Table 1.

Inhibition activities of isatin derivatives against SARS-CoV-2 3CL^pro.

Compds	R1	R2	IC50 or percentage (%) of inhibition at 50 μMb
Tideglusiba			1.91 ± 0.16
1		H	-c
2	-CH2OH	H	–
3		F	–
4		F	–
5		Cl	–
6		NO2	–
7	CH3	I	25% at 50 μM
8	CH3CH2CH2	I	51% at 50 μM
9	n-C4H9	I	41.8 ± 8.0
10	CH3	CO2CH3	53% at 50 μM
11	CH3CH2CH2	CO2CH3	53% at 50 μM
12	n-C4H9	CO2CH3	42% at 50 μM
13		CO2CH3	32% at 50 μM
14	PhCH2	CO2CH3	45% at 50 μM
15	CH3		45% at 50 μM
16	n-C4H9		47% at 50 μM
17	PhCH2		15.5 ± 1.2
18	CH3	CO2H	–
19	CH3CH2CH2	CO2H	–
20	n-C4H9	CO2H	–
21	PhCH2	CO2H	–
22	β-C10H7CH2	CO2H	32% at 50 μM
23		CONH2	0.053 ± 0.010
24	CH3CH2CH2	CONH2	10.2 ± 1.0
25	n-C4H9	CONH2	17.8 ± 0.7
26	β-C10H7CH2	CONH2	0.045 ± 0.007
27	β-(6-Br)-C10H7CH2	CONH2	0.047 ± 0.007
28	β-(6-Ph)-C10H7CH2	CONH2	24.9 ± 4.6
29	β-C10H7CH2	CH2CONH2	39.2 ± 10.5

^aTideglusib was used as positive control. The reported IC50 was 1.55 μM [8], which is in consistent with the value measured in the current study.

^bDose-response curves of compounds Tideglusib, 9, 17, 23, 24, 25, 27, 28 and 29 are shown in Fig. S1.

^cInhibition less than 25% at 50 μM.