Abstract
In the chloroform solution of tetrahydroprotoberberine-type alkaloids, the position of the equilibrium should be shifted to the B/C-trans side overwhelmingly in the alkaloids of group I (e.g., tetrahydropalmatine), considerably to the B/C-cis side in the group III (e.g., mesocorydaline), and to the B/C-cis side compared to that of group I and to the B/C-trans side compared to that of group III in the alkaloids of group II (e.g., capaurine), in which the amount of the B/C-cis form increases according to the bulkiness of substituent at C-1. In the crystal state, both the racemates and optically active compounds of groups I and III can adopt the preferred conformation present in the solution, while in the group II, the crystal contains one of the conformations and in certain cases, it adopts a different conformation between optically active compound and racemate.
