Synthetic studies on stevastelins. 1. Total synthesis of stevastelins B and B3.

[Chemical reaction: See text] The synthesis of stevastelin B3 (2) and B (5) are described. In a first approach, epoxy cyclodepsipeptide 8 was considered as a promising candidate for the synthesis of the [15]-membered ring members of the stevastelins; however, the oxirane ring opening, required for the completion of the natural stevastelin synthesis, failed. Thus, we synthesized stevastelin B (5), carrying out the oxirane ring opening earlier in the synthesis and following a synthetic scheme capable of delivering analogues. On the other hand, a translactonization reaction of the [15]-membered ring derivative 59 led to the total synthesis of the natural [13]-membered ring component of the stevastelins family, stevastelin B3 (2).