P4 and P1 0 optimization of bicycloproline P2 bearing tetrapeptidyl a-ketoamides as HCV protease inhibitors Yvonne Yip, Frantz Victor, Jason Lamar, Robert Johnson, Q. May Wang, John I. Glass, Nathan Yumibe, Mark Wakulchik, John Munroe and Shu-Hui Chen * Lilly Research Laboratory, A Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA Received 1 June 2004; accepted 2 July 2004 Available online 31 July 2004 Abstract—With the aim of improving HCV protease inhibitors reported in our previous manuscripts, we synthesized and evaluated a series of 1a-based tetrapeptidyl a-ketoamides with additional P4 modification. The promising analog discovered through this SAR, 5a, was further derivatized at P1 0 or P1 position. As a result of these efforts, we found that replacement of the P4 valine as seen in 1a with cyclohexylglycine (Chg) resulted in the discovery of 5a, 5c, and 5e endowed with improved cellular activity in comparison to 1a. Ó 2004 Elsevier Ltd. All rights reserved. 1. Introduction Heptatitis C virus (HCV), the major etiological agent of the non-A non-B hepatitis, was identified at the end of 1980s. Currently, HCV has infected about 170 million people worldwide and has become a major health prob- lem. About 70% of HCV infected patients become chronically infected, approximately 20% of those patients are at the risk of developing cirrhosis that can eventually lead to hepatocellular carcinoma. 1 Current interferon-based therapies are far less than ideal espe- cially for those infected with HCV genotype 1. The sub- optimal efficacy along with poor tolerance associated with current treatments necessitates the need for devel- opment of new therapeutics. 2 The HCV-encoded NS3 serine protease is essential for viral replication and thus has been considered as an attractive target for therapeu- tic intervention for the treatment of HCV-infected patients. 3–5 In order to address the unmet medical need, we became interested in the discovery of novel HCV protease inhibitors with therapeutic potentials. As docu- mented in a series of recent publications from Lilly 6 and Vertex, 7 we focused our research efforts on the design and subsequent optimization of the bicycloproline P2 incorporated a-ketoamides as HCV protease inhibitors including a number of tert-butylglycine P3 bearing derivatives 1a, 1b, and 1c as shown in Figure 1. We are pleased to find that compound 1a exhibited very good in vitro potency (enzyme and cellular), toxicity profiles, as well as adequate liver exposure upon oral administration. 8 To further optimize this novel series inhibitors, we embarked on P4 modification either alone or in combination with additional P1 0 optimization. On the basis of substrate preference determined for a set of hexapeptides (P1–P6) by Pessi and his collaborators, 9 we decided to incorporate several aliphatic and aromatic residues (e.g., IIe, Cha, and Phg, etc.) at the P4 position as listed in Figure 1. Moreover, in order to maintain good membrane permeability, we excluded charged res- idues at that pocket. It should be mentioned that each of the tetrapeptidyl a-ketoamide inhibitor discussed in this manuscript incorporates a diastereomeric center at P1 position due to synthetic convenience. In this communication, we report our recent progress achieved through such P4 optimization, which has led to the identification of a number of promising HCV NS3 protease inhibitors such as 5a, 5c, and 5e endowed with improved activity in both the enzyme inhibition and replicon assays relative to 1a. 2. Chemical synthesis The representative synthetic route devised for the P4 modified peptidyl a-ketoamides 2a through 7a is 0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2004.07.007 * Corresponding author. Fax: +86-21-50461087; e-mail: chen_shuhui@ pharmatechs.com Bioorganic & Medicinal Chemistry Letters 14 (2004) 5007–5011