First Direct Glycosylation of Unprotected Nonreducing Mono‐ and Disaccharides

Abstract

AbstractThe first single‐step random‐glycosylation methodology for fully unprotected glycosyl acceptors is reported by random glycosylation leading to all possible regioisomers. For such systems conventional glycosylation methods such as Koenigs–Knorr glycosylation, Schmidt's trichloroacetimidate glycosylation and reactions employing glycosyl fluoride donors fail entirely. Starting from unprotected nonreducing saccharides, the glycosylation of β‐glucosylated and β‐galactosylated monosaccharides (Glc, Gal), symmetric disaccharides (e.g. α,α‐trehaloses) as well as unsymmetric disaccharides (e.g. sucrose) were studied. The influence of base type and concentration were examined. Several libraries of di‐ and trisaccharides were generated. All regioisomers were formed in approximately equal proportions, and their partial separation was achieved by flash column chromatography. Even though it appears that overall yields are lower when comparing to classical protecting‐group chemistry, this synthetic effort may be superior especially for access to higher saccharides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)