Abstract:
A method of conducting radiofluorination of a substrate, includes: (a) contacting an aqueous solution of [ 18 F] fluoride with a polymer supported phosphazene base for sufficient time for trapping of [ 18 F] fluoride on the polymer supported phosphazene base; and (b) contacting a solution of the substrate with the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon obtained in step (a) for sufficient time for a radiofluorination reaction to take place.

Description:
[0001]    The present invention relates to a method of radiofluorination, in particular that can be used for dose-on-demand and/or bedside production of  18 F PET radiotracers. 
         [0002]    Positron emission tomography (PET) is an imaging method used to obtain quantitative molecular and biochemical information regarding physiological processes in the human body. The most common PET radiotracer in use is  18 F-fluorodeoxyglucose ( 18 F-FDG), a radiolabelled glucose molecule. PET imaging with  18 F-FDG allows the visualisation of glucose metabolism and has a broad range of clinical uses.  18 F is the most widely used positron emitter in the clinical environment. 
         [0003]      18 F fluoride is produced by the irradiation of water containing H 2   18 O with protons, resulting in the reaction  19 O(p,n) 18 F. Only a minor fraction of the  18 O is converted. For production efficiency and radiochemical purity, it is desirable to use water that is as highly enriched as possible. The  18 F isotope is then separated from the water and processed for reaction to produce a radiochemical agent, as, due to the high free energy of hydration of  18 F − , this species is nucleophilically inert in aqueous solution. Routinely, the removal of water is achieved by trapping  18 F −  on an ion exchange resin, eluting the trapped  18 F −  from the resin using a cryptand ligand and a base (for example Kryptofix 222-K 2 CO 3 ) dissolved in organic solvent, and removal of the water by repeated and time consuming azeotropic distillations, which process is unsuitable for miniaturisation. 
         [0004]    Improvement of the production of  18 F −  has been attempted. WO2008/128306 (Voccia et al) describes a method of removing water from the  18 F −  and providing it in an organic solvent suitable for conducting fluorination reactions, which method is conducted without the need for azeotropic distillation of water. This document teaches the use of a non-ionic solid support modified with a trapping agent which is a metal salt complex of a positively charged base such as a cryptand or polydentate amine ligand, which trapping agent is able to remain bound to the solid support in aqueous solution, but is released from the solid support when exposed to a polar aprotic solvent suitable for radiolabelling. Thus, the  18 F −  is bound to the solid support as a complex with the trapping agent, and is subsequently eluted in the chosen polar aprotic organic solvent in the form of an  18 F − -trapping agent complex. An intermediate elution step can eliminate the majority of the water while allowing the  18 F −  and trapping agent to remain bound to the solid support, if a suitable organic solvent is selected. The eluted  18 F − -trapping agent complex in solution in the polar aprotic solvent is suitable for conducting radiolabelling. 
         [0005]    Similarly, Lemaire et al (Angewandte Chemie Int Ed 2010, 49, 3161-3164) describe the elution of  18 F −  from a solid support using acetonitrile and a variety of bases such as BEMP, BTMG, P 2   Et  and P 4   tBu , followed by use of the eluted solution in the radiofluorination of a number of precursors of PET radiotracers. 
         [0006]    US2011/0006011 (Aerts et al) describes the trapping of  18 F −  on an anion exchange column, rinsing with organic solvent to remove water, and elution with an organic solution containing a tertiary alcohol and/or a phase transfer agent. The resulting solution can be used for radiolabelling reactions. 
         [0007]    KR20080078233 (Yoon et al) describes a method in which  18 F −  is trapped on a quaternary ammonium salt supported on a polymer support, the  18 F −  is eluted by a solution comprising a metal ammonium salt in an alcoholic solvent, and subsequently the eluted solution is reacted with an alkyl halide or alkyl sulphonate. 
         [0008]    U.S. Pat. No. 6,190,637 (Ino et al) describes a method of isolating  18 F −  from H 2   18 O by trapping it on a weakly basic anion exchange resin, and subsequently eluting it in the form of a complex with a phase transfer catalyst such as a cryptand. The eluted solution is an aqueous solution, and so the  18 F −  complex must be dried and redissolved in a suitable organic solvent before a radiolabelling reaction can be carried out. 
         [0009]    Schlyer et al (Appl Radiat Isot 1990, 41, 6, 531-533) also describes a method in which  18 F −  is isolated from H 2   18 O by binding to an anion exchange resin. The trapped  18 F −  is eluted from the resin using a dilute solution of caesium carbonate or potassium carbonate in water. 
         [0010]    US2006/0083677 (Brady et al) describes a method in which a precursor molecule for radiolabelling, in particular a benzothiazole compound, is bound to a solid support, and  18 F −  is contacted with the solid support and reacts with the precursor molecule by displacing the support to result in a labelled tracer molecule. 
         [0011]    WO2011/110994 describes a method of producing a radio tracer by nucleophilic displacement by  18 F −  of a labelled leaving group, and subsequent removal of unreacted precursor by use of an adsorbent recognising the labelled leaving group. 
         [0012]    Toorongian et al (Nucl Med Biol 1990, 17, 3, 273-279) describes the use of  18 F −  supported on a quaternary 4-(N,N-dialkylamino)-pyridinium functionalised polystyrene anion exchange resin for conducting radiofluorination reactions to produce radiolabelled  18 F-FDG. The  18 F −  is captured directly by the resin from H 2   18 O, acetonitrile is passed through the column to remove water from the resin, and an acetonitrile solution of the precursor compound for the radiofluorination passed through the column while heating in order to conduct the radiofluorination reaction. The resin columns are stated not to be reusable as the resin becomes strongly discoloured during normal reaction conditions, although the mechanism of decomposition of the resin is not known. 
         [0013]    Mathiessen et al (Chem Eur J 2011, 17, 7796-7805) describes the formation of phosphazenium hydrofluorides by trapping of gaseous HF, and H 18 F, by phosphazene bases. These phosphazenium hydrofluorides, in particular P 2   Et  and P 4   tBu  hydrofluorides, were used to carry out solution phase fluorination and radiofluorination reactions on alkyl halides and pseudohalides, and optimisation of the conditions for conducting the fluorination reactions was carried out. 
         [0014]    It is an aim of the present invention to provide an efficient method of trapping  18 F −  from aqueous solution and delivering it to a target molecule as a nucleophile. 
         [0015]    An aim of certain embodiments of the present invention is to provide such a method for preparation of radiotracers for PET imaging. 
         [0016]    An aim of certain embodiments of the present invention is to provide such a method that is suitable for bedside production of radiotracers, or other applications in which miniaturisation of the apparatus is desirable. 
         [0017]    An aim of certain embodiments of the present invention is to provide a method in which the apparatus can be re-used. 
         [0018]    An aim of certain embodiments of the present invention is to provide apparatus which is stable at room temperature. 
         [0019]    An aim of certain embodiments of the present invention is to remove the need for purification steps and/or the use of solution phase complexing agents in the generation and use of  18 F − . 
         [0020]    An aim of the present invention is to provide a method in which  18 F −  recovery and radiofluorination can take place within the same vessel or column. 
         [0021]    An aim of certain embodiments of the present invention is to provide more rapid methods of trapping  18 F −  and subsequent radiolabelling reactions, in particular to provide rapid on demand synthesis of radiotracers. 
         [0022]    An aim of certain embodiments of the present invention is to provide a disposable cartridge that can be used in the production of radiotracers. 
         [0023]    Accordingly, in a first aspect, the present invention provides a method of conducting radiofluorination of a substrate, comprising the steps of:
   (a) contacting an aqueous solution of [ 18 F] fluoride with a polymer supported phosphazene base selected from a phosphazene of the general formula   
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on polystyrene (P PS -P 2   R ), and a phosphazene of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on PEG-coated polystyrene (P PS-PEG -P 2   Bz ) for sufficient time for trapping of the [ 18 F] fluoride by the polymer-supported phosphazene base; and
   (b) contacting a solution of the substrate with the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon obtained in step (a) for sufficient time for a radiofluorination reaction to take place.   
 
         [0026]    Preferably, the radiofluorination method further comprises a step of preparing an aqueous solution of  18 F −  by  18 O(p, n)  18 F reaction in a cyclotron using enriched H 2   18 O water. 
         [0027]    Preferably, following step (a) and before step (b), residual water is removed from the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon by contacting it with a water-miscible solvent. The removal step may suitably be carried out by flowing the water miscible solvent over the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon, or by one or more iterations of immersing the polymer supported base having [ 18 F] fluoride trapped thereon in the water miscible solvent and then removing the water miscible solvent. Preferably, the water miscible solvent is selected from acetonitrile, THF, DMF and acetone. Suitably, the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon can be further dried by passing a flow of dry gas over it. 
         [0028]    Suitably, following step (a) and any drying steps, and prior to step (b), the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon can be contacted with organic solvent to allow for swelling of the polymer support. Preferably, the organic solvent is the same as the solvent used to prepare the substrate solution to be used in step (b). 
         [0029]    Preferably, the substrate solution is prepared using toluene, acetonitrile, dichloromethane or DMF as solvent. 
         [0030]    The substrate used in step (b) is an aliphatic or aromatic compound comprising a leaving group. The leaving group is suitably selected from the group consisting of fluorosulfonates, perfluoroalkysulfonates, alkanesulfonates, arenesulfonates, alkyl, perfluoroalkyl or arene esters, phosphate, sulphate or nitrate esters, alkyl or aryl diazonium salts, ammonium, tetraalkylammonium or pyridinium salts, ethers or thioethers, halogens (other than fluoride), nitro groups and diiodoaryliodonium salts. Preferably, the leaving group is selected from the group consisting of triflate, nosylate, mesylate, tosylate, chloride, bromide, iodide and nitro. Preferably, the compound comprising the leaving group is selected from naphthylethyl compounds, mannose, optionally substituted pyridine compounds and glycols. 
         [0031]    Preferably, the polymer supported phosphazene base is contained in a column. Suitably, the column can be re-used in more than one iteration of the method of the invention. Suitably, the column can be sealed and disposed of after a chosen number of iterations of the method of the invention. 
         [0032]    Preferably, where the polymer supported phosphazene base is of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on polystyrene, R is selected from the group consisting of methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl, pentyl, isopentyl, tert-pentyl, tert-octyl, and more preferably is selected from the group consisting of ethyl, tert-butyl and tert-octyl. 
         [0033]    Preferably, the polymer supported phosphazene base is selected from P PS -P 2   tBu    
         [0000]    
       
                 
         
             
             
         
       
     
       and P PS-PEG -P 2   Bz    
       [0034]    
       
                 
         
             
             
         
       
     
         [0035]    Preferably, step (b) comprises heating the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon in contact with the substrate solution to a temperature of from 50° C. to 120° C. 
         [0036]    Preferably, the product of the reaction in step (b) is isolated from the polymer supported phosphazene base. Where the polymer supported phosphazene base is contained in a column, this can be done by passing a suitable organic solvent, such as the solvent in which the substrate was dissolved, through the column. 
         [0037]    Preferably, following step (b), a purification step is conducted, in which the product of the reaction between the polymer supported phosphazene base having [ 18 F] fluoride trapped thereon and the substrate solution is contacted with a solid phase adsorbent. The solid phase adsorbent may conveniently be provided in a column or cartridge, in a known manner. 
         [0038]    Suitably, following step (b), the polymer supported phosphazene base can be cleaned for re-use by contact with an organic solvent, preferably the same solvent as that in which the substrate was dissolved, and optionally also by heating the polymer supported phosphazene base and solvent to a temperature of from 50° C. to 120° C. 
         [0039]    Suitably, more than one iteration of the steps (a) and (b), and, if desired, of one or more of the optional steps described above, may be carried out. 
         [0040]    In a second aspect, the present invention provides a method of preparation of a radiotracer for administration to a patient, comprising the radiofluorination method according to the first aspect of the invention, followed by a step of formulation of the product of step (b) for administration to the patient. Suitably, the formulation step comprises removal of the solvent from the product of step (b), which product may optionally have been purified as described in the first aspect of the invention, dissolution of the product in saline solution, and filtration of the saline solution through a sterile filter. 
         [0041]    In a third aspect, the present invention provides an apparatus for conducting radiofluorination reactions, such as those according to the first aspect of the invention, comprising a polymer supported phosphazene base selected from a phosphazene of the general formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on polystyrene (P PS -P 2   R ), and a phosphazene of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on PEG-coated polystyrene (P PS-PEG -P 2   Bz ) contained in a column. 
         [0042]    Preferably, where the polymer supported phosphazene base is of the formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    supported on PEG-coated polystyrene, R is selected from the group consisting of methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl, pentyl, isopentyl, tert-pentyl, tert-octyl, and more preferably is selected from the group consisting of ethyl, tert-butyl and tert-octyl. 
         [0043]    Preferably, the polymer supported phosphazene base is selected from P PS -P 2   tBu    
         [0000]    
       
                 
         
             
             
         
       
     
       and P PS-PEG -P 2   Bz    
       [0044]    
       
                 
         
             
             
         
       
     
         [0045]    Preferably, the apparatus further comprises one or more elements selected from: means, such as tubing, for connection of the column to other apparatus, such as a cyclotron, vessels containing solvents, substrate solutions, aqueous solutions of  18 F − ; means, such as tubing, for connection of the column to a gas line; one or more vessels for supply of solvent, substrate solution, aqueous solution of  18 F −  to the column, and for the collection of waste from the column; a second column containing solid phase adsorbent for purification of the product of the radiofluorination reaction; sealing means for isolating the column prior to disposal. 
         [0046]    Preferably, the column is for use in production of radiotracers, such as those according to the second aspect of the invention. 
         [0047]    In a fourth aspect, the present invention provides the use of a column according to the third aspect of the invention in conducting radiofluorination reactions, such as those according to the first aspect of the invention. 
         [0048]    Preferably, the use is in the production of radiotracers, such as those according to the second aspect of the invention. 
         [0049]    In a fifth aspect, the present invention provides an apparatus for production of a dose of a radiotracer for administration to a patient, which apparatus comprises:
   (a) a cyclotron;   (b) a radiosynthesis module, comprising a column according to the third aspect of the invention; and   (c) a formulation module.   
 
         [0053]    Preferably, the apparatus is shielded to prevent exposure of an operator to radiation. Preferably, the apparatus is arranged such that it can be operated remotely. 
         [0054]    Preferably, the cyclotron can operate at 7.8 MeV and is able to produce  18 F,  13 N and  11 C isotopes. However, any known cyclotron able to produce  18 F may suitably be used. 
         [0055]    Preferably, the radiosynthesis module further comprises one or more of: a heating element, a gas supply, syringe pumps, valve systems for control of the supply of gases and solutions to the column, and a second column containing solid phase adsorbent. 
         [0056]    Preferably, the formulation module comprises [apparatus for evaporation of solvent], such as a heating element and a supply of inert gas, provided in order that the solution can be heated under a flow of the inert gas; a vessel containing saline solution, [means for introducing the saline solution to the radiotracer], and a sterile filter. 
         [0057]    Suitably, the apparatus further comprises a quality control module, which suitably comprises a radio-HPLC, a gas chromatograph, and a pH meter. 
         [0058]    It is envisaged that preferred features described for one aspect of the invention may be combined with any other aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0059]      FIG. 1  shows a schematic representation of a dose-on-demand radiofluorination apparatus; 
           [0060]      FIG. 2  shows the apparatus for on-column  18 F −  recovery and radiofluorination; 
           [0061]      FIG. 3  shows a conceptual representation of on-column  18 F −  recovery and radiofluorination. 
       
    
    
     DETAILED DESCRIPTION 
       [0062]    Referring to  FIG. 1 , the dose-on-demand instrument  10  is a self-shielded, remotely operated instrument consisting of
       (1) a compact cyclotron  20  operating at 7.8 MeV and able to produce 18F, 13N, and 11C radioisotopes,   (2) a radiosynthesis module  30 , connected to the compact cyclotron and consisting of heating elements, gas line, syringe pumps, and a disposable radiochemical cartridge,   (3) A formulation module  40 ,   (4) A quality control module  50 .       
 
         [0067]    Referring to  FIG. 2 , the apparatus ( 100 ), ie the radiochemical cartridge included in the radiosynthesis module  30  of the dose-on-demand instrument  10 , comprises the following elements: the column ( 110 ), which performs [ 18 F] fluoride trapping and on-column radiofluorination, an optional solid phase extraction cartridge ( 120 ) for product purification, vessels to hold the substrate ( 130 ), [ 18 O] water (target water) ( 140 ), solvents ( 150 ), waste ( 160 ), waste [ 18 O] water ( 170 ) and the product ( 180 ), and the gas line ( 190 + 195 ). These elements are interconnected by tubing (arrows) and valves ( 135 ,  175 ,  185 ). 
         [0068]    The column ( 110 ) can be made of glass, such as borosilicate glass, or plastic, such as PTFE. The column is packed with appropriate polymer supported phosphazene base ( 113 ). Unreactive fillers, such as glass beads ( 111 ) and/or glass wool ( 112 ) can be optionally added to minimize the dead volume of the column. 
         [0069]    The said polymer supported phosphazene base ( 113 ) comprises a phosphazene base residue covalently bound to a solid phase support, which is insoluble in any solvents to be used in the process. Examples of suitable polymer support include, but are not limited to, polymers such as polyethylene, polystyrene, poly(ethylene terephthalate), polycaprolactam, poly(p-phenylene), polybenzimidazole, polyimide, poly(phenylene oxide), polyfluoroethylene, or any co-polymers or polyethylene glycol (PEG) derivatives of these. These polymers may be block grafted, and/or crosslinked with crosslinking agents, such as ethylene glycol diacrylate, N,N′-methylenebisacrylamide, divinylbenzene or any combination of these. The said polymer support may also comprise glass or silicon coated with such a polymer. Furthermore, said polymer support may also be in the form of small discrete particles such as beads, or as a coating on the inner surface of a cartridge or on a microfabricated vessel. 
         [0070]    A general structure for phosphazene bases is given below. The phosphazene residue can be optionally substituted with alkyl, aryl, benzyl or PEG groups, and/or any fluorinated derivatives thereof. The R 1 -R 15  groups can be a part of the same polymer or can be linked to the same or different polymers. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0071]    The polymer supported phosphazene base residue used in the present invention comprises a phosphazene with two or more phosphazene units (n≧0). 
         [0072]    The inventors have found that attempting fluoride trapping and subsequent fluorination of a substrate with a number of different polymer and glass supported bases occurs in good yield only with P PS -P 2   tBu  and P PS-PEG -P 2   Bz . Compounds such as P PS -P 2   Et+ Cl −  and P PS -P 2   Bz  are able to trap  18 F − , but are then unreactive towards the fluorination substrate. Bases such as diisopropylaminomethylbenzene supported on polystyrene, P-BEMP and G-P 2   Bz  were found to be unreactive towards trapping of  18 F −  from aqueous solution. These results differ from those that might be expected from the prior art: for example, BEMP is disclosed by Lemaire et al to trap and elute  18 F −  from aqueous solution; and P 2   Et  and P 2   tBu  hydrofluorides are taught to have similar reactivity towards fluorination reactions in solution. It is clear that the solid support has a significant effect on the reactivity of the supported base, as can be seen from the difference in reactivity between glass-supported (G-) P 2   Bz , polystyrene-supported (P PS -) P 2   Bz  and the same base supported on PEG-coated polystyrene (P PS-PEG -P 2   Bz ). These results are not P predictable based on the teachings of the prior art. 
         [0073]    It is expected that polymer supported phosphazene bases having a structure closely related to P PS -P 2   tBu  will also be useful in the present invention, as it is taught in Schwesinger et al that phosphazene bases of the following general formula have similar reactivity: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0074]    In use, the cartridge is unsealed and inserted into the radiosynthesis module  30  of the dose on demand apparatus  10 . It is then prepared for use by connecting its parts to the valves  135 ,  175 , and  185 , hosted by the dose on demand instrument. The connections use standard fittings, Luer locks and flanged PTFE tubing used in modern HPLC systems. The tubing is 1/16″ (1.59 mm) in diameter for liquid transfer and ⅛″ (3.18 mm) for gas transfer. The vessels  130 ,  140 ,  150 ,  160 ,  170  and  180  for reagents, solvents, starting materials and products are regular 10-100 mL vials made of borosilicate glass and fitted with rubber septa. These are connected to the valves  135 ,  175  and  185  via flanged tubing fitted with regular needles. The purification cartridge or cartridges  120  can be chosen from any commercially available solid phase extraction (SPE) cartridges based on silica, alumina, C18 or molecularly imprinted polymers and available from commercial vendors, such as Waters, Supelco, and Polyintell. A solution of substrate is loaded into vessel  130 , and solvent into vessel  150 . Gas line  195  is connected to a suitable gas supply. The aqueous solution of  18 F −  is then transferred from the cyclotron  20  in which it has been prepared in a known manner, and is introduced into the appropriate vessel  140 . As shown in step  220  of  FIG. 3 , valves  135  and  175  are then opened to allow the aqueous solution of [ 18 F] fluoride to flow to the said column  110 , containing phosphazene base bound to polymer support. The aqueous solution of  18 F −  can be allowed to flow through the column  110  at various flow rates, or alternatively, left on the column for a period of time enough to ensure sufficient absorption of [ 18 F] fluoride on to the phosphazene base. 
         [0075]    As shown in step  240  of  FIG. 3 , the residual water can then be removed from the column by a single-time or repeated rinsing of the column with dry organic solvent miscible with water, such as acetonitrile, THF, DMF or acetone, by opening valve  135  such that solvent can flow from vessel  150  and opening valve  175  such that the residual water can pass to waste vessel  170 . 
         [0076]    Further drying can be achieved by passing a flow of dry gas, such as air, nitrogen, argon or helium through the column. This can be achieved by opening valve  135  to permit gas flow from gas line  195  to the column, and opening valve  175  to permit gas flow from the column to pass to the gas exit line  190 . 
         [0077]    Once the column has been satisfactorily dried, valve  135  is opened to permit flow of the substrate solution from vessel  130  to the column. This is shown at step  250  of  FIG. 3 . The solution of substrate is then passed through the column at a suitable flow rate by opening valve  175  to permit the solution to flow from the column  110  towards the product vessel  180 , or alternatively, left on the column for a period of time previously determined to be enough to ensure a sufficient degree of substitution of the leaving group in the substrate by the [ 18 F] fluoride, by closing valve  175  once the desired quantity of substrate solution has entered column  110 . This reaction can be further assisted by heating the column to 50-120° C. The reaction step is shown at step  260  of  FIG. 3 . 
         [0078]    Prior to permitting flow of the substrate the column containing phosphazene base bound to polymer support may be optionally treated with an organic solvent to allow for swelling of the resin. This can be achieved by opening valve  135  so as to permit flow of solvent from vessel  150  to the column, and opening valve  175  to permit solvent leaving the column to pass to waste vessel  160 . 
         [0079]    A suitably substituted substrate is an aliphatic or aromatic compound comprising a leaving group. This leaving group may comprise, but is not limited to, fluorosulfate, perfluoroalkanesulfonates, such as triflate or nonaflate, alkane sulfonates, such as mesylate or tresylate, arenesulfonates, such as benzenesulfonate, tosylate, brosylate, nosylate, and trinosylate, the derivatives of alkyl and perfluoroalkyl esters, such as acetate and trifluoroacetate, the derivatives of arene esters, such as benzoate and p-nitrobenzoate, the derivatives of phosphate, sulphate and nitrate esters, alkyl or aryldiazonium salts, ammonium, tetralkylammonium and pyridinium salts, the derivatives of ethers and thioethers, such as phenolates, nitrophenolates, and thiophenolates, diiodoaryliodonium salts, nitro groups and halogens other than fluoride. 
         [0080]    The substrate can be dissolved in a suitable organic solvent, such as toluene, acetonitrile, dichloromethane, or DMF before applying to the column. 
         [0081]    After the reaction is taken to the desired degree of conversion, the reaction mixture is pushed from the column with a new portion of solvent, as shown in step  270  of  FIG. 3 . This is achieved by opening the valve  135  to allow solvent to flow from vessel  150  to column  110 , and opening valve  175  to allow the solution on the column to flow towards solid phase purification cartridge  120 . The cartridge  120  contains a solid phase suitable to adsorb any side products, starting material and other contaminants from the solution obtained from the column that must be removed prior to administration of the radiofluorinated product to a patient. The radiofluorinated product is eluted from cartridge  120  by continuing to pass solvent from vessel  150  through the system, and valve  185  is opened to permit flow of the product solution to product vessel  180 . When contaminants are eluted from the cartridge  120 , valve  185  is opened to permit flow of the eluted solution to waste vessel  160 . 
         [0082]    The purified product is then transferred to the formulation module where the organic solvent is evaporated, suitably by heating the solution and flowing an inert gas over it, and the product is dissolved in a saline solution and filtered through a sterile filter. The saline solution of the product is then passed to the quality control module, where it is analysed to determine that it is in a suitable condition to be administered to a patient, by analysis by radio-HPLC, gas chromatography and a pH meter. 
         [0083]    The column can be optionally cleaned in between the doses by opening the valves  150  and  175  and allowing the solvent from vial  150  to flow towards waste vessel  160 . The column  110  can be heated to 50-120° C. to assist desorption of impurities from the column. The column is then dried with a stream of gas. 
         [0084]    Once the apparatus has been used for the preparation of the desired number of doses of radiotracer, the disposable cartridge, consisting of the column and all the vessels and tubing described above are sealed and disconnected from the dose-on-demand apparatus  10  and are disposed of in a suitable manner. 
       EXAMPLES 
       [0085]    Materials and Equipment 
         [0086]    All solvents and reagents were purchased from Aldrich. Unless otherwise noted, diethyl ether, THF and toluene were distilled from sodium benzophenone; acetonitrile, dichloromethane, DMF, HMPA, tetramethylurea and mesitylene were dried over activated molecular sieves (220° C., 0.1 mbar, 4 hours) for at least 48 hours prior to use; hexane was used as received. Phosphazene base P 2   Et , phosphazene base P 2 - t Bu on polystyrene, polymer bound BEMP and diisopropylaminomethyl benzene supported on polystyrene were obtained from Aldrich. 
         [0087]    The columns were prepared using PTFE tubing (OD 0.25 inch (0.64 cm)) purchased from Aldrich. The glass beads (212-300 μm), used as neutral filler, were also purchased from Aldrich. All radiochemical yields were decay corrected.  18 F aqueous solutions were prepared by a  18 O(p,n) 18 F reaction in a GE PETtrace cyclotron using a 2.5 ml target of 95-98% enriched  18 O water irradiated by a 16.5 MeV proton beam at 55 μA for 60-90 min. RadioTLC was performed using Raytest MiniGita TLC-scanner. 
         [0088]    Column Preparation 
         [0089]    Polymer-P 2   t Bu (100 mg, P 2   t Bu loading 1.6 mmol/g resin) was mixed with glass beads (1200 mg) and packed in a PTFE tube. 
       Example 1 
       18 F −  Trapping and Radiofluorination of an Aliphatic Mesylate 
       [0090]    
       
                 
         
             
             
         
       
     
         [0091]      18 F −  trapping:  18 F −  (target water, 1.0 ml, 105 MBq) was mixed with water (3 ml) and passed through the column. MeCN (dry, 5 ml) was passed through the column at room temperature followed by MeCN (dry, 5 ml) by syringe pump (flow 30 ml/h, duration 10 min) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 98%. 
         [0092]    Radiofluorination: 1-(2-(methylsulfonyl)ethyl)naphthalene (56.0 mg, 224 μmol) was dissolved in toluene (dry, 5 ml) and passed through the column by syringe pump (flow 10 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 5 ml) was passed through the column by syringe pump (flow 20 ml/h, duration 15 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20). Radiochemical yield was 66% and radiochemical purity was 98%. 
       Example 2 
       18 F −  Trapping and Radiofluorination of an Aliphatic Tosylate 
       [0093]    
       
                 
         
             
             
         
       
     
         [0094]      18 F −  trapping:  18 F −  (fraction of target water, 1.0 ml, 311 MBq) was added to the column followed by water (5 ml). MeCN (dry, 5 ml) was passed through the column at room temperature followed by MeCN (dry, 5 ml) by syringe pump (flow 30 ml/h, duration 10 min) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 95%. 
         [0095]    Radiofluorination: 1-(2-tosylethyl)naphthalene (68.0 mg, 208 μmol) was dissolved in toluene (dry, 5 ml) and passed through the column by syringe pump (flow 10 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 5 ml) was passed through the column by syringe pump (flow 20 ml/h, duration 15 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20). Radiochemical yield was 64% and radiochemical purity was 92%. 
       Example 3 
       18 F −  Trapping and Radiofluorination of an Aliphatic Triflate (Mannose Triflate, FDG Precursor) 
       [0096]    
       
                 
         
             
             
         
       
     
         [0097]      18 F −  trapping:  18 F −  (target water, 1.5 ml, 460 MBq) was mixed with water (2 ml) and passed through the column. MeCN (dry, 2 ml) was passed through the column at room temperature followed by MeCN (dry, 8 ml) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 84%. 
         [0098]    Radiofluorination: Mannose triflate (50 mg, 100 μmol) was dissolved in toluene (dry, 4 ml) and passed through the column by syringe pump (flow 8 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 2 ml) was passed through the column by syringe pump (flow 10 ml/h, duration 12 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent benzene:MeCN 2:1). Radiochemical yield was 25% and radiochemical purity of acetylated  18 F FDG was 76%. 
       Example 4 
       18 F −  Trapping and Radiofluorination of a Nitrated Aromatic Compound 
       [0099]    
       
                 
         
             
             
         
       
     
         [0100]      18 F −  trapping:  18 F −  (target water, 0.5 ml, 201 MBq) was added to the column followed by water (5 ml). MeCN (dry, 5 ml) was passed through the column at room temperature followed by MeCN (dry, 5 ml) by syringe pump (flow 30 ml/h, duration 10 min) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 98%. 
         [0101]    Radiofluorination: 3-methoxy-2-nitropyridine (63.0 mg, 408 μmol) was dissolved in toluene (dry, 5 ml) and passed through the column by syringe pump (flow 10 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 5 ml) was passed through the column by syringe pump (flow 20 ml/h, duration 15 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent petroleum ether:EtOAc 3:1). Radiochemical yield was 14% and radiochemical purity was 45%. 
       Example 5 
       18 F −  Trapping and Radiofluorination of a Lipophilic Aliphatic Mesylate 
       [0102]    
       
                 
         
             
             
         
       
     
         [0103]      18 F −  trapping:  18 F −  (target water, 1.2 ml, 752 MBq) was mixed with water (5 ml) and passed through the column using a syringe pump (flow 20 ml/h, duration 9 min). MeCN (dry, 5 ml) was passed through the column at room temperature followed by another portion of MeCN (dry, 5 ml) by syringe pump (flow 30 ml/h, duration 10 min) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 92%. 
         [0104]    Radiofluorination: 2,3-bis(hexadecyloxy)propyl methanesulfonate (MsDHG, 63 mg, 101 μmol) was dissolved in toluene (dry, 5 ml) and passed through the column by syringe pump (flow 10 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 5 ml) was passed through the column by syringe pump (flow 20 ml/h, duration 15 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 95:5). Radiochemical yield was 1% and radiochemical purity was 5%. 
       Example 6 
       18 F −  Trapping and Radiofluorination of an Aliphatic Bromide 
       [0105]    
       
                 
         
             
             
         
       
     
         [0106]      18 F −  trapping:  18 F −  (target water, 0.5 ml, 721 MBq) was mixed with water (4.5 ml) and passed through the column at room temperature by syringe pump (flow 20 ml/h, duration 15 min). MeCN (dry, 5 ml) was passed through the column at 60° C. followed by another portion of MeCN (dry, 5 ml) by syringe pump (flow 20 ml/h, duration 15 min) while heating the column at 60° C. Argon gas was flushed through the column while heating at 60° C. until excess of solvent was removed. The  18 F −  trapping was 94%. 
         [0107]    Radiofluorination: NpEtBr (47.73 mg, 203 μmol) was dissolved in toluene (dry, 5 ml) and passed through the column by syringe pump (flow 10 ml/h, duration 30 min) while heating at 90° C. Toluene (dry, 2 ml) was passed through the column by syringe pump (flow 20 ml/h, duration 6 min) while heating at 90° C. to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20). Radiochemical yield was 16% and radiochemical purity was 61%. 
       Example 7 
     Investigation of Polymer Supported Bases in On-Column   18 F −  Trapping and Radiofluorination 
       [0108]    General Procedure: 
         [0109]    A borosilicate glass tube (OD 0.6 mm, length 12 cm) was packed with the polymer-supported base (100 μmol base) mixed with glass beads (212-300 μm, 100-500 mg) and placed in a column oven in a LabView controlled automation apparatus. 
         [0110]      18 F −  trapping:  18 F −  (target water, 3.5 mL, 500-5000 MBq) passed through the column at room temperature (flow 1.5 mL/min). MeCN (dry, 4 ml, flow 2 mL/min) was passed through the column at room temperature followed by a helium gas flush through the column until excess of solvent was removed. 
         [0111]    Radiofluorination: Toluene (dry, 4 mL, flow 2 mL/min) was passed through the column at room temperature followed by 1-naphthaleneethyl methanesulfonate (100 μmol, 25.03 mg) dissolved in toluene (dry, 3 mL) and passed through the column at 120° C. (flow 0.55 mL/min). Toluene (dry, 2 mL, flow 0.55 mL/min) was then passed through the column to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20) 
         [0112]    Synthesis of Polymer Supported Bases: 
         [0113]    Polymer-supported P 2   tBu  (1.6 mmol/g loading), BEMP (2.3 mmol/g loading) and diisopropylaminomethyl (3 mmol/g loading) were obtained from Sigma Aldrich. Amine-functionalized glass beads (30-50 micron, loading unknown) were obtained from Polysciences Europe GmbH. Benzylamine-functionalized polystyrene (0.8-1.2 mmol/g loading), and Merrifield resin (0.8-1.4 mmol/g) were purchased from Bachem. The amine-functionalized polystyrene resin with polyethylene glycol (PEG, 1500-2000 Da) spacer (TentaGel HL, particle size 160 μm, 0.4 mmol/g loading) was obtained from Rapp Polymere. 
         [0114]    The amine-functionalized resins/glass beads were reacted with P 2   Cl *BF 4  (1-chloro-1,1,3,3,3-pentakis(dimethylamino)-1λ 5 -diphosphazen-3-ium tetrafluoroborate) by mixing the support (200-1000 mg) with P 2   Cl *BF 4  (3 eq to amine) and Et 3 N (dry, 9 eq to amine) in DCM (dry, 5 mL) in a glass vial, which was sealed under vacuum. The reaction mixture was then heated with slight agitation at 90° C. for up to three days. This coupling procedure was repeated up to two times in order to ensure good coupling. The resulting resin was deprotonated by reacting the resin with a mixture of KOMe (1 eq to amine) in MeOH (dry, 5 mL) for one hour at room temperature in order to give the desired solid-supported phosphazene base. 
         [0115]    Alkylation of the Merrifield resin was done by mixing Merrifield resin with P 2   Et  (4 eq to chloride) in THF and shaking at room temperature for five days. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 On- 
                 On- 
               
               
                   
                   
                   
                   
                 column 
                 column 
               
               
                   
                   
                   
                 Chemical 
                   18 F -   
                 radio- 
               
               
                   
                 Structure 
                 Name 
                 class 
                 trapping 
                 fluorination 
               
               
                   
               
             
             
               
                 1 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 Diisopropyl- aminomethyl- benzene supported on polystyrene 
                 Non-ionic strong organic base  
                  0% 
                 0% 
               
               
                   
               
               
                 2 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 P-BEMP (2-  t Butylamino- 2-diethyl- amino-1,3- dimethyl- perhydro- 1,3,2-diaza- phosphorine on polystyrene 
                 Non-ionic phosphazene supported on propylene- diamine modified polystyrene 
                  0% 
                 0% 
               
               
                   
               
               
                 3 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 P PS -P 2   Bz  (from benzylamine- functional- ized polystyrene) 
                 Non-ionic phosphazene supported on polystyrene 
                 50% 
                 0% 
               
               
                   
               
               
                 4 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 G-P 2   Bz  (from amine- functionalized glass beads) 
                 Non-ionic phosphazene supported on glass beads  
                  0% 
                 0% 
               
               
                   
               
               
                 5 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 P PS -P 2   Et+ Cl −  (from Merrifield resin)  
                 Ionic phosphazene supported on polystyrene 
                 99% 
                 Trace 
               
               
                   
               
               
                 6 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 P PS -P 2   tBu  (Aldrich resin)  
                 Non-ionic phosphazene supported on polystyrene 
                 99% 
                 Good 
               
               
                   
               
               
                 7 
                 
                   
                             
                     
                         
                         
                     
                   
                 
                 P PS-PEG -P 2   Bz  (from PEG- coated polystyrene) 
                 Non-ionic phosphazene supported on polystyrene 
                 99% 
                 Good 
               
               
                   
               
             
          
         
       
     
       Example 8 
     Investigation of Radiofluorination of Different Substrates Using Polystyrene-Supported P 2   tBu    
       [0116]    General Procedure: 
         [0117]    A borosilicate glass tube (OD 0.6 mm, length 12 cm) was packed with PS-supported P 2   tBu  (150 μmol base, loading 1.6 mmol/g, 93.75 mg) mixed with glass beads (212-300 μm, 100-500 mg) and placed in a column oven in a LabView controlled automation apparatus. 
         [0118]      18 F −  trapping:  18 F −  (target water, 3.5 mL, 500-5000 MBq) passed through the column at room temperature (flow 1.5 mL/min). MeCN (dry, 4 ml, flow 2 mL/min) was passed through the column at room temperature followed by a helium gas flush through the column until excess of solvent was removed. 
         [0119]    Radiofluorination: Radiofluorination solvent (MeCN for mannose triflate, MeCN/tBuOH 1:5 for FLT-ONs, toluene for the naphthalene analogues and 2-nitro-3-methoxypyridine, dry, 4 mL, flow 2 mL/min) was passed through the column at room temperature followed by the substrate (50-100 μmol) dissolved in radiofluorination solvent (dry, 3 mL) and passed through the column at 120° C. (flow 0.55 mL/min). Radiofluorination solvent (dry, 2 mL, flow 0.55 mL/min) was then passed through the column to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20 for the naphthalene analogues, MeCN:H 2 O 95:5 for hydrolyzed FDG, DCM:MeOH 9:1 for hydrolyzed FLT, petroleum ether:EtOAc for the pyridine analogue). 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Radiochemical 
               
               
                 Entry 
                 Substrate 
                 Product 
                 Yield (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Mannose triflate 
                   18 F FDG 
                 40 
               
               
                 2 
                 FLT-ONs 
                   18 F FLT 
                 7 
               
               
                 3 
                 Naphthylethyl mesylate 
                   18 F NpEtF 
                 51 
               
               
                 4 
                 Naphthylethyl tosylate 
                   18 F NpEtF 
                 34 
               
               
                 5 
                 Naphthylethyl chloride 
                   18 F NpEtF 
                 16 
               
               
                 6 
                 Naphthylethyl bromide 
                   18 F NpEtF 
                 42 
               
               
                 7 
                 Naphthylethyl iodide 
                   18 F NpEtF 
                 18 
               
               
                 8 
                 2-nitro-3-methoxypyridine 
                   18 F 2-fluoro-3- 
                 23 
               
               
                   
                   
                 methoxypyridine 
               
               
                   
               
             
          
         
       
     
       Example 9 
     Investigation of Radiofluorination of Different Substrates using P PS-PEG -P 2   Bz    
       [0120]    General Procedure: 
         [0121]    A borosilicate glass tube (OD 0.6 mm, length 12 cm) was packed with P PS-PEG -P 2   Bz  (150 μmol base, loading 0.4 mmol/g, 375 mg) and placed in a column oven in a LabView controlled automation apparatus. 
         [0122]      18 F −  trapping:  18 F −  (target water, 3.5 mL, 500-5000 MBq) passed through the column at room temperature (flow 1.5 mL/min). MeCN (dry, 2 ml, flow 2 mL/min) was passed through the column at room temperature followed by MeCN (dry, 2 ml, flow 2 mL/min) at 50° C. 
         [0123]    Radiofluorination: Radiofluorination solvent (MeCN for mannose triflate, toluene for FLT-ONs, the naphthalene analogues and 2-nitro-3-methoxypyridine, dry, 4 mL, flow 2 mL/min) was passed through the column at 50° C. followed by the substrate (50-100 μmol) dissolved in radiofluorination solvent (dry, 3 mL) and passed through the column at 120° C. (85° C. for mannose triflate, flow 0.55 mL/min). Radiofluorination solvent (dry, 2 mL, flow 0.55 mL/min) was then passed through the column to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20 for the naphthalene analogues, benzene:MeCN 2:1 for unhydrolyzed FDG, EtOH:EtOAc 1:1 for unhydrolyzed FLT, petroleum ether:EtOAc for the pyridine analogue) 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Radiochemical 
               
               
                 Entry 
                 Substrate 
                 Product 
                 Yield (%) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Mannose triflate 
                   18 F FDG 
                 36 
               
               
                 2 
                 FLT-ONs 
                   18 F FLT 
                 5 
               
               
                 3 
                 Naphthylethyl mesylate 
                   18 F NpEtF 
                 38 
               
               
                 4 
                 Naphthylethyl tosylate 
                   18 F NpEtF 
                 24 
               
               
                 5 
                 Naphthylethyl chloride 
                   18 F NpEtF 
                 Trace 
               
               
                 6 
                 Naphthylethyl bromide 
                   18 F NpEtF 
                 Trace 
               
               
                 7 
                 Naphthylethyl iodide 
                   18 F NpEtF 
                 Trace 
               
               
                 8 
                 2-nitro-3-methoxypyridine 
                   18 F 2-fluoro-3- 
                 Trace 
               
               
                   
                   
                 methoxypyridine 
               
               
                   
               
             
          
         
       
     
       Example 10 
     Investigation of Reusability of the Polystyrene-Supported P 2   tBu  Radiofluorination Approach 
       [0124]    General Procedure: 
         [0125]    A borosilicate glass tube (OD 0.6 mm, length 12 cm) was packed with PS-supported P 2   tBu  (100-140 μmol base, loading 1.6 mmol/g) mixed with glass beads (212-300 μm, 100-500 mg) and placed in a column oven in a LabView controlled automation apparatus. Two columns, A and B, were prepared in this manner, and each was used for assessing reusability of the column. 
         [0126]      18 F −  trapping:  18 F −  (target water, 3.5 mL, 500-5000 MBq) passed through the column at room temperature (flow 1.5 mL/min). MeCN (dry, 4 ml, flow 2 mL/min) was passed through the column at room temperature followed by a helium gas flush through the column until excess of solvent was removed. 
         [0127]    Radiofluorination: Toluene, dry, 4 mL, flow 2 mL/min) was passed through the column at room temperature followed by the substrate (50 μmol) dissolved in toluene (dry, 3 mL) at 120° C. (flow 0.55 mL/min). Toluene (dry, 2 mL, flow 0.55 mL/min) was then passed through the column to elute the remaining product. The fluorinated product was analyzed by radio-TLC (eluent heptane:EtOAc 80:20). 
         [0128]    These procedures were repeated up to two times. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Exp. No. 
                 Column 
                 P—P 2   tBu  μmol 
                 Trapping % 
                 RCP % 
                 RCY % 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 First use 
                 A 
                 140 
                 100 
                 74 
                 43 
               
               
                 Second use 
                 A 
                 140 
                 100 
                 94 
                 69 
               
               
                 Third use 
                 A 
                 140 
                 100 
                 92 
                 61 
               
               
                 First use 
                 B 
                 100 
                 98 
                 80 
                 46 
               
               
                 Second use 
                 B 
                 100 
                 100 
                 89 
                 62 
               
               
                 Third use 
                 B 
                 100 
                 100 
                 93 
                 64