Abstract
In a recent publication, Eleftheriou et al. proposed that inhibitors of dipeptidyl peptidase-4 (DPP-4) are functional inhibitors of the main protease (M(pro) ) of SARS-CoV-2. Their predictions prompted the authors to suggest linagliptin, a DPP-4 inhibitor and approved anti-diabetes drug, as a repurposed drug candidate against the ongoing COVID-19 pandemic. We used an enzymatic assay measuring the inhibition of M(pro) catalytic activity in the presence of four different commercially available gliptins (linagliptin, sitagliptin, alogliptin and saxagliptin) and several structural analogues of linagliptin to study the binding of DPP-4 inhibitors to M(pro) and their functional activity. We show here that DPP-4 inhibitors like linagliptin, other gliptins and structural analogues are inactive against M(pro) .