Building Blocks for Glycopeptide Synthesis. Disaccharide Glycosyl Isothiocyanates

Abstract

The reaction of aldose oligosaccharides with aqueous ammonium hydrogencarbonate was revised and optimized for gram scale preparation of glycosylamines, using lactose, cellobiose, maltose, and melibiose as model compounds. The unprotected glycosylamines 1b-4b were transformed into the corresponding hepta-O-acetyl hydrochlorides 1e-4e via diethyl N-glycosylaminomethylenemalonates (1c-4c and 1d-4d). Reaction of le-3e with thiophosgene in a three-phased system led to the target hepta-O-acetylglycosyl isothiocyanates lf-3f in excellent yields. Under the same conditions, the melibiosyl derivative 4e underwent partial hydrolysis to give a mixture of melibiosyl isothiocyanate 4f and the reducing sugar derivative 4h. Treatment of 1f-4f with ammonia resulted in the quantitative formation of N-glycosylthioureas (1g-4g).