SYNTHESES OF MANNOSIDIC DISACCHARIDES FROM DERIVATIVES OF ETHYITHIO ALPHA-D-MANNOPYRANOSIDE

Derivatives of ethylthio alpha-D-mannopyranoside as glycosyl donors ar e compared in coupling efficiency and stereoselectivity with varying t hiophilic promoters from methyl triflate (MeOTf), dimethyl(methylthio) sulfonium triflate (DMTST) to iodonium dicollidine perchlorate (IDCP), solvents and glycosyl accepters. IDCP was the most efficient promoter in coupling of perbenzylated ethylthio-alpha-D-mannopyranosides (1 an d 2), giving alpha-D-mannosyl disaccharides preferentially, whereas in active in coupling of 4,6-O-benzylidene derivatives 3 and 4. MeOTf and DMTST promoted coupling of 4,6-O-benzylidene derivatives 3 and 4, but beta-D-mannopyranosyl disaccharides were formed preferentially. Coupl ing reaction was retarded as solvent polarity decreased.