Radiosynthesis of (Tetrazoyl-11C)irbesartan, a Non-Peptidic Angiotensin II Antagonist.

Summary With the aim of visualizing myocardial angiotensin II receptors (AT1 subtypes), [tetrazoyl-11C]2-n-butyl-1-[(2′-(1Htetrazol-5-yl)-1, 1′-biphenyl-4-yl)methyl]-4-spirocyclo-pentane-2-imidazoline-5-one ([tetrazoyl-11C]irbesartan (SR47436/BMS-186295)) 11 was synthesized in one pot in four steps from [11C]hydrogen cyanide. The labelling process which yielded [tetrazoyl-11 C]irbesartan is described in detail and could be applied to the labelling of other ligands which possess the (1H-tetrazol-5-yl) moiety. Positron emission tomography (PET) studies were performed in dogs. Heart, lung and blood time-activity curves did not change. Therefore this new radioligand is not suitable for studying myocardial angiotensin II receptors with PET.