Total Synthesis of Cryptophycins via a Chemoenzymatic Approach.

A highly convergent synthesis of cryptophycins in their enantiomerically-pure forms was achieved. Our strategy consists of the synthesis of the two units 3 and 4 and linking them together to form the macrocyclic ring. The upper unit 3 was prepared from 10 in four steps, and the lower unit 4 was prepared from 20 in three steps. Enantioselective biocatalytic methodology was used to prepare the requisite chiral building blocks, (R)-11 and (R)-19. The stereochemical versatility of this synthetic approach is demonstrated by the synthesis of cryptophycin A and the four diastereomers of cryptophycin C.