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

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