Stabilization of thiopyridone compounds and compositions comprising same

Abstract

The present invention relates to a composition comprising: (1) at least one thiopyridone compound; (2) at least one pH adjusting agent, and (3) water wherein the pH of the composition is from 4.5 to 6.5. The present invention can provide a composition comprising (1) one or more thiopyridone compounds having improved stability over time, particularly even when the composition is held at elevated temperatures for a relatively long period of time.

Description

Technical Field

[0001] The present invention relates to the stabilization of thiopyridone compounds in compositions comprising the thiopyridone compounds. Background Art

[0002] At various times in life, some people develop dark spots and / or pigmentation on their skin, more particularly on their face and hands, which lead to uneven skin. These spots are due in particular to a high melanin concentration in the keratinocytes located on the surface of the skin.

[0003] For the treatment of pigmented spots, it is most particularly desirable to use harmless topical depigmenting substances with good efficacy.

[0004] For example, arbutin, niacinamide, and kojic acid are known as skin depigmenting agents.

[0005] On the other hand, WO2017 / 102349 discloses a new decolorizing agent or whitening agent, namely a thiopyridone compound. The thiopyridone compound can exhibit a strong decolorizing or whitening effect by reducing melanin production. Summary of the invention

[0006] However, it has been found that thiopyridone compounds tend to become destabilized in compositions over time, particularly when compositions comprising thiopyridone compounds are maintained at elevated temperatures for relatively long periods of time.

[0007] It is therefore an object of the present invention to provide a composition comprising one or more thiopyridone compounds, wherein the stability of the one or more thiopyridone compounds over time is improved, in particular when the composition is kept at elevated temperature for a relatively long period of time.

[0008] The above object can be achieved by a composition comprising:

[0009] (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof:

[0010]

[0011] in

[0012] R1 represents a group selected from the following:

[0013] a) hydrogen atoms, and

[0014] b) Saturated straight chain C1-C 10 or branched C3-C 10Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0015] i)-O-R3, and

[0016] ii) -S-R3,

[0017] and

[0018] R2 represents a group selected from the following:

[0019] a) Hydrogen atoms,

[0020] b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0021] i) -O-R3,

[0022] ii) -S-R3,

[0023] iii) -C(O)-O-R3, and

[0024] iv) a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and

[0025] c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl

[0026] in

[0027] R3 represents a group selected from the following:

[0028] a) hydrogen atoms, and

[0029] b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl;

[0030] (2) at least one pH adjusting agent; and

[0031] (3) Water,

[0032] in

[0033] The pH of the composition is 4.5 to 6.5, preferably 5 to 6.

[0034] It may be preferred to:

[0035] R1 in formula (I) and (I') represents a hydrogen atom;

[0036] or

[0037] R1 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially linear (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably ethyl, in particular, the alkyl of R1 is unsubstituted.

[0038] It may be preferred to:

[0039] R2 in formula (I) and (I') represents a hydrogen atom;

[0040] or

[0041] R2 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; the alkyl of R2 is unsubstituted.

[0042] It may be preferred to:

[0043] R2 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; the alkyl is substituted by one or more groups selected from i), ii), iii) and iv) as defined above, preferably the alkyl is substituted by one or two groups selected from i), ii) and iii), more preferably by one or two groups selected from i) and iii), and more preferably by a group iii) which is a carboxyl group.

[0044] It may be preferred to:

[0045] R2 in formula (I) and (I') represents a (C3-C8) cycloalkyl group, preferably a (C5-C7) cycloalkyl group such as a cyclohexyl group;

[0046] or

[0047] R2 in formula (I) and (I') represents a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups. 12 Aryl, in particular unsubstituted phenyl, is preferred.

[0048] It may be preferred to:

[0049] R3 in formula (I) and (I') represents a hydrogen atom;

[0050] or

[0051] R3 in formula (I) and (I') represents a saturated straight chain C1-C 10 or branched C3-C 10 Alkyl; in particular straight chain (C1-C6) alkyl or branched chain (C3-C6) alkyl, preferably (C1-C4) alkyl such as methyl.

[0052] Perhaps more preferred is:

[0053] R1 in formula (I) and (I') represents a group selected from the following:

[0054] a) hydrogen atoms, and

[0055] b) a saturated straight-chain C1-C6 or branched C3-C6 alkyl group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0056] i)-O-R3, and

[0057] ii) -S-R3,

[0058] Preferably, it is optionally substituted with one or more groups i);

[0059] R2 in formula (I) and (I') represents a group selected from the following:

[0060] a) hydrogen atoms, and

[0061] b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0062] i) -O-R3,

[0063] ii) -S-R3,

[0064] iii) -C(O)-O-R3, and

[0065] iv) phenyl optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups such as methoxy groups,

[0066] Preferably substituted by one or more groups selected from i) and iii), preferably substituted by iii), such as carboxyl; and

[0067] R3 in formula (I) and (I') represents a group selected from the following:

[0068] a) hydrogen atoms, and

[0069] b) a saturated straight-chain C1-C6 or branched C3-C6 alkyl group,

[0070] Preferably, the compound of formula (I) and tautomer (I'), its salts, its solvates such as hydrates, its optical isomers, its racemates, and mixtures thereof have the following meanings:

[0071] R1 in formula (I) and (I') represents a group selected from the following:

[0072] a) hydrogen atoms, and

[0073] b) saturated straight-chain C1-C4 or branched C3-C4 alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from i) -OR3, more preferably unsubstituted;

[0074] R2 in formula (I) and (I') represents a group selected from the following:

[0075] a) hydrogen atoms, and

[0076] b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0077] i) -O-R3,

[0078] iii) -C(O)-O-R3, and

[0079] iv) C5-C4 optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups 12 aryl; and

[0080] R3 in formula (I) and (I') represents a group selected from the following:

[0081] a) Hydrogen atom;

[0082] b) Saturated straight-chain C1-C4 or branched C3-C4 alkyl groups, such as methyl or ethyl.

[0083] The (I) compound can be selected from the following compounds 1 to 24, their tautomers, their salts, their solvates such as hydrates, their optical isomers, their racemates, and mixtures thereof, in particular compounds 1, 2, 4, 6, 7, 9, 11, 12, 14, 15, 16, 17, 18, 19, 20 or 21, more particularly 1, 9, 16, 18, 19, 20 or 21, preferably 18, 19, 20 or 21, and more preferably 20:

[0084]

[0085]

[0086]

[0087]

[0088] The amount of the compound(s) (1) in the composition according to the invention may range from 0.01% to 10%, preferably from 0.05% to 5% and more preferably from 0.1% to 3% by weight relative to the total weight of the composition.

[0089] The (2) pH adjuster may be selected from acidifiers, alkalizers and mixtures thereof.

[0090] The amount of one or more (2) pH adjusters in the composition according to the present invention may be 0.01 wt% to 15 wt%, preferably 0.05 wt% to 10 wt%, more preferably 0.1 wt% to 5 wt%, relative to the total weight of the composition.

[0091] The amount of (3) water in the composition according to the invention may be 20 to 99 wt%, preferably 30 to 95 wt%, more preferably 40 to 90 wt%, relative to the total weight of the composition.

[0092] The composition according to the invention can be used for whitening keratinous substances, preferably the skin.

[0093] The present invention also relates to a cosmetic method for keratinous substances, preferably skin, preferably a whitening method, comprising the following steps:

[0094] A composition according to the invention is applied to this keratin material.

[0095] Another aspect of the present invention is the use of (2) at least one pH adjuster in a composition comprising (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof, so as to control the pH of the composition to be between 4.5 and 6.5, thereby stabilizing one or more of the compounds of (1):

[0096]

[0097] in

[0098] R1 represents a group selected from the following:

[0099] a) hydrogen atoms, and

[0100] b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0101] i)-O-R3, and

[0102] ii) -S-R3,

[0103] and

[0104] R2 represents a group selected from the following:

[0105] a) Hydrogen atoms,

[0106] b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0107] i) -O-R3,

[0108] ii) -S-R3,

[0109] iii) -C(O)-O-R3, and

[0110] iv) a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and

[0111] c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl

[0112] in

[0113] R3 represents a group selected from the following:

[0114] a) hydrogen atoms, and

[0115] b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl.

[0116] Best Mode for Carrying Out the Invention

[0117] After diligent research, the present inventors have discovered that it is possible to provide a composition comprising one or more thiopyridone compounds having improved stability over time, particularly even when the composition is maintained at elevated temperatures for relatively long periods of time.

[0118] Thus, the composition according to the invention comprises:

[0119] (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof (hereinafter, the compound is referred to as a "thiopyridone compound"):

[0120]

[0121] in

[0122] R1 represents a group selected from the following:

[0123] a) hydrogen atoms, and

[0124] b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0125] i)-O-R3, and

[0126] ii) -S-R3,

[0127] and

[0128] R2 represents a group selected from the following:

[0129] a) Hydrogen atoms,

[0130] b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0131] i) -O-R3,

[0132] ii) -S-R3,

[0133] iii) -C(O)-O-R3, and

[0134] iv) a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and

[0135] c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl

[0136] in

[0137] R3 represents a group selected from the following:

[0138] a) hydrogen atoms, and

[0139] b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl;

[0140] (2) at least one pH adjusting agent; and

[0141] (3) Water,

[0142] in

[0143] The pH of the composition is from 4.5 to 6.5, and preferably from 5 to 6.

[0144] The composition according to the present invention may exhibit improved stability of the (1) thiopyridone compound therein.

[0145] In other words, the composition according to the present invention can improve the stability of the (1) thiopyridone compound therein. The term "stability" of the (1) thiopyridone compound can be determined by the change in the amount of the (1) thiopyridone compound in the composition according to the present invention over a period of time. Improved "stability" means that the amount of the (1) thiopyridone compound changes more limitedly over time.

[0146] The composition according to the present invention can exhibit improved stability of the (1) thiopyridone compound therein even when the composition is kept at an elevated temperature (eg, 55° C.) for a relatively long period of time (eg, two weeks).

[0147] Therefore, the composition according to the invention can be stored for a long time even under hot conditions.

[0148] Furthermore, the increased stability of the (1) thiopyridone compound can provide improved or enhanced bioavailability of the (1) thiopyridone compound, which can act as a depigmenting or whitening agent. Thus, the composition according to the present invention can provide an enhanced or improved depigmenting or whitening effect.

[0149] The composition, use, etc. according to the present invention will be described below in a detailed manner.

[0150] [Composition]

[0151] The composition according to the invention comprises:

[0152] (1) at least one thiopyridone compound;

[0153] (2) at least one pH adjusting agent; and

[0154] (3) Water,

[0155] and

[0156] The pH of the composition is from 4.5 to 6.5.

[0157] The (1) thiopyridone compound, (2) pH adjuster, and (3) water, as well as other features of the composition according to the present invention will be explained below.

[0158] (Thiopyridone compounds)

[0159] The composition according to the present invention comprises (1) at least one thiopyridone compound. Two or more (1) thiopyridone compounds may be used in combination. Thus, a single type of (1) thiopyridone compound or a combination of different types of (1) thiopyridone compounds may be used.

[0160] (1) The thiopyridone compound is selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof:

[0161]

[0162] in

[0163] R1 represents a group selected from the following:

[0164] a) hydrogen atoms, and

[0165] b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0166] i)-O-R3, and

[0167] ii) -S-R3,

[0168] and

[0169] R2 represents a group selected from the following:

[0170] a) Hydrogen atoms,

[0171] b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0172] i) -O-R3,

[0173] ii) -S-R3,

[0174] iii) -C(O)-O-R3, and

[0175] iv) a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and

[0176] c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl

[0177] in

[0178] R3 represents a group selected from the following:

[0179] a) hydrogen atoms, and

[0180] b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl.

[0181] In the following, with respect to the present invention, and unless otherwise specified:

[0182] - "Saturated straight chain C1-C 12 or branched C3-C 12 "Hydrocarbon groups are equivalent to "straight chain (C1-C 12 ) alkyl or branched (C3-C 12 ) alkyl", which corresponds to a saturated straight-chain C1-C 12 or branched C3-C 12 A hydrocarbon group, preferably a straight chain C1-C 10 or branched C3-C 10 A hydrocarbon group, and more preferably a straight-chain C1-C6 or branched C3-C6 hydrocarbon group; preferably, the straight-chain or branched group may be selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl and tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl; more preferably, the saturated straight-chain or branched alkyl may be selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl and tert-butyl, pentyl, hexyl, heptyl and octyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl;

[0183] - saturated "cyclic C3-C8" hydrocarbon radicals are monocyclic or bicyclic cycloalkyl radicals containing 3 to 8 carbon atoms, especially C5 to C7 monocyclic cycloalkyl radicals, such as cyclohexyl,

[0184] - "Alkoxy" is an alkyloxy group in which alkyl is a straight or branched C1-C 16 and preferably a C1-C8 hydrocarbon group;

[0185] - when alkoxy is optionally substituted, this means that alkyl is optionally substituted as defined above;

[0186] - "Aryl" represents a fused or non-fused monocyclic or bicyclic carbonyl group containing 5 to 12 carbon atoms, preferably 6 to 10 carbon atoms, and wherein at least one ring is aromatic; preferably, the aryl group is phenyl, biphenyl, naphthyl, more preferably phenyl;

[0187] - the term "at least one" is equivalent to the term "one or more"; and

[0188] - The term "inclusive" used for a concentration range means that the limits of the range are included in the defined range.

[0189] Salts of compounds of formula (I), (I'), (II) or (II') as defined below include conventional non-toxic salts of said compounds, such as those formed from organic or inorganic acids or from organic or inorganic bases.

[0190] As salts of the compounds of formula (I), (I'), (II) or (II'), mention may be made of:

[0191] A salt obtained by adding a compound of formula (I) or (II) to:

[0192] - inorganic bases, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonium hydroxide, magnesium hydroxide, lithium hydroxide, and carbonates or bicarbonates of sodium, potassium or calcium;

[0193] or

[0194] - organic bases, such as primary, secondary or tertiary alkylamines, for example triethylamine or butylamine. The primary, secondary or tertiary alkylamines may contain one or more nitrogen and / or oxygen atoms and may thus contain, for example, one or more alcohol functions; mention may be made in particular of 2-amino-2-methylpropanol, ethanolamine, triethanolamine, 2-dimethylaminopropanol, 2-amino-2-(hydroxymethyl)-1,3-propanediol and 3-(dimethylamino)propylamine.

[0195] Mention may also be made of the salts of amino acids such as lysine, arginine, guanidine, glutamic acid and aspartic acid. Advantageously, the salts of the compounds of formula (I) or (II) when they contain a carboxyl group may be chosen from alkali metal or alkaline earth metal salts, such as sodium, potassium, calcium or magnesium salts and ammonium salts.

[0196] "Organic or inorganic acid salts" are more particularly selected from salts derived from: i) hydrochloric acid HCl, ii) hydrobromic acid HBr, iii) sulfuric acid H2SO4, iv) alkylsulfonic acids: Alk-S(O)2OH such as methanesulfonic acid and ethanesulfonic acid; v) arylsulfonic acids: Ar-S(O)2OH such as benzenesulfonic acid and toluenesulfonic acid; vi) citric acid; vii) succinic acid; viii) tartaric acid; ix) lactic acid; x) alkoxysulfinic acids: Alk-OS(O)OH such as methoxysulfinic acid and ethoxysulfinic acid; xi) aryloxysulfinic acids such as tolyloxysulfinic acid and phenoxysulfinic acid; xii) phosphoric acid H3PO4; xiii) acetic acid CH3C(O)OH; xiv) trifluoromethanesulfonic acid CF3SO3H; and xv) tetrafluoroboric acid HBF4.

[0197] The acceptable solvates of the compounds described in this specification include conventional solvates, such as those formed due to the presence of solvents during the preparation of the compounds. As examples, the solvates formed due to the presence of water or straight or branched alcohols (such as ethanol or isopropanol) can be mentioned.

[0198] Optical isomers are in particular enantiomers and diastereomers.

[0199] When a tautomeric equilibrium exists according to the following scheme, compound (I') is a tautomeric form of compound (I):

[0200]

[0201] According to one embodiment of the invention, R1 represents a hydrogen atom.

[0202] According to another embodiment of the present invention, R1 represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight chain (C1-C6)alkyl or branched chain (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably ethyl. In particular, the alkyl of R1 is unsubstituted.

[0203] According to one embodiment of the invention, R2 represents a hydrogen atom.

[0204] According to another embodiment of the present invention, R2 represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; the alkyl of R2 is unsubstituted.

[0205] According to another embodiment of the present invention, R2 represents a straight chain (C1-C10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; said alkyl is substituted by one or more groups selected from i), ii), iii) and iv) as defined above. Preferably, said alkyl is substituted by one or two groups selected from i), ii) and iii), more preferably by one or two groups selected from i) and iii), more preferably by a group iii) which is a carboxyl group.

[0206] A further variant of the radical R2 consists in that the alkyl radical is substituted by a radical iv), in particular by a phenyl radical.

[0207] According to another embodiment of the present invention, R2 represents (C3-C8)cycloalkyl, preferably (C5-C7)cycloalkyl, such as cyclohexyl.

[0208] According to another embodiment of the present invention, R2 represents a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups. 12 Aryl, in particular unsubstituted phenyl, is preferred.

[0209] According to one embodiment, R3 represents a hydrogen atom.

[0210] According to another embodiment, R3 represents a saturated straight-chain C1-C 10 or branched C3-C 10 Alkyl; in particular straight chain (C1-C6) alkyl or branched chain (C3-C6) alkyl, preferably (C1-C4) alkyl such as methyl.

[0211] Preferably, the compound of formula (I) and the tautomer (I') or their salts, their optical isomers, racemates and / or their solvates such as hydrates, alone or as a mixture;

[0212] Has the following meanings:

[0213] R1 represents a group selected from the following:

[0214] a) Hydrogen atom;

[0215] b) a saturated straight-chain C1-C6 or branched C3-C6 alkyl group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0216] i)-O-R3

[0217] ii) -S-R3;

[0218] Preferably, it is optionally substituted by one or more groups i)

[0219] R2 represents a group selected from the following:

[0220] a) Hydrogen atom;

[0221] b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0222] i)-O-R3

[0223] ii)-S-R3

[0224] iii) -C(O)-O-R3;

[0225] iv) phenyl optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups such as methoxy groups;

[0226] Preferably, it is substituted by one or more groups selected from i) and iii), preferably by iii), such as carboxyl. R3 represents a group selected from the following:

[0227] a) Hydrogen atom;

[0228] b) Saturated straight-chain C1-C6 or branched C3-C6 alkyl groups.

[0229] Preferably, the compound of formula (I) and the tautomer (I') or their salts, their optical isomers, racemates and / or their solvates such as hydrates, alone or as a mixture

[0230] Has the following meanings:

[0231] R1 represents a group selected from the following:

[0232] a) hydrogen atoms, and

[0233] b) saturated straight-chain C1-C4 or branched C3-C4 alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from i) -OR3, more preferably unsubstituted;

[0234] R2 represents a group selected from the following:

[0235] a) hydrogen atoms; and

[0236] b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0237] i)-O-R3

[0238] iii) -C(O)-O-R3;

[0239] iv) C5-C4 optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups 12 Aryl;

[0240] R3 represents a group selected from the following:

[0241] a) hydrogen atoms, and

[0242] b) Saturated straight-chain C1-C4 or branched C3-C4 alkyl groups, such as methyl or ethyl.

[0243] Preferably, the compound of formula (I) and the tautomer (I') or their salts, their optical isomers, racemates and / or their solvates such as hydrates, alone or as a mixture;

[0244] Has the following meanings:

[0245] R1 is a hydrogen atom; and

[0246] R2 represents a group selected from the following:

[0247] a) hydrogen atoms, and

[0248] b) a saturated straight-chain C1-C5 or branched C3-C5 or cyclic C3-C8, e.g. C5-C6 hydrocarbon radical, substituted by one or more radicals, which may be identical or different, selected from v) -C(O)-O-R3, preferably substituted by a radical iii) -C(O)-O-R3; R2 is even more preferably a saturated straight-chain C1-C4 or branched C3-C4 hydrocarbon radical substituted by a radical iii) -C(O)-O-R3, and

[0249] R3 represents a group selected from the following:

[0250] a) hydrogen atoms, and

[0251] b) Saturated straight-chain C1-C4 or branched C3-C4 alkyl groups such as methyl or ethyl.

[0252] According to another preferred embodiment, the compound of formula (I) and the tautomer (I') are selected from the compounds of formula (II) and the tautomers, salts, solvates and optical isomers thereof, and racemates thereof, alone or as a mixture:

[0253]

[0254] In formula (II) and (II'), R1 and R3 have the same meanings as R1 and R3 in the compounds of formula (I) and (I'), and X represents an alkylene group -(CH2) n -, wherein n is an integer from 1 to 10 (inclusive), preferably from 1 to 6, more preferably from 1 to 4, such as 1, preferably R3 represents a hydrogen atom.

[0255] Among the compounds of formula (I), preference is given to using the following compounds, as well as their tautomers or their salts, their optical isomers, racemates, and / or their solvates such as hydrates, alone or as a mixture:

[0256]

[0257]

[0258]

[0259]

[0260] Among these compounds, the following compounds are more particularly preferred:

[0261]

[0262]

[0263]

[0264]

[0265] More preferably, among these compounds, the following compounds are more particularly preferred:

[0266]

[0267]

[0268] Even more preferably, among these compounds, the following compounds are more particularly preferred:

[0269]

[0270]

[0271] In a most preferred embodiment, the compound according to the invention is the following compound:

[0272]

[0273] All of the above compounds can be obtained from commercially available reagents by chemical methods known to those skilled in the art.

[0274] The (1) thiopyridone compound can be prepared according to the method described in, for example, EP-A-3390363 or WO 2017 / 102349, which are incorporated herein by reference.

[0275] The (1) thiopyridone compound may be an active ingredient or active compound in a cosmetic or dermatological product. The term "active" ingredient or compound as used herein refers to an ingredient or compound having cosmetic or dermatologically active properties, such as antioxidant, whitening, UV filtering effect and antibacterial effect. The (1) thiopyridone compound used in the present invention may act as a decolorizing agent, bleaching agent or whitening agent, whereby the composition according to the present invention may be used as a whitening product or a cosmetic composition for whitening keratin substances.

[0276] The (1) thiopyridone compounds are useful as agents for depigmenting, bleaching or whitening the skin, body hair, eyelashes or hair and lips and / or nails, preferably the skin, particularly for removing pigmentation spots or age spots, and / or as sunscreens.

[0277] The amount of one or more (1) thiopyridone compounds in the composition according to the present invention may be 0.01 wt % or more, preferably 0.05 wt % or more, and more preferably 0.1 wt % or more, relative to the total weight of the composition.

[0278] On the other hand, the amount of one or more (1) thiopyridone compounds in the composition according to the present invention may be 10 wt % or less, preferably 5 wt % or less, and more preferably 3 wt % or less, relative to the total weight of the composition.

[0279] The amount of one or more (1) thiopyridone compounds in the composition according to the invention may be 0.01 to 10 wt %, preferably 0.05 to 5 wt %, more preferably 0.1 to 3 wt %, relative to the total weight of the composition.

[0280] (pH adjuster)

[0281] The composition according to the present invention comprises (2) at least one pH adjuster (pH regulator). Two or more pH adjusters may be used in combination. Thus, a single type of pH adjuster or a combination of different types of pH adjusters may be used.

[0282] (2) The pH adjuster is different from (1) the thiopyridone compound.

[0283] As (2) the pH adjuster, at least one acidifying agent and / or at least one alkalizing agent (alkaline agent) may be used.

[0284] The acidulant may be a monovalent or polyvalent acid, such as a divalent acid.

[0285] The acidulant may be, for example, a mineral (inorganic) acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, or an organic acid, such as a carboxylic acid, for example tartaric acid, citric acid and lactic acid, and a sulfonic acid.

[0286] The alkalizing agent may be a monovalent or polyvalent base, such as a divalent base.

[0287] The alkalizing agent may be mineral (inorganic) or organic, or a mixture.

[0288] The inorganic alkalizing agent may be selected from aqueous ammonia; alkali metal carbonates or bicarbonates, such as sodium carbonate or potassium carbonate and sodium bicarbonate or potassium bicarbonate; alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; and mixtures thereof.

[0289] The organic alkalizing agent may be chosen from organic amines having a pKb at 25° C. of less than 12, preferably less than 10, and even more advantageously less than 6. It should be noted that this is the pKb of the function corresponding to the highest basicity. Furthermore, the organic amine does not contain any alkyl or alkenyl fatty chain containing more than ten carbon atoms.

[0290] The organic alkalizing agent can be selected from, for example, alkanolamines, oxyethylenated and / or oxypropylenated ethylenediamines, amino acids and amine compounds of the following formula (III):

[0291]

[0292] in

[0293] W represents a C1-C6 divalent alkylene group, which is optionally substituted by one or more hydroxyl groups or C1-C6 alkyl groups and optionally interrupted by one or more heteroatoms such as O and N, and

[0294] Rx, Ry, Rz and Rt, which may be the same or different, represent a hydrogen atom or a C1-C6 alkyl, C1-C6 hydroxyalkyl or C1-C6 aminoalkyl group.

[0295] Examples of amine compounds of the formula (III) that may be mentioned include 1,3-diaminopropane, 1,3-diamino-2-propanol, spermine and spermidine.

[0296] The term "alkanolamine" refers to an organic amine comprising a primary, secondary or tertiary amine function and one or more linear or branched C1-C8 alkyl groups bearing one or more hydroxyl groups.

[0297] Alkanolamines containing one to three identical or different C1-C4 hydroxyalkyl groups, such as monoalkanolamines, dialkanolamines or trialkanolamines, may be suitable for the present invention. Among compounds of this type, mention may be made of monoethanolamine (MEA), diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, N-di-methylaminoethanolamine, 2-amino-2-methyl-1-propanol, triisopropanolamine, 2-amino-2-methyl-1,3-propanediol, 3-amino-1,2-propanediol, 3-dimethylamino-1,2-propanediol and tris(hydroxymethylamino)methane.

[0298] The amino acids that can be used are of natural or synthetic origin, in their L, D or racemic form, and contain at least one acid function more particularly chosen from carboxylic acid, sulfonic acid, phosphonic acid or phosphoric acid functions. The amino acids can be in neutral or ionic form.

[0299] As amino acids that can be used in the present invention, mention may be made especially of aspartic acid, glutamic acid, alanine, arginine, ornithine, citrulline, asparagine, carnitine, cysteine, glutamine, glycine, histidine, lysine, isoleucine, leucine, methionine, N-phenylalanine, proline, serine, taurine, threonine, tryptophan, tyrosine and valine.

[0300] It may be preferred that the amino acid is a basic amino acid containing an additional amine function optionally contained in a ring or ureido function.

[0301] Such basic amino acids may preferably be selected from those corresponding to the following formula (IV):

[0302]

[0303] in

[0304] R represents a group selected from the following:

[0305]

[0306] -(CH2)3-NH2,

[0307] -(CH2)2-NH2,

[0308]

[0309] Compounds corresponding to formula (IV) include histidine, lysine, arginine, ornithine and citrulline.

[0310] The organic alkalizing agent may be chosen from organic amines of the heterocyclic type. In addition to histidine already mentioned among the amino acids, mention may in particular be made of pyridine, piperidine, imidazole, triazole, tetrazole and benzimidazole.

[0311] The organic alkalizing agent may also be selected from amino acid dipeptides. As amino acid dipeptides that can be used in the present invention, carnosine, anserine and baleine may be mentioned in particular.

[0312] The organic alkalizing agent may also be chosen from compounds containing a guanidine function. As amines of this type which may be used in the present invention, in addition to the arginine already mentioned as an amino acid, mention may be made in particular of creatine, creatinine, 1,1-dimethylguanidine, 1,1-diethylguanidine, guanidinoacetic acid, metformin, agmatine, N-amidinoalanine, 3-guanidinopropionic acid, 4-guanidinobutyric acid and 2-([amino(imino)methyl]amino)ethane-1-sulfonic acid.

[0313] In a preferred embodiment of the present invention, the organic alkalizing agent may be selected from amino acids, preferably basic amino acids, more preferably arginine, lysine, histidine or a mixture thereof. Even more preferably, the organic alkalizing agent may be arginine.

[0314] Mixed compounds that may be mentioned include the salts of the previously mentioned amines with acids such as carbonic acid or hydrochloric acid. In particular, guanidine carbonate or monoethanolamine hydrochloride may be used.

[0315] The (2) pH adjuster may be present in an amount of 0.01 wt % or more, preferably 0.05 wt % or more, and more preferably 0.1 wt % or more, relative to the total weight of the composition.

[0316] The (2) pH adjuster may be present in an amount of 15 wt % or less, preferably 10 wt % or less, and more preferably 5 wt % or less, relative to the total weight of the composition.

[0317] The (2) pH adjuster may be present in an amount of 0.01 to 15 wt %, preferably 0.05 to 10 wt %, and more preferably 0.1 to 5 wt % or less, relative to the total weight of the composition.

[0318] Preferably the composition according to the invention has a pH of 4.5 or higher, and more preferably 5 or higher.

[0319] Preferably the composition according to the invention has a pH of 6.5 or lower, and more preferably 6 or lower.

[0320] Preferably the composition according to the invention has a pH of from 4.5 to 6.5, and more preferably from 5 to 6.

[0321] The pH of the composition refers to the pH of the aqueous phase of the composition according to the present invention. The pH can be measured according to JIS Z 8802 (2011).

[0322] It may be preferred to also use at least one buffer or buffering agent as (2) pH adjuster in combination with the acidifying agent and / or alkalizing agent in order to stabilize the pH of the composition according to the invention.

[0323] As a buffer, any commonly known buffer can be used. For example, a salt of an acid or a base, preferably a salt of a weak acid or a weak base, can be used. For example, if citric acid or lactic acid is used as an acidulant, sodium citrate or sodium lactate can be used as a buffer.

[0324] (water)

[0325] The composition according to the present invention comprises (3) water.

[0326] The amount of (3) water in the composition according to the present invention may be 20% by weight or more, preferably 30% by weight or more, and more preferably 40% by weight or more, relative to the total weight of the composition.

[0327] On the other hand, the amount of (3) water in the composition according to the present invention may be 99 wt% or less, preferably 95 wt% or less, and more preferably 90 wt% or less, relative to the total weight of the composition.

[0328] The amount of (3) water in the composition according to the invention may be 20 to 99 wt %, preferably 30 to 95 wt %, and more preferably 40 to 90 wt %, relative to the total weight of the composition.

[0329] (Optional Additives)

[0330] The composition according to the invention may also contain any optional additives commonly used in the cosmetic field, for example selected from solvents, antioxidants, chelating agents, cosmetic active agents other than ingredient (1), such as oils, preservatives, and mixtures thereof.

[0331] It is a routine matter for a person skilled in the art to adjust the nature and amount of the abovementioned optional additives that may be present in the compositions according to the invention so that they do not affect the desired cosmetic properties.

[0332] As solvents, mention may be made of one or more cosmetically acceptable organic solvents, which may be alcohols: in particular monovalent alcohols, such as ethanol, isopropanol, benzyl alcohol and phenylethyl alcohol; glycols, such as ethylene glycol, propylene glycol and butylene glycol; other polyols, such as glycerol, sugars and sugar alcohols; and ethers, such as ethylene glycol monomethyl ether, monoethyl ether and monobutyl ether, propylene glycol monomethyl ether, monoethyl ether and monobutyl ether, and butylene glycol monomethyl ether, monoethyl ether and monobutyl ether.

[0333] The one or more organic solvents may be present in a concentration of 0.01% to 30% by weight, preferably 0.1% to 20% by weight, and more preferably 1% to 10% by weight, relative to the total weight of the composition.

[0334] [preparation]

[0335] The compositions according to the present invention may be prepared by mixing the essential and optional ingredients described above in a conventional manner.

[0336] For example, the composition according to the present invention can be prepared by a method comprising the following steps:

[0337] mix

[0338] (1) at least one thiopyridone compound;

[0339] (2) at least one pH adjusting agent; and

[0340] (3) Water.

[0341] It is possible to further admix any optional ingredients.

[0342] The mixing can be carried out at any temperature, such as room temperature (e.g., 20-25°C, preferably 25°C), preferably at 30°C or higher, preferably 40°C or higher, and more preferably 50°C or higher. It is preferably further mixed with any of the above optional ingredients, such as a pH adjuster.

[0343] The form of the composition according to the present invention is not particularly limited, and may be in various forms, such as W / O emulsion, O / W emulsion, gel, solution, etc. Preferably, the composition according to the present invention is in the form of an emulsion, preferably an O / W emulsion, more preferably an O / W gel emulsion.

[0344] [Beauty Methods]

[0345] The composition according to the invention can be used as a cosmetic or dermatological composition, preferably a cosmetic composition, more preferably a cosmetic composition for keratinous substances. As keratinous substances, mention may be made of the skin, scalp, hair, mucous membranes such as the lips, and nails.

[0346] The composition according to the invention can be used as a depigmenting, bleaching or whitening product for keratinous substances such as the skin. In particular, the composition according to the invention can be used as a whitening product.

[0347] The composition according to the invention may preferably be intended for application to keratin substances such as the skin, the scalp and / or the lips, preferably to the skin.

[0348] Thus, the composition according to the invention can be used in a cosmetic method for keratinous materials, preferably the skin. In one embodiment, the invention relates to a cosmetic method for keratinous materials, preferably the skin, preferably a whitening method, comprising the step of applying a composition according to the invention to a keratinous material.

[0349] The composition according to the invention can be used as a topical cosmetic composition in the form of a lotion, milky lotion, cream, gel, paste, serum, foam or spray.

[0350] [use]

[0351] The present invention also relates to (2) the use of at least one pH adjuster in a composition comprising (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof, so as to control the pH of the composition to 4.5 to 6.5, thereby stabilizing one or more of the compounds of (1):

[0352]

[0353] in

[0354] R1 represents a group selected from the following:

[0355] a) hydrogen atoms, and

[0356] b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0357] i)-O-R3, and

[0358] ii) -S-R3,

[0359] and

[0360] R2 represents a group selected from the following:

[0361] a) Hydrogen atoms,

[0362] b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from:

[0363] i) -O-R3,

[0364] ii) -S-R3,

[0365] iii) -C(O)-O-R3, and

[0366] iv) a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and

[0367] c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl

[0368] in

[0369] R3 represents a group selected from the following:

[0370] a) hydrogen atoms, and

[0371] b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl.

[0372] The term "stabilize" has the same meaning as enhancing stability.

[0373] The use according to the present invention can improve (1) the stability of the thiopyridone compound in the composition containing the thiopyridone compound.

[0374] The use according to the invention thus enables the composition comprising the (1) thiopyridone compound to be stored for a long period of time, in particular even under hot conditions.

[0375] The above explanations about (1) the thiopyridone compound and (2) the pH adjuster of the composition according to the present invention may also apply to those used in the use according to the present invention.

[0376] The composition used in the use according to the invention may comprise any optional ingredients as explained above for the composition according to the invention. Example

[0377] The present invention is described in more detail by way of examples. However, these examples should not be construed as limiting the scope of the present invention.

[0378] [Examples 1-3 and Comparative Example 1]

[0379] [preparation]

[0380] Each composition according to Examples 1 to 3 and Comparative Example 1 was prepared by mixing the ingredients shown in Table 1. The numerical values ​​of the amounts of the ingredients are all based on "weight %" as active materials.

[0381] Table 1

[0382]

[0383]

[0384] N-[(2-thioxo-1,2-dihydropyridin-3-yl)carbonyl]glycine (2-mercaptonicotinoylglycine): Compound 20

[0385] [Evaluate]

[0386] (pH)

[0387] The pH of each composition according to Examples 1-3 and Comparative Example 1 at 25° C. was measured as follows.

[0388] equipment:

[0389] 1. pH meter: Laqua F-71 (Horiba)

[0390] 2. pH electrode; 9615S-10D (Horiba)

[0391] 3. pH standard solution (Horiba)

[0392] 4. pH probe internal solution (Horiba)

[0393] program:

[0394] 1. Open the internal solution filling port of the pH meter and supply the internal solution around the electrode.

[0395] 2. Calibrate using pH 9, 7 and 4 standard solutions.

[0396] 3. Wash the electrode with deionized water.

[0397] 4. The protective cap of one of the electrodes (glass electrode) was removed, and the electrode was immersed in each composition according to Examples 1-3 and Comparative Example 1.

[0398] 5. Record the pH after it stabilizes.

[0399] The results are shown in Table 1 in the "pH" row.

[0400] (Thiopyridone compound remaining ratio)

[0401] The amount of the thiopyridone compound in each composition according to Examples 1 to 3 and Comparative Example 1 was measured at the following times by HPLC-UV assay.

[0402] Time (1) just after preparing the composition (T0)

[0403] Time (2) 2 weeks after preparation, wherein the composition is kept at 55°C in a sealed and light-proof container.

[0404] The details of the HPLC-UV assay are as follows.

[0405] Equipment / reagents

[0406] HPLC System Ultra Performance LC (UPLC) HPLC columns RP18, 1.7μm, 2.1mm×100mm Eluent A 0.1% phosphoric acid in water Eluent B Methanol

[0407] HPLC conditions

[0408]

[0409] The remaining rate of the thiopyridone compound is determined by the following equation:

[0410] Remaining rate of thiopyridone compound (%) = amount of thiopyridone compound at time (2) / amount of thiopyridone compound at time (1)

[0411] The results are shown in the row of "Thiopyridone compound remaining rate" in Table 1.

[0412] The residual rate of thiopyridone compounds was also classified according to the following criteria:

[0413] Very good: 90% or higher

[0414] Good: 50% or better and less than 90%

[0415] Poor: less than 50%

[0416] The results are shown in Table 1 in the "Stability" row.

[0417] (result)

[0418] The compositions according to Examples 1-3, each comprising a thiopyridone compound and a pH adjuster controlling the pH of the composition to be between 4.5 and 6.5, were more stable even at elevated temperatures, such that most of the thiopyridone compound was retained compared to the composition according to Comparative Example 1 having a pH greater than 6.5.

Claims

1. A composition, preferably a cosmetic composition, comprising: (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof: in R1 represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from: i)-O-R3, and ii) -S-R3, and R2 represents a group selected from the following: a) Hydrogen atoms, b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from: i) -O-R3, ii) -S-R3, iii) -C(O)-O-R3, and iv) C5-C8 optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl in R3 represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl; (2) at least one pH adjusting agent; and (3) Water, in The pH of the composition is 4.5 to 6.5, preferably 5 to 6.

2. The composition according to claim 1, wherein: R1 in formula (I) and (I') represents a hydrogen atom; or R1 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially linear (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably ethyl, in particular, the alkyl of R1 is unsubstituted.

3. The composition according to claim 1 or 2, wherein: R2 in formula (I) and (I') represents a hydrogen atom; or R2 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; the alkyl of R2 is unsubstituted.

4. The composition according to claim 1 or 2, wherein: R2 in formula (I) and (I') represents a straight chain (C1-C 10 ) alkyl or branched (C3-C 10 )alkyl, especially straight-chain (C1-C6)alkyl or branched (C3-C6)alkyl, such as methyl, ethyl, n-pentyl, n-nonyl, isobutyl, more preferably methyl or ethyl; the alkyl is substituted by one or more groups selected from i), ii), iii) and iv) as defined above, preferably the alkyl is substituted by one or two groups selected from i), ii) and iii), more preferably by one or two groups selected from i) and iii), and more preferably by a group iii) which is a carboxyl group.

5. The composition according to claim 1 or 2, wherein: R2 in formula (I) and (I') represents a (C3-C8) cycloalkyl group, preferably a (C5-C7) cycloalkyl group such as a cyclohexyl group; or R2 in formula (I) and (I') represents a C5-C8 alkoxy group optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups. 12 Aryl, in particular unsubstituted phenyl, is preferred.

6. The composition according to any one of claims 1 to 5, wherein: R3 in formula (I) and (I') represents a hydrogen atom; or R3 in formula (I) and (I') represents a saturated straight chain C1-C 10 or branched C3-C 10 Alkyl; in particular straight chain (C1-C6) alkyl or branched chain (C3-C6) alkyl, preferably (C1-C4) alkyl such as methyl.

7. The composition according to any one of claims 1 to 6, wherein: R1 in formula (I) and (I') represents a group selected from the following: a) hydrogen atoms, and b) a saturated straight-chain C1-C6 or branched C3-C6 alkyl group, which is optionally substituted by one or more groups, which may be the same or different, selected from: i)-O-R3, and ii) -S-R3, Preferably, it is optionally substituted with one or more groups i); R2 in formula (I) and (I') represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from: i) -O-R3, ii) -S-R3, iii) -C(O)-O-R3, and iv) phenyl optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups such as methoxy groups, Preferably substituted by one or more groups selected from i) and iii), preferably substituted by iii), such as carboxyl; and R3 in formula (I) and (I') represents a group selected from the following: a) hydrogen atoms, and b) a saturated straight-chain C1-C6 or branched C3-C6 alkyl group, Preferably, the compound of formula (I) and tautomer (I'), its salts, its solvates such as hydrates, its optical isomers, its racemates, and mixtures thereof have the following meanings: R1 in formula (I) and (I') represents a group selected from the following: a) hydrogen atoms, and b) saturated straight-chain C1-C4 or branched C3-C4 alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from i) -OR3, more preferably unsubstituted; R2 in formula (I) and (I') represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 or a cyclic C3-C8 such as C5-C6 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from: i) -O-R3, iii) -C(O)-O-R3, and iv) C5-C4 optionally substituted by one or more hydroxyl groups and / or by one or more C1-C4 alkoxy groups 12 aryl; and R3 in formula (I) and (I') represents a group selected from the following: a) Hydrogen atom; b) Saturated straight-chain C1-C4 or branched C3-C4 alkyl groups, such as methyl or ethyl.

8. The composition according to any one of claims 1 to 7, wherein: The compound (I) is selected from the following compounds 1 to 24, their tautomers, their salts, their solvates such as hydrates, their optical isomers, their racemates, and mixtures thereof, in particular compounds 1, 2, 4, 6, 7, 9, 11, 12, 14, 15, 16, 17, 18, 19, 20 or 21, more in particular 1, 9, 16, 18, 19, 20 or 21, preferably 18, 19, 20 or 21, and more preferably 20:

9. The composition according to any one of claims 1 to 8, wherein the amount of one or more (1) compounds in the composition is 0.01% to 10% by weight, preferably 0.05% to 5% by weight, and more preferably 0.1% to 3% by weight, relative to the total weight of the composition.

10. The composition according to any one of claims 1 to 9, wherein the (2) pH adjuster is selected from the group consisting of an acidifier, an alkalizer, and a mixture thereof.

11. The composition according to any one of claims 1 to 10, wherein the amount of one or more (2) pH adjusters in the composition is 0.01 wt% to 15 wt%, preferably 0.05 wt% to 10 wt%, more preferably 0.1 wt% to 5 wt%, relative to the total weight of the composition.

12. The composition according to any one of claims 1 to 11, wherein the amount of (3) water in the composition is 20% to 99% by weight, preferably 30% to 95% by weight, more preferably 40% to 90% by weight, relative to the total weight of the composition.

13. The composition according to any one of claims 1 to 12, wherein the composition is for whitening keratinous substances, preferably the skin.

14. A cosmetic method for keratinous materials, preferably skin, preferably a whitening method, comprising the following steps: Applying a composition according to any one of claims 1 to 13 to the keratin material.

15. (2) Use of at least one pH adjuster in a composition comprising (1) at least one compound selected from the group consisting of a compound of the following formula (I), a tautomer of the following formula (I'), a salt thereof, a solvate thereof such as a hydrate, an optical isomer thereof, a racemate thereof, and a mixture thereof, so as to control the pH of the composition to 4.5 to 6.5, thereby stabilizing one or more of the compounds of (1): in R1 represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 Alkyl, which is optionally substituted by one or more groups, which may be the same or different, selected from: i)-O-R3, and ii) -S-R3, and R2 represents a group selected from the following: a) Hydrogen atoms, b) Saturated straight chain C1-C 12 or branched C3-C 12 or a cyclic C3-C8 hydrocarbon group, which is optionally substituted by one or more groups, which may be the same or different, selected from: i) -O-R3, ii) -S-R3, iii) -C(O)-O-R3, and iv) C5-C8 optionally substituted by one or more hydroxyl groups and / or by one or more C1-C8 alkoxy groups 12 Aryl, and c) C5-C8 substituted with one or more hydroxyl groups and / or with one or more C1-C8 alkoxy groups 12 Aryl in R3 represents a group selected from the following: a) hydrogen atoms, and b) Saturated straight chain C1-C 10 or branched C3-C 10 alkyl.

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