We report the first synthesis of a conformationally constrained 3,6-anhydroheptoside analogue of D-glycero-D-manno-heptopyranose 7-phosphate by a DAST (diethylaminosulfur trifluoride)-induced intramolecular cycloetherification. The reactivity of a series of constrained bicyclic 3,6-anhydro-thioheptosides as glycosyl donors was also studied in glycosylation reactions and compared with the reactivities of related unconstrained mannose and heptose scaffolds. Competition experiments confirmed that in the D-manno-heptose series, a reversal of chair conformation leads to an enhancement of the anomeric reactivity. A series of constrained bicyclic 3,6-anhydro-thioheptosides was prepared by regioselective cycloetherification, and their reactivities were compared to those of the corresponding heptosides.
- Conformation analysis