Identification of novel series of human CCR1 antagonists Yun Feng Xie, a,  Ila Sircar, a Kirk Lake, a Mallareddy Komandla, a Kathleen Ligsay, a Jian Li, b Kui Xu, b,à Jason Parise, b Lisa Schneider, b Dingqiu Huang, b Juping Liu, b Naoki Sakurai, b,§ Miguel Barbosa b,– and Rick Jack b, * a Department of Chemistry, Tanabe Research Laboratories USA, Inc., 4540 Towne Centre Court, San Diego, CA 92121, USA b Department of Biology, Tanabe Research Laboratories USA, Inc., 4540 Towne Centre Court, San Diego, CA 92121, USA Received 14 June 2007; revised 19 September 2007; accepted 19 September 2007 Available online 25 September 2007 Abstract—A hit-to-lead optimization process was carried out on the high throughput screening hit compound 1 resulting in the iden- tification of several potent and selective CCR1 receptor antagonists. Compound 37 shows the best overall profile with IC 50 values of <100 nM in binding and functional assays. Ó 2008 Published by Elsevier Ltd. Chemokines are a growing family of proteins that play an important role in leukocyte activation and migra- tion. 1–3 They are divided into four subfamilies: CC, CXC, XC, and CX3C defined by the position of the con- served cysteine residues near the N terminus. The che- mokines CCL3 (MIP-1a) and CCL5 (RANTES) bind to their shared receptor CCR1, which is expressed on a number of cell types including monocytes, macro- phages, dendritic cells, and T cells. A substantial body of evidence has linked the chemokine receptor CCR1 and its major ligands to the pathogenesis of chronic inflammatory diseases including rheumatoid arthritis (RA), 4,5 multiple sclerosis (MS), 6,7 and transplant rejec- tion. 8,9 The first clinical proof-of-concept in RA was ob- tained with a small molecule CCR1 antagonist that showed marked decrease in synovial inflammation and trend toward a decrease in clinical disease activity after 2 weeks of treatment. 10 Severe side effects were not re- ported from these studies. These results illustrate the therapeutic potential of small molecule CCR1 antago- nists in these diseases, and thus make CCR1 an attrac- tive target for drug discovery research. Here we report our work directed toward the identification of novel small molecule CCR1 antagonists. Several chemotypes have been described as CCR1 antag- onists: benzylpiperazines I (BX-471) 9,11 and II, 12 xan- thene-9-carboxamides (III), 13 4-hydroxypiperidines (IV and VI), 14,15 and hydroxyethylene peptide isosteres (VII) 16 (Chart 1). BX-471 and compound VI were ad- vanced to the clinic for multiple sclerosis and rheumatoid arthritis, respectively. To identify novel chemotypes we screened a library of 4277 compounds using a fluorescent calcium flux as measured by fluoresecent imaging plate reader (FLIPR). 17 The initial 12 screening hits were con- firmed by a competitive receptor binding assay. 18 The hydroxypiperidine compound 1 emerged as the best hit with moderate activity (IC 50 <6 lM; Fig. 1). Hit-to-lead modification strategies were developed around com- pound 1 to increase potency. Strategically, compound 1 was divided into four discrete areas: hydrophobe 1 (right aromatic), amide functional- ity, aliphatic linker, and hydrophobe 2 (4-hydroxy-4- phenylpiperidine (Fig. 2)). Systematic structure–activity relationship (SAR) studies were conducted in each por- tion to improve the potency. Initial efforts were focused on the hydrophobe 1 and the amide functionality. To that end, 1-(3-aminopropyl)-4-(4-chlorophenyl)piperi- 0960-894X/$ - see front matter Ó 2008 Published by Elsevier Ltd. doi:10.1016/j.bmcl.2007.09.068 Keywords: Chemokine receptor 1; CCR1 antagonist. * Corresponding author. Tel.: +1 858 622 7022; fax: +1 858 558 0650; e-mail: rjack@trlusa.com   Present address: Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, CA 92121, USA. à Present address: Amylin, 9360 Towne Centre Drive, San Diego, California 92121. § Present address: Mitsubishi Tanabe Pharma Corporation, 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa, 227-0033 Japan. – Present address: Johnson & Johnson Pharmaceutical Research & Development, 3210 Merryfield Row San Diego, California 92121. Available online at www.sciencedirect.com Bioorganic & Medicinal Chemistry Letters 18 (2008) 2215–2221