Structure–Activity Relationship Studies toward the Discovery of Selective Apelin Receptor Agonists

International audienc

Structure–Activity Relationship Studies toward the Discovery of Selective Apelin Receptor Agonists

Apelin is the endogenous ligand for the previously orphaned G protein-coupled receptor APJ. Apelin and its receptor are widely distributed in the brain, heart, and vasculature, and are emerging as an important regulator of body fluid homeostasis and cardiovascular functions. To further progress in the pharmacology and the physiological role of the apelin receptor, the development of small, bioavailable agonists and antagonists of the apelin receptor, is crucial. In this context, E339–3D6 (<b>1</b>) was described as the first nonpeptidic apelin receptor agonist. We show here that <b>1</b> is actually a mixture of polymethylated species, and we describe an alternative and versatile solid-phase approach that allows access to highly pure <b>27</b>, the major component of <b>1</b>. This approach was also applied to prepare a series of derivatives in order to identify the crucial structural determinants required for the ligand to maintain its affinity for the apelin receptor as well as its capacity to promote apelin receptor signaling and internalization. The study of the structure–activity relationships led to the identification of ligands <b>19</b>, <b>21</b>, and <b>38</b>, which display an increased affinity compared to that of <b>27</b>. The latter and <b>19</b> behave as full agonists with regard to cAMP production and apelin receptor internalization, whereas <b>21</b> is a biased agonist toward cAMP production. Interestingly, the three ligands display a much higher stability in mouse plasma (<i>T</i>_1/2 > 10 h) than the endogenous apelin-17 peptide <b>2</b> (<i>T</i>_1/2 < 4 min)