Facile synthesis of de-O-sulfated salacinols: Revision of the structure of neosalacinol, a potent α-glucosidase inhibitor

The structure of neosalacinol ( 8), a potent α-glucosidase inhibitor isolated recently from Ayurvedic medicine Salacia oblonga, was revised to salacinol de- O-sulfate ( 3c), by comparison of the spectroscopic properties of 8 with an authentic specimen synthesized by the coupling reaction of 9 and 10. Facile synthesis of de-O-sulfated salacinols ( 3) was developed by employing the coupling reaction of an epoxide, 1,2-anhydro-3,4-di- O-benzyl- d-erythritol ( 9) with 2,3,5-tri- O-benzyl-1,4-dideoxy-1,4-epithio- d-arabinitol ( 10) as the key reaction. The reported structure of a potent α-glucosidase inhibitor named neosalacinol ( 8), isolated recently from Ayurvedic medicine Salacia oblonga, was proved incorrect, and revised to be de-O-sulfated salacinol formate ( 3c) by comparison of the spectroscopic properties with those of the authentic specimen synthesized. Discrepancies and confusion in the literature concerning the NMR spectroscopic properties of salacinol ( 1) have also been clarified.