This paper describes a rare phenomenon of multi-conformers caused by conformational change of A-ring in the C-18- and C-19- 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 1 alpha-OCH3/1 alpha-OH and N-H groups, acid-base treatment, preparation methods, and work-up procedures.