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Triazole ligands reveal distinct molecular features that induce histamine H4 receptor affinity and subtly govern H4/H3 subtype selectivity.

Authors
  • Wijtmans, Maikel
  • de Graaf, Chris
  • de Kloe, Gerdien
  • Istyastono, Enade P
  • Smit, Judith
  • Lim, Herman
  • Boonnak, Ratchanok
  • Nijmeijer, Saskia
  • Smits, Rogier A
  • Jongejan, Aldo
  • Zuiderveld, Obbe
  • de Esch, Iwan J P
  • Leurs, Rob
Type
Published Article
Journal
Journal of Medicinal Chemistry
Publisher
American Chemical Society
Publication Date
Mar 24, 2011
Volume
54
Issue
6
Pages
1693–1703
Identifiers
DOI: 10.1021/jm1013488
PMID: 21348462
Source
Medline
License
Unknown

Abstract

The histamine H(3) (H(3)R) and H(4) (H(4)R) receptors attract considerable interest from the medicinal chemistry community. Given their relatively high homology yet widely differing therapeutic promises, ligand selectivity for the two receptors is crucial. We interrogated H(4)R/H(3)R selectivities using ligands with a [1,2,3]triazole core. Cu(I)-assisted "click chemistry" was used to assemble diverse [1,2,3]triazole compounds (6a-w and 7a-f), many containing a peripheral imidazole group. The imidazole ring posed some problems in the click chemistry putatively due to Cu(II) coordination, but Boc protection of the imidazole and removal of oxygen from the reaction mixture provided effective strategies. Pharmacological studies revealed two monosubstituted imidazoles (6h,p) with <10 nM H(4)R affinities and >10-fold H(4)R/H(3)R selectivity. Both compounds possess a cycloalkylmethyl group and appear to target a lipophilic pocket in H(4)R with high steric precision. The use of the [1,2,3]triazole scaffold is further demonstrated by the notion that simple changes in spacer length or peripheral groups can reverse the selectivity toward H(3)R. Computational evidence is provided to account for two key selectivity switches and to pinpoint a lipophilic pocket as an important handle for H(4)R over H(3)R selectivity.

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