Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1997-08-21
1999-12-28
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
422159, 422198, C07C 1710, F28D 700
Patent
active
060084219
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and a system for production of the positron emitting compound .sup.11 C-methyl iodide in high yields, with good radiochemical purity and high specific activity.
PRIOR ART
A group of medical diagnostic procedures utilize radioactive labeled compounds. This principle is also used for the diagnostic procedure PET (Positron Emitting Tomography), where the radioactive atoms are positron emitters. Some examples of positron emitting elements include nucleids of carbon (C), oxygen.(O), nitrogen (N) or fluorine (F). These elements are the backbone of almost all biological active compounds. To be able to use the method stable isotopes are replaced with a radioactive isotope. The radioactive labeled compounds, called tracers, are transported, accumulated and converted exactly the same way as for the non-radioactive compound. The PET method has possibilities to detect malfunction on a cellular level in the investigated tissues or organs. The method is very sensitive and requires only nanomole quantities of produced radioactive tracers. The half-life of these radioactive tracers range from 2 to 110 minutes and the production of the radioactive nucleids as well as the biological active tracer has to take place just prior to the use of it. The radioactive nucleids are produced in an accelerator and immediately processed to small molecules. These small molecules react with larger non-radioactive building blocks to yield the desired tracer.
One important and very useful starting compound is carbon-11 labeled methyl iodide (.sup.11 C--CH.sub.3 I). Carbon is the most frequent type of atom in biological active compounds and pharmaceuticals. With .sup.11 C-labeled methyl iodide it is possible to make a large variety of .sup.11 C-labeled compounds. These are of interest for diagnosis and follow up of a treatment of, for example, cancer, epilepsy or dementia.
Such a compound is today most often formed from .sup.11 C-labeled carbon dioxide (.sup.11 CO.sub.2) through reduction with lithium aluminum hydride (LAH) to .sup.11 C-labeled methanol and a reaction of this compound with hydrogen iodide to produce .sup.11 C-labeled methyl iodide. The reaction takes place in an organic solvent. This method has several disadvantages; the chemicals are cumbersome to use which makes the process unreliable and the LAH contains a variable amount of cold carbon dioxide lowering the relation between produced radioactive and non-radioactive .sup.11 C-labeled methyl iodide. In many investigations is it desirable to have a high ratio.
Another way to produce this compound is the halogenation of .sup.11 C-labeled methane (.sup.11 CH.sub.4) with iodine. The .sup.11 CH.sub.4 is formed from the catalytic reduction of .sup.11 C-labeled carbon dioxide. The halogenation reaction of the .sup.11 CH.sub.4 is a non-selective radical reaction taking place under elevated temperatures. As iodine always will be present in a large excess it is difficult to prevent polyhalogenation, leading to low radiochemical purity. In the published literature mixtures between mono-, di-, tri- and tetra-iodinated methane are formed (LIT REF). If the reaction conditions are suitable for formation of only the mono-halogenated compound in high purity, the yields are low (<10%) due to the very short reaction time necessary to prevent further halogenation.
DISCLOSURE OF THE INVENTION
The present invention solves the problem of the low chemical yields and low radio chemical purity of the radical iodination reaction. The reaction time and temperature are optimized to give a pure mono-halogenated methyl iodide. The small fraction of formed .sup.11 C-labeled methyl iodine is removed from the gas mixture, and the remaining .sup.11 C-labeled methane is purified and recirculated. Fresh iodine is added and the process is repeated until the conversion of the .sup.11 CH.sub.4 is complete.
According to a first object of the present invention a method for production of .sup.11 C-methyl iodide is disclosed by selectively monohalogena
REFERENCES:
patent: 5334788 (1994-08-01), Baucom et al.
Dahlstrom Kent
Larsen Peter
Orbe Martin
Ulin Johan
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