Patent Description:
[<NUM>F]-labelled pyridaben derivatives are known that find use in determining the presence or absence of a cardiovascular disease or condition in a subject. Methods for the synthesis of these [<NUM>F]-labelled pyridaben derivatives are described in <CIT> and comprise nucleophilic [<NUM>F]-fluorination of an imaging agent precursor to form an imaging agent. The synthesis of an injectable composition comprising the compound [<NUM>F]-flurpiridaz ([<NUM>F]-FPZ) is described wherein the method comprises nucleophilic [<NUM>F]-fluorination of a tosylate precursor compound, dilution with water followed by high-performance liquid chromatography (HPLC) purification. <CIT> relates to a method for the production of an 18F-labelled compound wherein the production comprises a hydrolytic deprotection step of the 18F-labelled compound.

Finding a purification method for [<NUM>F]-FPZ that avoids HPLC is highly desirable and would result in easier accessibility for commercial application. However, efforts to achieve this up to now have been hindered by the presence of an acetyl impurity that elutes very close to the desired product that to date can only be precisely removed using a purification method comprising HPLC.

The present invention provides a method comprising:.

In another aspect the present invention provides a cassette for carrying out the method as defined in Claim <NUM> comprising:.

The method and cassette of the invention are particularly useful where the crude reaction mixture includes one or more impurities have very similar chromatographic elution times. Purification using SPE alone is permitted such that the requirement for HPLC in the purification process is obviated.

To more clearly and concisely describe and point out the subject matter of the claimed invention, definitions are provided hereinbelow for specific terms used throughout the present specification and claims. Any exemplification of specific terms herein should be considered as a non-limiting example.

The terms "comprising" or "comprises" have their conventional meaning throughout this application and imply that the agent or composition must have the essential features or components listed, but that others may be present in addition. The term 'comprising' includes as a preferred subset "consisting essentially of" which means that the composition has the components listed without other features or components being present.

A "precursor compound" comprises a non-radioactive derivative of a radiolabelled compound, designed so that chemical reaction with a convenient chemical form of an in vivo-detectable label occurs site-specifically; can be conducted in the minimum number of steps (ideally a single step); and without the need for significant purification (ideally no further purification), to give the desired in vivo imaging agent. Such precursor compounds are synthetic and can conveniently be obtained in good chemical purity.

By the term "biological targeting moiety" (BTM) is meant a compound which, after administration, is taken up selectively or localises at a particular site of the mammalian body in vivo. Such sites may for example be implicated in a particular disease state or be indicative of how an organ or metabolic process is functioning.

The term "alkylene" refers to the bivalent group -(CH<NUM>)n- wherein n is preferably an integer from <NUM>-<NUM>.

The term "alkoxyalkylene" means an alkylene as defined above comprising an ether linkage, where the term "ether linkage" refers to the group -C-O-C-.

The term "leaving group" refers to an atom or group of atoms that is displaced as a stable species during a substitution or displacement radiofluorination reaction. Suitable leaving groups for the present invention are sulfonate-containing leaving groups, where "sulfonate" means -SO<NUM>.

The term "<NUM>F-fluoride" refers to <NUM>F-fluoride in a chemical form suitable for displacing LG of Formula I in a nucleophilic substitution reaction to result in a compound of Formula II. <NUM>F-fluoride is normally obtained as an aqueous solution from the nuclear reaction <NUM>O(p,n)<NUM>F and is made reactive by the addition of a cationic counterion and the subsequent removal of water. Suitable cationic counterions should possess sufficient solubility within the anhydrous reaction solvent to maintain the solubility of <NUM>F-. Suitable counterions include large but soft metal ions such as rubidium or caesium, potassium complexed with a cryptand such as Kryptofix™ <NUM> (K222), or tetraalkylammonium salts. A suitable tetraalkylammonium salt is tetrabutylammonium hydrogen carbonate. A detailed discussion of well-known <NUM>F labelling techniques can be found in <NPL>.

The term "solid phase extraction (SPE)" refers to the well-known sample preparation process by which compounds in a solution are separated from each other based on their respective affinities for a solid (the "solid phase", or "stationary phase") through which the sample is passed and the solvent (the "mobile phase" or "liquid phase") in which they are dissolved. The result is that a compound of interest is either retained on the solid phase or in the mobile phase. The portion that passes through the solid phase is collected or discarded, depending on whether it contains the compound of interest. If the portion retained on the stationary phase includes the compound of interest, it can then be removed from the stationary phase for collection in an additional step, in which the stationary phase is rinsed with another solution known as an "eluent". For the present invention SPE is suitably carried out using at least one "SPE cartridge" (also often referred to as an "SPE column"), a variety of which are readily available commercially and typically as a column packed with solid phase. Most known solid phases are based on silica that has been bonded to a specific functional group, e.g. hydrocarbon chains of variable length (suitable for reverse-phase SPE), quaternary ammonium or amino groups (suitable for anion exchange), and sulfonic acid or carboxyl groups (suitable for cation exchange). SPE in the context of the present invention specifically excludes HPLC. In one embodiment two SPE cartridges fluidly connected in series are used in the present invention.

The "organic solvent" suitably comprises a solvent known to those of skill in the art for SPE elution, for example tetrahydrofuran (THF), ethyl acetate and dichloromethane (DCM), dimethylformamide (DMF), acetonitrile (MeCN), dimethyl sulfoxide (DMSO), acetic acid, t-butanol, isopropanol, n-propanol, ethanol (EtOH) and methanol (MeOH). The organic solvent may be provided as an aqueous solution of said solvent.

The term "hydrolysing reagent" refers to a reagent capable of hydrolysis wherein "hydrolysis" is a technical term well known to those of skill in the art, i.e. a reaction involving the breaking of a bond in a molecule using water, where the reaction mainly occurs between an ion and water molecules and often changes the pH of a solution. In chemistry, there are three main types of hydrolysis: salt hydrolysis, acid hydrolysis, and base hydrolysis.

In one embodiment of the invention said BTM is a small molecule. The small molecule in one embodiment is an analogue of pyridaben. Methods to obtain suitable pyridaben analogues are known in the art.

In one embodiment certain compounds of Formula I can be obtained following or adapting the processes described in <CIT>, starting with etherification of the starting compounds comprising formulae:
<CHM>
where n is <NUM>,<NUM>,<NUM>,<NUM>, or <NUM>; R<NUM> is alkyl, optionally substituted; R<NUM> is hydrogen or halide; R<NUM> can be the same or different and are alkyl, heteroalkyl, or a carbonyl-containing group, each optionally substituted, R<NUM> is hydroxyl or halide; and R<NUM> is alkyl, heteroalkyl, or a carbonyl-containing group, each optionally substituted, wherein, when R<NUM> is hydroxyl, at least one of R<NUM> and R<NUM> comprises a leaving group; or wherein R<NUM> is halide, at least one of R<NUM> or R<NUM> comprises a hydroxyl, to produce a compound comprising formula:
<CHM>
wherein W is alkyl or heteroalkyl, optionally substituted; R<NUM> is alkyl, optionally substituted; R<NUM> is hydrogen or halide; each R<NUM> can be the same or different and is alkyl optionally substituted with hydroxyl or heteroalkyl optionally substituted with hydroxyl; wherein at least one R<NUM> comprises hydroxyl; and n is <NUM>,<NUM>,<NUM>,<NUM>, or <NUM>; R<NUM> is alkyl, optionally substituted; R<NUM> is hydrogen or halide; R<NUM> can be the same or different and are alkyl, heteroalkyl, or a carbonyl-containing group, each optionally substituted. Then reacting this compound with a sulfonate-containing species such that at least one R<NUM> is converted to alkyl substituted with a sulfonate-containing group or heteroalkyl substituted with a sulfonate-containing group. This sulfonate-containing compound is a precursor compound of Formula I. The sulfonate-containing precursor can then be reacted with <NUM>F-fluoride to obtain compounds of Formula II.

In one embodiment of the invention, said precursor compound is a compound of Formula la:
<CHM>
and said <NUM>F-labelled compound is a compound of Formula IIa:
<CHM>
wherein:.

In one embodiment R<NUM> of Formula la and Formula IIa is C<NUM>-<NUM> alkyl.

In one embodiment R<NUM> of Formula la and Formula IIa is methyl, ethyl, propyl, n-butyl, s-butyl, or t-butyl.

In one embodiment R<NUM> of Formula la and Formula IIa is halo.

In one embodiment R<NUM> of Formula la and Formula IIa is chloro.

In one embodiment W of Formula la and Formula IIa is heteroalkylene.

In one embodiment W of Formula la and Formula IIa alkoxyalkylene.

In one embodiment of the invention, said compound of Formula I is a compound of Formula Ib:
<CHM>
and said compound of Formula II is a compound of Formula IIb:
<CHM>
wherein R<NUM>, R<NUM>, LINKER and LG are as variously defined herein for Formula I and Formula II.

In one embodiment of the invention, said compound of Formula I is:
<CHM>
wherein LG is as variously defined herein; and said compound of Formula II is:
<CHM>.

In one embodiment of the invention LG is selected from mesylate, tosylate, triflate, nosylate, or <NUM>,<NUM>-cyclic sulfate.

In one embodiment of the invention LG is tosylate.

In one embodiment of the invention, said wash solution comprising an organic solvent of step (c)(iii) comprises <NUM>-<NUM>% of said organic solvent in water. In certain embodiments, as will be known to a person skilled in the art, the mobile phase used with the SPE cartridge will depend on choice of SPE cartridge. For example, in one embodiment where the SPE is an Affinisep polymer, aqueous acetonitrile is a suitable organic solvent, for step (iii), a non-limiting example of which would be <NUM>% acetonitrile and <NUM>% water. The eluent for the same SPE cartridge can be aqueous ethanol, a non-limiting example of which is <NUM>% ethanol and <NUM>% water. In one embodiment when the SPE is C18, an ethanol-based organic solvent for step (iii) and for elution can be used. As a non-limiting example <NUM>-<NUM>% ethanol in water for the solvent for step (iii) followed by ethanol elution, which can be less than <NUM>% ethanol.

In one embodiment said wash solution comprising an organic solvent of step (c)(iii) comprises <NUM>-<NUM>% of said organic solvent in water.

In one embodiment said wash solution comprising an organic solvent of step (c)(iii) comprises acetonitrile, methanol or ethanol.

In one embodiment said wash solution comprising an organic solvent is an aqueous solution of acetonitrile.

In one embodiment said aqueous solution of acetonitrile comprises <NUM>-<NUM>% acetonitrile, preferably <NUM>% acetonitrile.

In one embodiment said wash solution comprising an organic solvent is an aqueous solution of methanol.

In one embodiment said aqueous solution of methanol comprises <NUM>-<NUM>% methanol, preferably <NUM>-<NUM>% methanol.

In one embodiment said wash solution comprising an organic solvent is an aqueous solution of ethanol.

In one embodiment said aqueous solution of ethanol comprises <NUM>-<NUM>% ethanol.

In one embodiment said elution solution of step (v) comprises <NUM>-<NUM>% ethanol.

In one embodiment said elution solution of step (v) comprises <NUM>-<NUM>% ethanol, preferably <NUM>-<NUM>% ethanol and most preferably <NUM>% ethanol.

In one embodiment said elution solution of step (v) comprises <NUM>-<NUM>% ethanol, preferably <NUM>-<NUM>% ethanol, most preferably <NUM>% ethanol.

In one embodiment said ethanol of step (v) comprises <NUM>-<NUM>% ethanol.

In one embodiment said hydrolysing reagent is added to said crude reaction mixture in step (b).

In one embodiment said hydrolysing reagent is comprised in said water of step (ii).

In one embodiment said hydrolysing reagent is comprised in said water of step (iv) and steps (ii) and (iii) are repeated before carrying out step (v).

In one embodiment said SPE cartridge is selected from a tC18 SPE cartridge and a mixed mode SPE cartridge.

In one embodiment said SPE cartridge is a tC18 cartridge.

In one embodiment said method further comprises a step before step (v) of passing a solution comprising an organic solvent through said SPE cartridge and a fluidly connected second SPE cartridge and wherein step (v) is carried out with said second SPE cartridge.

In one embodiment, said SPE cartridge and said second SPE cartridge are selected from Affinisep "P3 polymer", Waters tC18 and UCT C18.

In one embodiment, said hydrolysing reagent is acidic. Any suitable acid may be used. In one embodiment said acidic hydrolysing reagent comprises hydrochloric acid, sulphuric acid or phosphoric acid.

In one embodiment, said acidic hydrolysing reagent is HCl.

In one embodiment, said hydrolysing reagent is alkaline. Any suitable base may be used. In one embodiment, alkoxide, alkali metal hydroxides, or thiooxide bases can be used. In a further embodiment, the base is selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium hydride, sodium thiomethoxide, sodium ethoxide, ammonia/ammonium hydroxide and sodium methoxide.

In one embodiment, said alkaline hydrolysing reagent is selected from NaOH, NH<NUM>OH and NaOMe. In another embodiment, said alkaline hydrolysing reagent is NaOH.

In one embodiment, step (c) includes prior to step (i) passing said diluted crude reaction mixture through a separate SPE cartridge configured to retain lipophilic components. In one embodiment said separate SPE cartridge is selected from a tC18 cartridge, or a polymeric cartridge from Affinisep.

In one embodiment, step (c) includes following step (v) passing said purified solution through a separate SPE cartridge configured to retain lipophilic components.

In one embodiment of the method of the invention (<NUM>,<NUM>,<NUM>,<NUM>-Tetramethylpiperidin-<NUM>-yl)oxyl (TEMPO) is included in reacting step (a). In one embodiment TEMPO is present in a molar ratio to the precursor compound of between <NUM>:<NUM> and <NUM>:<NUM>, preferably between <NUM>:<NUM> and <NUM>:<NUM>, most preferably between <NUM>:<NUM> and <NUM>:<NUM>, especially preferably around <NUM>:<NUM>, e.g. <NUM>:<NUM>.

The method of the invention can be carried out using an automated synthesizer apparatus. By the term "automated synthesizer" is meant an automated module based on the principle of unit operations as described by <NPL>). The term "unit operations" means that complex processes are reduced to a series of simple operations or reactions, which can be applied to a range of materials. Such automated synthesizers are commercially available from a range of suppliers including: GE Healthcare; CTI Inc; Ion Beam Applications S. (Chemin du Cyclotron <NUM>, B-<NUM> Louvain-La-Neuve, Belgium); Raytest (Germany) and Bioscan (USA).

An exemplary automated synthesizer carries out a radiosynthesis by means of a cassette. By the term "cassette" is meant a piece of apparatus designed to fit removably and interchangeably onto the automated synthesizer apparatus in such a way that mechanical movement of moving parts of the synthesizer controls the operation of the cassette from outside the cassette. Suitable cassettes comprise a linear array of valves, each linked to a port where reagents or vials can be attached, by either needle puncture of an inverted septum-sealed vial, or by gas-tight, marrying joints. Each valve has a male-female joint which interfaces with a corresponding moving arm of the automated synthesizer. External rotation of the arm thus controls the opening or closing of the valve when the cassette is attached to the automated synthesizer. Additional moving parts of the automated synthesizer are designed to clip onto syringe plunger tips, and thus raise or depress syringe barrels.

A typical cassette has several positions for reagents and several suitable for attachment of syringe vials of reagents or chromatography cartridges (e.g. SPE). The cassette always comprises a reaction vessel. Such reaction vessels are preferably <NUM> to <NUM><NUM>, most preferably <NUM> to <NUM><NUM> in volume and are configured such that <NUM> or more ports of the cassette are connected thereto, to permit transfer of reagents or solvents from various ports on the cassette. Preferably the cassette has <NUM> to <NUM> valves in a linear array, most preferably <NUM> to <NUM>, with <NUM> being especially preferred. The valves of the cassette are preferably each identical, and most preferably are <NUM>-way valves. The cassettes are designed to be suitable for radiopharmaceutical manufacture so are manufactured from materials of pharmaceutical grade and ideally also resistant to radiolysis.

In one embodiment the cassette is a disposable, single use cassette which comprises all the reagents, reaction vessels and apparatus necessary to carry out the method of the invention.

The cassette approach has the advantages of simplified set-up, reduced risk of operator error; improved GMP (Good Manufacturing Practice) compliance; multi-tracer capability; rapid change between production runs; pre-run automated diagnostic checking of the cassette and reagents; automated barcode cross-check of chemical reagents vs. the synthesis to be carried out; reagent traceability; single-use and hence no risk of cross-contamination, tamper and abuse resistance.

Therefore, in another aspect the present invention provides a cassette for carrying out the method as defined in Claim <NUM> where said cassette comprises:.

In one embodiment the cassette of the invention further comprises (xiii) a vessel containing TEMPO.

In one embodiment of the cassette of the invention the vessel containing the precursor compound contains the precursor compound in acetonitrile along with TEMPO in an amount as recited hereinabove for the method of the invention. Any feature of the cassette already recited in connection herein with the method of the invention has the same embodiments as described herein for the method of the invention.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.

[<NUM>F]-fluoride (ca. <NUM> GBq) was produced using a GE Medical Systems PETtrace cyclotron with a silver target via the [<NUM>O](p,n) [<NUM>F] nuclear reaction. Total target volumes of <NUM> - <NUM> were used. The radiofluoride was trapped on a Waters QMA cartridge (pre-conditioned with carbonate), and the fluoride was eluted with a solution of tetrabutylammnonium hydrogen carbonate (<NUM>) in water (<NUM>µL) and acetonitrile (<NUM>µL). Nitrogen was used to drive the solution off the QMA cartridge to the reaction vessel. The [<NUM>F]fluoride was dried for <NUM> minutes at <NUM> under a steady stream of nitrogen and vacuum. The precursor (<NUM>, synthesized according to known methods) in MeCN (<NUM>) was added to the dried [<NUM>F]-fluoride and the reaction mixture was heated at <NUM> for <NUM> minutes. The crude product was diluted with water (<NUM>) and analysed by HPLC.

The % of [<NUM>F]Flurpiridaz in the crude product was <NUM>% with <NUM>% of a late eluting radiolysis product (<FIG>). In once instance of the radiosynthesis the inventors observed only <NUM>% [<NUM>F]Flurpiridaz.

[<NUM>F]-fluoride (ca. <NUM> GBq) was produced using a GE Medical Systems PETtrace cyclotron with a silver target via the [<NUM>O](p,n) [<NUM>F] nuclear reaction. Total target volumes of <NUM> - <NUM> were used. The radiofluoride was trapped on a Waters QMA cartridge (pre-conditioned with carbonate), and the fluoride was eluted with a solution of tetrabutylammnonium hydrogen carbonate (<NUM>) in water (<NUM>µL) and acetonitrile (<NUM>µL). Nitrogen was used to drive the solution off the QMA cartridge to the reaction vessel. The [<NUM>F]-fluoride was dried for <NUM> minutes at <NUM> under a steady stream of nitrogen and vacuum. A mixture of the precursor (<NUM>) and TEMPO (<NUM>) in MeCN (<NUM>) was added to the dried [<NUM>F]-fluoride and the reaction mixture was heated at <NUM> C for <NUM> minutes. The crude product was diluted with water (<NUM>) and analysed by HPLC.

The % of [<NUM>F]Flurpiridaz in the crude product was <NUM>% with <NUM>% of the late eluting radiolysis product. The addition of TEMPO to the labelling reaction reduces the amount of the late eluting radiolysis product (<FIG>). The present inventors deduce from these results that even when carried out at high activity the addition of TEMPO to the radiolabelling reaction acts to reduce the late eluting radiolysis product.

[<NUM>F]-fluoride (ca. <NUM> GBq) was produced using a GE Medical Systems PETtrace cyclotron with a silver target via the [<NUM>O](p,n) [<NUM>F] nuclear reaction. Total target volumes of <NUM> - <NUM> were used. The radiofluoride was trapped on a Waters QMA cartridge (pre-conditioned with carbonate), and the fluoride was eluted with a solution of tetrabutylammnonium hydrogen carbonate (<NUM>) in water (<NUM>µL) and acetonitrile (<NUM>µL). Nitrogen was used to drive the solution off the QMA cartridge to the reaction vessel. The [<NUM>F]fluoride was dried for <NUM> minutes at <NUM> under a steady stream of nitrogen and vacuum. The precursor (<NUM>) in MeCN (<NUM>) was added to the dried [<NUM>F]-fluoride and the reaction mixture was heated at <NUM> C for <NUM> minutes. The crude product was diluted with <NUM> NaOH (<NUM>) and water (<NUM>) and left to stand for <NUM> seconds (see <FIG> for comparison of with and without NaOH hydrolysis). The crude product was then loaded onto a tC18 SPE cartridge (Waters, product number WAT036800) and purified using the method described below.

The SPE cartridge was washed with water (<NUM>) to wash away the acetonitrile, NaOH and hydrophilic chemical and radiochemical impurities. Then the SPE cartridge was washed with a <NUM>% ethanol solution in water (<NUM>) to remove the hydroxy impurity. After this, the first SPE cartridge was connected in series to a second SPE cartridge (Waters, product number WAT036800) and the two were washed with a <NUM>% ethanolic water solution (<NUM>) followed by a stream of nitrogen to transfer the [<NUM>F]Flurpiridaz onto the second cartridge and trap the more lipophilic chemical and radiochemical impurities. The second SPE cartridge was then eluted with a <NUM>% ethanolic solution (<NUM>) to elute the [<NUM>F]Flurpiridaz into the product vial. The <NUM> product vial was composed of water (<NUM>), ethanol (<NUM>) and ascorbic acid (<NUM>/mL). See <FIG> for a chromatogram of the SPE purified product with and without ascorbic acid present.

The non decay corrected yield was <NUM>%, resulting in a product with an RAC of <NUM>,<NUM> MBq/mL. The RCP of the final product was <NUM>%. Two radiolysis products were observed (<NUM>% and <NUM>% respectively). When ascorbic acid is excluded from the product vial, the RCP is <NUM>-<NUM>% (<FIG>).

The SPE cartridge was washed with water (<NUM>) to wash away the acetonitrile, NaOH and hydrophilic chemical and radiochemical impurities. Then the SPE cartridge was washed with a <NUM>% acetonitrile solution in water (<NUM>) to remove the hydroxy impurity. After this, the first SPE cartridge was connected in series to a second SPE cartridge (Waters, product number WAT036800) and the two were washed with <NUM>% acetonitrile (<NUM>) followed by a stream of nitrogen to transfer the [<NUM>F]Flurpiridaz onto the second cartridge and trap the more lipophilic chemical and radiochemical impurities. The second SPE cartridge was then eluted with a <NUM>% ethanolic solution (<NUM>) to elute the [<NUM>F]Flurpiridaz into the product vial. The <NUM> product vial was composed of water (<NUM>), ethanol (<NUM>) and ascorbic acid (<NUM>/mL).

The non decay corrected yield was <NUM>-<NUM>%, resulting in a product with an RAC of <NUM>,<NUM>-<NUM>,<NUM> MBq/mL. The RCP of the final product was <NUM>-<NUM>%. Two radiolysis products were observed (<NUM>% and <NUM>-<NUM>% respectively).

A FASTlab™ automated synthesizer (GE Healthcare Ltd) with cassette was used. The tC18 cartridge was obtained from Waters Limited (address as above). Precursor <NUM> was reacted with [<NUM>F]fluoride on the FASTlab™ according to Example <NUM> to give [<NUM>F]Flurpiridaz.

The cassette configuration is given in <FIG>. Three external solvent vials are used on the cassette for the SPE purification in addition to the formulation vial:.

In the following, P refers to the Position of the cassette. S2 and S3 refer to syringe <NUM> and syringe <NUM>:.

[<NUM>F]-fluoride (ca. <NUM> GBq) is produced using a GE Medical Systems PETtrace cyclotron with a silver target via the [<NUM>O](p,n) [<NUM>F] nuclear reaction. Total target volumes of <NUM> - <NUM> are used. The radiofluoride is trapped on a Waters QMA cartridge (pre-conditioned with carbonate), and the fluoride is eluted with a solution of tetrabutylammnonium hydrogen carbonate (<NUM>) in water (<NUM>µL) and acetonitrile (<NUM>µL). Nitrogen is used to drive the solution off the QMA cartridge to the reaction vessel.

The [<NUM>F]fluoride is dried for <NUM> minutes at <NUM> under a steady stream of nitrogen and vacuum. The precursor (<NUM>) in MeCN (<NUM>) is added to the dried [<NUM>F]-fluoride and the reaction mixture is heated at <NUM> for <NUM> minutes. The crude product is diluted with water (<NUM>) and loaded onto a tC18 SPE cartridge (Waters, product number WAT036800) and is purified using the method described below.

Claim 1:
A method comprising:
(a) reacting in acetonitrile a precursor compound of Formula I:

        BTM-LINKER-LG     (I)

wherein:
BTM is a biological targeting moiety;
LINKER is an alkylene or an alkoxyalkylene; and,
LG is a sulfonate-containing leaving group;
with <NUM>F-fluoride to obtain a crude reaction mixture comprising an <NUM>F-labelled compound of Formula II:

        BTM-LINKER-<NUM>F     (II)

wherein BTM and LINKER are as defined for Formula I;
(b) diluting the crude reaction mixture obtained in step (a) to obtain a diluted crude reaction mixture;
(c) purifying the diluted crude reaction mixture obtained in step (b) by means of one or more solid phase extraction (SPE) cartridges to obtain a purified compound of Formula II where said purifying comprises the sequential steps of:
(i) transferring said diluted crude reaction mixture to an SPE cartridge;
(ii) optionally passing water through said SPE cartridge;
(iii) passing a wash solution comprising an organic solvent through said SPE cartridge;
(iv) optionally passing water through said SPE cartridge to remove said organic solvent; and,
(v) passing an elution solution comprising ethanol through said SPE cartridge to elute said compound of Formula I from said SPE cartridge;
wherein step (b) includes adding a hydrolysing reagent to said crude reaction mixture and/or said water of step (ii) and/or step (iv) comprises a hydrolysing reagent; and
wherein said precursor compound is a compound of Formula Ia:
<CHM>
and said <NUM>F-labelled compound is a compound of Formula IIa:
<CHM>
wherein:
R' is an optionally substituted C<NUM>-<NUM> alkyl;
R<NUM> is hydrogen or halo; and
W is an optionally substituted alkylene or heteroalkylene.