Synthesis,Solution Conformation and Anti-HIV Activity of Novel 3-Substituted-2′,3′-Dideoxy-5-Hydroxymethyl-Uridines and Their 4,5-Substituted Analogues

Abstract

To decrease the toxicity of potent anti-HIV nucleosides 3-azido-2′,3′-dideoxythymidine (AZT) and 2,3′-dideoxy-3′-fluorothymidine (3-FddThd, FLT), their new analogues, 3-azido-2′,3′-dideoxy-5-hydroxymethyluridine (3-Az5HmddUrd) and 2,3′-dideoxy-3′-fluoro-5-hydroxymethyluridine (3′-F5HmddUrd), were synthesized. The reaction of 3′-azido-2′,3′-dideoxyuridine (3′-AzddUrd) and 2,3′-dideoxy-3′-fluorouridine (3′-FddUrd) with formaldehyde, under strongly alkaline conditions and at elevated temperature, proceeded after 4 days to completion to afford the corresponding 5-hydroxymethyl derivatives 3′-Az5HmddUrd and 3′-F5HmddUrd in good yield. These compounds were also prepared by oxidation of AZT and FLT with the use of K₂S₂O₈. ¹H NMR analyses were subjected to the series of 3′,4 and 5-substituted pyrimidine 2′-deoxy- and 2′,3′-dideoxynucleosides involving 3′-Az5HmddUrd and 3′-F5HmddUrd. Analysis of the sugar furanose ring puckering demonstrated that all 3′-fluorine derivatives exhibited strong domination of the S conformation (∼100%) while 3-substitution by electron-donating groups, such as NH₂, increased population of the N conformation. Experimentally observed substituent effect on the furanose ring puckering equilibrium was reconstructed in the 100 ps molecular dynamic trajectories obtained for AZT, FLT, dThd, 2′,3′-ddThd and 3′-amino-2′,3′-ddThd. It may be concluded that anti-HIV activity is linked to a direct interaction of the 3′-sub-stituent with reverse transcriptase (RT) binding site. Anti-HIV activities of 3′-Az5HmddUrd and 3′-F5HmddUrd are lower than activity of AZT and FLT; however, 3′-Az5HmddUrd and 3′-F5HmddUrd are less toxic than AZT and FLT.