D-Glucosamine trimethylene dithioacetal derivatives:: formation of six- and seven-membered ring amino carbasugars.: Synthesis of (-)-calystegine B3

By virtue of carefully chosen protecting groups, D-glucosamine trimethylene dithioacetal derivatives were successfully oxidized to the corresponding 6-aldehydes. This methodology reverses the donor and acceptor position on a normal open chain sugar and changes the relative position of the N-substituent. From the 6-aldehydes, heptose epoxide derivatives were prepared by a Corey-Chaykovsky reaction, and cyclized by the Corey-Seebach method. Depending on the designed protecting groups, the orthogonally protected six-and seven-membered ring amino carbasugars can be produced selectively and efficiently. (-)- Calystegine B-3 was synthesized from one of those products with high yield. This is the first anionic cyclization pathway to calystegine type structures.