Migration of the methylene imidazole side chain in the first reported selective drug-like AT 2 receptor agonist C21/M024 (1) delivered the AT 2 receptor antagonist C38/M132 (2). We now report that the AT 2 receptor antagonist compound 4, a biphenyl derivative that is structurally related to 2, is transformed to the agonist 6 by migration of the isobutyl group. The importance of the relative position of the methylene imidazole and the isobutyl substituent is highlighted herein.
KEYWORDS:AT 2 receptor, nonpeptide ligands, agonist, antagonist, C21/M024, C38/M132 T he sartans (angiotensin II receptor blockers, ABRs) have been on the market as antihypertensives for more than two decades and act as selective antagonists at the angiotensin II AT 1 receptor. More recently, the angiotensin AT 2 receptor has emerged as a new target for drug intervention.1−3 In 2004, the first selective and drug-like AT 2 receptor agonist C21/ M024 (1) was disclosed, 4 and thereafter, a series of structural analogues with agonistic properties have been reported. 5,6 The activation of the AT 2 receptor is known to render a large number of diverse biological responses. 7,8 For example, receptor activation stimulates neurite outgrowth in neuronal cells, which is one of the first steps in neuronal differentiation.
9In healthy adults the AT 2 receptor expression is low and mainly found in renal, cardiovascular, and brain tissues. 7,8 Notably, during certain pathological conditions, such as myocardial infarction, vascular injury, brain ischemia, renal failure, and cutaneous wounds, the AT 2 receptor expression is significantly up-regulated. 7,8 Recently, several studies conducted in experimental disease models have revealed that the selective potent AT 2 receptor agonist 1 acts as an anti-inflammatory agent and exerts pronounced tissue protective effects in particular in cardiovascular and renal disease. Hence, the compound has had a large impact on the view of the AT 2 receptor as a drug target.1,9−14 In addition, the AT 2 receptor is a promising drug target for antagonists. Thus, the AT 2 receptor antagonist EMA401 has demonstrated convincing efficacy data in patients suffering from neuropathic pain (postherpetic neuralgia) in a phase II study. 3 We discovered that migration of the methylene imidazole substituent of 1 from the para to the meta substitution pattern delivered a selective AT 2 receptor antagonist, compound C38/M132 (2) (Figure 1). 15,16 Thus, a minor structural alteration resulted in the interconversion of a selective AT 2 receptor agonist to a selective AT 2 receptor antagonist.Herein, we report the synthesis and biological evaluation of four AT 2 receptor ligands, the biphenyl derivatives, and regioisomers, 3, 4, 5, and 6 (Figure 2), and that the relative position of the imidazole and isobutyl substituent determines the functional outcome.The