Novel Tyrosinase Inhibitors, Process For The Preparation Thereof And Use Thereof In Human Medicine And Also In Cosmetics

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Novel tyrosinase inhibitors, process for the preparation thereof and use thereof in human medicine and also in cosmetics

The invention relates to novel tyrosinase inhibitor compounds as novel and useful industrial products. It also relates to the process for the preparation thereof and to the use thereof in pharmaceutical compositions for use in human or veterinary medicine, or else to the use thereof in cosmetic compositions, and to the nontherapeutic use of the latter.

Human skin pigmentation results from the synthesis of melanin by the dendritic cells, melanocytes. Melanocytes contain organelles called melanosomes which transfer the melanin into the upper layers of keratino- cytes which are then transported to the surface of the skin through the differentiation of the epidermis (Gilchrest BA, Part HY, Eller MS, Yaar M, Mechanisms of ultraviolet light-induced pigmentation. Photochem Photobiol 1996; 63: 1-10; Hearing VJ, Tsukamoto K, Enzymatic control of pigmentation in mammals. FASEB J 1991; 5: 2902-2909) .

Among the enzymes of melanogenesis, tyrosinase is a key enzyme which catalyses the first two steps of melanin synthesis. Homozygous tyrosinase mutations result in oculocutaneous albinism type I characterized by a complete lack of melanin synthesis (Toyofuku K, Wada I, Spritz RA, Hearing VJ1 The molecular basis of oculocutaneous albinism type 1 (OCAl) : sorting failure and degradation of mutant tyrosinases results in a lack of pigmentation. Biochem J 2001; 355: 259-269).

Since hyperpigmentation disorders result from an increase in melanin production, the development of novel therapeutic approaches through the inhibition of tyrosinase activity prove to be important. Most skin-lightening compounds that are already known are phenol/catechols. These compounds inhibit tyrosinase but most of them are cytotoxic towards melanocytes due to the formation of quinones . There is a risk that this toxic effect may cause permanent depigmentation of the skin.

It therefore appears to be advantageous, for application in humans, to have novel tyrosine inhibitor compounds with good effectiveness and good tolerance.

Now, the Applicant has now discovered, surprisingly and unexpectedly, novel compounds having tyrosinase- inhibiting activity.

These compounds find applications in human medicine, in particular in dermatology, and in cosmetics.

Thus, the present invention relates to compounds of formula (I) below:

(I) in which:

- Rl represents:

(i) a linear-chain, branched-chain or cyclic-chain alkyl radical containing from 2 to 10 carbon atoms, with the exception of tert-butyl, (ii) a linear-chain or branched-chain alkenyl radical containing from 2 to 10 carbon atoms,

(iii) a substituted or unsubstituted aryl radical, with the exception of unsubstituted phenyl, 3-bromophenyl, 4-trifluoromethylphenyl, unsubstituted n aphthalen-2-yl, u nsubstituted naphthalen-1-yl, 4-terfc-butylphenyl, 3,5- bistrifluoromethylphenyl, 4 -pentylphenyl, 4 chlorophenyl, 3, 5-dichlorophenyl, unsubstituted furan-2-yl, unsubstituted thiophen-2-yl, unsubstituted pyridin-3-yl, unsubstituted pyridin- 4-yl, unsubstituted pyrazin-2-yl, 4-methoxyphenyl, 4-hydroxyphenyl, 3-hydroxyphenyl, 2-ethylpyridin- 4-yl, unsubstituted pyridin-2-yl, 4-hydroxy-3, 5- di-tert-butylphenyl, 4-methoxyethoxymethoxy-3 , 5- di-tert-butylphenyl, 4-dimethylaminophenyl, 2,4- dichlorophenyl, 4-quinolyl, 4-acetamidophenyl and 4-aminophenyl,

(iv) a substituted or unsubstituted aralkyl radical with the exception of unsubstituted benzyl, 4-methoxybenzyl, 4-ethoxybenzyl, 4-pro- poxybenzyl, 4-butoxybenzyl, isopropoxybenzyl, isobutoxybenzyl, sec-butoxybenzyl and tert- butoxybenzyl .

(v) a cycloalkyl radical with the exception of unsubstituted adamantyl, or (vi) a substituted amine function; and the salts of the compounds of formula (I) , and also the tautomeric and geometric forms of the compounds of formula (I) .

The tautomeric forms can be represented in the following way:

When the compounds according to the invention are in the form of a salt, it is preferably an alkali metal or alkaline-earth metal salt, or alternatively a zinc salt or an organic amine salt .

According to the present invention, the expression "alkyl containing from 2 to 10 carbon atoms" is intended to mean preferably ethyl, 2-cycylopentylethyl, n-propyl, i-propyl, c-propyl, 2,2-dimethylpropyl, n- butyl, i-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl and n-decyl radicals.

The expression "alkenyl radical containing from 2 to 10 carbon atoms" is intended to mean preferably vinyl, propenyl, 2-methylpropenyl and butenyl radicals.

The term waryl radical" is intended to mean, given the exceptions mentioned above, an aromatic radical of the type biphenyl, phenyl substituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, and an amino function optionally substituted with at least one alkyl radical, or a heteroaromatic radical of the type pyrimidinyl, imidazole, quinoline, triazole, optionally condensed with one or more other rings and optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, and an amino function optionally substituted with at least one alkyl radical.

The term "aralkyl radical" is intended to mean a - (CH2) n-aryl radical of phenethyl type, or a heteroaromatic radical of quinolylmethyl, pyrimidinylmethyl, naphthalen-2-ylmethyl, thiophenmethyl or pyridylmethyl type, with the exception of benzyl; optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, a hydroxyl radical, and an amino function optionally substituted with at least one alkyl radical; and n having the value 1, 2, 3, 4 or 5. The term "halogen atom" is intended to mean preferably a chlorine, fluorine, iodine or bromine atom. Preferably, the halogen is a fluorine or bromine atom.

The term "alkoxyl radical" is intended to mean a radical containing from one to seven carbon atoms, such as methoxy, ethoxy, isopropyloxy, tert-butoxy, hexyloxy, benzyloxy or phenoxy radicals, which may be optionally substituted with an alkyl radical containing from 1 to 12 carbon atoms.

According to the present invention, the cycloalkyl radicals preferably contain from 3 to 6 carbon atoms. They are preferably chosen from cyclopropyl, cyclo- pentyl and cyclohexyl.

According to the present invention, the compounds of formula (I) that are more particularly preferred are those for which Rl represents:

(i) a linear-chain or branched-chain alkyl radical containing from 2 to 7 carbon atoms, with the exception of tert-butyl,

(ii) a linear-chain or branched-chain alkenyl radical containing from 2 to 10 carbon atoms,

(iii) a substituted or unsubstituted aryl radical, with the exception of unsubstituted phenyl, 3-bromophenyl , 4-trifluoromethylphenyl , unsubstituted n aphthalen-2-yl, u nsubstituted naphthalen-1-yl, 4- tert-butylphenyl, 3,5- bistrifluoromethylphenyl, 4 -pentylphenyl , 4 chlorophenyl, 3, 5-dichlorophenyl, unsubstituted furan-2-yl, unsubstituted thiophen-2-yl, unsubstituted pyridin-3-yl, unsubstituted pyridin- 4-yl, unsubstituted pyrazin-2-yl, 4-methoxyphenyl, 4-hydroxyphenyl , 3-hydroxyphenyl, 2-ethylpyridin- 4-yl, unsubstituted pyridin-2-yl, 4-hydroxy-3, 5- di-tert-butylphenyl, 4-methoxyethoxymethoxy-3,5- di-tert-butylphenyl, 4-dimethylaminophenyl, 2,4- dichlorophenyl, 4-quinolyl, 4-acetamidophenyl and 4-aminophenyl, said aryl radical preferably being an aromatic radical of substituted phenyl type or a heteroaromatic radical of pyrimidinyl, imidazole, quinoline or triazole type, in particular, said aromatic or heteroaromatic radical being optionally condensed with one or more other rings and optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical and an amino function optionally substituted with at least one alkyl radical, or (iv) a substituted or unsubstituted aralkyl radical of phenethyl or quinolylmethyl type, (unsubstituted benzyl, 4-methoxybenzyl, 4-ethoxybenzyl, 4-propoxybenzyl, 4-butoxybenzyl, isopropoxybenzyl, isobutoxybenzyl, sec-butoxybenzyl and tert-butoxybenzyl radicals therefore being excluded) , optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, a hydroxyl radical and an amino function optionally substituted with at least one alkyl radical,

(v) a cycloalkyl containing from 3 to 6 carbon atoms . The cycloalkyl is preferably cyclopentyl .

The term "halogen atom" is intended to mean preferably a fluorine atom.

More preferably, the compounds of formula (I) are those for which Rl represents: (i) a linear-chain, branched-chain or cyclic-chain alkyl radical containing from 2 to 10 carbon atoms, with the exception of tert-butyl,

(ii) a linear-chain or branched-chain alkenyl radical containing from 2 to 10 carbon atoms, (iii) an aryl radical chosen from radicals of the type biphenyl, phenyl, pyrimidinyl, imidazole, quinoline or triazole, substituted with one or more atoms, groups, functions or radicals chosen from a fluorine or bromine atom, a CF3 radical, an alkyl radical and an amino function, optionally substituted with at least one alkyl radical; with the exception of 3-bromophenyl, 4-trifluoro- methylphenyl, 4-terfc-butylphenyl, 3, 5-bistrifluoro- methylphenyl, 4-pentylphenyl, 4-dimethylaminophenyl, 4-quinolyl, 4-acetamidophenyl and 4-aminophenyl,

(iv) an aralkyl radical chosen from phenethyl and quinolylmethyl radicals, optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a fluorine or bromine atom, a

CF3 radical, an alkyl radical, an alkoxy radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, a hydroxyl radical and an amino function, optionally substituted with at least one alkyl radical,

(v) a cycloalkyl containing from 3 to 6 carbon atoms .

Among the compounds of formula (I) which fall into the context of the present invention, mention may in particular be made of the following:

L. 5- (2-methylpropenyl) -4H- [1,2,4] triazole-3-thiol 2. 5- (2,2-dimethylpropyl) -4H- [1,2,4] triazole-3-thiol 3. 5- (2-cyclopentylethyl) -4H- [1, 2, 4] triazole-3-thiol

4. 5- (2, 4-difluorophenyl) -4H- [1,2,4] triazole-3-thiol

5. 5-phenethyl-4H- [1, 2, 4] triazole-3-thiol

6. 5-quinolin-2-yl-4H- [1,2,4] triazole-3-thiol.

The reaction scheme described in Figure 1 is a general scheme for obtaining the compounds according to the invention.

The compounds of general formula (I) can be obtained by reaction of an acid halide or of an anhydride containing the radical Rl with thiosemicarbazide (A) so as to obtain the 2-cetylhyrazinecarbothioamide derivative (B) . The following step is cyclization in a basic medium so as to produce the corresponding triazole thiols of formula (I) .

The preferred compounds of the present invention have an inhibition constant with respect to tyrosinase of less than or equal to 100 μM, preferentially of less than or equal to 50 μM, preferably of less than or equal to 10 μM.

The invention is therefore directed towards the use of at least one compound of formula (I) as defined above, for preparing a pharmaceutical or cosmetic composition in which said compound has tyrosinase-inhibiting activity.

The compounds that are useful according to the invention are particularly suitable for the treatment and prevention of hyperpigmentary disorders such as melasma, chlosama, lentigines, senile lentigo, vitiligo, freckles, post-inflammatory hyperpigmen- tations caused by an abrasion, a burn, a scar, a dermatosis or a contact allergy; nevi, genetically determined hyperpigmentations, hyperpigmentations of metabolic or drug-related origin, melanomas or any other hyperpigmentary lesions.

A subject of the present invention is also a novel medicinal composition for use in particular in the treatment of the abovementioned conditions, and which is characterized in that it comprises, in a pharma- ceutically acceptable support compatible with the method of administration selected for said composition, at least one compound of formula (I) , an isomer thereof or a salt thereof. The administration of the composition according to the invention can be carried out orally, enterally, parenterally, topically or ocularly. Preferably, the pharmaceutical composition is packaged in a form that is suitable for topical application.

For oral administration, the composition can be in the form of tablets, gelatin capsules, sugar-coated tablets, syrups, suspensions, solutions, powders, granules, emulsions, suspensions of microspheres or nanospheres or lipid or polymeric vesicles for controlled release. For parenteral administration, the composition can be in the form of solutions or suspensions for infusion or for injection.

The compounds according to the invention are generally administered at a daily dose of approximately 0.01 mg/kg to 100 mg/kg of bodyweight, taken as 1 or more doses .

The compounds are used systemically at a concentration generally of between 0.001% and 10% by weight, preferably of between 0.01% and 1% by weight, relative to the weight of the composition.

When administered topically, the pharmaceutical composition according to the invention is more particularly for use in the treatment of the skin and the mucous membranes and can be in liquid, pasty or solid form, and more particularly in the form of ointments, creams, milks, salves, powders, impregnated pads, syndets, solutions, gels, sprays, mousses, suspensions, sticks, shampoos or washing bases. It may also be in the form of suspensions of microspheres or nanospheres or of lipid or polymeric vesicles or gelled or polymeric patches for controlled release.

The compounds are used topically at a concentration generally of between 0.001% and 10% by weight, preferably of between 0.01% and 1% by weight, relative to the total weight of the composition.

The compounds of formula (I) according to the invention also find an application in cosmetics, in particular in protection against the harmful aspects of sunlight, and for preventing and/or combating photoinduced or chronological ageing of the skin and the integuments .

A subject of the invention is therefore also a composition comprising, in a cosmetically acceptable support, at least one of the compounds of formula (I) .

A subject of the invention is also the cosmetic use of a composition comprising at least one compound of formula (I) for preventing and/or treating the signs of ageing and/or dry skin.

A subject of the invention is also the cosmetic use of a composition comprising at least one compound of formula (I) for body or hair hygiene.

The cosmetic composition according to the invention containing, in a cosmetically acceptable support, at least one compound of formula (I) or an optical or geometric isomer thereof or a salt thereof, may be in particular in the form of a cream, a milk, a gel, suspensions of microspheres or nanospheres or lipid or polymeric vesicles, impregnated pads, solutions, sprays, mousses, sticks, soaps, washing bases or shampoos .

The concentration of compound of formula (I) in the cosmetic composition is preferably between 0.001% and 3% by weight, relative to the total weight of the composition.

The term "a cosmetically acceptable medium" is intended to mean a medium that is compatible with the skin and optionally with its integuments (eyelashes, nails, hair) and/or the mucous membranes.

The pharmaceutical and cosmetic compositions as described above may also contain inert additives, or even pharmacodynamically active additives as regards the pharmaceutical compositions, or combinations of these additives, and in particular:

- wetting agents; - flavour enhancers;

- preserving agents such as para-hydroxybenzoic acid esters;

- stabilizers;

- moisture regulators; - pH regulators;

- osmotic pressure modifiers;

- emulsifiers;

- UV-A and UV-B screening agents;

- antioxidants such as α-tocopherol, butylhydroxy- anisole, butylhydroxytoluene, superoxide dismutase, ubiquinol ;

- emollients;

- moisturizers, such as glycerol, PEG 400, thia- morpholinone and its derivatives or urea; - antiseborrhoeic or anti-acne agents, such as S-carboxymethylcysteine, S-benzylcysteamine, salts thereof or derivatives thereof, or benzoyl peroxide;

- antibiotics, such as erythromycin and its esters, neomycin, clindamycin and its esters, and tetracyclins;

- antifungal agents such as ketoconazole or poly-4,5- methylene-3-isothiazolidones;

- agents for promoting hair regrowth, such as Minoxidil (2, 4-diamino-6-piperidinopyrimidine 3-oxide) and its derivatives, diazoxide (7-chloro-3-methyl-l, 2,4- benzothiadiazine 1,1-dioxide) and phenytoin (5,4- diphenylimidazolidine-2 , 4-dione) ;

- non-steroidal anti-inflammatories;

- carotenoids and in particular β-carotene; - antipsoriatic agents such as anthralin and its derivatives;

- eicosa-5, 8, 11, 14-tetraynoic acid and eicosa-5, 8, 11- triynoic acid, and esters and amides thereof; - retinoids, i.e. natural or synthetic RXR receptor ligands;

- corticosteroids or oestrogens;

- α-hydroxy acids and α-keto acids or derivatives thereof, such as lactic acid, malic acid, citric acid, glycolic acid, mandelic acid, tartaric acid, glyceric acid or ascorbic acid, and also salts, amides or esters thereof, or β-hydroxy acids or derivatives thereof, such as salicylic acid and its salts, amides or esters; - ion-channel blockers such as potassium-channel blockers;

- or alternatively, more particularly for pharmaceutical compositions, in combination with medicaments known to interfere with the immune system (for example, cyclosporin, FK 506, glucocorticoids, monoclonal antibodies, cytokines or growth factors, etc.)

Needless to say, a person skilled in the art will take care to select the optional compound(s) to be added to these compositions in such a way that the advantageous properties intrinsically attached to the present invention are not, or are not substantially, adversely affected by the envisaged addition.

Several examples of the production of active compounds of formula (I) according to the invention, biological activity results and also various concrete formulations based on such compounds will now be given, by way of illustration and with no limit in nature.

EXAMPLE 1 ; 5- (2-Methylpropenyl) -4H- [1,2,4] triazole- 3-thiol

A solution of thiosemicarbazide (100 mg, 1.1 mmol) in 10 ml of tetrahydrofuran is added to 3-methylbut- 2-enoyl chloride (110 μl, 1 mmol) . The entire mixture is stirred at ambient temperature for 3 hours and then evaporated to dryness. The solid obtained is taken up in 10 ml of a 10% aqueous potassium hydroxide solution and refluxed for 15 hours. The reaction medium is cooled and acidified to pH 3 by the addition of 2N hydrochloric acid. A precipitate forms and is filtered off, washed and then dried.

33 mg (21%) of the expected compound are obtained in the form of a bright yellow solid.

HPLC 100% ES+ [156]

1H NMR/DMSOdβ : 1.91 (s, 3H); 2.04 (s, 3H); 5.80 (d, j=1.17Hz, IH); 12.90-13.40 (m, 2H).

13C NMR/DMSOd6: 20.94 (CH3); 26.92 (CH3); 108.96 (CH);

146.65 (C); 149.52 (C); 165.25 (C).

EXAMPLE 2 : 5- (2,2-Dimethylpropyl) -4H- [1,2,4] triazole-

3 -thiol

Under the same conditions, using 3, 3-dimethylbutyryl chloride (140 μl, 1 mmol) , 107 mg (62%) of the expected compound are obtained in the form of a white solid.

HPLC 96% ES+ [172]

1H NMR/DMSOd6: 0.92 (s, 9H); 2.39 (s, 2H); 13.05 (s, IH) ; 13.25 (s, IH) .

13C NMR/DMSOd6 : 29.40 (CH3); 31.27 (C); 38.87 (CH2); 150.81 (C) ; 165.81 (C) . EXAMPLE 3 ; 5- (2-Cyclopentylethyl) -4H- [1,2,4] triazole- 3-thiol

Under the same conditions, using 3-cyclopentylpropionyl chloride (150 μl, 1 πunol) , 130 mg (66%) of the expected compound are obtained in the form of a white solid.

HPLC 99% ES+ [198]

1H NMR/DMSOd6 : 1.07-1.08 (m, 2H); 1.46-1.71 (7H), 2.50- 2.54 (m, 2H); 3.31-3.33 (m, 2H); 13.10 (s, IH); 13.20 (S, IH) .

13C NMR/DMSOd6: 24.65 (CH2); 25.00 (2CH2); 32.19 (2CH2); 32.93 (CH2); 39.16 (CH); 152.83 (C); 166.04 (C).

EXAMPLE 4 : 5- (2 , 4-Difluoropheny1) -4H- [1, 2 #4] triazole- 3 -thiol

Under the same conditions, using 2, 4-difluorobenzoyl chloride (125 μl, 1 mmol) , 104 mg (49%) of the expected compound are obtained in the form of a white solid.

HPLC 97% ES+ [214]

1H NMR/DMSOd6 : 7.29 (m, IH) ; 7.51 (m, IH) ; 7.88 (m, IH) ;

13.75 (S, IH) ; 13.80 (se, IH)

13C NMR/DMSOd6 : 105.68 (t, J=IOl.6 Hz, CH) ; 111.75 (d, j=34.5 Hz, C) ; 112.95 (t, j=84.0 Hz, CH) ; 131.34 (t, j=27.8 Hz, CH) ; 145.89 (C) ; 158.72 (d, j=50.8 Hz, C) ;

161.21 (C) ; 163.86 (dxd, J=48.8 Hz-J=IOOO Hz, C) . BXAMPLE 5: 5-Phenethyl-4H- [1,2,4] triazole-3-thiol

Under the same conditions, using 3 -phenylpropionyl chloride (150 μl, 1 mmol) , 190 mg (93%) of the expected compound are obtained in the form of a white solid.

HPLC 98% ES+ [206]

1H NMR/DMSOd6 : 2.81-2.85 (m, 2H); 2.92-2.95 (m, 2H); 7.17-7.23 (m, 3H); 7.26-7.31 (m, 2H); 13.20 (s, H); 13.25 (s, H)

13C NMR/DMSOd6: 26.81 (CH2); 31.97 (CH2); 126.19 (CH); 128.25 (CH); 128.36 (2CH); 128.70 (CH); 140.16 (C); 151.78 (C) ; 165.86 (C) .

EXAMPLE 6; 5-Quinolin-2-yl-4H- [1,2, 4-triazole-3-thiol

Under the same conditions, using quinoline-2-carbonyl chloride (1 g, 5.22 mmol), 1.18 g (99%) of the expected compound are obtained in the form of a pink solid. Melting point (m.p.>350°C)

HPLC 96% ES+ [219]

1H NMR/DMSOd6: 7.70 (t, j=7.8 Hz, IH); 7.85 (txd, j=7.1 Hz-J=I Hz, IH); 8.05-8.11 (m, 3H); 8.54 (d, j=8.6 HZ, IH); 13.90 (s, IH); 14.12 (bs, IH).

13C NMR/DMSOd6 : 118.45 (CH); 128.14 (CH); 128.37 (C); 128.51 (CH); 129.31 (CH); 130.97 (CH); 138.10 (CH); 144.92 (C); 147.25 (C); 150.83 (C); 168.29 (C). Example 7; Tyrosinase activity inhibition assay

The activity of the inhibitors is measured using a lysate of B16F1 cells (murine melanoma line) . In the presence of the L-tyrosine substrate, the tyrosinase present in these cells catalyses the hydroxylation of

L-tyrosine to L-DOPA and then the oxidation of the

L-DOPA to dopaquinone. In the presence of MBTH

(3-methyl-2-benzothiazolinone hydrazone) , the dopa- quinone is trapped so as to form a pink complex which absorbs at 520 run.

The B16F1 cells are cultured in DMEM medium + 10% foetal calf serum + 10'9 M α-SMH for 4 days at 37°C under 7% CO2. They are trypsinized, washed with PBS, counted and pelleted. The pellet is taken up at 107 cells/ml in lysis buffer (10 mM sodium phosphate, pH 6.8 - 1% Igepal) and the suspension is sonicated for 10 seconds. After centrifugation for 30 minutes at 4000 rpm, the supernatant obtained constitutes the cell lysate used as tyrosinase source in the enzymatic assay.

The assays are carried out in duplicate in 384-well plates in a total volume of 50 μl. Each well contains:

- 40 μl of solution containing 1.25 mM L-tyrosine, 6.25 μM L-DOPA (cofactor) and 3.75 mM MBTH in buffer B (62.25 mM sodium phosphate, pH 6.8-2.5% dimethyl- formamide) , - 5 μl of inhibitor diluted in DMSO,

- 5 μl of cell lysate diluted to M in 50 mM Tris HCl buffer, pH 7.5.

The plate is incubated at 370C and a spectrophotometric reading is carried out at 520 nm after 6 hours of incubation. In order to avoid any possible absorption of the products, the system uses corrected absorbance (absorbance at time 6 h - absorbance at time zero) . The inhibitors are assayed in terms of dose-response so as to calculate an IC50 (dose that inhibits 50% of the enzymatic activity) .

Several internal controls are added to each experiment :

- control for 100% activity: the 5 μl of inhibitor are replaced with 5 μl of DMSO,

- control for 50% activity: the 5 μl of inhibitor are replaced with 5 μl of phenylthiourea at 300 μM in DMSO,

- control for 0% activity: the L-tyrosine substrate is replaced with buffer B.

The results obtained for the compounds of the invention are given in Table A:

EXAMPLE 8; EXAMPLES OF FORMULATION

In this example, various concrete formulations based on the compounds according to the invention are illustrated.

A - ORAL ADMINISTRATION

(a) 0.2 g tablet

- Compound 1 0.001 g

- Starch 0.114 g - Dicalcium phosphate 0.020 g

- Silica 0.020 g

- Lactose 0.030 g

- Talc 0.010 g

- Magnesium stearate 0.005 g

(b) Oral suspension in 5 ml ampoules

- Compound 6 0.001 g

- Glycerol 0.500 g

- 70% sorbitol 0.500 g

- Sodium saccharinate 0.010 g

- Methyl para-hydroxybenzoate 0.040 g

- Flavouring qs

- Purified water qs 5 ml

(c) 0.8 g tablet

- Compound 1 0.500 g

- Pregelatinized starch 0.100 g

- Microcrystalline cellulose 0.115 g

- Lactose 0.075 g

- Magnesium stearate 0.010 g

(d) Oral suspension in 10 ml ampoules

- Compound 2 0.20O g

- Glycerol 1.000 g

- 70% sorbitol 1.000 g

- Sodium saccharinate 0.010 g

- Methyl para-hydroxybenzoate 0.080 g

- Flavouring qs

- Purified water qs 10 ml

- PARENTERAL ADMINISTRATION

(a) Composition

- Compound 4 0.002 g

- Ethyl oleate qs 10 g (b) Composition

- Compound 6 0.05%

- Polyethylene glycol 20%

- 0.9% NaCl solution qs 100

(c) Composition

- Compound 3 2.5%

- Polyethylene glycol 400 20%

- 0.9% NaCl solution qs 100

(d) Injectable cyclodextrin composition

- Compound 5 0.1 mg

- β-cyclodextrin 0.10 g

- Water for injectable preparation qs 10.00 g

C - TOPICAL ADMINISTRATION

(a) Salve

- Compound 1 0.020 g

- Isopropyl myristate 81.700 g

- Liquid petroleum jelly 9.100 g

- Silica ("Aerosil 200" sold by Degussa) 9.180 g

(b) Salve

- Compound 6 0.300 g

- Codex white petroleum jelly qs 100 g

(c) Nonionic water-in-oil cream

- Compound 1 0.100 g

- Mixture of emulsified lanolin alcohols, 39.900 g of waxes and of oils ("anhydrous Eucerin" sold by BDF)

- Methyl para-hydroxybenzoate 0.075 g

- Propyl para-hydroxybenzoate 0.075 g

- Sterile demineralized water qs 100 g (d) Lotion

- Compound 6 0.100 g

- Polyethylene glycol (PEG 400) 69.900 g

- 95% ethanol 30.000 g

(e) Hydrophobic salve

- Compound 2 0.30O g

- Isopropyl myristate 36.400 g

- Silicone oil ("Rhodorsil 47 V 300" sold 36.400 g by Rhone-Poulenc)

- Beeswax 13.600 g

- Silicone oil (wAbil 300.000 cst" sold qs 100 g by Goldschmidt)

(f) Nonionic oil-in-water cream

- Compound 4 1.000 g

- Cetyl alcohol 4.000 g

- Glyceryl monostearate 2.500 g

- PEG 50 stearate 2.500 g

- Shea butter 9.200 g

- Propylene glycol 2.000 g

- Methyl para-hydroxybenzoate 0.075 g

- Propyl para-hydroxybenzoate 0.075 g

- Sterile demineralized water qs 100 g

CLAIMS

1. Compounds of formula (I) below:

in which:

- Rl represents:

(i) a linear-chain, branched-chain or cyclic-chain alkyl radical containing from 2 to 10 carbon atoms, with the exception of tert-butyl,

(ii) a linear-chain or branched-chain alkenyl radical containing from 2 to 10 carbon atoms, (iii) a substituted or unsubstituted aryl radical, with the exception of unsubstituted phenyl, 3 -bromophenyl , 4-trifluoromethylphenyl , unsubstituted n aphthalen-2-yl, unsubstituted naphthalen-1-yl, 4- tert-butylphenyl, 3,5- bistrifluoromethylphenyl, 4 -pentylphenyl , 4 chlorophenyl , 3, 5-dichlorophenyl, unsubstituted furan-2-yl, unsubstituted thiophen-2-yl, unsubstituted pyridin-3-yl, unsubstituted pyridin- 4-yl, 2-ethylpyridin-4-yl, unsubstituted pyridin- 2-yl, unsubstituted pyrazin-2-yl, 4-methoxyphenyl, 4-hydroxyphenyl , 3-hydroxyphenyl , 4-hydroxy-3,5- di-tert-butylphenyl, 4-methoxyethoxymethoxy-3, 5- di-tert-butylphenyl, 4-dimethylaminophenyl, 2,4- dichlorophenyl , 4-quinolyl, 4-acetamidophenyl and

4-aminophenyl ,

(iv) a substituted or unsubstituted aralkyl radical with the exception of unsubstituted benzyl, 4-methoxybenzyl, 4-ethoxybenzyl, 4-propoxybenzyl , 4-butoxybenzyl, isopropoxybenzyl, isobutoxybenzyl, sec-butoxybenzyl and tert- butoxybenzyl , (v) a cycloalkyl radical with the exception of unsubstituted adamantyl, or (vi) a substituted amine function, and also the salts and the tautomeric forms thereof.

2. Compounds according to Claim 1, characterized in that the salt of the compounds of formula (I) is an alkali metal or alkaline-earth metal salt, or alternatively a zinc salt or an organic amine salt.

3. Compounds according to either of Claims 1 or 2, characterized in that the alkyl radicals containing from 2 to 10 carbon atoms are ethyl, 2-cyclopentyl- ethyl, n-propyl, 2,2-dimethylpropyl, i-propyl, c-propyl, n-butyl, i-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl and n-decyl radicals.

4. Compounds according to one of Claims 1 to 3 , characterized in that the alkenyl radicals containing from 2 to 10 carbon atoms are vinyl, propenyl, 2-methylpropenyl and butenyl radicals.

5. Compounds according to one of Claims 1 to 4 , characterized in that the aryl radicals are chosen from radicals of the type biphenyl, phenyl substituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CP3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, and an amino function optionally substituted with at least one alkyl radical, or a heteroaromatic radical of the type pyrimidinyl, imidazole, quinoline, triazole, in particular, optionally condensed with one or more other rings and optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, and an amino function optionally substituted with at least one alkyl radical .

6. Compounds according to one of Claims 1 to 5, characterized in that the aralkyl radicals are chosen from a phenethyl radical or a heteroaromatic radical of quinolylmethyl, pyrimidinylmethyl, naphthalen-2-yl- methyl, thiophenmethyl or pyridylmethyl type, optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, a hydroxyl radical, and an amino function optionally substituted with at least one alkyl radical.

7. Compounds according to one of Claims 1 to 6 , characterized in that the alkoxyl radicals are radicals containing from one to seven carbon atoms, such as methoxy, ethoxy, isopropyloxy, tert-butoxy, hexyloxy, benzyloxy or phenoxy radicals, which may be optionally substituted with an alkyl radical containing from 1 to 12 carbon atoms.

8. Compounds according to any one of Claims 1 to 7, characterized in that the halogen atom is a fluorine or bromine atom.

9. Compounds according to any one of the preceding claims, characterized in that the compound of formula

(I) is chosen from the group consisting of:

1. 5- (2-methylpropenyl) -4H- [1,2,4] triazole-3-thiol

2. 5- (2,2-dimethylpropyl) -4H- [1,2,4] triazole-3-thiol

3. 5- (2-cyclopentylethyl) -4H- [1, 2, 4] triazole-3-thiol 4. 5- (2, 4-difluorophenyl) -4H- [1,2,4] triazole-3-thiol

5. 5-phenethyl-4H- [1,2,4] triazole-3-thiol

6. 5-quinolin-2-yl-4H- [1,2,4] triazole-3-thiol.

10. Compounds according to any one of the preceding claims, characterized in that Rl represents:

(i) a linear-chain or branched-chain alkyl radical containing from 2 to 7 carbon atoms, with the exception of tert-butyl, (ii) a linear-chain or branched-chain alkenyl radical containing from 2 to 10 carbon atoms,

(iii) a substituted or unsubstituted aryl radical, with the exception of unsubstituted phenyl, 3-bromophenyl, 4-trifluoromethylphenyl, unsubstituted n aphthalen-2-yl, u nsubstituted pyridin-2-yl, unsubstituted naphthalen-1-yl, 4- tert-butylphenyl, 3, 5-bistrifluoromethylphenyl, 4- pentylphenyl, 4-chlorophenyl, 3, 5-dichlorophenyl, unsubstituted furan-2-yl, unsubstituted thiophen- 2-yl, unsubstituted pyridin-3-yl, unsubstituted pyridin-4-yl, 2-ethylpyridin-4-yl, unsubstituted pyrazin-2-yl, 4-methoxyphenyl, 4-hydroxyphenyl, 3- hydroxyphenyl, 4-hydroxy-3 , 5-di-tert-butylphenyl, 4-methoxyethoxymethoxy-3 , 5-di-tert-butylphenyl, 4-dimethylaminophenyl, 2, 4-dichlorophenyl, 4-quinolyl, 4-acetamidophenyl and 4-aminophenyl, said aryl radical preferably being an aromatic radical of substituted phenyl type or a heteroaromatic radical of pyrimidinyl, imidazole, quinoline or triazole type, in particular, said aromatic or heteroaromatic radical being optionally condensed with one or more other rings and optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical and an amino function optionally substituted with at least one alkyl radical, or (iv) a substituted or unsubstituted aralkyl radical of phenethyl or quinolylmethyl type, optionally mono- or disubstituted with one or more atoms, groups, functions or radicals chosen from a halogen atom, a CF3 radical, an alkyl radical, an alkoxyl radical, a nitro function, an alkyl ester group, a nitrile function, an amide function, a carboxyl function, a hydroxyl radical and an amino function optionally substituted with at least one alkyl radical,

(v) a cycloalkyl containing from 3 to 6 carbon atoms .

11. Compounds according to any one of Claims 1 to 10, as a medicament .

12. Process for preparing the compounds of formula (I) according to one of Claims 1 to 10, characterized in that they can be obtained by reaction of an acid halide or of an anhydride containing the radical Rl with thiosemicarbazide so as to obtain the 2-cetylhydrazine- carbothioamide derivative, and then by cyclization in a basic medium so as to produce the corresponding triazole thiols.

13. Use of a compound according to any one of Claims 1 to 10 in the manufacture of a composition for use in the treatment of melasma, chlosama, lentigines, senile lentigo, vitiligo, freckles, post-inflammatory hyper- pigmentations caused by an abrasion, a burn, a scar, a dermatosis or a contact allergy; nevi, genetically determined hyperpigmentations, hyperpigmentations of metabolic or drug-related origin, or melanomas.

14. Pharmaceutical composition, characterized in that it comprises, in a physiologically acceptable support, at least one of the compounds of formula (I) as defined in any one of Claims 1 to 10.

15. Composition according to Claim 14, characterized in that the concentration of compound (s) of formula (I) is between 0.001% and 10% by weight relative to the total weight of the composition.

16. Composition according to Claim 14 or 15, characterized in that the concentration of compound (s) of formula (I) is between 0.01% and 1% by weight relative to the total weight of the composition.

17. Cosmetic composition, characterized in that it comprises, in a cosmetically acceptable support, at least one of the compounds as defined in any one of Claims 1 to 10.

18. Composition according to Claim 17, characterized in that the concentration of compound (s) of formula (I) is between 0.001% and 3% by weight relative to the total weight of the composition.

19. Cosmetic use of a composition as defined in either of Claims 17 and 18, for preventing and/or treating the signs of ageing and/or dry skin.

20. Cosmetic use of a composition as defined in either of Claims 17 and 18, for body or hair hygiene.

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