Isolation of the MAO-inhibitor naringenin from Mentha aquatica L.
To isolate the compound(s) responsible for the MAO-inhibitory activity.  Six extracts of varying polarity of Mentha aquatica L. were tested in a photometric peroxidase linked MAO bioassay.  The 70% ethanol extract had highest inhibitory activity. ( S)-Naringenin was isolated from the extract by bioassay guided fractionation on VLC and preparative TLC.  The structure of the compound was determined by (1)H, (13)C and (13)C-DEPT NMR and optical rotation.  The IC(50) values for MAO inhibition by naringenin were 342+/-33 microM for the rat liver mitochondrial fraction, 955+/-129 microM for MAO-A and 288+/-18 microM for MAO-B. The content of naringenin in Mentha aquatica might explain its use in traditional medicine for depression-like conditions.