Stereoselective Synthesis of a Tetrasaccharide Fragment from Cellulosome Produced by Clostridium thermocellum

An efficient synthesis of a structurally congested tetrasaccharide portion from the cellulosome produced by Clostridium thermocellum has been accomplished through a stepwise glycosylation strategy. The key steps for the synthesis include the stereocontrolled construction of a range of challenging 1,2‐ cis glycosidic linkages. The 5‐ O ‐(2‐quinolinecarbonyl) substituted D‐galactofuranosyl thioglycoside 2 , 4,6‐ O ‐benzylidene protected 2‐azido‐2‐deoxyglucose thioglycoside 3 c , and 4,6‐ O ‐benzylidene protected D‐galactopyranosyl thioglycoside 4 were employed as glycosyl donors, respectively, for the high‐yielding and stereoselective formation of the corresponding 1,2‐ cis ‐α‐Gal f , α‐GlcNAc, and α‐Gal p linkages.