John Herbert Merrett

The Novel Nucleoside Analog R1479 (4′-Azidocytidine) Is a Potent Inhibitor of NS5B-dependent RNA Synthesis and Hepatitis C Virus Replication in Cell Culture

Hepatitis C virus (HCV) polymerase activity is essential for HCV replication. Targeted screening of nucleoside analogs identified R1479 (4′-azidocytidine) as a specific inhibitor of HCV replication in the HCV subgenomic replicon system (IC50 = 1.28 μm) with similar potency compared with 2′-C-methylcytidine (IC50 = 1.13 μm). R1479 showed no effect on cell viability or proliferation of HCV replicon or Huh-7 cells at concentrations up to 2 mm. HCV replicon RNA could be fully cleared from replicon cells after prolonged incubation with R1479. The corresponding 5′-triphosphate derivative (R1479-TP) is a potent inhibitor of native HCV replicase isolated from replicon cells and of recombinant HCV polymerase (NS5B)-mediated RNA synthesis activity. R1479-TP inhibited RNA synthesis as a CTP-competitive inhibitor with a Ki of 40 nm. On an HCV RNA-derived template substrate (complementary internal ribosome entry site), R1479-TP showed similar potency of NS5B inhibition compared with 3′-dCTP. R1479-TP was incorporated into nascent RNA by HCV polymerase and reduced further elongation with similar efficiency compared with 3′-dCTP under the reaction conditions. The S282T point mutation in the coding sequence of NS5B confers resistance to inhibition by 2′-C-MeATP and other 2′-methyl-nucleotides. In contrast, the S282T mutation did not confer cross-resistance to R1479.

Applications of Parallel Synthesis to Lead Optimization

Parallel synthesis of focused compound libraries for hit confirmation and lead optimization are certainly important drivers for shortening the lead discovery phase in the pharmaceutical and crop protection industries. In this article we show with permission of Roche and Syngenta three real case studies where Polyphor synthesized focused libraries for lead validation and optimization using high-throughput parallel synthesis and purification techniques. The three examples differ significantly in the synthetic strategies which were employed as well as in the chemical complexity of the final products. A multigeneration approach towards insecticidal triazines, the application of a sequential three-component reaction towards insecticidal and fungicidal thiazoles and finally a multistep synthesis approach of advanced building blocks followed by a two-step final derivatization towards novel antiviral N-hydroxy-indolin-2-ones are presented. In all cases 100-200 analogues were synthesized using parallel synthesis in solution followed by purification of the final products by parallel flash or high-throughput (unattended) HPLC (coupled to MS) within four months. Promising biological results were obtained in all three cases.