Table 1. Defining the essential HDAC binding elements of ortho-aminoanilides.

		HDAC isoform inhibition IC50 a (μM)			Ligand efficiency b (ligE)
Compound	Structure	HDAC1	HDAC2	HDAC3	HDAC1/HDAC2
Cl-994		0.041 ± 0.012	0.147 ± 0.066	0.046 ± 0.018	0.37/0.34
1		0.001 ± 0.001	0.013 ± 0.009	0.398 ± 0.105	0.36/0.32
		Residence time T 1/2 (min)
		>2400	∼4800	∼1200
2		0.023 ± 0.008	0.129 ± 0.006	1.68 ± 0.26	0.36/0.33
3		0.355 ± 0.012	8.71 ± 3.16	0.665 ± 0.063	0.40/0.32
4		>33.33	>33.33	>33.33

^aValues are the mean of a minimum of two experiments. Data are shown as IC₅₀ values in μM ± standard deviation. Compounds were tested in duplicate in a 12-point dose curve with 3-fold serial dilution starting from 33.33 μM.

^bLigand efficiency (ligE) = (–log IC₅₀)/number of non-hydrogen atoms.