Quinolizidines. XXXIII. A Chiral Synthesis of (-)-Ophiorrhizine, a Pentacyclic Quaternary Indole Alkaloid from Ophiorrhiza major RIDL.

Abstract

A detailed account is given of the first chiral synthesis of the Ophiorrhiza alkaloid ophiorrhizine [(-)-1]. The synthesis was started by coupling the lactim ether (+)-4, readily available from cincholoipon ethyl ester [(+)-3], with 6-benzyloxy-3-chloroacetylindole (6) to form the lactam ketone (+)-8 and proceeded through the intermediates (+)-9, (+)-10, 11, (-)-12, (-)-13, 14, (-)-15, and (-)-16. The identity of synthetic (-)-1·H₂O with natural ophiorrhizine unequivocally established the absolute stereochemistry of this alkaloid.