Kumar et al. 146  reported another series of peptide‐aldehyde inhibitors with reduced molecular weight. Selected examples (42, 43) are depicted in Figure 15. They were potent, cell‐membrane permeable, dual Mpro inhibitors of SARS‐CoV‐1 and MERS‐CoV, without cytotoxicity (CC50 > 100 µM). Compound 43, in particular, revealed highly potent activity against SARS‐CoV‐1 Mpro (IC50, 0.2 µM) and MERS‐CoV Mpro (IC50, 1.7 µM). It displayed antiviral activity (EC50, 0.06 µM) lowering the viral load and the secretion of virus particles in MERS‐CoV‐infected cells. Also, it displayed broad‐spectrum antiviral activity against other human α‐ and β‐CoVs.