Sun protecting cosmetic compositions comprising derivatives of dibenzoylmethane and of benzophenone

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DESCRIPTION

Sunscreen cosmetic compositions comprising derivatives of dibenzoylmethane and benzophenone.

The present invention relates to cosmetic compositions, hereinafter referred to as sunscreen formulations, containing photostable mixtures of bronzers. useful for protecting the skin and / or hair from ultraviolet radiation,

Background of the invention

It is well known that solar radiation between 280 and 400 nm is harmful to human skin; in particular, those radiations with a wavelength between 280 and 320 nm, the so-called UV-B radiations, cause erythema and skin burns, the severity of which depends on the duration of exposure on the skin type. It has also been proven that radiation between 320 and 400 nm, called UV-A and responsible for tanning the skin, can cause alterations in the skin and damage that cannot be ignored, especially in cases of sensitive skin or skin. in case of continuous exposure to radiation.

It has been shown that UV-A radiation other than that which causes damage to elastin and collagen, the consequence of which is the aging of the skin, can also be the cause of numerous phototoxic and photoallergic reactions. Furthermore, the damaging action of UV-B can be enhanced by the presence of UV-A (Willis et al .: Journal of Investigative Dermatology vol. 59, 416, 1972).

Some compounds derived from cinnamic acid, 4-aminobenzoic acid and benzylidene camphor are well known and are also used in the preparation of sunscreen formulations for the protection of UV-B radiation. These compounds, in addition to being less or sufficiently effective, do not show satisfactory photostability.

2-Ethylhexyl-cyano-e, e'-diphenylacrylate and 2-hydroxy-4-methoxybenzophenone show good photostability, however, their absorption is very low, and therefore their effectiveness is negligible.

To date, on the contrary, no sufficiently effective UV-A protection products have been available, even though different compounds have been proposed in the patent literature; but its behavior has not been satisfactory in practical uses.

Currently, UV-A (absorbent) suntan lotions used in practice are limited to derivatives of benzophenone and some derivatives of dibenzoylmethane.

The benzophenone derivatives have very good photostability, and can act both as filters for UV-B with absorption at approximately 290 nm, and as UV-A filters with absorption at approximately 325 nm.

However, the adsorptions at the two wavelengths are relatively weak, especially in the UV-A region at 325 nm, therefore, these compounds are not able to provide sufficient protection.

Among the derivatives of dibenzoyl methane, 4-methoxy-4'-tert-butyldibenzoyl methane and 4-isopropyldibenzoyl methane are commercially known. These compounds show good absorption at 360 nm and a weak solubility in solvents commonly used in cosmetics.

However, their use is difficult because they are not sufficiently photostable (Int. J. Cosm. Science 10, 53, 1988). Accordingly, the formulations containing these compounds cannot guarantee sufficient protection against UV-A, since the protective filter degrades rapidly due to the radiation itself.

In order to avoid this rapid degradation and provide these UV-A filters with a little photostability, it is proposed in patents GB 2,198,944, WO 91/11989 and WO 94/04131 particular combinations between UV-B filters belonging to the benzylidene camphor and diphenylcyanoacrylate classes, and derivatives of dibenzoylmethane have been proposed.

The results, however, still cannot be considered sufficient because even with large amounts of the above UV-B filters it is not possible to provide satisfactory photostability to the dibenzoylmethane derivatives.

For the photoprotection of the skin, a large number of sun protection formulations have been proposed, and in this case, there is an extensive patent literature.

Therefore, the real problem to be solved is the stabilization of bronzers in cosmetic formulations, in particular those derived from dibenzoylmethane. Furthermore, another real problem is the cosmetic treatment of the skin when it is exposed to sunlight to allow a pleasant tan without incurring sunburn.

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Summary of the invention

It has been surprisingly found that photostable sunscreen formulations with protective activity against UV radiation comprised between 290 and 380 nm, that is, UV-B and UV-A, are obtained by combinations comprising, with respect to the total weight of the composition, as the only UV absorber

a) between 1 and 10% of one or more compounds of formula (I)

<img file="ES2227646T3_D0001.tif" />

where Q is hydrogen, a linear or branched Ci -C alkoxy group₄ and G is a Ci -C alkyl₈ linear or branched,

b) between 0.5 and 10% of one or more compounds of formula (II)

<img file="ES2227646T3_D0002.tif" />

in which R₁ is a C alkyl₁-C₈ linear or branched, R₂ is hydrogen or a SO group₃M, where M is hydrogen, an alkali metal, or a mono- or polyalkyl substituted ammonium group;

provided that the weight ratio between the compounds of formula (II) and those of formula (I) is at least 0.5.

Therefore, an object of the present invention is a cosmetic composition comprising components a) and b) as described above in premix with a cosmetic substrate.

Another object of the present invention is a procedure for the cosmetic treatment of human skin when exposed to sunlight, the aforementioned procedure consists of applying a suitable amount of a cosmetic composition such as that described above.

Another additional object of the present invention is a process for stabilizing a cosmetic composition against UV radiation that comprises adding to the cosmetic substrate a light stabilizing mixture such as that described below.

Detailed description of the invention

Preferred compounds of formula (I) are those in which Q is methoxy and G is tert-butyl, or Q is hydrogen and G is isopropyl.

The preferred compounds of formula (II) are 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, both marketed by 3V SIGMA under the trade names Uvasorb® MET and Uvasorb® S 5.

By the combinations according to the present invention, particularly photostable sunscreen formulations with protective action for both UV-A and UV-B are obtained. Highlighting the fact that the present inventors do not wish to be bound by theoretical interpretations, it can be assumed that the compounds of formula (II) stabilize the UV-A filters of formula (I), which are not photostable per se.

The weight ratio between one or more compounds of formula (II) and one or more compounds of formula (I) must be at least 0.5.

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Examples of Ci-C alkyl₈ linear or branched are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl and their isomers, in particular isopropyl, tert-butyl, 2-ethylhexyl.

Examples of C alkoxy₁-C₄ linear or branched are methoxy, ethoxy, propoxy, butoxy, and their isomers.

Examples of the alkali metal are sodium, lithium, and potassium.

The dibenzoylmethane derivatives of formula (I) are described in US Patent Nos. 4,387,089 and 4,489,057. Commercial compounds are Parsol® 1789, (4-methoxy-4'-tert-butyldibenzoylmethane) from Givaudan and Eusolex^® 8020, (4-isopropyldibenzoylmethane) from Merck.

Very often, these sunscreen formulations are in the form of oil-in-water emulsions and contain, in varying concentrations, one or more lipophilic and / or hydrophilic organic bronzers, capable of absorbing more or less the UV radiation of sunlight.

The type of bronzers and their appropriate quantity are selected depending on the desired sun protection factor (SPF). The SPF is a protection index, and is expressed as the ratio between the irradiation time necessary to reach the erythematogenic threshold in the presence of the UV filter and the irradiation time necessary to reach the erythematogenic threshold in the absence of the UV filter. The SPF can be determined according to the procedure described by B. Diffey and J. Robson in J. Soc. Cosmet. Chem. 40, 127-133 (1989).

It is thus possible to prepare sun protection formulations with a high SPF, suitable to guarantee continuous protection of the skin also during prolonged exposures to sunlight, thus avoiding frequent and repeated applications necessary for effective protection.

According to the present invention, photostable cosmetic compositions suitable for protecting the skin from UV radiation with wavelengths between 290 and 380 nm comprise a cosmetic substrate containing, with respect to the weight of the composition, between 1 and 10% of one or more compounds of formula (I), between 0.5 and 10% of one or more compounds of formula (II) and between 1 and 10% of one or more compounds of formula (III), provided that the weight ratio between the compounds of formula (II) and those of formula (I) is at least 0.5.

The sun protection formulations according to the present invention, once applied to the epidermis, exert a protective action against the harmful effects of UV radiation, thus avoiding the formation of erythema or sunburn or premature aging of the skin. skin.

The compositions of the invention may also be useful for treating, and then protecting, hair or make-up in decorative cosmetics.

According to the present invention the cosmetic formulations can be solutions, lotions, emulsions of the water-in-oil or oil-in-water type; or they can also be in the form of gels, lipsticks and aerosols.

Compositions according to the present invention are prepared by formulating commonly used ingredients, such as, for example, oils, fats, emulsifiers, moisturizing agents, humectants, emollients, preservatives, surfactants, thickening agents, perfumes, pigments, dyes and others such as alcohols. , polyols, electrolytes, derivatives of silicone.

The most commonly used solvents are triglycerides of caprinic or caprylic acids, castor oil, esters of fatty acids with isopropanol, propylene glycol, glycerin, propylene glycol monomethyl- or monoethyl- or monobutyl ether.

The sunscreen formulations according to the present invention may also contain inorganic pigments commonly used in cosmetics, such as, for example, titanium dioxide, zinc oxide, silica or aluminum oxide.

The present invention also comprises the protection of the cosmetic compositions themselves from UV radiation by adding between 1 and 5% by weight relative to the composition of a compound of formula (I) and between 0.5 and 5% of a compound of formula (II). In this case, these are compositions whose components may suffer unwanted degradation or coloration induced by light, such as, for example, shampoos and hair sprays, hair styling lotions, hair coloring compositions, makeup formulations such as nail lacquers, makeup bases, lipsticks. The preferred cosmetic formulations are those for the protection of skin from solar radiation. Therefore, another object of the present invention is a photostabilizing mixture consisting of:

a) at least one compound of formula (I)

ES 2 227 646 T3

<img file="ES2227646T3_D0003.tif" />

where Q is hydrogen, a Ci-C alkoxy group₄ linear or branched and G is a Ci-C alkyl₈ linear or branched,

b) at least one compound of formula (II)

<img file="ES2227646T3_D0004.tif" />

in which R₁ is a C alkyl₁-C₈ linear or branched, R₂ is hydrogen or a SO group₃M, where M is hydrogen, an alkali metal or mono- or polyalkyl substituted ammonium group;

provided that the weight ratio between the compounds of formula (II) and those of formula (I) is at least 0.5.

This mixture can be used for the preparation of a medicine useful for the protection of human skin against sunlight.

The following examples further illustrate the invention.

Example A

Photostability

A solution of the tanning lotion or its combinations was prepared in a solvent mixture consisting of 70% ethyl alcohol and 30% isopropyl myristate.

Two 20 microliter samples were taken from each solution by means of a microsyringe, and placed on 2 X 5 cm microscope slides.

The samples thus prepared were allowed to air at room temperature for 30 minutes to allow evaporation of the ethanol. Then, one of the two samples was exposed to UV irradiation for 2 and 4 hours in a Suntest Heraeus CPS + equipment, equipped with a xenon lamp and a filter system to be able to eliminate UV radiation below 290 nm, as well as IR radiation.

After exposure, the slides were washed with 50 or 100 ml of ethanol, in order to quantitatively solubilize the deposited material.

In the ethanolic solutions thus obtained, without further dilution, the absorbance was measured in quartz cuvettes with an optical path of 1 cm using a Perkin-Elmer Lambda 2 spectrophotometer.

The photostability F was calculated as the percentage relationship between the absorbance at the wavelength of maximum absorption of the exposed sample and that of the unexposed sample.

For the combinations, the photostability was calculated only for the filter of formula (I).

The results are shown in the following table.

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TABLE

<td>Bronzers</td><td>g / 100 ml solvent</td><td>F 2 hours</td><td>F 4 hours</td>

<td>TO</td><td> 5</td><td> 23</td><td> 14</td>

<td>B</td><td> 5</td><td> 94</td><td> 86</td>

<td>C</td><td> 5</td><td> 75</td><td> 68</td>

<td>D</td><td> 5</td><td> 91</td><td> 84</td>

<td>A + B</td><td> 5 + 5</td><td> 89</td><td> 78</td>

<td>A + C</td><td> 5 + 5</td><td> 78</td><td> 65</td>

<td>A + D</td><td> 5 + 5</td><td> 81</td><td> 69</td>

<td>A + B</td><td> 4 + 2</td><td> 91</td><td> 85</td>

<td>A + C</td><td> 4 + 2</td><td> 81</td><td> 63</td>

<td>A + D</td><td> 4 + 2</td><td> 87</td><td> 72</td>

A = 4-methoxy-4'-tert-butyldibenzoyl methane

B = 2-hydroxy-4-methoxybenzophenone

C = 4-methylbenzylidene camphor

D = 2-ethylhexyl-cyano-p, P'-diphenylacrylate

Example 1

Solar milk

<td>Fatty acid triglyceride</td><td>20.0 g</td>

<td>Cetyl alcohol</td><td>2.0 g</td>

<td>Cetylostearyl alcohol</td><td>2.0 g</td>

<td>Lanolin</td><td>4.0 g</td>

<td>Silicone oil</td><td>0.4 g</td>

<td>4-methoxy-4'-tert-butyld¡benzo¡l methane</td><td>3.0 g</td>

<td>2-hydroxy-4-methoxybenzophenone</td><td>2.5 g</td>

<td>Abiol (3V SIGMA preservative)</td><td>0.2 g</td>

<td>Synthalen M (3V SIGMA thickening agent)</td><td>0.1 g</td>

<td>Triethanolamine</td><td>0.15g</td>

<td>Fragrance</td><td>0.3 g</td>

<td>Water</td><td>up to 100.0 g</td>

The fatty phase was heated to 80 ° C - 90 ° C, the tanning was added, then the mixture was added to the water containing the water soluble compounds, heated to 80 ° C - 90 ° C. Hot stirring was continued for 15-20 minutes. The mixture was slowly cooled and perfume was added.