Crystal and molecular structure of the m-bromobenzoate derivative of bisnorquassin

Abstract

The molecular structure of the in-bromobenzoate derivative of bisnorquassin, C,,H2,0,Br, has been determined by the heavy atom method. The compound crystallizes in the orthorhombic system, space group P2,2,2,, with unit cell dimensions n = 20.09 + 0.02 A, b = 14.63 f 0.02 A, c = 8.06 + 0.01 A and 4 molecules in the unit cell. Final atomic parameters have been obtained from a blockdiagonal least-squares refinement using anisotropic temperature parameters. The final agreement residual for I665 observed reflections is R = 0.107.The structure of bisnorquassin previously proposed by Findlay and Cropp, on the basis of spectroscopic and chemical evidence, is shown to be essentially correct.Canadian Journal of Chemistry, 48, 307 (1970) Introduction Bisnorquassin, C2,H2,0,, was first prepared by Robertson et al. (1,2) by the treatment of both quassin and norquassin with a warm mixture of concentrated hvdrochloric and acetic acids. The complete structure and relative stereochemistry of quassin, a bitter principle from Quassia atnara, has been established by Valenta et al. (3,4). Early studies showed that bisnorquassin was not a simple bis-demethylated quassin, but in view of its ultraviolet (u.v.) absorption spectrum, possessed an extended system of conjugation.A structure for bisnorquassin has been given by Findlay and Cropp (5) which is adequately supported by spectroscopic and chemical evidence. This structure is not comwlete in that the stereochemical co~lfiguration about certain carbon centers is not established. This X-ray analysis was undertaken to provide the complete stereochen~ical structure of this interesting compound.

Study of some bisnorquassin derivatives

“…Prior to the conclusion of the X-ray study (5) we were seeking corroborative chemical evidence for structure 2a with a view also to determining additional stereochemical features of the molecule. This involved, in part, reexamining some of the derivatives of 2a reported by Robertson's group (2,3).…”