CA1069054A

CA1069054A - 4-pyridoxinate derivatives as light screening agents

Info

Publication number: CA1069054A
Application number: CA224,730A
Authority: CA
Inventors: Richard Barner; Walter Boguth
Original assignee: F Hoffmann La Roche AG
Current assignee: F Hoffmann La Roche AG
Priority date: 1974-04-18
Filing date: 1975-04-16
Publication date: 1980-01-01
Also published as: AR219474A1; FR2267758A1; NL7504573A; JPS59104311A; GB1457495A; IT1059523B; JPS6050785B2; ATA295675A; AU7983275A; JPS6121949B2; NL181905B; ZA752062B; BR7502358A; DK166175A; JPS625884B2; AT351169B; CH602110A5; JPS50140462A; FR2267758B1; DE2514814C2

Abstract

ABSTRACT

A light-screening agent which contains as essential active ingredient one or more compounds of the general formula

Description

~069~:)S4 R~N 6402/6 The present invention relates to light-screenlng agents.
More particularly, the inventlon 18 concerned with ll~ht-~creening agent~, a proce3s for the manufacture thereof and a method or protecting the skin agalnst haxmful rays u~lng said agent~. The inventlon i8 alBo concerned with certain of the essential active ingredients of ~aid agents and with a proces~
for the preparation thereof.

The light-~creening agen~s disclosed herein contain as active ingredient one or more - -compounds of the general formula ~C~ Rl -'30~3,R2 ¦

, whereln when n stands for 1, R
represents hydrogen, alkyl, an alkali metal, amm~nium or ammonlum 3ubstltuted with one or more alkyl ox hydroxyalkyl group~, R2 repr~ent hydroxymethyl or alkoxymethyl and R3 represents hydrogen or Rl and R2 together repre~ent a methylene group and R3 represents hydrogen, me~hyl or ethyl; and when n ~tands for 2, Rl represent~ ~n alkaline earth metal, R2 repre~ents hydroxy~ethyl Hen/18~ ~ 975 - 2 -1~69C95~
or alkoxymethyl and R3 represents hydrogen O
Thus the present invention provides a method for protecting the skin against harmful rays which method comprises applying to the skin a light-screening agent which contains as essential active ingr.edien~ an e~fective amount up to 25 weight percent of one or more compounds chosen from those of the general formula ~C~' v Rl R3O ~ ~2 (I) , wherein Rl represents hydrogen, lower alkyl of 1 to 6 carbon atoms, an alkali metal, ammonium or ammonium substituted with one or more aIkyl or hydroxyalkyl groups, R2 represents hydroxymethyl or alkoxymethyl and R3 represents hydrogen or Rl and R2 together represent a methylene group and R3 represents hydrogen, methyl or ethyl; and acid addition salts thereof, and a compatible cosmetic base.
In another aspect the present invention provides a light-screening agent for protecting the skin against harmful rays, which contains as essential active ingredient from 2 to 6 weight percent of one or more compounds chosen from those of the general formula ~C~ -- R
~3 ~ ~2 C~3 (I) ~ _ 3 _ , A.~
~6g~(~S4 wherein Rl represents hydrogen, lower alkyl o~ 1 to 6 carbon atoms r an alkali metal, ammonium or ammonium substituted with one or more alkyl or hydroxyalkyl groups, R2 represents hydroxy-methyl or alkoxymethyl and R3 represents hydrogen or Rl and R2 together represent a methylene group and R3 represents hydrogen, methyl or ethyl; and acid addition salts thereof, one or more further organic compounds having an absorption maximum between 290 and 340 nm, and a compatible cosmetic base.
The screening action of the compounds of formula I is due to the fact that they shield the living epidermal cells from the erythema-producing ultraviolet rays of the sun (between 290 nm and 340 nm) by specific absorption.
The compounds of formula I, such as 4-pyridoxic acid or 4-pyridoxic acid lactone, are metabolites of pyridoxine (Vitamin B6) or derivatives of these metabolites. The compounds of formula I are accordingly not considexed as exogenous sub-stances in contrast to the UV-absorbing active substances present in customary light-screening agents.
The compounds of formula I accordingly have a very good tolerance on the skin. A further advantage of the light-screening agents provided by this invention lies in their selec-tive absorption, their lack of odour and their good chemical and~ photochemical stability.
Moreover, the compounds of formula I in which R3 represents hydrogen, re-emit a major portion of the absorbed, skin-harming UV light as long-wave fluorescent irradiation (420 nm). This fluorescent irradiation lies in the range of browning light so that in the skin a harmful irradiation is, in fact, converted into an irradiation useful for browning.

- 3(a) -~;~ -~.

... .. .

~L~;)6~0S`~

In this specifica~ion, the term "alkyl" alone or in comblnation as in "alkoxy" or "hydroxyalkyl" means a straight-chain or branched-chain hydrocarbon group containing up to 20 carhon atoms. "Lower alkyl" groups, whlch contain up to 7 carbon atoms, are preferred.

Compounds of formula I in which R2 is hydroxymethyl or alkoxymethyl, R3 is hydrogen and R1 is hydrogen, an alkali me~al, an alkaline earth metal or substituted ammonium are preferred. In this case, sodium and pota~slum are e~pecially preferred alkali metals, calcium and magnesium are especially preferred alkaline earth metals and dlethanolammonium and trlethanolammonium are especially preferred ~ubstituted-ammonlum groups. Particularly preferred compounds are:
sodlum 4-pyrldoxinate, potassium 4-pyridoxinate and triethanolammonium 4-pyridoxinate.

The wavelengths (measured in ethanol) of the absorption maxima of some of the compound~ of foxmula I are given in the following Table.

3 C~6~1~S~

Table , ... . ~ _ _ Compound of formula I max (nm) 4-Pyridoxic acid 316 Sodium 4-pyridoxinate 312 Methyl 4-pyridoxinate 320 n Hexyl 4-pyridoxinate 328 4-Pyridoxic acid lactone hydrochloride 312 4-Pyridoxic acid lactone 3-methyl ether 307 Triethylammonium 4-pyr1doxinate 312 Tri~(hydroxymethyl)aminomethane 4-pyridoxinate 315 5-(0-Cetyl)-4-pyridoxic acid 315 Sodium 5-(0-cetyl)-4-pyrldoxlnate 311 The light-screening agents provided by the present inventlon are manufactured by mixing one or more compounds of formula I and/or one or more acid addition ~alts thereof with a compatible cosmetic base.

As the cosmetic ba~e which ts pre~ent ln the llght-screening agenta provided by thls invention there can be used any customary cosmetlc base which accords wlth the cosmetic requirements and the ~olub~lity of the compounds of formula I
or acld addition salts thereof used. Thus, for example, cream~, milk, salve~, oils, solutlons, spray~, gels and the like can be manu~actured. The intensity of the llght-~creening action 1~ dapendent, however, on the base used and, with the same base, on the concentration of es~e~tial active ingredient. Sultable concentrations should~ however, not exceed 25%. The concentration pre~erably lie~ be~ween 2%
and 6%.

:. :

~ 1~69~5~

A further advantage of the e~sentlal active ing~edients defined earller al80 lies, in particular, in that the solubillty requlrements in the fini~hed agent ~an be substantlally taken into con~ideratlon by the choice of a cer~ain member (e.g. a salt can be chosen for an aqueous agent).

The essential ac~ive ingredients aforesaid can also be combined with other customary light-screening agents. ~y cu~tomary llght-~creening agents there are generally understood organlc compounds whose ab~orptlon maxlmum lle~ between about 290 and 340 nm. Since this fllter property is charac~eristic of many organic compounds, compounds from divers0 classes (of which only a few are named herelnafter) can be incorporated in the llght-screenlng agents of thls invention. Examples of such compounds are:
1) Derlvatives of p-aminobsnzoic acid, ~ncluding esters such as, for example, ethyl, propyl, butyl and l~obutyl p-aminobenzoate, e~hyl p-dimethylaminobenzoate, glyceryl p-aminobenzoate and amyl p~dlme~hylæminobenzoate.

~) Derivatlves of cinnamic acid such as, for example,

2-ethoxyethyl p-methoxycinnamlc acid es~er, ethylhexyl p-methoxycinnamic acld ester, p-methoxyclnnamic acid ester mixtures and cinna~ic acld ester mixtures.

3) Dibenzalhydrazines.

4) ~erivative~ o~ 2-phenylbenzlmldazole ~uch as, for example, 2-phenylbenzimidazole-5-~ulphonic acid.

.
,, .

95D5~

5) Derivatives of salicylic acid such as, for example, salicyllc acid menthyl ester, salicylic acid homomenthyl ester and salicylic acid phenyl ester.

6) Derivatives of benzophenone such as, for example, 4-phenylbenzophenone, 4-phenylbenzophenone-2-carboxyllc acid isooctyl ester and 5-chloro-2-hydroxybenzophenone.

7) Derlvatlve~ of coumarin such as, for example, 7~
hydroxycoumarin, ~-umbelliferoneactic acid and 6,7-dihydroxy-coumarin.

8) Derivatlves of gallic acid such as, for example, digalloyl trioleate.

9) Dehydroacetic acid (3-acetyl-6-methyl 1,2-pyran-2,4-dlone).

10) Derivative~ of quinoline such as, for,example, the sodium salt of 8-ethoxyquinoline-5-sulphonic acid.

11) Derivat$ves of anthranilic acid such as, for example, anthranilic acid menthyl ester.

12) Hydroxyphenylbenztrlazole.

Furthermore, purine'derivative~ ~uch as adenine or guanine or pyrimldlne derivatives such as cytoslne or uracll can also be present ln the light-scr~ening agents of this lnvention.

- .

i1~69Q5~

Yet again, antil~flammatory substances (e.g. pantothenic acid or pantothenic acld e~ter, phenylbutazone, azulene, azulene derivatives or azulene-containing subs~ances such as camomile extract) can also be present in the light-screening agents of this invention.

It will accordingly be appreciated from the foregoing that the inventlon includes within lts scope a method for protecting the skln against harmful rays, whlch method comprises applying to the skln a light-screening agent as herelnbefore defined.

With the exception o 4-pyrldoxic acid, 4-pyridoxlc acid lactone a~d 4-pyridoxlc acid lactone 3 methyl ether, the compounds of formula I are novel.

The specification discloses novel compound.~ of the general formula ~C ~ -R' L C~3 , whereln ~hen n stands for 1, R' represents hydrogen, alkyl, an alkali metal, ammonlum or ammonium substituted with one or more alkyl or hydroxyalkyl groups, R'2 represents hydroxymethyl or alkoxymethyl and R'3 represent3 hydrogen (with the proviso ~ ~;
that R'2 can not r~present hydroxymethyl ? ~
.' ~`,.7 _ ~ _ ' .' ' .'' i~i69~54 when R'l repre~ents hydrogen) or R'l and R'2 together represent a methylene group and R'3 represents ethyl; and when n stands for 2, R'l represents an alkaline earth metal, R'2 represents hydrox~methyl or alkoxymethyl and R'3 represents hydrogen, and acid addition ~alt~ th~reof.

: The compounds of formula II and their acid additlon salts are prepared according to the pre~ent invent~on by a) for the prepaxatlon of a compound of formula II in which n ~tands for 1, R'l and R'3 bo~h repxesent hydrogen and R'2 repre~ents alkoxymethyl, oxidising a compound of the : general formula H0 ~ R~2 (III) - CH

, wherein R'2 represents alkoxymethyl, to the corre~pondin~ acld, or b) for the preparation of a compound o~ formula II in which, when n stands for 1, R'l represents an alkali metal, ammonium or ammonium ~ub~tltuted with one or more alkyl or hydroxyalkyl group~, ~'2 repre~ents hydroxymethyl or alkoxy-methyl and R'3 represents hydrogen and, when n ~tand~ for 2, R'l repre3ents an alkaline earkh metal, R'2 represents hydroxy-methyl or alkoxymethyl and R'3 repre~ents hydro~en, treating an acid of the general formula _ g _ ~690S4 ~C ~
HO ~ R~2 ~ ' ~ (IV) ~7~

, wherein R'2 repre~ents hydroxymethyl or alkoxymethyl, with a ba~e of the general formula R'l(OH)m (V~

, whereln R'l represent3 an alkali metal, ammonium or ammonlum ~ubstltuted with one or more alkyl or hydroxyalkyl group~ and m stand3 for 1 ox R'l repre~ent~ an alkallne earth metal and m stands for 2, or c3 for the preparation of a compound of ormula II in which n stands for 1, R'l repre~ents alkyl, R'2 represents hydroxymethyl or alkoxym~thyl and R'3 represents hydrogen, reacting an acid of formula IV in which R'2 has the foregoing significance, or a 3alt thereof, wlth a compound of the ganeral formula R'lX (VI) , whereln X repre~ent~ fluorine, chlorine, bromlne, iodine or a p-toluenesulphonic acid eater and Rl ha~ the ~ignificance given earlier, or 05~

d) for the preparatlon of a compound of formula II in which R'l and R'2 together repre~snt a methylene group and R'3 represents ethyl, reacting 4-pyridoxic acid lactone with dlazoethane, and, if desired, converting a resul~ing compound of formula II
into an acid addition salt.

In embodiment a) of the foregoing process a compound of formula III is oxidi~ed to the corresponding acid.

The compounds of formula III are novel and can be obtained starting from the known compounds of formula VII
according to the following Formula Scheme.

Formula Scheme 3 ~ ~ C~2-0-Na C~3 1 ~ C~2--0--R~2 CH3 D-k~t~ ~ ~III) R'' = Alkyl ~VII) (VIII) The oxidatlon can be carried out ln the normal manner;
for example, in an analogous manner to the method given in Am.
Chem. Soc. 70, 3434 (1948) for the preparation of 4-pyridoxic : acid from pyridoxine.

In embodiment b) of the foregolng process, an acid of formula IV i5 converted into a sal~ with an equivalent amount of a base of formula V in the usual mann~r. The acids of 69C3~i~

formula IV in which R'2 repre~ent~ alkoxymethyl are novel and can be obtained as de~cribed in embodiment a~ hereinbefore.

In embodimen~ c) of the foregoing proce~s, an acid of formula IV or a salt thereof i9 reacted with a compound o~
formula VI. ~he reaction is preferably carried out under basic condltions at room temperature uslng an inert organic solvent such as dimethylformamide ~DMF).

In embodiment d) of the foregoing proces~, 4-pyridoxic acid lactone ls reacted with diazoethane. The reaction is preferably carried out in an inert organic ~olvent ~uch as, for example, in methanol, wlth the addition of an ethereal solution of diazoethane. This reaction i~ advantageously carrled out at a temperature between 0C and 20C.

.. ~ , .

~069~54 The followlng Example~ lllustrate the present invention.
Examples 1-4 illustrate the preparation of compounds of formula II and Examples 5-11 illustrate specific embodiments of the light-screening agents provided by the in~ention.

Example l 7.32 g ~40 mmol) of 4-p~ridoxic acld, prepared according to D. Heyl, J. Amer. Chem. Soc. 70, 3434 (1948), are dissolved in 20 ml of a freshly prepared 2-N aqueous sodium hydroxide solution (40 mmol). rhe resulting solution is subsequently diluted with ethanol and ~ubstantlally concentrated on a rotary evaporator, the bulk of the water be$ng removed by azeotropic distillatlon. The solution is finally treated with ethyl acetate to crystalllsation. There are obtained 4.96 g of colourless sodium salt as a first crystallisate while ~ ~urther 2.11 g of colourle~s sodium salt are obtained from the mother llquor after decolorisation with Norit. The 7.07 g of sodium salt ob~alned in this manner are present as a hydrate. By using sodium methylate as the base in m~thanol, the anhydrou sodium 4-pyridoxinate is obtained directly;
melting point 250-252C (decomposition). The salt is very soluble in water, soluble in ethanol and pooxly soluble in ethyl acetate.

Example 2 1.10 g (5 mmol~ of the sodium salt of pyridoxic acid, prepared according to Example 1, are dissolved in 15 ml of dimethylformamide at room temperature and treated dropwise with 784 mg (5 mmol) of methyl iodide while stirring, the ~ 13 -~169054 separation of fine crystals beginning after a few minutes.
After completion of the addition, the mixture is stirred for a further 2 hours at room temperature and the crystals are then filtered off under suction. Further crystals are separated from the filtrate by coollng. By recrystallisation of the crude product from methanol/water, 875 mg of weakly yellowish crystals of methyl 4-pyridoxinate are obtained;
melting point 256C (decomposition).

In an analogous manner, by reacting the sodium salt of pyridoxic acid wlth n-hexyl lodlde at 80C for 4 hours and working up the reaction mixture with water/chloroform, there i9 obtained, from chloroform/hexane, n-hexyl 4-pyridoxinate of melting point 154-155C.

Example 3 4.185 g t20 mmol) of 3-0-4~0-isopropyIidenepyridoxine Cprepared according to W. Korytnyk and M. Ikawa, Methods of Enzymology, Vol. XVIII, Part A, 527; Academic Press ~1970~
are converted in~o the sodium salt using 1.18 g (22 mmol) of sodium methylate in 20 ml of methanol by heating at reflux and the crystalline salt obtained after removal of the methanol is dried at room temperature and 0.01 Torr. The thus-obtained salt i~ dissolved in 50 ml of dimethylformamide and treated dropwise while stirring with 8.426 g (22 mmol) of cetyl iodide. After aompletion of the addition, the ~5 mixture is stirred overnight (15 hours) at room temperature.
The mixture is subsequently worked up with water and benzene and the organic phase dried over sodium sulphate. By chromatography of the evaporated organic phase on silica gel . . .

` ~IL069~i4 with benzene/ethyl acetate ~1:1), there are obtained 2~56 g of pure 3-0-4-0-isopropylldene-5-(0-cetyl)-pyridoxine (in the form of colourless crystals) which are converted into crystalline 5-(0-cetyl)-pyridoxine hydrochloride by heating at reflux for 90 m~nutes in a mixture of lo ml of dioxane and 10 ml of l-N hydrochloric acid. After recrystallisation from ethanol/ether, there are obtained 2.5 g of the hydro-chloride of melting point 120~122C. Oxidation of the free base (melting point 91-92C) with manganese dioxide in chloroform at room temperature for 3 hours gives 5-(0-cetyl)-pyridoxal (melting point 48.5-49.5C) in almost quantitative yield.

1.0 g of 5-(0-cetyl)-pyrldoxal are dlssolYed in methanolic potassium hydroxide (1.0 g of potassium hydroxide in 80 ml of absolute methanol) and stirred with 7.0 g of active manganese dioxide for 6 days at room temperature~ By the addition of 5 ml of 30% hydro~en peroxide, the dissolved manganese salts are oxidlsed to manganese dioxide. The mixture, which becomes hot, is immediately filtered and the separated manganes~ dioxide is washed with methanolic potassium hydroxide.
By acidification of the yellow filtrate with l-N hydrochloric acid to pH 4, the acid formed preferentially separates out first. AFter standlng at 0C for 30 mlnutes, the mixture is filtered through a glass frlt and the white-yellow resldue is washed succe~slvely with water, ethanol and ether. By dissolving the product in ethanolic potassium hydroxide (1~) followed by precipitation wlth l-N hydrochloric acid, 5-(0-cetylJ-4-pyridoxic acid can be freed from the last traces of aldehyde. The yield of pure acid amounts to 0.41 g. The melting point of the acid is 250C (decomposition).

16~169~S4 Example 4 102 mg (0.25 mmol) of 5-(0-cetyl)-4-pyridoxic acid are boiled under reflux for 1 hour in 5 ml of absolute methanol together with 13.5 mg ~0~25 mmol) of sodium methylate. After S distillation of the solvent on a rotary evaporator, the yellow sodium 5-(0-~etyl)-4-pyridoxinate is dried overnight in a high vacuum. ~he yield amounts to 70 mg.

Example_5 ~ ;

Cream * . ' Fat phase: 0.5 g of Emulgade 1000 NI
(saturated fatty alcohol glycol ether) 0.2 g of Lanette 0 (cetylstearyl alcohol) 3.0 g of Cetiol HE (fatty acid ester) 5.0 g of Vaseline (white) 15.0 g of Softisan 100 * ~ hard fats 3.0 g of Softisan 601 ' 4.0 g of hydrogenated groundnut fat 4.0 g of Eumulgin C 700 (saturated fatty alcohol polyglycol ether) 1.0 g of Dehymuls E (mixture of high molecular aliphatic esters) 0.5 g of perfume.
* :
Aqueous phase: 0.3 g of Dowicil 200 [1-(3-chloro-allyl)-3,5,7-triaza-1-azonia-adamantane chloride]
5 g of sodium 4-pyridoxinate 58.5 g of water *Trade Marks -- . . ~
~7 - 16 -1~6~5~

The cream is manufactured by melting together the various components of the fat phase at 45C to SoC while slowly stlxring. 5 g of sodlum 4-pyrldoxinate and 0.3 g of Dowlcil 200 are dissolved in 58.5 ml of cold water, the solution obtained is heated to 45C to 50C and mixed wlth the fat phase whlle continuously stirring. The mixture is stirred for a further 3 hours while cooling a~ room temperature.
Finally, the pH value of the resulting cream ls adjus~ed to 6 with ascorbic acid.

lo Examele 6 Cream Fat phase: 2.5 g of Emulgade loob NI (saturated fatty alcohol polyglycol ether) 1.0 g of cetyl alcohol 2.0 g of Vaseline (white) 2.0 g of hydrogenated groundnut fat 1.5 g of glycerine monostearate 2.0 g of Softisan 100 (hard fat) 1.0 g of Cremophor 0 (alkyl- or acyl-substituted polyaddition product of ethylene oxide) 1.0 g of Emulgin C 700 (saturated fatty alcohol polyglycol ether) 1.0 g of Cetiol HE (fatty acid ester) Aqueous phase: 6.0 g of sodium pyrldoxinate 20 ml of Tris buffer solution, 1%, adjusted to pH 8.1 with citric acid 54.0 g of Carbopol 940, 1% in wa~er, adjusted to pH 8 with Tris.

The fat phase is blended into the agueous phase at 80C.

*Trade~Marks i9!~354 The following solut~on is introduced at 50C:

0.2 g of perfume :
0.5 g of Pantyl 0.3 g of Dowicil 200 1-(3-chloro-allyl)-3,5,7-triaza-1-azonia-adamantane trichloride 2.Q g of water.
:, ,' ~:~ ,.

Cream __ .
Fat phase: 5.0 g of pyridoxic acid 8.15 g of triethanolamine 6.0 g of propyleneglycol :
3.55 g of Amphisol 1.2 g of stearic acid 1.2 g of cetyl alcohol .
3.0 g of Deltyl extxa (isopropyl myrlstate) 1.2 g of arachis oil 1.2 g of dlethyleneglycol mono-stearate 3.55 g of Lantrol (purified lanolin) 0.1 g of PCL-liquid (branched fatty acid ester) Aqueous phase: 50.0 g of 2~ Carbopol in water, neutralised to pH 7 0.2 g of Dowicil 15.65 g of water.

Example 8 Lotlon __ *Trade ~arks ~ 18 -- . ~

~C169~54 Fat phasa: 0.5 g of Emulgade 1000 NI
(saturated fatty alcohol polyglycol ether) 0.1 g of Lanette 0 (cetylstearyl : :
alcohol) 1.5 g of Cetiol HE (fatty acid ester) 2.5 g of Vaseline (whlte) 7.5 g of Softisan 100 1.5 y of Softisan 601 >
4.0 g of hydrogenated groundnut ~at 4.0 g of Emulgin C 700 ~saturated fatty alcohol polyglycol ether) 1.O q of Dehymuls E (mixture of hlgh molecular aliphatic esters) O.S g of perfume Aqueous phase 0.7 g of Dowicil 200 [1-(3-chloro-allyl)-3,5,7-triaza-1-azonia-adamantane chloride]
3.0 g of sodium 4-pyridoxinate ; 0.5 g of Dehymuls E
2.0 g of Emulgin C 700 71.0 g of water The lotion 1~ manufactured by melting together the various compOnentB of the fat pha~e at 45C to 50C. 2.0 g * *
of Emulgin C 700 and 0.5 g of Dehymuls E are dis~olved in 35 ml of water at 80C. At the same time, 3 g of sodium 4-pyridoxinate and 0.4 g of Dowicil 200 are dissolved in 36 ml of cold waker. The two aqueous solutions are combined and mixed with the fat phase while continuously stirring. The mixture is stirred ~or a further 3 hours while cooling at room temperature. Flnally, the pH value of the lotion obtained is adjusted to 6 with ascorblc acld.

*Trade Marks , .
19 - .

-:
.

Example 9 Gel Composition:
1.2 g of Carbopol 940 (acrylic acid polymerisate with high molecular weight) 2.5 g of triethanolamine 0.15 g of Dowlcil 200 4.0 g o~ sodium 4~pyridoxinate 92.15 ml of water The gel ls manufactured by completely dissolving 1.2 g of Carbopol 940 in 85 ml of wa~er heated to 70C. Subsequently, 2.5 g of triethanolamine and 0.15 g of Dowicil*200 are added to this solution. Flnally, the mixture is mixed at room temperature with 4.0 g of a ~olu~ion of sodium 4-pyridoxinate in 7.15 ml of water. The gel obtained has a pH of 7.2. -Exam~le 10 . .
Gel In a manner analogous to that descrlbed in Example 6, a gel of the foll.owlng compo~itlon is manufactured:
1.2 g of Carbopol 940 2.5 g of triethanolamine 0.15 g of Dowi~il 200 6.0 g of sodium 4-pyridoxinate 90.15 ml of water.

*Trade Marks . . .

' ~
.

~L~69~5~

Example 11 Gel 6.0 g of sodium pyridoxinate *
0.3 g of Tris 0.075 g of citric acid 0~3 g of Dowicil 200 33.325 g of water.

The foregoing solution is introduced lnto 60 g of Carbopol gel consisting of 1.8 g of Carbopol 940 3.6 g of Tris 54.6 g of water.

The pH of the gel amounts to 8~0.

*Trade Marks . .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for protecting the skin against harmful rays which method comprises applying to the skin a light-screening agent which contains as essential active ingredient an effective amount up to 25 weight percent of one or more compounds chosen from those of the general formula (I) , wherein R1 represents hydrogen, lower alkyl of 1 to 6 carbon atoms, an alkali metal, ammonium or ammonium substituted with one or more alkyl or hydroxyalkyl groups, R2 represents hydroxymethyl or alkoxymethyl and R3 represents hydrogen or R1 and R2 together represent a methylene group and R3 represents hydrogen, methyl or ethyl;
and acid addition salts thereof, and a compatible cosmetic base.

2. A method according to Claim 1, wherein the light-screening agent contains a compound of formula I wherein R1 represents hydrogen, an alkali metal or ammonium substituted with alkyl or hydroxyalkyl groups, R2 represents hydroxymethyl or alkoxymethyl and R3 represents hydrogen.

3. A method according to Claim 1, wherein the light-screening agent contains 4-pyridoxic acid, sodium 4-pyridoxinate, potassium 4-pyridoxinate, triethanolammonium 4-pyridoxinate, 5-(0-cetyl)-4-pyridoxic acid, methyl 4-pyridoxinate, n-hexyl 4-pyridoxinate, 4-pyridoxic acid lactone hydrochloride, 4-pyridoxic acid lactone 3-methyl ether, 5-(o-cetyl)-4-pyridoxinate, or tris(hydroxymethyl)amino-methane-4-pyridoxinate.

4. A method according to Claim 1, wherein the light-screening agent contains as active ingredient the compound sodium 4-pyridoxinate.

S. A method according to Claim 1, 2 or 4, wherein the light-screening agent contains 2 to 6 weight per cent of one or more compounds of formula I.

6. A light-screening agent for protecting the skin against harmful rays, which contains as essential active ingredient from 2 to 6 weight percent of one or more compounds chosen from those of the general formula (I) wherein R1 represents hydrogen, lower alkyl of 1 to 6 carbon atoms, an alkali metal, ammonium or ammonium substituted with one or more alkyl or hydroxyalkyl groups, R2 represents hydroxymethyl or alkoxymethyl and R3 represents hydrogen or R1 and R2 together represent a methylene group and R3 represents hydrogen, methyl or ethyl;
and acid addition salts thereof, one or more further organic compounds having an absorption maximum between 290 and 340 nm, and a compatible cosmetic base.

7. A light-screening agent as in Claim 6 wherein the active ingredient is the compound sodium 4-pyridoxinate.