Regioselective Synthesis of Pyrazolo[3,4-D]Pyrimidine Based Carbocyclic Nucleosides as Possible Antiviral Agent

Pyrazolo[3,4-d]pyrimidine-based neplanocin analogues identified as potential de novo pharmacophores for dual-target HBV inhibition

The discovery of selective and potent inhibitors through de novo pathways is essential to combat drug resistance in chronic hepatitis B (CHB) infections. Recent studies have highlighted that neplanocin A (NepA) derivatives are biologically selective inhibitors of the hepatitis B virus (HBV). In this study, we designed, synthesized, and evaluated various pyrazolo[3,4-d]pyrimidine-based NepA analogues (4a-h) for their anti-HBV activity. Notably, analogue 4g demonstrated significant activity against HBV replication, with EC50 (HBV DNA) = 0.96 μM, CC50 > 100 μM and EC50 (HBsAg) = 0.82 μM, showing selective inhibition of HBsAg secretion. The SAR analysis concluded that replacing the polar 4-NH2 group with -CH3 also acted as a weak H-bonding donor, and the presence of 3-iodo was found to be desirable for the activity/toxicity profile. The nucleoside analogues exhibited a distinct mechanism of action compared to existing nucleoside analogues for the selective inhibition of HBsAg secretion. Based on these findings, compound 4g represents a promising lead molecule for the development of new anti-HBV agents with unique mechanisms of action.

Synthesis and anti-HBV activity of carbocyclic nucleoside hybrids with salient features of entecavir and aristeromycin

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.