We report a detailed computational study of the inhibition of SARS-CoV-2 M pro with two proposed covalent (peptidyl) inhibitors: B3 and B4. Both inhibitors share the same recognition part, which is equivalent to the one proposed in our previous study, but differ in the activated carbonyl derivative warhead motifs. The results provide information on the warhead effect in proposed SARS-CoV-2 M pro covalent inhibitors.