Structure elucidation of the binary indole alkaloid uncaramine

Abstract

The structure elucidation of uncaramine (1), a binary alkaloid derived from gambirine and pseudoyohimbine moieties linked together through a C(10)–C(21′) bond, has been performed mainly using ¹H and ¹³ n.m.r. spectroscopy. The presence of a hydrogen bond between the 9-hydroxy proton and the 4′-nitrogen atom established a preferred orientation of the two halves, the C(11)–C(10)–C(21′)–H(21′) dihedral angle being ca. 20°. A complete assignment for the ¹H n.m.r. spectrum of gambirine (2) is also presented.