Patent Abstract:
Methods and reagents for photo-initiated carbonylation with carbon-isotope labeled carbon monoxide using alkyl/aryl iodides with sulfoxides and triethylamine are provided. The resultant carbon-isotope labeled acids, and pharmaceutical acceptable salts and solvates are useful as radiopharmaceuticals, especially for use in Positron Emission Tomography (PET). Associated kits and method for PET studies are also provided.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and an apparatus for the use of carbon-isotope monoxide in labeling synthesis. More specifically, the invention relates to a method and apparatus for producing an [ 11 C]carbon monoxide enriched gas mixture from an initial [ 11 C]carbon dioxide gas mixture, and using the produced gas mixture in labeling synthesis by photo-initiated carbonylation. Radiolabeled acids are provided using alkyl or aryl iodides as precursors, as well as sulfoxides and triethylamine. 
     BACKGROUND OF THE INVENTION 
     Tracers labeled with short-lived positron emitting radionuclides (e.g.  11 C, t 1/2 =20.3 min) are frequently used in various non-invasive in vivo studies in combination with positron emission tomography (PET). Because of the radioactivity, the short half-lives and the submicromolar amounts of the labeled substances, extraordinary synthetic procedures are required for the production of these tracers. An important part of the elaboration of these procedures is development and handling of new  11 C-labelled precursors. This is important not only for labeling new types of compounds, but also for increasing the possibility of labeling a given compound in different positions. 
     During the last two decades carbonylation chemistry using carbon monoxide has developed significantly. The recent development of methods such as palladium-catalyzed carbonylative coupling reactions has provided a mild and efficient tool for the transformation of carbon monoxide into different carbonyl compounds. 
     Carbonylation reactions using [ 11 C]carbon monoxide has a primary value for PET-tracer synthesis since biologically active substances often contain carbonyl groups or functionalities that can be derived from a carbonyl group. The syntheses are tolerant to most functional groups, which means that complex building blocks can be assembled in the carbonylation step to yield the target compound. This is particularly valuable in PET-tracer synthesis where the unlabelled substrates should be combined with the labeled precursor as late as possible in the reaction sequence, in order to decrease synthesis-time and thus optimize the uncorrected radiochemical yield. 
     When compounds are labeled with  11 C, it is usually important to maximize specific radioactivity. In order to achieve this, the isotopic dilution and the synthesis time must be minimized. Isotopic dilution from atmospheric carbon dioxide may be substantial when [ 11 C]carbon dioxide is used in a labeling reaction. Due to the low reactivity and atmospheric concentration of carbon monoxide (0.1 ppm vs. 3.4×10 4  ppm for CO 2 ), this problem is reduced with reactions using [ 11 C]carbon monoxide. 
     The synthesis of [ 11 C]carbon monoxide from [ 11 C]carbon dioxide using a heated column containing reducing agents such as zinc, charcoal or molybdenum has been described previously in several publications. Although [ 11 C]carbon monoxide was one of the first C-labelled compounds to be applied in tracer experiments in human, it has until recently not found any practical use in the production of PET-tracers. One reason for this is the low solubility and relative slow reaction rate of [ 11 C]carbon monoxide which causes low trapping efficiency in reaction media. The general procedure using precursors such as [ 11 C]methyl iodide, [ 11 C]hydrogen cyanide or [ 11 C]carbon dioxide is to transfer the radioactivity in a gas-phase, and trap the radioactivity by leading the gas stream through a reaction medium. Until recently this has been the only accessible procedure to handle [ 11 C]carbon monoxide in labeling synthesis. With this approach, the main part of the labeling syntheses with [ 11 C]carbon monoxide can be expected to give a very low yield or fail completely. 
     There are only a few examples of practically valuable  11 C-labelling syntheses using high pressure techniques (&gt;300 bar). In principal, high pressures can be utilized for increasing reaction rates and minimizing the amounts of reagents. One problem with this approach is how to confine the labeled precursor in a small high-pressure reactor. Another problem is the construction of the reactor. If a common column type of reactor is used (i.e. a cylinder with tubing attached to each end), the gas-phase will actually become efficiently excluded from the liquid phase at pressurization. The reason is that the gas-phase, in contracted form, will escape into the attached tubing and away from the bulk amount of the liquid reagent. 
     The cold-trap technique is widely used in the handling of  11 C-labelled precursors, particularly in the case of [ 11 C]carbon dioxide. The procedure has, however, only been performed in one single step and the labeled compound was always released in a continuous gas-stream simultaneous with the heating of the cold-trap. Furthermore, the volume of the material used to trap the labeled compound has been relative large in relation to the system to which the labeled compound has been transferred. Thus, the option of using this technique for radical concentration of the labeled compound and miniaturization of synthesis systems has not been explored. This is especially noteworthy in view of the fact that the amount of a  11 C-labelled compound usually is in the range 20-60 nmol. 
     Recent technical development for the production and use of [ 11 C]carbon monoxide has made this compound useful in labeling synthesis. WO 02/102711 describes a system and a method for the production and use of a carbon-isotope monoxide enriched gas-mixture from an initial carbon-isotope dioxide gas mixture. [ 11 C]carbon monoxide may be obtained in high radiochemical yield from cyclotron produced [ 11 C]carbon dioxide and can be used to yield target compounds with high specific radioactivity. This reactor overcomes the difficulties listed above and is useful in synthesis of  11 C-labelled compounds using [ 11 C]carbon monoxide in palladium or selenium mediated reaction. With such method, a broad array of carbonyl compounds can be labeled (Kilhlberg, T.; Långström, B. J., Org. Chem. 1999, 9201-9205). The use of transition metal mediated reactions is, however, restricted by problems related to the competing β-hydride elimination reaction, which excludes or at least severely restricts utilization of organic electrophiles having hydrogen in β-position. Thus, a limitation of the transition metal mediated reactions is that most alkyl halides could not be used as substrates due to the β-hydride elimination reaction. One way to circumvent this problem is to use free-radical chemistry based on light irradiation of alkyl halides. We earlier succeeded in using free-radical chemistry for the carbonylation of alkyl iodides using amines to yield labeled amides. 
     However, the attempt to yield labeled esters and acids in an analogous way (using water as a reactant instead of amines) is challenged by dissimilar solubility of water and alkyl or aryl iodides in solvents due to very different polarities of the reactants. Another problem of this approach is the low reactivity of water in these reaction conditions (typically the yields of esters and acids compared to those of amides are lower by 10 to 100 times). Therefore, there is a need for a method in order to use photo-induced free radical carbonylation to overcome the problems of weakly reacting water and dissimilar solubility of water and alkyl or aryl iodides and provide target structures with high yield to further increase the utility of [ 11 C]carbon monoxide in preparing useful PET tracers. 
     Discussion or citation of a reference herein shall not be construed as an admission that such reference is prior art to the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for labeling synthesis, comprising: 
     (a) providing a UV reactor assembly comprising a high pressure reaction chamber with a gas inlet and a liquid inlet, a UV spot light source with a light guide, wherein the light guide is used to provide photo irradiation of a reaction mixture through a window in the reaction chamber, 
     (b) dissolving triethylamine (TEA) and a sulfoxide in a solvent, 
     (c) adding an alkyl or aryl iodide to the solution of step (b) to give a reagent volume to be labeled, 
     (d) introducing a carbon-isotope monoxide enriched gas-mixture into the reaction chamber of the UV reactor assembly via the gas inlet, 
     (e) introducing at high-pressure said reagent volume into the reaction chamber via the liquid inlet, 
     (f) turning on the UV spot light source and waiting a predetermined time while the labeling synthesis occur, and 
     (g) collecting labeled acid from the reaction chamber. 
     The present invention also provides a system for labeling synthesis, comprising: a UV reactor assembly comprising a high pressure reaction chamber with a gas inlet and a liquid inlet, a UV spot light source with a light guide, wherein a light guide is used to provide photo irradiation of the reaction mixture through a window in the reaction chamber thereof, wherein the photo irradiation from the light source, which stands at the distance from the reaction chamber, is delivered through the window of the reaction chamber. 
     The present invention further provides a method for the synthesis of labeled acids, using photo-initiated carbonylation with [ 11 C]carbon monoxide using alkyl or aryl iodides, TEA and a sulfoxide, preferably dimethysulfoxide (DMSO). 
     In another embodiment, the invention also provides [ 11 C]-labeled acids, and pharmaceutically acceptable salts and solvates thereof. In yet another embodiment, the invention provides kits for use as PET tracers comprising effective amount of [ 11 C]-labeled acids, or pharmaceutically acceptable salts and solvates thereof. In still another embodiment, the invention provides a method for conducting PET of a subject comprising administering to the subject a kit of the instant invention and measuring distribution within the subject of the [ 11 C]-labeled acids by PET. 
     Other features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a flow chart over the method according to the invention 
         FIG. 2  is a schematic view of a carbon-isotope monoxide production and labeling-system according to the invention. 
         FIG. 3  is the cross-sectional view of the reaction chamber. 
         FIG. 4  is a view of the UV spot light source. 
         FIG. 5  shows how the reaction chamber, magnetic stirrer, and the UV spot light source are arranged into the UV reactor assembly. 
         FIGS. 6   a  and  6   b  show alternative embodiments of a reaction chamber according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The main advantage of the present invention is to overcome the limitations of transition metal-mediated reaction and provide a simple approach to synthesize  11 C-labeled acids under very mild conditions using alkyl/aryl iodides as precursors. The levels of specific radioactivity are high compared with alternative methods such as the use of Grignard reactions for preparation of [carbonyl- 11 C]esters and acids. Iodides used in this invention have a formula RI, where R is linear or cyclic alkyl or substituted alkyl, aryl or substituted aryl, and may contain fluoro, ester and carboxyl groups, which are separated by at least one carbon atom from the carbon atom bearing the iodide atom. Sulfoxides are defined as compounds having the structure R′ 2 S═O, wherein R′ is a lower (less than 10 carbons) alkyl or aryl. Examples of sulfoxides include DMSO and diphenylsulfoxide (Ph 2 S═O). 
     The resultant labeled acids have a formula 
                                
wherein R is defined as above. They and their pharmaceutically acceptable salts and/or solvates thereof provide valuable PET tracers in various PET studies.
 
     It is to be clear that the present invention includes pharmaceutically acceptable salts and solvates of labeled compounds of the instant invention, and mixtures comprising two or more of such labeled compounds, pharmaceutically acceptable salts of the labeled compounds and pharmaceutically acceptable solvates of labeled compounds. 
     The term “pharmaceutically acceptable” means compatible with the treatment of animals, in particular, humans. 
     The term “pharmaceutically acceptable salt” refers to salt forms that are pharmacologically suitable for or compatible with the treatment of patients. 
     If the inventive compound is a base, the desired pharmaceutically acceptable salt may be prepared by an suitable method available in the art, for example, treatment of the free base with an inorganic acid, such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like, or with an organic acid, such as acetic acid, maleic acid, succinic acid, mandelic acid, fumaric acid, malonic acid, pyruvic acid, oxalic acid, glycolic acid, salicylic acid, a pyranosidyl acid, such as glucuronic acid or galacturonic acid, an α-hydroxy acid, such as citric acid or tartaric acid, an amino acid, such as aspartic acid or glutamic acid, an aromatic acid, such as benzoic acid or cinnamic acid, a sulfonic acid, such as p-toluenesulfonic acid or ethanesulfonic acid, or the like. 
     If the inventive compound is an acid, the desired pharmaceutically acceptable salt may be prepared by any suitable method, for example, treatment of the free acid with an inorganic or organic base, such as an amine (primary, secondary or tertiary), an alkali metal hydroxide or alkaline earth metal hydroxide, or the like. Illustrative examples of the suitable salts include organic salts derived from amino acids, such as glycine and arginine, ammonia, primary, secondary, and tertiary amines, and cyclic amines, such as piperidine, morpholine and piperazine, and inorganic salts derived from sodium, calcium, potassium, magnesium, manganese, iron, copper, zinc, aluminum and lithium. 
     The term “solvate” as used herein means a compound of the invention, wherein molecules of a suitable solvent are incorporated in the crystal lattice. A suitable solvent is physiologically tolerable at the dosage administered. Examples of suitable solvents are ethanol, water and the like. When water is the solvent, the molecule is referred to as a “hydrate”. 
     General reaction scheme for the synthesis of labeled acids are as illustrated below: 
                                
wherein R and sulfoxide are as defined above. * indicates the  11 C-labeled position.
 
     The radiolabelled compounds, or pharmaceutically acceptable salts and solvates thereof, of the invention are suitably formulated into pharmaceutical or radiopharmaceutical compositions for administration to human subjects in a biologically compatible form suitable for administration in vivo. Accordingly, in another aspect, the present invention provides a pharmaceutical composition comprising a radiolabelled compound or pharmaceutically acceptable salts and solvates thereof, of the invention in admixture with a suitable diluent or carrier. 
     The term an “effective amount” as used herein is that amount sufficient to effect desired results, including clinical results, and, as such, an “effective amount” depends upon the context in which it is being applied. 
     The term “subject” as used herein includes all members of the animal kingdom including human. The subject is preferably a human. 
     In preferred embodiment of the present invention, it provides kits for use as PET tracers comprising an effective amount of carbon isotope-labeled esters and acids, or pharmaceutically acceptable salts and solvates thereof. 
     Such kits are designed to give sterile products suitable for human administration, e.g. direct injection into the bloodstream. Suitable kits comprise containers (e.g. septum-sealed vials) containing the adrenergic interfering agent and precursor of the adrenergic imaging agent. 
     The kits may optionally further comprise additional components such as radioprotectant, antimicrobial preservative, pH-adjusting agent or filler. 
     By the term “radioprotectant” is meant a compound which inhibits degradation reactions, such as redox processes, by trapping highly-reactive free radicals, such as oxygen-containing free radicals arising from the radiolysis of water. The radioprotectants of the present invention are suitably chosen from: ascorbic acid, para-aminobenzoic acid (i.e. 4-aminobenzoic acid), gentisic acid (i.e. 2,5-dihydroxybenzoic acid) and salts thereof. 
     By the term “antimicrobial preservative” is meant an agent which inhibits the growth of potentially harmful micro-organisms such as bacteria, yeasts or moulds. The antimicrobial preservative may also exhibit some bactericidal properties, depending on the dose. The main role of the antimicrobial preservative(s) of the present invention is to inhibit the growth of any such micro-organism in the pharmaceutical composition post-reconstitution, i.e. in the radioactive diagnostic product itself. The antimicrobial preservative may, however, also optionally be used to inhibit the growth of potentially harmful micro-organisms in one or more components of the kit of the present invention prior to reconstitution. Suitable antimicrobial preservatives include: the parabens, i.e., ethyl, propyl or butyl paraben or mixtures thereof; benzyl alcohol; phenol; cresol; cetrimide and thiomersal. Preferred antimicrobial preservative(s) are the parabens. 
     The term “pH-adjusting agent” means a compound or mixture of compounds useful to ensure that the pH of the reconstituted kit is within acceptable limits (approximately pH 4.0 to 10.5) for human administration. Suitable such ph-adjusting agents include pharmaceutically acceptable buffers, such as tricine, phosphate or TRIS [i.e. tris(hydroxymethyl)aminomethane], and pharmaceutically acceptable bases such as sodium carbonate, sodium bicarbonate or mixtures thereof. When the ligand conjugate is employed in acid salt form, the pH-adjusting agent may optionally be provided in a separate vial or container, so that the user of the kit can adjust the pH as part of a multi-step procedure. 
     By the term “filler” is meant a pharmaceutically acceptable bulking agent which may facilitate material handling during production and lyophilisation. Suitable fillers include inorganic salts such as sodium chloride, and water soluble sugars or sugar alcohols such as sucrose, maltose, mannitol or trehalose. 
     The present invention also includes a method for conducting positron emission tomography of a subject comprising administering to the subject an effective amount of a radiolabelled compound, or pharmaceutically acceptable salts and solvates thereof, of the instant invention and measuring the distribution within the subject of the compound by PET. In a preferred embodiment, the invention provides a method for conducting PET of a subject comprising administering to the subject a kit of the instant invention and measuring distribution within the subject of the [ 11 C]-labeled esters or acids by PET. 
     In accordance with the methods of the invention, the radiolabeled compounds of the invention may be administered to a patient in a variety of forms depending on the selected route of administration, as will be understood by those skilled in the art. The compositions of the invention are preferably administered by intravenous administration, and the radiopharmaceutical compositions formulated accordingly, for example together with any physiologically and radiologically tolerable vehicle appropriate for administering the compound systemically. 
     In a preferred embodiment of the instant invention, it provides a method and system is that nearly quantitative conversion of carbon-isotope monoxide into labeled products can be accomplished. 
     There are several other advantages with the present method and system. The high-pressure technique makes it possible to use low boiling solvents such as diethyl ether at high temperatures (e.g. 200° C.). The use of a closed system consisting of materials that prevents gas diffusion, increases the stability of sensitive compounds and could be advantageous also with respect to Good Manufacturing Practice (GMP). 
     Still other advantages are achieved in that the resulting labeled compound is highly concentrated, and that the miniaturization of the synthesis system facilitates automation, rapid synthesis and purification, and optimization of specific radioactivity through minimization of isotopic dilution. 
     Most important is the opening of completely new synthesis possibilities, as exemplified by the present invention. 
     Embodiments of the invention will now be described with reference to the figures. 
     The term carbon-isotope that is used throughout this application preferably refers to  11 C, but it should be understood that C may be substituted by other carbon-isotopes, such as  13 C and  14 C, if desired. 
       FIG. 1  shows a flow chart over the method according to the invention, which firstly comprises production of a carbon-isotope monoxide enriched gas-mixture and secondly a labeling synthesis procedure. More in detail the production part of the method comprises the steps of:
         Providing carbon-isotope dioxide in a suitable carrier gas of a type that will be described in detail below.   Converting carbon-isotope dioxide to carbon-isotope monoxide by introducing said gas mixture in a reactor device which will be described in detail below.   Removing traces of carbon-isotope dioxide by flooding the converted gas-mixture through a carbon dioxide removal device wherein carbon-isotope dioxide is trapped but not carbon-isotope monoxide nor the carrier gas. The carbon dioxide removal device will be described in detail below.   Trapping carbon-isotope monoxide in a carbon monoxide trapping device, wherein carbon-isotope monoxide is trapped but not said carrier gas. The carbon monoxide trapping device will be described in detail below.   Releasing said trapped carbon-isotope monoxide from said trapping device, whereby a volume of carbon-isotope monoxide enriched gas-mixture is achieved.       

     The production step may further comprise a step of changing carrier gas for the initial carbon-isotope dioxide gas mixture if the initial carbon-isotope dioxide gas mixture is comprised of carbon-isotope dioxide and a first carrier gas not suitable as carrier gas for carbon monoxide due to similar molecular properties or the like, such as nitrogen. More in detail the step of providing carbon-isotope dioxide in a suitable second carrier gas such as He, Ar, comprises the steps of:
         Flooding the initial carbon-isotope dioxide gas mixture through a carbon dioxide trapping device, wherein carbon-isotope dioxide is trapped but not said first carrier gas. The carbon dioxide trapping device will be described in detail below.   Flushing said carbon dioxide trapping device with said suitable second carrier gas to remove the remainders of said first carrier gas.   Releasing said trapped carbon-isotope dioxide in said suitable second carrier gas.       

     The labeling synthesis step that may follow the production step utilizes the produced carbon-isotope dioxide enriched gas-mixture as labeling reactant. More in detail the step of labeling synthesis comprises the steps of:
         Providing a UV reactor assembly comprising a UV spot light source and a high pressure reaction chamber having a liquid reagent inlet and a labeling reactant inlet in a bottom surface thereof. In a preferred embodiment, the UV reactor assembly further comprises a magnetic stirrer and a magnetic stirring bar. In another preferred embodiment, the UV reactor assembly further comprises a protective housing and a bench where the reaction chamber, UV spot light guide and the magnetic stirrer can be mounted. The UV reactor assembly and the reaction chamber will be described in detail below.   Providing a reagent volume that is to be labeled. The reagent volume can be prepared in following steps: 1. Dissolve TEA and a sulfoxide in a solvent; 2. Add alkyl or aryl iodide to the solution of step 1 to form a reagent volume as late as possible before being introduced into the high pressure reaction chamber. Definition and examples of sulfoxides are provided above. In a preferred embodiment, a sulfoxide is a DMSO. Solvent can be any organic solvent or water.   Introducing the carbon-isotope monoxide enriched gas-mixture into the reaction chamber via the labeling reactant inlet.   Introducing, at high pressure, said liquid reagent into the reaction chamber via the liquid reagent inlet.   Turning on the UV spot light source and waiting a predetermined time while the labeling synthesis occurs.   Collecting the solution of labeled acid from the reaction chamber.       

     The step of waiting a predetermined time may further comprise adjusting the temperature of the reaction chamber such that the labeling synthesis is enhanced. 
       FIG. 2  schematically shows a [ 11 C]carbon dioxide production and labeling-system according to the present invention. The system is comprised of three main blocks, each handling one of the three main steps of the method of production and labeling:
         Block A is used to perform a change of carrier gas for an initial carbon-isotope dioxide gas mixture, if the initial carbon-isotope dioxide gas mixture is comprised of carbon-isotope dioxide and a first carrier gas not suitable as carrier gas for carbon monoxide.   Block B is used to perform the conversion from carbon-isotope dioxide to carbon-isotope monoxide, and purify and concentrate the converted carbon-isotope monoxide gas mixture.   Block C is used to perform the carbon-isotope monoxide labeling synthesis.       

     Block A is normally needed due to the fact that carbon-isotope dioxide usually is produced using the 14N(p,α) 11 C reaction in a target gas containing nitrogen and 0.1% oxygen, bombarded with 17 MeV protons, whereby the initial carbon-isotope dioxide gas mixture comprises nitrogen as carrier gas. However, compared with carbon monoxide, nitrogen show certain similarities in molecular properties that makes it difficult to separate them from each other, e.g. in a trapping device or the like, whereby it is difficult to increase the concentration of carbon-isotope monoxide in such a gas mixture. Suitable carrier gases may instead be helium, argon or the like. Block A can also used to change the pressure of the carrier gas (e.g. from 1 to 4 bar), in case the external system does not tolerate the gas pressure needed in block B and C. In an alternative embodiment the initial carbon-isotope dioxide gas mixture is comprised of carbon-isotope dioxide and a first carrier gas that is well suited as carrier gas for carbon monoxide, whereby the block A may be simplified or even excluded. 
     According to a preferred embodiment ( FIG. 2 ), block A is comprised of a first valve V 1 , a carbon dioxide trapping device  8 , and a second valve V 2 . 
     The first valve V 1  has a carbon dioxide inlet  10  connected to a source of initial carbon-isotope dioxide gas mixture  12 , a carrier gas inlet  14  connected to a source of suitable carrier gas  16 , such as helium, argon and the like. The first valve V 1  further has a first outlet  18  connected to a first inlet  20  of the second valve V 2 , and a second outlet  22  connected to the carbon dioxide trapping device  8 . The valve V 1  may be operated in two modes A, B, in mode A the carbon dioxide inlet  10  is connected to the first outlet  18  and the carrier gas inlet  14  is connected to the second outlet  22 , and in mode B the carbon dioxide inlet  10  is connected to the second outlet  22  and the carrier gas inlet  14  is connected to the first outlet  18 . 
     In addition to the first inlet  20 , the second valve V 2  has a second inlet  24  connected to the carbon dioxide trapping device  8 . The second valve V 2  further has a waste outlet  26 , and a product outlet  28  connected to a product inlet  30  of block B. The valve V 2  may be operated in two modes A, B, in mode A the first inlet  20  is connected to the waste outlet  26  and the second inlet  24  is connected to the product outlet  28 , and in mode B the first inlet  20  is connected to the product outlet  28  and the second inlet  24  is connected to the waste outlet  26 . 
     The carbon dioxide trapping device  8  is a device wherein carbon dioxide is trapped but not said first carrier gas, which trapped carbon dioxide thereafter may be released in a controlled manner. This may preferably be achieved by using a cold trap, such as a column containing a material which in a cold state, (e.g. −196° C. as in liquid nitrogen or −186° C. as in liquid argon) selectively trap carbon dioxide and in a warm state (e.g. +50° C.) releases the trapped carbon dioxide. (In this text the expression “cold trap” is not restricted to the use of cryogenics. Thus, materials that trap the topical compound at room temperature and release it at a higher temperature are included). One suitable material is porapac Q®. The trapping behavior of a porapac-column is related to dipole-dipole interactions or possibly Van der Waal interaktions. The said column 8 is preferably formed such that the volume of the trapping material is to be large enough to efficiently trap (&gt;95%) the carbon-isotope dioxide, and small enough not to prolong the transfer of trapped carbon dioxide to block B. In the case of porapac Q® and a flow of 100 ml nitrogen/min, the volume should be 50-150 μl. The cooling and heating of the carbon dioxide trapping device  8  may further be arranged such that it is performed as an automated process, e.g. by automatically lowering the column into liquid nitrogen and moving it from there into a heating arrangement. 
     According to the preferred embodiment of  FIG. 2  block B is comprised of a reactor device  32  in which carbon-isotope dioxide is converted to carbon-isotope monoxide, a carbon dioxide removal device  34 , a check-valve  36 , and a carbon monoxide trapping device  38 , which all are connected in a line. 
     In the preferred embodiment the reactor device  32  is a reactor furnace comprising a material that when heated to the right temperature interval converts carbon-isotope dioxide to carbon-isotope monoxide. A broad range of different materials with the ability to convert carbon dioxide into carbon monoxide may be used, e.g. zinc or molybdenum or any other element or compound with similar reductive properties. If the reactor device  32  is a zinc furnace it should be heated to 400° C., and it is important that the temperature is regulated with high precision. The melting point of zinc is 420° C. and the zinc-furnace quickly loses it ability to transform carbon dioxide into carbon monoxide when the temperature reaches over 410° C., probably due to changed surface properties. The material should be efficient in relation to its amount to ensure that a small amount can be used, which will minimize the time needed to transfer radioactivity from the carbon dioxide trapping device  8  to the subsequent carbon monoxide trapping device  38 . The amount of material in the furnace should be large enough to ensure a practical life-time for the furnace (at least several days). In the case of zinc granulates, the volume should be 100-1000 μl. 
     The carbon dioxide removal device  34  is used to remove traces of carbon-isotope dioxide from the gas mixture exiting the reactor device  32 . In the carbon dioxide removal device  34 , carbon-isotope dioxide is trapped but not carbon-isotope monoxide nor the carrier gas. The carbon dioxide removal device  34  may be comprised of a column containing Ascarite® (i.e. sodium hydroxide on silica). Carbon-isotope dioxide that has not reacted in the reactor device  32  is trapped in this column (it reacts with sodium hydroxide and turns into sodium carbonate), while carbon-isotope monoxide passes through. The radioactivity in the carbon dioxide removal device  34  is monitored as a high value indicates that the reactor device  32  is not functioning properly. 
     Like the carbon dioxide trapping device  8 , the carbon monoxide trapping device  38 , has a trapping and a releasing state. In the trapping state carbon-isotope monoxide is selectively trapped but not said carrier gas, and in the releasing state said trapped carbon-isotope monoxide is released in a controlled manner. This may preferably be achieved by using a cold trap, such as a column containing silica which selectively trap carbon monoxide in a cold state below −100° C., e.g. −196° C. as in liquid nitrogen or −186° C. as in liquid argon, and releases the trapped carbon monoxide in a warm state (e.g. +50° C.). Like the porapac-column, the trapping behavior of the silica-column is related to dipole-dipole interactions or possibly Van der Waal interactions. The ability of the silica-column to trap carbon-isotope monoxide is reduced if the helium, carrying the radioactivity, contains nitrogen. A rationale is that since the physical properties of nitrogen are similar to carbon monoxide, nitrogen competes with carbon monoxide for the trapping sites on the silica. 
     According to the preferred embodiment of  FIG. 2 , block C is comprised of a first and a second reaction chamber valve V 3  and V 4 , a reagent valve V 5 , an injection loop  70  and a solvent valve V 6 , and the UV reactor assembly  51  which comprises a UV lamp  91 , a concave mirror  92  and a reaction chamber  50 . 
     The first reaction chamber valve V 3  has a gas mixture inlet  40  connected to the carbon monoxide trapping device  38 , a stop position  42 , a collection outlet  44 , a waste outlet  46 , and a reaction chamber connection port  48  connected to a gas inlet  52  of the reaction chamber  50 . The first reaction chamber valve V 3  has four modes of operation A to D. The reaction chamber connection port  48  is: in mode A connected to the gas mixture inlet  40 , in mode B connected to the stop position  42 , in mode C connected to the collection outlet  44 , and in mode D connected to the waste outlet  46 . 
       FIG. 3  shows the reaction chamber  50  (micro-autoclave) which has a gas inlet  52  and a liquid inlet  54 , which are arranged such that they terminate at the bottom surface of the chamber. Gas inlet  52  may also be used as product outlet after the labeling is finished. During operation the carbon-isotope monoxide enriched gas mixture is introduced into the reaction chamber  50  through the gas inlet  52 , where after the liquid reagent at high pressure enters the reaction chamber  50  through the liquid inlet  54 .  FIGS. 6   a  and  6   b  shows schematic views of two preferred reaction chambers  50  in cross section.  FIG. 6   a  is a cylindrical chamber which is fairly easy to produce, whereas the spherical chamber of  FIG. 6   b  is the most preferred embodiment, as the surface area to volume-ratio of the chamber is further minimized. A minimal surface area to volume-ratio optimizes the recovery of labeled product and minimizes possible reactions with the surface material. Due to the “diving-bell construction” of the reaction chamber  50 , both the gas inlet  52  and the liquid inlet  54  becomes liquid-filled and the reaction chamber  50  is filled from the bottom upwards. The gas-volume containing the carbon-isotope monoxide is thus trapped and given efficient contact with the reaction mixture. Since the final pressure of the liquid is approximately 80 times higher than the original gas pressure, the final gas volume will be less than 2% of the liquid volume according to the general gas-law. Thus, a pseudo one-phase system will result. In the instant application, the term “pseudo one-phase system” means a closed volume with a small surface area to volume-ratio containing &gt;96% liquid and &lt;4% gas at pressures exceeding 200 bar. In most syntheses the transfer of carbon monoxide from the gas-phase to the liquid phase will probably not be the rate limiting step. After the labeling is finished the labeled volume is nearly quantitatively transferred from the reaction chamber by the internal pressure via the gas inlet/product outlet  52  and the first reaction chamber valve V 3  in position C. 
     In a specific embodiment,  FIG. 3  shows a reaction chamber made from stainless steel (Valco™) column end fitting  101 . It is equipped with sapphire window  102 , which is a hard material transparent to short wavelength UV radiation. The window is pressed between two Teflon washers  103  inside the drilled column end fitting to make the reactor tight at high pressures. Temperature measurement can be accomplished with the thermocouple  104  attached by solder drop  105  to the outer side of the reactor. A magnet stirrer (not shown) drives small Teflon coated magnet stirring bar  106  placed inside the reaction chamber. The magnetic stirrer can be attached against the bottom of the reaction chamber. Distance between the magnet stirrer and the reactor should be minimal. 
       FIG. 4  shows a commercial UV spot light source  110  (for example, Hamamatsu Lightningcure™ LC5), which is an example of UV spot light sources that can be used in the instant invention. Light source  110  has necessary means of operating and controlling the photo irradiation that is produced, of the light source is available from the manufacturer (Hamamatsu Photonics K. K. Thus intensity and time duration of the photo irradiation are easily adjusted by an operator. Light source  110  may be externally controlled by a computer, providing a possibility for automating the reactor assembly. The photo irradiation is delivered to the reaction vessel through a flexible light guide, which is an accessory of Hamamatsu Lightningcure™ LC5. Thus light source  110  may be placed at the distance from the reaction chamber providing the possibility to save precious space inside a sheltered hot-cell, where the radiolabeling syntheses are carried out. Light source  110  complies with the existing industrial safety standards. Further, optional accessories (e.g. changeable lamps, optical filters) are provided which may be advantageously used for adjusting the properties of the photo irradiation. 
       FIG. 5  shows the reaction chamber  50  situated a magnetic stirrer  201 , with gas inlet/product outlet  52  and liquid inlet  54  facing the magnetic stirrer  201 . Top of the reaction chamber  50  is connected through the flexible light guide  202  to the UV spot light source (not shown). 
     Referring back to  FIG. 2 , the second reaction chamber valve V 4  has a reaction chamber connection port  56 , a waste outlet  58 , and a reagent inlet  60 . The second reaction chamber valve V 4  has two modes of operation A and B. The reaction chamber connection port  56  is: in mode A connected to the waste outlet  58 , and in mode B it is connected to the reagent inlet  60 . 
     The reagent valve V 5 , has a reagent outlet  62  connected to the reagent inlet  60  of the second reaction chamber valve V 4 , an injection loop inlet  64  and outlet  66  between which the injection loop  70  is connected, a waste outlet  68 , a reagent inlet  71  connected to a reagent source, and a solvent inlet  72 . The reagent valve V 5 , has two modes of operation A and B. In mode A the reagent inlet  71  is connected to the injection loop inlet  64 , and the injection loop outlet  66  is connected to the waste outlet  68 , whereby a reagent may be fed into the injection loop  70 . In mode B the solvent inlet  72  is connected to the injection loop inlet  64 , and the injection loop outlet  66  is connected to the reagent outlet  62 , whereby reagent stored in the injection loop  70  may be forced via the second reaction chamber valve V 4  into the reaction chamber  50  if a high pressure is applied on the solvent inlet  72 . 
     The solvent valve V 6 , has a solvent outlet  74  connected to the solvent inlet  72  of the reagent valve V 5 , a stop position  76 , a waste outlet  78 , and a solvent inlet  80  connected to a solvent supplying HPLC-pump (High Performance Liquid Chromatography) or any liquid-pump capable of pumping organic solvents at 0-10 ml/min at pressures up to 400 bar (not shown). The solvent valve V 6 , has two modes of operation A and B. In mode A the solvent outlet  74  is connected to the stop position  76 , and the solvent inlet  80  is connected to the waste outlet  78 . In mode B the solvent outlet  74  is connected to the solvent inlet  80 , whereby solvent may be pumped into the system at high pressure by the HPLC-pump. 
     Except for the small volume of silica in the carbon monoxide trapping devise  38 , an important difference in comparison to the carbon dioxide trapping device  8 , as well as to all related prior art, is the procedure used for releasing the carbon monoxide. After the trapping of carbon monoxide on carbon monoxide trapping devise  8 , valve V 3  is changed from position A to B to stop the flow from the carbon monoxide trapping devise  38  and increase the gas-pressure on the carbon monoxide trapping devise  38  to the set feeding gas pressure (3-5 bar). The carbon monoxide trapping devise  38  is then heated to release the carbon monoxide from the silica surface while not significantly expanding the volume of carbon monoxide in the carrier gas. Valve V 4  is changed from position A to B and valve V 3  is then changed from position B to A. At this instance the carbon monoxide is rapidly and almost quantitatively transferred in a well-defined micro-plug into the reaction chamber  50 . Micro-plug is defined as a gas volume less than 10% of the volume of the reaction chamber  50 , containing the topical substance (e.g. 1-20 μL). This unique method for efficient mass-transfer to a small reaction chamber  50 , having a closed outlet, has the following prerequisites:
         A micro-column 38 defined as follows should be used. The volume of the trapping material (e.g. silica) should be large enough to efficiently trap (&gt;95%) the carbon-isotope monoxide, and small enough (&lt;1% of the volume of a subsequent reaction chamber  50 ) to allow maximal concentration of the carbon-isotope monoxide. In the case of silica and a reaction chamber  50  volume of 200 μl, the silica volume should be 0.1-2 μl.   The dead volumes of the tubing and valve(s) connecting the silica column and the reaction chamber  50  should be minimal (&lt;10% of the micro-autoclave volume).   The pressure of the carrier gas should be 3-5 times higher than the pressure in the reaction chamber  50  before transfer (1 atm.).       

     In one specific preferred embodiment specifications, materials and components are chosen as follows. High pressure valves from Valco®, Reodyne® or Cheminert® are used. Stainless steel tubing with o.d. 1/16″ is used except for the connections to the porapac-column 8, the silica-column 38 and the reaction chamber  50  where stainless steel tubing with o.d. 1/32″ are used in order to facilitate the translation movement. The connections between V 1 , V 2  and V 3  should have an inner diameter of 0.2-1 mm. The requirement is that the inner diameter should be large enough not to obstruct the possibility to achieve the optimal flow of He (2-50 ml/min) through the system, and small enough not to prolong the time needed to transfer the radioactivity from the porapac-column 8 to the silica-column 38. The dead volume of the connection between V 3  and the autoclave should be minimized (&lt;10% of the autoclave volume). The inner diameter (0.05-0.1 mm) of the connection must be large enough to allow optimal He flow (2-50 ml/min). The dead volume of the connection between V 4  and V 5  should be less than 10% of the autoclave volume. 
     The porapac-column 8 preferably is comprised of a stainless steel tube (o.d.=⅛″, i.d.=2 mm, l=20 mm) filled with Porapac Q® and fitted with stainless steel screens. The silica-column 38 preferably is comprised of a stainless steel tube (o.d= 1/16″, i.d.=0.1 mm) with a cavity (d=1 mm, h=1 mm, V=0.8 μl) in the end. The cavity is filled with silica powder (100/80 mesh) of GC-stationary phase type. The end of the column is fitted against a stainless steel screen. 
     It should be noted that a broad range of different materials could be used in the trapping devices. If a GC-material is chosen, the criterions should be good retardation and good peak-shape for carbon dioxide and carbon monoxide respectively. The latter will ensure optimal recovery of the radioactivity. 
     Below a detailed description is given of a method of producing carbon-isotope using an exemplary system as described above. 
     Preparations of the system are performed by the steps 1 to 5:
         1. V 1  in position A, V 2  in position A, V 3  in position A, V 4  in position A, helium flow on with a max pressure of 5 bar. With this setting, the helium flow goes through the porapac column, the zinc furnace, the silica column, the reaction chamber  50  and out through V 4 . The system is conditioned, the reaction chamber  50  is rid of solvent and it can be checked that helium can be flowed through the system with at least 10 ml/min. UV lamp  91  is turned on.   2. The zinc-furnace is turned on and set at 400° C.   3. The porapac and silica-columns are cooled with liquid nitrogen. At −196° C., the porapac and silica-column efficiently traps carbon-isotope dioxide and carbon-isotope monoxide respectively.   4. V 5  in position A (load). The injection loop (250 μl), attached to V 5 , is loaded with the reaction mixture.   5. The HPLC-pump is attached to a flask with freshly distilled THF (or other high quality solvent) and primed. V 6  in position A.       

     Production of carbon-isotope dioxide may be performed by the steps 6 to 7:
         6. Carbon-isotope dioxide is produced using the 14N(p,α) 11 C reaction in a target gas containing nitrogen (AGA, Nitrogen 6.0) and 0.1% oxygen (AGA. Oxygen 4.8), bombarded with 17 MeV protons.   7. The carbon-isotope dioxide is transferred to the apparatus using nitrogen with a flow of 100 ml/min.       

     Synthesis of carbon-isotope may thereafter be performed by the steps 8 to 16
         8. V 1  in position B and V 2  in position B. The nitrogen flow containing the carbon-isotope dioxide is now directed through the porapac-column (cooled to −196° C.) and out through a waste line. The radioactivity trapped in the porapac-column is monitored.   9. When the radioactivity has peaked, V 1  is changed to position A. Now a helium flow is directed through the porapac-column and out through the waste line. By this operation the tubings and the porapac-column are rid of nitrogen.   10. V 2  in position A and the porapac-column is warmed to about 50° C. The radioactivity is now released from the porapac-column and transferred with a helium flow of 10 ml/min into the zinc-furnace where it is transformed into carbon-isotope monoxide.   11. Before reaching the silica-column (cooled to −196° C.), the gas flow passes the ascarite-column. The carbon-isotope monoxide is now trapped on the silica-column. The radioactivity in the silica-column is monitored and when the value has peaked, V 3  is set to position B and then V 4  is set to position B.   12. The silica-column is heated to approximately 50° C., which releases the carbon-isotope monoxide. V 3  is set to position A and the carbon-isotope monoxide is transferred to the reaction chamber  50  within 15 s.   13. V 3  is set to position B, V 5  is set to position B, the HPLC-pump is turned on (flow 7 ml/min) and V 6  is set to position B. Using the pressurised THF (or other solvent), the reaction mixture is transferred to the reaction chamber  50 . When the HPLC-pump has reached its set pressure limit (e.g 40 Mpa), it is automatically turned off and then V 6  is set to position A.   14. UV spot light source  110 , magnetic stirrer  201  and magnet stirring bar  106  in reaction chamber  50  are turned on.   15. After a sufficient reaction-time (usually 5 min), V 3  is set to position C and the content of the reaction chamber  50  is transferred to a collection vial.   16. The reaction chamber  50  can be rinsed by the following procedure: V 3  is set to position B, the HPLC-pump is turned on, V 6  is set to position B and when maximal pressure is reached V 6  is set to position A and V 3  is set to position  3  thereby transferring the rinse volume to the collection vial.       

     With the recently developed fully automated version of the reaction chamber  50  system according to the invention, the value of [ 11 C]carbon monoxide as a precursor for  11 C-labelled tracers has become comparable with [ 11 C]methyl iodide. Currently, [ 11 C]methyl iodide is the most frequently used  11 C-precursor due to ease in production and handling and since groups suitable for labeling with [ 11 C]methyl iodide (e.g. hetero atom bound methyl groups) are common among biologically active substances. Carbonyl groups, which can be conveniently labeled with [ 11 C]carbon monoxide, are also common among biologically active substances. In many cases, due to metabolic events in vivo, a carbonyl group may even be more advantageous than a methyl group as labeling position. The use of [ 11 C]carbon monoxide for production of PET-tracers may thus become an interesting complement to [ 11 C]methyl iodide. Furthermore, through the use of similar technology, this method will be applicable for synthesis of  13 C and  14 C substituted compounds. 
     EXAMPLES 
     The invention is further described in the following examples which are in no way intended to limit the scope of the invention. 
     Example 1 
     Precursors and Resultant Products 
     Precursors that were used to label acids are shown in List. 1. 
                                
List 1. Iodides Used as Precursors in the Synthesis of Labeled Acids
 
     The following experiments illustrate the present invention. Radical carboxylation using submicromolar amounts of [ 11 C]carbon monoxide is performed yielding labeled with the acids shown in Table 1 as target compounds. 
     
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Radiochemical yields for  11 C-labelled acids 
               
             
          
           
               
                   
                   
                   
                   11 CO 
                   
                 Isolated 
               
               
                   
                   
                 Base 
                 conv. 
                 Yield b   
                 Yield 
               
               
                 Labelled compound a   
                 Solvents 
                 (mmol) 
                 (%) 
                 (%) 
                 (%) 
               
               
                   
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 DMSO 
                 TEA 
                 25 
                 N/A 
                 34 
               
               
                   
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 DMSO 
                 TEA 
                 82 
                 64 
                 50 
               
               
                   
               
               
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 DMSO DMSO/THF (1:9) 
                 TEA TEA 
                 81 74 
                 69 67 
                 59 58 
               
               
                   
               
               
                 C 16 H 33 [ 11 C]O 2 H 
                 DMSO/THF (2:3) 
                 TEA 
                 86 
                 67 
                 N/A 
               
               
                   
               
               
                   a The position of  11 C label is denoted by * and  13 C substitution by †. 
               
               
                   b Decay-corrected radiochemical yield determined by LC. 
               
             
          
         
       
     
     Example 2 
     Experimental Setup 
     [ 11 C]Carbon dioxide production was performed using a Scanditronix MC-17 cyclotron at Uppsala Imanet. The  14 N(p,α) 11 C reaction was employed in a gas target containing nitrogen (Nitrogen 6.0) and 0.1% oxygen (Oxygen 4.8), that was bombarded with 17 MeV protons. 
     [ 11 C]Carbon monoxide was obtained by reduction of [ 11 C]carbon dioxide as described previously (Kihlberg, T.; Långström, B.  Method and apparatus for production and use of [   11   C]carbon monoxide in labeling synthesis. Swedish Pending Patent Application No.  0102174-0). 
     Liquid chromatographic analysis (LC) was performed with a gradient pump and a variable wavelength UV-detector in series with a β + -flow detector. An automated synthesis apparatus, Synthia (Bjurling, P.; Reineck, R.; Westerberg, G.; Gee, A. D.; Sutcliffe, J.; Långström, B.  In Proceedings of the VIth workshop on targetry and target chemistry ; TRIUMF: Vancouver, Canada, 1995; pp 282-284) was used for LC purification of the labelled products. 
     Radioactivity was measured in an ion chamber. Xenon-mercury lamp was used as a photo-irradiation source. 
     In the analysis of the  11 C-labeled compounds, isotopically unchanged reference substances were used for comparison in all the LC runs. 
     NMR spectra were recorded at 400 MHz for  1 H and at 100 MHz for  13 C, at 25° C. Chemical shifts were referenced to TMS via the solvent signals. 
     LC-MS analysis was performed with electrospray ionization. 
     Solvents: THF was distilled under nitrogen from sodiuni/benzophenone; all other solvents were commercial grade, The solvents were purged with helium. 
     Alkyl iodides were commercially available or otherwise prepared from commercial allyl bromides by the Finkelstein reaction. 
     Example 3 
     Preparation of [carboxyl- 11 C] Acids 
     General procedure. Triethylamine (25 μL) was placed in a capped vial (1 mL, flushed beforehand with nitrogen to remove oxygen) and dissolved in DMSO (500 μL). An alkyl or aryl iodide (0.1 mol) was added to the solution ca. 7 min before the start of the synthesis. The resulting mixture was pressurized (over 40 MPa) into the micro-autoclave (270 μL), pre-charged with [ 11 C]carbon monoxide (10 −8 -10 −9  mol) mixed with He. The mixture was irradiated with a UV source for 6 min with stirring at 35° C. The crude reaction mixture was then transferred from the autoclave to a capped vial, held under reduced pressure. After measurement of the radioactivity the vial was purged with nitrogen and the radioactivity was measured again. The crude product was diluted with acetonitrile or methanol (0.6 mL) and injected on the semi-preparative LC. Analytical LC and LC-MS were used to assess the identity and radiochemical purity of the collected fraction. 
     Specific Embodiments 
     Citation of References 
     The present invention is not to be limited in scope by specific embodiments described herein. Indeed, various modifications of the inventions in addition to those described herein will become apparent to these skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims. 
     Various publications and patent applications are cited herein, the disclosures of which are incorporated by reference in their entireties.

Technology Classification (CPC): 2