A series of 4-nitrobenzyloxycarbonyl prodrug derivatives of O6-benzylguanine (O6-BG), conceived as prodrugs of O6-BG, an inhibitor of the resistance protein O6-alkylguanine-DNA alkyltransferase (AGT), were synthesized and evaluated for their ability to undergo bioreductive activation by reductase enzymes under oxygen deficiency. Three agents of this class, 4-nitrobenzyl (6-(benzyloxy)-9H-purin-2-yl)carbamate (1), and its monomethyl (2) and gem-dimethyl analogues (3) were tested for activation by reductase enzyme systems under oxygen deficient conditions. Compound 3, the most water-soluble of these agents, gave the highest yield of O6-BG following reduction of the nitro group trigger. Compound 3 was also evaluated for its ability to sensitize 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (laromustine)-resistant DU145 human prostate carcinoma cells, which express high levels of AGT, to the cytotoxic effects of this agent under normoxic and oxygen deficient conditions. While 3 had little or no effect on laromustine cytotoxicity under aerobic conditions, significant enhancement occurred under oxygen deficiency, providing evidence for the preferential release of the AGT inhibitor O6-BG under hypoxia.

No abstract

Various 2',3'-dideoxy-L-cytidine,2',3'-dideoxy-L-uridine, and 3'-deoxy-L-thymidine analogues have been synthesized and evaluated in vitro as potential anti-HIV and anti-HBV agents. Coupling of 1-O-acetyl-5-O-(tert-butyldimethylsilyl)-2,3-dideoxy-L-ribofuranose (1) with silylated derivatives of 5-fluorocytosine, cytosine, 5-fluorouracil, uracil, and thymine in the presence of ethylaluminum dichloride gave the corresponding nucleosides 2, 3, 4, 5, 10, 11, 12, 16, 17, and 18 as a mixture of alpha- and beta-anomers, which were then deblocked to yield the corresponding 2',3'-dideoxy-L-5-fluorocytidine derivatives, 6 and 7, 2',3'-dideoxy-L-cytidine derivatives, 8 and 9, 2',3'-dideoxy-beta-L-fluorouridine (13), 2',3'-dideoxy-beta-L-uridine (14), and 3'-deoxy-L-thymidine derivatives, 15 and 19. Among these 2',3'-dideoxy-L-nucleoside analogues, 2',3'-dideoxy-beta-L-5-fluorocytidine (6, beta-L-FddC) was found to be the most active against HIV-1, which is approximately 3 and 4 times more active against HIV-1 in vitro than 2',3'-dideoxy-beta-D-cytidine (ddC) and 2',3'-dideoxy-beta-D-5-fluorocytidine (beta-D-FddC) with ED50 values of 0.5, 1.5, and 2 microM, respectively. The dose-limiting toxicity of ddC is severe neuropathy which may be caused by the inhibition of the synthesis of mitochondrial DNA. ddC has an IC50 value of 0.022 microM against host mitochondrial DNA synthesis. Conversely, the IC50 values for beta-L-FddC and beta-L-ddC are > 100 microM; therefore, neuropathy may not present itself to be a problem with beta-L-FddC and beta-L-ddC as chemotherapeutic agents. In addition, beta-L-FddC and 2',3'-dideoxy-beta-L-cytidine (8, beta-L-ddC) demonstrated equally potent activity against HBV in vitro by having the same ED50 value of 0.01 microM. Both beta-L-FddC and beta-L-ddC, which have an "unnatural" L-configuration in the sugar moiety, are approximately 1000 and 280 times more potent, respectively, against HBV than the D-configuration beta-D-FddC and ddC which have an ED50 values of 10 and 2.8 microM. In view of the potent antiviral activity of beta-L-FddC against both HIV-1 and HBV and potent antiviral activity of beta-L-ddC against HBV in vitro, their low cytotoxicity, and especially the negligible inhibitory effect on host mitochondrial DNA synthesis, beta-L-FddC and beta-L-ddC merit further development as potential anti-HIV and anti-HBV agents.