Synthesis of L-altro-1-deoxynojirimycin, D-allo-1-deoxynojirimycin, and D-galacto-1-deoxynojirimycin from a single chiral cyanohydrin.

The chemoenzymatic synthesis of three 1-deoxynojirimycin-type iminosugars is reported. Key steps in the synthetic scheme include a Dibal reduction-transimination-sodium borohydride reduction cascade of reactions on an enantiomerically pure cyanohydrin, itself prepared employing almond hydroxynitrile lyase (paHNL) as the common precursor. Ensuing ring-closing metathesis and Upjohn dihydroxylation afford the target compounds.