N-(Substituted-anilinoethyl)acylamides: Design, Synthesis and Pharmacological Characterization of a New Class of Melatonin Receptor Ligands

A novel series of melatonin receptor ligands, characterized by a N-(substituted-anilinoethyl)amido scaffold, along with preliminary structure–activity relationships (SARs), is presented. MT1 and MT2 receptor binding affinity and intrinsic activity have been modulated by the introduction of different substituents on the aniline nitrogen, on the benzene ring, and on the amide side chain. Modulation of intrinsic activity and MT2 selectivity of the newly synthesized compounds has been achieved by applying SAR models previously developed, providing compounds with different binding and intrinsic activity profiles. Compound 3d, with a bulky ß-naphthyl group on the aniline nitrogen, behaves as an MT2-selective antagonist with sub-nM affinity. Size reduction of the substituent enhances intrinsic activity, as in the nonselective N-methyl-anilino agonist 3i. The phenyl derivative 3g is an MT2-selective partial agonist, with MT2 binding affinity higher than melatonin, showing promising sleep-promoting and antianxiety properties in animal models.