Abstract:
Novel 3-hydroxy-4-alkyloxyphenyl aliphatic carbonates particularly well suited as sweeteners in foodstuffs having the following basic structure: ##STR1## .

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a novel group of compounds and more particular to a novel group of compounds particularly well suited as sweeteners in edible foodstuff. 
     2. Description of the Prior Art 
     Sweetness is one of the primary taste cravings of both animals and humans. Thus, the utilization of sweetening agents in foods in order to satisfy this sensory desire is well established. 
     Naturally occurring carbohydrate sweeteners such as sucrose, are still the most widely used sweetening agents. While these naturally occurring carbohydrates, i.e., sugars, generally fulfill the requirements of sweet taste, the abundant usage thereof does not occur without deleterious consequence, e.g., high caloric intake and nutritional imbalance. In fact, oftentimes the level of these sweeteners required in foodstuffs is far greater than the level of the sweetener that is desired for economic, dietic or other functional consideration. 
     In an attempt to eliminate the disadvantages concomitant with natural sweeteners, considerable reasearch and expense have been devoted to the production of artificial sweeteners, such as for example, saccharin, cyclamate, dihydrochalcone, aspartame, etc. While some of these artificial sweeteners satisfy the requirements of sweet taste without caloric input, and have met with considerable commercial success, they are not, however, without their own inherit disadvantages. For example, many of these artificial sweeteners have the disadvantages of high cost, as well as delay in the perception of the sweet taste, persistent lingering of the sweet taste, and a very objectionable bitter, metallic aftertaste when used in food products. 
     Since it is believed that many disadvantages of artificial sweeteners, particularly aftertaste, is a function of the concentration of the sweetener, it has been previously suggested that these effects could be reduced or eliminated by combining artificial sweeteners such as saccharin, with other ingredients or natural sugars, such as sorbitol, dextrose, maltose etc. These combined products, however, have not been entirely satisfactory either. Some U.S. Patents which disclose sweetener mixtures include for example, U.S. Pat. No. 4,228,198; U.S. Pat. No. 4,158,068; U.S. Pat. No. 4,154,862; U.S. Pat. No. 3,717,477. 
     Also much work has continued in an attempt to develop and identify compounds that have a sweet taste. For example, in Yamato, et al., Chemical Structure and Sweet Taste Of Isocoumarin and Related Compounds, Chemical Pharmaceutical Bulletin, Vol. 23, p. 3101-3105 (1975) and in Yamato et al. Chemical Structure and Sweet Taste Of Isocoumarins and Related Compound, Chemical Senses And Flavor, Vol. 4 No. 1, p. 35-47(1979) a variety of sweet structures are described. For example, 3-Hydroxy-4-methoxybenzyl phenyl ether is described as having a faint sweet taste. 
     Despite the past efforts in this area, research continues. Accordingly, it is desired to find a compound that provides a sweet taste when added to foodstuff or one which can reduce the level of sweetener normally employed and thus eliminate or greatly diminish a number of disadvantages associated with prior art sweeteners. 
     SUMMARY OF THE INVENTION 
     This invention pertains to a composition having a structure selected from the group consisting of: ##STR2## wherein: 
     R is selected from the group consisting of methyl, ethyl and propyl; and 
     R 1  is an aliphatic or cycloaliphatic hydrocarbyl group containing not more than 12 carbon atoms with the proviso that the cycloaliphatic group contain not more than 7 carbon atoms in the ring. In particular R 1  is alkyl, alkenyl, alkadienyl, cycloalkyl, cycloalkenyl, cycloalkyadienyl, bicycloalkyl and bicycloalkenyl, the total number of carbon atoms in R 1  being not greater than 12, the total number of ring carbon atoms in said cycloalkyl, cycloalkenyl, cycloalkyadienyl, bicycloalkyl and bicycloalkenyl being not greater than 7; and salts thereof. 
     Most of the compounds of the formula and, in particular, the preferred compounds described hereinabove are sweeteners, the sweetness of which is many times that of comparable amounts of sucrose. The sweetness of compounds of the formula can be readily determined by a simple test procedure described herein. 
     Several compounds of the formula when tested for sweetness showed little, if any, sweetness to sucrose, whereas most compounds have greater sweetness than sucrose, e.g., 50-500 times greater. Compounds in which R 1  is methyl, showed no sweetness and are not within the preview of this invention. In general, the sweetener compound should possess a sweetness at least five times greater and preferably at least thirty times and more preferably 50 times greater than sucrose on comparable weight basis. 
     These compounds in addition to having sweet taste, function as a low calorie sweetening agent when employed with a foodstuff. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the present invention, the preferred novel compounds are of the formula: ##STR3## wherein: 
     R is selected from the group consisting of methyl, ethyl and propyl; 
     R 1  is selected from the group consisting of ##STR4## each R 11  is selected from the group consisting of ##STR5## wherein 
     n is an integer from 1 to 5, p is an integer from 0 to 2, q is an integer from 0 to 2 and the sum of p and q is equal to or less than 3; 
     each R 12  is selected from the group consisting of ##STR6## wherein 
     q&#39; is an integer from 1 to 4, r is an integer from 0 to 2, s is an integer from 0 to 2 and the sum of r and s is equal to or less than 2; 
     each R 10  is selected from the group consisting of H, CH 3 , CH 2  CH 3 , CH 2  CH 2  CH 3 , and CH(CH 3 ) 2  ; 
     each R 2  is selected from the group consisting of ##STR7## 
     each R 14  is selected from the group consisting of ##STR8## wherein 
     t is an integer form 1 to 3, u is an integer from 0 to 1, v is an integer from 0 to 1 and the sum of u and v is equal to or less than 1; 
     each R 15  is selected from the group consisting of ##STR9## wherein 
     w is an integer from 1 to 3, x is an integer from 0 to 1, y is an integer from 0 to 1 and the sum x plus y is equal to or less than 1; 
     each R 13  is selected from the group consisting of H, CH 3  and CH 2  CH 3  ; 
     each R 3  is selected from the group consisting of ##STR10## 
     each R 4  is selected from the group consisting of ##STR11## 
     each R 5  is selected from the group consisting of H and CH 3  with the provision that R 1  contain no more than 12 carbon atoms and with the proviso that when R 1  is ##STR12## then R 2  can not both be H and salts thereof. 
     Preferably R 1  will contain no more than 10 carbon atoms and more preferably will contain no more than 8 carbon atoms. 
     Illustrative compounds within the above formula include: 
     3-hydroxy-4-methoxyphenyl propyl carbonate 
     3-hydroxy-4-ethoxyphenyl propyl carbonate 
     3-hydroxy-4-propoxyphenyl butyl carbonate 
     3-hydroxy-4-ethoxyphenyl butyl carbonate 
     3-hydroxy-4-methoxyphenyl butyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-methylpropyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-ethylbutyl carbonate 
     3-hydroxy-4-methoxyphenyl 3,3-dimethylbutyl carbonate 
     3-hydroxy-4-methoxyphenyl cyclopropyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-methylcyclopropyl carbonate 
     3-hydroxy-4-methoxyphenyl cyclobutyl carbonate 
     3-hydroxy-4-methoxyphenyl cyclopentyl carbonate 
     3-hydroxy-4-methoxyphenyl cyclohexyl carbonate 
     3-hydroxy-4-methoxyphenyl cycloheptyl carbonate 
     3-hydroxy-4-methoxyphenyl cyclopentylmethyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-norbornyl carbonate 
     3-hydroxy-4-methoxyphenyl 5-norbornyl-2-carbonate 
     3-hydroxy-4-methoxyphenyl 3-cyclohexyl-1-carbonate 
     3-hydroxy-4-methoxyphenyl 3-methyl-2-butyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-cyclopentenylmethyl carbonate 
     3-hydroxy-4-methoxyphenyl 1-cyclopentenyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-methylbutyl carbonate 
     3-hydroxy-4-methoxyphenyl cis-2-methyl-2-butyl carbonate 
     3-hydroxy-4-methoxyphenyl 2-propyl-2-pentyl carbonate 
     3-hydroxy-4-methoxyphenyl 4-pentenyl carbonate 
     3-hydroxy-4-methoxyphenyl 3-cyclohexenyl-1-carbonate. 
     These novel compounds are effective sweetness agents when used alone or in combination with other sweeteners in foodstuffs. For example, other natural and/or artificial sweeteners which may be used with the novel compounds of the present invention include sucrose, fructose, corn syrup solids, dextrose, xylitol, sorbitol, mannitol, acetosulfam, thaumatin, invert sugar, saccharin, cyclamate, dihydrochalcone, hydrogenated glucose syrups, aspartame (L-aspartyl-L-phenylalanine methyl ester) and other dipeptides, glycyrrhizin and stevioside and the like. 
     Typical foodstuffs, including pharmaceutical preparations, in which the sweetness agents of the present invention may be used are, for example, beverages including soft drinks, carbonated beverages, ready to mix beverages and the like, infused foods (e.g. vegetables or fruits), sauces, condiments, salad dressings, juices, syrups, desserts, including puddings, gelatin and frozen desserts, like ice creams, sherbets and icings, confections, toothpaste, mouthwash, chewing gum, cereals, baked goods, intermediate moisture foods (e.g. dog food) and the like. 
     In order to achieve the effects of the present invention, the compounds described herein are generally added to the food product at a level which is effective to perceive sweetness in the food stuff and suitably is in an amount in the range of from about 0.0005 to 2% by weight based on the consumed product. Greater amounts are operable but not practical. Preferred amounts are in the range of from about 0.001 to about 1% of the foodstuff. Generally, the sweetening effect provided by the present compound is experienced over a wide pH range, e.g. 2 to 10 preferably 3 to 7 and in buffered and unbuffered formulations. 
     It is preferred then when the compounds are used in the foodstuff that the compounds have a sucrose equivalent of at least 1 percent by weight, more preferably that they have a sucrose equivalent of at least 5 percent by weight and most preferably they have a sucrose equivalent of at least 7 percent by weight. 
     A test procedure for determination of sweetness merely involves the determination of sucrose equivalency. 
     Sucrose equivalency for sweetness is readily determined. For example, the amount of a sweetener that is equivalent to 10 weight percent aqueous sucrose can be determined by having a panel of tasters taste the solution of a sweetener and match its sweetness to the standard solution of sucrose. Obviously, sucrose equivalents for other than 10 weight percent are determined by matching the appropriate sucrose solutions. 
     It is desired that when the sweetening agent of this invention is employed in combination with another sweetener the sweetness equivalent of the other sweetener is equal to or above about 1 percent sucrose equivalent. Preferably the combination of sweeteners provides a sucrose equivalent in the range of from about 3 weight percent to about 40 weight percent and most preferably 4 weight percent to about 15 weight percent. 
     In order to prepare the compounds of the present invention an esterification reaction is employed. A 3-benzyloxy-4-R-oxyphenol is esterified with a chloroformate of the R 1  moiety (e.g., R 1  OCOCl). This provides a 3-benzyloxy-4-R-oxyphenyl R 1  carbonate. This is subsequently converted to the desired 3-hydroxy-4-R-oxyphenyl R 1  carbonate. 
     For example, when R is methyl then 3-benzyloxy-4-methoxyphenol is used for the esterification reaction. To obtain 3-benzyloxy-4-methoxyphenol, isovanillin which is also known 3-hydroxy-4-methoxybenzaldehyde is used as a starting material. Isovanillin is a commercially available material. If R is to be other than methoxy then the appropriate 4-alkoxy compound is used as the starting material. The 4-alkoxy compound is made by alkylation is 3,4-dihydroxybenzaldehyde which is commercially available. Isovanillin is converted to 3-benzyloxy-4-methoxybenzaldehyde which is then converted to 3-benzyloxy-4-methoxyphenyl formate by the following reactions. 
     Performic acid is prepared by first heating a mixture of 30% by weight hydrogen peroxide and 97% by weight formic acid in a weight ratio of 1:5 to 60° C. and then cooling the mixture in an ice bath. The mixture is then added dropwise over a three hour period to an ice-cold 1M solution of 3-benzyloxy-4-methoxybenzaldehyde in methylene chloride. After the addition is completed a saturated solution of sodium bisulfite is added dropwise until the mixture exhibits a negative starch-iodide test for peroxides. The reaction mixture is poured into an equal volume of water. The phases separate and the aqueous phase is extracted with two parts of methylene chloride per part of aqueous phase. The combined organic phases are washed with water, dried over magnesium sulfate and the solvent is evaporated. The 3-benzyloxy-4-methoxyphenyl formate is recrystallized from 95% by weight ethanol. 
     The 3-benzyloxy-4-methoxyphenyl formate is then converted to 3-benzyloxy-4-methoxyphenol by the following reaction. A mixture of 3-benzyloxy-4-methoxyphenyl formate, methanol and 1M sodium hydroxide in a weight ratio of 1:6:10 is heated under reflux conditions for one hour, the mixture is allowed to cool and an equal volume of water is added. The solution is washed with ether and acidified to pH 3 with concentrated hydrochloric acid. The resulting mixture is extracted with ether. The combined extracts are washed with water and dried over magnesium sulphate and the solvent is evaporated to yield a tan solid which is 3-benzyloxy-4-methoxyphenol. 
     The 3-benzyloxy-4-methoxyphenol is reacted with the R 1  chloroformate as follows. The phenol (1.0 equiv.) and triethylamine (1.1 equiv.) are first dissolved in methylene chloride. The R 1  chloroformate (1.1 equiv.) is added and the mixture is stirred for a number of hours. The solvent is then evaporated and the residue is dissolved in a 1:1 mixture of ether and ethyl acetate. This solution is washed with 1M hydrochloric acid, saturated sodium bicarbonate, and water, and dried over magnesium sulfate. The solvent is evaporated to yield the desired product. 
     The benzyl protecting group is then removed by catalytic hydrogenation. The above product is dissolved in absolute ethanol and 10 percent palladium on carbon is added. The mixture is placed on a Parr hydrogenator, which is then charged with hydrogen to a pressure of 50 lb./in. 2 . Upon the cessation of hydrogen uptake (approximately 2-5 hours) the mixture is filtered through a celite pad and the solvent evaporated to yield the desired product. 
     Further details are described in McMurray et al. Journal Chemical Society, pages 1491-8 (1960) and Robinson et al. Journal Chemical Society, pages 3163-7 (1931). 
     The requisite chloroformate of the desired R 1  moiety is either commercially available, known in the art, or prepared from commercially available starting materials by known synthetic procedures. 
     Commercially available chloroformate precursors can be found in Chem. Sources U.S.A., Directories Publishing Co., Inc. Ormond Beach, Fla. as well as Chem. Sources Europe, Chem. Sources Europe Puglisher, Mountain Lakes, N.J. 
     Chloroformates, in general, can be prepared by the reaction of alcohols with phosgene. For a review of this method, as applied to the synthesis of chloroformates, see Matzner, Kurkjy, and Cotter, Chemical Reviews, 64, pages 645-687, (1964). 
     Alcohols, in general, can be prepared by a host of synthetic procedures from other available starting materials. Examples of these methods including specifics and reaction conditions can be found, in Survey of Organic Synthesis, Vols. 1 and 2, C. Buehler &amp; D. Pearson, Wiley Interscience Inc., New York and Advanced Organic Chemistry; Reactions, Mechanisms and Structure, J. March, McGraw-Hill, New York. 
     In addition to these referenced methods, alcohols can be obtained by conversion of other chemical functionalities. A reference for the interconversion of chemical functionalities can be found in, Compendium of Organic Synthetic Methods, Vols. I &amp; II, I. T. Harrison &amp; S. Harrison, Wiley Interscience Inc., New York. 
     The synthetic procedures disclosed incorporate the benzyl group as a protecting agent for the phenolic hydroxy moiety during various synthetic reactions. Other groups may be employed in place of the benzyl group to achieve this protection. Examples of these groups include 2-methoxyethoxymethyl, methylthiomethyl, t-butyldimethylsilyl, t-butyl ethers, and the 2,2,2-trichloroethyl carbonate. Other protecting groups, as well as specific reaction conditions and references, can be found in &#34;Protective Groups in Organic Synthesis&#34; by Theodora W. Greene, John Wiley &amp; Sons, NY, 1981, and in &#34;Protective Groups in Organic Chemistry&#34; by J. F. W. McOmie, Plenum Press, London, 1973. 
     The present new compounds form salts due to the presence of the phenolic hydroxy group. Thus, metal salts can be formed by reaction with alkali such as aqueous ammonia, alkali and alkaline earth metal compounds such as sodium, potassium and calcium oxides, hydroxides, carbonates and bicarbonate. The salts are of higher aqueous solubility than the parent compound and are useful for purification or isolation of the present products. 
    
    
     The following examples are presented to further illustrate this invention. 
     EXAMPLE 1 
     3-Hydroxy-4-methoxyphenyl ethyl carbonate 
     In this example 3-hydroxy-4-methoxyphenyl ethyl carbonate was prepared as follows. An amount of 2.30 gms. of 3-benzyloxy-4-methoxyphenol and 1.11 gms. of triethylamine was dissolved in 50 ml. of methylene chloride and the mixture was stirred at room temperature. To the mixture was added 1.19 gms of ethyl chloroformate and the resultant mixture was stirred for 2 hours. The reaction was then quenched with 1 ml. of water, and the solvent evaporated. The residue was dissolved in 100 ml. of a 1:1 mixture of ether and ethyl acetate. This solution was washed with equal volumes of 1M hydrochloric acid, saturated sodium bicarbonate, and water, dried over magnesium sulfate, and the solvent evaporated to yield 2.53 gm. of a tan solid which was 3-benzyloxy-4-methoxyphenyl ethyl carbonate. 
     This compound was deprotected by dissolving 2.45 gms. of the compound in 250 ml. of absolute ethanol and then adding 10% palladium on carbon. This mixture was then placed on a Parr hydrogenator which was then charged with hydrogen gas to a pressure of 50 lb./in. 2 . After 3 hours the hydrogen uptake ceased and the mixture was filtered through a celite pad. The solvent was evaporated to yield 0.95 gms. of a light yellow oil which was ethyl 3-hydroxy-4-methoxyphenyl carbonate. The structure was confirmed using nuclear magnetic resonance (NMR) methods. 
     A panel of experts determined that a 0.1 weight percent aqueous solution of this product had a sucrose equivalency of 4 weight percent. 
     EXAMPLE 2 
     In this example 3-hydroxy-4-methoxyphenyl 2-methylpropyl carbonate was prepared substantially as in Example 1 except 2.30 gms. of 3-benzyloxy-4-methoxyphenol was coupled with 1.50 gms. of isobutyl chloroformate. The structure was confirmed using NMR. 
     A panel of experts determined that aqueous 0.01 weight percent and 0.05 weight percent solutions of this product had sucrose equivalencies of 4.0 weight percent and 6.0 weight percent, respectively. 
     EXAMPLE 3 
     In this example 3-hydroxy-4-methoxyphenyl butyl carbonate was prepared substantially as in Example 1 except 2.30 gms. of 3-benzyloxy-4-methoxyphenol was coupled with 1.50 gms. of butyl chloroformate. The structure was confirmed using NMR. 
     A panel of experts determined that a 0.01 weight percent aqueous solution of this product had a sucrose equivalency of 3 weight percent. 
     EXAMPLE 4 
     In this example 3-hydroxy-4-methoxyphenyl propyl carbonate was prepared substantially as in Example 1 except 2.30 gms. of 3-benzyloxy-4-methoxyphenol was coupled with 1.35 gms. of propyl chloroformate. The structure was confirmed using NMR. 
     A panel of experts determined that a 0.03 weight percent aqueous solution of this product had a sucrose equivalency of 3 weight percent. 
     EXAMPLE 5 
     A cherry flavored beverage is prepared by mixing 1.48 gms. of an unsweetened cherry flavored instant beverage base mix with 438 gms. of water, 0.13 gms. aspartame (APM) and 0.04 gms. (0.01 weight percent) of 3-hydroxy-4-methoxyphenyl 2-methylpropyl carbonate. The base contains a malic acid and monocalcium phosphate buffer. 
     EXAMPLE 6 
     A mixed fruit gelatin is prepared by mixing 5.16 gms. of unsweetened gelatin base mix with 237 gms. of water, 0.07 gms. (0.029 weight percent) saccharin and 0.07 gms. (0.03 weight percent) of 3-hydroxy-4-methoxyphenyl butyl carbonate. The gelatin base contains an adipic acid and disodium phosphate buffer. 
     EXAMPLE 7 
     A vanilla flavored pudding is prepared by mixing 474 gms. of milk, 21.7 gms. of an unsweetened pudding base mix containing 1.35 gms. of sodium acid pyrophosphate, 36.0 gms. sucrose (6.8 weight percent) and 0.04 gms. (0.008 weight percent) of 3-hydroxy-4-methoxyphenyl 2-methylpropyl carbonate. 
     EXAMPLE 8 
     A lemon flavored beverage is prepared by mixing 8.1 gms. unsweetned lemon beverage base mix with 875 gms. of water and 0.88 gms. (0.1 weight percent) of 3-hydroxy-4-methoxyphenyl propyl carbonate. The lemon mix contains a citric acid, potassium citrate, and tricalcium phosphate buffer.