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. 2022 Mar 2;23(5):2766. doi: 10.3390/ijms23052766

Table 1.

Affinities of fentanyl-based MOR/I2-IBS ligands and reference compounds for the intended molecular targets.

Structure
(Refer to Figure 3B for Structural Explanations)		 Affinity
[Ki (nM)] 1
Compound X Y dNC 2 MOR 3 I2-IBS 4 Ref.
fentanyl (1.1) - - - 6 ± 1.5 5 5462 ± 1343 6 [26]
2.9 ± 1.5 8593 ± 738 [28]
idazoxan (2.1) - - - - 307 ± 183 6 [26]
28 ± 11 [27,28]
BU224 (2.5) - - - - 9.8 ± 0.3 [48]
2.6 mPh gu 5 7.8 ± 2.5 5 1890 ± 499 6 [26]
2.7 mPh amim 5 7119 ± 4089 5 9630 ± 6731 6 [26]
2.8 -(CH2)3- gu 5 37 ± 12 5 2022 ± 949 6 [26]
23 ± 4.5 1920 ± 996 [27]
2.9 -(CH2)3- amim 5 1751 ± 1135 5 2327 ± 811 6 [26]
2.10 -(CH2)2- gu 4 433 ± 83 437 ± 228 [27]
2.11 -(CH2)4- gu 6 0.59 ± 0.18 >10,000 [28]
2.12 -(CH2)6- gu 8 1.04 ± 0.28 409 ± 238 [27]
2.13 -(CH2)7- gu 9 0.37 ± 0.19 6627 ± 3106 [28]
2.14 -(CH2)8- gu 10 37 ± 9.7 126 ± 72 [27]
2.15 -(CH2)9- gu 11 26 ± 6 58 ± 46 [28]
2.16 -(CH2)12- gu 14 477 ± 75 6.5 ± 3.0 [27]
2.17 mXyl gu 7 0.0098 ± 0.0033 >10,000 [28]
0.448 ± 0.079 7 [49]
2.18 -(CH2)3- bu 12 6142 ± 2123 875 ± 713 [28]
2.19 -(CH2)6- bu 15 2168 ± 66 323 ± 270 [28]
2.20 -(CH2)8- bu 17 339 ± 35 >10,000 [28]
2.21 -(CH2)12- bu 21 545 ± 179 547 ± 316 [28]

1 Ki, inhibition constant (nM) with standard error of the mean, 2 dNC—topological distance (number of bonds) between the nitrogen attached at the position 4 of the piperidine ring and the central carbon atom in guanidine, 2-aminoimidazoline or imidazoline moieties, see Figure S1C, 3 unless specified otherwise, competitive assays done in membrane preparations of post-mortem human frontal cortex, 2 nM [3H]DAMGO as radioligand, 4 unless specified otherwise, competitive assays done in membrane preparations of post-mortem human frontal cortex, 1 nM [3H]2-BFI as radioligand, 5 competitive assays done in neural membrane preparations of mice brain, 2 nM [3H]DAMGO as radioligand, 6 competitive assays done in neural membrane preparations of mice brain, 1 nM [3H]2-BFI as radioligand, 7 competitive assays done in membrane preparations of rat brain, 0.72 nM [3H]DAMGO as radioligand.