The X-ray analyses of acutumine and its acetate; a trial of a short cut in the structure elucidation

Abstract

The crystal and moleular structures of acutumine, a novel type of alkaloid containing chlorine, and of its acetate, have been solved by X-ray analysis using a three-dimensional Patterson superposition method and repeated application of least squares and three-dimensional Fourier methods. The result agreed with the chemical evidence obtained by concurrent degradative studies. The structure of acutumine is closely related to that of hasubanonine which was isolated from a species of the same plant family, but has a spiran-type juncture of the five-membered rings A and B, with a chlorine atom attached to the latter. The usefulness of applying the least-squares method at an unusually early stage for distinguishing real atoms from the spurious peaks appearing in the maps of minimum functions or of Fourier synthesis was clearly demonstrated. In particular, observation of the behaviour of temperature factors through several cycles of least-squares with fixed atomic co-ordinates was found to provide a rapid method.