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. © 1968, The Royal Society of Chemistry. All Rights Reserved.