NHC-mediated cross-coupling of sugar-derived cyclic nitrones with enals: general and efficient synthesis of polyhydroxylated pyrrolizidines and indolizidines.

A general and efficient method for the synthesis of polyhydroxylated pyrrolizidines and indolizidines has been developed based on the NHC-catalyzed cross-coupling of sugar-derived cyclic nitrones with enals, which afforded the key intermediates, γ-hydroxyl amino esters, in good to excellent yields. Thus, a variety of polyhydroxylated pyrrolizidines and indolizidines have been synthesized and assayed against various glycosidases, which showed that aryl or alkyl substituents at C-7 of pyrrolizidines or at C-8 of indolizidines reduced the potency of the glycosidase inhibition of these bicyclic iminosugars.