An O-to-N intramolecular acyl migration in C₁₉-diterpenoid alkaloids

The O-acyl group at C-1 of two C₁₉-diterpenoid alkaloids 2 and 5 was transferred to the secondary amine nitrogen to form amides 3 and 6 in the basic condition. This kind of O-to-N intramolecular acyl migration could be caused by the near distance between the nucleophilic nitrogen atom and the carbonyl group of the ester at C-1 in the C₁₉-diterpenoid alkaloids, which is consistent with the conformation of rings A and E in the C₁₉-diterpenoid alkaloids.