A PROCESS FOR THE SYNTHESIS OF CARBON LABELED ORGANIC COMPOUNDS

Abstract

A process for the synthesis of a carbon labeled organic compound containing a carbon labeled carboxyl group is described. A method of using carbon labeled organic compounds containing a carbon labeled carboxyl group according to the present disclosure; a process for manufacturing labeled pharmaceuticals and agrochemicals comprising synthesis of carbon labeled organic compounds containing a carbon labeled carboxyl group according to the present disclosure; and a process for producing tracers comprising synthesis of carbon labeled organic compounds containing a carbon labeled carboxyl group according to the present disclosure are also described.

Claims

1. A process for the synthesis of a carbon labeled organic compound containing a carbon labeled carboxyl group according to formula (I) ##STR00075## wherein *C is a .sup.11C, .sup.13C or .sup.14C isotope; R.sub.1, R.sub.2 and R.sub.3 are, independently, a hydrogen atom, an aryl, a heteroaryl, a heterocycle, an alkyl, an alkyl halide, an alkene or an alkyne, said aryl, heteroaryl, heterocycle, alkene, alkyne and alkyl groups being optionally substituted, or R.sub.1 and R.sub.2 form together with the carbon atom to which they are linked a carbonyl (—(C═O)— and R.sub.3 is as defined above, or R.sub.1 and R.sub.2 form together with the carbon atom to which they are linked an alkene with at least one double bond being alpha to the carboxyl group, said alkene being optionally substituted, and R.sub.3 is as defined above, or R.sub.1, R.sub.2 and R.sub.3 form together with the carbon atom to which they are linked an aryl, a heteroaryl, or a heterocycle, said aryl, heteroaryl and heterocycle being optionally substituted; M.sub.1 is a hydrogen atom, a silver cation (Ag.sup.+), an alkaline cation selected from lithium (Li.sup.+), sodium (Na.sup.+), potassium (K.sup.+), rubidium (Rb.sup.+), or cesium (Cs.sup.+); characterized in that an organic compound containing a carboxyl group according to formula (II) ##STR00076## wherein R.sub.1, R.sub.2, R.sub.3 and M.sub.1 are as defined above, is reacted with a labeled *CO.sub.2 wherein *C is an isotope as defined above, in the presence of a catalyst system comprising an inorganic salt of formula (III)
M.sub.2(L).sub.m   (III) wherein M.sub.2 is a transition metal selected from Cu, Pd, Ni, Ru, Ag, Rh, Fe, Co, Zn, Ir, Au, Pt, m is 1 or 2; L is a halogen atom selected from fluorine, chlorine, bromine, and iodide, a triflate or trifluoromethylsulfonate, a tosylate or p-toluenesulfonate, a mesylate or methanesulfonate, —CN, (CH.sub.3)COO—, and a ligand of formula (IV), formula (V) or formula (VI) ##STR00077## wherein n is 0 or 1; n′ is 0 or 1; n″ is 0 or 1; n′″ is 0 or 1; p is 0 or 1; o is 0 or 1; q is 0 or 1; r is 0 or 1; t is 0, 1, 2 or 3; E is a single bond, ##STR00078##  —C(R.sub.13R.sub.14)— with R.sub.13 and R.sub.14, independently being a hydrogen atom, an alkyl, an aryl, —CN, —NO.sub.2, a halogen atom selected from F, Cl, Br, I; X is N(R.sub.15).sub.n′, O, P, S(R.sub.15).sub.n′, or P(R.sub.15).sub.n′ with R.sub.15 being a hydrogen atom or an alkyl and with the proviso that when X is N(R.sub.15).sub.n′, S(R.sub.15).sub.n′, or P(R.sub.15).sub.n′, and n′=n=0, is a double bond; Z is N(R.sub.15).sub.n″, O, P, S(R.sub.15).sub.n″, or P(R.sub.15).sub.n″, with R.sub.15 being a hydrogen atom or an alkyl and with the proviso that when Z is N(R.sub.15).sub.n″, S(R.sub.15).sub.n″, or P(R.sub.15).sub.n″, and n″=p=0, is a double bond; A is N or P; Y is a single bond, ##STR00079##  with R.sub.x being a hydrogen atom or an alkyl; D is N(R.sub.15).sub.n′″, O, P, S(R.sub.15).sub.n′″, or P(R.sub.15).sub.n′″ with R.sub.15 being a hydrogen atom or an alkyl and with the proviso that when D is N(R.sub.15).sub.n′″, S(R.sub.15).sub.n′″, or P(R.sub.15).sub.n′″ and n′″=n=0, is a double bond; R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are, independently, a hydrogen atom, an alkyl, an alkoxy, an aryl, or —CN, said alkyl and aryl being optionally substituted, or R.sub.4, R.sub.5, R.sub.8, R.sub.9, and R.sub.12 are, independently, a hydrogen atom, an alkyl, an alkoxy, an aryl, or —CN, R.sub.6 and R.sub.7 and/or R.sub.10 and R.sub.11 form together with the carbon atoms to which they are linked a heterocycle, said alkyl, aryl and heterocycle being optionally substituted; R.sub.18, R.sub.19, R.sub.20, R.sub.21, R.sub.22, R.sub.23, R.sub.24, R.sub.25, R.sub.26, R.sub.27, R.sub.28, R.sub.29, R.sub.30, R.sub.31, R.sub.32 and R.sub.33 are, independently, a hydrogen atom, an alkyl, an alkoxy, an aryl, or a —CN, said alkyl and aryl being optionally substituted, or when Y is a single bond, n=0, is a double bond, R.sub.18, R.sub.21, R.sub.22, R.sub.25, R.sub.26, R.sub.27, R.sub.28, R.sub.29, R.sub.30, R.sub.31, R.sub.32 and R.sub.33 are, independently, a hydrogen atom, an alkyl, an alkoxy, an aryl, or —CN, and R.sub.19 and Rao and/or R.sub.23 and R.sub.24 form together with the carbon atoms to which they are linked an aryl, said alkyl and aryl being optionally substituted; R.sub.16, R.sub.17 and R.sub.34 are, independently, a hydrogen atom, an alkyl, an alkoxy, an aryl, a heteroaryl, a heterocycle, said alkyl, aryl, heteroaryl and heterocycle being optionally substituted, —(C═S)—NR.sub.35R.sub.36, —(C═O)—NR.sub.35R.sub.36, —(CH.sub.2).sub.t—NR.sub.35R.sub.36, —(CH.sub.2).sub.t—PR.sub.35R.sub.36 with R.sub.35 and R.sub.36 being independently, a hydrogen atom, an alkyl, an alkene, an alkyne, an aryl, a heteroaryl, a heterocycle, said alkyl, alkene, alkyne, aryl, heteroaryl and heterocycle being optionally substituted, R.sub.35 and R.sub.36 form together with the nitrogen atom to which they are linked an optionally substituted heteroaryl or heterocycle.

2. The process according to claim 1, wherein the ligand is of formula (IV) ##STR00080## wherein p is 0 or 1; E is a single bond, ##STR00081##  —C(R.sub.13R.sub.14)— with R.sub.13 and R.sub.14, independently being a hydrogen atom, a C.sub.1-C.sub.8 alkyl, or —CN; X is N(R.sub.15).sub.n′, n′=n=0, and is a double bond; Z is O; R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9, R.sub.10, R.sub.11 and R.sub.12 are, independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, an aryl having 6 to 14 carbon atoms, or a —CN, said alkyl and aryl being optionally substituted, or R.sub.5, R.sub.8, R.sub.9, and R.sub.12 are, independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, an aryl having 6 to 14 carbon atoms, or —CN, R.sub.6 and R.sub.7 and/or R.sub.10 and R.sub.11 form together with the carbon atoms to which they are linked a 5 to 10 membered heterocycle, said alkyl, aryl and heterocycle being optionally substituted.

3. The process according to claim 1, wherein the ligand of formula (IV) is ##STR00082##

4. The process according to claim 1, wherein the ligand is of formula (V) ##STR00083## wherein o is 0 or 1; q is 0 or 1; r is 0 or 1; t is 0, 1, 2 or 3; A is N or P; R.sub.16, R.sub.17 and R.sub.34 are, independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl, a 5 to 10 membered heterocycle, said alkyl, aryl, heteroaryl and heterocycle being optionally substituted, —(C═S)—NR.sub.35R.sub.36, —(C═O)—NR.sub.35R.sub.36, —(CH.sub.2).sub.t—NR.sub.35R.sub.36, —(CH.sub.2).sub.t—PR.sub.35R.sub.36 with R.sub.35 and R.sub.36 being independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl, said alkyl, aryl, and heteroaryl being optionally substituted.

5. The process according to claim 1, wherein the ligand of formula (V) is ##STR00084## ##STR00085##

6. The process according to claim 1, wherein the ligand is of formula (VI) ##STR00086## wherein n is 0 or 1; n′″ is 0 or 1; ##STR00087## Y is a single bond, with R.sub.x being a hydrogen atom or a C.sub.1-C.sub.8 alkyl; D is N(R.sub.15).sub.n′″, O, P, S(R.sub.15).sub.n′″, or P(R.sub.15).sub.n′″ with R.sub.15 being a hydrogen atom or a C.sub.1-C.sub.8 alkyl and with the proviso that when D is N(R.sub.15).sub.n′″, S(R.sub.15).sub.n′″, or P(R.sub.15).sub.n′″ and n′″=n=0, is a double bond; R.sub.4 is a hydrogen atom, a C.sub.1-C.sub.8 alkyl, an alkoxy, an aryl having 6 to 14 carbon atoms, or —CN, said alkyl and aryl being optionally substituted; R.sub.18, R.sub.19, R.sub.20, R.sub.21, R.sub.22, R.sub.23, R.sub.24, R.sub.25, R.sub.26, R.sub.27, R.sub.28, R.sub.29, R.sub.30, R.sub.31, R.sub.32 and R.sub.33 are, independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, a C.sub.1-C.sub.8 alkoxy, an aryl having 6 to 14 carbon atoms, or a —CN, said alkyl and aryl being optionally substituted, or when Y is a single bond, n=0, is a double bond, R.sub.18, R.sub.21, R.sub.22, R.sub.25, R.sub.26, R.sub.27, R.sub.28, R.sub.29, R.sub.30, R.sub.31, R.sub.32 and R.sub.33 are, independently, a hydrogen atom, a C.sub.1-C.sub.8 alkyl, a C.sub.1-C.sub.8 alkoxy, an aryl having 6 to 14 carbon atoms, or —CN, and R.sub.19 and R.sub.20 and/or R.sub.23 and R.sub.24 form together with the carbon atoms to which they are linked an aryl having 6 to 14 carbon atoms, said alkyl and aryl being optionally substituted.

7. The process according to claim 1, wherein the ligand of formula (VI) is ##STR00088##

8. The process according to claim 1, wherein in the inorganic salt of formula (III)
M.sub.2(L).sub.m   (III) M.sub.2 is a transition metal selected from Cu, Pd, Ni, Ru, Ag, Rh, Fe, Co, Zn, Ir, Au, Pt, m is 1; L is a halogen atom selected from chlorine, bromine, and iodide, a triflate or trifluoromethylsulfonate, a tosylate or p-toluenesulfonate, a mesylate or methanesulfonate, —CN, (CH.sub.3)COO—.

9. The process according to claim 1, wherein R.sub.1, R.sub.2 and R.sub.3 are, independently, a hydrogen atom, an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl, a C.sub.1-C.sub.8 alkyl, a C.sub.1-C.sub.8 alkyl halide, said aryl, heteroaryl and alkyl groups being optionally substituted.

10. The process according to claim 1, wherein R.sub.1 and R.sub.2 form together with the carbon atom to which they are linked a carbonyl (—(C═O)— and R.sub.3 is a hydrogen atom, an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl, a C1-C8 alkyl, a C1-C8 alkyl halide, said aryl, heteroaryl and alkyl groups being optionally substituted.

11. The process according to claim 1, wherein R.sub.1 and R.sub.2 form together with the carbon atom to which they are linked an alkene having C.sub.2-C.sub.8 carbon atoms and one or more carbon-carbon double bonds with at least one double bond being alpha to the carboxyl group, said alkene being optionally substituted, and R3 is a hydrogen atom, an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl, a C1-C8 alkyl, a C1-C8 alkyl halide, said aryl, heteroaryl and alkyl groups being optionally substituted.

12. The process according to claim 1, wherein R.sub.1, R.sub.2 and R.sub.3 form together with the carbon atom to which they are linked an aryl having 6 to 14 carbon atoms, a 5 to 10 membered heteroaryl or a 5 to 10 membered heterocycle, said aryl, heteroaryl and heterocycle groups being optionally substituted.

13. The process according to claim 1, wherein M.sub.1 is a hydrogen atom, an alkaline cation selected sodium (Na.sup.+), potassium (K.sup.+), or cesium (Cs.sup.+).

14. The process according to claim 1, wherein the organic compound containing a carboxyl group of formula (II), used for the synthesis of a carbon labeled organic compound containing a carbon labeled carboxyl group according to formula (I), is ##STR00089## ##STR00090##

15. The process according to claim 14, wherein the source of *CO.sub.2 is a gas.

16. The process according to claim 15, wherein the *CO.sub.2 pressure in the reaction vessel is between 0.5 to 100 bar (50 kPa to 10 MPa).

17. The process according to claim 1, wherein the catalyst system is present in an amount of 1 to 100 mole percent (mol %), in particular, between 5 and 25 mole percent (mol %), with respect to compound (II).

18. The process according to claim 1, wherein the molar ratio of the inorganic salt of formula (III) and the ligands of formula (IV) to (V) in the catalyst system is between 1 to 100.

19. A method of using carbon labeled organic compounds containing a carbon labeled carboxyl group of formula (I) by the process according to claim 1, in the manufacture of pharmaceuticals and agrochemicals.

20. A process for manufacturing labeled pharmaceuticals and agrochemicals having a free carboxylic acid functionality, comprising a step of synthesis of carbon labeled organic compounds containing a carbon labeled carboxyl group of formula (I) by the process according to claim 1.

21. A process for producing tracers, characterized in that it comprises a step of synthesis of carbon labeled organic compounds containing a carbon labeled carboxyl group of formula (I) by the process according to claim 1.

Description

[0282] Other features and advantages of the present invention appear from the figures and the following non limiting examples.

[0283] FIG. 1 represents the labeling of Valsartan (angiotensin II receptor antagonist) with .sup.3H in one single operation using the appropriate catalyst and readily commercially available Valsartan.

[0284] FIG. 2 represents the labeling of Valsartan (angiotensin II receptor antagonist) with .sup.14C in eight steps using the appropriate catalyst and readily commercially available Valsartan.

[0285] FIG. 3 represents the mechanism of the catalytic dynamic carbon isotope exchange with CO.sub.2 according to the process of the invention.

[0286] FIG. 4 represents the principle for the dynamic carbon isotope exchange according to the invention.

[0287] FIG. 5 represents the applicability of the process of the invention to all organic compounds containing a carboxylic acid functionality, independently of the orbital hybridization of the carbon atom attached to the carboxyl function (sp, sp.sup.2 or sp.sup.3 carbon).

[0288] FIG. 6 represents different ligand families that were screened for optimizing the reaction conditions.

EXAMPLES

[0289] NMR data were recorded with RMN Bruker Avance 400 Mhz with topspin 2.1.

[0290] Mass data were recorded with a Waters ZQ 2000, with electrospray positif/negatif source. Direct Introduction (4 min), ACN/MeOH 50/50+1/1000 HCO.sub.2H.

[0291] Glove box model: mb-unilab plus sp (http://www.mbraun.com/products/glovebox-workstations/unilab-glovebox).

[0292] Wilmad Young NMR tube were purchased from Sigma Aldrich (https://www.sigmaaldrich.com/catalog/product/aldrich/z514160?lang=fr&region=FR)

[0293] All carboxylic acids substrates, ligands and catalysts are commercially available and purchased from different Sigma-Aldrich, Alfa Aesar and Acros Organics.

[0294] .sup.13CO.sub.2 is commercially available from Sigma Aldrich. It was charger to the TRITEC cartridge according to the specifications of the manifold (see http://www.rctritec.com/en/tritium-handling-technology/c-14-manifold-system.html)

[0295] For the preparation of .sup.11CO.sub.2, see Clin Transl Imaging, 2017, 5, 275-289.

[0296] .sup.14CO.sub.2 was purchased from TRITEC, for the preparation of .sup.14CO.sub.2 and BaCO.sub.2 see: Preparation of Compounds Labeled with Tritium and Carbon-14 Rolf Voges, J. Richard Heys and Thomas Moenius© 2009 John Wiley & Sons, page 211 (chapter 5).

I. Synthesis of Carbon Labeled Compounds of Formula (I)—General Protocol Cesium Salt Preparation

[0297] Adapted from the literature (Gerard Cahiez, Alban Moyeux, Olivier Gager, Mal Poizatb, Adv. Synth. Catal. 2013, 355, 790-796): a flask was charged with the desired organic compound containing a carboxyl group (2-nitrobenzoic acid) and methanol (5-10 mL). After stirring for 5 min, Cs.sub.2CO.sub.3 (1 eq.) was slowly added to the solution. The reaction mixture was then stirred for 1 h at room temperature (20+5° C.). Methanol was removed under vacuum and the resulting solid was dried in a vacuum oven at 40° C. for 24 h to provide cesium 2-nitrobenzoate.

[0298] The dryness of the resulting cesium salt was checked: an argon-filled glovebox, a Wilmad® NMR tube (5 mm diam. 7 In.) with Young valve was charged with the cesium salt and a proton NMR was performed adding internal standard (trimethoxybenzene, 3 eq.) in MeOD. The peaks integrations revealed the salt purity, that was useful to calculate the correct amount of catalyst loading.

Potassium Salt Preparation

[0299] In an argon-filled glovebox, a Schlenk flask was charged with the desired organic compound containing a carboxyl group (2-nitrobenzoic acid) and THF (5-10 mL). After stirring for 5 min, KH (1 eq.) was slowly added to the solution. The reaction mixture was then stirred for 1-2 h at room temperature. THF was removed under vacuum and the resulting solid was dried under vacuum for 24 h to provide potassium 2-nitrobenzoate.

[0300] The dryness of the resulting potassium salt was checked: an argon-filled glovebox, a Wilmad® NMR tube (5 mm diam. 7 In.) with Young valve was charged with potassium 2-nitrobenzoate and a proton NMR was performed adding internal standard (trimethoxybenzene, 3 eq.) in TDF. The peaks integrations revealed the salt purity, that was useful to calculate the correct amount of catalyst loading.

3. General Carbon Isotopic Exchange Reaction

[0301] An argon-filled glovebox, a Wilmad® NMR tube (5 mm diam. 7 In.) with Young valve, was charged with the cesium or potassium salt of desired organic compound containing a carboxyl group (leq), the ligand (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol, 20% mol) and copper bromide (I) (2.9 mg, 2×10.sup.−5 mol, 20% mol). Subsequently, dry DMSO (0.5 ml) is added to the mixture.

[0302] The loaded NMR tube was removed from the glovebox and connected to carbon TRITEC manifold according to the disclosure in:

[0303] http://www.rctritec.com/en/tritium-handling-technology/c-14-manifold-system.html

[0304] The NMR tube mixture was frozen using a liquid nitrogen bath and the system is degassed under high vacuum. The NMR tube is then charged with labeled CO.sub.2 (3 eq.). The Wilmad® NMR tube is subsequently sealed and the reaction mixture was allowed to warm at room temperature (20±5° C.) (2 min) and stirred at 150° C. for 2 hours.

[0305] The reaction mixture is then allowed to cool at room temperature (20+5° C.) and quenched with HCl 1M (5 mL) and stirred for 2 minutes. Then the mixture was extracted with ethyl acetate (3-5 mL, 3 times). The combined organic layers were extracted with sodium hydroxide (1M) or with a saturated solution of sodium bicarbonate, until basic pH was reached. The basic aqueous phase was slowly acidified to pH 2 with HCl (2M) and extracted with ethyl acetate (3-5 mL, 3 times).

[0306] The combined organic layers in ethyl acetate were dried (MgSO.sub.4) and concentrated under reduced pressure to obtain the isotopically enriched final compound.

Example 1: Synthesis of .SUP.13.C-2-Nitrobenzoic Acid

[0307] ##STR00031##

[0308] The title compound was synthesized according to general protocol from the cesium salt of 2-nitrobenzoic acid (29.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0309] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 50% yield (8.3 mg) and 72% of isotopic enrichment.

[0310] .sup.1H NMR (400 MHz, DMSO) δ 7.98 (d, J=7.8 Hz, 1H), 7.88-7.84 (m, 1H), 7.82-7.75 (m, 1H)

[0311] .sup.13C NMR (400 MHz, DMSO) δ 165.9, 148.4, 133.1, 132.4, 129.9, 127.2 (J=73.4 Hz), 123.7

[0312] Mass M-1=166, [M-1]+1 (13C): 72.1%

Example 2: Synthesis of .SUP.13.C-4-Nitrobenzoic acid

[0313] ##STR00032##

[0314] The title compound was synthesized according to general protocol from the cesium salt of 4-nitrobenzoic acid (29.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture. Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 65% yield (10.8 mg) and 14% of isotopic enrichment. 1H NMR (400 MHz, DMSO) δ 8.33 (dt, J=9.0 Hz, 1.8 Hz, 2H), 8.1 (dt, J=8.7 Hz, 2.2 Hz, 2H), 13C NMR (400 MHz, DMSO) δ 165.8, 150.1, 136.4, 130.7, 123.8,

[0315] Mass M-1=166, [M-1]+1 (13C): 14%

Example 3: Synthesis of .SUP.13.C-6-Methyl-2-Nitrobenzoic acid

[0316] ##STR00033##

[0317] The title compound was synthesized according to general protocol from the cesium salt of 6-Methyl-2-Nitrobenzoic acid (31.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0318] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 48% yield (8.7 mg) and 73% of isotopic enrichment.

[0319] 1H NMR (400 MHz, DMSO) δ 7.9 (d, J=8.2 Hz, 1H), 7.7 (d, J=7.6 Hz, 1H), 7.5 (t, J=7.9 Hz, 1H), 2.37 (s, 3H)

[0320] 13C NMR (400 MHz, DMSO) δ 167.3, 145.9, 136.7, 136.4, 129.8, 121.8, 19.0

[0321] Mass M-1=180, [M-1]+1 (13C): 73%

Example 4: Synthesis of .SUP.13.C-5-Methyl-2-Nitrobenzoic acid

[0322] ##STR00034##

[0323] The title compound was synthesized according to general protocol from the cesium salt of 5-Methyl-2-Nitrobenzoic acid (31.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0324] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 45% yield (8.3 mg) and 44% of isotopic enrichment.

[0325] 1H NMR (400 MHz, DMSO) δ 7.9 (d, J=8.3 Hz, 1H), 7.6 (d, J=2.3 Hz, 1H), 7.5 (dd, J=8.4 Hz, 1.3 Hz, 1H)

[0326] 13C NMR (400 MHz, DMSO) δ 166.3, 145.6, 144.3, 132.1, 129.8, 128.1 (J=73.3 Hz), 123.8, 20.7

[0327] Mass M-1=180, [M-1]+1 (13C): 44%

Example 5: Synthesis of .SUP.13.C-4-Methyl-2-Nitrobenzoic acid

[0328] ##STR00035##

[0329] The title compound was synthesized according to general protocol from the cesium salt of 4-Methyl-2-Nitrobenzoic acid (31.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0330] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 42% yield (7.5 mg) and 57% of isotopic enrichment.

[0331] 1H NMR (400 MHz, DMSO) δ 7.8 (d, J=2.3 Hz, 1H), 7.7 (s, 1H), 7.6 (d, J=7.9 Hz, 1H), 2.43 (s, 3H)

[0332] 13C NMR (400 MHz, DMSO) δ 165.4, 148.7, 143.3, 133.9, 129.8, 123.6, 123.5 (d, J=9.9 Hz), 20.4

[0333] Mass M-1=180, [M-1]+1 (13C): 57%

Example 6: Synthesis of .SUP.13.C-4-Methoxy-2-Nitrobenzoic acid

[0334] ##STR00036##

[0335] The title compound was synthesized according to general protocol from the cesium salt of 5-Methoxy-2-Nitrobenzoic acid (32.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0336] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 53% yield (10.3 mg) and 39% of isotopic enrichment.

[0337] 1H NMR (400 MHz, DMSO) δ 8.0 (d, J=8.5 Hz, 1H), 7.2-7.1 (m, 2H), 3.9 (s, 3H),

[0338] 13C NMR (400 MHz, DMSO) δ 166.6, 163.1, 139.5, 132 (J=38.1 Hz), 126.6, 115.9, 113.9, 56.5

[0339] Mass M-1=166, [M-1]+1 (13C): 46%

Example 7: Synthesis of .SUP.13.C-4,5-dimethoxy-2-Nitrobenzoic acid

[0340] ##STR00037##

[0341] The title compound was synthesized according to general protocol from the cesium salt of 4,5-dimethoxy-2-Nitrobenzoic acid (35.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0342] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 41% yield (9.4 mg) and 10% of isotopic enrichment.

[0343] 1H NMR (400 MHz, DMSO) δ 8.0 (d, J=8.5 Hz, 1H), 7.2-7.1 (m, 2H), 3.9 (s, 3H),

[0344] 13C NMR (400 MHz, DMSO) δ 166.6, 163.1, 139.5, 132 (J=38.1 Hz), 126.6, 115.9, 113.9, 56.5

[0345] Mass M-1, 166, [M-1]+1 (13C): 10%

Example 8: Synthesis of .SUP.13.C-4-chloro-2-Nitrobenzoic acid

[0346] ##STR00038##

[0347] The title compound was synthesized according to general protocol from the cesium salt of 4-chloro-2-Nitrobenzoic acid (33.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0348] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 29% yield (5.6 mg) and 12.5% of isotopic enrichment.

[0349] 1H NMR (400 MHz, DMSO) δ 8.1 (d, J=1.6 Hz, 1H), 7.9-7.8 (m, 2H),

[0350] 13C NMR (400 MHz, DMSO) δ 164.5, 150.7, 136.5, 132.5, 131.6, 124.3, 123.5

[0351] Mass M-1=166, [M-1]+1 (13C): 12.5%

Example 9: Synthesis of .SUP.13.C-3-Nitrobenzoic acid

[0352] ##STR00039##

[0353] The title compound was synthesized according to general protocol from the cesium salt of 3-nitrobenzoic acid (29.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0354] Hence loaded with .sup.13CO.sub.2 as described, the temperature was set to 190° C. After the reaction and purification the enriched final compound with 88% yield (14.6 mg) and 20% of isotopic enrichment.

[0355] 1H NMR (400 MHz, DMSO) δ 13.6 (broad peak, 1H), 8.61 (s, 1H), 8.47 (dd, J=8.0, 1.7 Hz, 1H), 8.35 (d, J=7.7 Hz, 1H), 7.8 (t, J=8.0, 7.8 Hz, 1H)

[0356] 13C NMR (400 MHz, DMSO) δ 165.9, 147.8, 133.1, 135.4, 132.5, 127.4, 123.7

[0357] Mass M-1=166, [M-1]+1 (13C): 20%

Example 10: Synthesis of .SUP.13.C-3-methylbenzofuran-2-carboxylic acid

[0358] ##STR00040##

[0359] The title compound was synthesized according to general protocol from the cesium salt of 3-methylbenzofuran-2-carboxylic acid (30.8 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.0.5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0360] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 69% yield (12.1 mg) and 37% of isotopic enrichment.

[0361] 1H NMR (400 MHz, DMSO) δ 13.4 (broad peak, 0.7H), 7.7 (d, J=7.8 Hz, 1H), 7.6 (d, J=8.3 Hz, 1H), 7.5 (t, J=7.8 Hz, 1H), 7.3 (t, J=7.8 Hz, 1H), 2.5 (s, 3H)

[0362] 13C NMR (400 MHz, DMSO) δ 161.4, 153.4, 128.8, 127.5, 123.7, 123.1, 121.3, 111.8, 10

[0363] Mass M-1=175.16, [M-1]+1 (13C): 37%

Example 11: Synthesis of .SUP.13.C-thiophene-2-carboxylic acid

[0364] ##STR00041##

[0365] The title compound was synthesized according to general protocol from the cesium salt of thiophene-2-carboxylic acid (25.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0366] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 30% yield (3.8 mg) and 30% of isotopic enrichment.

[0367] 1H NMR (400 MHz, DMSO) δ 13.1 (broad peak, 0.9H), 7.8 (d, J=4.7 Hz, 1H), 7.7 (d, J=3.4 Hz, 1H), 7.2 (t, J=4.2 Hz, 1H)

[0368] 13C NMR (400 MHz, DMSO) δ 162.9, 134.9, 133.1, 133.0, 128.4

[0369] Mass M-1=127.14, [M-1]+1 (13C): 30%

Example 12: Synthesis of .SUP.13.C-3-methylthiophene-2-carboxylic acid

[0370] ##STR00042##

[0371] The title compound was synthesized according to general protocol from the cesium salt of 3-methylthiophene-2-carboxylic acid (27.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0372] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 36% yield (5.1 mg) and 17% of isotopic enrichment.

[0373] 1H NMR (400 MHz, DMSO) δ 12.8 (broad peak, 1H), 7.7 (d, J=5.5 Hz, 1H), 7.0 (d, J=4.4 Hz, 1H), 2.4 (s, 3H)

[0374] 13C NMR (400 MHz, DMSO) δ 163.7, 145.0, 132.1, 130.8, 127.4, 15.6

[0375] Mass M-1=141.16, [M-1]+1 (13C): 17%

Example 13: Synthesis of .SUP.13.C-2-cyanobenzoic acid

[0376] ##STR00043##

[0377] The title compound was synthesized according to general protocol from the cesium salt of 2-cyanobenzoic acid (27.8 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0378] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 63% yield (9.3 mg) and 10% of isotopic enrichment.

[0379] 1H NMR (400 MHz, DMSO) δ 13.8 (broad peak, 1H), 8.1 (d, J=7.8 Hz, 1H), 7.9 (d, J=7.9 Hz, 1H), 7.8 (m, 2H)

[0380] 13C NMR (400 MHz, DMSO) δ 165.2, 145.0, 135.0, 133.2, 133.0, 130.9, 130.7, 117.7, 111.6

[0381] Mass M-1=146, [M-1]+1 (13C): 10%

Example 14: Synthesis of .SUP.13.C-1-methoxy-2-naphthoic acid

[0382] ##STR00044##

[0383] The title compound was synthesized according to general protocol from the cesium salt of 1-methoxy-2-naphthoic acid (33.3 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0384] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 50% yield (10.1 mg) and 25% of isotopic enrichment.

[0385] 1H NMR (400 MHz, DMSO) δ 13.0 (broad peak, 0.9H), 8.2 (dd, J=7.2, 2.0, Hz, 1H), 7.9 (dd, J=6.8, 2.0 Hz, 1H), 7.7 (dd, J=20.0, 8.6 Hz, 2H) 7.6 (m, 2H)

[0386] 13C NMR (400 MHz, DMSO) δ 160.2, 149.6, 128.8, 120.2, 119.9, 119.5, 118.3, 118.2, 115.2, 114.8, 111.4, 54.21

[0387] Mass M-1=201.2, [M-1]+1 (13C): 25%

Example 15: Synthesis of .SUP.13.C-2-oxo-2H-chromene-3-carboxylic acid

[0388] ##STR00045##

[0389] The title compound was synthesized according to general protocol from the cesium salt of 2-oxo-2H-chromene-3-carboxylic acid (32.1 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0390] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 56% yield (10.6 mg) and 40% of isotopic enrichment.

[0391] 1H NMR (400 MHz, DMSO) δ 13.3 (broad peak, 0.8H), 8.7 (s, 1H), 7.9 (dd, J=7.8, 1.5, Hz, 1H), 7.7 (td, J=7.9, 2.0 Hz, 1H), 7.44 (d, J=8.5 Hz, 1H) 7.4 (dd, J=7.4, 1.1, Hz, 1H)

[0392] 13C NMR (400 MHz, DMSO) δ 164.0, 156.6, 154.4, 148.4, 134.3, 130.1, 124.8, 118.3, 117.9, 116.1

[0393] Mass M-1=189.15, [M-1]+1 (13C): 40%

Example 16: Synthesis of .SUP.13.C-1-methyl-1H-pyrrole-2-carboxylic acid

[0394] ##STR00046##

[0395] The title compound was synthesized according to general protocol from the cesium salt of 1-methyl-1H-pyrrole-2-carboxylic acid (25.6 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0396] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 42% yield (5.3 mg) and 16% of isotopic enrichment.

[0397] 1H NMR (400 MHz, DMSO) δ 12.1 (broad peak, 0.8H), 7.0 (t, J=2.1 Hz, 1H), 6.7 (dd, J=4.0, 1.8, Hz, 1H), 6.0 (dd, J=4.2, 2.4, Hz, 1H), 3.88 (s, 3H)

[0398] 13C NMR (400 MHz, DMSO) δ 162.0, 129.7, 122.4, 117.3, 107.1, 36.3

[0399] Mass M-1=124.13, [M-1]+1 (13C): 16%

Example 17: Synthesis of .SUP.13.C-2-methyl-3-nitrobenzoic acid

[0400] ##STR00047##

[0401] The title compound was synthesized according to general protocol from the cesium salt of 2-methyl-3-nitrobenzoic acid (31.2 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry NMP/DMSO (8:2 mixture) 0.5 ml is added to the mixture.

[0402] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 50% yield (9 mg) and 48% of isotopic enrichment.

[0403] 1H NMR (400 MHz, DMSO) δ 13.5 (broad peak, 0.8H), 8.0 (d, J=8.5 Hz, 2H), 7.5 (t, J=7.8 Hz, 1H), 2.5 (s, 3H)

[0404] 13C NMR (400 MHz, DMSO) δ 167.8, 151.5, 134.4 (t, J=37 Hz) 133.2, 130.8, 127.1, 126.2, 15.5

[0405] Mass M-1=180.15, [M-1]+1 (13C): 48%

Example 18: Synthesis of .SUP.13.C-2,6-difluorobenzoic acid

[0406] ##STR00048##

[0407] The title compound was synthesized according to general protocol from the cesium salt of 2,6-difluorobenzoic acid (28.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0408] Hence loaded with .sup.13CO.sub.2 as described, reaction time 1 h. After the reaction and purification the enriched final compound with 25% yield (3.95 mg) and 40% of isotopic enrichment.

[0409] 1H NMR (400 MHz, DMSO) δ 13.9 (broad peak, 0.9H), 7.5 (m, 1H), 7.2 (t, J=7.6 Hz, 1H)

[0410] 13C NMR (400 MHz, DMSO) δ 165, 162.1, 132.9, 112.4, 112.1

[0411] Mass M-1=157, [M-1]+1 (13C): 40%

Example 19: Synthesis of .SUP.13.C-2-methoxy-4-nitrobenzoic acid

[0412] ##STR00049##

[0413] The title compound was synthetized according to general protocol from the cesium salt of 2-methoxy-4-nitrobenzoic acid (32.8 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry NMP/DMSO (8:2 mixture) 0.5 ml is added to the mixture.

[0414] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 81% yield (15.5 mg) and 15% of isotopic enrichment.

[0415] 1H NMR (400 MHz, DMSO) δ 13.4 (broad peak, 0.9H), 7.87-7.799 (m, 3H), 3.9 (s, 3H)

[0416] 13C NMR (400 MHz, DMSO) δ 166.3, 157.1, 149.6, 130.8, 128.0, 115.1, 106.8, 56.56

[0417] Mass M-1=196, [M-1]+1 (13C): 15%

Example 20: Synthesis of .SUP.13.C-2-(4-(trifluoromethyl)phenyl)acetic acid

[0418] ##STR00050##

[0419] The title compound was synthesized according to general protocol from the cesium salt of 2-(4-(trifluoromethyl)phenyl)acetic acid (32.8 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0420] Hence loaded with .sup.13CO.sub.2 as described, reaction temperature 100° C. After the reaction and purification the enriched final compound with 22% yield (4.5 mg) and 56% of isotopic enrichment.

[0421] 1H NMR (400 MHz, DMSO) δ 7.6 (d, J=7.4 Hz, 2H), 7.5 (d, J=7.4 Hz, 2H), 3.7 (t, J=3.9 Hz, 2H)

[0422] 13C NMR (400 MHz, DMSO) δ 172.2, 140.0, 130.3, 127.0, 124.5, 123.0

[0423] Mass M-1=203.15, [M-1]+1 (13C): 56%

Example 21: Synthesis of .SUP.13.C-4-oxo-4H-chromene-2-carboxylic acid

[0424] ##STR00051##

[0425] The title compound was synthesized according to general protocol from the cesium salt of 4-oxo-4H-chromene-2-carboxylic acid (32.1 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0426] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 72% yield (14 mg) and 17% of isotopic enrichment.

[0427] 1H NMR (400 MHz, DMSO) δ 8.0 (d, J=9 Hz, 1H), 7.8 (t, J=7.7 Hz, 1H), 7.7 (d, J=10.3 Hz, 1H), 7.5 (t, J=7.7 Hz, 1H), 6.9 (s, 1H)

[0428] 13C NMR (400 MHz, DMSO) δ 177.6, 161.4, 155.3, 153.4, 135.0, 125.9, 124.9, 123.7, 118.8, 113.8

[0429] Mass M-1=189.13, [M-1]+1 (13C): 17%

Example 22: Synthesis of .SUP.13.C Labeled Aromatic Compounds

[0430] The aromatic compounds represented below were synthesized following the general protocol for the preparation of the cesium salt and the general carbon isotopic exchange reaction described in section 3 using 3 eq of .sup.13CO.sub.2.

[0431] The isotopic enrichment (IE) measured by ESI mass spectrometry is indicated for each compound.

[0432] Depending on the substrate, an IE of 75% can be achieved, which is the theoretically highest incorporation possible with 3 eq of labeled *CO.sub.2 (1 eq. of unlabeled .sup.12CO.sub.2 is released from the carboxylic acid reagent).

[0433] When 10 eq. of labeled .sup.13CO.sub.2 are used, IE can attain 90%. In addition, if .sup.14CO.sub.2 is used, similar enrichments are observed.

##STR00052##

Example 23: Synthesis of .SUP.13.C Labeled Heteroaromatic and Vinylic Compounds

[0434] The heteroaromatic and vinylic compounds represented below were synthesized following the general protocol for the preparation of the cesium salt and the general carbon isotopic exchange reaction described in section 3 using 3 eq of .sup.13CO.sub.2.

[0435] The isotopic enrichment (IE) measured by ESI mass spectrometry is indicated for each compound.

##STR00053##

Example 24: Synthesis of .SUP.13.C Labeled Non Aromatic Compounds

[0436] The non aromatic compounds represented below were synthesized following the general protocol for the preparation of the cesium salt and the general carbon isotopic exchange reaction described in section 3 using 3 eq of .sup.13CO.sub.2.

[0437] The isotopic enrichment (IE) measured by ESI mass spectrometry is indicated for each compound.

##STR00054##

Example 25: Synthesis of .SUP.13.C-5-Methoxy-2-Nitrobenzoic Acid

[0438] ##STR00055##

[0439] The title compound was synthesized according to general protocol from the cesium salt of 5-Methoxy-2-Nitrobenzoic acid (32.9 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0440] Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 59% yield (11.5 mg) and 46% of isotopic enrichment.

[0441] 1H NMR (400 MHz, DMSO) δ 8.0 (d, J=8.5 Hz, 1H), 7.2-7.1 (m, 2H), 3.9 (s, 3H),

[0442] 13C NMR (400 MHz, DMSO) δ 166.6, 163.1, 139.5, 132 (J=38.1 Hz), 126.6, 115.9, 113.9, 56.5

[0443] Mass M-1=196, [M-1]+1 (13C): 46%

Example 26: Labeling of a Pharmaceutical

A) 13C-9-fluoro-5-methyl-1-oxo-6,7-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-2-carboxylic acid (Flumequine)

[0444] ##STR00056##

[0445] The process of the invention was applied to Flumequine, a synthetic fluoroquinolone antibiotic used to treat bacterial infections.

[0446] The title compound was also synthesized according to general protocol from the cesium salt of 9-fluoro-5-methyl-1-oxo-6,7-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-2-carboxylic acid (39.2 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture. Hence loaded with .sup.13CO.sub.2 as described. After the reaction and purification the enriched final compound with 42% yield (10.9 mg) and 47% of isotopic enrichment.

[0447] 1H NMR (400 MHz, DMSO) δ 15.1 (s, 1H), 9.0 (s, 1H), 7.8 (dd, J=8.3, 2.9 Hz, 1H), 7.7 (dd, J=9, 2.9 Hz, 1H), 4.99-4.92 (m, 1H), 3.26-3.12 (m, 1H), 3 (dt, J=17.3, 3.9 Hz, 1H), 2.2-2 (m, 2H), 1.4 (d, J=6.8 Hz, 3H)

[0448] 13C NMR (400 MHz, DMSO) δ 176.9, 166, 160.2, 157.9, 147.2, 132.8, 132.3, 132.2, 121.8, 121.6, 108.0, 107.5, 107.5, 107.1, 106.7, 57.3, 25.0, 21.4, 20.0

[0449] Mass M-1=260.25, [M-1]+1 (13C): 47%

B) 13C-4-(N,N-dipropylsulfamoyl)benzoic acid (Probenecid)

[0450] ##STR00057##

[0451] The title compound was synthetized according to general protocol from the cesium salt of 4-(N,N-dipropylsulfamoyl)benzoic acid (41.7 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0452] Hence loaded with .sup.13CO.sub.2 as described, reaction temperature 190° C. After the reaction and purification the enriched final compound with 50% yield (14.2 mg) and 25% of isotopic enrichment.

[0453] 1H NMR (400 MHz, DMSO) δ 13.4 (s, 0.8H), 8.1 (d, J=9.2 Hz, 2H), 7.9 (d, J=9.7 Hz, 2H), 3.0 (t, J=7.9 Hz, 4H), 1.4 (dt, J=22.4, 7.1 Hz, 4H), 0.8 (t, J=7.4 Hz, 6H)

[0454] 13C NMR (400 MHz, DMSO) δ 166.1, 143.1, 134.2, 130.2, 126.9, 49.5, 21.6, 10.9

[0455] Mass M-1=284.36, [M-1]+1 (13C): 25%

C) 13C-2-(3-benzoylphenyl)propanoic acid (Ketoprofen)

[0456] ##STR00058##

[0457] The title compound was synthesized according to general protocol from the cesium salt of 2-(3-benzoylphenyl)propanoic acid (38.5 mg, 1×10.sup.−4 mol), (E)-2-(4-phenyl-4,5-dihydrooxazol-2-yl)-2-(4-phenyloxazolidin-2-ylidene)acetonitrile (6.6 mg, 2×10.sup.−5 mol) and copper bromide (2.9 mg, 2×10.sup.−5 mol) after that dry DMSO 0.5 ml is added to the mixture.

[0458] Hence loaded with .sup.13CO.sub.2 as described, reaction temperature 130° C., 1 h. After the reaction and purification the enriched final compound with 64% yield (16.2 mg) and 10% of isotopic enrichment.

[0459] 1H NMR (400 MHz, DMSO) δ 12.4 (s, 0.8H), 7.7-7.6 (m, 4H), 7.6-7.5 (m, 5H), 3.8 (dd, J=14.8, 7.2 Hz, 1H), 1.4 (d, J=6.3 Hz, 3H)

[0460] 13C NMR (400 MHz, DMSO) δ 195.5, 175.0, 141.7, 137.0, 136.9, 132.7, 131.9, 129.6, 128.7, 128.6, 128.5, 128.3, 44.4, 18.5

[0461] Mass M-1=253, [M-1]+1 (13C): 10%

Example 27: Synthesis of .SUP.13.C-3-methyl-2-nitrobenzoic acid

[0462] ##STR00059##

[0463] The title compound was prepared according to general procedure, starting from the cesium salt of 3-methyl-2-nitrobenzoic acid (31.3 mg, 0.1 mmol), then heated for 2 hours. The enriched final compound was obtained with 16.4% yield (3.0 mg, 0.033 mmol) and 44% of isotopic enrichment.

[0464] .sup.1H NMR (400 MHz, DMSO-d6) δ 7.83 (d, J=7.9 Hz, 1H), 7.68 (d, J=6.6 Hz, 1H), 7.59 (t, J=7.9 Hz, 1H), 2.26 (s, 3H)

[0465] .sup.13C NMR (100 MHz, DMSO-d6) δ 164.7, 150.1, 135.3, 130.4, 129.6, 128.6, 16.2 (1C missing)

[0466] HRMS (ESI) m/z calcd for C.sub.7.sup.13CH.sub.6NO.sub.4 [M-H].sup.−: 181.0334; found: 181.0337

[0467] Isotopic Enrichment: +1 .sup.13C, 43.85%

Example 28: Synthesis of .SUP.13.C-5-chloro-2-nitrobenzoic acid

[0468] ##STR00060##

[0469] The title compound was prepared according to general procedure, starting from the cesium salt of 5-chloro-2-Nitrobenzoic acid (33.3 mg, 0.1 mmol), then heated for 1.5 hours. The enriched final compound was obtained with 10% yield (2.1 mg, 0.010 mmol) and 66% of isotopic enrichment.

[0470] .sup.1H NMR (400 MHz, CDCl.sub.3) δ 7.85 (d, J=10.3 Hz, 1H), 7.75 (s, 1H), 7.57 (d, J=10.3 Hz, 1H)

[0471] .sup.13C NMR (100 MHz, CDCl.sub.3) δ 168.4, 146.5, 139.8, 132.2, 130.3, 125.6 (1C missing)

[0472] HRMS (ESI) m/z calcd for C.sub.6.sup.13CH.sub.3CH.sub.3FNO.sub.4 [M-H].sup.−: 200.9790; found: 200.9788

[0473] Isotopic Enrichment: +1 .sup.13C, 66.13%

Example 29: Synthesis of .SUP.13.C-5-fluoro-2-nitrobenzoic acid

[0474] ##STR00061##

[0475] The title compound was prepared according to general procedure, starting from the cesium salt of 5-Fluoro-2-Nitrobenzoic acid (31.7 mg, 0.1 mmol), then heated for 1.5 hours. The enriched final compound was obtained with 17% yield (3.0 mg, 0.03 mmol) and 70% of isotopic enrichment.

[0476] .sup.1H NMR (400 MHz, CDCl.sub.3) δ 7.99 (dd, J=8.9, 4.7 Hz, 1H), 7.49 (dd, J=7.9, 2.5 Hz, 1H), 7.36-7.29 (m, 1H)

[0477] .sup.13C NMR (100 MHz, CDCl.sub.3) δ 168.3 (2C, .sup.13C+C-F), 144.6, 127.1, 127.0, 119.3 (d, J=23.9 Hz, 1C), 117.7 (d, J=30.7 Hz, 1C)

[0478] .sup.19F NMR (400 MHz, CDCl.sub.3) δ −102.27

[0479] HRMS (ESI) m/z calcd for C.sub.6.sup.13CH.sub.3FNO.sub.4 [M-H].sup.−: 185.0085; found: 185.0083

[0480] Isotopic Enrichment: +1 .sup.13C, 70.17%

Example 30: Synthesis of .SUP.13.C-fluorobenzoic acid

[0481] ##STR00062##

[0482] The title compound was prepared according to general procedure, starting from the cesium salt of fluorobenzoic acid (27.2 mg, 0.1 mmol), then heated for 1 hour. The enriched final compound was obtained with 10% yield (1.60 mg, 0.010 mmol) and 31% of isotopic enrichment.

[0483] .sup.1H NMR (400 MHz, DMSO-d6) δ 13.22 (bs, 1H), 7.89-7.83 (m, 1H), 7.68-7.60 (m, 1H), 7.34-7.21 (m, 1H)

[0484] .sup.13C NMR (100 MHz, DMSO-d6) δ 165.0, 134.7, 134.6, 131.9, 124.4, 117.0, 116.8

[0485] .sup.19F NMR (400 MHz, DMSO-d6) δ −110.60

[0486] HRMS (ESI) m/z calcd for C.sub.6.sup.13CH.sub.4FO.sub.2 [M-H].sup.−: 140.0235; found: 140.0235

[0487] Isotopic Enrichment: +1 .sup.13C, 30.84%

Example 31: Synthesis of .SUP.13.C-4-methylthiazole-5-carboxylic acid

[0488] ##STR00063##

[0489] The title compound was prepared according to general procedure, starting from the cesium salt of 4-methylthiazole-5-carboxylic acid (27.5 mg, 0.1 mmol), then heated for 1 hour. The enriched final compound was obtained with 30% yield (4.3 mg, 0.03 mmol) and 52% of isotopic enrichment.

[0490] .sup.1H NMR (400 MHz, DMSO-d6) δ 9.13 (s, 1H), 2.64 (s, 3H)

[0491] .sup.13C NMR (100 MHz, DMSO-d6) δ 163.1, 159.0, 156.9, 123.0 (t, J=41.3 Hz, 1C), 16.9

[0492] HRMS (ESI) m/z calcd for C.sub.4.sup.13CH.sub.4NO.sub.2S [M-H].sup.−: 143.0002; found: 143.0004

[0493] Isotopic Enrichment: +1 .sup.13C, 51.92%

Example 31: Synthesis of .SUP.13.C-1-methyl-1H-indole-2-carboxylic acid

[0494] ##STR00064##

[0495] The title compound was prepared according to general procedure, starting from the cesium salt of 1-methyl-1H-pyrrole-2-carboxylic acid (30.7 mg, 0.1 mmol), then heated for 2 hours. The enriched final compound was obtained with 35% yield (6.12 mg, 0.035 mmol) and 65% of isotopic enrichment.

[0496] .sup.1H NMR (400 MHz, DMSO-d6) δ 12.92 (bs, 1H), 7.66 (d, J=8.4 Hz, 1H), 7.56 (d, J=8.4 Hz, 1H), 7.32 (t, J=7.7 Hz, 1H), 7.21 (s, 1H), 7.11 (t, J=7.5 Hz, 1H), 4.02 (s, 3H)

[0497] .sup.13C NMR (100 MHz, DMSO-d6) δ 163.0, 139.2, 128.5 (t, J=42.5 Hz, 1C), 125.3, 124.5, 122.1, 120.3, 110.8, 109.3, 31.4

[0498] HRMS (ESI) m/z calcd for C.sub.9.sup.13CH.sub.8NO.sub.2 [M-H].sup.−: 175.0594; found: 175.0593

[0499] Isotopic Enrichment: +1 .sup.13C, 64.59%

Example 32: Synthesis of .SUP.13.C-benzofuran-2-carboxylic acid

[0500] ##STR00065##

[0501] The title compound was prepared according to general procedure, starting from the cesium salt of 3-methylbenzofuran-2-carboxylic acid (30.8 mg, 0.1 mmol), then heated for 2 hours. The enriched final compound was obtained with 53% yield (8.6 mg, 0.053 mmol) and 47% of isotopic enrichment.

[0502] .sup.1H NMR (400 MHz, DMSO-d6) δ 7.78 (d, J=8.0 Hz, 1H), 7.69 (dd, J=8.3, 0.8 Hz, 1H), 7.64 (S, 1H), 7.51-7.46 (m, 1H), 7.37-7.31 (m, 1H)

[0503] .sup.13C NMR (100 MHz, DMSO-d6) δ 160.2, 154.9, 146.7, 127.4, 126.9, 123.8, 123.0, 113.1, 112.0

[0504] LCMS (ESI) m/z calcd for C.sub.8.sup.13CH.sub.5O.sub.3 [M-H].sup.−: 162.3; found: 162.3

[0505] Isotopic Enrichment (LCMS): +1 .sup.13C, 47%

Example 33: Synthesis of .SUP.13.C-3-oxo-3H-benzo[f]chromene-2-carboxylic acid

[0506] ##STR00066##

[0507] The title compound was prepared according to general procedure, starting from the cesium salt of 3-oxo-3H-benzo[f]chromene-2-carboxylic acid (18.6 mg, 0.05 mmol), then heated for 1 hour. The enriched final compound was obtained with 26% yield (3.1 mg, 0.012 mmol) and 34% of isotopic enrichment.

[0508] .sup.1H NMR (400 MHz, CDCl.sub.3-d1) δ 9.70 (t, J=2.6 Hz, 1H), 8.43 (d, J=8.2 Hz, 1H), 8.23 (d, J=8.9 Hz, 1H), 7.98 (d, J=8.6 Hz, 1H), 7.84-7.80 (m, 1H), 7.71-7.67 (m, 1H), 7.56 (d, J=9.0 Hz, 1H)

[0509] .sup.13C NMR (100 MHz, CDCl.sub.3-d1) δ 164.4, 163.2, 151.7, 147.2, 144.5, 143.1, 138.1, 130.8, 130.2, 129.6, 127.7, 122.3, 122.1, 116.6

[0510] HRMS (ESI) m/z calcd for C.sub.13.sup.13C H.sub.7O.sub.4 [M-H].sup.−: 240.0384; found: 240.0383

[0511] Isotopic Enrichment: +1 .sup.13C, 34.35%

Example 34: Synthesis of .SUP.13.C-2-(3-cyano-4-isobutoxyphenyl)-4-methylthiazole-5-carboxylic acid

[0512] ##STR00067##

[0513] The title compound was prepared according to general procedure, starting from the cesium salt of 2-(3-cyano-4-isobutoxyphenyl)-4-methylthiazole-5-carboxylic acid (44.9 mg, 0.1 mmol), then heated for 1.5 hours. The enriched final compound was obtained with 10% yield (3.0 mg, 0.001 mmol) and 66% of isotopic enrichment.

[0514] .sup.1H NMR (400 MHz, DMSO-d6) δ 13.28 (bs, 1H), 8.29 (d, J=2.0 Hz, 1H), 8.23 (dd, J=8.8, 2.0 Hz, 1H), 7.38 (d, J=9.3 Hz, 1H), 4.01 (d, J=6.3 Hz, 2H), 2.66 (s, 3H), 2.13-2.06 (m, 1H), 1.02 (d, J=7.7 Hz, 6H)

[0515] .sup.13C NMR (100 MHz, DMSO-d6) δ 172.1, 162.9, 133.0, 131.4, 125.4, 115.4, 113.9, 101.5, 75.1, 48.5, 30.1, 29.0, 27.6, 18.7, 17.1, 16.9

[0516] HRMS (ESI) m/z calcd for C.sub.15.sup.13CH.sub.15N.sub.2O.sub.3S [M-H].sup.−: 316.0842; found: 316.0839

[0517] Isotopic Enrichment: +1 .sup.13C, 65.89%

Example 35: Synthesis of .SUP.14.C-2-nitrobenzoic acid

[0518] ##STR00068##

[0519] The title compound was prepared according to general procedure, starting from the cesium salt of 2-nitrobenzoic acid (15 mg, 0.05 mmol), then .sup.14CO.sub.2 (0.160 mmol/347.43 MBq) was added and heated for 2 hours. The enriched final compound was obtained after extraction and concentration in 21.608 MBq

[0520] Specific activity (MS (ESI)): 1505.9 MBq/mmol

[0521] Isotopic Enrichment: +2 .sup.14C, 65%

[0522] TLC (silicagel 60F254, DCM/MeOH/AcOH (90/10/05)); Radiochemical purity: 99%.

Example 36: Synthesis of .SUP.14.C-benzofuran-2-carboxylic acid

[0523] ##STR00069##

[0524] The title compound was prepared according to general procedure, starting from the cesium salt of 3-methylbenzofuran-2-carboxylic acid (30.8 mg, 0.1 mmol), then .sup.14CO.sub.2 (0.277 mmol/601.62 MBq) was added and heated for 2 hours. The enriched final compound was obtained after extraction and concentration in 54.279 MBq.

[0525] Specific activity (MS (ESI)): 1080.4 MBq/mmol

[0526] Isotopic Enrichment: +2 .sup.14C, 46.8%

[0527] TLC (silicagel 60F254, DCM/MeOH/AcOH (90/10/05)); Radiochemical purity: 99%.

Example 37: Synthesis of .SUP.14.C-4-(N,N-dipropylsulfamoyl)benzoic acid

[0528] ##STR00070##

[0529] The title compound was prepared according to general procedure, starting from the cesium salt of 4-(N,N-dipropylsulfamoyl)benzoic acid (20.8 mg, 0.05 mmol), then .sup.14CO.sub.2 (0.143 mmol/310.578 MBq) was added and heated for 2 hours. The enriched final compound was obtained after extraction and concentration in 28.416 MBq.

[0530] Specific activity (MS (ESI)): 923.52 MBq/mmol

[0531] Isotopic Enrichment: +2 .sup.14C, 40%

[0532] TLC (silicagel 60F254, DCM/MeOH/AcOH (90/10/05)); Radiochemical purity: 99%.

Example 38: Synthesis of .SUP.14.C-9-fluoro-5-methyl-1-oxo-6,7-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-2-carboxylic acid

[0533] ##STR00071##

[0534] The title compound was prepared according to general procedure, starting from the cesium salt of 9-fluoro-5-methyl-1-oxo-6,7-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-2-carboxylic acid (39.2 mg, 0.1 mmol), then .sup.14CO.sub.2 (0.270 mmol/586.413 MBq) was added and heated for 2 hours. The enriched final compound was obtained after extraction and concentration in 41.107 MBq.

[0535] Specific activity (MS (ESI)): 1075.96 MBq/mmol

[0536] Isotopic Enrichment: +2 .sup.14C, 46%

[0537] TLC (silicagel 60F254, DCM/MeOH/AcOH (95/5/05)); Radiochemical purity: 99%.

Example 39: Synthesis of .SUP.14.C-2-(3-cyano-4-isobutoxyphenyl)-4-methylthiazole-5-carboxylic acid

[0538] ##STR00072##

[0539] The title compound was prepared according to general procedure, procedure mentioned before, starting from the cesium salt of 2-(3-cyano-4-isobutoxyphenyl)-4-methylthiazole-5-carboxylic acid (44.9 mg, 0.1 mmol), then .sup.14CO.sub.2 (0.269 mmol/584.6 MBq) was added and heated for 1.5 hours. The enriched final compound was obtained after extraction and concentration in 23.68 MBq.

[0540] Specific activity (MS (ESI)): 1253.56 MBq/mmol

[0541] Isotopic Enrichment: +2 .sup.14C, 54.3%

[0542] TLC (silicagel 60F254, DCM/MeOH/AcOH (95/5/05)); Radiochemical purity: 98.3%.

Example 40: Synthesis of 2,2,2-trifluoroacetic-1-.SUP.13.C Acid

[0543] ##STR00073##

[0544] The title compound was prepared starting from the potassium salt of trifluoroacetic acid (15.2 mg, 0.1 mmol), adding Pd(O.sub.2CCF.sub.3).sub.2 20 mol % and neocuprine ligand 20 mol % and dissolved in a NMP/DMSO mixture (1:1). Afterwards, the NMR tube was charged with 3 equivalents of .sup.13CO.sub.2 then heated for 2 hours at 150° C.

[0545] The crude mixture was filtered on a celite plug and extracted with AcOEt/HCl (1M).

[0546] Mass M-1=114, [M-1].sup.+1 (.sup.13C): 15%.

II. Optimization of Reaction Conditions for the Synthesis of Carbon Labeled Compounds of Formula (I)—

[0547] ##STR00074##

[0548] As already mentioned and not wishing to be bound by theory, the isotope exchange at the carbon atom of the carboxyl function in one step is the result of a dynamic decarboxylation/carboxylation reaction. The catalyst system used in the process of the invention is able to reversibly decarboxylate and re-carboxylate the carboxylic moiety. This is illustrated in FIGS. 3 and 4. Still not wishing to be bound by theory, the transformation takes place by the following mechanism: at first a metal catalyzed decarboxylation of the metal-ligand coordinated carboxylate generates a metal-ligand intermediate. Under the suitable reaction conditions the metal-ligand intermediate will carboxylate in presence of labeled *CO.sub.2 to form the labeled metal-ligand coordinated carboxylate, which upon quenching yields the labeled compound of formula (I).

[0549] It seems that the catalyst system plays an important role in the reversible decarboxylation/carboxylation of the carboxyl containing organic compound.

[0550] Initial conditions for the CO.sub.2 exchange (decarboxylation/carboxylation of the carboxyl containing organic compound) were found using N,N,N,N-tetramethylethane-1,2-diamine (TMEDA, 0.4 eq.), and CuBr (0.2 eq.) dissolved in a mixture (1:4) of anhydrous DMSO and NMP (0.50 ml). The NMR tube was then charged with 3 equivalents of .sup.13CO.sub.2, then heated at 150° C. for 2 hours. The reaction promoted the formation of the desired enriched product with low isolated yield (<5%) and 21% of isotopic enrichment (IE), confirmed by mass.

[0551] In a first attempt, the catalyst loading was investigated (Table 1).

[0552] Inspired by the work of Moran's group (Richmond, E.; Moran, J. Synlett, Harnessing Complex Mixtures for Catalyst Discovery. 2016, 27, 2637-2643), different ligand families, as shown in FIG. 6, were screened in the same tube, in order to improve the catalytic system: The ligands tested were 2,2-bypiridyl, 1,10-phenanthroline, nitrogen containing ligands, mono and bi-dentate phosphines, terpyridine, ureas and thioureas, BOX and PYBOX. The details of the ligand screening is given in (Table 2). Among the ligand families tested, the most interesting family was the BOX ligands. Table 3 shows the results with different BOX ligands.

[0553] Using the BOX ligands, the influence of the solvents (Table 4), time reaction (Table 5) and temperature (Table 6) on isotopic enrichment was subsequently studied.

General Conditions for the Screening:

[0554] In an argon-filled glovebox, a Wilmad® NMR tube (5 mm diam. 7 In.) with Young valve was charged with cesium 2-nitrobenzoate (29.9 mg, 0.1 mmol), 0.2 equivalent of the ligands mix (shown in FIG. 6 and selected as in Table 2) and 0.2 equivalent of CuBr (I) in a mixture (1:4) of anhydrous DMSO and NMP (0.5 mL). The loaded NMR tube was removed from the glovebox and connected to carbon TRITEC manifold (See: http://www.rctritec.com/en/tritium-handling-technology/c-14-manifold-system.html).

[0555] The NMR tube mixture was frozen using a liquid nitrogen bath. After degassing the tube, .sup.13CO.sub.2 (3 eq.) was charged. The reaction mixture was allowed to come back to room temperature (2 min) and subsequently heated and stirred at 150° C. for 2 hours. After cooling down to room temperature (20+5° C.), the mixture was quenched with aqueous HCl 2M (5 mL), stirred for 2 minutes and extracted with ethyl acetate (3-5 mL, 3 times). The combined organic layers were then extracted with sodium hydroxide (1M) until basic pH is reached. The basic aqueous phase was slowly acidified to pH 2 with HCl 2M, and extracted with ethyl acetate (3-5 mL, 3 times). The combined organic layers (ethyl acetate) were dried over MgSO.sub.4 filtered and concentrated under reduced pressure to obtain the isotopically enriched final compound. IE was determined by mass spectroscopy. The different reaction conditions and IE results are summarized in the following tables.

TABLE-US-00001 TABLE 1 Study of the influence of metal catalyst loading; temperature: 150° C. Metal catalyst (catalyst loading Ligand IE Entry in eq) (eq.) Solvent (%) 1 CuBr(I) (0.2) TMEDA (0.4) NMP/DMSO (4/1) 21 2 CuI(I) (0.4) TMEDA (0.4.) NMP/DMSO (4/1) 16 3 CuBr(I) (0.2) TMEDA (0.2) NMP/DMSO (4/1) 23 4 CuBr(I) (0.1) TMEDA (0.1) NMP/DMSO (4/1)  6

TABLE-US-00002 TABLE 2 Study of the influence of different ligands families in FIG. 6. The reaction conditions are temperature: 150° C., solvent: NMP/DMSO, catalyst: CuBr(I), time: 2 h. Ligands IE Entry (0.2 eq. total) (%) 1 1, 2, 3, 4, 14 8.2 2 5, 6, 15 0 3 7, 8, 9, 11 1.5 4 10, 12, 13 1 5 16, 17, 18, 19 8.2 6 20, 21, 22 2.2 7 23, 24, 25 10 8 26, 27, 28, 29 2.2 9 30, 31, 32 2 10 33, 34, 35, 36 1.6 11 37, 38 6 12 39, 40, 41 29 13 42, 43, 44, 45 32

[0556] Following the general procedure described above (Table 1), the IE summarized in Table 2 were determined after work-up by mass analysis. The best ligand family was the BOX one (L39-45), entries 12 and 13.

TABLE-US-00003 TABLE 3 Study of the influence of different BOX ligands. The reaction conditions are temperature: 150° C., solvent: NMP/DMSO, time: 2 h Metal catalyst Ligand IE Entry (0.2 eq) (0.2 eq.) (%) 1 CuBr(I) 39 9 2 CuI(I) 40 45 3 CuBr(I) 41 2 4 CuBr(I) 42 70 5 CuBr(I) 43 62 6 CuBr(I) 44 60 7 CuBr(I) 45 75 8 CuBr(II) 40 20 9 CuOAc(II) 40 13.5

[0557] Following the general procedure described above (Table 1) and using the ligands and copper catalysts (0.2 eq. for 0.1 mmol of the corresponding cesium salt) in Table 3, the IE summarized in Table 3 were determined after work-up, by mass analysis. The best ligands were 40, 42 (L2), 43, 44 and in particular the 45 (L1) with an IE of 75%. On the other hand the use of Cu (II) did not improve the reaction.

TABLE-US-00004 TABLE 4 Influence of the solvent on the IE. The reaction conditions other than the solvents are temperature: 150° C., CuBr (I) and L1 (ligand 45): 0.2 eq., time: 2 h Entry Solvent IE (%) 1 DMSO 72 2 NMP 70 4 DMSO/NMP (1:4) 70 5 DMA 70

[0558] Following the general procedure described above (Table 1) and using L1 (ligand 45) (6.6 mg, 0.2 eq.) and CuBr (I) (2.9 mg, 0.2 eq.) the subsequent solvent (0.5 mL for 0.1 mmol of the corresponding cesium salt of the acid), the IE summarized in Table 4 were determined after work-up, by mass analysis. For the model substrate (2-nitrobenzoic acid Cs salt) anhydrous DMSO showed to be the best solvent. A mixture of solvents DMSO/NMP (1:4) was used in case of solubility problem of some compounds.

TABLE-US-00005 TABLE 5 Influence of the temperature on the IE. The reaction conditions other than the temperature are: solvent: DMSO, CuBr (I) and L1 (ligand 45): 0.2 eq., time: 2 h Entry Temperature (° C.) IE (%) 1 150 72 2 130 10 3 100  8

[0559] Following the general procedure described above (Table 1) and using L1 (ligand 45) (6.6 mg, 0.2 eq.) and CuBr (I) (2.9 mg, 0.2 eq.) and cesium 2-nitrobenzoate. (29.9 mg, 0.1 mmol) and DMSO (0.5 mL), the reaction temperature was changed as in Table 5. The IE summarized in Table 5 were determined after work-up, by mass analysis. The best temperature showed to be 150° C.

TABLE-US-00006 TABLE 6 Influence of reaction time on IE. The reaction conditions other than the time are: temperature: 150° C., solvent: DMSO, CuBr(I) and L1 (ligand 45): 0.2 eq. Entry Time (h) IE (%) 1 2 h 72 2 1 h 23 3 30 min  0

[0560] Following the general procedure described above (Table 1) and using L1 (6.6 mg, 0.2 eq.), CuBr (I) (2.9 mg, 0.2 eq.) and cesium 2-nitrobenzoate. (29.9 mg, 0.1 mmol) and DMSO (0.5 mL), the reaction was heated at 150° C., then time was changed as in the table. The IE summarized in Table 6 were determined after work-up, by mass analysis. The best reaction time showed to be 2 h.