Monoamine oxidase inhibitory coumarins from the aerial parts of Dictamnus albus

The methanol extract from the aerial parts of Dictamnus albus was active in inhibiting monoamine oxidase (MAO) from the mouse brain. Activity-guided fractionation led to the isolation of four known coumarins, 7-(6'R-hydroxy-3', 7'-dimethyl-2'E, 7'-octadienyloxy) coumarin (1), auraptene (2), umbelliferone (3), and xanthotoxin (4), as active compounds along with an inactive alkaloid, skimmianine (5). Compounds 1 and 2 inhibited MAO activity in a concentration-dependent manner with IC50 values of 0.7 and 1.7 mu M, respectively. Compounds 1 and 2 showed a slight and potently selective inhibitory effect against MAO-B (IC50 0.5 and 0.6 mu M, respectively) compared to MAO-A (IC50 1.3 and 34.6 mu M, respectively). According to kinetic analyses derived by Lineweaver-Burk reciprocal plots, compounds 1 and 2 exhibited a competitive inhibition to MAO-B.