Syntheses of nucleosides with 2′-spirolactam and 2′-spiropyrrolidine moieties as potential inhibitors of hepatitis C virus NS5B polymerase

Synthesis of novel rhodamine type Anthrone Spiro-lactam (ASL) analogues and evaluation of antiviral activity against dengue and chikungunya viruses

A series of Rhodamine type Anthrone-Spirolactam (ASL) derivatives Benzylimin-Anthrone-Spirolactam (ASL-1 to ASL-10) and Benzamide-Anthrone-Spirolactam (ASL-11 and ASL-12) were synthesized via a simple condensation reaction between Anthrone Spiro-lactamine (2) and various aromatic aldehyde and acyl chlorides respectively. Since rhodamine-based compounds were reported to have antiviral activity, the ASL derivatives were examined for in vitro antiviral activity against dengue and chikungunya viruses. Among all the analogues, ASL-3, ASL-6, ASL-7, ASL-8, ASL-9 and ASL-10 were the most potent against dengue virus (DENV) and exerted around one log reduction in virus titre under post-treatment conditions. At the same time ASL-3 was effective under co-treatment conditions. Two analogues ASL-6 and ASL-12 exerted anti-chikungunya virus (CHIKV) activity under post-treatment conditions. In silico docking studies revealed that the ASL derivatives interacted with the proteins of DENV and CHIKV. Together, the results suggest the anti-DENV and CHIKV activity of ASL derivatives which may be exploited further for therapeutic purposes.

Asymmetric Synthesis of 2'-C-Methyl-4'-selenonucleosides as Anti-Hepatitis C Virus Agents

In search of a new template for anti-hepatitis C virus (HCV) agents, we designed and synthesized the 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides and their phosphoramidate prodrugs to replace a furanose oxygen of anti-HCV nucleos(t)ides with a selenium atom on the basis that selenium is a chemical isostere of oxygen. These nucleosides are expected to show different physicochemical properties such as better lipophilicity which might enhance the penetration across cell membranes and the conformational constraint induced by a bulky selenium atom in the sugar ring. The 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides 8 and 9 were synthesized from 2-C-methyl-d-ribono-γ-lactone (14) via construction of 2-C-methyl-d-selenosugar 18 through C-4 epimerization and S_N2 cyclization with Se^2- as key steps. The key 4'-selenosugar was converted to the 2'-C-methyl-4'-selenopyrimidine and -purine nucleosides using Pummerer-type rearrangement and Vorbrüggen glycosylation, respectively. In addition, the ProTide strategy has been applied to synthesize the adenine and uracil phosphoramidate derivatives 10a and 10b to overcome the limitations associated with parent nucleosides such as inefficient conversion to their corresponding 5'-monophosphate form and poor cellular uptake. The regio- and stereochemistry of 4'-selenonucleosides were confirmed by 2D NOESY NMR spectroscopy and X-ray crystallography. None of the final pyrimidine and purine nucleosides and their prodrugs exhibited significant anti-HCV activity up to 100 μM.

Construction of quaternary stereocentres on carbohydrate scaffolds

This review describes a glimpse of the various strategies for constructing stereo-defined quaternary centres in densely functionalised carbohydrates moiety of structurally intriguing and biologically potent natural products and building blocks.