5-Methylmellein and nectriapyrone, two new monoamine oxidase inhibitors

In the course of screening for monoamine oxidase (MAO) inhibitors among microbial metabolites, we found that unidentified fungal strain 8082 produced 5-methylmellein, which slows potent inhibitory activity against mouse brain MAO. Although, 5-methylmellein has been previously isolated as a phytotoxin, its MAO inhibitory activity has not hitherto been reported. During the purification of 5-methylmellein, we also isolated nectriapyrone as a minor component. Nectriapyrone has not been previously reported as MAO inhibitor either. We describe the inhibitory activities of 5-methylmellein and nectriapyrone on MAO. 5-Methylmellein and nectriapyrone inhibited MAO in a dose-dependent manner and their IC₅₀ values were 1.06 and 8.9 μM respectively.