Abstract
Methyl 3,4‐di‐O‐benzyl‐[(S)‐1,2‐O‐(1‐cyanoethylidene)]‐α‐d‐glucopyranuronate (12), methyl 3,4‐di‐O‐benzyl‐[(S)‐1,2‐O‐(1‐ethoxyethylidene)]‐α‐d‐glucopyranuronate (14), methyl 2‐O‐acetyl‐3,4‐di‐O‐benzyl‐α‐d‐glucopyranuronate bromide (15), methyl (2‐O‐acetyl‐3,4‐di‐O‐benzyl‐α‐d‐glucopyranosyl)uronate trichloroacetimidate (17), and methyl (2,3,4‐tri‐O‐benzyl‐α/β‐d‐glucopyranosyl)uronate trichloroacetimidate (30) were synthesized and used as glycosyl donors. Glycosylation reactions of 12 with (5‐R)‐2,3,4,5 − tetrahydro‐5‐trityloxymethyl‐2‐furanone (32) and 14,15,17 with the corresponding (5‐R)‐2,3,4,5‐tetrahydro‐5‐hydroxymethyl‐2‐furanone (31) provided the exclusively β‐linked glucuronide 33 in 69%, 28%, 45%, and 71% yield, respectively. The coupling of donor 30 with acceptor 31 furnished the glucuronated lactone 35 in 70% yield with a surprisingly high content (20%) of the undesired α‐linked sugar residue. The structure of 33 was proved by NMR and X‐ray diffraction studies. In a model reaction a complete deprotection procedure of the glucuronic acid lactone conjugation was demonstrated.
Acknowledgments
The authors are grateful to the Deutschen Forschungsgemeinschaft as well as the Fonds der Chemischen Industrie for financial support.