Chemical compounds derived from normemantine and use of same in the medical field

Abstract

The present invention concerns novel chemical compounds corresponding to formulae (I) and (II): (I) (II) which, when marked with fluorine-18, can be used as markers of NMDA receptors for carrying out studies with a scanner.

Claims

1. A chemical compound of formula (I): ##STR00006## or a salt thereof of formula (II): ##STR00007## wherein X.sup. indicates a counteranion from a biological environment or selected from the ions chloride, bromide, iodide, acetate, methane sulphonate, benzene sulphonate, camphosulphonate, tartrate, dibenzoate, ascorbate, fumarate, citrate, phosphate, salicylate, oxalate, bromohydrate, or tosylate.

2. The compound according to claim 1, wherein the fluorine atom is a fluorine-18 (.sup.18F) atom.

3. An aqueous solution of at least one compound of claim 1 which can be injected intravenously.

4. The compound of formula P2 ##STR00008##

5. The compound of formula P1 as a precursor of the compound P2 ##STR00009##

6. A method for the evaluation of the behaviour of NMDA receptors during the study of neurological diseases in a mammal which comprises injecting said mammal with a compound according to claim 1 or 2 and carrying out a positron emission scanner to locate the .sup.18F atoms.

7. A method for treating a neurological disease selected from Alzheimer's disease, schizophrenia, Parkinson's disease, Huntington's disease, epilepsy and perinatal ischemia, in a subject in need thereof comprising the administration of at least one compound selected from the group consisting of compounds (I), (II), (P1) or (P2) to the said subject ##STR00010## formula wherein X.sup. indicates a counteranion from the biological environment or selected from the ions chloride, bromide, iodide, acetate, methane sulphonate, benzene sulphonate, camphosulphonate, tartrate, dibenzoate, ascorbate, fumarate, citrate, phosphate, salicylate, oxalate, bromohydrate, tosylate, ##STR00011##

Description

Example 1

METHOD FOR PREPARING 3-AMINO-1-ADAMANTANE ETHANOL (B)

(1) The starting product used is the hydrochloride of formula (A):

(2) ##STR00005##
which is a product marketed by the company Alinda under item number HLS0044-025.

(3) In a 50 ml three-neck round-bottom flask, 338 mg of the product (A) (1.38 mmol) is suspended in 22 ml of anhydrous tetrahydrofuran, in an argon atmosphere. The flask is equipped with a condenser and a thermometer; the suspension is cooled to 0 C. Next, 0.66 ml of BH.sub.3SMe.sub.2 (6.9 mmol) is added dropwise: the reaction is highly exothermic and the reactor is cooled so as to maintain the reaction medium below 5 C. The addition is carried out over 30 minutes, low-temperature stirring is maintained for 8 hours, and then the temperature is allowed to return to room temperature for 8 hours. Heat is then applied to maintain the reaction medium at 50 C. for 16 hours in order to complete the binding reaction of the molecules (A) on borane-dimethyl-sulfide.

(4) The medium is then cooled to 0 C. and the complex is hydrolyzed by slowly introducing 4.5 ml of methanol. Aqueous soda solution (10%) is then added to the reaction medium in order to obtain a pH above 10. Stirring is maintained for 1 hour and then the medium is concentrated to dryness at 40 C. under reduced pressure of 1 kPa.

(5) The residue is then taken up in 6 ml of water which is then acidified by means of 33% hydrochloric acid solution until a pH of 1 is obtained. The aqueous phase is washed three times with 6 ml of methyl-tertiobutyl-ether. The aqueous solution is then brought to pH 10 by means of 30% sodium hydroxide solution. The product (B) is then collected by three extractions with 6 ml of dichloromethane. The fractions are combined and evaporated under reduced pressure of 1 kPa until a white solid is obtained (127 mg, yield: 47%).

(6) The product is characterized by NMR:

(7) .sup.1H NMR (CDCl.sub.3, Bruker 400 MHz) 3.72 (2H, dt J=12 Hz, CH.sub.2OH), 2.8 (1H, OH), 2.21 (2H, broad, NH.sub.2), 0.75-1.40 (14H, CH.sub.2).

Example 2

PREPARATION OF N(3-ETHANOL ADAMANTANE)-O-TERTIOBUTYL CARBAMATE (C)

(8) The product (B) obtained in example 1 is used as the starting product.

(9) 195 mg of the compound (B) is diluted in 1 ml of dioxane and 1 ml of water. 260 mg of sodium carbonate and then 400 mg of di-tert-butyl-dicarbonate in solution in 2 ml of dioxane are added. The medium is stirred for 72 hours.

(10) 10 ml of water is then added to the medium, the pH of which is adjusted to 3 by means of 1 N hydrochloric acid solution. The product is then extracted by successive extractions with 10 ml of ethyl acetate. The extractions are combined, dried over MgSO.sub.4 and then the product (C) is collected by evaporation under reduced pressure of 1 kPa.

(11) The product (C) is obtained in the form of a white solid (250 mg, yield 84%) and is characterized by NMR:

(12) .sup.1H NMR (CDCl.sub.3, Bruker 300 MHz) 4.35 (1H, br, NH); 3.7 (2H, dt J=7 Hz, CH.sub.2OH), 2.65 (1H, OH), 1.2-1.85 (29H, CH.sub.2)

Example 3

PREPARATION OF N(3-(2-TOSYLATE-ETHYL)ADAMANTANE)-O-TERTIOBUTYL CARBAMATE (P1)

(13) The product (C) obtained in example 2 is used as the starting product.

(14) 295 mg of compound C is diluted in 1 ml of dichloromethane. 200 mg of triethyl amine diluted in 1 ml of dichloromethane is then added. 200 mg of tosyl chloride diluted in 2 ml of dichloromethane is then added. The medium is stirred for 24 hours.

(15) The medium is washed three times with 5 ml of water at acidic pH and then three times with 5 ml at pH 7. The organic phase is dried over MgSO.sub.4 and then the product P1 is collected by evaporation under reduced pressure of 1 kPa.

(16) The product (P1) is obtained in the form of a white solid (425 mg, yield 95%) and is characterized by NMR:

(17) .sup.1H NMR (CDCl.sub.3, Bruker 300 MHz): 7.79 (2H, d, J=8.1 Hz, aromatic CH), 7.36 (2H, d, J=8.1 Hz, 2 aromatic CH), 4.34 (1H, broad, NH), 4.1 (2H, dt J=7.8 Hz, CH.sub.2OH), 2.46 (3H, CH.sub.3 tosyl), 2.08 (2H, m, CH.sub.2CH.sub.2OH), 1.81 (4H, m, CH.sub.2CN), 1.63 (2H, CH.sub.2), 1.55 (6H, CH.sub.2), 1.4-1.43 (9H, CH.sub.3).

Example 4

PREPARATION OF N(3-(2-FLUORO-ETHYL)ADAMANTANE)-O-TERTIOBUTYL CARBAMATE (P2)

(18) The product (P1) obtained in example 3 is used as the starting product.

(19) In a 100 ml three-neck round-bottom flask equipped with a condenser and a thermometer, under an anhydrous argon atmosphere, 225 mg of the compound (P1) (0.5 mmol) is dissolved in 30 ml of dichloroethane dried beforehand over P.sub.2O.sub.5.

(20) The temperature of the reaction medium is lowered to 42 C. to avoid the strong exothermicity of the reaction.

(21) 1 mmol (13 l) of (diethyl-amino)-sulfur trifluoride (hereafter DAST) is then introduced into the flask dropwise. The medium is maintained at 42 C. for 2 hours and then the temperature is allowed to return to room temperature. After 16 hours under these conditions the temperature is lowered to 78 C. and the reagents are slowly hydrolyzed with aqueous potassium carbonate solution (3.5 g of K.sub.2CO.sub.3 in 12 ml of water; 25 mmol). After 2 hours the reaction is allowed to return to room temperature.

(22) After one hour under these conditions the organic phase is collected, washed twice with water at pH 7, dried over magnesium sulfate and then concentrated under reduced pressure to obtain a pale yellow oil (66 mg, 45%).

(23) The product is characterized by NMR as being the compound (P2):

(24) .sup.1H NMR (CDCl.sub.3, Bruker 300 MHz): 4.50 (2H, dt J=7.8 Hz and J=43 Hz, CH.sub.2F), 4.38 (1H, broad, NH), 1.95-1.43 (25H, CH.sub.3).

Example 5

PREPARATION OF 1-AMINO-3-FLUOROETHYL-ADAMANTANE HYDROCHLORIDE (II) AND 1-AMINO-3-FLUOROETHYL-ADAMANTANE (I)

(25) The following procedure is carried out starting with the compound obtained in example 4.

(26) In a 50 ml round-bottom flask, 100 mg of the compound (P2) is solubilized in 3 ml of dichloromethane. The temperature of the medium is lowered to 0 C. and then 10 ml of hydrochloric ethyl ether is added.

(27) After 8 hours at room temperature, 10 ml of 10.sup.3 M hydrochloric acid solution is added. The aqueous phase is collected and this extraction is repeated twice.

(28) The fractions are combined and concentrated under vacuum. The oil obtained (55 mg) is taken up in 1 ml of water and the product is precipitated by adding 1 ml of ethanol. The precipitate, which is recovered via filtration (50 mg, 75%), is the compound (II) (characterized by mass spectrometry, M+=197.1567 C.sub.12H.sub.20FN (calculated 197.158); m/z (Cl) 196.15 (M1), 181.1 (M-NH.sub.2), 150.1 (M-C.sub.2H.sub.4F).

(29) The compound (II) is transformed into the compound (I) according to the following protocol.

(30) 50 mg of the compound (II) is diluted in 3 ml of water. The pH of the solution is brought to 9 by means of 10% sodium hydroxide solution. Extraction is carried out with 6 ml of dichloromethane, and the extraction is repeated twice. The fractions are combined and dried over magnesium sulfate. The solvent is evaporated under vacuum and the compound (I) is collected in the form of a pale yellow oil characterized by NMR:

(31) .sup.1H NMR (CDCl.sub.3, Brker 400 MHz): 4.54 (2H, dt J=12 Hz and J=48 Hz, CH.sub.2F), 2.15 (2H, broad, NH.sub.2), 1.65-1.26 (16H, CH.sub.3).

(32) For the following examples the term fluoroethyl normemantine will be used as a generic term to refer to the compound I or to its chloride salt II. The reason for this choice is that the salt II is used to produce injectable solutions whereas the molecule located in the cell extracts is the neutral hydrophobic molecule.

Example 6

PROPERTIES OF 18F-FLUOROETHYL NORMEMANTINE MAKING IT SUITABLE FOR LABELING NMDA RECEPTORS IN MEDICAL IMAGING

(33) Toxicity

(34) The objective of this test is to assess, qualitatively and quantitatively, possible toxic phenomena and the delay before onset thereof after a single administration of a predetermined dose of 0.125 g/kg of body weight (which would correspond to more than 10.sup.4 times the dose administered to humans). The tests were carried out on 5 male mice and the results were compared with those of 3 control mice receiving only 0.2 ml of 0.9% NaCl solution. All the mice are the species C57/Black 6J provided by Charles River Laboratories (France) and about 8 weeks old. The average weight of the mice at the beginning of the tests is about 32 g after an acclimation period of 2 weeks. The animals are housed three per cage (31 cm46 cm19 cm) at a temperature of 25 C.2 C.

(35) A 20 g/l stock solution of .sup.18F-fluoroethyl normemantine was prepared and then distributed in sterile 15 ml bottles. The volume administered to each mouse is defined as 0.125 g/kg and is administered once intravenously by means of a suitable syringe and needle.

(36) The animals are observed regularly the day of administration (after 30 minutes, 1 hour, 2 hours, 3 hours and 4 hours), and then once each day for at least 14 days. All the observations were unremarkable. After 14 days all the animals were euthanized and autopsied: no pathological change was noted.

(37) These tests lead to the conclusion that .sup.18F-fluoroethyl normemantine is not toxic at the doses tested. As these doses are much higher than those envisaged for labeling NMDA receptors, this product will be well tolerated for this application.

Example 7

PHYSICOCHEMICAL CHARACTERISTICS OF 18F-FLUOROETHYL NORMEMANTINE

(38) Solubility in water superior to 100 mM, which is favorable for an injectable.

(39) Lipophilicity: determined by log(P)=log([I].sub.n-octanol/[I].sub.water), by placing the compound (I) in a 50/50 mixture by volume of pH 7.4 buffer solution and octanol, separating the phases, then assaying by means of HPLC the level of the compound (I) present in each of said phases. One finds log(P)=3.1 (0.5), which shows the Lipophilicity of I. This value is favorable to penetration in the brain.

Example 8

MOUSE STUDY OF DISTRIBUTION IN THE BODY

(40) The tests were carried out on 3 batches of male mice and the results were compared with those of 3 control mice receiving only 0.2 ml of 0.9% NaCl solution. All the mice are the species C57/Black 6J provided by Charles River Laboratories (France) and about 8 weeks old.

(41) A 20 g/l stock solution of .sup.18F-fluoroethyl normemantine was prepared and then distributed in sterile 15 ml bottles. The volume administered to each mouse is defined as 0.125 g/kg and is administered once intravenously by means of a suitable syringe and needle.

(42) At the prescribed time the mice are sacrificed, ground material from the organs is extracted and the concentration therein is analyzed by HPLC-MS assays.

(43) The following results are obtained when sacrificing at 3 minutes

(44) Sacrifice at 3 minutes:

(45) Brain: 12% of the injected dose

(46) Kidneys: 18%

(47) Liver: 20%

(48) Sacrifice at 30 and 60 minutes:

(49) Brain/blood ratio (60 minutes): 6.015

(50) One notes, with respect to the prior art, that fluoroethyl normemantine has a strong affinity for the brain (here, fluoromemantine was measured at 3% instead of 12%) and that the brain/blood ratio is comparable.

(51) This experiment shows that the structural difference between memantine and the F-fluoroethyl normemantine compound leads to a different distribution behavior in the organs.

Example 9

RELATIVE AFFINITY OF 18F-FLUOROETHYL NORMEMANTINE FOR NMDA RECEPTORS

(52) In this example, the affinity of fluoroethyl normemantine for NMDA receptors will be compared with that of glutamate (Glu) and of the product Dizocilpine (called MK-801), which are known NMDA receptor antagonists (see Neuroscience Letters, Vol. 80 (1), p. 111-114). MK-801 binds to two different sites in rat brain (Brain Res. 378, p. 133).

(53) To that end, a material containing NMDA receptors will first be immersed in a solution containing labeled MK-801 (first experiment) or glutamate (second experiment) and then these materials are incubated in solutions containing fluoroethyl normemantine at various concentrations. Next, the radioactive emissions before and after this second incubation are compared. Lower emissions mean that fluoroethyl normemantine has a stronger affinity for NMDA receptors than that of the references and that NMDA receptors are inhibited thereby.

(54) By means of these measurements, a correlation can be established between the concentration of the compound IE and NMDA receptor inhibition. The magnitude of the half-maximal inhibitory concentration (IC.sub.50) is deduced therefrom.

(55) First Experiment:

(56) The compound MK-801 is thus used as an antagonist (product R0). As the product to be tested (product R1), either memantine or compound I is used. The experimental protocol is as follows: a homogenate of cerebral cortex membrane (140 g of proteins) is prepared and then incubated for 2 hours at 37 C. with 10 nM [.sup.3H]phencyclidine (tritiated MK-801) in the absence or presence of compound R1 (in buffer containing 5 mM HEPES/Tris (pH=7.4) and 0.1 mM ethyleneglycol tetraacetic acid). The comparison is made with an incubation of 10 mM MK-801. The samples are quickly filtered under vacuum through glass-fiber filters and rinsed with 50 mM iced Tris-HCl. The filters are dried and their radioactivity is counted on a scintillation counter. The concentration of compound R1 varies, and by comparing for each concentration the difference in emission between the control filter (MK-801 alone) and the MK-801/R1 mixture filter, the ratio of inhibition of compound R1 for each concentration is obtained. The result of this study is summarized in the following table I:

(57) TABLE-US-00001 TABLE I Emission Emission R0 R1 [R1] Mol/l ratio 1.sup.st test (%) ratio 1.sup.st test (%) Mean IC.sub.50 (Mol/l) MK-801 Memantine 1 .Math. 10.sup.9 97.8 95.5 96.9 1.1 .Math. 10.sup.6 3 .Math. 10.sup.9 111.5 95 103.3 1 .Math. 10.sup.8 105.5 97.3 101.4 3 .Math. 10.sup.8 98.5 96.5 97.5 1 .Math. 10.sup.7 86.2 91.4 88.8 3 .Math. 10.sup.7 77.1 69.2 73.1 1 .Math. 10.sup.6 54.8 49.8 52.3 3 .Math. 10.sup.6 27.9 30.1 29.0 1 .Math. 10.sup.5 12.2 9.3 10.8 Fluoroethyl 1 .Math. 10.sup.9 107.3 98.9 103.1 6.1 .Math. 10.sup.6 normemantine 3 .Math. 10.sup.9 102.1 98.8 100.5 1 .Math. 10.sup.8 98.4 107.7 103.1 3 .Math. 10.sup.8 107.4 102.1 104.8 1 .Math. 10.sup.7 92.5 98.6 95.5 3 .Math. 10.sup.7 92.2 88.9 90.5 1 .Math. 10.sup.6 79.4 91.8 85.6 3 .Math. 10.sup.6 58.2 68.4 63.3 1 .Math. 10.sup.5 42.9 41.5 42.2

(58) From this measurement it is seen that fluoroethyl normemantine is an NMDA receptor inhibitor since it displaces MK-801. Its affinity is of an order of magnitude comparable with that of memantine (10.sup.6 M). When fluoroethyl normemantine is functionalized by a fluorine-18 atom it will thus be able, by binding to free NMDA receptors, to make it possible to locate said receptors using a positron emission scanner. It can thus be imagined that if one wished to study the effect of a novel drug on these receptors, the receptors remaining free in the presence of the novel drug could be mapped.

(59) Second Experiment:

(60) The experimental protocol is much the same as in the first experiment: a homogenate of cerebral cortex membrane (140 g of protein) is prepared and then incubated for 1 hour at 4 C. with 5 nM tritiated glutamate (tritiated Glu) in the absence or presence of fluoroethyl normemantine (in buffer containing 5 mM Tris-HCl (pH=7.7) and 10 mM ethyleneglycol tetraacetic acid). The comparison is made with an incubation comprising 100 mM tritiated L-Glu. Following the incubation, the samples are quickly filtered under vacuum through glass-fiber filters and rinsed with 50 mM iced Tris-HCl. The filters are dried and their radioactivity is counted on a scintillation counter. The concentration of compound R1 varies, and by comparing for each concentration the difference in emission between the control filter (MK-801 alone) and the MK-801/R1 mixture filter, the ratio of inhibition of compound R1 for each concentration is obtained. The result of this study is summarized in the following table II:

(61) TABLE-US-00002 TABLE II Emission Emission ratio ratio R0 R1 [R1] (M) 1.sup.st test (%) 1.sup.st test (%) Mean Glu Fluoroethyl- 1 .Math. 10.sup.9 106.4 88.8 97.6 normemantine 3 .Math. 10.sup.9 101.9 101.6 101.8 1 .Math. 10.sup.8 92.3 105.7 99.0 3 .Math. 10.sup.8 108.0 91.0 99.5 1 .Math. 10.sup.7 108.4 111.0 109.7 3 .Math. 10.sup.7 94.2 109.0 101.6 1 .Math. 10.sup.6 105.3 100.2 102.8 3 .Math. 10.sup.6 104.3 92.5 98.4 1 .Math. 10.sup.5 95.4 108.6 102.0

(62) These results show that Glu is a better inhibitor than fluoroethyl normemantine. In this case, therefore, IC.sub.50 cannot be measured.

(63) These two experiments show that fluoroethyl normemantine has an affinity for NMDA receptors that would make it possible to use a fluorine-18 labeled derivative of fluoroethyl normemantine for imaging by positron emission scanning. Its ability to displace inhibitors such as MK-801 while being unable to displace Glu makes it possible to target the use of this compound for analyzing the mechanisms of action of drugs on psychiatric disorders such as Alzheimer's disease, schizophrenia, Parkinson's disease or others by PET scan, for example.