Melanin-Concentrating Hormone Receptor 1 Antagonists Lacking an Aliphatic Amine: Synthesis and Structure-Activity Relationships of Novel 1-(Imidazo[1,2-a]pyridin-6-yl)pyridin-2(1H)-one Derivatives

Published in: Journal, Article, Volume : 59, Issue : 3, Pages : 1116-1139

DOI : 10.1021/acs.jmedchem.5b01704

Author : Igawa, Hideyuki; Takahashi, Masashi; Kakegawa, Keiko; Kina, Asato; Ikoma, Minoru; Aida, Jumpei; Yasuma, Tsuneo; Kawata, Yayoi; Ashina, Shuntaro; Yamamoto, Syunsuke; Kundu, Mrinalkanti; Khamrai, Uttam; Hirabayashi, Hideki; Nakayama, Masaharu; Nagisa, Yasutaka; Kasai, Shizuo; Maekawa, Tsuyoshi

Abstract : Aiming to discover melanin-concentrating hormone receptor 1 (MCHR1) antagonists with improved safety profiles, we hypothesized that the aliphatic amine employed in most antagonists reported to date could be removed if the bicyclic motif of the compound scaffold interacted with Asp123 and/or Tyr272 of MCHR1. We excluded aliphatic amines from our compound designs, with a cutoff value of pKa < 8, and explored aliphatic amine-free MCHR1 antagonists in a CNS-oriented chem. space limited by four descriptors (TPSA, ClogP, MW, and HBD count). Screening of novel bicyclic motifs with high intrinsic binding affinity for MCHR1 identified the imidazo[1,2-a]pyridine ring, and subsequent cyclization of the central aliphatic amide linkage led to the discovery of a potent, orally bioavailable MCHR1 antagonist 4-[(4-chlorobenzyl)oxy]-1-(2-cyclopropyl-3-methylimidazo[1,2-a]pyridin-6-yl)pyridin-2(1H)-one (I). It exhibited low potential for hERG inhibition and phospholipidosis induction as well as sufficient brain concentration to exert antiobesity effects in diet-induced obese rats.