Abstract
Essential hypertension occurs in approximately 25% of the adult population and one cause of hypertension is primary aldosteronism. Targeting the angiotensin II AT~1~ receptor using PET and an appropriate tracer may offer a diagnostic method for adrenocortical tissue. This report describes the synthesis of the selective AT~1~ receptor antagonist [carboxyl‐^11^C]eprosartan 10, 4‐[2‐butyl‐5‐((E)‐2‐carboxy‐3‐thiophen‐2‐yl‐propenyl)‐imidazol‐1‐ylmethyl]‐[carboxyl‐^11^C]benzoic acid, and its precursor (E)‐3‐[2‐butyl‐3‐(4‐iodo‐benzyl)‐3__H__‐imidazol‐4‐yl]‐2‐thiophen‐2‐ylmethyl‐acrylic acid 9. ^11^C‐carboxylation of the iodobenzyl moiety was performed using a palladium‐mediated reaction with [^11^C]carbon monoxide in the presence of tetra‐n‐butyl‐ammonium hydroxide in a micro‐autoclave using a temperature gradient from 25 to 140°C over 5 min. After purification by semipreparative HPLC, [carboxyl‐^11^C]eprosartan 10 was obtained in 37–54% decay‐corrected radiochemical yield (from [^11^C]carbon monoxide) with a radiochemical purity >95% within 35 min of the end of bombardment (EOB). A 5‐µAh bombardment gave 2.04 GBq of 10 (50% rcy from [^11^C]carbon monoxide) with a specific activity of 160 GBq µmol^−1^ at 34 min after EOB. Frozen‐section autoradiography shows specific binding in kidney, lung and adrenal cortex. In vivo experiments in rats demonstrate a high accumulation in kidney, liver and intestinal wall. Copyright © 2009 John Wiley & Sons, Ltd.