Multi-conformers caused by conformational change of A-ring in the C₁₈- and C₁₉-N-dealkyl diterpenoid alkaloids

This paper describes a rare phenomenon of multi-conformers caused by conformational change of A-ring in the C₁₈- and C₁₉- N-dealkyl diterpenoid alkaloids. The possible reasons for the generation of multiple conformational isomers are complex, which could be affected by the substituents at C-1, C-3, C-13, C-14, and C-15, pH, solvents, the intramolecular hydrogen bond between 1α-OCH₃/1α-OH and N-H groups, acid-base treatment, preparation methods, and work-up procedures.