Five new C19-diterpenoid alkaloids from Delphinium pachycentrum Hemsl. and Delphinium majus Ulbr. as potential acetylcholinesterase inhibitors

Two new C19-diterpenoid alkaloids, named pachycenines F-G (1-2), along with three known diterpenoid alkaloids (3-5), were extracted from the whole plant of Delphinium pachycentrum Hemsl. Additionally, three new C19-diterpenoid alkaloids, majuszine A-C (6-8), along with twenty-four known compounds (9-32) were isolated from the whole plant of Delphinium majus Ulbr. The structures of all these compounds were identified using IR, HR-ESI-MS, 1D and 2D NMR. Notably, compounds 1-2 are rare diterpenoid alkaloids that are characterized by the absence of an oxygenated substituent at the C-16 position. Compounds 6-8, on the other hand, all possess a special cyclic ketone structure, which is known to play a crucial role in various pharmacological activities. Furthermore, majuszine A (6) exhibited significant acetylcholinesterase inhibitory activity with an IC50 value of 5.74 mu M. Finally, molecular docking simulations revealed the binding mechanism and interaction mode between majuszine A (6) and acetylcholinesterase.