A macrolactonization approach to the stevastelins

A synthesis of the stevastelins, a novel class of immunosuppressant agents, is reported based on a macrolactonization approach. This synthesis commenced with the stereoselective preparation of the stearic acid segment from tetradecanal using Evans asymmetric synthesis methodology and an aldol reaction with a thioester. After a high yielding coupling reaction between the fatty acid residue and the corresponding tripeptide, we proceeded with the macrolactonization key step. Thus, macrolactonizations of hydroxy acid 27 and dihydroxy acid 30, according to Yamaguchi conditions, afforded the corresponding 13-membered ring stevastelin derivatives 28 and 31 in 90 and 82% yields, respectively. In this latter case, the corresponding 15-membered lactone was not formed. Finally, depsipeptide derivative 31 was converted into stevastelin C3 (5).