of SDS lysis buffer (62.5 mM Tris, pH 6.8, 2% SDS, 10% glycerol, 50 mM DTT, with protease inhibitors and phosphatase inhibitors added according to the manufacturers' recommendations). After 30 minutes on ice, the samples were sonicated for 5 seconds before centrifugation at 13,000 rpm 4° C. for 10 minutes to remove cell debris. 10 μl of the resulting gel samples were loaded per lane on NOVEX 4-12% Bis-Tris MOPS gels. Membranes from western transfer of gels were blotted with anti-phospho MAPKAP2, anti-phospho HSP27 and anti GAPDH according to the manufacturers' instructions. Signal was visualised using HRP-linked anti-rabbit or anti-mouse antibodies, ECL reagent and ECL film. IC50 values for the various compounds were visualised from the resulting photographic images, using both band-shift and signal intensity.

LPS-Stimulation of THP-1 Cells

THP-1 cells were plated in 100 μl at a density of 4×10⁴cells/well in V-bottomed 96 well tissue culture treated plates and incubated at 37′C in 5% CO₂for 16 hours. 2 hours after the addition of the inhibitor in 100 μl of tissue culture media, the cells were stimulated with LPS (E. coli strain 005:B5, Sigma) at a final concentration of 1 μg/mL and incubated at 37′C in 5% CO₂for 6 hours. TNF-α levels were measured from cell-free supernatants by sandwich ELISA (R&D Systems #QTA00B)

HCE-1 Carboxylesterase Assay

Hydrolysis of esters to the corresponding carboxylic acids by hCE-1 can be measured using the following procedure. At zero time, 100 μl of recombinant hCE-1 at a concentration of 6 μg/mL in phosphate assay buffer (K₂PO₄100 mM, KCl 40 mM, pH 7.4) was added to an equal volume of assay buffer containing 5 μM ester substrate. After thorough mixing, triplicate samples were incubated for 0, 20 or 80 minutes at 37° C. At the appropriate time, hydrolysis was stopped by the addition of 600 μl of acetonitrile. For zero time samples, the acetonitrile was added prior to the enzyme. The samples were analysed for the ester and its corresponding carboxylic acid at room temperature by LCMS (Sciex API 3000, HP1100 binary pump, CTC PAL). Chromatography was based on a MeCN (75×2.1 mm) column and a mobile phase of 5-95% acetonitrile in water/0.1% formic acid. Levels of the acid, the hydrolysis product, after 80 minutes are expressed in ng/mL.

Broken Cell Carboxylesterase Assay

Any given compound of the present invention wherein ester conjugate according to the invention may be tested to determine whether it meets the requirement that it be hydrolysed by intracellular esterases, by testing in the following assay.

Preparation of Cell Extract

U937 or HCT 116 tumour cells (˜10⁹) were washed in 4 volumes of Dulbeccos PBS (˜1 litre) and pelleted at 525 g for 10 min at 4° C. This was repeated twice and the final cell pellet was re-suspended in 35 mL of cold homogenising buffer (Trizma 10 mM, NaCl 130 mM, CaCl₂0.5 mM pH 7.0 at 25° C.). Homogenates were prepared by nitrogen cavitation (700 psi for 50 min at 4° C.). The homogenate was kept on ice and supplemented with a cocktail of inhibitors at final concentrations of:

- Leupeptin 1 μM
- Aprotinin 0.1 μM
- E64 8 μM
- Pepstatin 1.5 μM
- Bestatin 162 μM
- Chymostatin 33 μM

After clarification of the cell homogenate by centrifugation at 525 g for 10 min, the resulting supernatant was used as a source of esterase activity and was stored at −80° C. until required.

Measurement of Ester Cleavage

Hydrolysis of esters to the corresponding carboxylic acids can be measured using the cell extract, prepared as above. To this effect cell extract (˜30 μg/total assay volume of 0.5 mL) was incubated at 37° C. in a Tris-HCl 25 mM, 125 mM NaCl buffer, pH 7.5 at 25° C. At zero time the ester (substrate) was then added at a final concentration of 2.5 μM and the samples were incubated at 37° C. for the appropriate time (usually 0 or 80 minutes). Reactions were stopped by the addition of 3× volumes of acetonitrile. For zero time samples the acetonitrile was added prior to the ester compound. After centrifugation at 12000 g for 5 min, samples were analysed for the ester and its corresponding carboxylic acid at room temperature by LCMS (Sciex API 3000, HP1100 binary pump, CTC PAL). Chromatography was based on a MeCN (75×2.1 mm) column and a mobile phase of 5-95% acetonitrile in water/0.1% formic acid. Rates of hydrolysis are expressed in μg/mL/min.

Cell Accumulation Assay

Cells (8×10⁴/mL) were incubated at 37° C. in culture medium containing 6 μM compound in a 5% (v/v) CO₂-humidified atmosphere. Incubations were terminated after 6 h by centrifugation of 25 mL aliquots of the cell suspension at 300 g for 5 minutes at 4° C. 0.2 mL samples of the culture media supernatants were added to 4 volumes of acetonitrile (Sigma-Aldrich). After decanting the supernatant, the residual cell pellet (2×10⁶cells) was extracted into 1 mL of acetonitrile. Samples were then analysed for the ester and acid metabolite at room temperature by LC/MS/MS (Sciex API3000). Chromatography was based on a MeCN (75×21 mm) column with a 5-95% (v/v) acetonitrile, 0.1% (v/v) formic acid mobile phase. For the zero time samples, the cell suspension was chilled and centrifuged as soon as the ester had been added and then extracted into acetonitrile as described. Levels in cells are expressed as ng/mL.

TABLE 1

							Cell
			Inhibi-				ac-
			tion of				cum-
			phos-			Cleav-	u-
			phoryl-			age	lation
			ation	Ratio		by cell	in
		Inhibi-	of	cell		lysate	U937
		tion	MAPKAP-	IC50s	Cleav-	from	cells
		of	2 in U937	to	age	U937	at 6
		P38	cells	en-	by	cells	hours
		(IC50	(IC50,	zyme	HCE-	pg/mL/	(ng/
Compound		nM)	nM)	IC50	1	min	mL)

	Com- pound I (parent)	50	300	6	NA	NA	NA

	Ex- ample 1	Es- ter 50	Acid 50	10	0.2	198	165	987

Table 1 shows that the acid of Example 1 has a similar IC50 in the enzyme assay to the parent compound (Compound I): (WO 03/076405) indicating that binding to the enzyme has not been disrupted by attachment of the esterase motif. Di-substituted compounds, e.g. Example 1, are hydrolysed by hCE-1 and as a consequence the acid accumulates in cells. This accumulation of acid results in Example 1 being significantly more potent than the parent compound in the cellular assay. These data highlight the potency benefit that can be achieved by the attachment of the esterase motif and the resulting cellular accumulation of the corresponding acid.

TABLE 2

		Inhibi-	Inhibi-
		tion of	tion of
		phos-	phos-
		phoryl-	phoryl-
		ation	ation
		of	of
		MAPKAP-	MAPKAP-			Ac-
		2 in	2 in		Ac-	cum-
		U937	HUT 78		cum-	ula-
		cells	cells	Ratio	ula-	tion
		(IC50,	(IC50,	IC50s	tion	in
		nM)	nM)	in	in	HUT
		(mono-	(non-	HUT	U937	78
		cyte	mono-	78 to	cells	cells
		cell	cytic	U937	(ng/	(ng/
Compound		line)	cell line)	cells	mL)	mL)

Parent		300	450	1.5	NA	NA
Compound I
Example 1		10	1000	100	987	3

	Ex- ample 3	100	10000	100	ND	ND

Table 2 shows that the parent compound (Compound I) is equipotent in monocytic and non monocytic cell lines whereas Examples 1 and 3 are 100 times more potent in the monocytic cell line. Example 1 only accumulates in the monocytic cell line showing that cell selectivity is achieved by the attachment of an esterase motif that is only cleaved in the monocytic cell line.

TABLE 3

			Inhibition of
			phosphorylation
		Inhibition of	of	Ratio
		phosphorylation of	MAPKAP-2 in	IC50s
		MAPKAP-2 in	HUT 78	in HUT
		U937	cells (IC50, nM)	78 to
		cells (IC50, nM)	(non-monocytic	U937
Compound		(monocyte cell line)	cell line)	cells

	Parent Com- pound II	10	10	1

	Com- pound III	1	1	1

	Ex- ample 5	5	100	20

Table 3 indicates that a C-linked dialkyl compound (Example 5) is macrophage selective whereas the parent compound (Compound II; WO 03/076405) and a compound (Compound III; WO 2007/129036) lacking an alkyl group at the alpha carbon of the amino acid derivative are not. This illustrates that macrophage selectivity can be achieved by the introduction of a second substituent at the alpha carbon of the amino acid ester motif.

TABLE 4

	Inhibition of	Inhibition of	Ratio cell IC50s
	HDAC	proliferation	to enzyme	Cleavage by
Compound	(IC50 nM)	in U937 cells	IC50	HCE-1

	Parent Compound IV	2600	13%@10 μM	>3.85	NA

Example 7	Ester 4200	Acid 6120	180	0.043	>12600 pg/mL/min

Example 9	4900	6242	190	0.04	ND

Table 4 shows that the acid of Examples 7 and 9 have similar IC50s in the enzyme assay to the parent compound (Compound IV): indicating that binding to the enzyme has not been disrupted by attachment of the esterase motif. Di-substituted compounds, e.g. Example 7, are hydrolysed by hCE-1 and as a consequence the acid accumulates in monocytic cells. This accumulation of acid results in Examples 7 and 9 being significantly more potent than the parent compound in the cellular assay. These data highlight the potency benefit that can be achieved by the attachment of the esterase motif.

TABLE 5

			Inhibition of	Inhibition of	Ratio IC50s
		Inhibition of	proliferation	proliferation in	in
		HDAC	in U937 cells	HUT78 cells	HUT 78 to
Compound		(IC50 nM)	(IC50 nM)	(IC50 nM)	U937 cells

	Parent Compound IV	2600	13%@10 μM	10%@10 μM	~1

Example 7	Ester 4200	Acid 6120	180	6200	34

Example 9	4900	6242	190	5500	30

Table 5 shows that the parent compound (Compound IV) has similar potencies in monocytic (U937) and non monocytic (Hut78) cell lines whereas Examples 7 and 9 are 30 times more potent in the monocytic cell line than the non-monocytic cell line. This illustrates that a second substituent at the alpha position of the amino acid motif confers macrophage selectivity on the compounds.

Claims

1. A covalent conjugate of an α,α-disubstituted glycine ester and a modulator of the activity of a target intracellular enzyme or receptor, wherein:

the ester group of the conjugate is hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid; and

the α,α-disubstituted glycine ester is conjugated to the modulator at a position remote from the binding interface between the inhibitor and the target enzyme or receptor.

2. A covalent conjugate of an α,α-disubstituted glycine ester and a modulator of the activity of a target intracellular enzyme or receptor, wherein:

the α,α-disubstituted glycine ester is conjugated to the modulator such that the binding mode of the conjugated modulator and the said corresponding acid to the target enzyme or receptor is the same as that of the unconjugated modulator.

3. A method of increasing or prolonging the intracellular potency and/or residence time of modulator of the activity of a target intracellular enzyme or receptor comprising structural modification of the modulator by covalent attachment thereto of an α,α-disubstituted glycine ester at a position remote from the binding interface between the inhibitor and the target enzyme or receptor, the ester group of the conjugate being hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid

4. A method of increasing or prolonging the intracellular potency and/or residence time of modulator of the activity of a target intracellular enzyme or receptor comprising structural modification of the modulator by covalent attachment thereto of an α,α-disubstituted glycine ester such that the binding mode of the conjugated modulator and the said corresponding acid to the target enzyme or receptor is the same as that of the unconjugated modulator, the ester group of the conjugate being hydrolysable by one or more intracellular carboxylesterase enzymes to the corresponding acid.

5. A conjugate or method as claimed in any of the preceding claims wherein the α-substituents of the α,α-disubstituted glycine ester conjugated to the modulator are independently selected from phenyl and groups of formula —CR_aR_bR_cin which:

each of R_a, R_band R_cis independently hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, (C₃-C₈)cycloalkyl; or

R_cis hydrogen and R_aand R_bare independently phenyl or heteroaryl such as pyridyl; or

R_a, R_band R_ctogether with the carbon atom to which they are attached form a tricyclic ring (for example adamantyl); or

R_aand R_bare each independently (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or a group as defined for R_cbelow other than hydrogen, or R_aand R_btogether with the carbon atom to which they are attached form a cycloalkyl or heterocyclic ring, and R_cis hydrogen, —OH, —SH, halogen, —CN, —CO₂H, (C₁-C₄)perfluoroalkyl, —CH₂OH, —O(C₁-C₆)alkyl, —O(C₂-C₆)alkenyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —S(C₂-C₆)alkenyl, —SO(C₂-C₆)alkenyl, —SO₂(C₂-C₆)alkenyl or a group -Q-W wherein Q represents a bond or —O—, —S—, —SO— or —SO₂— and W represents a phenyl, phenylalkyl, (C₃-C₈)cycloalkyl, (C₃-C₈)cycloalkylalkyl, (C₄-C₈)cycloalkenyl, (C₄-C₈)cycloalkenylalkyl, heteroaryl or heteroarylalkyl group, which group W may optionally be substituted by one or more substituents independently selected from, hydroxyl, halogen, —CN, —CONH₂, —CONH(C₁-C₆)alkyl, —CONH(C₁-C₆alkyl)₂, —CHO, —CH₂OH, (C₁-C₄)perfluoroalkyl, —O(C₁-C₆)alkyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —NO₂, —NH₂, —NH(C₁-C₆)alkyl, —N((C₁-C₆)alkyl)₂, —NHCO(C₁-C₆)alkyl, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, (C₃-C₈)cycloalkyl, (C₄-C₈)cycloalkenyl, phenyl or benzyl.

6. A conjugate or method as claimed in any of claims 1 to 4 wherein the α-substituents of the α,α-disubstituted glycine ester conjugated to the modulator, taken together with the α-carbon itself, form a 3-6 membered saturated cycloalkyl or heterocyclyl ring; or wherein at least one of the said α-substituents is a C₁-C₆alkyl substituent.

7. A conjugate or method as claimed in any of claims 1 to 4 wherein one of the α-substitutents of the α,α-disubstituted glycine ester conjugated to the modulator is a C₁-C₆alkyl substituent, and the other is selected from the group consisting of methyl, ethyl, n- and iso-propyl, n-, sec- and tert-butyl, phenyl, benzyl, thienyl, cyclohexyl, and cyclohexylmethyl.

8. A conjugate or method as claimed in any of claims 1 to 4 wherein one of the α-substitutents of the α,α-disubstituted glycine ester conjugated to the modulator is methyl. and the other is methyl, ethyl, or n- or iso-propyl; or the said α-substitutents taken together with the carbon to which they are attached form a cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl ring.

9. A conjugate or method as claimed in any of the preceding claims wherein the α,α-disubstituted glycine ester is covalently conjugated to the modulator via the amino group of the α,α-disubstituted glycine ester.

10. A conjugate or method as claimed in any of the preceding claims wherein the α,α-disubstituted glycine ester is covalently conjugated to the modulator via one of the α substituents of the α,α-disubstituted glycine ester.

11. A conjugate or method as claimed in any of the preceding claims wherein the ester is selectively hydrolysable to the corresponding α,α-disubstituted glycine conjugate by cells containing the intracellular carboxylesterase enzyme hCE-1 relative to cells containing hCE-2 or hCE-3 but not hCE-1.

12. A pharmaceutical composition comprising a conjugate as claimed in any of claims 1, 2 and 5 toll and one or more pharmaceutically acceptable carriers or excipients.

13. A method of identifying a covalent conjugate of an α,α-disubstituted glycine ester of a given modulator of the activity of a target intracellular enzyme or receptor, said conjugate having increased or prolonged cellular potency relative to the given modulator, which method comprises:

(i) identifying a position or positions on a given modulator of the activity of a target intracellular enzyme or receptor, or on a plurality of given modulators of the activity of a target intracellular enzyme or receptor sharing the same binding mode for the target enzyme or receptor, said position or positions being remote from the binding interface between the modulators and the target enzyme or receptor;

(ii) covalently modifying the modulator(s) by attachment of an α,α-disubstituted glycine ester radical, or a range of different α,α-disubstituted glycine ester radicals at one or more of the positions identified in (i);

(iii) testing the alpha amino acid-conjugated modulator(s) prepared in (ii) to determine their activity against the target enzyme or receptor; and

(iv) from data acquired in (iii), selecting one or more of the tested α,α-disubstituted glycine ester-conjugated versions of the given modulator(s) which cause modulation of enzyme or receptor activity inside cells, are converted to and accumulate as the corresponding carboxylic acid inside cells, and which show increased or prolonged cellular potency.