Cholinesterase inhibitory alkaloids from the rhizomes of Coptis chinensis

Coptis chinensis has been used as a medicinal herb in traditional oriental medicine. In this study, chemical investigation of a water extract of C. chinensis identified two new quaternary protoberberines (1, 2), a new tricyclic amide (3), together with five known compounds. Their chemical structures were elucidated by analysis with 1D and 2D NMR and high-resolution mass spectroscopy, as well as by comparison with those reported in the literature. Compounds 4, 5, and 7 showed potent inhibition against acetylcholinesterase (AChE) with IC₅₀ values of 1.1, 5.6, and 12.9 μM, respectively. Compounds 2 and 4 showed inhibition of butyrylcholinesterase (BChE) with IC₅₀ values of 11.5 and 27.8 μM, respectively. The kinetic activities were investigated to find out the type of enzyme inhibition involved. The types of AChE inhibition shown by compounds 5 and 7 were noncompetitive; BChE inhibition by compound 2 was also noncompetitive.