Acetylcholinesterase Inhibitory Alkaloids from the Flowers and Seeds of Erythrina caffra

Chemical investigation of flower and seed extracts of Erythrina caffra Thunb., Fabaceae, resulted in the isolation of an undescribed alkaloid, 11β-methoxy-8-oxoerythraline, and its structural characterization is reported here, along with nine known alkaloids: crystamidine, 8-oxoerythraline, 11β-methoxyerythraline, erythraline, erythrinine, 8-oxoerythrinine, 11β-methoxyerythraline N –oxide, cristanine A, and hypaphorine. All compounds are reported in the species for the first time except erythraline, erythrinine and hypaphorine. Structures of the isolated compounds were elucidated based on their spectroscopic analyses (1D- and 2D-nucler magnetic resonance and electrospray ionization mass spectrometry). The acetylcholinesterase inhibitory activity of some of the isolated alkaloids was investigated through both in silico and in vitro studies. Docking results revealed that the alkaloids erythraline, erythrinine, and cristanine A possess promising inhibitory potential toward human acetylcholinesterase enzyme which was confirmed through in vitro testing. Graphical abstract