Geissoschizine methyl ether, a corynanthean-type indole alkaloid fromUncaria rhynchophyllaas a potential acetylcholinesterase inhibitor

Abstract

Geissoschizine methyl ether (1), a newly discovered strong acetylcholinesterase (AChE) inhibitor, along with six weakly active alkaloids, vallesiachotamine (2), hisuteine (3), hirsutine (4), isorhynchophylline (5), cisocorynoxeine (6) and corynoxeine (7) have been isolated from Uncaria rhynchophylla. Geissoschizine methyl ether (1) inhibited 50% of AChE activity at concentrations of 3.7 ± 0.3 µg mL⁻¹ while the IC₅₀ value of physostigmine as a standard was 0.013 ± 0.002 µg mL⁻¹. The mode of AChE inhibition by 1 was reversible and non-competitive. In addition, molecular modelling was performed to explore the binding mode of inhibitor 1 at the active site of AChE.