Synthesis and biological activity of bi/tricyclic azasugars fused thiazolidin-4-one and thiazinan-4-one by microwave-assisted tandem Staudinger/aza-Wittig/cyclization.

A convenient synthesis of novel bi/tricyclic azasugars fused thiazolidin-4-one and thiazinan-4-one by the one-pot tandem Staudinger/aza-Wittig/cyclization reaction under microwave radiation was demonstrated. The reactions were carried out with the azidosugar 1 and mercaptan acids via a key intermediate Schiff base and stereoselectively afforded the titled bi/tricyclic azasugars in good yield. All the dominant products were in the 1,2-trans form and the reaction stereoselectivity mainly depended upon the steric hindrance of the neighboring rigid cyclic isopropylidene groups on C-2, 3 which favors the exo-attack of the sulfur atom (in mercaptan acids) to the intermediate imine. The preliminary biological evaluation of the compounds 10-17 showed that compounds 10b, 11a, 12b, 14b, 16b, 17a, and 17b were found to active the natural killer (NK) cells significantly (immunopotentiating activity) and compounds 10a, 10b, 12a, 16b, and 17b exhibited weak inhibitory activity against β-glucosidase. Yet none of these tested compounds have obvious effects on T cell proliferation, or show inhibition against α-amylase and α-glucosidase.