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Abstract: The 3′,5′-cyclic phosphate prodrug 9-[β-d-2′-deoxy-2′-α-fluoro-2′-β-C-methylribofuranosyl]-2-amino-6-ethoxypurine, PSI-352938 1, has demonstrated promising anti-HCV efficacy in vitro and in human clinical trials. A structure–activity relationship study of the nucleoside 3′,5′-cyclic phosphate series of β-d-2′-deoxy-2′-α-fluoro-2′-β-C-methylribofuranosyl nucleoside prodrugs was undertaken and the anti-HCV activity and in vitro safety profile were assessed. Cycloalkyl 3′,5′-cyclic phosphate prodrugs were shown to be significantly more potent as inhibitors of HCV replication than branched and straight chain alkyl 3′,5′-cyclic phosphate prodrugs. No cytotoxicity and mitochondrial toxicity for prodrugs 12, 13 and 19 were observed at concentrations up to 100μm in vitro. Cycloalkyl esters of 3′,5′-cyclic phosphate nucleotide prodrugs demonstrated the ability to produce high levels of active triphosphate in clone-A cells and primary human hepatocytes. Compounds 12, 13 and 19 also demonstrated the ability to effectively deliver in vivo high levels of active nucleoside phosphates to rat liver. [Copyright &y& Elsevier]

Abstract: A series of novel 2′-deoxy-2′-α-fluoro-2′-β-C-methyl 3′,5′-cyclic phosphate nucleotide prodrug analogs were synthesized and evaluated for their in vitro anti-HCV activity and safety. These prodrugs demonstrated a 10–100-fold greater potency than the parent nucleoside in a cell-based replicon assay due to higher cellular triphosphate levels. Our structure–activity relationship (SAR) studies provided compounds that gave high levels of active triphosphate in rat liver when administered orally to rats. These studies ultimately led to the selection of the clinical development candidate 24a (PSI-352938). [ABSTRACT FROM AUTHOR]