Discovery of highly selective and potent monoamine oxidase B inhibitors: Contribution of additional phenyl rings introduced into 2-aryl-1,3,4-oxadiazin-5(6H)-one.

Monoamine oxidase B (MAO-B) is a flavin adenine dinucleotide (FAD)-containing enzyme that plays a major role in the oxidative deamination of biogenic amines and neurotransmitters. Inhibiting MAO-B activity is a promising approach in the treatment of neurological disorders. Here, we report a series of 2-aryl-1,3,4-oxadiazin-5(6H)-one derivatives as highly selective and potent MAO-B inhibitors. Analysis of the binding sites of hMAO-A and hMAO-B led to design of linear analogs of 2-aryl-1,3,4-oxadiazin-5(6H)-one with an additional phenyl ring. Biological evaluation of the 26 new derivatives resulted in the identification of highly potent and selective inhibitors with optimal physicochemical properties to potentially cross the blood-brain barrier (BBB). Compounds 18a, 18b, 18e and 25b potently inhibited MAO-B, with IC values of 4-25 nM and excellent SI over MAO-A (18a > 25000, 18b > 8333 and 18e > 4000 and 25b > 4545). Docking results suggest that an optimal linker between two aromatic rings on the 2-aryl-1,3,4-oxadiazin-5(6H)-one scaffold is a key element in the binding and inhibition of MAO-B.