Received: 23 January 2018 | Revised: 28 April 2018 | Accepted: 2 May 2018 DOI: 10.1002/ardp.201800017 FULL PAPER Expanding the chemical space of anti-HCV NS5A inhibitors by stereochemical exchange and peptidomimetic approaches Triveena M. Ramsis 1 | Shereen E. Abdel Karim 1 | Niki Vassilaki 2 | Efseveia Frakolaki 2 | Ahmed A. M. Kamal 3 | Grigoris Zoidis 4 | Nermin S. Ahmed 1 | Ashraf H. Abadi 1 1 Faculty of Pharmacy and Biotechnology, Department of Pharmaceutical Chemistry, German University in Cairo, Cairo, Egypt 2 Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece 3 Pharmaceutical and Medicinal Chemistry, Department of Drug Design Optimization, Saarland University and Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Saarbrücken, Germany 4 Faculty of Pharmacy, Department of Pharmaceutical Chemistry, School of Health Sciences, National and Kapodistrian University of Athens, Athens, Greece Correspondence Prof. Ashraf H. Abadi, Faculty of Pharmacy and Biotechnology, Department of Pharmaceutical Chemistry, German University in Cairo, 11835 Cairo, Egypt. Email: ashraf.abadi@guc.edu.eg Funding information Science and Technology Development Fund (Egypt), Grant number: 22848 Abstract Here we report a series of potent anti-HCV agents bearing a symmetrical benzidine L-prolinamide backbone with different capping groups including alkyl/aryl carbamates of natural and unnatural valine and leucine amino acids. All compounds were investigated for their inhibitory activity in an HCV replicon assay on genotype 1b. The novel compounds share some chemical and clinical attributes of commercially available NS5A inhibitors. Compounds 5 and 6 with unnatural capping residue and ethyl and isobutyl carbamates showed EC 50 values in the picomolar range with a low toxicity profile and selectivity indices of several orders of magnitude. These findings enlarge the chemical space from which NS5A inhibitors may be discovered by adopting unnatural amino acids, amino acids other than valine and carbamates other than methyl as the capping groups. KEYWORDS anti-HCV, bivalent ligands, NS5A inhibitors, peptidomimetics 1 | INTRODUCTION Hepatitis C virus (HCV) is the leading cause of chronic liver disease worldwide as well as the primary cause of liver transplantations. The World Health Organization (WHO) estimates that about 3% of the world's population, i.e., 170 million people, is currently infected with HCV. [1] Each year, 3 to 4 million people are newly infected with HCV. [2] The pathogen causes significant morbidity, with approximately 399000 deaths per year as a direct result of complications involved in end-stage liver diseases. [3] Most of the infected individuals (∼80%) will develop chronic infection, the latter is often associated with the development of hepatitis, steatosis, fibrosis, and liver cirrhosis. HCV is currently classified into six main genotypes (identified as 1 through 6), with 31–33% nucleotide sequence divergence. Each genotype is further divided into subtypes (designated by lower case letters), with each subtype differing from one another by 20–25%. [4] The combination of molecular cloning and development of a replicon assay has enabled the discovery of novel DAAs targeting viral proteins. [5,6] HCV is an enveloped positive-stranded RNA virus, the RNA is translated into a polyprotein consisting of 10 proteins. This polyprotein is then processed by both cellular and viral proteases to form three structural (S) elements (core [C], E1, and E2), and seven non- structural (NS) proteins (p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B). NS5A is a hydrophilic phosphoprotein containing an N-terminal amphipathic α-helix that mediates virus association with the ER membrane. This phosphoprotein exists in two forms: a basally Arch Pharm Chem Life Sci. 2018;1–10. wileyonlinelibrary.com/journal/ardp © 2018 Deutsche Pharmazeutische Gesellschaft | 1