Table 1. TSPO Ligands Based on 10a: Dependence of Binding Affinity, Lipophilicity, and Genotype Sensitivity on Side Chain Alkyl Substituents.

ligand	R1	R2	R3	rat Ki (nM)a	cLogD	LipE	LAB Ki (nM)b	HAB Ki (nM)c	(LAB Ki)/(HAB Ki)
1 (PK 11195)				0.5 ± 0.3	3.97	4.3 ± 0.2	4 ± 1	4 ± 1	1.0 ± 0.5
10a	Me	Et	Et	2.1 ± 0.6	4.33	4.4 ± 0.1
(R)-10a (PK 14067)	(R)-Me	Et	Et	0.90 ± 0.09	4.33	4.72 ± 0.04	743 ± 190	10 ± 2	76 ± 27
(S)-10a (PK 14068)	(S)-Me	Et	Et	73 ± 36	4.33	2.9 ± 0.1
10b	H	Et	Et	32 ± 11	4.84	2.7 ± 0.2
10c	Et	Et	Et	14 ± 6	5.26	2.6 ± 0.2
10d	CH2-R2	CH2-R1	Me	53 ± 22	3.69	3.6 ± 0.2
10e	Me	Me	Me	40 ± 8	4.58	2.8 ± 0.1

^aMean ± SD for n = 6, except for 1 (n = 60), and (R)-10a (n = 5).

^bMean ± SD for n = 6, except for 1 (n = 12).

^cMean ± SD for n = 6, except for 1 (n = 14).