Abolishing Dopamine D-2long/D-3 Receptor Affinity of Subtype-Selective Carbamoylguanidine-Type Histamine H-2 Receptor Agonists

摘要

3-(2-Amino-4-methylthiazol-5-yl)propyl-substituted carbamoylguanidines are potent, subtype-selective histamine H-2 receptor (H2R) agonists, but their applicability as pharmacological tools to elucidate the largely unknown H2R functions in the central nervous system (CNS) is compromised by their concomitant high affinity toward dopamine D-2-like receptors (especially to the D3R). To improve the selectivity, a series of novel carbamoylguanidine-type ligands containing various heterocycles, spacers, and side residues were rationally designed, synthesized, and tested in binding and/or functional assays at H1-4 and D-2(lon)g/3 receptors. This study revealed a couple of selective candidates (among others 31 and 47), and the most promising ones were screened at several off-target receptors, showing good selectivities. Docking studies suggest that the amino acid residues (3.28, 3.32, E2.49, E2.51, 5.42, and 7.35) are responsible for the different affinities at the H2- and D-2(lon)g/3-receptors. These results provide a solid base for the exploration of the H2R functions in the brain in further studies.