The difficulties that arose when an X-ray crystal structure analysis showed that podopetaline has the structure and stereochemistry previously assigned to ormocastrine have been resolved by showing that ormocastrine is in fact podopetaline hydrochloride. It has also been demonstrated that, of the other three constituents that had been isolated from O. semicastrata, 18-epiormosanine was obtained as its hydrochloride but ormosanine and piptanthine were free bases. The pKa values of the alkaloids have been determined.