Synthesis of by using multivariate strategies for optimization of radiochemical yields

11C-labelling of the analgesic tramadol and its major metabolites by selective O- and N-methylation

For in vivo pharmacokinetic studies with PET, the analgesic Tramadol(1-(3-methoxyphenyl)-2-dimethylaminomethyl-cyclohexan-1-ol ) and its major O- and N-desmethylated metabolites M1 and M2 were labelled with carbon-11. Starting with the corresponding desmethyl precursors, (1R,2R)-(+), (1S,2S)-(-)-[O-methyl-11C]Tramadol and racemic-[N-methyl-11C]Tramadol were prepared by methylation with n.c.a. [11C]methyl iodide in DMSO with radiochemical yields of 85 and 90%, respectively. Specific n.c.a. N-methylation of bis-desmethyl-Tramadol (M5) was achieved without base obtaining 11C-labelled (1R,2R)-(+)- and (1S,2S)-(-)-M1 with 90% radiochemical yield. However, a selective O-methylation of (+)- and (-)-M5 was not possible even with an excess of NaOH, and only 70% of (1R,2R)-(+)- and (1S,2S)-(-)-[O-methyl-11C]M2 was obtained. Quaternization of Tramadol or M1 was greater than 15 times slower than O-methylation, and was only observed in the presence of added CH3I carrier.

Brain and plasma kinetics of the opioid 11C-hydromorphone in two macaque species

The regional brain kinetics of the opioid receptor agonist, hydromorphone, labelled with 11C, were studied with positron emission tomography in two Macaque species. Rhesus and Cynomolgus monkeys. The plasma kinetics of 11C-hydromorphone was simultaneously determined. Rapid plasma elimination was obvious in both monkey species. Brain radioactivity was generally low in both, but 1.4 times higher in the Rhesus than in the Cynomolgus monkey brain. This observation might explain the more rapid development of tolerance in the Rhesus monkey.

Preparation of [11C]- and [125I]IMB: a dopamine D-2 receptor antagonist

A new dopamine D-2 receptor ligand, N-[2-(N'-4-iodobenzyl-N'-methyl)aminoethyl]-5-chloro-2-methoxy-4- (methylamino)benzamide (IMB) was synthesized and labelled with 11C and 125I at high specific activities. Both radiotracers were prepared by alkylation reactions with [11C]iodomethane and [125I]4-iodobenzyl bromide and appropriate 2 degrees amine precursors. Isolated radiochemical yields of 12-20% for [11C]IMB and 35-50% for [125I]IMB were achieved in 24 and 130-150 min respectively. [11C]IMB and [123I]IMB may prove suitable for a direct comparison of PET and SPECT in the localization and quantification of neuroreceptors.

The radiosynthesis of [N-methyl-11C]-sertraline

[N-methyl-11C]Sertraline, a potential agent for the study of the serotonergic system in vivo with positron emission tomography, was prepared by N-methylation of the corresponding norcompound with [11C]iodomethane, which was itself prepared from cyclotron-produced [11C]carbon dioxide. Under the best conditions found [norsertraline free base (20 mM) in DMF (0.70 mL), 120 degrees C for 8 min] [N-methyl-11C]-sertraline can be prepared in 43% radiochemical yield from [11C]iodomethane (decay-corrected), corresponding to 20% overall radiochemical yield from [11C]carbon dioxide (decay-corrected), with high specific radioactivity. Preparations can be ready for i.v. injection 50 min from the end of radionuclide production.

Synthesis of racemic (+) and (-) N-[methyl-11C]nomifensine, a ligand for evaluation of monoamine re-uptake sites by use of positron emission tomography

The synthesis of racemic or enantiomeric N-[methyl-11C]nomifensine (1,2,3,4-tetrahydro-2-[11C]methyl-4-phenyl-8-isoquinolinamine), a potential ligand for the evaluation of monoamine re-uptake sites at the presynaptic dopaminergic terminals, using the appropriate N-desmethylcompounds and [11C]methyl iodide is described. The radiochemical conversion of [11C]methyl iodide to [11C]nomifensine was in the order of 85-95%. Radiochemical purity of the LC-purified radiopharmaceutical was in the order of 98-99%. In a typical run, starting with 120 mCi (4.4 GBq) of [11C]carbon dioxide, 380 MBq (8.6% not decay corrected) of a final solution was obtained within 55 min (roughly 20 min of that is related to transport time). The specific radioactivity corresponding to the [11C]methyl iodide was 30-100 mCi/mumol (typical: a total mass of 30 micrograms and 150 MBq was administered in the PET-studies). A procedure for resolving the racemate of N-desmethylnomifensine (1,2,3,4-tetrahydro-4-phenyl-8-isoquinoline) into its enantiomers using triacetylcellulose as the stationary phase and methanol/ethanol as solvents by use of LC is also described.

Syntheses of [11C]methyl esters of prostaglandins D2 and E2

Prostaglandins (PG) are endogenous compounds that have been extensively studied by various techniques. In this paper, the syntheses of methyl esters of PGD2 and PGE2, labelled with 11C for PET investigations, are reported. The prostaglandin was esterified via its carboxylate anion, with [11C]methyl iodide as alkylating reagent, in a dimethyl sulphoxide-dimethylformamide mixture. To minimize the base-catalysed degradations, the carboxylate anion was generated in situ by use of tetramethylpiperidine. The radiochemical yield, including purification, was 70%, with a total synthesis time of 20-25 min counted from the end of the [11C]methyl iodide synthesis.