WO1989011484A1

WO1989011484A1 - Phosphoramides useful as antitumor agents

Info

Publication number: WO1989011484A1
Application number: PCT/US1989/002299
Authority: WO
Inventors: Richard F. Borch; Gregory W. Canute; Ronald R. Valente
Original assignee: Research Corporation Technologies, Inc.
Priority date: 1988-05-25
Filing date: 1989-05-25
Publication date: 1989-11-30
Also published as: EP0418292A1; EP0418292A4; JPH04501253A

Abstract

An antitumor compound of formula (I), wherein R1 and R2 may be the same or different and are selected from the group consisting of hydrogen or lower alkyl which is non-substituted with halo, hydroxy or lower alkoxy, provided that the substituent is not on the -carbon; or R1 and R2 taken together with the nitrogen to which they are attached form a morpholion ring. R is a nitro-substituted aryl or nitro-substituted nitrogen, sulfur or oxygen containing heteroaromatic groups R3 and R4 are each independently hydrogen, an electron withdrawing group or lower alkyl which is unsubstituted or mono-substituted with alkyl or an electron withdrawing group.

Description

PHOSPHORAMIDES USEFUL AS ANTITUMOR AGENTS

This invention relates to novel phosphoramides which have useful pharmaceutical properties and are useful as anti-tumor agents. Cyclophosphamide (also known as cytoxan) is one of the most widely used anti-cancer drugs in the world. It is administered in combination with a number of other drugs to treat a wide variety of hematolgic and solid tumors. However, there are several features of the drug that can detract from its clinical efficacy. First, the drug requires metabolic activation in the liver to produce metabolities that are toxic to cancer cells. Second, the drug is specifically toxic to the urinary bladder and also displays the bone marrow toxicity typical of the alkylating agent class of anti-cancer drugs. Third, cyclophosphamide is a potent suppressor of the immune system at the doses used to treat cancer, thus decreasing the infection-fighting ability of patients already debilitated by their disease. Finally repeated use of cyclophosphamide frequently results in the development of resistance to the drug in a patient's cancer cells, thus rendering the drug ineffective.

The present invention describes new phosphoramide compounds that will circumvent one or more of these problems. Place sentence on. The compounds of the present invention are effective in treating tumors in animals

that have developed resistance to cyclophosphamide itself. Finally these compounds are free of the urinary bladder toxicity exhibited by cyclophosphamide

The present invention relates to new chemical phosphoramides possessing anti-tumor activity or capable of possessing anti-tumor activity. These compounds are capable of liberating phosphoramide mustard (the cytotoxic metabolite derived from cyclophosphamides) when exposed to the reducing environment of oxygen-deficient (i.e., hypoxic) cells. The compounds of the present invention have the formula:

wherein

R₁ and R₂ may be the same or different and are selected from the group consisting of hydrogen, or lower alkyl which is substituted with halo, hydroxy or lower alkoxy, provided that the substituent is not on the α-carbon; or R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring;

R₃ and R₄ are independently hydrogen an electron withdrawing group or alkyl containing up to 6 carbon atoms in the main chain and up to a total of 10 carbon atoms and which is unsubstituted or monosubstituted with alkyl or an electron withdrawing group;

R is aryl or a nitrogen, sulfur or oxygen containing heteroaromatic group which is monosubstituted with a nitro group and a pharmaceutically acceptable salt thereof. As used herein, the lower alkyl groups singly or in combination with other groups containing up to six carbon atoms, which may be in the normal or branched configuration, including methyl, ethyl, propyl, isopropyl, butyl, t-butyl, sec-butyl, isobutyl, amyl, pentyl, hexyl and the like. The preferred alkyl groups contain one to three carbon atoms. As used herein, the terms lower alkenyl group contains two to six carbon atoms and at least one double bond and not more than three double bonds. These groups may be in the normal or branched configuration and include such groups as ethenyl, butenyl, isobutenyl and the like.

The term alkynyl as used herein refers to a hydrocarbyl group containing up to two to six carbon atoms and contains a triple bond. These groups may be in a normal or branched configuration. These groups include ethynyl, butynyl, hexynyl, and the like.

The aryl groups are aromatic rings containing from 6 to 10 ring carbon atoms. The aryl groups include phenyl, α-naphthyl or β-naphthyl. The aryl group is preferably phenyl.

As employed herein, the expression "nitrogen, sulfur or oxygen heterocyclic ring" is meant to include those heterocyclic rings which include at least one sulfur, nitrogen or oxygen ring atom but which may include one or several of said atoms. The expression also includes saturated, and unsaturated heterocyclics as well as the heteroaromatic rings. These groups contain from 5 to 10 ring atoms on the heterocyclic moiety. Representative heterocyclic include furan, thiophene, pyrrole, pyridine, pyrazole, pyrazine, pyrimidine, pyridazine, oxazole, imidazole, quinoline, isoquinoline, indole, benzothiophene, benzofuran, benzoxazole, piperazine, tetrahydrofuran, and the like. The preferred heteroaromatic is pyridyl. Moreover, as used herein the terms aryl and nitrogen, sulfur or oxygen heterocyclic rings also includes the alkyl substituted aryl and heterocyclic rings. For example, said term includes toluene, ethyl benzene, alkyl imidazoles, including N-alkylimidazole, alkyl quinoline, e.g., methyl quinoline, and the like.

The R groups as defined herein are nitro substituted aryl or heteroaromatic. The nitro group may be substitued on any position of the aryl or heteroaromatic rings. Preferred R groups include nitrophenyls e.g. 2-nitro or 4-nitro phenyls, nitropyridyls, such as 4-nitro-2-pyridyl or 5-nitro-2-pyridyl and nitropyrroles, nitroimidazoles and nitro quinoline.

The preferred nitroimidazoles are lower alkyl substituted nitroimidazoles wherein lower alkyl contains from 1 to 6 carbon atoms. Especially preferred lower alkyl imidazoles are N-lower alkyl imidazoles. Moreover, the preferred N-alkyl imidazoles have the formula:

wherein R₅ is lower alkyl.

The preferred nitro quinolines have the formula:

wherein the nitro group is on the 2,3,or 4-position of the quinoline.

The preferred R₁ and R₂ are hydrogen or alkyl containing 1 to 3 carbon atoms on the main chain. Both R₁ and R₂ may be monosubstituted with halogen, lower alkoxy or hydroxy at any position except at the α- position (i.e., the carbon adjacent to the nitrogen in the phosphoramide). It is preferred that the alkyl group be substituted on the omega carbon i.e., the last carbon on the chain away from the nitrogen. Preferred substituents are chloro, hydroxy or ethoxy. The preferred R₁ and R₂ groups are hydrogen, CH₂CH₂Cl, CH₂CH₂OH and CH₂CH₂OCH₂CH₃. Moreover, it is preferred that R₁ is the same as R₂.

Moreover, as defined hereinabove, R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring. This is also a preferred value, of R₁ and

R₂.

The R₃ and R₄ substituents are either independently hydrogen atom or an alkyl group, with said alkyl group being unsubstituted or substituted with alkyl or an electron-withdrawing group. As used herein, an electron withdrawing group is a group that will draw electrons to itself more than a hydrogen atom would if it occupied the same position in the molecule. See, Jerry March, "Advanced

Organic Chemestry," 2nd ed., McGraw Hill, New York, p. 21, (1977). Electron withdrawing groups include lower alkoxy, lower alkanoyl, formyl, lower alkenyl, lower alkynyl, aryl, arylalkyl, hydroxy, mercapto, lower thioalkyl, carboxy, lower carbalkoxy, aryloxy, halo, nitro, cyano, lower trialkylamino, and the like. The function of the electron withdrawing group is to make the hydrogen on R₄CH-R₃ acidic, that is, easily removable by base. It is preferred that the electron withdrawing group, when present, is on the alpha carbon ofR₃ or R₄, that is, on the first carbon atom on the R₃ or R₄ chain, respectively. The preferred R₃ groups are hydrogen or carbalkyoxy, especially carbomethoxy, COOCH₃. The preferred R₄ substituent is hydrogen.

The compounds of the present invention can be prepared by art recognized techniques. An exemplary procedure is outlined below:

An alkoxide of Formula II is reacted with N,N- bis (2-chloroethyl) phosphoramidic dichloride followed by the addition of an amine R₁R₂NH to form the compound of Formula I. It is preferrable that the reaction take place in an inert organic solvent such as dioxane, tetrahydrofuran, hexane and the like. The reaction can take place at temperatures ranging from the melting point of the solvent to reflux temperatures, but it is preferred that the reaction take place from about - 60°C to room temperature.

The alkoxide of Fromula II can be prepared by reacting the corresponding alcohol with a

strong base, such as alkali metal, an hydroxide or amide of an alkali metal, or a strong metal organic base, e.g., alkoxide, metal alkylamides, and the like or an organo metallic compound, such as metallic alkyls, such as n-butyl lithium, sodium methylate and the like, in accordance with procedures known to one skilled in the art.

R

An alternative procedure for forming the alkoxide of Formula II is to couple an aldehyde having the formula RCHO with an organometallic reagent containing a (CHR₃R₄) moiety. For example the organometallic may be on alkali metal, e.g., Li(CHR₃R₄) or an Grignard reagent such as CHR₃R₄Mg X, wherein X is halo and the like. The alkali organometallic can be generated by procedures known to one skilled in the art. For example, the Grignard can formed by reacting Mg with the halide of Formula

wherein X is halo, under Grignard forming conditions. Alternatively, when the electron withdrawing group is on the alpha carbon of R₃ or R₄, CHR₃R₄ can be metallated by active metals, such as alkali metals to form the MCHR₃R₄, wherein M is the active metal using metallation reagents, such as lithium bis (trimethylsilyl) amide and the like, under metallation conditions. See, Jerry March, "Advanced Organic Chemisrty," 2nd ed, McGraw Hill, NY, NY p. 555 (1977). For example, methyl acetate can be converted to methyllithioacetate LiCH₂COOMe by treatment with LiN(SiMe₃)₂ in tetrahydrofuran at - 78°C.

The present new compounds which contain basic nitrogen can form salts with acids. All such acid salts are contemplated by the invention but especially preferred are salts with pharmaceutically acceptable acids, such as hydrochloric, sulfuric, nitric, toluenesulfonic, acetic, propionic, tar tar ic , malic and similar such acids well known in this art. In addition, quaternary salts can be formed using standard techniques of alkylation employing, for example, hydrocarbyl halides or sulfates such as methyl, ethyl, benzyl, propyl or allyl halides or sulfates. The compounds of the present invention can be administered to the host in a variety of forms adapted to the chosen route of administration, i.e., orally, intravenously, intramuscularly or subcutaneous routes.

The active compound may be orally administered, for example, with an inert diluent or with an assimilable edible carrier, or it may be enclosed in hard or soft shell gelatin capsules, or it may be compressed into tablets, or it may be incorporated directly with the food of the diet. For oral therapeutic administration, the active compound may be incorporated with excipient and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 0.1% of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 2 to about 60% of the weight of the unit. The amount of active compound in such therapeutically useful compositions is such that a suitable dosage will be obtained. Compositions or preparations according to the present invention are prepared so that an oral dosage unit form contains an amount ranging from about 100mg to about 5 g of active compound. Preferred dosage ranges from about 50 to about 1000 mg of active compound. Especially preferred dosage ranges from about 100 to about 500mg of active compound. The tablets, troches, pills, capsules and the like may also contain the following: A binder such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, lactose or saccharin or a flavoring agent such as peppermint, oil of wintergreen, or cherry flavoring may be added. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify, the physical form of the dosage unit. For instance, tablets, pills, or capsules may be coated with shellac, sugar or both. A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propylparabens as preservatives, a dye and flavoring such as cherry or orange flavor. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially non-toxic in the amounts employed. In addition, the active compound may be incorporated into sustained-release preparations and formulations.

The active compound may also be administered parenterally or intraperitoneally. Solutions of the active compound as a free base or pharmacologically acceptable salt can be prepared in water suitably mixed with a surfactant such as hydroxypropylcellulose. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof and in oils. Under ordinary conditions of storage and use these preparations contain a preservative to prevent the growth of microorganisms.

The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It may be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for. example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the active compound in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredient into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from previously sterile-filtered solutions thereof.

The following examples further illustrate the invention:

EXAMPLE I

Preparation of Bis-(2-chloroethyl)phosphoramide dichloride A solution of phosphorus oxychloride (15.33 g, 0.10 mol) in CH₂Cl₂ (80 ml) was cooled to 0°. Bis-(2-chloroethyl) amine hydrochloride (17.85 g, 0.10 mol) was added directly. Thiethylamine (30.66 ml, 0.22 mol) was added dropwise with constant stirring at 0° with a steady flow of nitrogen exiting through an aqueous solution of NaHCO₃. The reaction was then warmed to room temperature by allowing the ice bath to melt. After stirring for 34 hours, 10% KH₂PO₄ in water

(60 ml) was added. The solution was extracted with CH₂Cl₂ (3 × 30 ml) and the combined organic extracts washed again with 10% aq. KH₂PO₄ (3 × 20 ml), and then dried over MgSO₄. Removal of solvent under reduced pressure gave a crude solid which was distilled (b.p. 121-122°, 0.5 mm) to provide pure product (19.3 g, 84%) as a white solid; R_f= 0.67 (EtOAc:hex 1:2); m.p. 57-59°C.

³¹P NMR (CHCl₃)α= -7.14 ppm

IR (nujol) 1290, 1275, 1260, 1220 (P=O), 1195, 1160, 1150, 1110, 1095, 1060, 1030, 1010, 980, 975, 940, 920, 885, 850, 770, 750, 710, 665 cm^-1.

EXAMPLE 2

Preparation of 2-nitrobenzyl N,N-bis(2-chloroethyl)phosphorodiamidate. A solution of 2-nitrobenzyl alcohol (3.03 g, 19.8 mmol) in 125 ml of THF was placed under an atmosphere of nitrogen and cooled to 0°. A solution of n-butyl lithium (13 ml, 20.8 mmol) in hexanes was added dropwise. The resulting solution of alkoxide was added over 1 hour to a stirred solution of N,N-bis(2-chloroethyl)-phosphoramidic dichloride (5.19 g, 20.0 mmol) in 250 ml of THF. After stirring at 0° for an additional hour, ammonia gas was bubbled through the reaction mixture. Stirring was continued for 1 hour at 0°, and the reaction mixture was filtered through a bed of diatomaceous earth and evaporated to dryness in vacuo. The crude product was purified by flash chromatography on silica gel (ethyl acetate, then methanol) to give 1.8 g (26%) of product as a pale yellow oil.

EXAMPLE 3

Preparation of methyl 3-(4-nitrophenyl)-3-(N,N-bis-(2-chloroethyl)phosphorodiamido) propionate. A solution of lithium bis (trimethylsilyl)amide (20 ml of 1 M, 20 mmol) was cooled to -78°, methyl acetate (1.5 g, 20 mmol) was added, and the resulting solution was stirred for 15 minutes. 4-Nitrobenzaldehyde (3.0 g, 20 mmol) was dissolved in a minimum volume of THF, and the resulting solution was added and stirred for an additional 15 minutes. The resulting alkoxide solution was added to a solution of N,N-bis(2-chloroethyl)phosphoramidic dichloride (10.4 g, 40 mmol) in 100 ml of THF at -40°. When the addition was complete, stirring was continued for an additional 15 minutes, and the mixture was allowed to warm to 0°. Ammonia gas was bubbled through the solution for 15 minutes, and the resulting mixture was purified by flash chromatography on silica gel (ethyl acetate) to give 3.0 g (35%) of product as an oil.

Similarly, using the procedures described herein and the appropriate starting materials the following compounds can also be prepared: methyl 3-(2-nitrophenyl)-3-(N,N-bis(2-chloroethyl)phosphorodiamido)propionate. methyl 3-(4-nitrophenyl)-3-(N,N,N,'N' tetrakis-(2-chloroethyl)phosphoramido)propionate.

The strategy for the design of these compounds is based upon the concept of selective cell kill directed against oxygen-deficient (i.e., hypoxic) cells. Hypoxic cells in tumors are generally resistant to radiation and chemotherapy and thus represent a population of cells that are very difficult to eradicate. Most mammaliam cells operate under conditions of oxygen excess and utilize oxidative metabolism. Hypoxic cells, however, represent a reducing environment; if a prodrug could be designed that was activated by the reducing environment inside these cells, it would provide a mechanism to deliver a cytotoxic species specifically to the tumor cell and thus offer a potential therapeutic advantage. The compounds of the present invention are prodrugs that will liberate phosphoramide mustard (the cytotoxic metabolite derived from cyclophosphamide) when exposed to the reducing environment of the hypoxic cell. The compounds of the present invention are non-cytotoxic under oxic conditions and highly cytotoxic in the presence of hypoxia.

The effectiveness of these compounds is believed to result from the reduction of the nitro groups in the hypoxic cells. It is believed that this reduction facilitates expulsion of the cytotoxic phosphoramide mustard moiety.

The anti-tumor activity has been conducted as follows: The In Vitro cytotoxic activity of representative compounds of the present invention were evalutated as follows:

A soft agar colony-forming assay according to the procedure of Chu and Fischer, Biochem. Pharmacol., 17, 753-767 (1968) was used and modified where necessary. Cultured mouse L1210 and P388 sensitive cells were purchased from EG&G Mason Research Institute, Tumor Bank, Worchester, MA. Cultured cyclophosphamide resistant L1210 and P388 cells were obtained from Dr. Robert Struck of Southern Research Institute, Birmingham, Ala. Typically, the desired cells (2-3 × 10⁶ cells/ml) in exponential growth and suspended in 6.5 ml of Fischer's medium (Gibco Lab., Grand Island, N.Y.) were divided into six groups (1 control and 5 treated groups) containing an equal number of cells in 1 ml. These cells were then treated with varying doses of drug (solution of perhydrooxazine in media or 20% ethanol-water), diluted with media to give a total volume of 10 ml, and incubated for one hour at 37°C. The cells were washed three times with 3 ml of supplemented Fischer's medium (containing 10% horse serum) by centrifuge (800 × g), removal of media by suction, and resuspension of the pellet in media (5 ml). A 1-ml portion was used to determine the cell count with a Coulter counter. From the remainder, a 5-ml suspension of cells was prepared at a density of 10 ⁵ cells/ml, and between 10² and 10⁵ cells were placed on soft agar and incubated at 37°C. Colonies were counted after 10 days. The log of the surviving fraction was plotted vs. drug concentration and from this plot the LC was obtained. (By definition, the LC₉₉ value represents the concentration of drug necessary to effect a

99% cell kill.)

The results of the cytotoxic activity studies are tabulated hereinbelow:

The hypoxic cell selectivity exhibited by compounds by the present invention was evaluated as follows:

Protocol for evaluation of hypoxic cell selectivity.

KHT/iv cells were adapted to cell culture from the mouse KHT sarcoma by Dietmar Siemann, University of Rochester. Cells were maintaimed in Eagle's basal medium and

10% fetal calf serum for all experiments. Cells in exponential growth were trypsinized from monolayer cultures and separated from one another by agitation in a gas-tight syringe at a density of 1-2 × 10⁷ cells/ml for 15 minutes at

37°. The cells were then resuspended in HEPES-buffered

Eagle's medium contained in stirred gas-tight vials at a final density of 2 × 10⁷ cells/ml; before cells or drugs were added, the vials were pre-equilibrated with humidified gas having the composition 95:5 air:CO₂ for aerobic treatment or 95:5 nitrogen:CO₂ from hypoxic treatment. Oxygen tension in the hypoxic medium was approximately 100 ppm after the equilibration period. Drug was dissolved a volume of ethanol that would give a final ethanol concentration of 1% in the medium; this concentration of ethanol had no effect on the plating efficiency of control cell preparations. Cells were incubated with drug under aerobic or hypoxic conditions at 37° for 4 hours. The cells were then removed from the vials, washed with drug-free medium, counted, and plated for cell survival using a standard clonogenic assay. Cell surviving fraction was plotted vs. drug concentration, and the LC₉₉ values were obtained from the least squares equation.

Comments on aerobic vs. hypoxic cell data.

In this assay, smaller values for the LC₉₉ correspond to the more potent drug and/or conditions, because equivalent (99%) cell kill requires less drug. Thus selectivity for tumor cell killing under oxygen deficient conditions has been demonstrated.

As shown by the data compounds of the present invention exhibit a selectivity factor of at least three in KHT sarcoma and adenocarcinoma cell lines. In other words, compounds of the present invention are at least three times more toxic to these tumor lines under hypoxic conditions than to identical cells under normal oxic conditions. Thus, selectivity for tumor cell killing under oxygen deficient conditions has been demonstrated.

The above preferred embodiments and examples are given to illustrate the scope and spirit of the present invention. These embodiments and examples will make apparent to those skilled in the art other embodiments and examples. These other embodiments are examples within the contemplation of the present invention. Therefore the present invention should be limited only by the appended claims.

Claims

WHAT IS CLAIMED IS

1. A compound of the formula

wherein

R₁ and R₂ may be the same or different and are selected from the group consisting of hydrogen or lower alkyl which is mono-substituted with halo, hydroxy or lower alkoxy, provided that the substituent is not on the -carbon; or

R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring;

R is a nitro-substituted aryl or nitro-substituted nitrogen, sulfur or oxygen containing heteroaromatic groups;

R₃ and R₄ are each independently hydrogen, an electron withdrawing group, or lower alkyl which is unsubstituted or mono-substituted with an alkyl group or an electron withdrawing group; and a pharmaceutically acceptable salt thereof.

2. The compound according to Claim 1 wherein R₃ and R₄ are independently hydrogen, an electron withdrawing group or lower alkyl which is unsubstituted or mono-substituted with a electron withdrawing group, wherein the electron withdrawing group is on the α carbon of R₃ or R₄.

3. The compound according to Claim 1 or 2 wherein the electron withdrawing group is selected from the group consisting of lower alkoxy, lower alkanoyl, formyl, lower alkenyl, lower alkynyl, aryl, hydroxy, mecapto, lower thioalkyl, carboxy, carbalkoxy, aryloxy, halo, nitro, cyano, or lower trialkylamino.

4. The compound according to any of Claims 1 to 3 wherein R₃ is hydrogen or an electron withdrawing group and

R₄ is hydrogen.

5. The compound according to Claim 4 wherein R₃ is hydrogen or lower carbalkoxy and R₄ is hydrogen.

6. The compound according to any of Claims 1 to 5wherein R is nitrophenyl, nitropyridyl, nitropyrrolyl, nitroquinolyl or nitroimidazolyl.

7. The compound according to Claim 6 wherein R is 2-nitrophenyl, 4-nitrophenyl, 4-nitro-2-pyridyl, 5-nitro-2-pyridyl, 2-nitroquinolyl, 3-nitroquinolyl, 4-nitroquinolyl or

whe

rein R₅ is lower alkyl

8. The compound according to any of Claims 1 to 7 wherein R₁ and R₂ are each hydrogen or alkyl mono-substituted with halogen, hydroxy or lower alkoxy, wherein the substituent is on the omega carbon or R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring.

9. The compound according to Claim 8 wherein R₁ and R₂ are each independently hydrogen, -CH₂CH₂Cl, CH₂CH₂OCH₃ or CH₂CH₂OH or R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring.

10. The compound according to any of Claims 1 to 9 wherein R₁ and R₂ are the same or R₁ and R₂ taken together with the nitrogen to which they are attached form a morpholino ring.

11. The compound according to Claim 1 which is

2-nitrobenzyl N,N-bis(2-chloroethyl)phosphorodiamidate, methyl 3-(4-nitrophenyl)-3-(N,N-bis-(2-chloroethyl)phosphoramido)propionate, methyl 3-(2-nitrophenyl)-3-(N,N-bis(2-chloroethyl)phosphoramido) propionate or methyl 3-(4-nitrophenyl)-3-(N,N,N'N'-tetrakis-(2-chloroethyl)phosphoroamido)propionate.

12. A pharmaceutical composition comprising a pharmaceutically effective amount of the compound in any of Claims 1 to 11 and a pharmaceutical carrier therefor.

13. The compound of any of Claims 1 to 11 for preparing compositions useful in treating tumors.