Field of the Invention

The present invention relates to the use of N-functionalized fatty acid amides of formula I as self-tanning substances for skin, for stimulating melanin synthesis, for improving melanin transport, for boosting natural tanning and/or improving the distribution of melanin in suprabasal layers of the skin, and to preparations comprising these amides.

Background of the Invention

The trend away from refined paleness towards "healthy, sporty brown skin" has been uninterrupted for years. In order to achieve a tanned complexion, people expose their skin to sunlight, since this causes pigmentation due to melanin formation. However, the UV radiation in sunlight also has a damaging effect on the skin. Besides acute damage (sunburn), long-term damage occurs on excessive irradiation with light from the UVB region (wavelength 280-320 nm), such as, for example, an increased risk of contracting skin cancer. Excessive exposure to UVB and UVA radiation (wavelength: 320- 400 nm) generates highly reactive free-radical species, which multiply further even after termination of the irradiation, and wrinkling and skin ageing occur as a consequence thereof. Also highly reactive free-radical species generated by infrared light or visible light contribute to wrinkling and skin ageing.

Tanning (pigmentation) of the skin offers natural protection against the adverse consequences of sunlight. The epidermis contains individual pigment-forming cells, the melanocytes, besides the basal cells in its lowest layer, the basal layer. UV light stimulates the production of melanin in these cells, which is transported into the kerantinocytes (horny cells), where it becomes visible as brown skin colour. Melanin protects the cell nuclei against further irradiation and the adverse effects it causes on the cell DNA. Depending on the chemical composition of the pigments formed biochemically, a distinction is made between brownish-black eumelanin and reddish- yellow pheomelanin. The skin hue observed is determined by the ratio of these two types of melanin.

This pigment formation starting from the amino acid tyrosine is initiated predominantly by UVB radiation and is known as "indirect pigmentation". Its development runs over a number of days; the suntan obtained in this way lasts a few weeks. In the case of "direct pigmentation", which commences with the solar irradiation, predominantly colourless melanin precursors are oxidised by UVA radiation to dark-coloured melanin. Since this oxidation is reversible, it results in skin tanning which only lasts briefly.

Artificial tanning of the skin can be produced externally with the aid of make-up and orally by taking e.g. carotenoids.

Much more popular, however, is artificial tanning of the skin which can be achieved by the application of so-called artificial self-tanning agents.

These compounds have, as a chemical structural feature, keto or aldehyde groups in the vicinity of alcohol functions and predominantly belong to the class of substances of the sugars. Particularly frequently employed artificial self-tanning substances are 1 ,3-dihydroxyacetone (DHA), which is used in an amount of 700t/a, and erythrulose.

Said self-tanning agents can be reacted with the proteins and amino acids of the homy layer of the skin in the sense of a Maillard reaction or via a Michael addition, where polymers which give the skin a brownish hue form via a reaction route which has not yet been clarified completely. This reaction is complete after about 4 to 6 hours. The tan achieved in this way cannot be washed off and is only removed with the normal skin desquamation.

However, these coloured products often do not look like a natural tan. JPH04112817 describes a composition for hair, which exhibits white hair prevention and improvement effects.

GB455603 describes a process of improving hides and skins by treating the untanned hide and skin with a basic compound such as the free bases or salts or quaternary compounds of laurimidazolines, isoheximidomethyl ether, isoheptimidoethyl ether or the amidine of palm-nut oil fatty acid.

W02007039057 describes a cosmetic or pharmaceutical composition comprising a fatty acid containing 6 to 18 carbon atoms, which carries one or two hydroxy, alkoxy, C2-C4-acylprotected amino, or oxo group, or a salt, ester or amide of such acids and a carrier used in cosmetic or pharmaceutical compositions.

US20080025940 describes novel products containing a sulfanyl group for caring for and/or treating human keratin fibers or human skin, which promotes their pigmentation and/or limits their depigmentation. It further describes that the programs of differentiation of the keratinocytes of the epidermis and of the hair follicle are clearly different.

H. Chiang et al, Focus on Skin Care: Ethnic, Whitening & Tanning - Supplement to Household and Personal Care TODAY, n 1/2011 , “Fatty acids and their related products modulate melanogenesis” describes the use of fatty acids as melanogenesis stimulating agents and unsaturated fatty acids as pigmentation suppressors in vitro and in vivo.

P. Chaikul et al, Advanced Science Letters, 2012, 17, 251 to 256 describes melanogenesis enhancement of saturated fatty acid methyl esters in B16F10 melanoma cells. In the IP.com disclosure 2011 , disclosed anonymously, with the title “Suncare compositions with new cosmetic raw materials”, dimethyl capramide is described as an emollient for cosmetic suncare formulations.

LIS2010240754 describes a method for treating skin ageing and/or intended for treating keratinisation and pigmentation disorders comprising the application of a dermatocosmetological composition comprising an unsaturated fatty amino-acid derivative to a person in need thereof.

WO201 5082857 relates to a combination of two compounds stemming from fatty acids and to the cosmetic and dermatological uses of said combination, the latter being a combination of at least one compound stemming from the condensation of at least one fatty acid with an alkanolamine, and at least one hydrosoluble compound, each of them being present in a proportion of at least 1 mass % in relation to the mass of the combination.

Shuyang Chen et al, Nature 2017, 549, 399 to 416 describe a potential MC1 R-targeted intervention strategy in mice to rescue loss-of-function MC1 R in MC1R RHC variants for therapeutic benefit by activating MC1 R protein palmitoylation.

Sardorbek Abdubakiev, Hongliang Li, Xueying Lu, Jun Li & H. A. Aisa (2019): N-Alkylamides from Piper longumg L. and their stimulative effects on the melanin content and tyrosinase activity in B16 melanoma cells, Natural Product Research, DOI: 10.1080/14786419.2018.1539982 describe unsaturated N-Alkylamides from Piper longum L. and their stimulative effects on the melanin content and tyrosinase activity in B16 melanoma cells.

However, there continues to be a demand for dermatologically tolerated skin-colouring substances which are suitable for use in cosmetic and/or dermatological preparations or medical devices and which enhance the natural tanning of the skin by increasing melanin synthesis and at the same time enable inherent skin protection or sun protection, in particular against UVB radiation.

Consequently, it is an object of the present application to provide such a solution.

Summary of the Invention

The present inventors have now found that the above object may be attained by using compounds of formula I as further described below.

The present inventors have now found that certain functionalized fatty acid amides of formula I are suitable as self-tanning substances, in particular as self-tanning substances which facilitate natural tanning of the skin or which enhance natural tanning of the skin, preferably human skin including face and body, by e.g. affecting melanin synthesis and/or melanin distribution. The strengthening of natural tan is believed to be a boosting effect/amplifying effect achieved through the compounds of formula I as described below as these compounds continue to stimulate the melanin synthesis without further exposure to sun or any related radiation.

The invention relates to the use of compounds of formula I where

R ¹ and R ² are, independently of one another, H or a straight-chain or branched alkyl group having 1 to 5 C atoms, with the proviso that at least one of R ¹ or R ² is a straight-chain or branched alkyl group having 1 to 5 C atoms and R ³ is a straight-chain or branched alkyl group having 7 C atoms, and/or salts or solvates thereof, as self-tanning substance for skin, preferably human skin including face and body.

The invention furthermore relates to the use of compounds of formula I where

R ¹ and R ² are, independently of one another, H or a straight-chain or branched alkyl group having 1 to 5 C atoms, with the proviso that at least one of R ¹ or R ² is a straight-chain or branched alkyl group having 1 to 5 C atoms and

R ³ is a straight-chain or branched alkyl group having 7 C atoms, and/or salts or solvates thereof, for stimulating melanin synthesis, for improving melanin transport, for boosting natural tanning and/or for improving the distribution of melanin in suprabasal layers of the skin, preferably human skin including face and body.

The invention furthermore relates to a preparation comprising a vehicle which is suitable for topical applications, at least one compound of formula I in an amount of 0.01 to 10% by weight, where

R ¹ and R ² are, independently of one another, H or a straight-chain or branched alkyl group having 1 to 5 C atoms, with the proviso that at least one of R ¹ or R ² is a straight-chain or branched alkyl group having 1 to 5 C atoms and

R ³ is a straight-chain or branched alkyl group having 7 C atoms, and/or salts or solvates thereof, and at least one further self-tanning substance and a process for the manufacturing of said preparation.

The invention furthermore relates to a non-therapeutically method for tanning the skin naturally, comprising providing a cosmetic composition or a medical device containing at least one compound of formula I as described and applying said cosmetic composition or medical device on skin, preferably on human skin including face and body.

Detailed Description of the Invention

For the purposes of the invention, the term self-tanning active compound is used synonymously with self-tanning substance or self-tanner substance.

Preferably, said skin is from humans. Preferably, face and body of a human is tanned or natural tanning of face and body is intensified.

For the purposes of the invention, the compounds of the formula I are defined such that they are also taken to mean pharmaceutically or cosmetically usable salts and solvates. Solvates of the compounds are taken to mean adductions of inert solvent molecules onto the compounds, which form owing to their mutual attractive force. Solvates are, for example, mono- or dihydrates or alcoholates. Said salt forms include, for example, alkali metal salts such as sodium and potassium salts, alkaline earth metal salts such as calcium and magnesium salts, amine salts such as methylamine salts, dimethylamine salts, trimethylamine salts, methylpiperidine salts, ethanolamine salts, diethanolamine salts, triethanolamine salts and lysine salts or ammonium salts or basic amino salts.

The preferred salts here include, in particular, alkali and alkaline-earth metal salts, zinc salts and ammonium salts, but in particular sodium salts and potassium salts. A straight-chain or branched alkyl group having 1 to 5 C atoms is, for example, methyl, ethyl, isopropyl, n-propyl, n-butyl, sec-butyl or tert-butyl, pentyl, 1 -, 2- or 3-methylbutyl, 1 ,1 -, 1 ,2- or 2,2-dimethylpropyl or 1 -ethylpropyl.

Compounds of formula I are preferably used if the substituent R ³ in formula I is a straight-chain heptyl group.

The invention therefore furthermore relates to the use of compounds of the formula I, as described above, in which the substituent R ³ is a straightchain heptyl group.

Compounds of formula I are preferably used if the substituents R ¹ and R ² in formula I are identical and are a straight-chain alkyl group having 1 to 5 C atoms.

The invention therefore furthermore relates to the use of compounds of formula I, as described above or preferably described before, in which the substituents R ¹ and R ² are identical and are a straight-chain alkyl group having 1 to 5 C atoms.

Compounds of formula I are preferably used if the substituents R ¹ and R ² in formula I are both independently of each other a straight-chain alkyl group having 1 to 5 C atoms.

The invention therefore furthermore relates to the use of compounds of formula I, as described above or preferably described before, in which the substituents R ¹ and R ² are both independently of each other a straightchain alkyl group having 1 to 5 C atoms.

Preferred examples of compounds of formula I are the compounds la, lb and Ic:

The invention therefore furthermore relates to the use of compounds of formula I, where the compound of formula I is represented by formula la, lb or Ic.

The most preferred compound of formula I is represented by formula la.

The compounds of the formula I are commercially available or can be prepared by syntheses known to the person skilled in the art. They can be prepared, for example, by reaction of a corresponding fatty acid chloride of the formula II in which R ³ has a meaning as described before or preferably described before, with an amine of formula III in which the substituents R ¹ and R ² have one of the meanings indicated or preferably indicated above.

A person skilled in the art in the area of organic synthesis will easily be able to find the reaction condition necessary for this purpose in the generally available literature on organic reactions. Examples of reaction conditions are described in the experimental part.

The reaction is preferably carried out in an organic solvent, e.g. dichloromethane.

Suitable purification steps include separating off readily volatile components by distillation or condensation, extraction with an organic solvent, precipitation by addition of an organic solvent, salt exchange or a combination of these methods. Any known separation method can be used or combined for this purpose. In general, the desired reaction product precipitates out of the reaction mixture and is separated off and purified correspondingly.

Further details are given in the examples, which also apply correspondingly to the general synthesis description.

Compounds of formula I as described before or preferably described before surprisingly stimulate and/or increase melanin synthesis and/or improve melanin transport from the melanocytes to the keratinocytes and or boost natural tanning and/or distribute melanin better in suprabasal layers. Said compound of formula I can therefore also be referred to as melanogenesis promoter or propigmentation active compound. Said compounds of formula I preferably increase melanin synthesis. This affects the colour of the skin and causes a tanning effect. This property is surprising inasmuch as the opposite effect, namely inhibition of melanin synthesis, is described for similar compounds.

Said compounds of formula I as described before or preferably described before stimulate said melanin synthesis of the skin without irradiation of the skin and are therefore sunless self-tanning substances. Especially no UV irradiation is necessary.

Besides the tanning action, said compounds of formula I are also well tolerated by the skin. In addition, preferred compounds of those described here are colourless or only weakly coloured and thus do not lead to discolorations of the preparations, or only do so to a slight extent. In addition, the preferred compounds have improved solubility in cosmetic oils.

In order that the compounds of formula I as described before or preferably described before are able to develop their positive action on the skin particularly well, it may be preferred to allow said compounds of formula I to penetrate into deeper skin layers. A number of possibilities are available to this end. Firstly, the compounds of formula I may have adequate lipophilicity in order to be able to penetrate through the outer skin layer into epidermal layers. As a further possibility, corresponding transport means, for example liposomes, which enable transport of the compounds of formula I through the outer skin layers, may also be provided in the topical preparation. Finally, systemic transport of the compounds of formula I is also conceivable.

The uses according to the invention preferably take place non-therapeuti- cally.

The invention further relates to the use of a compound of formula I as described before or preferably described before where it is applied to skin, preferably human skin (face and body), in a cosmetic composition, a dermatological composition or a medical device.

The present invention furthermore relates to a preparation comprising a vehicle which is suitable for topical applications and at least one compound of formula I in an amount of 0.01 to 10% by weight, as described before or preferably described before.

The present invention furthermore relates to a preparation comprising a vehicle which is suitable for topical applications, at least one compound of formula I in an amount of 0.01 to 10% by weight, as described before or preferably described before, and at least one further self-tanning substance.

The topically usable preparation here is usually a cosmetic or dermatological formulation or a medical device. In this case, the preparations comprise a cosmetically or dermatologically suitable vehicle or a vehicle which is suitable for a medical device and, depending on the desired property profile, optionally further suitable ingredients.

For the purposes of the present invention, the term "composition" is also used synonymously alongside the term "preparation".

The preparations here are usually preparations which can be applied topically, such as, for example, cosmetic or dermatological preparations or medical devices. “Can be applied topically” means that the preparation is applied externally and locally, i.e. that the preparation must be suitable, for example, for being able to be applied to the skin, e.g. face and body. In this case, the preparations comprise a cosmetically, or dermatologically suitable vehicle and, depending on the desired property profile, optionally further suitable ingredients. The topical preparations are preferably employed as cosmetic or dermatological composition, particularly preferably as cosmetic composition. Suitable vehicles and assistants or fillers are described in detail in the following part.

The preparations may include or comprise, essentially consist of or consist of the necessary or optional constituents mentioned above and/or below. All compounds or components which can be used in the preparations are either known and commercially available or can be synthesised by known processes.

The preparation is preferably a cosmetic or dermatological preparation; the preparation is particularly preferably a cosmetic preparation. The at least one compound of formula I, as described above or as preferably described is employed in the preparations according to the invention in amounts of 0.01 to 10% by weight, preferably in amounts of 0.05 to 10% by weight, particularly preferably in amounts of 0.1 % by weight to 5% by weight and very particularly preferably in amounts of 0.5 to 2% by weight, based on the total amount of the preparation. The person skilled in the art is presented with absolutely no difficulties here in selecting the amounts appropriately depending on the intended action of the preparation.

Furthermore, the preparations according to the invention comprise at least one further self-tanning substance as further ingredient. This can be either a self-tanning agent which reacts with the amino acids of the skin in the sense of a Maillard reaction or via a Michael addition, or a melanogenesis promoter or propigmentation active compound which promotes the natural tanning of the skin.

Advantageous self-tanning substances which can be employed are, inter alia: 1 ,3-dihydroxyacetone, glycerolaldehyde, hydroxymethylglyoxal, y- dialdehyde, erythrulose, 6-aldo-D-fructose, ninhydrin, 5-hydroxy-1 ,4-naph- toquinone (juglone) or 2-hydroxy-1 ,4-naphtoquinone (lawsone). Very particular preference is given to 1 ,3-dihydroxyacetone, erythrulose or a combination thereof.

Propigmentation substances can in principle be all active compounds known to the person skilled in the art. Examples thereof are glycyrrhetinic acid, melanocyte-stimulating hormone (alpha-MSH), peptide analogues, thymidine dinucleotides, L-tyrosine and esters thereof or bicyclic monoterpenediols (described in Brown et al., Journal of Photochemistry and Photobiology B: Biology 63 (2001 ) 148-161 ), compounds as described in EP3522993, compounds as described in EP3522863, or hexadecanoic acid 5-hydroxy-2-methyl-4-oxo-4H-chromen-7-yl ester, which is marketed by Merck under the trade name RonaCare® Bronzyl™. Particularly suitable active compounds for combination with at least one compound of the formula I, as described above, are 1 ,3-dihydroxyacetone, erythrulose and/or hexadecanoic acid 5-hydroxy-2-methyl-4-oxo-4H-chromen-7-yl ester and/or 1 ,3-Benzodioxol-5-ylmethylurea.

The at least one further self-tanning substance is preferably present in the preparation in an amount of 0.01 to 20% by weight, particularly preferably in an amount of 0.1 to 15% by weight and very particularly preferably in an amount of 0.2 to 8% by weight, based on the total amount of the preparation.

Preparations having self-tanner properties, in particular those which comprise dihydroxyacetone, tend towards malodours on application to the human skin, which are thought to be caused by degradation products of dihydroxyacetone itself or by products of side reactions and which are regarded as unpleasant by some users. It has been found that these malodours are prevented on use of formaldehyde scavengers and/or flavonoids. The preparation according to the invention may therefore preferably also comprise formaldehyde scavengers and optionally flavonoids for improving the odour.

The formaldehyde scavenger is preferably selected from the group alkali metal, alkaline-earth metal or ammonium disulfite. Particular preference is given to a preparation which comprises, in combination DHA Plus, a mixture of DHA, sodium disulfite and magnesium stearate.

DHA Plus is a product mixture which comprises sodium metabisulfite, synonymous with Na2S20s or INCI: sodium disulfite, for the masking, elimination or neutralisation of formaldehyde. The addition of sodium metabisulfite in finished formulations results in significant reduction or suppression of the unpleasant odour. DHA Plus is marketed by Merck, Darmstadt. The preparation according to the invention comprising at least one compound of the formula I, as described above with the substituents indicated and also preferably mentioned, and dihydroxyacetone as self tanner, may particularly preferably comprise flavonoids for improving the odour and optionally for accelerating tanning.

The flavonoid here additionally acts as stabiliser for the self-tanner or the self-tanning substances and/or reduces or prevents or improves storagedependent malodours, which may also arise due to additives or assistants present.

This is preferably a flavonoid in which one or more phenolic hydroxyl groups have been blocked by etherification or esterification. For example, hydroxyethyl-substituted flavonoids, such as, preferably, troxerutin, troxe- quercetin, troxeisoquercetin or troxeluteolin, and flavonoid sulfates or flavonoid phosphates, such as, preferably, rutin sulfates, have proven to be particularly highly suitable flavonoids here. In the sense of this use, particular preference is given to rutin sulfate and troxerutin. Very particular preference is given to the use of troxerutin. The preferred flavonoids have a non- positively charged flavan skeleton. It is thought that metal ions, such as, for example, Fe ² 7Cu ²⁺ , are complexed by these flavonoids and auto-oxidation processes in the case of fragrances or compounds whose degradation results in malodours are thus prevented or reduced.

Particular preference is given to a preparation which, besides at least one compound of the formula I, as described above or preferably described, comprises DHA Rapid. DHA Rapid is a product mixture comprising di- hydroxyacetone and troxerutin, from Merck, Darmstadt. This particularly preferred preparation may optionally also comprise a formaldehyde scavenger, for example sodium disulfite. Corresponding premixes and preparations which comprise formaldehyde scavengers and optionally flavonoids in order to improve the odour on the skin are described in the German patent application DE 102007 013 368 A1.

Besides the compounds of the formula I, as described above or described as preferred, the preparations according to the invention may additionally also comprise at least one UV filter.

Organic UV filters, so-called hydrophilic or lipophilic sun-protection filters, which are effective in the UVA region and/or UVB region and(/or IR and/or VIS region (absorbers). These substances can be selected, in particular, from dibenzoylmethane derivatives, cinnamic acid derivatives, salicylic acid derivatives, camphor derivatives, triazine derivatives, p,0-diphenylacrylate derivatives, p-aminobenzoic acid derivatives and polymeric filters and silicone filters, which are described in the application WO-93/04665. Further examples of organic filters are indicated in the patent application EP-A 0487 404. The said UV filters are usually named below in accordance with INCI nomenclature.

Particularly suitable for a combination are Ethylhexyl salicylate, Phenylbenzimidazolesulfonic acid, Benzophenone-3, Benzophenone-4, Benzophenone-5, n-Hexyl 2-(4-diethylamino-2-hydroxybenzoyl)benzoate, 4-Methylbenzylidenecamphor, Terephthalylidenedicamphorsulfonic acid, Disodium phenyldibenzimidazoletetrasulfonate, Methylenebis(benzotriazolyl)tetramethylbutylphenol, Butyl Methoxydibenzoylmethane, Ethylhexyl Triazone, Diethylhexyl Butamido Triazone, Drometrizole trisiloxane, Phenylene bis-diphenyltriazine, Polysilicone-15, 1 ,1 -Dicarboxy(2,2'-dimethylpropyl)-4,4-diphenylbutadiene, 2,4-bis[5-1 (dimethylpropyl)benzoxazol-2-yl(4-phenyl) imino]-6-(2-ethyl- hexyl)imino-1 ,3,5-triazine and mixtures thereof. These organic UV filters are generally incorporated into preparations in an amount of 0.01 % by weight to 20% by weight, preferably 1 % by weight to 10% by weight.

The compounds listed should only be regarded as examples. It is of course also possible to use other UV filters.

Besides the compounds of formula I and the optional organic UV filters, as described above, the preparations may comprise further inorganic UV filters, so-called particulate UV filters.

These combinations with particulate UV filters are possible both as powder and also as dispersion or paste of the following types.

Preference is given here both to those from the group of the titanium dioxides, such as, for example, coated titanium dioxide (for example Eusolex® T-2000, Eusolex®T-AQUA, Eusolex®T-AVO, Eusolex®T- PRO, Eusolex® T-EASY), zinc oxides (for example Sachtotec®), iron oxides or also cerium oxides and/or zirconium oxides.

It may furthermore be preferred for the preparations to comprise inorganic UV filters which have been aftertreated by conventional methods, as described, for example, in Cosmetics & Toiletries, February 1990, Vol. 105, pp. 53 64. One or more of the following aftertreatment components can be selected here: amino acids, beeswax, fatty acids, fatty acid alcohols, anionic surfactants, lecithin, phospholipids, sodium, potassium, zinc, iron or aluminium salts of fatty acids, polyethylenes, silicones, proteins (particularly collagen or elastin), alkanolamines, silicon dioxide, aluminium oxide, further metal oxides, phosphates, such as sodium hexametaphosphate, or glycerine.

These inorganic UV filters are generally incorporated into the preparations in an amount of 0.1 % by weight to 25% by weight, preferably 2% by weight to 10% by weight. By combination of one or more of the said compounds having a UV filter action, the protective action against harmful effects of the UV radiation inducing photo-ageing can be optimised.

All said UV filters can also be employed in encapsulated form. In particular, it is advantageous to employ organic UV filters in encapsulated form.

The capsules in preparations to be employed in accordance with the invention are preferably present in amounts which ensure that the encapsulated UV filters are present in the preparation in the per cent by weight ratios indicated above.

The preparations described, which in accordance with the invention comprise the at least one compound of the formula I, may furthermore also comprise coloured pigments, where the layer structure of the pigments is not limited.

The coloured pigment should preferably be skin-coloured or brownish on use of 0.5 to 5% by weight. The selection of a corresponding pigment is familiar to the person skilled in the art.

Preferred preparations may likewise comprise at least one further cosmetic active compound to further support advantages of the cosmetic, or dermatological composition or medical device. Further cosmetic active compounds are for example selected from humectants, antioxidants, antiageing, anti-wrinkle, anti-dandruff, anti-acne, anti-cellulite active compounds, deodorants or vitamins.

The protective action of preparations against oxidative stress or against the effect of free radicals can be improved if the preparations comprise one or more antioxidants, the person skilled in the art being presented with absolutely no difficulties in selecting antioxidants which act suitably quickly or with a time delay.

There are many proven substances known from the specialist literature which can be used as antioxidants, for example amino acids (for example glycine, histidine, tyrosine, tryptophan) and derivatives thereof, imidazoles, (for example urocanic acid) and derivatives thereof, peptides, such as D,L- carnosine, D-carnosine, L-carnosine and derivatives thereof (for example anserine), carotinoids, carotenes (for example a-carotene, p-carotene, lycopene) and derivatives thereof, chlorogenic acid and derivatives thereof, lipoic acid and derivatives thereof (for example dihydrolipoic acid), aurothioglucose, propylthiouracil and other thiols (for example thioredoxin, glutathione, cysteine, cystine, cystamine and the glycosyl, N-acetyl, methyl, ethyl, propyl, amyl, butyl and lauryl, palmitoyl, oleyl, y-linoleyl, cholesteryl and glyceryl esters thereof) and salts thereof, dilauryl thiodipropionate, distearyl thiodipropionate, thiodipropionic acid and derivatives thereof (esters, ethers, peptides, lipids, nucleotides, nucleosides and salts), and sulfoximine compounds (for example buthionine sulfoximines, homocysta sulfoximine, buthionine sulfones, penta-, hexa- and heptathionine sulfoximine) in very low tolerated doses (for example pmol to pmol/kg), and also (metal) chelating agents, (for example a-hydroxyfatty acids, palmitic acid, phytic acid, lactoferrin), a-hydroxy acids (for example citric acid, lactic acid, malic acid), humic acid, bile acid, bile extracts, bilirubin, biliverdin, EDTA, EGTA, pentasodium ethylenediamine tetramethylene phosphonate and derivatives thereof, unsaturated fatty acids and derivatives thereof, vitamin C and derivatives (for example ascorbyl palmitate, magnesium ascorbyl phosphate, ascorbyl acetate), tocopherols and derivatives (for example vitamin E acetate), vitamin A and derivatives (for example vitamin A palmitate) and coniferyl benzoate of benzoin resin, rutin ic acid and derivatives thereof, a-glycosylrutin, ferulic acid, furfurylideneglucitol, carnosine, butylhydroxytoluene, butylhydroxyanisole, nordihydroguaiaretic acid, trihydroxy- butyrophenone, quercetin, uric acid and derivatives thereof, mannose and derivatives thereof, zinc and derivatives thereof (for example ZnO, ZnSCM), selenium and derivatives thereof (for example selenomethionine), stilbenes and derivatives thereof (for example stilbene oxide, trans-stilbene oxide).

Suitable antioxidants are also compounds of the formulae A or B in which

R ¹ can be selected from the group -C(O)CH3, -CO2R ³ , -C(O)NH2 and -C(O)N(R ⁴ ) ₂ ,

X denotes 0 or NH, '

R ² denotes linear or branched alkyl having 1 to 30 C atoms,

R ³ denotes linear or branched alkyl having 1 to 20 C atoms,

R ⁴ in each case, independently of one another, denotes H or linear or branched alkyl having 1 to 8 C atoms,

R ⁵ denotes H, linear or branched alkyl having 1 to 8 C atoms or linear or branched alkoxy having 1 to 8 C atoms and

R ⁶ denotes linear or branched alkyl having 1 to 8 C atoms, preferably derivatives of 2-(4-hydroxy-3,5-dimethoxybenzylidene)malonic acid and/or 2-(4-hydroxy-3,5-dimethoxybenzyl)malonic acid, particularly preferably bis(2-ethylhexyl) 2-(4-hydroxy-3,5-dimethoxybenzylidene)malo- nate (for example Oxynex® ST Liquid) and/or bis(2-ethylhexyl) 2-(4- hydroxy-3,5-dimethoxybenzyl)malonate (for example RonaCare® AP). Furthermore, the combination with bis(isopropyl) 2-(4-hydroxy-3- methoxybenzylidene)-malonate is preferred. Mixtures of antioxidants are likewise suitable for use in the cosmetic preparations according to the invention. Known and commercial mixtures are, for example, mixtures comprising, as active ingredients, lecithin, L-(+)-ascorbyl palmitate and citric acid, natural tocopherols, L-(+)-ascorbyl palmitate, L-(+)-ascorbic acid and citric acid (for example Oxynex® K LIQUID), tocopherol extracts from natural sources, L-(+)-ascorbyl palmitate, L-(+)-ascor- bic acid and citric acid (for example Oxynex® L LIQUID), DL- a-tocopherol, L-(+)-ascorbyl palmitate, citric acid and lecithin (for example Oxynex® LM) or butylhydroxytoluene (BHT), L-(+)-ascorbyl palmitate and citric acid (for example Oxynex® 2004). Antioxidants of this type are usually employed in such preparations with the compounds according to the invention in per cent by weight ratios in the range from 1000:1 to 1 :1000, preferably in per cent by weight ratios of 100: 1 to 1 : 100.

Suitable anti-ageing active compounds and/or humectants, in particular for skin-care preparations, are preferably so-called compatible solutes. The compatible solutes are preferably substances selected from the group consisting of pyrimidinecarboxylic acids (such as ectoin and hydroxyectoin), proline, betaine, glutamine, cyclic diphosphoglycerate, N. -acetylornithine, trimethylamine N-oxide di-myo-inositol phosphate (DIP), cyclic 2,3- diphosphoglycerate (cDPG), 1 ,1 -diglycerol phosphate (DGP), !3>-mannosyl glycerate (firoin), p-mannosyl glyceramide (firoin-A) dimannosyl diinositol phosphate (DMIP) or an optical isomer or derivative, for example an acid, salt or ester, of these compounds, and combinations thereof.

Such humectant(s) is/are preferably present in the topical preparation in an amount of 0.01 to 20% by weight, particularly preferably in an amount of 0.1 to 15% by weight and very particularly preferably in an amount of 0.2 to 8% by weight, based on the total amount of the preparation.

Additionally, anti-aging active compounds which can be used are products from Merck, such as, for example, 5,7-dihydroxy-2-methylchromone, mar- keted under the trade name RonaCare®Luremin®, or the commercial products RonaCare®ASCIII®, RonaCare®RenouMer, RonaCare® Nicotinamide, RonaCare®VTA, RonaCare®Poppy SE, RonaCare®lsoquercetin or RonaCare®Cyclopeptide 5, RonaCare®Balmance.

The preparations to be employed may comprise vitamins as further ingredients. Preference is given to vitamins and vitamin derivatives selected from vitamin A, vitamin A propionate, vitamin A palmitate, vitamin A acetate, retinol, vitamin B, thiamine chloride hydrochloride (vitamin Bi), riboflavin (vitamin B2), nicotinamide, vitamin C (ascorbic acid), vitamin D, ergocalciferol (vitamin D2), vitamin E, DL-a-tocopherol, tocopherol E acetate, tocopherol hydrogensuccinate, vitamin Ki , esculin (vitamin P active compound), thiamine (vitamin Bi), nicotinic acid (niacin), pyridoxine, pyridoxal, pyridox- amine, (vitamin Be), pantothenic acid, biotin, folic acid and cobalamine (vitamin B12), particularly preferably vitamin A palmitate, vitamin C and derivatives thereof, DL-a-tocopherol, tocopherol E acetate, nicotinic acid, pantothenic acid and biotin. In the case of cosmetic application, vitamins are usually added with the flavonoid-containing premixes or preparations in ranges from 0.01 to 5.0% by weight, based on the total weight. Nutrition- physiological applications are oriented towards the respective recommended vitamin requirement.

The retinoids described are at the same time also effective anti-cellulite active compounds. A likewise known anti-cellulite active compound is caffeine.

The preparations may preferably comprise assistants, such as, for example, cosmetic oils (for example Caprylic/Capric Triglycerides, C12-15 alkyl Benzoate, isopropyl myristate, arylalkyl benzoates, such as, for example, phenethyl benzoate (X-Tend 226) or oil components of the Cosmacol brand, such as Dimyristyl Tartrate, Tri C14-C15 Alkyl Citrate, C12-C13 Alkyl Lactate, Tridecyl Salicylate, C12-C13 Alkyl Octanoate, C12-C13 Alkyl Malate, C12-C13 Alkyl Citrate, C12-C13 Alkyl Tartrate), or polar-protic assistants (for example propylene glycol, glycerol, isopropanol, ethanol) or so-called solubilisers (for example Butylphthalimide, Isopropylphthalimide, Dimethylisosorbide). Very particularly preferred cosmetic oils are C12-C13 Alkyl Lactate, commercially available as Cosmacol ELI and phenethyl benzoate, commercially available as X-Tend 226.

The present invention also relates to a process for the preparation of a preparation, as described above, characterised in that at least one compound of formula I is mixed with a vehicle which is suitable for topical preparations together with the at least one further self-tanning substance and optionally with assistants and or fillers. Suitable vehicles and assistants or fillers are described in detail in the following part.

The preparations as described before may be synthesized in that at least one compound of formula I is mixed with a vehicle which is suitable for such preparations and optionally with assistants and or fillers. Suitable vehicles and assistants or fillers are described in detail in the following part.

The said constituents of the preparation can be incorporated in the usual manner, with the aid of techniques which are well known to the person skilled in the art.

Preparations suitable for external use, for example can be applied or sprayed onto the skin as cream or milk (O/W, W/O, O/W/O, W/O/W) for face and body, as lotion or emulsion for face and body, in the form of oily- alcoholic, oily-aqueous or aqueous-alcoholic gels or solutions. They can be in the form of solid sticks or formulated as aerosol. They can be in the form of shampoo, shower gel, cleansing milk or serum. The following, for example, may be mentioned as application form of the preparations to be employed: solutions, suspensions, emulsions, PIT emulsions, pastes, ointments, gels, creams, lotions, powders, soaps, surfactantcontaining cleansing preparations, oils, aerosols plasters, compresses, bandages and sprays.

Preferred assistants originate from the group of preservatives, stabilisers, solubilisers, colorants, odour improvers, thickeners, plasticisers, humectants, interface-active agents, emulsifiers, preservatives, antifoaming agents, perfumes, waxes, lanolin, propellants and other ingredients usually used in cosmetics.

Ointments, pastes, creams and gels may comprise the customary vehicles which are suitable for topical application, for example animal and vegetable fats, waxes, paraffins, starch, tragacanth, cellulose derivatives, polyethylene glycols, silicones, bentonites, silica, talc and zinc oxide, or mixtures of these substances.

Powders and sprays may comprise the customary vehicles, for example lactose, talc, silica, aluminium hydroxide, calcium silicate and polyamide powder, or mixtures of these substances. Sprays may additionally comprise the customary readily volatile, liquefied propellants, for example chlorofluorocarbons, propane/butane or dimethyl ether. Compressed air can also advantageously be used.

Solutions and emulsions e.g. face and body emulsions may comprise the customary vehicles, such as solvents, solubilisers and emulsifiers, for example water, ethanol, isopropanol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, propylene glycol, 1 ,3-butyl glycol, oils, in particular cottonseed oil, peanut oil, wheatgerm oil, olive oil, castor oil and sesame oil, XTend 226, glycerol fatty acid esters, polyethylene glycols and fatty acid esters of sorbitan, or mixtures of these substances. Suspensions may comprise the customary vehicles, such as liquid diluents, for example water, ethanol or propylene glycol, suspension media, for example ethoxylated isostearyl alcohols, polyoxyethylene sorbitol esters and polyoxyethylene sorbitan esters, microcrystalline cellulose, aluminium metahydroxide, bentonite, agar-agar and tragacanth, or mixtures of these substances.

Soaps may comprise the customary vehicles, such as alkali metal salts of fatty acids, salts of fatty acid monoesters, fatty acid protein hydrolysates, isothionates, lanolin, fatty alcohol, vegetable oils, plant extracts, glycerol, sugars, or mixtures of these substances.

Surfactant-containing cleansing products may comprise the customary vehicles, such as salts of fatty alcohol sulfates, fatty alcohol ether sulfates, sulfosuccinic acid monoesters, fatty acid protein hydrolysates, isothionates, imidazolinium derivatives, methyl taurates, sarcosinates, fatty acid amide ether sulfates, alkylamidobetaines, fatty alcohols, fatty acid glycerides, fatty acid diethanolamides, vegetable and synthetic oils, lanolin derivatives, ethoxylated glycerol fatty acid esters, or mixtures of these substances.

Face and body oils may comprise the customary vehicles, such as synthetic oils, such as fatty acid esters, fatty alcohols, silicone oils, natural oils, such as vegetable oils and oily plant extracts, paraffin oils, lanolin oils, or mixtures of these substances.

Further typical cosmetic application forms are also lipsticks, lip-care sticks, powder make-up, emulsion make-up and wax make-up, and sunscreen, pre-sun and after-sun preparations.

The preferred preparation forms also include, in particular, emulsions for face and body. Emulsions are advantageous and comprise, for example, the said fats, oils, waxes and other fatty substances, as well as water and an emulsifier, as usually used for a preparation of this type. Emulsifiers that can be used are, for example, known W/O and O/W emulsifiers. It is advantageous to use further conventional co-emulsifiers in preferred O/W emulsions.

The lipid phase may advantageously be selected from the following group of substances:

- mineral oils, mineral waxes

- oils, such as triglycerides of capric or caprylic acid, furthermore natural oils, such as, for example, castor oil;

- fats, waxes and other natural and synthetic fatty substances, preferably esters of fatty acids with alcohols having a low carbon number, for example with isopropanol, propylene glycol or glycerol, or esters of fatty alcohols with alkanoic acids having a low carbon number or with fatty acids;

- silicone oils, such as dimethylpolysiloxanes, diethylpolysiloxanes, diphenylpolysiloxanes and mixed forms thereof.

For the purposes of the present invention, the oil phase of the emulsions, oleogels or hydrodispersions or lipodispersions is advantageously selected from the group of esters of saturated and/or unsaturated, branched and/or unbranched alkanecarboxylic acids having a chain length of 3 to 30 C atoms and saturated and/or unsaturated, branched and/or unbranched alcohols having a chain length of 3 to 30 C atoms, or from the group of esters of aromatic carboxylic acid and saturated and/or unsaturated, branched and/or unbranched alcohols having a chain length of 3 to 30 C atoms.

The oil phase may furthermore advantageously be selected from the group branched and unbranched hydrocarbons and hydrocarbon waxes, silicone oils, dialkyl ethers, the group of saturated or unsaturated, branched or unbranched alcohols, and fatty acid triglycerides, specifically the triglycerol esters of saturated and/or unsaturated, branched and/or unbranched alkanecarboxylic acids having a chain length of 8 to 24, in particular 12-18 C atoms. The fatty acid triglycerides may, for example, advantageously be selected from the group of synthetic, semi-synthetic and natural oils, for example olive oil, sunflower oil, soya oil, peanut oil, rapeseed oil, almond oil, palm oil, coconut oil, palm kernel oil and the like.

Preferred oils and/or lipids for said topical preparations include: paraffin, isoparaffin, dicaprylyl ether, PPG-15, stearyl ether, beeswax, candelilla wax, carnauba wax, ethylhexyl stearate, caprylic/capric triglycerides, cetyl lactate, stearyl stearate, isononyl isononanoate, octyldodecanol, hexyldecanol, squalene, natural triglycerides such as cherry kernel oil (Prunes Cerasus), Persea Gratissima oil, Carthamus Tinctorius seed oil, Macadamia Ternifolia seed oil, cocoa butter (Theobroma Cacao), Butyrospermum Parkii butter and mixtures thereof.

The aqueous phase of the preparations to be employed optionally advantageously comprises alcohols, diols or polyols having a low carbon number, and ethers thereof, preferably ethanol, isopropanol, propylene glycol, glycerol, ethylene glycol, ethylene glycol monoethyl or monobutyl ether, propylene glycol monomethyl, monoethyl or monobutyl ether, diethylene glycol monomethyl or monoethyl ether and analogous products, furthermore alcohols having a low carbon number, for example ethanol, isopropanol, 1 ,2- propanediol, glycerol, and, in particular, one or more thickeners, which may advantageously be selected from the group silicon dioxide, aluminium silicates, polysaccharides and derivatives thereof, for example hyaluronic acid, xanthan gum, hydroxypropylmethylcellulose, particularly advantageously from the group of the polyacrylates, preferably a polyacrylate from the group of the so-called Carbopols, for example Carbopol grades 980, 981 , 1382, 2984, 5984, in each case individually or in combination. In particular, mixtures of the above-mentioned solvents are used. In the case of alcoholic solvents, water may be a further constituent.

In a preferred embodiment, the preparations to be employed comprise hydrophilic surfactants. The hydrophilic surfactants are preferably selected from the group of the alkylglucosides, acyl lactylates, betaines and coconut amphoacetates.

The dispersant or solubiliser used can be an oil, wax or other fatty bodies, a lower monoalcohol or a lower polyol or mixtures thereof. Particularly preferred monoalcohols or polyols include ethanol, i-propanol, propylene glycol, glycerol and sorbitol.

A preferred embodiment of the invention is an emulsion which is in the form of a protective cream or milk and comprises, for example, fatty alcohols, fatty acids, fatty acid esters, in particular triglycerides of fatty acids, lanolin, natural and synthetic oils or waxes and emulsifiers in the presence of water.

Further preferred embodiments are oily lotions based on natural or synthetic oils and waxes, lanolin, fatty acid esters, in particular triglycerides of fatty acids, or oily-alcoholic lotions based on a lower alcohol, such as ethanol, or a glycerol, such as propylene glycol, and/or a polyol, such as glycerol, and oils, waxes and fatty acid esters, such as triglycerides of fatty acids.

The preparation may also be in the form of an alcoholic gel which comprises one or more lower alcohols or polyols, such as ethanol, propylene glycol or glycerol, and a thickener, such as siliceous earth. The oily- alcoholic gels also comprise natural or synthetic oil or wax.

The solid sticks consist of natural or synthetic waxes and oils, fatty alcohols, fatty acids, fatty acid esters, lanolin and other fatty substances. If a preparation is formulated as an aerosol, use is generally made of the customary propellants, such as alkanes, fluoroalkanes and chlorofluoroalkanes, preferably alkanes.

Preferred absorbing and/or texturizing agents for said preparations include modified maize starch, silica, talc, zinc stearate, magnesium sulfate, zinc oxide, calcium and aluminium borosilicate, starches and derivatives, polyurethanes, and mixtures thereof.

The invention further relates to a non-therapeutically process or cosmetic treatment for tanning of the skin preferably for face and body, comprising providing a cosmetic composition or medical device containing at least one compound of formula I as described before or preferably described before and applying said cosmetic composition or medical device on skin.

The invention furthermore relates to a non-therapeutically method for tanning the skin naturally, comprising providing a cosmetic composition or medical device containing at least one compound of formula I as described before or preferably described before and applying said cosmetic composition or medical device on skin. Preferably, said method for naturally tanning the skin is performed without irradiation.

The application is carried out using standard techniques, for example by the application of shampoo, shower gel, cream, cleansing milk, paste, gel, lotion, serum to the skin to be treated, or the dissolution of predertermined amount of the preparation comprising a compound of formula I as described before.

In a further aspect, the invention relates to a method for the treatment of the skin of a mammal, preferably a human, comprising a step of applying a medical device comprising a compound of formula I as described above or preferably described before, preferably in form of a topical preparation or as part of a kit of parts or as part of a container, to the skin thus enabling a tanning effect as described before. The application is carried out using standard techniques as explained before.

According to a further aspect, the invention relates to a cosmetic, dermatological product or medical device comprising a) a container delimiting a least one compartment closed by a respective closure element and b) a cosmetic, or dermatological preparation comprising at least one compound of formula I as described before, arranged within said compartment.

The container may have any appropriate form. It may in particular be in the form of a bottle, a tube, a capsule, a can, a jar, a box or a bag.

The closure element may be in the form of a removable stopper, lid, ribbon, or tearing sheet. It may also be in the form of a dispensing element, in particular a pump, a valve or a cap with a spray nozzle. The closure element may be coupled to the container in any way known in the art, such as by a screw, bayonet, snap coupling, by welding, gluing or by magnetic attraction. The material of the container is not limited in any way but shall have no influence on the stability of the contained preparation able to be topically applied. Suitable materials are plastic materials, such as polypropylene or polyethylene, glass, metal or metal alloy.

It should be pointed out that variations of the embodiments described in the present invention are covered by the scope of this invention. Any feature disclosed in the present invention may, unless this is explicitly ruled out, be exchanged for alternative features which serve the same purpose or an equivalent or similar purpose. Thus, any feature disclosed in the present invention, unless stated otherwise, should be considered as an example of a generic series or as an equivalent or similar feature. All features of the present invention may be combined with one another in any manner, unless particular features and/or steps are mutually exclusive. This is especially true of preferred features of the present invention.

Equally, features of non-essential combinations may be used separately (and not in combination).

The technical teaching disclosed with the present invention may be abstracted and combined with other examples.

Examples:

Example 1 : Synthesis of Dimethylhexadecanamide (la)

10.72g of palmitic acid chloride (39mmol) is weighed out into a 100mL round-bottomed flask together with 10mL n-heptane. Subsequently, a solution of 7.65g of dimethylamine (169.68mmol) in n-heptane is added at 5°C. The reaction solution is stirred for 2 hours. The reaction mixture is then extracted with water, the organic phase filtered and the filtrate is cooled to crystallize Dimethylhexadecanamide.

Weighing: 9.29g yellow solid (83.2% of the theoretical yield).

Example 2: reconstructed human epidermis experiment

The pro-pigmenting effect (natural tanning) of the compound of formula la is evaluated on melanin synthesis in a 3D reconstituted human epidermis model.

Assay Setup:

Reconstructed human epidermis from a Caucasian donor was used. The tissues were cultivated at the air-liquid interface and treated daily for 14 days in a suitable culture medium within a humid atmosphere at 37°C with 5% CO ₂ .

The test compound of formula la was applied at 23pM (DMSO/water) in 3 replicates for each condition. DMSO 0.01 % was used as reference control condition. IBMX at 100pM was used as reference pro-tanning substance to validate the experiment. Untreated reconstructed skin is used as negative control. Palmitic acid was used to show advantageous efficacy compared to the prior art. After 14 days the epidermis pigmentation was analyzed through pictures.

IBMX denotes the compound 3-isobutyl-1 -methylxanthine.

Compound of formula la, tested at 23pM stimulated the melanin synthesis. It was observed that compound of formula la was darkening the skin compared to DMSO 0.1 %. Palmitic acid as known promotor of the melanogenesis did not visually stimulate the melanin synthesis at 23pM in this model.

In a second reconstructed human epidermis model using the same assay setup as explained before, a dose-dependency of compound of formula la was shown in relation to the melanin content measured with a mexameter. The following concentrations were used: 23pM, 13 pM, 4.5 pM, 1.5 pM, 0.5pM.

It was shown that the compound of formula la had a melanogenesis stimulating effect in a dose-dependency manner. The most promising results of the compound of formula la were observed at 4.5pM. This concentration led to an increase of the melanin index by 14% compared to DMSO and 34% compared to untreated reconstructed skin.

Example 3: Compound of formula la on human skin living explants ex vivo The pro-pigmenting effect of the compound of formula la was evaluated on melanin synthesis stimulation on human skin living explant. The activity has been assessed with:

- a control of the cellular viability after Masson’s trichrome staining

- a staining of melanin. Compound of formula la was tested at 3 concentrations (0.1 %, 1 % and 5%).

Explant preparation

27 human skin explants of an average diameter of 12mm were prepared on an abdoplasty coming from a 33-year-old Caucasian woman (reference: P2203-AB33 - phototype Il-Ill). The explants were kept in survival in BEM culture medium within a humid atmosphere at 37°C with 5% CO2.

Explant distribution

The explants were distributed into 9 batches as follows:

Product application

On day 0 (DO), D1 , D4, D6 and D7, before each products application, for all the batches, 30 pl of absolute ethanol were applied on paper discs. The discs were applied on the surface of the skin explants and stay in contact with the skin for 2 minutes.

On day 0 (DO), D1 , D4, D6 and D7, just after the disc application, the excipient E and the tested products P1 , P2 and P3 were applied topically using a small spatula on the basis of 2 pl per explant (2mg/cm ² ).

The reference R was incorporated in the culture medium on day 0 (DO).

The treatment with the reference R was renewed on D1 , D4, D6 and D7 (1 ml/well). Control explants did not receive any treatment except the renewal of the culture medium. The culture medium was half renewed (1 mL/well) on D1 , D4, D6 and D7.

Sampling

On day 0 (DO), the 3 explants from the batch TO were collected and cut into 2 parts: half was fixed in formol buffered solution and one half was frozen at -80°C.

On D9, the 3 explants of each batch were collected and processed in the same way than on day 0.

Histological processing

After fixation for 24 hours in buffered formalin solution, the samples were dehydrated and impregnated in paraffin using a Leica PEARL dehydration automat.

The samples were then paraffin-embedded using a Leica EG 1160 embedding station.

5-pm-thick sections of paraffin-embedded formol fixed sections were realized using a Leica RM 2125 Minot-type microtome, and the sections were then mounted on Superfrost® Plus glass slides.

Microscopical observations were realized using a Leica DMLB or a BX43 Olympus microscope. Pictures were digitized with an Olympus DP72 camera and the Cell ^A D data storing software. The images analyses were performed on all the images of each batch.

Melanin visualization

Melanin was visualized after silver impregnation according to Masson’s Fontana staining method.

The staining was assessed by microscopical observation and guantified by image analysis.

Stained surfaces comparisons The stained surface percentage (surface %) for each treatment is compared to the untreated condition P (compound of formula la) vs. T (untreated control).

Results

Compound of formula la, tested at 0.1 %, 1 % and 5% induced no modification of the cell viability.

Compound of formula la induced a significant increase of melanin content compared to the untreated control (TJ9) at 5% (+34%*).

The activity is similar to the one observed with reference IBMX at 50pM (R3).

Compound of formula la induced a significant increase of melanin content compared to the excipient batch (parraffin oil, EJ9) at 5% (+38%**).

The activity is similar to the one observed with reference IBMX at 50pM (R3).

* = significant with p<0.05 (95%) ** = significant with p<0.01 (99%)

Formulation examples

Example 1 : O/W formulation

Preparation process:

Firstly, phase A is warmed to 75°C and phase B to 80°C. Phase B is then slowly added to phase A with stirring and stirred until a homogeneous mixture forms. Add phase C below 40°C.

Example 2: O/W formulation Preparation process:

Firstly, phases A and B are warmed to 80°C. Phase B is then slowly added to phase A with stirring and homogenised. The mixture is then cooled, and phase C is added at 40°C. Then pase D is added below 40°C.

Example 3: W/O formulation

Preparation process:

Firstly, phase B is dissolved and then added to phase A. The pH is adjusted to the value pH = 6.0 using sodium hydroxide solution or citric acid. The mixture is stirred and homogenised. Then phase C is added below 40°C.

Example 4: O/W anti-ageing cream with UV A/B protection

Preparation process:

Firstly, phases A and B are mixed separately and warmed to 80°C. Phase B is then slowly added to phase A with stirring. The mixture is homogenised and cooled to room temperature. Then phase C is added.

Example 5: O/W formulation containing a tanning agent

Preparation process:

Firstly, phases A and B are mixed separately and warmed to 80°C. Phase B is then slowly added to phase A with stirring. The mixture is homogenised and cooled to room temperature. Then phase C is added.

Example 6: O/W emulsion

Preparation process:

Keltrol and Natrosol are dispersed in water. Phase A is warmed at 75°C and Phase B at 80°C. Phase B is then added to phase A without stirring. The mixture is homogenised and cooled to room temperature.