Ghosh et al. 172  studied the SARs of halopyridinyl indole carboxylates and identified a series of analogs (96–101; Figure 27) as SARS‐CoV‐1 Mpro inhibitors in the nanomolar potency range. The best derivative (100) had high enzymatic inhibitory potency (IC50, 0.030 µM) and antiviral activity (EC50, 6.9 µM). Compound 97 was also observed to inhibit the MERS‐CoV Mpro both in enzymatic and cell‐based (EC50, 12.5 µM) bioassays. 173  This molecule covalently modified Mpro, which was confirmed by MALDI‐TOF studies.