DEUTERATED AND TRITIATED N-(4,5-DIMETHYLTHIAZOLO-2(3H)-YLIDEN)-2,2,3,3-TETRAMETHYLCYCLOPROPANE-1-CARBOXAMIDE DERIVATIVES AND THE USE THEREOF

Abstract

Compounds of general formula I

##STR00001##

X.sup.1 is a CD.sub.2 group or a CT.sub.2 group; X.sup.2 is oxygen or a group (CZ.sup.1Z.sup.2).sub.n, wherein Z.sup.1 and Z.sup.2 on each occurrence independently each are hydrogen, deuterium, or tritium and n is an integer from 1 to 12; X.sup.3 is a CD.sub.2 group or a CT.sub.2 group; and R is selected from the group consisting of hydroxy, -NO.sub.2, halogen, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulphoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate.

Claims

1-15. (canceled)

16. A compound of general formula I ##STR00030## wherein X.sup.1 is a CD.sub.2 group or a CT.sub.2 group; X.sup.2 is oxygen or a group (CZ.sup.1Z.sup.2).sub.n, wherein Z.sup.1 and Z.sup.2 on each occurrence independently each are hydrogen, deuterium, or tritium and n is an integer from 1 to 12; X.sup.3 is a CD.sub.2 group or a CT.sub.2 group; and R is selected from the group consisting of hydroxy, -NO.sub.2, halogen, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulphoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate.

17. The compound according to claim 16, wherein X.sup.1 is a CD.sub.2 group or a CT.sub.2 group; X.sup.2 is selected from the group consisting of (CH.sub.2).sub.n, (CD.sub.2).sub.n, (CT.sub.2).sub.n, and O, wherein n is an integer from 1 to 12; X.sup.3 is a CD.sub.2 group or a CT.sub.2 group; and R is selected from the group consisting of hydroxy, -NO.sub.2, halogen, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulphoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate.

18. The compound according to claim 16, wherein X.sup.1 is a CD.sub.2 group; X.sup.2 is selected from the group consisting of (CH.sub.2).sub.n, (CD.sub.2).sub.n, and O, wherein n is an integer from 1 to 12; X.sup.3 is a CD.sub.2 group; and R is selected from the group consisting of hydroxy, -NO.sub.2, halogen, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulphoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate.

19. The compound according to claim 16, wherein n is 1, 2, 3, 4, 5, or 6.

20. The compound according to claim 16, wherein R is fluorine.

21. The compound according to claim 16, wherein R is [.sup.18F]fluorine.

22. The compound according to claim 16, wherein it is N-(3-(4-([.sup.18F]fluoro)butyl-1,1,4,4-d.sub.4)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide; N-(3-(4-fluorobutyl-1,1,4,4-d.sub.4)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide; 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,4,4-d.sub.4-4-methylbenzene sulphonate; N-(3-(4-([.sup.18F]fluoro)butyl-1,1,2,2,3,3,4,4-d.sub.8)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide; N-(3-(4-fluorobutyl-1,1,2,2,3,3,4,4-ds)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide; or 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,2,2,3,3,4,4-ds-4-methylbenzene sulphonate.

23. A compound according to claim 16 for use as a medicament.

24. A compound according to claim 16 for use as a medicament for the diagnostics and therapy of diseases in which a cannabinoid receptor 2 is involved.

25. The compound according to claim 23, wherein the medicament is a radiopharmaceutical for the nuclear-medical imaging of the cannabinoid receptor 2 by means of positron emission tomography (PET).

26. A medicament containing a compound according to claim 16 or a pharmaceutically acceptable salt thereof.

27. Use of a compound of general formula I-P ##STR00031## wherein X.sup.1 is a CD.sub.2 group or a CT.sub.2 group; X.sup.2 is oxygen or a group (CZ.sup.1Z.sup.2).sub.n, wherein Z.sup.1 and Z.sup.2 on each occurrence independently each are hydrogen, deuterium, or tritium and n is an integer from 1 to 12; X.sup.3 is a CD.sub.2 group or a CT.sub.2 group; and AG is selected from the group consisting of hydroxy, -NO.sub.2, chlorine, bromine, iodine, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulfoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate, for the preparation of a compound of general formula [.sup.18F]I-F ##STR00032## wherein X .sup.1, X.sup.2, and X.sup.3 have the meanings given in connection with general formula I-P.

28. A method for the preparation of a compound of general formula I-F, ##STR00033## wherein X.sup.1 is a CD.sub.2 group or a CT.sub.2 group; X.sup.2 is oxygen or a group (CZ.sup.1Z.sup.2).sub.n, wherein Z.sup.1 and Z.sup.2 on each occurrence independently each are hydrogen, deuterium, or tritium and n is an integer from 1 to 12; and X.sup.3 is a CD.sub.2 group or a CT.sub.2 group; wherein the method comprises the steps of: (a) reacting a compound of formula 11 ##STR00034## ##STR00035## wherein X.sup.1, X.sup.2, and X.sup.3 have the meanings given in connection with general formula I-P; Y is a sulphonate; and AG is selected from the group consisting of hydroxy, -NO.sub.2, chlorine, bromine, iodine, a diazonium ion, a diazonium salt, a trialkylammonium ion, a trialkylammonium salt, a dialkoxyarene, a sulfoxide, a boronic acid, a boronic acid ester, an organotin compound, an iodonium ion, an iodonium salt, an iodonium ylide, and a sulphonate; to a compound of general formula I-P ##STR00036## wherein X.sup.1, X.sup.2, X.sup.3, and AG have the meanings given in connection with general formula II; and (b) reacting the compound of general formula I-P with a fluorinating agent to the compound of general formula I-F.

29. The method according to claim 28, wherein Y is -O-Ts or -O-Ms, wherein Ts designates a tosyl group and Ms a mesyl group.

30. The method according to claim 28, wherein Y is -O-Ts, wherein Ts designates a tosyl group.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0072] In the following the invention is explained in detail with the help of examples not intended to limit the invention with reference to the drawings. Here,

[0073] FIG. 1 shows an UV-HPLC chromatogram of the reference compound JHU94620-D4;

[0074] FIG. 2 shows a radio-HPLC chromatogram of compound [.sup.18F]JHU94620-D4 according to the invention;

[0075] FIG. 3 shows a radio-HPLC chromatogram of cerebral homogenate 30 p.i. of [.sup.18F]JHU94620; and

[0076] FIG. 4 shows a radio-HPLC chromatogram of cerebral homogenate 30 p.i. of [.sup.18F]JHU94620-D4.

DETAILED DESCRIPTION

Example 1 Synthesis of N-(3-(4-([.SUP.18.F]fluoro)butyl-1,1,4,4-d.SUB.4.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([.SUP.18 F]JHU94620-D4)

[0077] Scheme 5 shows the preparation of compound [.sup.18F]JHU94620-D4 according to the invention by reacting N-(4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethyl-cyclopropane-1-carboxamide (11) with butane-1,4-diyl-1,1,4,4-d.sub.4-bis(4-methylbenzene sulphonate) (12) to the precursor (3) and the subsequent reaction of compound 3 to [.sup.18F]JHU94620-D4.

##STR00025##

Compound 12 is a compound of general formula II, in which X.sup.1 is CD.sub.2, X.sup.2 is (CH.sub.2).sub.2, X.sup.3 is CD.sub.2, Y is -OTs and AG is -OTs. K[.sup.18F]F-K.sub.222 designates the [.sup.18F]F.sup.-/K.sub.222/K.sup.+ complex the preparation of which is described below.

Step (a): Synthesis of 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,4,4-d.SUB.4.-4-methylbenzene sulphonate (3)

[0078] To a solution of compound 11 (1 eq, 0.6 mmol) and compound 12 (1.5 eq, 0.9 mmol) in 3 mL of DMF NaH (60%, 2 eq, 1.2 mmol) was added and the mixture was heated for 1 h to 60° C. under an argon atmosphere. Subsequently, the solvent was removed at the rotary evaporator. The residue was taken up in ethyl acetate (EA) (10 mL) and washed with an aqueous 5% NaHCO.sub.3 solution (10 mL) and subsequently with a saturated NaCl solution (100 mL). Drying with MgSO.sub.4 und removal of the solvents gave a yellow oil which was purified by means of column chromatography (silica gel, EA : petroleum ether (PE) of 1/20 to 1/4). Compound 3 was obtained as a white solid with a yield of 33%.

[0079] .sup.1H-NMR (400 MHz, CDCl.sub.3) δ 7.81 (d, J = 8.3 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 2.47 (s, 3H), 2.16 (s, 6H), 1.75 (m, 4H) 1.50 (s, 1H), 1.33 (s, 6H), 1.21 (s, 6H). HRMS (ESI+): m/z (%) = 483.2278, calc. 483.2284 for C.sub.24H.sub.31D.sub.4FN.sub.2O.sub.4S.sub.2.sup.+ [M+H].sup.+.

Step (b): Synthesis of N-(3-(4-([.SUP.18.F]fluoro)butyl-1,1,4,4-d.SUB.4.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([.SUP.18.F]JHU94620-D4)

[0080] The aqueous [.sup.18F]fluoride (2 to 3 GBq) obtained after radiation was added to 1 mL of water, fixed on an anion exchange cartridge (QMA) and eluted with an aqueous K.sub.2CO.sub.3 solution (1.8 mg in 300 mL water) in a solution of 1 mL of MeCN and Kryptofix (K.sub.222, 5.6 mg). Azeotropic drying of the complex was microwave assisted (power cycling, 75W, 50 - 60° C., argon stream) under vacuum. To the [.sup.18F]F.sup.-/K.sub.222/K.sup.+ complex formed 2 mg of the precursor 3 (in 600 ml MeCN) were added. Subsequently, the reaction mixture was stirred at 90° C. for 10 min.

[0081] To determine the labeling yield an aliquot was taken and analyzed with radio-DC (49±4%, n=3) and radio-HPLC (48±5%, n=2). Purification and isolation of the radiotracer was carried out by means of semi-preparative RP-HPLC (column: ReproSil-Pur 120 C18-AQ, 250x20 mm, 5 mm; eluting agent: 65% MeCN/20 mM NH.sub.4OAc.sub.aq.; flow: 4.2 mL/min). The collected product fraction was diluted with water (20 mL), sorbed on an Sep-Pak.sup.®-C18 Plus cartridge and eluted with ethanol (EtOH) (1.0 mL). Subsequently, the solvent was removed under heating in the argon stream and formulated in 0.9% saline (≤10% ethanol, v/v). The product [.sup.18F]JHU94620-D4 was isolated within a synthesis time of ca. 102 min and analyzed by radio-HPLC and radio-DC, whereby the identity of the product was confirmed by co-injection of the reference compound (see, FIGS. 1 and 2). The radiochemical purity was ≥ 99%. The radiochemical yield was about 20 to 25%. The molar activity was 200±20 GBq/.Math.mol.

Comparative Example 1 Synthesis of N-(3-(4-([.SUP.18.F]fluoro)butyl)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([.SUP.18.F]JHU94620)

[0082] For comparison, [.sup.18F]JHU94620 was prepared using a bromine precursor, as described in Moldovan et al. J. Med. Chem. 2016, 59, 7840-7855. [.sup.18F]JHU94620 was obtained with a radiochemical yield of 16% and a molar activity of 170 GBq/.Math.mol.

Example 2 Synthesis of N-(3-(4-fluorobutyl-1,1,4,4-d.SUB.4.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide (JHU94620-D4)

[0083] Scheme 6 shows the preparation of compound JHU94620-D4 according to the invention by reacting N-(4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcy-clopropane-1-carboxamide (11) with butane-1,4-diyl-1,1,4,4-d.sub.4-bis(4-methylbenzene sulphonate) (12) to the precursor (3) and the subsequent reaction of compound 3 to JHU94620-D4.

##STR00026##

TBAF designates tetrabutyl ammonium fluoride.

Step (a): Synthesis of 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,4,4-d.SUB.4.-4-methylbenzene sulphonate (3)

[0084] Step (a) of the method shown in Scheme 6 was carried out as described in example 1, step (a).

Step (b): Synthesis of N-(3-(4-fluorobutyl-1,1,4,4-d.SUB.4.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide (JHU94620-D4)

[0085] To a solution of compound 3 (1 eq, 0.5 mmol) in 3 mL of THF TBAF (1 M in THF, 2 eq, 1 mmol) was added and the mixture was heated for 1 hr to 50° C. under an argon atmosphere. Subsequently, the solvent was removed at the rotary evaporator. The residue was taken up in ethyl acetate (EA) (10 mL) and washed with an aqueous 5% NaHCO.sub.3 solution (10 mL) and subsequently with a saturated NaCl solution (100 mL). Drying with MgSO.sub.4 und removal of the solvents gave a yellow oil which was purified by means of column chromatography (silica gel, EA : petroleum ether (PE) from 1/20 to 1/4). Compound JHU94620-D4 was obtained as a white solid with a yield of 72%.

[0086] .sup.1H-NMR (300 MHz, CDCl.sub.3) δ 2.20 (s, 3H), 2.18 (s, 3H), 1.55 (s, 1H), 1.36 (s, 6H), 1.24 (s, 6H). HRMS (ESI+): m/z (%) = 331.2152, calc. 331.2152 for C.sub.17H.sub.24D.sub.4FN.sub.2OS.sup.+ [M+H].sup.+.

Example 3 Synthesis of N-(3-(4-([.SUP.18.F]fluoro)butyl-1,1,2,2,3,3,4,4-d.SUB.8.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([.SUP.18.F]JHU94620-D8)

[0087] Scheme 7 shows the preparation of compound [.sup.18F]JHU94620-D8 according to the invention by reacting N-(4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethyl-cyclopropane-1-carboxamide (11) with butane-1,4-diyl-1,1,2,2,3,3,4,4-ds-bis(4-methylbenzene sulphonate) (13) to the precursor (4) and the subsequent reaction of compound 4 to [.sup.18F]JHU94620-D8.

##STR00027##

Compound 13 is a compound of general formula II, in which X.sup.1 is CD.sub.2, X.sup.2 is (CD.sub.2).sub.2, X.sup.3 is CD.sub.2, Y is -OTs and AG is -OTs.

Step (a): Synthesis of 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,2,2,3,3,4,4-d.SUB.8.-4-methylbenzene sulphonate (4)

[0088] Compound 4 was prepared in the same way as in example 1, step (a), except that compound 13 was used instead of compound 12.

[0089] .sup.1H-NMR (400 MHz, CDCl.sub.3) δ 7.81 (d, J = 8.3 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 2.47 (s, 3H), 2.16 (s, 6H), 1.50 (s, 1H), 1.33 (s, 6H), 1.21 (s, 6H). HRMS (ESI+): m/z (%) = 487.2537, calc. 487.2535 for C.sub.24H.sub.27D.sub.8N.sub.2O.sub.4S.sub.2.sup.+ [M+H].sup.+.

Step (b): Synthesis of N-(3-(4-([.SUP.18.F]fluoro)butyl-1,1,2,2,3,3,4,4-d.SUB.8.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide ([.SUP.18.F]JHU94620-D8)

[0090] [.sup.18F]JHU94620-D8 was prepared in the same way as in example 1, step (b), except that compound 4 was used instead of compound 3.

Example 4 Synthesis of N-(3-(4-fluorobutyl-1,1,2,2,3,3,4,4-ds)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide (JHU94620-D8)

[0091] Scheme 8 shows the preparation of compound JHU94620-D8 according to the invention by reacting N-(4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide (11) with butane-1,4-diyl-1,1,2,2,3,3,4,4-ds-bis(4-methylbenzene sulphonate) (13) to the precursor (4) and the subsequent reaction of compound 4 to JHU94620-D8.

##STR00028##

Step (a): Synthesis of 4-(4,5-dimethyl-2-((2,2,3,3-tetramethylcyclopropane-1-carbonyl)-imino)thiazole-3(2H)-yl)butyl-1,1,2,2,3,3,4,4-d.SUB.8.-4-methylbenzene sulphonate (4)

[0092] Step (a) of the method shown in scheme 8 was carried out as described in example 1, step (a).

Step (b): Synthesis of N-(3-(4-fluorobutyl-1,1,2,2,3,3,4,4-d.SUB.8.)-4,5-dimethylthiazole-2(3H)-ylidene)-2,2,3,3-tetramethylcyclopropane-1-carboxamide (JHU94620-D8)

[0093] JHU94620-D8 was prepared in the same way as in example 2, step (b), except that compound 4 was used instead of compound 3.

[0094] .sup.1H-NMR (300 MHz, CDCl.sub.3) δ 2.20 (s, 3H), 2.18 (s, 3H), 1.93 - 1.81 (m, 2H), 1.77 = 1.68 (m, 2H), 1.55 (s, 1H), 1.36 (s, 6H), 1.24 (s, 6H). HRMS (ESI+): m/z (%) = 335.2402, calc. 335.2403 for C.sub.17H.sub.20D.sub.8FN.sub.2OS.sup.+ [M+H].sup.+.

Example 5 Analysis of the Metabolic Stability of [.SUP.18.F]JHU94620-D4

[0095] The metabolic stability of [.sup.18F]JHU94620-D4 was determined in accordance with the method described by Moldovan et al., J. Med. Chem. 2016, 59, 7840-7855. In the same way, the metabolic stability of JHU94620 and [.sup.18F]JHU94620 was determined. The radio-HPLC chromatograms shown in FIGS. 3 and 4 were determined using a ReproSil-Pur C18 AQ column (250×4.6 mm, 5 mm; eluting agent: 10-90-10% MeCN/20 mM NH.sub.4OAc; flow: 1 ml/min). JHU94620 has the following formula:

##STR00029##

JHU94620 is the non-radio-fluorinated and non-deuterated analogue to [.sup.18F]JHU94620-D4 and [.sup.18F]JHU94620-D8.

[0096] It is seen in FIG. 4 that in the in vivo metabolite study in female CD-1 mice the percentage of intact radiotracer [.sup.18F]JHU94620-D4 in the brain was ~80% (radio-HPLC, extraction yield >97%) and in the plasma was ~15% (radio-HPLC, extraction yield >95%) 30 min after the injection. FIG. 3 shows that the percentage of intact radiotracer [.sup.18F]JHU94620 was only 38%. Thus, [.sup.18F]JHU94620-D4 has a substantially higher metabolic stability than [.sup.18F]JHU94620.

[0097] In the in vivo metabolite study in female CD-1 mice in case of JHU94620 the percentage of intact radiotracer in the brain was 36% (radio-HPLC, n=3, extraction yield 93%) and in the plasma was 7% (radio-HPLC, n=3, extraction yield 94%) of the total activity 30 min after the injection.

[0098] The metabolic stability of [.sup.18F]JHU94620-D8 is highly similar to that of [.sup.18F]JHU94620-D4.

Example 6 Determination of the CBR.SUB.2 Equilibrium Dissociation Constant K.SUB.D of [.SUP.18.F]JHU94620-D8

[0099] The equilibrium dissociation constant K.sub.D was determined by means of a homolog competition assay. For that, a constant amount of binding protein (homogenate of CHO cells that were stably transfected with human CBR.sub.2 receptor; 2 Mio. cells/mL of the batch) was incubated with a constant amount of [.sup.18F]JHU94620-D8 (0.101 nM in the batch) and an increasing concentration of JHU94620 (0.01 nM-10 .Math.M in the batch) for 60 minutes at room temperature in binding buffer (50 mM TRIS-HCl, pH 7.4, with 5 mM of MgCl.sub.2, 1 mM EDTA, 1% BSA). Separation of receptor-bound and free radioligand was carried out by filtration over GF/B glass fiber filter incubated with 0.3% of polyethylene imine. Quantification of receptor-bound radioligand was carried out by measuring the filter-bound radioactivity in a gamma counter. Determination of the unspecific bonding of [.sup.18F]JHU94620-D8 was carried out by co-incubation with CP55940 (10 .Math.M in the batch), determination of the adsorption of the radioligand at the glass fiber filter was carried out by incubation without binding protein. From the IC.sub.50 value (2.82 nM) obtained in this experiment the K.sub.D value of compound [.sup.18F]JHU94620-D8 over human CBR.sub.2 receptors of the radioligands can be calculated via the Cheng-Prusoff equation simplified corresponding to the experimental approach (K.sub.D = IC.sub.50 (M) - radioligand (M)): K.sub.D = 2.72 nM. CP55940 is a synthetic cannabinoid.

Example 7 Determination of the CBR.SUB.2 Equilibrium Dissociation Constant K.SUB.i of JHU94620

[0100] Using the Cheng-Prusoff equation

[00001]$K_i=\frac{I{C}_{50}}{\left(1+\frac{L}{K_D}\right)}$

the CBR.sub.2 equilibrium dissociation constant K.sub.i of JHU94620 was determined. Here, L designates the concentration of the free ligand. Compound JHU94620 had a CBR.sub.2 affinity of K.sub.i = 0.4 nM (n = 3). Replacing hydrogen atoms by deuterium ions shall not have any influence on the K.sub.i value. This also applies to the replacement of hydrogen atoms by tritium ions.