THE BRUCINE HYDRATE SYSTEM

Fokke J.J. Dijksma, Robert O. Gould, Simon Parsons, Malcolm D. Walkinshaw

University of Edinburgh, Departments of Chemistry and Biochemistry, Kings Buildings, EH9 3JJ Edinburgh, U.K.

Keywords: Brucine, Differential Scanning Calorimetry, Hydrates, X-ray powder diffraction

The alkaloids brucine and strychnine have long been used to separate racemic mixtures by co-crystallisation, especially for compounds with acid functional groups. Brucine may also act as an agent to induce crystallisation of substances which crystallise with difficulty or not at all. We here present the simplest brucine structures: anhydrous brucine and its di- and tetrahydrate, which have been crystallised in a general study of brucine packing and solubility. In its cocrystals, brucine shows a preference for the formation sheets made up of head-to-tail ribbons ^{1, 2, 3}. This is found in 8 of the 17 brucine structures in the CCDB. This packing mode is indicated by two cell dimensions of 8 and 12 , normally with a 2₁ axis parallel to the 12 direction. These sheets may be seen in anhydrous brucine and in the tetrahydrate. The dihydrate shows a different packing.

Brucine

We are using Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and X-ray powder diffraction to unravel the coherency of these 3 structures. Current evidence suggests that the dehydration of the tetrahydrate proceeds via

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dihydrate, and that its very different structure mediates the reversal of the layers between the tetrahydrate and anhydrous brucine.

References:

1. S.S.B. Glover, R.O. Gould and M. D. Walkinshaw, Acta Cryst.C41, 990-994,1985
2. R.O. Gould and M. D. Walkinshaw, J. Am. Chem Soc.106, 7840 -7842, 1984
3. F.J.J. Dijksma, R.O. Gould, S. Parsons, P Taylor and M. D. Walkinshaw, Chem Comm., 1998, in press