Synthesis and biological evaluation of some novel 4'-thio-L-ribonucleosides with modified nucleobase moieties

1,2,3,5-tetra-O-acetyl-4-thio-beta-L-ribofuranose (13) was synthesized by an improved five-step sequence starting from methyl alpha-D-lyxopyranoside. Compound 13 was then converted to the corresponding L-4'-thionucleosides 4-6 and 19 by a modified Vorbrüggen procedure. All of these nucleoside analogues were tested for their antitumour activity in vitro.