Nucleic acid related compounds. 53. Synthesis and biological evaluation of 2′-deoxy-β-threo-pentofuranosyl nucleosides. "Reversion to starting alcohol" in Barton-type reductions of thionocarbonates

Treatment of selectively 3′,5′-protected β-D-xylofuranosyl nucleosides (4) with phenyl chlorothionocarbonate and DMAP followed by hydrogenolysis of the resulting (2′-O-phenoxythiocarbonyl) phenyl thionocarbonate esters (6) with tributylstannane/AIBN, and deprotection, gave 2′-deoxy-β-D-threo-pentofuranosyl nucleosides (7). Formation of a by-product bis(nucleosid-2′-yl)thionocarbonate dimer (8) was detected in the uracil nucleoside reaction sequence. Its subsequent reduction provides one explanation for "reversion to starting alcohol" in Barton-type deoxygenation reactions. Only the guanine 2′-deoxynucleoside analogue (7b) had (weak) antiviral activity (against herpes simplex virus type 1).