Identification of novel thiazole derivatives as flaviviral protease inhibitors against DENV and JEV

Flaviviruses are the causative agents of viral hemorrhagic fever (VHF) globally and have demonstrated the capacity to result in fatal outcomes if not managed effectively. Among different types of flaviviruses, dengue (DENV) and Japanese encephalitis (JEV) are the most common in tropical and subtropical countries. Given the scarcity of effective vaccines against flaviviral infections, small molecule agents that target crucial viral proteins emerge as the sole feasible option. This study outlines the synthesis of novel thiazole compounds as flavivirus NS2B-NS3 protease inhibitor and characterization of their antiviral activity against DENV and JEV. We synthesized a heterocyclic template derived from a substrate-based retrotripeptide dengue protease inhibitor, leading to forty-eight thiazole derivatives. Two compounds demonstrated significant inhibition of dengue virus protease activity in vitro. Comprehensive characterization of these two compounds was conducted through biochemical assay which revealed an uncompetitive mode of inhibition. Subsequent cell-based assays using Dengue and Japanese encephalitis viruses as representatives Flaviviruses imparted the potential of these compounds to block viral RNA synthesis, and viral replication. Finally time-course experiments unveiled that the two compounds impeded the accumulation of viral genomic RNA primarily at later stages of infection, aligning with their capacity to hinder NS2B-NS3 protease activity, polyprotein processing and viral genomic RNA replication. Together our work presents the development and validation of flavivirus protease inhibitors with therapeutic potential against Dengue and Japanese encephalitis virus.