Table 2.

Selective inhibition (IC₅₀) against various protease by isatin derivatives 4k and 4o^a

Entry	SARS CoV 3CLprob (cysteine protease)	Papainc (cysteine protease)	Chymotrypsind (serine protease)	Trypsine (serine protease)
4k	0.98 μM	103.00 μM	10.40 μM	362.40 μM
4o	0.95 μM	87.24 μM	1.00 mM	243.30 μM

^aThe IC₅₀ values were measured by FRET as in Table 1.

^bSubstrate (6 μM) and SARS CoV 3CL^pro (50 nM).

^cSubstrate (10 μM) and papain (13.3 nM).

^dSubstrate (200 μM) and chymotrypsin (5 nM).

^eSubstrate (200 μM) and trypsin (9 nM).