An expeditious synthesis of an analogue of (-)-steviamine by way of the 1,3-dipolar cycloaddition of a nitrile oxide with a 1-C-allyl iminosugar

In our continuing effort to develop inhibitors of the mycobacterial galactan biosynthesis, we planned to synthesize original iminosugar-based analogues of UDP-galactofuranose by way of the 1,3-dipolar cycloaddition reaction between a 1-C-allyl iminosugar and a nitrile oxide, followed by the reductive cleavage of the resulting isooxazoline. In initial studies, it was found that this last step led in one pot to a new poly-hydroxylated indolizidine derivative closely related to the recently isolated (-)-steviamine, in good yield, by way of a sequence involving at least five individual reactions. The activity of this new compound as a glycosidase inhibitor was evaluated against a panel of glycosidases and compared to (-)-steviamine.