New insights in the discovery of novel h-MAO-B inhibitors: structural characterization of a series of N-phenyl-4-oxo-4H-chromene-3-carboxamide derivatives

Six N-substituted-phenyl 4-oxo-4H-chromene-3-carboxamides, namely N-(2-nitro­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(16)H(10)N(2)O(5) (2b), N-(3-meth­oxy­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(17)H(13)NO(4), (3a), N-(3-bromo­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(16)H(10)BrNO(3), (3b), N-(4-methoxy­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(17)H(13)NO(4), (4a), N-(4-methyl­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(17)H(13)NO(3), (4d), and N-(4-hy­droxy­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C(16)H(11)NO(4), (4e), have been structurally characterized. All compounds exhibit an anti conformation with respect to the C—N rotamer of the amide and a trans-related conformation with the carbonyl groups of the chromone ring of the amide. These structures present an intra­molecular hydrogen-bonded network comprising an N—H⋯O hydrogen bond between the amide N atom and the O atom of the carbonyl group of the pyrone ring, forming an S(6) ring, and a weak C(ar)—H⋯O hydrogen bond in which the carbonyl group of the amide acts as acceptor for the H atom of an ortho-C atom of the exocyclic phenyl ring, which results in another S(6) ring. The N—H⋯O intra­molecular hydrogen bond constrains the carboxamide moiety such that it is virtually coplanar with the chromone ring.