Abstract. M r = 401. 89, m.p. 503-505 K, orthorhombic, P212,2~, a=19.256(8), b--14.326(5), c= 7.224 (3)/~,, Z= 4, V= 1992.8 (1.4) A 3, Dx= 1.339 Mg m -3. Diffractometer data were collected at 293.0 (5) K with Mo Kct radiation (2 = 0.71073 A) to a limit in (sin 0)/2= 0.65 A -~ and corrected for coincidence loss but not for absorption ~= 0.222 mm-~). The structure solution was initiated by the heavy-atom method with C1 positions determined from Harker sections. Least-squares refinement including H atoms converged at R=0.031 for 2512 F o. Refinement of both enantiomers suggests that the absolute configuration of sinomenine is opposite to that of natural (-)-morphine. The sinomenine molecule has the usual T shape common to morphine alkaloids. Strain in the A ring of these alkaloids gives rise to aplanar distortions; the directions of the principal atomic shifts apparently depend on whether a 4,5 ether bridge is present or not. Ring C in sinomenine adopts a half-chair conformation with five C atoms roughly coplanar. The torsion angles in the phenylethylamine chain are 9.0 and 81.4 ° compared to 0.2 and -93.2 ° , respectively, in morphine.
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