Table 1: Opioid receptor affinities of opioid ligands 1–50.

Nos.CompoundsKiμ (nM)Kiδ (nM)Kiδ/KiμReference

1H-Tyr-Pro-Trp-Phe-NH2(EM-1)0.361,5104,190[4]
2H-Tyr-Pro-Phe-Phe-NH2(EM-2)0.699,23013,380[4]
3D-D-D-D(EM-2)1,04116,57998[5]
4L-L-D-D(EM-2)24.31,24951[5]
5D-D-L-L(EM-2)2,75519,4597[5]
6D-L-L-L(EM-2)32.14,121128[5]
7L-D-D-D(EM-2)2,01313,2786.6[5]
8L-L-L-D(EM-2)45.98,159177[5]
9D-D-D-L(EM-2)107.97,20367[5]
10L-L-D-L(EM-2)203.24,23021[5]
11D-D-L-D(EM-2)7,05118,6242.6[5]
12L-D-L-L(EM-2)512.430,64160[5]
13D-L-D-D(EM-2)363.521,26458[5]
14D-L-L-D(EM-2)557.34,1877.5[5]
15L-D-D-L(EM-2)4,70716,6623.5[5]
16D-L-D-L(EM-2)651.614,58422[5]
17L-D-L-D(EM-2)1,31126,21120[5]
18H-Tyr-Pro-Phe-NH246.115,900344[9]
19H-Dmt-Pro-Trp-Phe-NH20.0545.6104[10]
20H-Dmt-Pro-Phe-Phe-NH20.1528.2188[9]
21H-Dmt-Pro-Phe-NH20.1253.2443[9]
22H-Dmt-Pro-Phe-NH-C2H4-Ph0.511835[9]
23H-Dmt-Pro-Phe-NH-Bzl0.5213.827[11]
24H-Dmt-Pro-Phe-NH-Ph1.1120.619[11]
25H-Dmt-Pro-Phe-NH-4-Pyr0.3652.6146[11]
26H-Dmt-Pro-Phe-NH-3-Pyr0.172871,690[11]
27H-Dmt-Pro-Phe-NH-2-Pyr0.131571,210[11]
28H-Dmt-Pro-Phe-NH-1-Nph0.2919.968[11]
29H-Dmt-Pro-Phe-NH-3-Qln0.33190575[11]
30H-Dmt-Pro-Phe-NH-5-Qln0.1130272[11]
31H-Dmt-Pro-Phe-NH-6-Qln0.2246.6212[11]
32H-Dmt-Pro-Phe-NH-8-Qln0.4933.168[11]
33H-Dmt-Pro-Phe-NH-5-Isq0.1998.3517[11]
34H-Mmt-Pro-Phe-Phe-NH20.132528.64,005[12]
35H-Emt-Pro-Phe-Phe-NH20.06355.7884[12]
36H-Imt-Pro-Phe-Phe-NH20.151901,226[12]
37H-Det-Pro-Phe-Phe-NH20.08469.7830[12]
38H-Dit-Pro-Phe-Phe-NH22.2910546[12]
39H-Tmt-Pro-Phe-Phe-NH20.111593.55,347[12]
40H-Dmt-Pro-Mmp-Phe-NH20.184.6126[13]
41H-Dmt-Pro-3,5Dmp-Phe-NH20.1111.6105[13]
42H-Dmt-Pro-Dmp-Phe-NH20.0692.2733[13]
43H-Dmt-Pro-Dmt-Phe-NH20.09280.8878[13]
44H-Dmt-Pro-Tmp-Phe-NH20.181.8310[13]
45H-Dmt-Pro-Emp-Phe-NH20.213.0314[13]
46H-Dmt-Pro-Imp-Phe-NH20.324.6114[13]
47[N-allyl-Dmt1]EM-10.2610.340[10]
48[N-allyl-Dmt1]EM-20.455601,244[10]
491,6-bis[N-allyl-Dmt-NH]hexane12.451.54[10]
503,6-bis[N-allyl-Dmt-NH-propyl]-5-methyl-2(1H)-pyrazinone6.9477.811[10]

Opioid receptor affinities are determined using rat brain P2  synaptosomal preparations with [3H]DAMGO for μ-opioid receptors and [3H]DPDPE for  δ-opioid receptors.