Identification of 7,8-dihydroxy-3-phenylcoumarin as a reversible monoamine oxidase enzyme inhibitor

We herein report the biological evaluation of 3-arylcoumarin derivatives (3a-l) as potential human monoamine oxidase-A and -B (hMAO-A and hMAO-B) inhibitors. The result indicated that 7,8-dihydroxy-3-(4-nitrophenyl)coumarin (3j) was most effective against MAO-A (inhibition concentration [IC₅₀ ] = 6.46 ± 0.02 µM) and MAO-B (IC₅₀  = 3.8 ± 0.3 µM) enzymes than other synthesized compounds and reference compounds (pargyline and moclobemide). Furthermore, compound (3j) showed (a) nonselectivity against hMAO enzymes, (b) reversible hMAO enzymes inhibition, and (c) neuroprotection against H₂ O₂ -treated human neuroblastoma (N2a) cells. Finally, a molecular modeling study revealed that the hMAO enzymes inhibitory activity of the compound (3j) may be due to the orientation where the nitro (NO₂ ) group lies deep into the receptor and the phenyl ring directed toward flavin adenosine dinucleotide via hydrogen bond interaction, and possible π-π interaction with various important residues. Thus, the results of the present study demonstrate that compound (3j) can be considered as a promising scaffold for the development of hMAO-A and hMAO-B inhibitors.