Fig. 2. M^pro inhibitory activity and serum stability of GM4 and its mutants.

a, Dose response analysis of peptides against M^pro. The M^pro inhibitory activities of peptides were investigated by solid-phase extraction purification coupled to MS analysis using a RapidFire 365 high-throughput sampling robot (Agilent) connected to an iFunnel Agilent 6550 accurate mass quadrupole TOF mass spectrometer³⁹. IC₅₀ values were determined by the mean of three or five independent replicates each performed in technical duplicate. Data are presented as mean values ± standard deviation, s.d. (n = 5 for GM4, GM4γ¹4A and GM4H3Q; n = 3 for GM4γ¹4N, GM4H3A and GM4H3E). Extended Data Fig. 2 shows other peptides. b, Serum stability assay of macrocyclic peptides. GM4, GM4γ¹4A and GM4H3Q were co-incubated with an internal standard peptide in human serum (37 °C). At each time point, the relative intensity of each peptide to the standard peptide was estimated by LC/MS. The relative intensity at 0 h was defined as 100%. Half-lives (t_1/2) were determined by analysing the mean of three technical replicates of each sample by nonlinear regression using GraphPad Prism 9. Data are presented as mean values ± s.d. (n = 3). Extended Data Fig. 3 shows results for other peptides.