Synthesis and antiviral activity of 7-deazaneplanocin A against orthopoxviruses (vaccinia and cowpox virus)

Chemical Approaches to Carbocyclic Nucleosides

Nucleoside analogues are at the forefront of antiviral therapy for last decades. To circumvent some of their limitations, based on their metabolism, and in order to improve their anti-viral potency and selectivity, several families of nucleoside analogues have been described through structural modifications at the sugar and heterocycles. The replacement of the oxygen of the nucleoside by a methylene has led to the family of carbocyclic (or cyclopentane) nucleoside analogues. Various potent anti-HIV and anti-HBV drugs belong to this family. Main syntheses of carbocyclic analogues of nucleosides used Diels-Alder reactions (in racemic or asymmetric series), but also started from carbohydrates (ribose, glucose), as a source of optically active compounds, which then had to be transformed into carbacycles under various conditions. The growing interest in carbocyclic nucleosides has led several groups, including ours, to develop new analogues and to explore novel routes. This article will review some of the recent chemistry developed on selected five-membered ring carbocyclic nucleosides.

Synthesis of 7-trifluoromethyl-7-deazapurine ribonucleoside analogs and their monophosphate prodrugs

Novel 7-trifluoromethyl-7-deazapurine ribonucleoside analogs (13a-c) and their Protides (15a-c) were successfully synthesized from ribolactol or 1-α-bromo-ribose derivatives using Silyl-Hilbert-Johnson or nucleobase-anion substitution reactions followed by key aromatic trifluoromethyl substitution. Newly prepared compounds were evaluated against a panel of RNA viruses, including HCV, Ebola or Zika viruses.

3,7-Dideazaneplanocin: Synthesis and antiviral analysis

Objective

To synthesize 3,7-dideazaneplanocin and evaluate its antiviral potential.

Methods

The target 3,7-dideazaneplanocin has been prepared in five steps from a readily available cyclopentenol. A thorough in vitro antiviral analysis was conducted versus both DNA and RNA viruses.

Results

A rational synthesis of 3,7-dideazaneplanocin was conceived and successfully pursued in such a way that it can be adapted to various analogs of 3,7-dideazaneplanocin. Using standard antiviral assays, no activity for 3,7-dideazaneplanocn was found.

Conclusion

Two structural features are necessary for adenine-based carbocyclic nucleosides (like neplanocin) for potential antiviral properties: (i) inhibition of S-adenosylhomocysteine hydrolase and/or (ii) C-5′ activation via the mono-nucleotide. These two requisite adenine structural features to fit these criteria are not present in in the target 3,7-dideazaneplanocin: (i) an N-7 is necessary for inhibition of the hydrolase and the N-3 is claimed to be essential for phosphorylation at C-5′. Thus, it is not surprising that 3,7-dideazaneplaoncin lacked antiviral properties.

Structure-Activity Relationships of Neplanocin A Analogues as S-Adenosylhomocysteine Hydrolase Inhibitors and Their Antiviral and Antitumor Activities

On the basis of the potent inhibitory activity of neplanocin A (1) against S-adenosylhomocysteine (AdoHcy) hydrolase, we analyzed the comprehensive structure-activity relationships by modifying the adenine and carbasugar moiety of 1 to find the pharmacophore in the active site of the enzyme. The introduction of 7-deazaadenine instead of adenine eliminated the inhibitory activity against the AdoHcy hydrolase, while 3-deazaadenine maintained the inhibitory activity of the enzyme, indicating that N-7 is essential for its role as a hydrogen bonding acceptor. The substitution of hydrogen at the 6'-position with fluorine increased the inhibitory activity of the enzyme. The one-carbon homologation at the 5'-position generally decreased the inhibitory activity of the enzyme, indicating that steric repulsion exists. A molecular docking study also supported these experimental data. In this study, 6'-fluoroneplanocin A (2) was the most potent inhibitor of AdoHcy hydrolase (IC50 = 0.24 μM). It showed a potent anti-VSV activity (EC50 = 0.43 μM) and potent anticancer activity in all the human tumor cell lines tested.

Synthesis, antimicrobial and antiviral activity of substituted benzimidazoles

In the present study we have synthesized (4-nitrophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanones, (2-bromophenyl)-[2-(substituted phenyl)-benzoimidazol-1-yl]-methanone analogues (1-14) and evaluated them for their antimicrobial and antiviral potential. The results of antimicrobial screening indicated that none of the synthesized compounds were effective against the tested bacterial strains. Compounds 3, 11, 13 and compounds 5, 11, 12 were found to be active against Aspergillus niger and Candida albicans respectively, and may be further developed as antifungal agents. Furthermore, evaluation against a panel of different viruses pointed out the selective activity of compounds 5 and 6 against vaccinia virus and Coxsackie virus B4.

Synthesis and anti-hepatitis B virus and anti-hepatitis C virus activities of 7-deazaneplanocin A analogues in vitro

A series of 7-deazaneplanocin A (7-DNPA, 2) analogues were synthesized and evaluated for in vitro antiviral activity against HBV and HCV. The syntheses of target carbocyclic nucleosides were accomplished via a convergent procedure. 7-Substitutions were introduced by using 7-substituted-7-deaza heterocyclic base precursors (F, Cl, Br, and I) or via substitution reactions after the synthesis of the carbocyclic nucleosides. Among the synthesized compounds, 2, 13-15, 24, and 27 exhibited significant anti-HCV activity (EC(50) ranged from 1.8 to 20.1 microM) and compounds 2, 15, 22, and 24 demonstrated moderate to potent anti-HBV activity (EC(50) = 0.3-3.3 microM). In addition, compound 24 also showed activity against lamivudine- and adefovir-associated HBV mutants.

Enantioselective synthesis and antiviral activity of purine and pyrimidine cyclopentenyl C-nucleosides

The enantiomerically pure carbocyclic purine and pyrimidine C-nucleosides 1–4 were synthesized via the key intermediate, 2,3-(isopropylidenedioxy)-4-(trityloxymethyl)-4-cyclopenten-1-ol (5), which was prepared from d-ribose in eight steps. Synthesized compounds were evaluated as potential antiviral agents against HIV, SARSCoV, Punta Toro, West Nile, and Cowpox viruses. However, only 9-deazaneplanocin A (1) exhibited moderate anti-HIV activity.