Abstract:
Disclosed are α-amides of L-amino acids that produce fragrance or attenuate or mask malodor. In particular, threonine amides, glycine amides, serine amides, and alanine amides can be used in the invention. Such α-amides of L-amino acids are useful for generating pleasant fragrances or attenuating or masking malodor upon cleavage of the α-amides of L-amino acids by bacteria in axillae. The α-amides of L-amino acids can be incorporated into skin treatment compositions and personal care products, such as deodorants, body sprays and antiperspirants, and used in methods for producing fragrance or attenuating or masking malodor.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to α-amides of L-amino acids that are precursors of fragrances and which are useful in the formulation of deodorants, antiperspirants, body sprays, and other skin treatment compositions. 
     In humans, axillary malodors are produced by enzymatic cleavage of malodor precursors found in apocrine secretions. The enzymes that release the malodors are produced by axillary bacteria such as Staphylococcus sp. and Corynebacteria. Typical deodorants mask or decrease this malodor. 
     SUMMARY OF THE INVENTION 
     It has now been shown that various α-amides of L-amino acids can be cleaved by axillary bacterial enzymes, releasing pleasant fragrances and/or attenuating malodor. Such amino acid amides, therefore, are useful in skin treatment compositions such as deodorants, antiperspirants, and body sprays. Accordingly, the invention relates to α-amides of L-amino acids that are precursors of fragrances, or which can attenuate or mask malodor. 
     In one aspect, the invention features a skin treatment composition (e.g., a deodorant composition) for application to human skin; the skin treatment composition includes a dermatologically acceptable vehicle and an α-amide of an L-amino acid having the structure:                           
     wherein R 1  is H, CH 3 , CH 2 OH, or CH(OH)CH 3 ; and R 2  is selected so that cleavage of the α-amide of the L-amino acid leaves an R 2 —CO 2 H having a neutral or pleasant odor, or which is useful in attenuating or masking malodor. In general, these α-amides of L-amino acids are cleaved by bacterial enzymes by the reaction shown below.                           
     The α-amide of the L-amino acid is present in an amount sufficient to produce fragrance or attenuate or mask malodor. Preferably, the α-amide of L-amino acid is present in the skin treatment composition at a concentration of 0.01 to 10.0% (preferably 0.1 to 5.0%) by weight. If desired, the skin treatment composition can include an antiperspirant active (e.g., aluminum chlorohydrate)or a deodorant active (e.g., an antimicrobial). In various preferred embodiments, the skin treatment composition is formulated as a lotion, cream, stick, gel, or aerosol. 
     The composition may be formulated as a skin moisturizer, shampoo, shave preparation, body spray, body wash, soap, and the like. 
     The invention offers several advantages. For example, when the α-amides of L-amino acids are formulated as skin treatment compositions, fragrance is released slowly over time. Consequently, the fragrance is long-lasting and fading of the scent over time is minimized. In many instances, the α-amide of L-amino acid competes with the malodor precursor and attenuates malodor production over a prolonged period. 
     Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In preferred α-amides of L-amino acids, R 2  has 1 to 30 carbon atoms and is alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl or heterocyclic. These groups may be unsubstituted or substituted with one or more halo, hydroxyl, amino, nitro, amide, alkoxyl, carboxyl, cyano, thio, phosphoro, or other heteroatoms, phenyl or heterocyclic groups. The amino, amide, alkoxyl, carboxyl, thio, phosphoro, phenyl, or heterocyclic groups may be unsubstituted or substituted with one or more halo, hydroxyl, amino, nitro, alkyl, amide, alkoxyl, carboxyl, cyano, thio, or phosphoro groups. 
     R 2  can be, for example, methyl, ethyl, propyl, isopropyl, tert-butyl, sec-butyl, isobutyl, n-butyl, pentyl, hexyl, heptyl, octyl, 2-octyl, nonyl, 2-nonyl, decyl, 2-decyl, undecyl, 2-undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, or octadecyl, or any mono or poly unsaturated form thereof, cyclopentyl, cyclohexyl, 2-cyclohexylethyl, 2,6-dimethylheptyl, geranyl, neryl, citronellyl, 9-decenyl, 2,6-dimethyl-5-heptenyl, 2,6-dimethyl-1,5-heptadienyl, 8,11-heptadecadienyl, 8-heptadecenyl, cyclopentenyl, cyclohexenyl, phenyl, p-methoxyphenyl, benzyl, 2-phenylethyl, 1-phenylethyl, 2-(p-methoxyophenyl)-ethenyl, 3-(p-methylphenyl)-2-propyl, 3-(p-isopropylphenyl)-2-propyl, 3-(p-tert-butylphenyl)-2-propyl,2,5,8-trioxanonyl, acetonyl, aminomethyl, hydroxymethyl, 1-hydroxyethyl, dimethylaminomethyl, 1-phenyl-1-aminoethyl, carboxymethyl, 2-carboxyethyl, 3-carboxypropyl, 4-carboxybutyl, 5-carboxypentyl, 6-carboxyhexyl, 7-carboxyheptyl, 8-carboxyoctyl, 9-carboxynonyl, 10-carboxy-2,5,8-trioxanonyl, 7-carboxamido-5-carboxy-4-aza-3-oxo-heptyl, 8-carboxamido-6-carboxy-5-aza-4-oxo-octyl, 9-carboxamido-7-carboxy-6-aza-5-oxo-nonyl, 10-carboxamido-8-carboxy-7-aza-6-oxo-decyl, 11-carboxamido-9-carboxy-8-aza-7-oxo-undecyl, 14-carboxamido-12-carboxy-11-aza-10-oxo-tetradecyl, 2-pentyl-cyclopropyl, menthyl, or terpineyl. 
     Preferred α-amides of L-amino acids for use in the invention include, without limitation, N-methylpentenylserine, N-methylpentenylalanine, N-phenylacetylserine, N-phenylacetylalanine, N-indolacetylserine, N-indolacetylalanine, N-cyclohexylcarboxylserine, N-cyclohexylcarboxylalanine, N-ethylbutyrylserine, N-ethylbutyrylalanine, N-pheylpropionylserine, N-phenylpropionylalanine, N-benzoylserine, N-benzoylalanine, N-cyclohexylacetylserine, N-cyclohexylacetylalanine, N-vanilloylserine, N-vanilloylalanine, N-methylpentenylthreonine, N-methylpentenylglycine, N-phenylacetylthreonine, N-phenylacetylglycine, N-indolacetylthreonine, N-indolacetylglycine, N-cyclohexylcarboxylthreonine, N-cyclohexylcarboxylglycine, N-ethylbutyrylthreonine, N-ethylbutyrylglycine, N-phenylpropionylthreonine, N-phenylpropionylglycine, N-benzoylthreonine, N-benzoylglycine, N-cyclohexylacetylthreonine, N-cyclohexylacetylglycine, N-vanilloylthreonine, N-vanilloylglycine. 
     The preferred α-amides of L-amino acids generally can be prepared by coupling a carboxylic acid to a protected amino acid by known procedures. The carboxylic acids and protected amino acids generally are known in the art; they generally are either commercially available or can be made by known procedures. 
    
    
     EXAMPLES 
     Various α-amides of L-amino acids were synthesized and tested for cleavage by  Staphylococcus haemolyticus , which is commonly found on human skin, especially in the axilla. In the following examples, amide analogs of the amino acids serine and alanine in which R 2  was phenylacetic acid (PAA) or methylpentenoic acid (MPA) were synthesized. Other known fragrant carboxylic acids (e.g., ethylbutyric acid, cyclohexylcarboxylic acid, or indole-3-acetic acid) can be substituted for PAA or MPA. The α-amides of the L-amino acids were synthesized as described below. The following working examples also provide general guidance for synthesis and testing of other α-amides of L-amino acids in accordance with the invention. These examples are meant to illustrate, not limit, the invention, the metes and bounds of which are defined by the claims. 
     Synthesis of α-Amides of L-Amino Acids 
     Coupling Carboxylic Acids to Protected Amino Acids: To couple the carboxylic acid to a protected amino acid (e.g. O-t-butylserine t-butylester-HCl, alanine methyl ester hydrochloride) the carboxylic acid (7.4 mmol), the protected amino acid (7.1 mmol), 4-dimethylaminopyridine (0.1 g), diisopropylethylamine (0.92 g, 7.1 mmol) and methylene chloride (40 mL) were stirred, under nitrogen in a 100 mL flask, until the amino acid was dissolved. The reaction was cooled in an ice-water bath and a solution of dicyclohexylcarbodiimide (DCC) (1.5 g, 7.3 mmol) dissolved in methylene chloride (20 mL) was added. Stirring was continued in the ice water bath for approximately 15 minutes, during which time a white precipitate of dicyclohexylurea (DCU) began to form. The reaction was then stirred overnight at room temperature under nitrogen. The following day, the DCU was suction-filtered off, and the filtrate was washed twice with 50 mL of 10% sodium bicarbonate, washed twice with 1M hydrochloric acid (50 ml) then washed once with 50 mL of saturated sodium chloride. The organic layer was dried over anhydrous magnesium sulfate for at least two hours, filtered, and rotary evaporated to dryness. The product can be analyzed with thin layer chromatography (TLC, using silica gel plates) in order to determine the optimal solvent for purification via flash chromatography (e.g., with the FLASH 40 system from Biotage). In general 30-40% ethyl acetate/hexane is suitable. Dissolution of the product prior to chromatography in the eluting solvent may leave additional DCU undissolved, which can be suction-filtered off. 
     Removal of the Methyl Ester Protecting Group: To remove the methyl ester protecting group, the N-acylamino acid methyl ester (approximately 5 mmol), 95% ethanol (15 mL), and 10M potassium hydroxide (15 mL) were stirred at room temperature for approximately one hour. The solution was then cooled in an ice-water bath and acidified to pH 1-2 with 10M hydrochloric acid. The solution was extracted with chloroform (2×50 mL) after adding a minimum amount of water to dissolve the potassium chloride formed during the acidification. The organic layers were combined and dried over anhydrous magnesium sulfate for several hours. After filtering off the solids, the filtrate was rotary evaporated, followed by vacuum-oven drying at room temperature. 
     Removal of the t-Butyl Ether and Ester Protecting Groups: The protected amino acid (approximately 10 mmol) was dissolved in trifluoroacetic acid (TFA; 25 mL), and the solution was stirred at room temperature for approximately 3 hours (until the reaction was completed, as determined by TLC using the solvents identified for chromatographic purification). The TFA was removed via rotary evaporation and vacuum-oven drying. 
     In an alternative method, the protected amino acid (10 mmol) was dissolved in ethyl acetate (25 mL), the solution was cooled in an ice-water bath, and hydrogen chloride gas was bubbled into the solution for approximately 15 minutes. The ice-water bath was removed, and the solution was stirred overnight. The solvent then was removed by rotary evaporation and vacuum-oven drying. The products from the reactions were analyzed by TLC on silica gel plates and by  1 H NMR with a Bruker AC-250 NMR Spectrometer. 
     Assay of the α-Amides Of L-Amino Acids for Cleavage by Bacteria 
     The synthesized α-amides of L-amino acids were tested for their ability to be cleaved by bacteria normally found in human axilla. For this example, a 100 mL culture of  Staphylococcus haemolyticus  was grown overnight at 37° C. in Trypticase Soy Broth medium. The cells were pelleted by centrifuging the culture at 5,000 rpm for 12 minutes, and the pelleted cells were resuspended in sterile saline. The cells were again pelleted and resuspended in sterile saline. After pelleting the cells once again, the cells were weighed and resuspended in sterile assay buffer (50 mM phosphate, pH 6.8, 1% glucose/dextran). The final concentration of cells was 0.05 g cells/mL (for the gas chromatography (GC) assay) or 0.1 g cells/mL (for the NMR assay). These cell suspensions can be stored at 4° C. 
     The α-amides of L-amino acids were prepared as stock solutions at a concentration of approximately 5 mg/mL in 50 mM potassium phosphate buffer (pH 6.8). If necessary, the pH can be adjusted to 6.8-7.0 with 1N NaOH. The amino acid stock solutions were sterilized by filtering them through 0.22 μm filters. 
     Gas Chromatography Assay 
     To demonstrate that the α-amides of L-amino acids can be cleaved by bacteria normally found in axilla, a 100 μL aliquot of the α-amide of L-amino acid stock was added to 100 μL of cells in sterile tubes. For a negative control, the cells were incubated with 100 μL sterile phosphate buffer. The samples were incubated for 16-18 hours at 37° C., and the reactions were quenched with 10 μL of 10 N HCl. The samples then were extracted with 100 μL chloroform and analyzed by gas chromatography. 
     NMR Assay 
     In addition to analyzing the cleavage reactions by gas chromatography, NMR analysis was used. A 500 μL aliquot of the α-amide of the L-amino acid stock solution was added to 500 μL of cells in sterile tubes. The cells and α-amides of L-amino acids were incubated for 16-18 hours at 37° C., with shaking, and the cleavage reactions were quenched with 50 μL of 10 N HCl. Each sample then was extracted with 600 μL of CDCl 3 , and the extracts were filtered through a Na 2 SO 4  pipette filter to remove water from the samples.  1 H NMR spectra of the samples then were taken (64-128 scans generally is sufficient), zooming in on a region that would contain peaks from the cleavage product. The presence or absence of these peaks allowed for a qualitative determination of whether the α-amides of L-amino acids were cleaved. Each of the α-amides of L-amino acids (phenylacetylalanine, methylpentenylalanine, and methylpentenylserine) was cleaved by the  Staphylococcus haemolyticus  cells, as determined by gas chromatography or  1 H NMR. Thus, these α-amides of L-amino acids can be used as fragrance precursors in skin treatment compositions. 
     Formulation of Skin Treatment Compositions 
     A variety of skin treatment (e.g., deodorant or antiperspirant) compositions are known in the art, and the α-amides of L-amino acids of the invention can be used in the formulation of such skin treatment compositions. A variety of skin treatment compositions can be made that include an effective amount of the α-amides of L-amino acids in a dermatologically acceptable vehicle. Such vehicles for use in deodorant or antiperspirant compositions and other ingredients that can be used in deodorant or antiperspirant compositions are known in the art A preferred form is one containing a deodorant active (e.g. an antimicrobial). Another preferred form is one containing an antiperspirant active. The α-amides of L-amino acids of the invention are used in an amount sufficient to produce fragrance or attenuate or mask malodor when the skin treatment composition is applied topically to skin. Suitable formulations also are well known in the art. Generally, the α-amides of L-amino acids are used at a concentration of 0.01 to 10%, preferably 0.1 to 5.0%, by weight. A single α-amide of an L-amino acid can be used in a skin treatment composition, or multiple α-amides of L-amino acids can be used in combination. 
     Examples of suitable deodorant actives include, without limitation, triclosan, triclocarban, zinc phenolsulfonate, other zinc salts, lichen extract, and usnic acid. Examples of suitable antiperspirant actives include, without limitation, salts of aluminum chlorohydrate; aluminum sesquichlorohydrate, aluminum dichlorohydrate, aluminum chlorohydrex PG or PEG, aluminum sesquichlorohydrex PG or PEG, aluminum dichlorohydrex PG or PEG, aluminum zirconium trichlorohydrate, aluminum zirconium tetrachlorohydrate, aluminum zirconium tetrachlorohydrex PG or PEG, aluminum zirconium pentachlorohydrate, aluminum zirconium octachlorohydrate, aluminum zirconium trichlorohydrex-gly, aluminum zirconium tetrachlorohydrex-gly, aluminum zirconium pentachlorohydrex-gly, aluminum zirconium octachlorohydrex-gly, aluminum zirconium chloride, aluminum zirconium sulfate, potassium aluminum sulfate, sodium aluminum chlorohydroxylacetate, and aluminum bromohydrate. These deodorant or antiperspirant actives can be incorporated into the deodorant compositions in accordance with conventional methods for producing deodorant and antiperspirant compositions. 
     Methods for preparing various suitable skin treatment compositions are known in the art. Various deodorant, antiperspirant, and personal care compositions are within the invention; several examples are provided below. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Deodorant Stick 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Propylene glycol 
                 70.300 
               
               
                   
                 Water 
                 20.500 
               
               
                   
                 Sodium Stearate 
                 7.000 
               
               
                   
                 Triclosan 
                 0.300 
               
               
                   
                 Fragrance 
                 1.400 
               
               
                   
                 α-amide of L-amino acid 
                 0.50 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Aerosol Antiperspirant 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Cyclomethicone 
                 10.0 
               
               
                   
                 Dimethicone 
                 2.0 
               
               
                   
                 Cyclomethicone (and) Quaternium 18 
                 2.0 
               
               
                   
                 Hectorite (and) SDA 40 
               
               
                   
                 SDA 40, Anydrous 
                 0.5 
               
               
                   
                 Aluminum Chlorohydrate 
                 10.0 
               
               
                   
                 α-amide of L-amino acid 
                 1.0 
               
               
                   
                 Propellant A-31 
                 74.5 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Suspension Antiperspirant Stick 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Cyclomethicone 
                 54.5 
               
               
                   
                 Stearyl Alcohol 
                 20.0 
               
               
                   
                 PPG-14 Butyl Ether 
                 2.0 
               
               
                   
                 Hydrogenated Castor Oil 
                 1.0 
               
               
                   
                 Talc 
                 2.0 
               
               
                   
                 Aluminum Zirconium Tetrachlorohydrex- 
                 20.0 
               
               
                   
                 Gly 
               
               
                   
                 α-amide of L-amino acid 
                 0.5 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Anydrous Roll-On Antiperspirant 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Cyclomethicone 
                 69.0 
               
               
                   
                 Dimethicone 
                 5.0 
               
               
                   
                 Cyclomethicone (and) Quaternium 18 
                 3.0 
               
               
                   
                 Hectorite (and) SDA 40 
               
               
                   
                 SDA 40, Anhydrous 
                 2.0 
               
               
                   
                 Aluminum Zirconium Tetrachlorohydrex- 
                 20.0 
               
               
                   
                 Gly 
               
               
                   
                 α-amide of L-amino acid 
                 1.0 
               
               
                   
                 Fragrance Oil 
                 q.s. 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Transparent Antiperspirant Gel 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Phase A 
                   
               
               
                   
                 Cyclomethicone (and) Dimethicone 
                 10.0 
               
               
                   
                 Copolyol 
               
               
                   
                 Cyclomethicone 
                 7.0 
               
               
                   
                 Phase B 
               
               
                   
                 Aluminum Chlorohydrate (and) Water 
                 50.0 
               
               
                   
                 Propylene Glycol 
                 16.0 
               
               
                   
                 Water 
                 16.0 
               
               
                   
                 α-amide of L-amino acid 
                 1.0 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Nonionic OW, Emollient Cream 
               
             
          
           
               
                   
                 Ingredients 
                 % w/w 
               
               
                   
                   
               
             
          
           
               
                   
                 Water 
                 73.000 
               
               
                   
                 Stearic acid 
                 7.200 
               
               
                   
                 Glyceryl monostearate 
                 4.500 
               
               
                   
                 Lanolin 
                 1.000 
               
               
                   
                 Isopropyl myristate 
                 4.300 
               
               
                   
                 Polyethylene glycol 1000 monostearate 
                 6.000 
               
               
                   
                 Propylene glycol 
                 2.500 
               
               
                   
                 α-amide of L-amino acid 
                 1.00 
               
               
                   
                 Preservative 
                 0.300 
               
               
                   
                 Perfume 
                 0.200 
               
               
                   
                 Total 
                 100.00 
               
               
                   
                   
               
             
          
         
       
     
     Other Embodiments 
     If desired, the α-amides of L-amino acids can be used in combination with other fragrance producing molecules or perfumes as indicators that the products are working, or to enhance the fragrance. In addition, the α-amides of L-amino acids can be used in personal care compositions to produce fragrance or attenuate or mask malodors. 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.