Synthesis of 3′-modified xylofuranosyl nucleosides bearing 5′-silyl or -butyryl groups and their antiviral effect against RNA viruses

D-xylofuranosyl nucleoside analogues bearing alkylthio and glucosylthio substituents at the C3′-position were prepared by photoinitiated radical-mediated hydrothiolation reactions from the corresponding 2′,5′-di-O-silyl-3′-exomethylene uridine. Sequential desilylation and 5′-O-butyrylation of the 3′-thiosubstituted molecules produced a 24-membered nucleoside series with diverse substitution patterns, and the compounds were evaluated for their in vitro antiviral activity against three dangerous human RNA viruses, SARS-CoV-2, SINV and CHIKV. Eight compounds exhibited SARS-CoV-2 activity with low micromolar EC₅₀ values in Vero E6 cells, and two of them also inhibited virus growth in human Calu cells. The best anti-SARS-CoV-2 activity was exhibited by 2′,5′-di-O-silylated 3′-C-alkylthio nucleosides. Twelve compounds showed in vitro antiviral activity against CHIKV and fourteen against SINV with low micromolar EC₅₀ values, with the 5′-butyryl-2′-silyl-3′-alkylthio substitution pattern being the most favorable against both viruses. In the case of the tested nucleosides, removal of the 2′-O-silyl group completely abolished the antiviral activity of the compounds against all three viruses. Overall, the most potent antiviral agent was the disilylated 3′-glucosylthio xylonucleoside, which showed excellent and specific antiviral activity against SINV with an EC₅₀ value of 3 μM and no toxic effect at the highest tested concentration of 120 μM.