SynthesisandEvaluationofOpticallyPureDioxolanesas InhibitorsofHepatitisCVirusRNAReplication Sanjib Bera, a Leila Malik, a Balkrishen Bhat, a Steven S. Carroll, b Malcolm MacCoss, c David B. Olsen, b Joanne E. Tomassini b and Anne B. Eldrup a, * a Department of Medicinal Chemistry, Isis Pharmaceuticals, Carlsbad, CA 92008, USA b Department of Biological Chemistry, Merck Research Laboratories, West Point, PA 19486, USA c Department of Medicinal Chemistry, Merck Research Laboratories, Rahway, NJ 07065, USA Received 19 June 2003; revised 3 September 2003; accepted 4 September 2003 Abstract—A series of optically pure 1,3-dioxolane nucleoside mimics was synthesized by a synthetic route that allowed incor- poration of a 5R-methyl substituent from commercially available starting materials. The pyrrolo[2,3-d]pyrimidine heterocycle was chosen as a substitute for the purine derivative. Coupling of the pyrrolo[2,3-d]pyrimidine and the dioxolane was performed under solid–liquid phase transfer conditions. The ability to inhibit HCV RNA replication was assessed in a cell based subgenomic replicon assay. None of the described compounds displayed significant anti-HCV activity. # 2003 Elsevier Ltd. All rights reserved. Hepatitis C virus (HCV) is the pathogen associated with the majority of chronic hepatitis infections world wide and is a major cause of liver disease and transplanta- tions. The currently recommended antiviral therapy consists of interferon alpha and ribavirin, a treatment that leads to only moderate sustained response rates. HCV encodes a series of viral proteins: the NS2/3 autoprotease, the NS3 serine protease and NTPase/ helicase, and NS5B, the RNA dependent RNA poly- merase (RdRp). 1 The polymerase is essential to viral replication and proliferation, and hence represents a valid drug discovery target. Non-nucleoside inhibitors (NNIs) and nucleoside inhibitors (NIs) of virally enco- ded polymerases have been validated for other targets, for example, HIV. While a range of NNI inhibitors of HCV RNA replication have been reported, 2 5 few NIs have been identified. 6 10 Some of the NS5B NIs described have encompassed alteration of the 2 0 position, either in the form of a 2 0 -O- methyl 6 ora2 0 -C-methyl modification 6 8 (Fig. 1). Other reports 9,10 have indicated dioxolane based nucleoside triphosphates to be inhibitors of HCV RdRp mediated RNA synthesis. Hence, it remains unclear if the pre- sence of a 2 0 -OH/2 0 -O-methyl is strictly necessary for activity in a cell based assay. Nucleosides where the 3 0 carbon has been replaced by a heteroatom such as oxygen or sulfur, have been demonstrated to be effective in cancer and viral chemo- therapy. 11 18 For example, ()-l-b-1,3-oxathionyl cyto- sine (3TC, Lamivudine) 4 is an effective anti-HIV and anti-HBV agent while ()-l-b-1,3-dioxanyl cytosine 5 (O-ddC) has demonstrated anti-tumor, 19 anti-HIV and anti-HBV activity 15 (Fig. 2). In the purine series, 1,3- dioxanylguanine 6 17,20 has demonstrated significant anti-HIV activity. Furthermore, dideoxynucleosides containing a 4-aminopyrrolo[2,3-d]pyrimidine moiety havebeendemonstratedtodisplayincreasedchemicaland enzymatic stability 21 relative to the corresponding purine derivatives. Based on the above findings, we decided to 0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmcl.2003.09.008 Bioorganic & Medicinal Chemistry Letters 13 (2003) 4455–4458 Figure1. Examples of known HCV polymerase inhibitors, modified at the C2 or O2 position. *Corresponding author. Tel.: +1-760-603-3852; fax: +1-760-603- 4654; e-mail: aeldrup@isisph.com