X-ray structure of the curare alkaloid (+)-tubocurarine dibromide

X-ray structure determination of the compound (C37H42N2O6)2+ .2Br-.4CH3OH, confirms that (+)-tubocurarine is a monoquaternary salt and has established that the molecule adopts different conformations in crystals of the dibromide and dichloride salts. The crystal structure is stabilised by a number of hydrogen bonds involving the two free hydroxyl groups and the tertiary nitrogen of the tubocurarine molecule, the bromide ions and the solvent molecules. The absolute configuration of the molecule, determined by X-ray anomalous scattering, confirms the configuration assigned earlier by chemical studies.