Ormosianines A-P, Structurally Diverse Quinolizidine Alkaloids with AChE Inhibitory Effects from Ormosia yunnanensis .

Sixteen new quinolizidine alkaloids (QAs), named ormosianines A-P ( 1 - 16 ), and 18 known congeners ( 17 - 34 ) were isolated from the stems and leaves of Ormosia yunnanensis . The structures were elucidated based on spectroscopic analyses and electron circular dichroism (ECD) calculations. Structurally, ormosianines A ( 1 ) and B ( 2 ) are the first examples of cytisine and Ormosia- type alkaloids with the cleavage of the piperidine ring. Results of the acetylcholinesterase (AChE) inhibitory assay revealed that the pentacycline Ormosia- type QAs, including 1 , 16 , 24 , and 27 - 29 , are good AChE inhibitors. Ormosianine A ( 1 ) exhibited more potent AChE inhibitory activity with an IC 50 value of 1.55 μM. Molecular docking revealed that 1 might bind to the protein 1DX4, forming two hydrogen bonds with residues SER-238 and HIS-480.