Pyrimidine nucleosides. 5. Syntheses of carcinostatic halogenocyclonucleosides

Synthesis and cytotoxic activity of novel 5-substituted-1-(β-L-arabinofuranosyl) pyrimidine nucleosides

A series of new 5-halogeno-1-(ß-L-arabinofuranosyl)uracils and their cytosine analogues were synthesized by halogenation of ara-L-uridine and ara-L-cytidine, respectively. The 5-(2-thienyl) and 5-halogenothienyl derivatives of both series were also prepared in excellent yields by Stille coupling followed by halogenation. All of these syntheses were based on benzoyl-protected derivatives. In vitro cytotoxicity experiments carried out using L1210 mouse leukemia cells showed that 5-(2-thienyl)-ara-L-uridine was the most potent compound of the new compounds; the majority of the analogues were not effective up to 200 μM concentrations.

Evaluation of 2,2'-anhydro-1-(3'-Ok-acetyl-beta-D-arabinofuranosyl)-5-iodocytosine hydrochloride and related compounds as antineoplastic and antiviral agents

2,2'-Anhydro-1-(3'-O-acetyl-beta-D-arabinofuranosyl)-5-iodocytosine (anhydro-araIC 3'-acetate), previously synthesized and isolated as a crude product by Moffatt and his coworkers, was purified and characterized. The availability of pure anhydro-araIC 3'-acetate made possible a comparative study of the antineoplastic, antiviral and biochemical potencies of anhydro-araIC 3'-acetate with the structurally related agents 2,2'-anhydro-1-(3'-O-acetyl-beta-D-arabinofuranosyl)cytosine (anhydro-araC 3'-acetate) and 2,2'-anhydro-1-(beta-D-arabinofuranosyl)-5-iodocytosine (anhydro-araIC). The presence of the 5-iodo substituent and/or the 3'-O-acetyl group on 2,2'-anhydro1-(beta-D-arabinofuranosyl)cytosine (anhydro-araC) did not alter the capacity of these agents to exert cytotoxic and antineoplastic activity against L1210, P388, L5178Y and human leukemia cells and against human colon and rectal carcinomas, as well as antiviral activity against herpes simplex virus Type 1. All of the compounds caused inhibition of [3H]thymidine incorporation into the DNA of L1210 cells in culture, with anhydro-araIC 3'-acetate being significantly less inhibitory than the other derivatives. Little or no interference with RNA and protein synthesis was produced by these pyrimidine nucleosides. Both anhydro-araIC 3'-acetate and anhydro-araIC were potent inhibitors of the activity of DNA polymerase alpha from the L1210 leukemia at the nucleoside level, while anhydro-araC 3'-acetate and anhydroaraC were non-inhibitory; none of the agents caused inactivation of DNA polymerase beta. The findings suggest that the antineoplastic and antiviral activities of the 2,2'-anhydro-arabinosylcytosine nucleosides may be the result of biochemical actions different from those of araC.