Synthesis and Biological Evaluation of 2′,3′-Didehydro-2′,3′-dideoxy-5- fluorocytidine (D4FC) Analogues: Discovery of Carbocyclic Nucleoside Triphosphates with Potent Inhibitory Activity against HIV-1 Reverse Transcriptase1

The discovery of a novel cytosine nucleoside, â-D-2′,3′-didehydro-2′,3′-dideoxy-5-fluorocytidine (D-D4FC), as a potent antihuman immunodeficiency virus (HIV) agent led us to synthesize a series of analogues and derivatives of â-D-D4FC that could be more selective and also possess increased glycosidic bond stability. The synthesized D-D4FC analogues were evaluated for antiHIV-1 activity, anticancer activity, and cytotoxicity in various cells. The biological data demonstrated that the 5-substitution of â-D-D4FC with bromine (6c) and iodine (6d) resulted in the loss of antiviral activity, and the R-D anomer (7a) of D-D4FC was also devoid of activity. The 5-fluorouracil analogues (6b and 7b) of D-D4FC were less potent and more cytotoxic than the parent compound, whereas the â-L-D4FU (11) showed both potent anti-HIV-1 activity and cytotoxicity. N4and 5′-O-acyl derivatives (17, 15a-c) of â-D-D4FC exhibited comparable antiviral activity to â-D-D4FC. In contrast, the N4-isopropyl derivative (20) of â-D-D4FC was not active against HIV-1, even at 100 μM. The carbocyclic analogues (26a,b) of D4FC demonstrated weak activity against HIV-1 and no toxicity in various cells. The triphosphates (27a,b) of the carbocyclic nucleosides demonstrated potent inhibitory activity against recombinant HIV-1 reverse transcriptase at submicromolar concentrations. Of the compounds tested as potential anticancer agents, â-D-, R-D-, and â-L-D4FU (6b, 7b, 11) showed inhibitory activity against rat glioma and modest activity against human lung carcinoma, lymphoblastoid, and skin melanoma cells.