Synthesis and Functional Characterization of Imbutamine Analogs as Histamine H₃ and H₄ Receptor Ligands

Abstract

Imbutamine (4-(1H-imidazol-4-yl)butanamine) is a potent histamine H3 (H3R) and H4 receptor (H4R) agonist (EC50 values: 3 and 66 nM, respectively). Aiming at improved selectivity for the H4R, the imidazole ring in imbutamine was methyl-substituted or replaced by various differently substituted heterocycles (1,2,3-triazoles, 1,2,4-triazoles, pyridines, pyrimidines) as potential bioisosteres. Investigations in [(35)S]GTPγS binding assays using membranes of Sf9 insect cells expressing the respective human histamine receptor subtype revealed only very weak activity of most of the synthesized hetarylalkylamines at both receptors. By contrast, the introduction of substituents at the 4-imidazolyl ring was most effective regarding H4R selectivity. This holds for methyl substitution in position 2 and, especially, in position 5. 5-Methylimbutamine (H4R: EC50 = 59 nM, α = 0.8) was equipotent with imbutamine at the hH4R, but revealed about 16-fold selectivity for the hH4R compared to the hH3R (EC50 980 nM, α = 0.36), whereas imbutamine preferred the hH3R. The functional activities were in agreement with radioligand binding data. The results support the hypothesis that, by analogy with histamine, methyl substitution in histamine homologs offers a way to shift the selectivity in favor of the H4R.

Molecular determinants for the high constitutive activity of the human histamine H4 receptor: functional studies on orthologues and mutants

“…For the construction of the cDNA for hH 4 R‐F169V, hH 4 R‐S179A/M, hH 4 R‐F169V+S179A/M, mH 4 R‐V171F and mH 4 R‐V171F+M181S, SDS‐PAGE, Western blotting and cell culture, compare with Supporting Information. Cell culture, the generation of recombinant baculoviruses and membrane preparation (Gether et al ., ; Schneider et al ., ; Brunskole et al ., ) as well as H 4 receptor binding studies with [ 3 H]‐histamine and [ 35 S]‐GTPγS assays (Geyer and Buschauer, ; Geyer et al ., ) were essentially performed as previously described with minor modifications (cf. Supporting Information).…”

[3H]UR‐DE257: Development of a Tritium‐Labeled Squaramide‐Type Selective Histamine H2 Receptor Antagonist

“…2-3 drops Et 3 N were added and succinimidyl propionate (0.7-1.6 equiv), dissolved in CH 3 CN or MeOH, was added and the solution stirred at RT for 30 min to 18 h. The product was purified by preparative HPLC. gy with the previously reported protocols, [20,51,53,56] using Micro Beta2 1450 scintillation counter (PerkinElmer, Rodgau, Germany) in the 96-well plate format.…”

Synthesis, Biological Evaluation, and Computational Studies of Tri- and Tetracyclic Nitrogen-Bridgehead Compounds as Potent Dual-Acting AChE Inhibitors andhH3Receptor Antagonists

“…33,56−59 The accordant membranes were thawed and sedimented by a 10 min centrifugation at 4°C and 13 000g. Membranes were resuspended in binding buffer ( 60 (American Radiolabeled Chemicals, St. Louis, MO), increasing concentrations of unlabeled ligands in hH 3 R binding assay and for hH 1 R, hH 2 R, and hH 4 R experiments, a single concentration (10 μM) of unlabeled ligand was used. The assays were conducted in 96-well plates (Greiner Bio-One GmbH, Frickenhausen, Germany) and incubated for 60 min at 25°C under shaking at 250 rpm using a Heidolph Titramax 101 instrument (Heidolph Instruments GmbH & Co. KG, Schwabach, Germany).…”