Effect of substituents α to the γ-lactam carbonyl on M^pro inhibition.

	γ-Lactam	aIC50 [μM]		γ-Lactam	aIC50 [μM]
i		3.9 ± 0.1	vi		2.7 ± 0.1
ii		>100	vii		3.5 ± 0.2
iii		3.2 ± 0.8	viii		>100
iv		16 ± 2	ix		61 ± 4
v		4.0 ± 0.4	x		>100

^aAssays were performed as reported using SPE-MS, employing SARS-CoV-2 M^pro (0.05 μM) and substrate peptide (2.0 μM).⁴² Results are means of two independent runs each composed of technical duplicates (n = 2; mean ± SD). Representative dose–response curves of selected γ-lactams are shown in Fig. 2.