) is a selective inhibitor of hepatitis C virus (HCV) replication that targets the NS5B polymerase. R7128, the prodrug of PSI-6130, has shown antiviral efficacy in patients chronically infected with HCV genotype 1a (GT-1a) and GT-1b. We observed that the compound exhibited potent in vitro activity against laboratory-optimized HCV replicons as well as against a panel of replicons containing NS5B HCV polymerases derived from GT-1a and GT-1b clinical isolates. We used the HCV replicon cell system to examine the emergence of variants with reduced sensitivity to PSI-6130. Shortterm treatment of cells harboring the HCV subgenomic replicon with PSI-6130 cleared the replicon without generating resistant variants. Long-term culture of the cells under the compound selection generated the S282T substitution in a complex pattern with other amino acid substitutions in the NS5B polymerase. The presence of the coselected substitutions did not increase the moderate three-to sixfold loss of sensitivity to PSI-6130 mediated by the S282T substitution; however, their presence enhanced the replication capacity compared to the replication levels seen with the S282T substitution alone. We also observed a lack of cross-resistance between PSI-6130 and R1479 and demonstrated that long-term culture selection with PSI-6130 in replicon cells harboring preexisting mutations resistant to R1479 (S96T/N142T) results in the emergence of the S282T substitution and the reversion of S96T to wild-type serine. In conclusion, PSI-6130 presents a high barrier to resistance selection in vitro, selects for variants exhibiting only low-level resistance, and lacks cross-resistance with R1479, supporting the continued development of the prodrug R7128 as a therapeutic agent for the treatment of HCV infection.Hepatitis C virus (HCV) is a positive-strand RNA virus and a member of the Hepacivirus genus in the Flaviviridae family. Acute infection with HCV progresses into chronic infection for approximately 80% of infected patients and is a major cause of liver cirrhosis and hepatocellular carcinoma. The current use of pegylated alpha interferon (IFN-␣) in combination with ribavirin for chronic HCV infection treatment (10,14,16) results in a 37 to 50% sustained viral response in patients infected with HCV genotype 1 (GT-1) (15). This suboptimal sustained viral response, combined with the high prevalence of undesirable side effects, has prompted focused efforts to develop specifically targeted antiviral therapies for HCV infections. The HCV NS5B RNA-dependent RNA polymerase (RdRp) is a critical enzyme for viral RNA replication and presents an attractive therapeutic target.

The Cu 2+ complexes formed by a series of cyclen derivatives bearing sulfur pendant arms, 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis[2-(methylsulfanyl)ethyl]-4,10-diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S), were studied in aqueous solution at 25 °C from thermodynamic and structural points of view to evaluate their potential as chelators for copper radioisotopes. UV–vis spectrophotometric out-of-cell titrations under strongly acidic conditions, direct in-cell UV–vis titrations, potentiometric measurements at pH >4, and spectrophotometric Ag + –Cu 2+ competition experiments were performed to evaluate the stoichiometry and stability constants of the Cu 2+ complexes. A highly stable 1:1 metal-to-ligand complex (CuL) was found in solution at all pH values for all chelators, and for DO2A2S, protonated species were also detected under acidic conditions. The structures of the Cu 2+ complexes in aqueous solution were investigated by UV–vis and electron paramagnetic resonance (EPR), and the results were supported by relativistic density functional theory (DFT) calculations. Isomers were detected that differed from their coordination modes. Crystals of [Cu(DO4S)(NO 3 )]·NO 3 and [Cu(DO2A2S)] suitable for X-ray diffraction were obtained. Cyclic voltammetry (CV) experiments highlighted the remarkable stability of the copper complexes with reference to dissociation upon reduction from Cu 2+ to Cu + on the CV time scale. The Cu + complexes were generated in situ by electrolysis and examined by NMR spectroscopy. DFT calculations gave further structural insights. These results demonstrate that the investigated sulfur-containing chelators are promising candidates for application in copper-based radiopharmaceuticals. In this connection, the high stability of both Cu 2+ and Cu + complexes can represent a key parameter for avoiding in vivo demetalation after bioinduced reduction to Cu + , often observed for other well-known chelators that can stabilize only Cu 2+ .

RNA polymerases effectively discriminate against deoxyribonucleotides and specifically recognize ribonucleotide substrates most likely through direct hydrogen bonding interaction with the 2-␣-hydroxy moieties of ribonucleosides. Therefore, ribonucleoside analogs as inhibitors of viral RNA polymerases have mostly been designed to retain hydrogen bonding potential at this site for optimal inhibitory potency. Here, two novel nucleoside triphosphate analogs are described, which are efficiently incorporated into nascent RNA by the RNA-dependent RNA polymerase NS5B of hepatitis C virus (HCV), causing chain termination, despite the lack of ␣-hydroxy moieties. 2-Deoxy-2-␤-fluoro-4-azidocytidine (RO-0622) and 2-deoxy-2-␤-hydroxy-4-azidocytidine (RO-9187) were excellent substrates for deoxycytidine kinase and were phosphorylated with efficiencies up to 3-fold higher than deoxycytidine. As compared with previous reports on ribonucleosides, higher levels of triphosphate were formed from RO-9187 in primary human hepatocytes, and both compounds were potent inhibitors of HCV virus replication in the replicon system (IC 50 ‫؍‬ 171 ؎ 12 nM and 24 ؎ 3 nM for RO-9187 and RO-0622, respectively; CC 50 >1 mM for both). Both compounds inhibited RNA synthesis by HCV polymerases from either HCV genotypes 1a and 1b or containing S96T or S282T point mutations with similar potencies, suggesting no cross-resistance with either R1479 (4-azidocytidine) or 2-C-methyl nucleosides. Pharmacokinetic studies with RO-9187 in rats and dogs showed that plasma concentrations exceeding HCV replicon IC 50 values 8 -150-fold could be achieved by low dose (10 mg/kg) oral administration. Therefore, 2-␣-deoxy-4-azido nucleosides are a new class of antiviral nucleosides with promising preclinical properties as potential medicines for the treatment of HCV infection. Hepatitis C virus (HCV)3 infection is a major cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma and is the leading cause of liver transplantation. Current treatment options available to HCV-infected persons have limitations with regard to efficacy and tolerability. Only about 50% of individuals infected with HCV genotype 1 achieve sustained virological response when treated with a combination of pegylated interferon ␣ and ribavirin (1, 2). In addition, high viral load, age, body weight, co-infection with human immunodeficiency virus, and cirrhosis negatively affect the probability of achieving sustained virological response (3, 4). Therefore, there is an urgent need to develop new and more effective therapies for the treatment of HCV infection. A number of new antiviral candidates are currently being evaluated in clinical studies, the majority targeting either the HCV protease or HCV polymerase enzymes, which are essential for viral replication (5). The HCV RNA-dependent RNA polymerase, NS5B, contains the active site responsible for viral RNA synthesis and functions as part of a membrane-associated replicase complex. Nucleoside and non-nucleoside inhibitors of HCV polymerase h...

Wormholes through chemical space: Spirocyclic oxetanes are described as analogues of morpholine and also as topological siblings of their carbonyl counterparts. They are particularly promising in terms of both their physicochemical properties and the ease with which they can be grafted onto molecular structures. The data collected highlight oxetanes as both the hydrophilic sister of a gem‐dimethyl unit and the carbonyl group's lipophilic brother.

Wurmlöcher im chemischen Raum: Spirocyclische Oxetane werden als Analoga von Morpholin und als topologische Gegenstücke entsprechender Carbonylverbindungen beschrieben. Solche Oxetane sind vielversprechend bezüglich ihrer physikochemischen Eigenschaften und der Leichtigkeit, mit der sie in Molekülstrukturen eingebaut werden können. Die gesammelten Daten präsentieren die Oxetan‐Gruppe einerseits als hydrophile Entsprechung einer geminalen Dimethyleinheit und andererseits als lipophile Entsprechung einer Carbonylgruppe.