Crystal structure of indoline alkaloids kopsinilam, kopsinine, and the salts of the latter

Abstract

Indoline alkaloids kopsinilam and kopsinine extracted from the plant Vinca erecta have been studied by X-ray crystallography; mono and double salts of the latter alkaloid also have been examined. Experimentally determined positions of Н atoms suggest sp³ hybridization of the indoline nitrogen atom N1 in the bases and the salts. Tetrahedral hybridization of the atom N1 in indoline alkaloids favors the formation of their double salts, what is unlikely for indole and indolinine alkaloids. In the halogen double salts there is an intramolecular Н bond between one of the protons of the NH₂ group and the oxygen of the methoxycarbonyl group, that is absent in the mono salts and pure bases.