Peroxyl radical scavenging by a series of coumarins

Sixteen plant-derived or synthetic coumarins with various hydroxyl and other substitutions were tested for their ability to scavenge alkylperoxyl radicals generated in the aqueous phase by the controlled thermolysis of 2,2'-azo-bis-(2-amidinopropane) dihydrochloride (ABAP). Protection by coumarins against inactivation of lysozyme by the radicals was assayed by measuring the loss of turbidity of suspensions of M. lysodeikticus. Ten of the coumarins were potent scavengers of aqueous peroxyl radicals with activities comparable to n-propyl gallate, desferrioxamine, ferrioxamine and trolox c, yielding IC50 values in the range 21 to 92 micromolar. The presence of 6,7-ortho-dihydroxy functions gave compounds of the greatest potency. Scavenging activity was unrelated to ability to chelate iron ions. The active coumarins are attractive candidates for evaluation as protective agents against disorders in which oxidative stress is implicated.