Betulonic Acid Derivatives Interfering with Human Coronavirus 229E Replication via the nsp15 Endoribonuclease

To develop antiviral therapeutics against human coronavirus (HCoV) infections, suitable drug targets and corresponding lead molecules must be urgently identified. Here, we describe the discovery of a class HCoV inhibitors acting on nsp15, hexameric protein component viral replication-transcription complexes, endowed with immune evasion-associated endoribonuclease activity. Structure–activity relationship exploration these 1,2,3-triazolo-fused betulonic acid derivatives yielded molecule 5h as strong inhibitor (antiviral EC50: 0.6 ?M) HCoV-229E replication. An nsp15 active site mutant virus was markedly less sensitive to 5h, selected resistance compound mapped mutations in N-terminal part at an interface between two monomers. The biological findings were substantiated by binding mode for predicted docking. Hence, besides delivering distinct inhibitors, our study revealed druggable pocket hexamer relevance anti-coronavirus development.