3-[(Imidazolidin-2-yl)imino]indazole ligands with selectivity for the alpha(2)-adrenoceptor compared to the imidazoline I-1 receptor

A series of 3-[(4,5-dihydroimidazolidin-2-yl)imino]indazoles has been synthesized as positional analogues of marsanidine, a highly selective alpha(2)-adrenoceptor ligand. Parent compound 4a and its 4-chloro (4c) and 4-methyl (4d) derivatives display alpha(2)-adrenoceptor affinity at nanomolar concentrations (K-i = 39.4, 15.9 and 22.6 nM, respectively) and relatively high alpha(2)/I-1 selectivity ratios of 82, 115 and 690, respectively. Evidence was obtained that these compounds act as partial agonists at alpha(2A)-adrenoceptors. Compound 4d with intrinsic activity comparable with that of marsanidine, but lower than that of clonidine, elicited pronounced cardiovascular effects in anesthetized rats at doses as low as 0.01 mg/kg iv (C) 2010 Elsevier Ltd. All rights reserved.