Table 1. Compounds 2 and 7 HDAC Isoform Biochemical and Cellular Activity Data^a.

	Biochemical class IIa (catalytic domain) HDAC IC50 (μM)				Biochemical class I HDAC IC50 (μM)				Class IIb HDAC IC50 (μM)	Cellular HDAC activity Lys (substrate)d IC50 (μM)			MDCK-MDR1f
Cpd	4	5	7	9	1	2	3b	8	6c	TFA	Ac	MLM Clint (mL/min/kg)e	EER	Papp (nm/s)	Kinetic solubility (μM)
2	0.003	0.01	0.01	0.01	6.0	9.3	2.5	2.9	6.4	0.02	3.0	834	1.3	541	140
7	0.03	0.09	0.14	0.07	13	26	5.1	2.8	9.8	0.25	3.7	76	1.2	604	169

^aGeometric mean of three experiments as described previously;²⁵ standard deviations are <25% of the mean.

^bHDAC3-NCoR1.

^cDetermined utilizing HDAC6 overexpression in HEK cell lysate (Supporting Information). Assay–substrate combinations are described in SI Table 4, Supporting Information.

^dTFA: the Boc-Lys-(TFA)-AMC substrate is specific to class IIa HDACs and HDAC8, with the majority of class IIa HDAC activity in the Jurkat E6.1 cell line derived from HDAC4.¹⁹ Ac: the Boc-Lys-(Ac)-AMC substrate is specific to class I/IIb HDACs.

^eIntrinsic clearance (Cl_int) values of >257 mL/min/kg in mouse liver microsomes (MLM) indicate a rapid rate of oxidative metabolism by CYP450 enzymes under the assay conditions. A Cl_int value of <65 mL/min/kg indicates a low rate of metabolism.

^fEER is defined as the efflux ratio in MDCK-MDR1 cells/efflux ratio in MDCK wild-type cells with the efflux ratio being P_app(B to A)/P_app(A to B).