48V radionuclidic impurity in product streams from liquid cyclotron targets with titanium windows.

Vanadium-48, a positron emitter with a 16.0 day half-life, was observed in the aqueous product stream from a liquid cyclotron target equipped with a titanium window, a type of target system commonly used for preparing [13N]NH3 at PET centers. The amount of 48V activity is directly related to bombardment time and beam current. It is apparently present as vanadate ion, and it is efficiently removed by anion exchange cartridges. More generally, it is likely that the specie would be present in the product stream of any titanium-window-equipped liquid target which contains water and which is bombarded with protons or deuterons. Incidental to the 48V investigation, was quantitation of 18F in the system under study.

9-[(3-[18F]-fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]-FHPG): a potential imaging agent of viral infection and gene therapy using PET.

A no-carrier-added synthesis of 9-[(3-[18F]-fluoro-1-hydroxy-2-propoxy)methyl]-guanine ([18F]-FHPG) is reported. The 9-[(1,3-dihydroxy-2-propoxy)methyl)guanine (DHPG) was converted to 9-[N2,O-bis(methoxytrityl)-3-(tosyl)-2-propoxy-methyl]guanine by treatment with methoxytrityl chloride followed by tosylation. The tosylate was reacted with [18F]-KF in the presence of kryptofix 2.2.2. to produce the 3-fluoro-N2-O-bis-(methoxytrityl) derivative. Removal of the methoxytrityl protecting groups by acid hydrolysis produced [18F]-FHPG. The labeled product was purified by HPLC on a reverse-phase C18 column, and eluted in 9 min with a mobile phase of 5% acetonitrile in water. The radiochemical yield was 7-17%, with an average of 10% in 10 runs (corrected for decay to EOB). The radiochemical purity was > 99%, and specific activities with an average of 526 mCi/mumol were obtained. The synthesis time was 70-80 min, including HPLC purification and determination of radiochemical purity and specific activity.

Facile synthesis of [11C]buprenorphine for positron emission tomographic studies of opioid receptors.

We have developed a simple and rapid method for the production of buprenorphine (BPN), a potent opioid partial agonist, labelled with carbon-11 at the 6-methoxy position. The procedure uses a precursor synthesized in high yield (89%) from BPN in two steps and employs [11C]iodomethane as the radiolabelling reagent. [11C]BPN of 97% radiochemical purity can be prepared in high specific activity (41 GBq/mumol; 1120 mCi/mumol) in a radiochemical yield of 10% at end-of-synthesis (not decay corrected). The [11C]BPN is available for use in studies of cerebral opioid receptors by positron emission tomography within 24 min from end-of-bombardment, including radiosynthesis, purification, formulation for i.v. injection and determination of specific activity.