Anti versus syn opening of epoxides derived from 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine with Me3Al: factors controlling the stereoselectivity

Synthesis of 3',4'-difluoro-3'-deoxyribonucleosides and its evaluation of the biological activities: discovery of a novel type of anti-HCV agent 3',4'-difluorocordycepin

Upon reacting 3',4'-unsaturated cytosine (8 and 9) and adenine nucleosides (13 and 14) with XeF(2)/BF3 · OEt(2), the respective novel 3',4'-difluoro-3'-deoxyribofuranosyl nucleosides (10-12 and 15-18) could be obtained. Formation of anti-adducts (11, 16 and 18) revealed that the fluorination involved oxonium ions as incipient intermediates. TBDMS-protected 3',4'-unsaturated adenosine provided the β-face adducts as sole stereoisomers whereas α-face-selectivity was observed with the TBDPS-protected adenosine 14. The evaluation of the novel 3'-deoxy-3',4'-difluororibofuranosylcytosine-(19-21) and adenine nucleosides (22-25) against antitumor and antiviral activities revealed that 3',4'-difluorocordycepin (24) was found to possess anti-HCV activity. The SI of 24 was comparable to that of the anti-HCV drug ribavirin. However, sofosbuvir, FDA-approved novel anti-HCV drug, showed better SI value. Our finding revealed that the introduction of the fluoro-substituent into the 4'-position of cordycepin derivatives decreased the cytotoxicity to the host cell with retention of the antiviral activity.

From the chemistry of epoxy-sugar nucleosides to the discovery of anti-HIV agent 4'-ethynylstavudine-Festinavir

Branched sugar nucleosides have attracted much attention due to their biological activities. We have demonstrated that epoxysugar nucleosides serve as versatile precursor for the stereo-defined synthesis of these nucleoside derivatives on the basis of its ring opening with organoaluminum or organosilicon reagents. In this review article, novel methods for the synthesis of nucleoside analogues branched at the 1' and 4'-position will be described. During this study, we could discover an anti-HIV agent, 4'-ethynylstavudine (Festinavir). Festinavir showed more potent anti-HIV activity than the parent compound stavudine (d4T). Other significant properties of Festinavir are as follows: 1) much less toxic to various cells and also to mitochondorial DNA synthesis than d4T, 2) better substrate for human thymidine kinase than d4T, 3) resistant not only to chemical glycosidic bond cleavage but also to catabolism by thymidine phosphorylase, 4) the activity improves in the presence of a major mutation, K103N, associated with resistance to non-nucleoside reverse transcriptase inhibitors. Detailed profile of the antiviral activities, biology and pharmacology of Festinavir are also described.

Preparation of 4'-benzenesulfonyl-3'-deoxythymidine and its reaction with organoaluminum and organosilicon reagents

The 4'-benzenesulfonyl derivative of 3'-deoxythymidine was prepared from 3'-deoxythymidine-5'-aldehyde. The 4'-benzenesulfonyl leaving group undergoes a nucleophilic substitution with organoaluminum and organosilicon reagents to furnish a variety of 4'-substituted (Me, Et, i-Bu, trimethylsilylethynyl, CH(2)CH=CH(2), CN, N(3)) analogues.

Synthesis and Antiviral Evaluation of 4'-alkoxy Analogues of 9-(β-D-xylofuranosyl)adenine

Background:

Motivated by the reported biological activity of 9-(β-D-xylofuranosyl)adenine (xylo-A), the synthesis of its 4'-alkoxy analogues was carried out.

Methods:

The starting material 9-(3-deoxy-β-D-glycero-pento–3-enofuranosyl)adenine (1) was prepared from adenosine. Compound 1 was converted to the 2',5'-bis-0–(tert-butyldimethylsilyl) derivative (2) and then to the N6-pivaloyl derivative (3). When 3 was reacted with meta- chloroperbenzoic acid in the presence of a series of alcohols, the β-D-isomer of the respective 4'-alkoxy derivative was obtained exclusively in high yield. Deprotection of these products led to the isolation of the desired 4'alkoxy analogues (8a-I) of xylo-A.

Results:

Antiviral evaluation revealed that none of these analogues showed inhibitory activity against a wide variety of DNA and RNA viruses.

Conclusions:

We assume that conformational difference of the sugar moiety of 8a-1 from that of xylo-A could be attributable to their inactivity.

Synthetic use of epoxy-sugar nucleosides

Preparation of 1',2 '-, 3 ',4 '-, and 4 ',5 '-epoxy derivatives of nucleosides and their use for the stereoselective synthesis of 1'- and 4 '-branched analogues are described.