The crystal and molecular structure of echitamine iodide, C22H29O4N2I

Abstract

The paper reports the detailed x-ray analysis of the structure of echitamine iodide. This substance and the chloride which are isomorphous belong to the orthorhombic space group P212121 with four molecules in the unit cell. The axial dimensions of the iodide are a = 18.45 Å, b = 13.83 Å, c = 8.48 Å. The structure has been solved from the hk0, h0l and 0kl data by Fourier-projection methods, use being made of the ‘isomorphous replacement’ technique and the ‘heavy atom’ method to obtain the phases of the reflections. The final R index for 379 reflections of measurable intensity is 0.145. The molecular configuration of the quarternary echitamine ion has been established, and it has been shown that this dihydro-indole alkaloid is unique in having two five-membered rings fused to a ‘boat’-shaped substituted cyclohexane ring along a common bond. The positions of all the side-groups are well explained by postulating weak intramolecular hydrogen bonds.