Design and synthesis of substituted N-methylbenzamide analogues derived from SR 48,968 as neurokinin-2 receptor antagonists.

A series of N-methylbenzamide analogues (2-18) that is structurally derived from SR 48,968, a potent neurokinin-2 (NK(2)) receptor antagonist (pK(b)9.1), has been obtained using asymmetric synthesis. Isothiocyanato-N-methylbenzamide (10-12) and bromoacetamido-N-methylbenzamide derivatives (16-18) have been designed to serve as potential electrophilic affinity labels. Nitro-N-methylbenzamide (4-6) and acetamido-N-methylbenzamide (13-15) were designed to serve as the nonelectrophilic controls for these ligands. Functional assay results using guinea pig trachea indicate that electrophilic N-methylbenzamide analogues exhibit potent but surmountable NK(2) receptor antagonist activity. Several members of this series (2, 3, 7-9) exhibit potent NK(2) receptor antagonist potencies with pK(b) values in the range of 9.1-9.7. para-Fluoro substituted analogue 3 was found to be highly potent with a pK(b) of 9.7.