Bioassay-guided isolation of acetyl cholinesterase inhibitors from Mesua Elegans (King) Kosterm

Abstract

A bioassay-guided study of the bark from Mesua elegans (King) Kosterm was performed. The hexane extract showed potent acetyl cholinesterase (AChE) inhibitory activity with 90 % of inhibition at 10 μg/mL concentration. Thus, this extract had been carried forward for the further fractionation steps. The hexane : ethyl acetate _ 95 : 5 fraction of hexane extract gave 100 % of inhibition at 10 μg/mL concentration. Further purification and structural elucidation of compounds were performed on this fraction. Chromatographic separation of compounds from this fraction had afforded nine 4-phenylcoumarins, namely 5-hydroxy-2-methyl-6-(3-methylbutanoyl)-2-(4-methylpent-3- enyl)-10-phenyl-2H-pyrano[2,3-f]chromen-8-one 156, 5-hydroxy-2-methyl-6-(2- methylbutanoyl)-2-(4-methylpent-3-enyl)-10-phenyl-2H-pyrano[2,3-f]chromen-8-one 157, isomammeigin 158, 5,7-dihydroxy-8-(2-methylbutanoyl)-6-[(E)-3,7-dimethylocta-2,6- dienyl]-4-phenyl-2H-chromen-2-one 159, 5,7-dihydroxy-8-(3-methylbutanoyl)-6-[(E)-3,7- dimethylocta-2,6-dienyl]-4-phenyl-2H-chromen-2-one 160, 4-hydroxy-2-(2-hydroxy-6- methylhept-5-en-2-yl)-5-(3-methylbutanoyl)-9-phenyl-2H-furo[2,3-f]-chromen-7(3H)-one 161, 5,7-dihydroxy-8-isobutyryl-6-[(E)-3,7-dimethylocta-2,6-dienyl]-4-phenyl-2H- chromen-2-one 162, mammea A/BA 163 and mammea A/BA cyclo F 164, in which compounds 156, 161 and 162 are new. The isolated compounds had been tested for the AChE inhibitory activity, and it was discovered that compounds 156, 157, 159 and 161 are the ones responsible as AChE inhibitors, especially compound 157 which is the most potent with an activity of 80 % of inhibition at 10 μg/mL concentration.