Table 1. Mean inhibition percentages of the 19 coumarin-based derivatives (1a–p and 2a–c) against SARS-CoV-2 M^pro at 100 µM using the FRET assay.

Compound	R	Mean inhibition%
1a	4-Cl-3-CF3	3.0
1b	3,5-(CF3)2	7.4
1c	3-Cl-4-F	36.7
1d	3-CF3	31.9
1e	4-CF3	65.9
1f	3,5-Di-Cl	56.7
1g	2,4-Di-Cl	12.0
1h	4-F	32.8
1i	4-Br	7.7
1j	4-n-Butyl	15.6
1k	3,5-Di-CH3	33.5
1l	4-Butoxy	31.6
1m	4-Cl-2-CH3	0.1
1n	2-Cl-6-CH3	4.8
1o	2,4-Di-F	14.5
1p	2,6-Di-Br-4-F	18.2
2a	4-Cl-3-CF3	22.2
2b	3,5-(CF3)2	0.9
2c	2,4-Di-F	0.7
GC376	—	100.0
Boceprevir	—	88.0
Baicalein	—	100.1