Synthesis of new nucleoside phosphoraziridines as potential site-directed antineoplastic agents.

With the aim of increasing the selectivity of the 2,2-dimethylphosphoraziridine type antitumor agents toward the intracellular site of DNA synthesis, a series of new compounds was synthesized in which the reactive bis(2,2-dimethyl-1-aziridinyl)phosphinyl (2,2-DMAP) group was linked through a carbamate or amide linkage to thymidine or cytosine nucleoside moieties. The 3'- and 5'-(2,2-DMAP)carbamates of thymidine (1 and 2) were found to be highly unstable, therefore the corresponding O-acetyl derivatives 5 and 6 were prepared by reacting 5'- and 3'-acetylthymidine, respectively, with dichloroisocyanatophosphine oxide followed by the addition of 2,2-dimethylaziridine and triethylamine. The 3'- and 5'-(2,2-DMAP)amides of thymidine 14 and 15 were prepared by reacting the appropriate thymidinylamines with bis(2,2-dimethyl-1-aziridinyl)phosphinyl chloride (17). The N4-(2,2-DMAP)amides of cytidine, 2'-deoxycytidine, and cytosine arabinoside (18, 19, and 20, respectively) were prepared by reacting the hydrochlorides of the O-peracetylated cytosine nucleosides with triethylamine and POCl3 and, subsequently, with 2,2-dimethylaziridine and triethylamine, to give the corresponding N4-(2,2-DMAP)cytosine nucleoside peracetates 21, 22, and 23, respectively, which were then deacetylated by aminolysis. However, the peacetate intermediates were found to be more stable and, probably for the same reason, also more active against P388 leukemia in mice than the deacetylated products. Particularly, 22 and 23 showed sufficient activity in this in vivo assay system to warrant further evaluation. The relationships between the antitumor activities, the chemical alkylating activities, and the cholinesterase inhibitory activities of these agents are discussed.

Synthesis and properties of bis(2,2-dimethylaziridinyl)phosphinic amides: a series of new antineoplastic agents.

In continuation of efforts to improve the antitumor selectivity of the 2,2-dimethylaziridine class of alkylating agents, a series of N-substituted bis(2,2-dimethyl-1-aziridinyl)phosphinic amides has been synthesized and evaluated. All of these compounds (3-15) were tested in vivo against leukemia P-388 in mice, where most of them caused significant increase of survival time at nontoxic dose levels. Some of the most active compounds were also tested against leukemia L1210, B16 melanoma, and colon 26 carcinoma; in the latter tests, the parent unsubstituted amide 3 appeared to show the highest antitumor activity. Since the dose-limiting toxicity of the clinically tested prototypes of this class of anticancer agents AB-132 (1) and AB-163 (2) had been found to be CNS toxicity attributable mainly to the inhibition of cholinesterase, the compounds were tested in vitro against the cholinesterases from horse serum, electric eel, and bovine erythrocytes, as well as in vivo for the inhibition of the cholinesterase present in the whole blood of mice. In all of these assays, the various members of the present series showed a wide range of anticholinesterase activities, ranging from almost zero (for 3) to even higher potency than that of the prototype 2. A similarly wide range of stability was observed toward hydrolytic ring opening of the 2,2-dimethylaziridine moieties. Several of the compounds, particularly 3, deserve further study.