Abstract:
Disclosed is a chemically stable tyrosinase activity inhibitor having high tyrosinase activity inhibition effect and low toxicity. The tyrosinase activity inhibitor has a structure of the formula: ##STR1## wherein R 1 , R 3  and R 4  are a hydrogen atom or an alkyl or alkenyl group having 1 to 9 carbon atoms, and R 2  is an alkyl or alkenyl group having 2 to 9 carbon atoms.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a tyrosinase activity inhibitor which is useful for facial cosmetics, stain-resistant substances for marine paint and melanin production inhibitors. 
     BACKGROUND OF THE INVENTION 
     Several phenolic compounds have hitherto been known as tyrosinase activity inhibitors, and some of them are used for the application such as facial cosmetics and the like. However, these phenolic compounds often have a problem on safety for human body, chemical stability and efficacy. 
     As the tyrosinase activity inhibitor, hydroquinones and resorcinols having a long chain alkyl group at 4-position are known at present. However, the tyrosinase activity inhibitions as described in Japanese Patent Kokai Nos. 61-21007, 61-21008, 61-21009, 61-21010, 61-21011 and 61-21012 functions as non-competitive antagonist and seems toxic to human body in view of maintenance of hemostasis in human body. Since the tyrosinase activity inhibitor as described in Japanese Patent Kokai No. 3-28462 has a long chain alkyl group at 4-position of resorcinol, it is inferior in solubility to water. Therefore, it is difficult to use for normal cosmetics, satisfactorily. Further, arbutin which has hitherto been used has toxicity, and tranexamic acid described in Japanese Patent Kokai No. 4-169515 has low tyrosinase activity inhibition effect. 
     OBJECTS OF THE INVENTION 
     Main object of the present invention is to provide a chemically stable tyrosinase activity inhibitor having high tyrosinase activity inhibition effect and low toxicity. 
     This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a tyrosinase activity inhibitor having a structure of the formula: ##STR2## wherein R 1 , R 3  and R 4  are a hydrogen atom or an alkyl or alkenyl group having 1 to 9 carbon atoms, and R 2  is an alkyl or alkenyl group having 2 to 9 carbon atoms. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferably, the tyrosinase activity inhibitor of the present invention is at least one sort which is selected from the group consisting of the compounds of the formula (III). More preferably, it is tyrosinase activity inhibitor having a structure of the formula: ##STR3## 
     A method for preparing the compounds having a structure of the formulas (I), (II) and (III) is not specifically limited. These compounds may be synthesized by a method known to the art. For example, they can be synthesized by the following methods, respectively. 
     Process for the production of the compound of the formula (I) 
     Firstly, an alkylcarboxylic acid is reacted with resorcinol to obtain a 2,4-dihydroxyalkylphenone. This is then reduced with zinc amalgam obtained from zinc and mercuric chloride to give a 4-alkylresorcinol. 
     Process for the production of the compound of the formula (II) 
     Firstly, 1,3-dimethoxy-5-benzoyl chloride is reacted with an alkylmagnesium bromide to obtain a 1,3-dimethoxy-alkylphenone. This is then reduced with zinc amalgam obtained from zinc and mercuric chloride. The reaction is promoted by adding concentrated hydrochloric acid (10 to 50 cc) every one hour. After the completion of the reaction, the reaction product is cooled and purified by a known method to obtain a 5-alkylresorcinol. 
     Process for the production of the compound of the formula (III) 
     Firstly, a 1,3-dimethoxy-5-alkylbenzene is reacted with phenoxyacetyl chloride and aluminum chloride to obtain a 6,6&#39;-dialkyl-2,2&#39;,4,4&#39;-tetramethoxydiphenylmethane. This is then hydrolyzed by a known method to obtain a 6,6&#39;-dialkyl-2,2&#39;,4,4&#39;-tetrahydroxydiphenylmethane. 
     When the tyrosinase activity inhibitor of the present invention is used for cosmetics, at least one sort of a compound selected from the compounds of the formulas (I), (II) and (III) is dissolved or dispersed in bases (e.g. oils such as olive oil, mink oil, etc.; waxes such as lanolin, beeswax, etc.; hydrocarbons such as vaseline, squalane, etc.; esters such as isopropyl palmitate, etc.; higher alcohols such as cetyl alcohol, lauryl alcohol, etc.; higher fatty acids such as stearic acid, palmitic acid, etc.; sterols such as cholesterol, etc.) and alcohols (e.g. ethanol, isopropyl alcohol, propylene glycol, etc.), which are normally used for cosmetics. Thus, the tyosinase activity inhibitor of the present invention can be widely applied for various cosmetics (e.g. various basic cosmetics such as cosmetic cream, milky lotion, skin lotion, pack, cleansing cream, etc.; various makeup cosmetics such as foundation, cheek rouge, blusher, lipstick, etc.; other cosmetics such as soap, shampoo, rinse, perfume, cologne, etc.). The trypsine activity inhibitor can be used in combination with various additives for cosmetics (e.g. surfactants, solvents, pigments, perfumes, preservatives, antioxidants, humectants, vitamin E, organic and plant extracts, other additives, etc.). Further, above-mentioned various cosmetics can take any form such as solution, emulsion, ointment, oil, wax, gel, sol, powder, spray and the like. 
     The amount of the tyrosinase activity inhibitor to be formulated varies depending upon the form of the cosmetic used. In principle, it may be present in an active amount. Normally, the tyrosinase activity inhibitor is formulated in the amount of 0.001 to 20% by weight, preferably 0.01 to 5% by weight, based on the total weight of the cosmetic composition. 
     The tyrosinase activity inhibitor of the present invention has low toxicity and irritation to skin as well as high stability to light and heat. Further, it has high stability to various cosmetic bases and additives, and can be used in combination with cosmetic bases and additives. 
     As described above, according to the present invention, there is provided a chemically stable tyrosinase activity inhibitor having high tyrosinase activity inhibition effect and low toxicity. 
    
    
     BRIEF EXPLANATION OF THE DRAWINGS 
     FIG. 1 shows a  1  H-NMR chart of the compound obtained in Example 3. 
     FIG. 2 shows a  13  C-NMR chart of the compound obtained in Example 3 
    
    
     EXAMPLES 
     The following Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. 
     Synthesis 1 
     Synthesis of 4-ethylresorcinol 
     Zinc chloride (151 g) was dissolved in butyric acid (162 g). Then, resorcinol (110 g) was added and the mixture was reacted at 150° C. for 20 minutes. After the completion of the reaction, concentrated hydrochloric acid (250 ml) and water (250 ml) were added to the reaction product, which was cooled and purified by a normal method to obtain 100 g of a compound, 2,4-dihydroxyethylphenone. Then, the reduction was conducted by adding water (300 cc), concentrated hydrochloric acid (300 cc) and 2,4-dihydroxyethylphenone (100 g) to zinc amalgam obtained from zinc (400 g) and mercuric chloride (20 g). Further, concentrated hydrochloric acid (10 to 15 cc) was added every one hour. After the completion of the reaction, the reaction solution was cooled and saturated with sodium chloride, and then extracted with ether to obtain 88 g of 4-ethylresorcinol. 
     Synthesis 2 
     Synthesis of 5-methylresorcinol 
     Methylmagnesium bromide (35 g) was added to 1,3-dimethoxy-5-benzoyl chloride (100 g) to obtain 1,3-dimethoxy-methylphenone in a yield of 45%. Then, the reduction was conducted by adding water (300 cc), concentrated hydrochloric acid (300 cc) and 1,3-dimethoxy-methylphenone (100 g) to zinc amalgam obtained from zinc (400 g) and mercuric chloride (20 g). Further, concentrated hydrochloric acid (10 to 15 cc) was added every one hour. After the completion of the reaction, the reaction solution was cooled and saturated with sodium chloride, and then extracted with ether to obtain 40 g of 1,3-dimethoxy-5-methylbenzene. Hydrogen iodide was added to the resulting 1,3-dimethoxy-5-methylbenzene and stirred at 115° to 125° C. for 3 hours under nitrogen atmosphere. After cooling, the product was extracted with methylene chloride to obtain 30 g of 5-methylresorcinol. 
     Synthesis 3 
     Synthesis of 6,6&#39;-di-n-propyl-2,2&#39;,4,4&#39;-tetrahydroxydiphenylmethane 
     To benzene (70 ml) were added 1,3-dimethoxy-5-propylbenzene (11 g), phenoxyacetyl chloride (11 g) and aluminum chloride (9 g), followed by stirring at 5° C. for 1.5 hours. The mixture was hydrolyzed with hydrochloric acid under ice cooling and extracted with ether to obtain 0.3 g of 6,6&#39;-di-n-propyl-2,2&#39;,4,4&#39;-tetramethoxydiphenylmethane. Hydrogen iodide was added to the resulting 6,6&#39;-di-n-propyl-2,2&#39;,4,4&#39;-tetramethoxydiphenylmethane and stirred at 115° to 125° C. for 3 hours. After cooling, the mixture was extracted with methylene chloride to obtain 0.3 g of 6,6&#39;-di-n-propyl-2,2&#39;,4,4&#39;-tetrahydroxydiphenylmethane. The resulting compound was subjected to  1  H-NMR and  13  C-NMR spectrum and the charts thereof are shown in FIGS. 1 and 2. 
     EXAMPLE 
     Measurement of tyrosinase activity inhibition % of tyrosinase activity inhibitors obtained in Synthesis 1 to 3 and other inhibitors, as shown in Table 2, which is within or outside (contrast) the present claims, and which were prepared as generally described in Synthesis 1 to 3 
     The measurement was conducted by the following method. 
     (1) Reaction reagent 
     The reaction reagent used are as follows: 
     Substrate: 2 mM L-DOPA (Wako Junyaku Co.) 
     Buffer: 0.1 mM phosphate-potassium solution (pH 6.8) 
     Inhibitor: 1% solution of the compound of the formula (I), 4-ethylresorcinol, compound of the formula (II), 5-methylresorcinol and compound of the formula (III), 6,6&#39;-di-n-propyl-2,2&#39;,4,4&#39;-tetrahydroxydiphenylmethane 
     Enzyme: tyrosinase (Sigma Co.), 0.5 mg/ml 
     (2) Measurement of tyrosinase activity inhibition % 
     Preparation of reaction solution 
     In the case of measuring tyrosinase activity inhibition %, a sample solution (No.1 to No.3) was prepared in a spectrophotometric cell (1 ml), by mixing each ingredient in the following formulation shown in Table 1. 
     
                       TABLE 1______________________________________Formulation of sample solution (ml)      No. 1     No. 2   No. 3______________________________________Buffer       0.50        0.50    0.50Substrate    --          0.20    0.20Inhibitor    --          --      0.10Deionized water        0.48        0.28    0.18______________________________________ 
    
     Measurement 
     An enzyme solution (0.20 ml) was added to the cell. Three minutes later, the measurement of temporal changes of an absorbance (417 nm) by means of a spectrophotometer had started. The inhibition % was calculated based on the following equation: 
     
         Inhibition %=[1-(Ab.3-Ab.1/Ab.2-Ab.1)]×100 
    
     wherein Ab.2 is an absorbance of No.2 solution, Ab.1 is an absorbance of No.1 solution (at the time when the absorbance of No.2 solution exhibits maximum) and Ab.3 is an absorbance of No.3 solution (at the time when the absorbance of No.2 solution exhibits maximum). IC 50 , which shows a concentration (μM) of tyrosinase activity inhibitor when the tyrosinase activity inhibition (%) is 50%, are shown in Table 2. 
     
                       TABLE 2______________________________________ of RVariation     ##STR4##                     ##STR5##______________________________________Methyl   8               5,000    (contrast)Ethyl    2               700n-Propyl 0.9             500n-Pentyl 0.8             200n-Heptyl 0.7             200n-Nonyl  0.9             200Compound of    25Example 3______________________________________ Numbers in Table 2 have a unit of μM.