Chemoenzymatic synthesis of isogalactofagomine.

A new chemoenzymatic synthesis of optically pure isogalactofagomine 2 starting from achiral starting materials is presented. Dimethyl 4-hydroxypyridine-3,5-dicarboxylate (7) was synthesized and converted to the corresponding saturated piperidine 8. Then the key step of the synthesis was carried out: Lipase M catalyzed hydrolysis of the prochiral diester 8 to cause formation of an asymmetric monoacid with at least 98% enantiomeric excess. Reduction of the acid, saponification of the remaining ester, and radical iododecarboxylation gave an iodide that after substitution with silver trifluoroacetate and hydrolysis gave 2.