Drug – bio-affecting and body treating compositions – Topical sun or radiation screening – or tanning preparations
Reexamination Certificate
2001-02-20
2002-12-10
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Topical sun or radiation screening, or tanning preparations
C424S401000
Reexamination Certificate
active
06491901
ABSTRACT:
STABILIZATION OF OXIDATION- AND/OR UV-SENSITIVE ACTIVE INGREDIENTS
The present invention relates to combinations for the stabilization of oxidation-sensitive and/or UV-sensitive active ingredients, and to cosmetic and dermatological formulations containing oxidation-sensitive and/or UV-sensitive active ingredients stabilized in this way. In particular, it relates to cosmetic and dermatological light protection formulations and to formulations containing UV-sensitive light protection filter substances which are stabilized by the use of these combinations.
The harmful effect of the ultraviolet part of solar radiation on the skin is generally known. Depending on their respective wavelength, the rays have different effects on the skin organ: So-called UV-C radiation with a wavelength of less than 290 nm is absorbed by the ozone layer in the earth's atmosphere and is therefore of no physiological importance. By contrast, rays in the range between 290 nm and 320 nm, the so-called UV-B region, cause erythema, simple sunburn or even burns of varying severity. A maximum erythema activity of sunlight is given as the narrower region around 308 nm.
To protect against UV-B radiation, numerous compounds are known; these are mostly derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone, and also 2-phenylbenzimidazole.
An advantageous light protection filter substance is, for example, 2-ethylhexyl p-methoxycinnamate (4-methoxycinnamic 2′-ethylhexyl ester), which is available from Givaudan under the name Parsol® MCX and which is characterized by the following structure:
The main disadvantage of 2-ethylhexyl p-methoxycinnamate is a certain instability toward UV radiation, meaning that preparations with a content of this substance should automatically also contain certain UV stabilizers.
For a long time it has incorrectly been assumed that the long-wave UV-A radiation with a wavelength between 320 nm and 400 nm has only a negligible biological action and that, accordingly, the UV-B rays are responsible for most photodamage to the human skin. However, in the mean time numerous studies have shown that UV-A radiation is much more harmful than UV-B radiation with regard to the triggering of photodynamic, specifically phototoxic, reactions and chronic changes in the skin. The harmful effect of UV-B radiation can also be further intensified by UV-A radiation.
Thus, it has, inter alia, been proven that even UV-A radiation under quite normal every day conditions is sufficient to damage within a short period the collagen and elastin fibers which are of essential importance for the structure and strength of the skin. This results in chronic light-induced changes in the skin—the skin “ages” prematurely. The clinical manifestation of light-aged skin includes, for example, wrinkles and lines, and also an irregular, furrowed relief. In addition, the areas affected by light-induced skin aging may have irregular pigmentation. The formation of brown spots, keratoses and even carcinomas or malignant melanomas is also possible. Skin which has been aged prematurely as a result of every day UV stress is further characterized by a lower activity of the Langerhans' cells and slight, chronic inflammation.
Approximately 90% of the ultraviolet radiation which reaches the earth consists of UV-A rays. While the UV-B radiation varies widely depending on numerous factors (e.g. time of year and day or degree of latitude), the UV-A radiation remains relatively constant day after day irrespective of the time of year and day or geographical factors. At the same time, the majority of the UV-A radiation penetrates into the living epidermis, while about 70% of the UV-B rays are retained by the horny layer.
Preventive protection against UV-A rays, for example by applying light protection filter substances in the form of a cosmetic or dermatological formulation to the skin, is therefore of fundamental importance.
Known and advantageous light protection filter substances which, in particular, also offer protection against UV-A radiation are dibenzoylmethane derivatives, in particular 4-(tert-butyl)-4′-methoxydibenzoylmethane, which is characterized by the structure
and is sold by Givaudan under the name Parsol® 1789.
The main disadvantage of this substance too is a certain instability towards UV radiation. The photochemical decomposition of all dibenzoylmethane derivatives which absorb in the UV rays follows a Norrish type I acyl cleavage. This is illustrated in the reaction scheme below using the example of 4-(tert-butyl)-4′-methoxydibenzoylmethane:
In principle, what has already been said applies for mixtures of these cinnamates and dibenzoylmethanes already mentioned. In contrast to some light protection filter combinations which are characterized by increased stabillity toward the respective individual substances, for mixtures of cinnamates and dibenzoylmethanes, an even stronger destabilization toward UV-light is generally observed than for the respective individual substances. This is the case in particular for mixtures of 2-ethylhexyl p-methoxycinnamate and 4-(tert-butyl)-4′-methoxydibenzoylmethane. With some certainty, these two components react under the effect of UV to give inactive products and are therefore no longer available for the UV absorption.
Possible solutions to this problem which have been proposed at different times are to protect the active ingredients from degradation by the addition of one or more stabilizers, e.g. antioxidants, or to use them in the form of more stable derivatives.
2-Ethylhexyl 2-cyano-3,3-diphenylacrylate (INCI: Octocrylene)—a UV filter substance liquid at room temperature—is also said to have a stabilizing effect on 4-(tert-butyl)-4′-methoxydibenzoylmethane. 2-Ethylhexyl 2-cyano-3,3-diphenylacrylate is characterized by the following structure:
and is available, for example, from BASF under the name Uvinul® N 539.
A similar effect has also already been described for diethylhexyl naphthalate, which is given by the structural formula
However, in all cases the effect achieved falls a long way short of that which is desired.
The prior art was unable to give any indications which would have permitted inferences to the preparations according to the invention.
The object of the present invention was to overcome the disadvantages of the prior art and to increase the stability of oxidation-sensitive and/or UV-sensitive light protection filter substances, and to provide stable preparations containing oxidation-sensitive and/or UV-sensitive light protection filter substances, the effectiveness of which is retained over a long period.
It was surprising and could in no way have been foreseen by the person skilled in the art that
synergistic combinations of
a) 2-ethylhexyl 2-cyano-3,3-diphenylacrylate with
b) one or more dialkyl naphthalates
would overcome the disadvantages of the prior art.
The combinations according to the invention surprisingly have a synergistic action, i.e. have a superadditive action with regard to the individual components. By combining the individual substances according to the invention, the oxidation- and/or UV-sensitive light protection filter substance(s), in particular in cosmetic or dermatological formulations, is/are protected in an excellent manner against UV-radiation-induced decomposition. This applies in particular for dibenzoylmethane derivatives.
Of the dibenzoylmethane derivatives, 5-isopropyidibenzoylmethane (CAS No. 63250-25-9)
and 4-(tert-butyl)-4′-methoxydibenzoylmethane (CAS No. 70356-09-1)
are advantageously used.
By following the teaching according to the invention, light protection preparations are obtainable which have higher stability, in particular stability toward decomposition under the effect of light, very particularly UV light, than the prior art would have suggested. In particular, the stability of 4-(tert-butyl)-4′-methoxydibenzoylmethane toward the decomposition and UV light is drastically increased. It was very particularly surpr
Gers-Barlag Heinrich
Grundt Wiebke
Wendel Volker
Beiersdorf AG
Dees Jose′ G.
George Konata M.
Norris & McLaughlin & Marcus
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