Chandralata Bal

Herein, we report a new and cost‐effective methodology for synthesizing N‐substituted 2‐pyridone‐3‐carboxylic acids (2) from 2‐pyrone‐3‐carboxamides (1) with a good yield at room temperature. The notable feature of this reaction is the promotion of amidate ion formation mediated by NaH to initiate intramolecular ring transformation. In addition to ring transformation, simultaneous decarboxylation and substitution under the metal‐free condition in one pot have been achieved to yield N‐substituted 2‐pyridones (3) from 1.

Modified carbocyclic nucleosides (4a–g) constituting 7-deazapurine, 4′-methyl, exocyclic double bond and 2′,3′-hydroxy were synthesized. NOE and X-ray studies of 4c confirmed the α-configuration of 4′-methyl. The anti-HBV assay demonstrated 4e (IC₅₀ = 3.4 μM) without notable cytotoxicity (CC₅₀ = 87.5 μM) as a promising lead for future exploration.

The need of long-term treatment for chronic HBV, emergence of drug-resistant viruses and inefficiency of currently approved therapies to eliminate covalently closed circular DNA (cccDNA), mandates identification of potent and selective inhibitors of HBV replication with novel mechanisms of action. Entecavir, a carbocyclic guanosine nucleoside analog, is the most potent inhibitor of HBV replication on the market. Moreover, the naturally occurring carbocyclic nucleosides aristeromycin are known for their wide range of antiviral activities. In this research, we have utilized BINAP directed rhodium catalyzed reductive carbocyclization of 1,6-enynes (8a–b) through asymmetric hydrogenation which is an approach, not yet explored in carbocyclic sugar synthesis. Interestingly, we obtained exclusive anti-(9a) and Z-anti (9b) carbocyclic sugars. The new aristeromycin analogs (10a–b) with scaffold combination of entecavir and aristeromycin were then synthesized using the Mitsunobu reaction followed by deprotection.

The present study includes the exploration of new possible nucleoside mimetics based on 4-methoxy-7H-pyrrolo[2,3-d]pyrimidine carbocyclic nucleosides (4a–g), which were synthesized by 10–15 synthetic steps and characterized adequately. We report the anti-HCV activities and cytotoxicities of 4a–g. Compound 4a was analyzed by single crystal X-ray diffraction which showed some puckering in the cyclopentene ring with a 2′-endo conformation and anti-base disposition (χ = −125.7°).

Potential anti-HSV lead candidate 3d (EC ₅₀ = 9.8 μg ml ⁻¹ ) and its possible binding mode to utilize cavity-A and cavity-B of viral enzyme HSV polymerase.

High genetic variability in hepatitis C virus (HCV), emergence of drug resistant viruses and side effects demand the requirement for development of new scaffolds to show an alternate mechanism. Herein, we report discovery of new scaffold I based on 4-hydroxyamino α-pyranone carboxamide as promising anti-HCV agents. A comprehensive structure–activity relationship (SAR) was explored with several newly synthesized compounds. In all promising compounds (17–19, 21–22, 24–25, and 49) with EC₅₀ ranging 0.15 to 0.40 μM, the aryl group at C-6 position of α-pyranone were unsubstituted. In particular, 25 demonstrated potential anti-HCV activity with EC₅₀ of 0.18 μM in cell based HCV replicon system with lower cytotoxicity (CC₅₀ > 20 μM) and provided a new scaffold for anti-HCV drug development. Further investigations, including biochemical characterization, are yet to be performed to elucidate its possible mode of action.

Computer‐aided approaches coupled with medicinal chemistry were used to explore novel carbocyclic nucleosides as potential anti‐hepatitis C virus (HCV) agents. Conformational analyses were carried out on 6‐amino‐1H‐pyrazolo[3,4‐d]pyrimidine (6‐APP)‐based carbocyclic nucleoside analogues, which were considered as nucleoside mimetics to act as HCV RNA‐dependent RNA polymerase (RdRp) inhibitors. Structural insight gained from the modeling studies revealed the molecular basis behind these nucleoside mimetics. The rationally chosen 6‐APP analogues were prepared and evaluated for anti‐HCV activity. RdRp SiteMap analysis revealed the presence of a hydrophobic cavity near C7 of the nucleosides; introduction of bulkier substituents at this position enhanced their activity. Herein we report the identification of an iodinated compound with an EC₅₀ value of 6.6 μM as a preliminary anti‐HCV lead.