Two methods are presented for the synthesis of acrylamides labelled with C-11 (beta(+), t(1/2) = 20.4 min) and C-11 in the carbonyl position. In the first method, [1-C-11]acrylic acid is synthesised from [C-11]carbon monoxide by palladium-mediated hydroxy-carbonylation of acetylene. The labelled carboxylic acid is converted into the acyl chloride and subsequently treated with amine to yield N-benzyl[carbonyl(11)C]acrylamide, The second method utilizes [C-11]carbon monoxide in a palladium-mediated carbonylative cross-coupling of vinyl halides and amines. A higher radiochemical yield is achieved with the latter method and the amount of amine needed is decreased to 1/20. The C-11-labelled acrylamides were isolated in up to 81 % decay-corrected radiochemical yield. Starting from 10 +/- 0.5GBq of [C-11]carbon monoxide, N-benzyl[carbonyl-C-11]acrylamide was obtained in 4 min with a specific radioactivity of 330 +/- 4 GBq mu mol-(1). Co-labelling with C-11 and C-13 enabled confirmation of the labelled position by C-13 NMR spectroscopy.

As part of our ongoing investigation into the imaging of angiogenic processes, a small library of eight vascular endothelial growth factor receptor-2 (VEGFR-2)/platelet-derived growth factor receptor beta dual inhibitors based on the N-phenyl-N'-4-(4-quinolyloxy)-phenyl-urea was labelled with C-11 (beta(+), t(1/2) = 20.4 min) in the urea carbonyl position via rhodium-mediated carbonylative cross-coupling of an aryl azide and different anilines. The decay-corrected radiochemical yields of the isolated products were in the range of 38-81% calculated from [C-11]carbon monoxide. Starting with 10.7+/-0.5 GBq of [C-11]carbon monoxide, 1-[4-(6,7-dimethoxy-quinolin-4-yloxy)-3-fluoro-phenyl]-3-(4-fluoro-phenyl)-[C-11]-urea (2.1 GBq) was isolated after total reaction time of 45 min with a specific activity of 92+/-4 GBq mu mol(-1).

Essential hypertension occurs in approximately 25% of the adult population and one cause of hypertension is primary aldosteronism. Targeting the angiotensin II AT₁ receptor using PET and an appropriate tracer may offer a diagnostic method for adrenocortical tissue. This report describes the synthesis of the selective AT₁ receptor antagonist [carboxyl-¹¹C]eprosartan 10, 4-[2-butyl-5-((E)-2-carboxy-3-thiophen-2-yl-propenyl)-imidazol-1-ylmethyl]-[carboxyl-¹¹C]benzoic acid, and its precursor (E)-3-[2-butyl-3-(4-iodo-benzyl)-3H-imidazol-4-yl]-2-thiophen-2-ylmethyl-acrylic acid 9. ¹¹C-carboxylation of the iodobenzyl moiety was performed using a palladium-mediated reaction with [¹¹C]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-¹¹C]eprosartan 10 was obtained in 37–54% decay-corrected radiochemical yield (from [¹¹C]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 [¹¹C]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.

Three C-11-radiolabelled high-affinity nonpeptide AT(2) receptor-selective ligands were synthesized and one of these was evaluated as positron emission tomography (PET) tracer. The labelling reaction was performed via palladium(0)-mediated aminocarbonylation of the aryl iodide substrate using [C-11] carbon monoxide as the labelled precursor. As an example, starting with 10.0 GBq [C-11] carbon monoxide, 1.10 GBq of the product N-butoxycarbonyl-3-[4-(N-benzyl-[C-11] carbamoyl)phenyl]-5-isobutylthiophene-2-sulphonamide [C-11]4d was obtained in 36% decay-corrected radiochemical yield (from [C-11] carbon monoxide), 42 min from end of bombardment with a specific activity of 110 GBq.mu mol(-1). The N-isopropyl-[C-11] carbamoyl-analogue [C-11]4c (radiochemical purity >95%) was studied employing autoradiography, organ distribution, and small animal PET. In vitro autoradiography showed specific binding in the pancreas and kidney. Organ distribution in six rats revealed a high uptake in the liver, intestine, kidney, and adrenals. Small animal PET showed rapid and reversible uptake in the kidneys followed by accumulation in the urinary bladder suggesting fast renal excretion of the tracer. In addition, high accumulation was also seen in the liver. For future studies, more metabolically stable tracers will need to be developed. To the best of our knowledge, this is the first attempt of the use of PET imaging for the detection of expressed, fully functional AT(2) receptors in living subjects.