Chemical synthesis of cholesteryl β-d-galactofuranoside and -pyranoside

Two isomeric cholesteryl galactosides, cholesteryl β-d-galactofuranoside and -pyranoside, have been synthesized by the Koenigs–Knorr reaction. Glycosylation of cholesterol with 2,3,5,6-tetra-O-benzoyl-d-galactofuranosyl bromide, followed by Zemplén saponification with sodium methoxide, gave cholesteryl β-d-galactofuranoside. By using 2,3,4,6-tetra-O-acetyl-d-galactopyranosyl bromide as the glycosyl donor, followed by alkaline hydrolysis, cholesteryl β-d-galactopyranoside was obtained. The title compounds were characterized by their IR spectra and by their 1H and 13C NMR spectra. Structure considerations of the two cholesteryl galactosides correlated with data in the literature, thus confirming that cholesteryl β-d-galactopyranoside is an antigenic lipid of Lyme disease agent, Borrelia burgdorferi.