Table 2. Binding affinities of compounds (9a–f) ^a .

Compound	MOR	KOR	DOR	M/K	M/D
	K i (nM)
9a	7.02 ± 0.77	>100	173.4 ± 43.6	>14.2	24.7
9b	6.91 ± 0.88	>100	103.7 ± 17.0	>14.5	15.0
9c	2.00 ± 0.17	77.9 ± 31	65 ± 19.0	39.0	32.5
9d	1.25 ± 0.23	18.97 ± 5.3	34.4 ± 5.00	15.2	27.5
9e	3.73 ± 0.14	>100	198.4 ± 69	>26.8	53.2
9f	3.29 ± 0.36	119 ± 50.4	130.3 ± 37	36.2	39.6
9g	40.59 ± 3.65	>100	423.9 ± 88	>2.5	10.4
1 b	0.37 ± 0.07	277.51 ± 7.97	60.72 ± 5.58	747	163
2 c	0.10 ± 0.02	2.90 ± 0.66	10.26 ± 6.76	29.0	102.6
Morphine	4.60 ± 1.81

^a[¹²⁵I]BNtxA (0.1 nM) competition binding assays were performed in membranes prepared from CHO cells expressing mouse MOR, DOR, or KOR, as previously described. Protein concentrations were between 10–20 μg mL^–1 and the incubation time was 90 minutes.19K_i was determined by nonlinear regression analysis (GraphPad Prism). Assays were performed at least 3 times and means ± SEM are reported.

^bValues are taken from ref. 12.

^cValues are taken from ref. 13.