[11C]Methyl‐losartan as a potential ligand for PET imaging angiotensin II AT1 receptors

The renin-angiotensin system regulates blood pressure via activation of the angiotensin II type 1 receptor (AT(1)R). The AT(1)R is involved in the pathology of cardiac and renal diseases such as heart failure and diabetic nephropathy. The aim of this study was to synthesize and characterize the O-[C-11] methylated derivative of the clinically used AT(1) receptor blocker losartan as a novel AT(1)R PET imaging radioligand. [C-11] Methyl-losartan was reliably synthesized (n >= 40) via methylation of tetrazole-protected losartan followed by deprotection using HCl in an overall yield of 30%-60% (decay-corrected from [C-11] Mel). Radiochemical purity was > 99% and specific activity 700-3600mCi/mu mol.