Synthesis and preliminary evaluation of ( R,S)-1-[2-((Carbamoyl-4-hydroxy)phenoxy)-ethylamino]-3-[4-(1-[ 11C]-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol ([ 11C]CGP 20712A) as a selective β1-adrenoceptor ligand for PET

Abstract

The most selective β 1-adrenoceptor ligand known at this moment is ( S)-1-[2-((carbamoyl-4-hydroxy) phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol (CGP 26505), the S-isomer of CGP 20712A. We prepared the racemic 11C analogue by methylation with [ 11C]CH 3I of the corresponding desmethyl compound using a microwave oven to accelerate the reaction. Several radioactive by-products (about 70% of the non-volatile radioactive products) were formed. After HPLC purification [ 11C]CGP 20712A with a specific activity of 35 TBq/mmol was dissolved in a propylene glycol-ethanol-saline mixture to prepare it for injection. The total preparation time was 35 min. The radiochemical yield was 5% (calculated from [ 11C]CH 3I, not corrected for decay). The identity of [ 11C]CGP 20712A was proved by liquid chromatography-mass spectrometry (LC-MS). Tissue distribution studies in male Wistar rats have been performed. At 20 min after injection of the radioligand (0.1 nmol) the DAR [differential absorption ratio = (counts per minute recovered/g tissue)/(counts per min injected/g body weight)] in heart tissue decreased significantly ( P < 0.005) from 1.84 ± 0.11 to 1.21 ± 0.12 after blocking of β-adrenoceptors with 500/μg ( R,S)-propranolol. A preliminary PET study in a Wistar rat showed maximal uptake in the time frame 10–20 min after injection. The ratio of specific/non-specific binding at this interval was 2.6.