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High specific radioactivity is required for receptor studies with PET. Hereby we wish to report our experience using Nuclear Interface PET Tracer Synthesizer for preparation of Carbon-11 radioligands and module's modifications, which allowed to achieve high specific radioactivity

The radiolabelling with the positron-emitter Carbon-11 and the biological evaluation in rats of 3-[2-[4-(2-[C-11]methoxyphenyl)piperazin-1 -yl]ethyl] pyrimido [5,4-b] indole-2,4-dione ([C-11]RN5), alpha(1)-adrenoceptor antagonist (K-i = 0.21 nM), as a putative radioligand for the noninvasive assessment of alpha(1)-adrenoceptors with positron emission tomography (PET) is reported. The radiosynthesis procedure consisted of O-methylation of des-methyl precursor with [C-11]methyl iodide in the presence of potassium hydroxide in dimethylformamide (DMF) at 80 degreesC. [C-11]RN5 was obtained in >99% radiochemical purity in 25 min with a radiochemical yield in the 20-30% range, end of synthesis (EOS) (non-decay corrected) and a specific radioactivity of 92.5 18.5 GBq/mumol. Pre-clinical studies in rats showed a high uptake of [C-11]RN5 in heart, spleen, adrenal gland. lung and kidney but not in the brain. Inhibition studies with high doses of different adrenergic antagonists indicate that more than 70% of myocardial uptake of [C-11]RN5 is due to specific binding to alpha(1)-adrenoceptors. Our results indicate that [C-11]RN5 is suitable to be further developed as a potential radioligand for the in vivo PET imaging of myocardial alpha(1)-adrenoceptors in humans. (C) 2002 Published by Elsevier Science B.V

(+/-)-1-[4-(2-Isopropoxyethoxymethyl)-phenoxy]-3-isopropylamino-2-propanol (bisoprolol) is a potent, clinically used beta(1)-adrenergic agent. (R)-(+) and (S)-(-) enantiomers of bisoprolol were labelled with carbon-11 (t(1/2)=20.4 min) as putative tracers for the non-invasive assessment of the beta(1)-adrenoceptor subtype in the human heart and brain with positron emission tomography (PET). The radiosynthesis consisted of reductive alkylation of des-iso-propyl precursor with [2-11C]acetone in the presence of sodium cyanoborohydride and acetic acid. The stereo-conservative synthesis of (R)-(+) and (S)-(-)-1-[4-(2-isopropoxyethoxymethyl)-phenoxy]-3-amino-2-propanol to be used as the precursors for the radiosynthesis of [11C]bisoprolol enantiomers was readily accomplished by the use of the corresponding chiral epoxide in three steps starting from the commercially available hydroxybenzyl alcohol. The final labelled product (either (+) or (-)-1-[4-(-isopropoxyethoxymethyl)-phenoxy]-3- [11C]isopropylamino-2-propanol) was obtained in 99% radiochemical purity in 30 min with 15+/-5% (EOS, non-decay corrected) radiochemical yield and 3.5+/-1 Ci/micromol specific radioactivity. Preliminary biological evaluation of the tracer in rats showed that about 30% of heart uptake of [11C](S)-bisoprolol is due to specific binding. The high non-specific uptake in lung might mask the heart uptake, thus precluding the use of [11C](S)-bisoprolol for heart and lung studies by PET. The remarkably high uptake of the tracer in rat brain areas rich of beta-adrenergic receptors such as pituitary (1.8+/-0.3% I.D. at 30 min) was blocked by pre-treatment with the beta-adrenergic antagonists propranolol (45%) and bisoprolol (51%, p<0.05). [11C](S)-bisoprolol deserves further evaluation in other animal models as a putative beta(1) selective radioligand for in vivo investigation of central adrenoceptors.

Erytro-(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[ iso-propylamino]-2-butanol (ICI 118551) a potent clinically used beta2 adrenergic antagonist, was labelled with carbon-11 (t1/2 = 20.4 min) as a potential radioligand for the non-invasive assessment of beta2 adrenergic receptors in the lung with positron emission tomography (PET). The radiolabelled compound was prepared by reductive N-alkylation of its des-isopropyl precursor with [2-11C]acetone. (+/-)-[11C]ICI 118551 was obtained in greater than 98% radiochemical purity in 30 min with a radiochemical yield of 15 + 5% (non-decay corrected) and a specific radioactivity 2.5 +/- 0.5 Ci/micromol. The biological evaluation of racemic erythro (+/-)-[11C]ICI 118551 in rats and Macaca Nemestrina shows a high radioactivity uptake in lung and heart. However, in both animal models no detectable displacement of lung radioactivity concentration was observed after pre-treatment with propranolol or ICI 118551, which indicates that in this organ, radioligand uptake is mostly due to non-specific binding. The biological data suggest that erythro (+/-)-[11C]ICI 118551 is not adequate to be further developed as a tracer for beta2 adrenergic receptor imaging in vivo

This paper describes the radiosynthesis of [C-11]CGP62349, a potential ligand to assess GABA, receptors in vivo. C-11 was introduced by O-methylation of the corresponding des-methyl precursor, namely CGP67780. The final product was obtained with a reliable method in good yield. The radioligand was tested in monkey, revealing negligible blood brain barrier penetration and brain uptake, thus prompting us to search for a new target structure with a better lipophilicity. NUCL MED BIOL 27;6:565-569, 2000. (C) 2000 Elsevier Science Inc. All rights reserved.

Carbon-11 labeled acetone is a useful radiosynthetic precursor. Previously, strict control of no-carrier-added stoichiometry was required to prepare it from reaction of CO2 and methyl lithium. However, excess methyl lithium may be selectively quenched to avoid reaction with nascent acetone to give tert-butanol. We report a simple pKa-based strategy to sequentially and selectively quench MeLi and acetone to give yields of up to 100% acetone even in the presence of a large excess of MeLi. The method gives good yields of acetone under conditions that previously precluded its synthesis