Triterpene alkaloids from Buxus sinica and their anti-AChE activities

Fifteen previously undescribed Buxus alkaloids, designated as buxsinines A-O (1-15), together with nine known congeners (16-24), were isolated from Buxus sinica (Rehder & E.H. Wilson) M. Cheng. Buxsinine A (1) represents the first reported Buxus alkaloid featuring a rare 6/7/5/6 tetracyclic ring system with a cyclopropane derivative. Compounds 3-5 represent a novel subclass of Buxus alkaloids characterized by an additional five-membered ether or lactone ring fused at C-23 and C-2 or C-10. Their structures and absolute configurations were determined through comprehensive spectroscopic analyses (NMR, UV, HRESIMS, and single-crystal X-ray diffraction). Notably, compounds 6 and 20-23 exhibited inhibitory effects on acetylcholinesterase (AChE) (IC₅₀ = 5.7-16.3 μM).