Structures of Brucinium Cholate: Bile Acid and Strychnine Derivatives Meet in the Crystals

Single crystals concomitantly containing brucine 1a and a bile acid derivative (cholic acid 2H or 3-epicholic acid 3H) were successfully constructed. In these crystals, cholate 2− constructs inherent robust hydrogen bonded 21 helical assemblies and brucinium 1aH+ achieves 21 helical assemblies through weak interactions. These assemblies excellently synchronize helical pitches to one another. 3-Epicholate 3−, on the other hand, is unable to form a robust hydrogen-bonded motif because of inversion of the hydroxyl group at the 3 position. The present systems are the first example of steroidal bile acid molecules that cocrystallize with equal-sized alkaloidal molecules even when a salt bridge is formed.