Synthesis of L-enantiomers of 4'-thioarabinofuranosyl pyrimidine nucleosides.

L-Enantiomers of 4'-thioarabinofuranosyl pyrimidine nucleosides were synthesized from D-xylose. Methyl 2,3,5-tri-O-benzyl-D-xylofuranoside 6 was converted to the corresponding xylitol 7, which was treated with MsCl and then Na2S to give 1,4-anhydro-L-4-thioarabitol 8. As previously reported, Pummerer rearrangement of 8 followed by glycosylation with a silylated thymine and N4-acetylcytosine derivative and deprotection gave the corresponding alpha- and beta-L-4'-thioarabinofuranosyl pyrimidine nucleosides.