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

Abstract

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 μM. Finally, molecular docking simulations revealed the binding mechanism and interaction mode between majuszine A (6) and acetylcholinesterase.