PAPER A Novel Peptide Mimetic Inhibitors of Hepatitis C Serine Protease Derived from Isomannide Novel Peptide Mimetic Inhibitors of Hepatitis CSerine Protease Thalita G. Barros, a,b Sergio Pinheiro, b John S. Williamson, c Amílcar Tanuri, d Helena S. Pereira, d,e Rodrigo M. Brindeiro, d José B. A. Neto, d Octávio A. C. Antunes, f Estela M. F. Muri* a a Faculdade de Farmácia, Universidade Federal Fluminense (UFF), Rua Mario Viana 523, Santa Rosa, Niterói, RJ 24241000, Brazil Fax +55(21)26299588; E-mail: estelamuri@yahoo.com.br b Instituto de Química, Campus do Valonguinho, UFF, Niterói, RJ 24020150, Brazil c School of Pharmacy, Department of Medicinal Chemistry, University of Mississippi, MS 38677, USA d Laboratório de Virologia Molecular, ICB, UFRJ, Rio de Janeiro, RJ 21941570, Brazil e Faculdade de Odontologia de Nova Friburgo, Universidade Federal Fluminense (FOUFF), Nova Friburgo, RJ 28625650, Brazil f Laboratório de catálise, Instituto de Química, UFRJ, Rio de Janeiro, RJ 21941909, Brazil Received 29 August 2008; revised 23 October 2008 SYNTHESIS 2009, No. x, pp 000A–000Gxx.xx.2009 Advanced online publication: xx.xx.2009 DOI: 10.1055/s-0028-1083332; Art ID: M04608SS © Georg Thieme Verlag Stuttgart · New York Abstract: Hepatitis C (HCV) infection is a cause of chronic liver disease such as cirrhosis, carcinoma, or liver failure, and the current therapy is effective in only 50% of patients. Serine proteases, which are present in HCV, are the most studied class of proteolytic enzymes, and are a primary target in the drug development field. In this paper, we describe the synthesis and biological studies of a novel class of peptide mimetic compounds as potential HCV serine protease inhibitors. Key words: peptides, antiviral agent, fused-ring systems, isoman- nide, hepatitis C More than 170 million people worldwide are affected by the hepatitis C virus (HCV). HCV infection is a leading cause of chronic liver disease such as cirrhosis, carcino- ma, or liver failure. 1 The current pegylated interferon and ribavirin combination therapy is effective in only 50% of patients. Its moderate efficacy and apparent side effects underscore the need for safer and more effective treat- ments. 2 HCV NS3 protease is a serine protease presenting a characteristic catalytic triad (His51, Asp75, and Ser135) conserved in all flaviviruses. 3,4 The NS3pro activity is es- sential for viral replication, representing a suitable target for the development of new medicines in the treatment of hepatitis C. However, the lack of a robust in vitro cell cul- ture system and the absence of a convenient small animal model have hampered the assessment of both in vitro and in vivo efficacy of any antiviral compounds. As part of our antiviral program for flaviviruses, we de- scribe here the synthesis and biological studies of a series of peptide mimetic compounds designed as potential in- hibitors of HCV serine protease. Studies on the development of peptide mimetic inhibitors have demonstrated the importance of the peptide ap- proach in drug research. Compounds presenting a fused bicyclic structure, such as Danuravir (TMC-114) 5 and VX-950, 6 represent an effort toward the design and devel- opment of new drugs. We envisaged the use of the isomannide rigid scaffold 7 by its structural analogy with cyclic rigid dipeptides. 8 So the rigidity of this scaffold would fix a conformation of our peptide mimetic compound as demonstrated previously for our esters and amides possessing C 2 symmetry. The first step of our synthesis consisted in the transforma- tion of isomannide (1) to its monotosyl derivative 2 using tosyl chloride in pyridine. The crude product, which con- sisted mainly of the monotosylate 2, was purified by chro- matography on silica gel (hexane–EtOAc). Isomannide monotosylate 2 was then O-alkylated under phase-trans- fer conditions with benzyl chloride in 50% aqueous sodi- um hydroxide affording the product, O-benzylated 3. 9,10 Several solvents can be used in the nucleophilic substitu- tion step, such as N,N-dimethylformamide and dimethyl sulfoxide. However, the ionic liquid, 1-butyl-3-methyl- imidazolium tetrafluoroborate {[bmim] + [BF 4 ] – }, shows different advantages over the organic solvents, as well as having improved the reaction yield. The ionic liquid [bmim] + [BF 4 ] – was synthesized following the methodolo- gy described in literature. 11,12 Ionic solvents possess sev- eral properties, such low melting point, negligible vapor pressure, low coordinating ability, and excellent thermal and chemical stability, which make them attractive alter- natives to traditional solvents; for these reasons they are called ‘green’ solvents. 13 The S N 2-type reaction of 3 with sodium azide was performed in ionic liquid, [bmim] + [BF 4 ] – , yielding the azido derivative 4 with inver- sion of configuration. The azido reduction of 4 with hydrogen over palladium-on-carbon gave the amino de- rivative 5 in quantitative yield (Scheme 1). 14–16 Initially, the oxazolones (so-called azalactones) 8a–o were synthesized from commercially available glycine (6) and benzoyl chloride or acetic anhydride obtaining the N- benzoylglycine (7a) and N-acetylglycine (7b), which re- acted with different aldehydes in presence of anhydrous sodium acetate/acetic anhydride by Erlenmeyer condi- tions; 17,18 this methodology gives only the thermodynam- ically stable Z-isomer (Scheme 2). 19,20 The last step consisted of the ring opening of the oxazolones 8a–o, ob- tained via Erlenmeyer synthesis, by the amine 5 yielding the final peptide mimetic products 9a–o (Scheme 3). 21–23