Further SAR Studies on Novel Small Molecule Inhibitors of the Hepatitis C (HCV) NS5B Polymerase T. Jagadeeswar Reddy,* Laval Chan, Nathalie Turcotte, Melanie Proulx, Oswy Z. Pereira, Sanjoy K. Das, Arshad Siddiqui, Wuyi Wang, Carl Poisson, Constantin G. Yannopoulos, Darius Bilimoria, Lucille L’Heureux, Hicham M. A. Alaoui and Nghe Nguyen-Ba Shire BioChem Inc., 275 Armand-Frappier, Laval, Quebec, Canada H7V 4A7 Received 13 February 2003; accepted 9 May 2003 Abstract—Herein, we describe the structure–activity relationship (SAR) of N,N-disubstituted phenylalanine series of NS5B poly- merase inhibitors of hepatitis C. The NS5B polymerase inhibitory activity of the most active compound exhibited an IC 50 of 2.7 mM. # 2003 Elsevier Ltd. All rights reserved. It is estimated that 170 million people worldwide are infected with Hepatitis C virus (HCV) including 4 mil- lion in the United States. Within 20 years of infection, about 4–5% of them will develop cirrhosis and hepato- cellular carcinoma, often resulting in death. 1 The recommended current treatment, interferon a (IFN-a, 2a or 2b or a polyethylene glycol conjugate) in combi- nation with ribavirin provides a sustained viral response in only 54–56% of the treated patients. However, for patients infected with HCV genotype 1a/b, the pre- dominant genotype found in the USA, Japan and parts of Europe, the response is at best 42–46% and, further- more, treatment is expensive and side effects can be severe. 2 The lack of an effective and well-tolerated treatment has therefore spurred intense research efforts to develop affordable, oral and novel anti-HCV agents. HCV is a 9.6-kb positive strand RNA virus of the Fla- viviridae, genus hepacivirus which encodes a 3011–3033 amino acid polyprotein variable in several genotypes. 3 This polyprotein is further processed into various structural (core, E1 and E2, p7) and non-structural (NS2, NS3, NS4A, NS4B, NS5A and NS5B) viral pro- teins by host and viral proteases. 4 The NS3 chymo- trypsin-like protease and the NS5B RNA dependent RNA polymerase (RdRp) are probably the most stud- ied targets for anti-HCV therapy as they are crucial for viral replication. 5 Despite intense research effort on NS3 protease, NS5B polymerase inhibitors started appearing recently in the patent literature. 6 Only, NS5B poly- merase inhibitor (JTK-002/JTK-003) from Japan Tobacco Inc. 7 has been reported to be undergoing Phase II clinical trials. We have recently reported the identification of a novel class of HCV NS5B polymerase inhibitors (e.g., 1). 8 These N,N-disubstituted phenylalanine analogues dis- played not only potent inhibition of HCV polymerase but also selectivity over human polymerases. 8 Further- more, X-ray crystal structures of these inhibitors bound to NS5B polymerase enzyme revealed an allosteric site in the thumb region 8c about 30 A ˚ from the catalytic site and about 10 A ˚ from the recently identified rGTP binding site. 9 As part of ongoing research on Hepatitis C programme, 8a herein we disclose the detailed struc- ture–activity relationship (SAR) of the benzamide portion of 1. The test compounds (e.g., 1) were synthesized according to Scheme 1. Reductive amination of the C-protected l-phenylalanine with m-bromobenzaldehyde using ZnCl 2 and NaCNBH 3 in MeOH at room temperature gave the 0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0960-894X(03)00670-X Bioorganic & Medicinal Chemistry Letters 13 (2003) 3341–3344 *Corresponding author. Tel.: +1-450-978-7820; fax: +1-450-978- 7777; e-mail: treddy@ca.shire.com