Total synthesis of 275A lehmizidine frog skin alkaloid (or of its enantiomer)

A concise asymmetric total synthesis of the potentially bioactive 275A lehmizidine frog skin alkaloid (or of its enantiomer) is described. Key features of the protocol include an acyliminium butenyl Grignard addition and a seven-membered intramolecular reductive amination step. Both reactions ensure a high degree of diastereocontrol, with installation of the same relative configuration at the C3, C5 and C10 stereocentres as in the natural product 275A. Despite this total synthesis, the absolute configuration of the natural product remains unknown, due to the lack of specific rotation data for alkaloid 275A.