The structures of the brucine complexes with (+)-(1R,2S,4R)-bicyclo[2.2.1]hept-5-ene-2-cyanohydrin and (+)-(1R,2R,4R)-7-oxabicyclo[2.2.1]hept-5-ene-2-cyanohydrin {(6) 2,3-dimethoxystrychnidine-2-hydroxybicyc-lo[2.2.1]hept-5-ene-2-carbonitr ile (1/1) and (7) 2,3-dime-thoxystrychnidine-2-hydroxy-7-oxabicyclo[2.2. I]hept-5-ene-2-carbonitrile (1/1)} have been determined. The primary interaction in the complexes is a hydrogen bond between the OH group of the cyanohydrin and the most basic N atom of brucine. Molecular-mechanics calculations on the 7-oxa derivative indicate that the enantiomeric cyanohydrin will fit into the same cavity in the brucine matrix at the cost of ca 71 kJ mol-1