GB2435471A

GB2435471A - 11C & 18F-labelled carbamates as kappa-opioid receptor ligands in therapy or diagnosis

Info

Publication number: GB2435471A
Application number: GB0603884A
Authority: GB
Inventors: Gjermund Henriksen
Original assignee: Universitetet i Oslo
Current assignee: Universitetet i Oslo
Priority date: 2006-02-27
Filing date: 2006-02-27
Publication date: 2007-08-29
Also published as: WO2007096193A3; GB0603884D0; WO2007096193A2

Abstract

An <11>C or <18>F-labelled carbamate may be prepared by reacting a primary or secondary amine with optionally <11>C-labelled carbon dioxide and a compound of formula RX or R<1>X, ```wherein: <DL TSIZE=3> <DT>X<DD>is a leaving group <DT>R<DD>is a group which comprises an alkyl or alkylene group <DT>R<1><DD>is a group which comprises both an alkyl or alkylene group and an <18>F-label provided that when R is present, R and/or the carbon dioxide has a <11>C-labelled carbon atom. </DL> Also disclosed are compounds of formula: <EMI ID=1.1 HE=30 WI=110 LX=505 LY=1175 TI=CF> <PC>wherein the molecule is optionally further substituted, excluding such compounds wherein R is not <11>CH3. R is preferably alkyl and R<1> an <18>F-labelled alkyl. X is preferably halide or sulphonate ester (e.g. triflate). The process is preferably conducted in the presence of a carbonate (e.g. caesium carbonate) and an ammonium salt. The carbamate may be used in the treatment or diagnosis of drug addiction, Tourette's syndrome, epilepsy, psychosis or Alzheimer's disease.

Description

-. Radiolabelled carbamates This invention relates to a process for the

production of 8F or "C-labelled carbamates, to their uses in radiopharmaceutical evaluation and investigation, to their use in clinical studies in humans as well as to certain new 8F or "C-labelled carbamates themselves.

The carbamation of amines has been utilized in the synthesis of organic carbamates for many years. The literature comprises many different ways of forming carbamates from amines although many of these processes involve phosgene, a noxious gas whose use is now discouraged. The vast majority of carbamate syntheses described in the literature concern the formation of non radioactive species and the chemistry involved is therefore quite simple and process requirements are undemanding compared to synthesis of radioactive compounds.

Where, however, radioactive carbamates are being synthesised, especially with radionuclides of short half-life such as "C and "F, syntheses are much more complicated and the synthetic chemist is faced with a number of major challenges.

"C and "'F-labelled carbamates can be used in positron emission tomography (PET) to allow the non-invasive imaging of, inter alia, biological structures, particularly those of mammals. This can involve depiction and quantification of receptors and transporters. To be generally useful, a radiopharmaceutical based on short lived radionuclides such as "C and "'F, needs to be obtainable rapidly in high radiochemical yield and with high specific radioactivity. "C and "'F have relatively short physical half lives of 20.3 mm and 109.7 mm respectively, which means that any process for the manufacture of C or "'F-labelled compounds needs to occur in a short time period and be capable of providing the desired yields and specific activity of the compounds in question.

High radiochemical yield is obviously desirable in the same way that high yield is desirable in any organic synthesis. If more "C is incorporated into the final product then the amount of active compound formed is higher and there is less wasted expensive starting material.

1-ugh specific radioactivity is an important issue in PET studies where amount of tracer should be minimized to keep the biological system unperturbed.

Especially for compounds intended for use in quantifying receptors in the central nervous system (CNS), which often present at a relatively low concentration, these requirements are often limiting. Thus, these requirements impose significant limitations on the chemical-synthetical procedures used for the preparation of the "C or 8F-labelled compounds relative to non-radioactive compounds.

A further problem faced during the synthesis of "C or 8F labelled compounds is the possibility of side reactions, in conventional non radioactive synthesis, stoichiometric amounts of reactants would be used. This is often not possible in or 8F compound synthesis and there is typically considerable molar excess of reagents and reactants other than the or 8F -containing species. I'he difference in the molar ratio of the 11C or 8F-containing reagent relative to other reagents present in the reaction mixture (including the molecule or species to be radiolabelled, called the precursor for radiolabelling) can represent an important difference to procedures in which the stoichiometry of reagents is in the range normally encountered in the synthesis of non-radioactive compounds. In particular, due to the relatively low amount of' C or 8F -containing reactant present, impurities in the reaction mixture can, if they possess a comparable or higher reactivity than the precursor for radiolabelling, be an important loss of yield. Thus, side-reactions that are of low importance for a high yield of a given product in a non-radioactive syntheses, can be a limiting factor for "C and 8F-radiolabelling reactions.

A further issue with "C and 8F syntheses is the potential exposure of the chemist to radiation. and 8F syntheses of radiopharmaceuticals for use in PET are typically performed in lead shielded boxes (called hot-cells) and the manipulation of reagents, reactants and equipment is performed via a remote controlled apparatus (called the syntheses module). Under such conditions, the number of synthetic steps performed with the radioactivity present greatly affects the performance, including reliability and reproducibility, of the procedure. It is therefore advantageous to have as few steps in the procedure as possible in order to ensure a high performance of the radiosynthesis and reduce the complexity of the apparatus required.

"C and 8F-labelled carbamates may have utility in the evaluation of several biological targets. One example is the use of a or 8F - labelled carbamates for the investigation of kappa-opioid receptors (K-OR). The opioid receptors (ORs) belong to the superfamily of G protein-coupled receptors (GPCRs) that produce their effects by activation of intracellular G proteins. The kappa-opioid receptor (K-OR) is one of three well-defined classes of ORs. The central opioid system plays a role in several physiological and pathophysiological phenomena. Different drugs of abuse, such as heroine, cocaine and amphetamine stimulate dopamine release in the ventral striatum, which includes the nucleus accumbens. Striatal dopamine release is stimulated by K-OR-activation, the center of origin of mesolimbic dopaminergic projections to the ventral striatum, and inhibited by striatal K-OR. Moreover, dynorphin-mediated K-OR-activation may represent a homeostatic mechanism that limits cocaine-induced dopamine release in the ventral striatum. It is also likely that during cocaine withdrawal, K-OR-activation contribute to dysphoric mood states and thus increase the relapse risk.

In vivo brain imaging with K-OR selective radioligands has the potential to allow assessment of the opioidergic system in drug-dependent humans, to examine the psychologic correlates of its functional state, and to develop new strategies to target drug effects and alleviate drug addiction. The K-OR has also been implied in Alzheimer's disease, Tourette's syndrome, and epilepsy. It is thus extremely interesting for commercial and academic researchers to compare the neurologic and psychologic correlates of K-OR function across these different neurological and psychiatric disorders and to explore potential neuroprotective effects with molecular imaging.

Several opioid receptor (OR) radiotracers are currently available for PET in humans, including ["C]carfentanil, [8F]diprenorphine, [h1 C]buprenorphine, [8F]fluorocyclofoxy and "C-inethyl]naltrindole but none is selective for the kappa-opioid receptors (K-OR).

(+)-4-Methoxycarbonyl-2-[( I -pyrrolidinylmethyl] -1 -[(3,4-dichlorophenyl)acetyl]-piperidine (GR89696) NN-f

CI

* stereoccntre is a highly potent and selective K-OR agonist (J Med Chem 36, 2075-83, 1993 Naylor et a!). The (-)-isomer, (-)-4-methoxycarbonyl-2-[(1-pyrrolidinylmethyl]-1 -[(3,4-dichlorophenyt)acetyl]-piperidine, also known as GR103545, is the more potent optical isomer of GR89696. In Nucl. Med Biol 1999, 26:737-741, Ravert et a!. reported the radiolabelling of the racemic [ C]GR89696 using the reaction of"C methyl chloroformate with the normethylcarbamoyl GR 89696 (i.e. GR89696 without the COOCH3 group).

The synthetic procedure is based on reacting the amine precursor in question with ["C]methyl chloroformate obtained via reduction of cyclotron produced ["C]carbon dioxide to ["C]methanol followed by reaction with phosgene. A recent report of the synthesis of ["C]GR103545 indicated the method to give only a very low radiochemical yield of the product (-2 %) and low specific activity of 5.55 to 18.3 lGBq/imol (l50-49OmCi4imol) in a syntheses time of -50 mm after end-of-bombardment. (Talbot et al. J Nucl Med 2005; 46:484-494).

Both these factors severely limit the applicability of the compound for preclinical and clinical use. Moreover, for the preparation of radiopharmaceuticals for use in PET-investigations using remote controlled syntheses, a high operational complexity is limiting and disadvantageous. This methodology for "C-carbamate formation is limited by the need for complex procedures and the reaction also relies on the use of toxic phosgene.

It has now been surprisingly found that 11C or 8F-labelled carbamates can be prepared in high yield and rapidly by the conversion of an amine to a carbamate in a one-pot, two-step reaction sequence comprising reacting carbon dioxide with a primary or secondary amine followed by reaction of the intermediate with an alkylating agent. The reaction can be performed in two ways: i) using radioactive ["C]C02 in the first step and a non-radioactive alkylating agent in the second or ii) using non-radioactive CO2 in the first step and a radioactive alkylating agent in the second, for example a "C or 8F-labelled alkylating agent.

The reaction is particularly effective when the amine reacts in the presence of a carbonate and/or an ammonium salt, especially in the presence of excess carbon dioxide.

Thus, viewed from one aspect the invention provides a process for the preparation of a 11C of 8F-labelled carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula RX or R'X, preferably in the presence of a metal carbonate and an ammonium salt, wherein X represents a leaving group; R represents an alkyl or alkylene containing group; R' represents an alkyl or alkylene containing group which group comprises a 8F-label; and said group R and/or the carbon dioxide has a "C-labelled carbon atom.

Viewed from another aspect the invention provides a process for the preparation of a "C-labelled carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula RX, preferably in the presence of a metal carbonate and an ammonium salt, wherein X represents a leaving group; and R represents an alkyl or alkylene containing group; said group R and/or the carbon dioxide having a "C-labelled carbon atom.

Viewed from another aspect the invention provides a process for the preparation of a 8F-labelled carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula R1X, preferably in the presence of a metal carbonate and an ammonium salt, wherein R' represents an alkyl or alkylene containing group which group comprises a 8F-label; and X represents a leaving group.

Viewed from another aspect the invention provides a or 8F-labelled carbamate prepared by a process as hereinbefore described. Viewed from another aspect, the invention provides a pharmaceutical composition containing such a carbamate, e.g. a pharmaceutically acceptable solution of said carbamate.

Viewed from another aspect, the invention provides the use of a "C or 8F-labelled carbamate prepared by the process of the invention in the manufacture of a medicament /radiopharmaceutical for use in a method of diagnosis or treatment, such as a method for investigation of the status of receptors in the CNS.

Investigation of K-opioid receptors may allow the diagnosis or treatment of diseases, such as those of the central nervous system. Specific diseases/conditions which could be treated or diagnosed include drug abuse and drug addiction, pathological pain, Tourette's syndrome, epilepsy, psychosis, hallucinations, or neurodegenerative diseases such as Parkinson's and Alzheimer's disease and prion-mediated disease.

Viewed from another aspect the invention provides a method of diagnosis or treatment of a condition/disease as described above comprising administering to a patient a carbamate made by the process of the invention and detecting the presence of the carbamate in the patient (e.g. using PET).

As used herein a carbamate is a compound comprising the linkage -N-CO-O-R where the group R contains a "C-labelled carbon atom and/or the carbony! carbon is "C labelled. It will be appreciated however that it is highly preferred if only one carbon atom is labelled. A 8F labelled carbamate will comprise the linkage -N-CO-O-R' with an 8F label in the R' group. Again, whilst it is possible that, for example, "C labelled CO2 could be used to give a label in this linkage, preferably 8F is the only radio centre in the molecule (i.e. non radioactive carbon dioxide is employed in the synthesis when the compound R'X is utilised).

The group X is a leaving group. The skilled chemist is aware of numerous leaving groups regularly used in organic synthesis and any of these may be used here. Preferred leaving groups are listed in standard text books such as Jerry March, Advanced Organic Chemistry and include alkoxys, halides and sulphonate esters. Preferred halides are chloride and iodide. Preferred sulphonate esters are brosylate, nosylate, mesylate, nonaflate, tresylate, triflate or tosylate, especially triflate, tosylate or mesylate. Halides and sulphonate esters are preferred in particular suiphonate esters of low molecular mass. Preferably therefore X is iodide or triflate, especially triflate (trifluoromethane sulphonyl CF3SO2O).

The leaving group X is preferably bound to a saturated aliphatic carbon atom in the group R or R'. Hence the group must contain an alkyl group or alkylene group. Thus, the R!R' group must comprise at least an alkyl group such as methyl or alkylene group such as -CH2-from which the leaving group X can be substituted.

The group R can also contain many other functional groups such as aryl, cycloalkyl, heterocyclic groups as well as functionalities such as hydroxyl, and other non nucleophilic and non electrophilic groups. R can therefore vary considerably as long as other functional groups present therein do not interfere with the desired carbamate formation reaction.

Whilst it is possible for the "C label to be introduced via the carbon dioxide, better yields are obtained when non-radioactive carbon dioxide is employed and the "C label is introduced into the carbam ate through the R group. Preferably therefore, the R group contains a carbon atom. The "C-label is preferably present on a saturated aliphatic carbon atom, especially the atom which binds to the leaving group X. Preferred groups R are C,2o hydrocarbyl groups, more preferably C,,0-hydrocarbyl groups. Representative groups R therefore include "C-labelled benzyl (e.g. "CH2-Ph) and 11C-labelled ethylphenyl (e.g. "CH2CH2-Ph).

Most preferably however, R is any "C-labelled alkyl group, preferably a C,7 alkyl group, especially linear alkyl group such linear C,7 alkyl group, e.g. a "C-ethyl or a "C-labelled methyl group.

Highly preferred groups RX are therefore "C labelled C,.7 alkyl halides or sulphonates esters, especially methyl halides or methyl sulphonate esters. Most preferably, RX is labelled methyl iodide or "C-labelled methyl triflate.

When a 8F labelled carbamate is required, it is necessary to use an alkylating agent of formula R'X. It will be appreciated that in this reaction, it is highly preferred if the carbon dioxide used is non radioactive. The group R' comprises an 8F label as opposed to a "C label which can be present in the group R but can otherwise have the same structure. Preferred groups R' are therefore a C.20 hydrocarbyl group carrying an substituent, more preferably C,.,0-hydrocarbyl group carrying an 8F substituent. Representative groups R therefore include 8F-labelled benzyl (e.g. 8FCH2-Ph) and 8F-Iabelled ethyiphenyl (e.g. 8FCI-12CH2-Ph).

Most preferably however, R' is any 8F-labelled alkyl group, preferably a C1 alkyl group carrying an 8F substituent, especially 8F-labelled linear alkyl group such linear C7 alkyl group carrying an 8F substituent. It is preferred, if possible, that the 8F substituent is attached to a different carbon atom than the leaving group x.

Especially preferred groups R' are [8F]fluoromethyl, 2-[8F]fluoroethyl, 3- [1 8F]-fluoropropyl, 4-[ 8F]fluorobutyl, 5-[I 8F}fluoropentyl 6-[ 8F]-fluoroehexyl and 7-['8F]fluoroheptyl and isomer thereof.

8F is a poor leaving group so it is easily possible to avoid substitution of the radioactive atom by the use of an X group which is a more potent leaving group.

Halides such as iodide, bromide and chloride as well as the sulphonate esters are all much better leaving groups than F. It is preferred if the reaction of the carbon dioxide, amine and compound RX/R'X is effected in the presence of a metal carbonate. The metal carbonate can be formed from any metal in the periodic table such as a Al, a transition metal or rare earth metal. Preferably, however the metal carbonate is from group (I) or (II) especially group (I). Highly preferably, the carbonate is sodium, potassium or caesium carbonate, especially caesium carbonate.

It is preferred if the reaction of the carbon dioxide, amine and compound RX/R'X is effected in the presence of an ammonium salt. The ammonium salt may be of formula NR'4Y where each R' is independently hydrogen, aryl or an C110 alkyl. Preferably, R' is an C1 alkyl group such as methyl, ethyl, propyl, isopropyl, n-butyl (Bu) or tertbutyl. Most preferably all R' groups are the same. A highly preferred ammonium ion is NBu4.

The group Y can be any suitable counterion such as a halide ion, or sulphonate ester anion, e.g. as described above. Y is preferably iodide or triflate (OSO2CF3). Highly preferred ammonium salts are therefore NBu4I and NBu4Tf.

Ideally, both a metal carbonate and an ammonium salt will be employed.

The amounts each reagent used will be readily determined by the skilled man. It will be appreciated that all reagents/reactants other than the radio labelled material will likely be in excess. A typical quantity, in terms of activity from a alkylating agent, is in the range of 37OMBq-37GBq (lOmCi-lCi) (although it is possible to have starting activities of less than 37OGBq too). The typical specific activity of a "C-alkylating agent is 1000-6000mCi/.imol (37-222 GBqIimol). Thus, the quantity of the "C-species used in a typical labelling would be in the range l0nmol-l p.mol.

It is preferred also if there are molar excesses of the ammonium salt and the carbonate relative to the amine. Thus the molar ratio of amine to ammonium salt andlor carbonate may be 2 to 10, preferably about 2 to 5, especially around 3.

Carbon dioxide is preferably present in excess (assuming it is non radioactive).

The reaction occurs very rapidly. Thus, the time between addition of the radiolabelled material to starting isolation of the target material may be less than 10 mins, preferably less than 5 minutes. High yields are obtained in the examples in as little as 2 minutes. The overall reaction time from the end of bombardment (i.e. from the formation of the radiolabelled starting material), to isolation of the desired carbamate can be less than 45 mins, preferably less than 40 mins.

The reaction can be carried out at any desired temperature but it is preferred if the reaction is not heated. It has been found that the best yields of carbamate are achieved at ambient temperature (i.e. 25 C). Preferably therefore the reaction temperature is in the range 15 to 40 C, preferably 20 to 35 C.

Typically, the reaction will take place in a non protic solvent. The skilled chemist can select any known non-protic solvent but preferred solvents include DMF, THF, DMSO or acetamide. DMF is preferred.

The radiochemical reaction yield is preferably at least 10%, more preferably at least 20%, e.g. at least 25%, especially at least 30 %. Yields of greater than 50%, e.g. greater than 60% can also be achieved.

The reactions described herein are preferably effected with no carrier added.

"C-labelled starting materials can be prepared by conventional techniques typically from cyclotron produced 1C-labelled carbon dioxide. For example, "C-labelled methylene iodide can be prepared from cyclotron produced "C-labelled CO2 by a catalytic iodination reaction via "C-labelled methane as is well known in the art. Conversion to the triflate is achieved readily, e.g. as described in the examples. Alternative procedure is the "wet phase" iodination, reduction of C02 to methanol with LAH followed by HI treatment (see fx. Stone-Elander et al. J Med Chem 1985 Sep;28(9):1325-8.

8F labelled starting materials can be prepared using published techniques such as described previously by Henriksen et al. (J Labeld Compds Radiopharm.

2005; 48: 77 1-779) and Iwata et al. (Appi Radiat Isot. 2002;57:347-352), for [I fluoroethyl tosylate and [8F}fluromethyl bromide, respectively.

The amine on which this reaction is carried out can vary greatly but it needs to be a primary or secondary amine. Ideally, the amine will be free of other functional groups which would interfere with carbamate formation, e.g. other highly nucleophilic functionalities unless protecting groups are introduced on such functionalities. The amine can however comprise all manner of organic structures such as alkyl, alkenyl, alkynyl, aryl, heterocycles, and groups such as esters, epoxides, ethers, halides etc. The person skilled in the art will appreciate that this technique is broadly applicable and the nature of the amine on which the reaction is carried out is not critical as long as the reactive amine group is primary or secondary.

In a highly preferred embodiment, the amine on which the reaction is carried out is the normethylcarbamoyl of( ) GR 89696, (+)GR 89696 or (-) GR89696 (also known as GR103545) (i.e. GR89696 without the COOCH3 group).

Thus, viewed from another aspect the invention provides a process for the conversion of a compound of formula (II) /-\ c çr NJNH (II) to a "C-labelled or 8F labelled carbamate of formula (iii) or (iv) N"N_f NN_f2 CI CI (J\ (iii) (iv) ( represents a chiral centre which may be (+), (-) or racemic) comprising reacting said compound of formula (II) with a compound RX or R'X as hereinbefore defined and carbon dioxide, preferably in the presence of a metal carbonate and an ammonium salt.

Preferably R represents "C labelled methyl group. Preferably the metal carbonate is caesium carbonate. Preferably the ammonium salt is NBu4Tf or NBu4I.

Preferably X is triflate or a halide.

This process for the manufacture of GR89696, in particular its (-) enantiomer GR103545, yields the compounds in higher labelling yields and higher specific activities than previously have been obtainable.

This technique is, of course, applicable to other similar amino compounds.

Viewed from another aspect therefore, the process of the invention may be carried out on an optionally substituted amine of formula (V)

N NH

\____/ (V) The amine of formula (V) may carry a wide variety of substituents although again, these should not interfere with the reaction claimed. Any nucleophilic substituents should therefore be protected. The skilled man will appreciate that all manner of substitutions could be made to this backbone.

It is preferred however, if the phenyl ring carries at least one halide substituent, e.g. two halides. Preferably, these are chlorides, most preferably meta and para to the acetyl linker. The piperazine ring may be substituted by a group (CH2) NR3R4 wherein R3 or R1 independently represents a hydrocarbyl group (e.g. a C,6 hydrocarbyl group such as a C16 alkyl group) or both R3 and R4 taken together form an optionally substituted non aromatic hydrocarbyl ring, e.g. a live or 6 membered ring, which may be saturated or unsaturated. This ring may itself have substituents such as halides, hydroxyl, oxo, alkyl, alkenyl, alkoxy, alkyl ester, or CCO2Ci6alkyl.

The invention also encompasses compounds having the backbone of formula (V) which have undergone the process claimed to form a 18 F or 11C labelled carbamate. Viewed from another aspect therefore, the invention provides an optionally substituted, "C or 8F labelled compound of formula (VI) or (VII) (Vi) (VII) where RIR' are as hereinbefore defined with the proviso that R is not "CH The compound GR89696 or an enantiomer thereof "C labelled on the ester carbonyl is of particular interest and also forms an aspect of the invention.

Since the reaction described here is carried out in one pot, it lends itself to ready automation using conventional techniques. The reaction claimed can therefore be readily carried out in hot-cells thus minimising exposure of workers to hazardous radiation.

8F and "C-labelled carbamates formed by the process of the invention can be formed into medicaments and used as radioligands for imaging, in particular for imaging the ic-opioid receptors. Imaging of this system may allow advances in the treatment and/or diagnosis of various conditions such as drug abuse and drug addiction, pathological pain, I'ourett&s syndrome, epilepsy, psychosis, hallucinations, or neurodegenerative diseases such as Parkinson's and Alzheimer's disease and prion-mediated disease. The opioid system is also critical in addiction and psychosis and the assessment of this system in individuals with these ailments may allow new diagnoses to be made. Individuals addicted to alcohol, cocaine, amphetamines and opioid based drugs such as heroin may benefit from treatments or diagnoses made using the carbamates of the invention.

The carbamates of the invention can be used immediately after lbrmation in the techniques described above. Since time is so critical in the use of these compounds, they will typically be administered by injection in a saline solution.

The skilled worker in this field is aware of the necessary injection protocols and dosages which needto be used.

The carbamates are of particularly utility in PET and the invention further comprises therefore the use of the carbamates of the invention in the manufacture of a medicament /radiopharmaceutical and formulation thereof for use in a method of diagnosis using positron emission tomography.

The invention will now be described with reference to the following non-

limiting examples.

Example 1.

NH C02, [11C]methyl iodide Cs2CO3, TBAI DMF 1 2 Carbamate 2 was found in moderate yield (range 18-36 %) via the three component coupling of amine 1, C02, and [ "C]methyl iodide. Full results are presented in Table 1. Here, 2 mg of! was dissolved in 300 gi of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium iodide.

CO2 (15 ml/min) was bubbled through the solution for one hour. Cyclotron produced ["C]C02 was converted to [ C]CH3I by the catalytic gas-phase iodination reaction via ["C]CI-14. ["C]CI-131, swept with a He-flow at 50 mi/mm into the reaction vial. The reaction mixture was allowed to stir at different temperatures for different time intervals up to 5 mm. Aliquots drawn from the reaction mixture were analyzed by means of UV/radio-HPLC. Product identity was confirmed by coelution of the radioactive product with authentic, non radioactive, 2.

Example 2

C02, [1C]methyI triflate Cs2CO3, TBATf, DMF H 1 2 Carbamate 2 was found in high yields (range 54-72 %) through the three component coupling of amine I, C02, and [ "C]methyl triflate. Full results are presented in Table 1. Here, 2 mg of! was dissolved in 300 lii of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium trifluoromethane sulfonate. CO2 (15 mllmin) was bubbled through the solution for one hour. Cyclotron produced ["C]C02 was converted to ["C]C1131 by the catalytic gas-phase iodination reaction via [ C]CH4. ["C JCI-131, swept with a He-flow at 50 mi/mm through a column of 1.6mm internal diameter, length 50 mm column filled with silver triflate and thereafter into the reaction vial. The reaction mixture was allowed tostir at different temperatures for different time intervals up to 5 mm.

Aliquots drawn from the reaction mixture were analyzed by means of UV/radio-HPLC. Product identity was confirmed by coelution of the radioactive product with authentic non radioactive 2.

Table 1. Reaction yield' of N-benzyl methyl-carhamate (2) under various conditions Tetrabutyl Methylation Reaction Reaction Yield of ammonium reagent temperature time carbamate compound2 ( C) interval product (mm) (%) TBAI ["CJCH3I 25 5 36 TBAI ["C]CH3I 50 5 21 TBAI ["C] CH3I 70 5 18 TBATf ["C]CH3I 50 5 25 TBATf [HC]CH3I 70 5 19 TBATf [11C]CII3OTf 25 2 69 TBATf tC1CH3OTf 25 5 72 TBATf ["C]CH3O'l'f 35 2 62 Analytical yield as measured by radio-HPLC. 2 TBAI = tetrabutyl ammonium ioidide, TBATf = tetabutyl ammonium trifluoromethane sulfonate.

Example 3.

N'N_f ç;j( NiN H

CI CI 3 4

The fumarate acid salt of 3 (GR89696) 75 mg (0.14 mmol) was dissolved in I'HF (4 mL) and heated and stirred at reflux. Bu4NF (1.8 mL, 1 M in TI-IF) was added and the reaction mixture was refluxed for 5 h. After cooling, a solution of K2C03 satd.

(10 mL) was added and the aqueous phase was extracted with EtOAc (3 xl 0 mL).

The combined organic layers were dried over MgSO4, filtered and the solvent was removed under reduced pressure. The resulting oil was purified by chromatography using kieselgel 60 (0.040-0.063 mm) n-hexane and ethyl acetate as eluents (50:50, volume/volume). The fractions containing the products were combined and solvent was removed under reduced pressure yielding 4 (41 mg, 82 %).

Example 4

In preparation for "C-labeling reactions, 2 mg of the 4 was dissolved in 300 p1 of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium iodide. CO2 (15 mI/mm) was bubbled through the solution for one hour. Cyclotron produced [I C]C02 was converted to ["C1CH3I by the catalytic gas-phase iodination reaction via L"CJCH4. ["C]C113l, swept with a lie-flow at 50 mi/mm into the reaction vial. The reaction mixture was allowed to stir at different temperatures for different time intervals up to 5 mm. Aliquots were drawn from the reaction mixture and analyzed by means of UV/radio-HPLC. Product identity was confirmed by coelution of the radioactive product with authentic 3.

Example 5

2 mg of 4 was dissolved in 300 p1 of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium trifluoromethane sulfonate. CO2 (15 mI/mm) was bubbled through the solution for one hour.

Cyclotron produced ["C]C02 was converted to ["CJCH3I by the catalytic gas-phase iodination reaction via ["C]CH4. In some experiments ["CJCH3I, swept with a He-flow at 50 mI/mm through a column of 1.6mm internal diameter, length 50 mm column filled with silver triflate and thereafter into the reaction vial. The reaction mixture was allowed to stir at different temperatures for different time intervals up to 5 mm. Aliquots were drawn from the reaction mixture and analyzed by means of UV/radio-HPLC. Product identity was confirmed by coelution of the radioactive product with authentic 3. Results are presented in 1'able 2.

Table 2. Reaction yield' of GR89696 (3) under various conditions Tetrabutyl Methylation Reaction Reaction Yield of ammonium reagent temperature time interval product (%) compound2 TBATf ["C]CH3I 25 5 34 TBATf ["C]CFI3OTf 25 2 65 TBA'l'f ["CJCH3OTf 25 5 69 Analytical yield as measured by radio-HPLC. 2 TBATf= tetrabutyl ammonium trifluoromethane sulfonate.

Example 6

2 mg of the 4 was dissolved in 300.il of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium trifluoromethane sulfonate. CO2 (15 ml/min) was bubbled through the solution for one hour.

Cyclotron produced ["CJCO2 was converted to CJCH3I by the catalytic gas-phase iodination reaction via ["C]CH4. ["C}CH3I, swept with a He-flow at 50 ml/min through a column of 1.6mm internal diameter, length 50 mm column filled with silver triflate and thereafter into the reaction vial. The reaction mixture was stirred at ambient temperature for 2 mm. The mixture was added 1 ml of a mixture consisting of acetonitrile 0.1 M ammonium formiate (25:75, v/v) and purified by preparative HPLC on a j.t-Bondapak 10 mm internal diameter, length 250 mm, 5 pm particles, eluted with acetonitrile: 0.1 M ammonium formate ( 25:75, v/v) at a flow rate of 8 ml/min The product eluting at 12.3 mm were collected. Product identity of[11C]3 was confirmed by coelution with authentic 3 as analyzed by UV/radio-HPLC.

["C]3 was isolated in a radiochemical yield of 58 4 %, a specific activity in the range of 1247-1562mCi/ jtmol in a syntheses time of 32 mm after end-of-bombardment, and with a radiochemical purity of> 97 %.

Example 7

The 8F-fluoroalkylating agents 2-['8F]fluoroethyltosylate and [8F]fluoromethyl bromide were prepared as described previously by Henriksen et al. (J. Labeld.

Compds. Radiopharm. 2005; 48: 77 1-779) and Iwata et al. (Appi Radiat Isot.

2002;57:347-352), respectively.

2 mg of I was dissolved in 300 il of DMF containing 3 molar equivalents of Cs2CO3 and 3 molar equivalents of tetrabutyl ammonium trifluoromethanc sulfonate. CO2 (15 mI/mm) was bubbled through the solution for one hour. After addition of the 8F-fluoroalkylating agent in question, the reaction mixture was allowed to stir at different temperatures for different time intervals. Aliquots drawn from the reaction mixture were analyzed by means of UV/radio-HPLC.

NH2 CO2,I18CH2Br NHAOCH218F Cs2CO3, TBAOTf, DMF 1 5 co2,l CH2CH2OTs NHAOCH2CH218F Cs2CO3, TBAOTf, DMF 1 6 Carbamic acid derivatives 5 and 6 was found in yields within the range of 2-23 % via the three component coupling of amine 1, CO, and 8F-fluoroalkylation agents.

Full results are presented in Table 3.

Table 3. Reaction yield' of N-benzyl -8F-fluoroalkyl-carbamic acid derivatives under various conditions Tetrabutyl Fluoro-alkylating Reaction Reaction Yield of ammonium reagent temperature time carbamate compound2 ( C) interval product (mm) (%) TBAO'l'f [F]CH2Br 70 10 7 i'BAOTf [8F]CH2Br 50 10 11 TBAOTf [8F]CH2Br 35 5 18 TBAOTf [8F]CH2Br 35 10 23 TBAOTf [8F]CH2CH2OTs 70 10 <3 TBAO'l'f [18F]CH2CH2OTs 50 5 6 TBAOTf [8F]CH2CH2OTs 50 1 10 TBAOTf [8FJCH2CH2OTs 50 15 12 Analytical yield as measured by radio-HPLC. 2 TBAOTf tetrabutyl ammonium trifluoromethane sulfonate.

Claims

Claims 1. A process for the preparation of a 11C of 8F-labelled

carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula RX or R'X, wherein X represents a leaving group; R represents an alkyl or alkylene containing group; R' represents an alkyl or alkylene containing group which group comprises a 8F-label; and said group R and/or the carbon dixoide has a "C4abelled carbon atom.

2. A process as claimed in claim I for the preparation of a "C-labelled carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula RX, wherein X represents a leaving group; and R represents an alkyl or alkylene containing group; said group R and/or the carbon dioxide having a 1'C-labelled carbon atom.

3. A process as claimed in claim 1 for the preparation of a 8F-labelled carbamate comprising reacting a primary or secondary amine with carbon dioxide and a compound of formula R'X, wherein R' represents an alkyl or alkylene containing group which group comprises a 8F-label; and X represents a leaving group.

4. A process as claimed in any preceding claim wherein X is a halide or sulphonate ester.

5. A process as claimed in any preceding claim wherein X is iodide or triflate.

6. A process as claimed in any preceding claim wherein R is a C-labelled C17 alkyl group.

7. A process as claimed in any preceding claim wherein R is "C labelled methyl.

8. A process as claimed in any preceding claim wherein the carbon dioxide is non radioactive.

9. A process as claimed in any preceding claim wherein R' is C,7 alkyl group carrying an 8F label.

10. A process as claimed in any preceding claim wherein the reaction is effected in the presence of a metal carbonate.

11. A process as claimed in any preceding claim wherein said carbonate is caesium carbonate.

12. A process as claimed in any preceding claim wherein the reaction is effected in the presence of a ammonium salt.

13. A process as claimed in any preceding claim wherein the ammonium salt is N(C,6 alkyl)44 halide or sulphonate ester.

14. A process as claimed in any preceding claim wherein the ammonium salt is NBu4Tf or NBu4I.

15. A process as claimed in any preceding claim wherein said amine is an optionally substituted amine of formula (V) /-\

 NJNH (V)

16. A process as claimed in any preceding claim wherein the amine is the normethylcarbamoyl analogue of GR 89696 or an enatiomer thereof.

17. A 8F or "C-labelled carbamate prepared by a process as hereinbefore described.

18. A pharmaceutical composition containing such a carbamate, e.g. a saline solution of said carbamate.

19. The use of a or "C-labelled carbamate as hereinbefore described in the manufacture of a medicament for use in a method of diagnosis or treatment of a disease or condition, such as drug addiction, Tourette's syndrome, epilepsy, psychosis or Alzheimer's disease.

20. A method of diagnosis or treatment of a condition as described above comprising administering to a patient a carbamate of the invention.

21. An optionally substituted "C or 8F labelled compound of formula (VI) or (VII) (VI) (VII) where RIR' are as hereinbefore defined with the proviso that R is not "CH3.

22. The compound GR89696 or an enatiomer thereof "C labelled on the ester carbonyl.