Synthesis of Methyl 1-Thio-L-Rhamnopyranoside-Derivatives

Abstract
Both anomers of methyl 1-thio-L-rhamnopyranosides were prepared through methylation of the corresponding isothiouronium salt. 2,3-0-Isopropylidene-, benzylidene-and the until now unknown diphenyl-methylene acetals were synthesized. Phase-transfer catalysed benzylation and LiA1H4-AlCl3-type hydrogenolysis of benzylidene acetals were used to obtain partially benzylated derivatives. Comparing the C NMR data of the synthesized compounds with those of their 0-glycoside analogues revealed that the 0→S exchanges at the anomeric centres caused drastic upfield shifts (∼15 ppm) at C-1 and moderate downfield shifts at C-2 and C-5, as well. The chemical shift values of other carbons are not sensitive to the 0→S replacement.