Synthesis and conformational analysis of 1,2-cis fused bicyclic α- d-galactofuranosyl thiocarbamate from per- O- tert-butyldimethylsilyl-β- d-galactofuranosyl isothiocyanate

Abstract

Per- O- tert-butyldimethylsilyl-α,β- d-galactofuranosyl isothiocyanate ( 4) was synthesized by the reaction of per- O-TBS-β- d-galactofuranose ( 1) with KSCN, promoted by TMSI. Upon O-desilylation (1,2-dideoxy-α- d-galactofuranoso)[1,2 d]-1,3-oxazolidine-2-thione ( 6), the cis-fused bicyclic thiocarbamate was obtained as the only product. Conformational analysis, aided by molecular modelling, showed two stable twist forms ( 3T 4 and 4T O) for the five-membered sugar ring in 6. In aqueous solution, the equilibrium favours the first conformation (3:1 ratio). On the other hand, this ratio decreases for less polar solvents.