Discovery of Novel Nucleotide Prodrugs with Improved Potency Against HCV Variants Carrying NS5B S282T Mutation

Palladium-Catalyzed Asymmetric [3 + 2] Annulation of Vinylethylene Carbonates with Alkenes Installed on Cyclic N-Sulfonyl Imines: Highly Enantio- and Diastereoselective Construction of Chiral Tetrahydrofuran Scaffolds Bearing Three Vicinal and Quaternary Stereocenters

A multisubstituted tetrahydrofuran building block bearing three vicinal chiral carbon centers widely exists in a broad spectrum of bioactive natural products, and the development of efficient and convenient methods to establish this skeleton remains a challenging task. Herein, we have developed an efficient method for the construction of significant tetrahydrofuran scaffolds bearing three vicinal and α-quaternary chiral carbon stereocenters through Pd-catalyzed asymmetric [3 + 2] annulation of vinylethylene carbonates with alkenes installed on cyclic N-sulfonyl imines. A series of multisubstituted tetrahydrofuran derivatives are obtained in high efficiencies with excellent enantioselectivities and diastereoselectivities. Density functional theory (DFT) studies are accomplished to rationalize the stereocontrol of the annulation process and disclose that methanol could be applied to stabilize the reactive zwitterionic π-allylpalladium via the H-bond interaction.

Simultaneous determination of ZL-01, a novel nucleotide prodrug, and its metabolites in rat plasma by LC-MS/MS: Application to pharmacokinetic study

ZL-01 is a novel dual-prodrug which shows promise to be an antiviral candidate for hepatitis C virus. Here we have established a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of ZL-01 and its four metabolites (M1, M7, M8, and M9) in rat plasma with special consideration of ex vivo ZL-01, M1, and M7 stability. Several factors affecting the stability were investigated. EDTA and citric acid solution (1 M) were added to plasma to maintain the stability of analytes. The protein-precipitation method was selected with acetonitrile containing sofosbuvir as internal standard (IS). Adequate separation of ZL-01 and its metabolites was achieved on XSelect HSS T3 (3.5 µm, 4.6 × 150 mm) column by a gradient-elution with a mobile phase consisting of 0.1% formic acid and acetonitrile at a flow rate of 0.5 mL/min. The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode to monitor the precursor-to-product ion transitions of m/z 599.2→418.5 for ZL-01, m/z 529.7→398.2 for M1, m/z 330.5→182.0 for M7, m/z 260.3→112.1 for M8, m/z 261.3→113.2 for M9 and m/z 530.4→243.4 for IS. The calibration curves exhibited good linearity (r＞0.997) for all components. The lower limit of quantitation (LLOQ) was in the range of 1-2 ng/mL. The intra-day and inter-day precisions (RSD) at three different levels were both less than 10.2% and the accuracies (RE) ranged from -3.7-7.6%. The matrix effect and extraction recovery of them ranged from 84% to 110.3% and 88.3-106.3%. This LC-MS/MS method for the simultaneous quantitation of ZL-01 and its metabolites was developed successfully and applied in the pharmacokinetic studies of these in rats. Pharmacokinetic results indicated ZL-01 would be metabolized rapidly and M8 might be the main metabolites after oral absorption.

Aryl H-phosphonates. 19. New anti-HIV pronucleotide phosphoramidate diesters containing amino- and hydroxypyridine auxiliaries

We have designed a new type of AZT and ddU phosphoramidate diesters containing various combinations of 2-, 3-, 4-aminopyridine and 2-, 3-, 4-hydroxypyridine moieties attached to the phosphorus center, as potential anti-HIV pronucleotides. Depending on the pK_a values of the aminopyridines and the hydroxypyridines used, alternative synthetic strategies based on H-phosphonate chemistry were developed for their preparation. Synthetic aspects of these transformations and the biological activity of the synthesized compounds are discussed.

Discovery of pyrimidine nucleoside dual prodrugs and pyrazine nucleosides as novel anti-HCV agents

To explore the application potential of dual prodrug strategies in the development of anti-HCV agents, a variety of sofosbuvir derivatives with modifications at the C4 or N3 position of the uracil moiety were designed and synthesized. Some compounds exhibited potent anti-HCV activities, such as 4e and 8a-8c with similar EC₅₀ values (0.20-0.22 μM) comparative to that of sofosbuvir (EC₅₀ = 0.18 μM) in a genotype 1b based replicon Huh-7 cell line. Moreover, 8b displayed a good human plasma stability profile, and was easily metabolized in human liver microsomes expectantly. On the other hand, aiming to discover novel anti-HCV nucleosides, pyrazin-2(1H)-one nucleosides and their phosphoramidate prodrugs were investigated. Several active compounds were discovered, such as 25e (EC₅₀ = 7.3 μM) and S-29b (EC₅₀ = 19.5 μM). This kind of nucleosides were interesting and would open a new avenue for the development of antiviral agents.

Simultaneous determination of gemcitabine prodrug, gemcitabine and its major metabolite 2', 2'-difluorodeoxyuridine in rat plasma by UFLC-MS/MS

To improve bioavailability and provide resistance to deamination, an array of gemcitabine (dFdC) prodrugs carrying the acyl modifications has been successful in the optimization of pharmacokinetic properties of dFdC, but the reports about 4-N-carbobenzoxy-dFdC (Cbz-dFdC), a dFdC prodrug bearing alkyloxycarbonyl modification, are relatively rare. Notably, in vivo enzymatic hydrolysis was an absolutely essential factor for the activation of these prodrugs, which is correlated with the anti-tumor activity. Therefore, detailed metabolism studies of Cbz-dFdC should be carried out for a more authentic pharmacodynamic evaluation. In order to detect the pharmacokinetic characteristics of Cbz-dFdC, a selective, sensitive and accurate method for the simultaneous determination of Cbz-dFdC, along with dFdC and its major metabolite dFdU in rat plasma was developed and validated using UFLC-MS/MS techniques. Column was at 40 °C for separation using an eluent with acetonitrile and 0.1% formic acid, 1 mM ammonium formate at a flow rate of 0.2 mL/min. Detection was performed using ESI source in positive ion selected reaction monitoring mode by monitoring the following ion transitions m/z 398.1 → 202.2 (Cbz-dFdC), m/z 264.1 → 112.0 (dFdC), m/z 265.3 → 113.2 (dFdU) and m/z 246.1 → 112.0 (IS). Analytes were extracted by simple precipitation with acetonitrile containing internal standards followed by liquid-liquid extraction with ethyl acetate. The calibration curves of Cbz-dFdC, dFdC and dFdU were linear in the concentration range of 2 to 500 ng/mL, 2 to 500 ng/mL and 40 to 10,000 ng/mL, respectively. The assay ranges selected for the three analytes were appropriate and minimized the need for reanalysis. All the validation data, such as intra- and inter-day precision, accuracy, selectivity and stability, were within the required limits. In conclusion, the sensitive analytical assay was selective and accurate for the determination of rat plasma concentrations of Cbz-dFdC, dFdC and dFdU from a single LC-MS/MS analysis and well-suited to support pharmacokinetic studies.

Enantioselective Synthesis of Carbocyclic Nucleosides via Asymmetric [3 + 2] Annulation of α-Purine-Substituted Acrylates with MBH Carbonates

An efficient route to chiral carbocyclic nucleoside analogues containing a quaternary stereocenter and a C═C double bond has been established via a highly enantioselective [3 + 2] annulation of Morita-Baylis-Hillman (MBH) carbonates with α-purine-substituted acrylates. With 20 mol % (S)-SITCP as the catalyst, various chiral carbocyclic nucleoside analogues with a quaternary stereocenter and a C═C double bond were obtained in high yields (up to 92%) with good diastereoselectivities (up to 10:1 dr) and excellent enantioselectivities (up to 96% ee). Furthermore, the corresponding products were subjected to diverse transformations to afford interesting and potentially useful chiral carbocyclic nucleosides.

Synthesis and biological evaluation of a novel β-D-2'-deoxy-2'-α-fluoro-2'-β-C-(fluoromethyl)uridine phosphoramidate prodrug for the treatment of hepatitis C virus infection

A novel β-D-2'-deoxy-2'-α-fluoro-2'-β-C-(fluoromethyl)uridine phosphoramidate prodrug (1) has been synthesized. This compound exhibits submicromolar-level antiviral activity in vitro against HCV genotypes 1b, 1a, 2a, and S282T replicons (EC₅₀ = 0.18-1.13 μM) with low cytotoxicity (CC₅₀ > 1000 μM). Administered orally, prodrug 1 is well tolerated at doses of up to 4 g/kg in mice, and produces a high level of the corresponding triphosphate in rat liver.