Telaprevir-d 4 is the deuterium labeled Telaprevir. Telaprevir (VX-950) is a highly selective, reversible, and potent peptidomimetic inhibitor of the HCV NS3-4A protease, the steady-state inhibitory constant (Ki) of Telaprevir is 7 nM against a genotype 1 (H strain) NS3 protease domain plus a NS4A cofactor peptide. Telaprevir inhibits SARS-CoV-2 3CLpro activity.