2,3-Diaryl-5-anilino[1,2,4]thiadiazoles as Melanocortin MC4 Receptor Agonists and Their Effects on Feeding Behavior in Rats Kevin Pan, y Malcolm K. Scott, Daniel H. S. Lee, { Louis J. Fitzpatrick, Jeffery J. Crooke, Ralph A. Rivero, x Daniel I. Rosenthal, Anil H. Vaidya, Boyu Zhao and Allen B. Reitz* Drug Discovery Division, Johnson & Johnson Pharmaceutical Research and Development, Welsh and McKean Rds., PO Box 776, Spring House, PA 19477, USA Received 29 May 2002; accepted 16 August 2002 Abstract—The melanocortin-4 receptor (MC4) modulates physiological functions such as feeding behavior, nerve regeneration, and drug addiction. Using a high throughput screen based on 125 I-NDP-MSH binding to the human MC4 receptor, we discovered 2,3-diaryl-5-anilino[1,2,4]thiadiazoles 3 as potent and selective MC4 receptor agonists. Through SAR development on the three attached aryl rings, we improved the binding affinity from 174 nM to 4.4 nM IC 50 . When delivered intraperitoneally, compounds 3a, 3b, and 3c induced significant inhibition of food intake in a fasting-induced feeding model in rats. When delivered orally, these compounds lost activity, mainly due to rapid metabolism to inactive imidoylthiourea reduction products. # 2002 Elsevier Science Ltd. All rights reserved. Introduction Five melanocortin G-protein receptor subtypes (MC1– MC5) have been cloned and characterized. 1 Melanocyte- stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH), which are produced from the pro- teolytic cleavage of a 31–36 KD glycosylated protein called pro-opiomelanocortin (POMC), are two natural agonists of MC receptors. a-MSH contains the first 13N-terminal amino acids of ACTH. Homologous to a-MSH are two additional peptides, b-MSH and g-MSH, contained in the POMC sequence. All of these natural ligands bind to MC receptors with differing affinities, with the exception of MC2 which is activated by only ACTH. 2 MC receptors are among the very few receptors that have both natural agonists and antagonists. For example, the agouti signaling protein (ASIP) is an antagonist of MC1 and MC4 receptors. 3 Through a homology search of the genes for proteins related to ASIP, another protein, agouti-gene related protein (AGRP), was cloned and found to be an antagonist of MC3 and MC4 receptors. 4 All five MC receptors exhibit diverse physiological functions mainly through cAMP stimulation and downstream signal transduction. Expressed in melano- cytes of the dermis, the MC1 receptor plays a major role in controlling the formation of the pigment melanin and animal coat coloration. The MC2 receptor is highly expressed in the adrenal cortex and adipose tissues, and is believed to be responsible for the ACTH-mediated control of glucocorticoid and mineralcorticoid produc- tion. The MC3 receptor is expressed in the CNS, pla- centa, gut and heart. Although the functions of the MC3 receptor are not well understood, MSH and ACTH peptides are believed to induce sexual behavior in animals via the stimulation of the MC3 receptor at a hypothalamic site. The MC4 receptor is primarily expressed in the brain and plays an important role in regulating feeding behavior. 5 The MC4 receptor is also involved in drug addiction, 6 nerve regeneration, 7,8 and the regulation of the cardiovascular system together with non-melanocortin receptors. The role of the MC4 receptor in controlling feeding behavior and body weight is well supported by several studies. For example, direct injection of a-MSH or ACTH-(1–24) into the hypothalamus caused a sig- nificant reduction of food intake in rats. 9 Similar effects were also observed when the unnatural agonistic peptide 0968-0896/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0968-0896(02)00428-5 Bioorganic & Medicinal Chemistry 11 (2003) 185–192 *Corresponding author. Tel.:+1-215-628-5615; fax:+1-215-628-4985; e-mail: areitz@prdus.jnj.com y Present affiliation: Shanghai Hutchinson Pharmaceuticals. { Presentaffiliation:BiogenInc.,14,CambridgeCenter,Cambridge,MA. x Present affiliation: GlaxoSmithKline, King of Prussia, Pennsylvania.