SYNTHESIS OF 2-DEOXY-4-THIO-D-RIBOFURANOSE AND ITS 3-AZIDO ANALOG FROM L-ARABINOSE - INTERMEDIATES IN THE SYNTHESIS OF 4'-THIODEOXYNUCLEOSIDES

O-benzoyl-2-deoxy-4-thio-alpha,beta-D-ribofuranose and its 3-azido ana logue have been prepared by an efficient route starting from L-arabino se. A key intermediate in this route is 2-deoxy-4,5-O-isopropylidene-L -erythro-pentose dibenzyl dithioacetal which is readily substituted in the 3-position thus offering extensive scope for the synthesis of 3-s ubstituted 2-deoxy-4-thio-alpha,beta-D-ribofuranoses and subsequent nu cleoside derivatives.