Synthesis of thioswainsonine as a potential glycosidase inhibitor

The synthesis of a bicyclic sulfonium-ion analogue of a naturally occurring glycosidase inhibitor, swainsonine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, has been achieved by a multi-step synthesis starting from 1,4-anhydro-2,3-di-O-benzyl-4-thio-d-lyxitol. The synthetic strategy relies on the intramolecular displacement of a leaving group on a pendant acyclic chain by a cyclic thioether. This bicyclic sulfonium salt will serve as a candidate to test the hypothesis that a sulfonium salt carrying a permanent positive charge would be an effective glycosidase inhibitor.