Abstract An efficient asymmetric total synthesis of the potent cytotoxic marine natural product (−)-callystatin A and its 20-epi analogue has been achieved. The synthetic pathway involved the preparation of three fragments to be coupled with each other at the end of the route. The first fragment 3 was obtained using a biocatalytic enantioselective reduction of a 3, 5- dioxocarboxylate as the key step. For the second intermediate 4 the asymmetric α- ...