Synthesis and biological activity of heteroaryl 3-(1,1-dioxo-2H-(1,2,4)-benzothiadizin-3-yl)-4-hydroxy-2(1H)-quinolinone derivatives as hepatitis C virus NS5B polymerase inhibitors.

Modification of the benzo rings of 3-(1,1-dioxo-2H-(1,2,4)-benzothiadiazin-3-yl)-4-hydroxy-2(1H)-quinolinones into heteroaromatic systems was investigated to enhance physicochemical properties and potency profile of this class of inhibitors. The synthesis and biological activity of the derived compounds is discussed.

Substituted benzothiadizine inhibitors of Hepatitis C virus polymerase.

The synthesis and optimisation of HCV NS5B polymerase inhibitors with improved potency versus the existing compound 1 is described. Substitution in the benzothiadiazine portion of the molecule, furnishing improvement in potency in the high protein Replicon assay, is highlighted, culminating in the discovery of 12h, a highly potent oxyacetamide derivative.

3-(1,1-dioxo-2H-(1,2,4)-benzothiadiazin-3-yl)-4-hydroxy-2(1H)-quinolinones, potent inhibitors of hepatitis C virus RNA-dependent RNA polymerase.

Recently, we disclosed a new class of HCV polymerase inhibitors discovered through high-throughput screening (HTS) of the GlaxoSmithKline proprietary compound collection. This interesting class of 3-(1,1-dioxo-2H-1,2,4-benzothiadiazin-3-yl)-4-hydroxy-2(1H)-quinolinones potently inhibits HCV polymerase enzymatic activity and inhibits the ability of the subgenomic HCV replicon to replicate in Huh-7 cells. This report will focus on the structure-activity relationships (SAR) of substituents on the quinolinone ring, culminating in the discovery of 1-(2-cyclopropylethyl)-3-(1,1-dioxo-2H-1,2,4-benzothiadiazin-3-yl)-6-fluoro-4-hydroxy-2(1H)-quinolinone (130), an inhibitor with excellent potency in biochemical and cellular assays possessing attractive molecular properties for advancement as a clinical candidate. The potential for development and safety assessment profile of compound 130 will also be discussed.

Studies on acyl pyrrolidine inhibitors of HCV RNA-dependent RNA polymerase to identify a molecule with replicon antiviral activity.

The SAR development is described for a series of N-acyl pyrrolidine inhibitors of the Hepatitis C virus RNA-dependent RNA polymerase, NS5B, from tractable Delta21 enzyme inhibitors to an example with antiviral activity in a cellular assay (HCV replicon).

An efficient, asymmetric solid-phase synthesis of benzothiadiazine-substituted tetramic acids: potent inhibitors of the hepatitis C virus RNA-dependent RNA polymerase.

An efficient, asymmetric solid-phase synthesis of benzothiadiazine-substituted tetramic acids is reported. Starting from commercially available chiral Fmoc-protected alpha-amino acids loaded onto Wang resin, Fmoc removal, reductive amination followed by amide bond formation, and base-catalyzed cyclization with simultaneous cleavage from the resin provided the desired products. Compounds described are potent inhibitors of the hepatitis C virus RNA-dependent RNA polymerase.

Identification of small molecule inhibitors of the hepatitis C virus RNA-dependent RNA polymerase from a pyrrolidine combinatorial mixture.

HTS of the compound collection for inhibition of the HCV RNA dependent RNA polymerase identified two 168 member N-acyl pyrrolidine combinatorial mixture hits. Deconvolution and expansion of these mixtures by solid phase synthesis to establish initial SAR and identify a potent inhibitor is reported.

Mapping cooperative activity of the hepatitis C virus RNA-dependent RNA polymerase using genotype 1a-1b chimeras.

The nonstructural protein 5B (NS5B) of hepatitis C virus (HCV) encodes an RNA-dependent RNA polymerase (RdRp) which is essential for viral replication. NS5B expression in bacteria generated 20- to 50-fold lower yield and 100-fold less product per mol of enzyme for gentoype 1a RdRp than type 1b. Further, unlike type 1b RdRp, type 1a enzyme failed to exhibit cooperative properties in the assays described herein. Differences in thermal stability may partially account for the inability to efficiently oligomerize. Superose gel filtration analyses confirm differences between these RdRp preparations, although affinity for the column rather than size may account for the differences in migration. To further address this complexity, a panel of RdRp type 1a-type 1b chimeras were evaluated and implicate a role for the thumb subdomain of genotype 1b RdRp as critical for cooperative function.

Enzymatic activities of the GB virus-B RNA-dependent RNA polymerase.

The GB virus-B (GBV-B) nonstructural protein 5B (NS5B) encodes an RNA-dependent RNA polymerase (RdRp) with greater than 50% sequence similarity to the hepatitis C virus (HCV) NS5B. Recombinant GBV-B NS5B was reported to possess RdRp activity (W. Zhong et al., 2000, J. Viral Hepat. 7, 335-342). In this study, the GBV-B RdRp was examined more thoroughly for different RNA synthesis activities, including primer-extension, de novo initiation, template switch, terminal nucleotide addition, and template specificity. The results can be compared with previous characterizations of the HCV RdRp. The two RdRps share similarities in terms of metal ion and template preference, the abilities to add nontemplated nucleotides, perform both de novo initiation and extension from a primer, and switch templates. However, several differences in RNA synthesis between the GBV-B and HCV RdRps were observed, including (i) optimal temperatures for activity, (ii) ranges of Mn(2+) concentration tolerated for activity, and (iii) cation requirements for de novo RNA synthesis and terminal transferase activity. To assess whether the recombinant GBV-B RdRp may represent a relevant surrogate system for testing HCV antiviral agents, two compounds demonstrated to be active at nanomolar concentrations against HCV NS5B were tested on the GBV RdRp. A chain terminating nucleotide analog could prevent RNA synthesis, while a nonnucleoside HCV inhibitor was unable to affect RNA synthesis by the GBV RdRp.

Identification and biological characterization of heterocyclic inhibitors of the hepatitis C virus RNA-dependent RNA polymerase.

The hepatitis C virus (HCV) NS5B protein encodes an RNA-dependent RNA polymerase (RdRp), the primary catalytic enzyme of the HCV replicase complex. We established a biochemical RNA synthesis assay, using purified recombinant NS5B lacking the C-terminal 21 amino acid residues, to identify potential polymerase inhibitors from a high throughput screen of the GlaxoSmithKline proprietary compound collection. The benzo-1,2,4-thiadiazine compound 1 was found to be a potent, highly specific inhibitor of NS5B. This agent interacts directly with the viral polymerase and inhibits RNA synthesis in a manner noncompetitive with respect to GTP. Furthermore, in the absence of an in vitro-reconstituted HCV replicase assay employing viral and host proteins, the ability of compound 1 to inhibit NS5B-directed viral RNA replication was determined using the Huh7 cell-based HCV replicon system. Compound 1 reduced viral RNA in replicon cells with an IC(50) of approximately 0.5 microm, suggesting that the inhibitor was able to access the perinuclear membrane and inhibit the polymerase activity in the context of a replicase complex. Preliminary structure-activity studies on compound 1 led to the identification of a modified inhibitor, compound 4, showing an improvement in both biochemical and cell-based potency. Lastly, data are presented suggesting that these compounds interfere with the formation of negative and positive strand progeny RNA by a similar mode of action. Investigations are ongoing to assess the potential utility of such agents in the treatment of chronic HCV disease.