Cholinesterase Inhibitory Compounds from Peltophorum Pterocarpum Flowers

Neurodegenerative disorders (NDs), such as Alzheimer’s and Parkinson disease, affect millions of people worldwide. Natural cholinesterase inhibitors are an important class of lead drugs that have gained much interest for the management of NDs in recent time. They continue to provide promising alternatives to synthetic ones because of their more superior drug-like properties. The aerial part of Peltophorum petrocarpum is popularly used in the African ethnomedicine as a remedy for memory loss. The leaves have been explored for their cholinesterase compounds, while the flowers are yet to be investigated. Therefore, the study evaluated the flower extract for its cholinesterase inhibitory compounds. An activity-guided fractionation of the extract led to the isolation and characterization of two cholinesterase inhibitory compounds, namely: bergenin (1) and a newly described coumarin derivative, 3,4,5,5a-tetrahydroxy-2-(hydroxymethyl)-3-(4-hydroxyphenyl)-9-methoxy-3,5,5,5a-tetrahydro-2 H-oxepino[3,2-c]chromen-6-(11bH)one, named peltophorin (2). The compounds were isolated on repeated silica gel and Sephadex LH-20 column chromatography of the ethyl acetate fraction. Their structures were elucidated by comparison of the mass spectrometry (ESI-MS) and the nuclear magnetic resonance spectroscopy (1D- and 2D-NMR) data to literature reports. Both compounds demonstrated in vitro inhibitory activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes involved in neurodegeneration. The identified compounds exhibited a comparable AChE inhibitory activity (IC50 = 90 µM), which is lower than eserine, the positive control at IC50 of 12.4 ± 0.4 and 21.0 ± 1.0 µM against AChE and BuChE enzymes, respectively. Bergenin (1) notably demonstrated better BuChE inhibitory activity, with an IC50 of 57.1 ± 8.0 µM compared to peltophorin (2). In conclusion, this study has shown that the flowers of P. pterocarpum contain cholinesterase inhibitors such as bergenin and the newly described peltophorin, thus adding to the repository of natural coumarins with anti-cholinesterase activity.