WO2007083263A1

WO2007083263A1 - Process to prepare flavones

Info

Publication number: WO2007083263A1
Application number: PCT/IB2007/050133
Authority: WO
Inventors: Eric Frerot
Original assignee: Firmenich Sa
Priority date: 2006-01-23
Filing date: 2007-01-16
Publication date: 2007-07-26

Abstract

The present invention relates to the field of flavor ingredients. More particularly it provides, a process for making 5- hydroxy -polyitιethoxy-f lavones (5-OH-PMF) (I) or improving the organoleptic properties of natural polymethoxy-f lavones (PMF) . The invention's process comprises treating flavones (II) in the presence of a HCl solution in a non-acidic and non -aqueous solvent. (I) (II).

Description

PROCESS TO PREPARE FLAVONES

Technical field

The present invention relates to the field of flavor ingredients. More particularly it provides a process for making 5-hydroxy-polymethoxyflavones (5-OH-PMF) or improving the organoleptic properties of polymethoxyflavones (PMF).

Prior art

The compounds of formula (I) are natural compounds known as flavor ingredients or additives. A method to obtain them in good yields and in a food compatible form is of high interest for the flavor industry.

Classically, phenols can be obtained by converting the corresponding methyl aryl ethers using reactants such as AlBr₃, AlCl₃ or BBr₃. However such methods result in a poor selectivity in case of presence of several groups which may react. Furthermore, the final product is contaminated with aluminium or boron salts which would prevent the use of the resulting phenols, here the 5-hydroxy-flavones, as food ingredients.

An alternative, disclosed in the prior art, to the above-mentioned method implies the use of a hot mixture of concentrated aqueous HCl and acetic acid (see L.Quijano et al. in Phytochemistry, 1987, 26, 2075). Although this method shows relatively good selectivity, it suffers from the fact that the use of acetic acid is undesired, especially if the final product is intended for a use as food ingredient. Indeed acetic acid is known to be difficult to be completely removed and that even trace can substantially modify the organoleptic properties of products containing it. Yields of de-methylation are not reported, however the mention that purification by chromatography is needed suggests that a significant amount of residues and/or by-products is also obtained. This is also unsuitable since the latter can alter the organoleptic properties of the resulting compound.

Other articles report the selective conversions of methyl aryl ethers into phenols, using substrates relatively different from the ones of formula (II). Said articles are the ones from M. Celia et al, in Phytochemistry (1981) pg 147, or from D.L.Dreyer et al, in Phytochemistry (1981) pg 493. However all of said prior arts disclose methods providing only very poor results when tried on the substrate of the present invention. B. Talapatra et al, in J.Indian Chem.Soc (1985) pg 408, use experimental conditions quite similar to the ones disclosed in the present invention, bur with different substrates. However this paper teaches away from the present invention since it states clearly that this method can work only for a specific isomer and is therefore not a general one. Furthermore, since the substrate used bears only one methoxy group, there is no real teaching on the selectivity of the disclosed experimental conditions and on its usefulness for the substrates of formula (II).

Description of the invention In order to solve the problems aforementioned, the present invention provides a process for making a compound of formula

wherein each R, R' or R", simultaneously or independently, represents a hydrogen atom or a OMe group and at least one R group is a OMe group; using as starting material the corresponding compound of formula (II)

wherein each R, R' or R" has the same meaning as defined in formula (I); characterized in that the compound of formula (II) is reacted with an alcoholic HCl solution at a temperature above 5O⁰C; said alcoholic HCl solution containing less than 50%, relative to its total weight, of water.

According to a particular embodiment of the invention, the above-mentioned process is advantageously used for making compounds of formula (I) wherein two or three R are OMe groups. Alternatively, or simultaneously, R" is a OMe group and one or two R' may represent a OMe group.

In particular one may cite as starting material, the following one: isosinensetin (3',4',5,7,8-pentamethoxyflavone), sinensetin (3',4',5,6,7-pentamethoxyflavone), nobiletin (3',4',5,6,7,8-hexamethoxyflavone), tangeretin (4',5, 6,7,8- pentamethoxyflavone), TOM-scutellarein (4',5,6,7-tetramethoxyflavone), HOM- quercetagenin (3',4',3,5,6,7-hexamethoxyflavone) or 3,5,6,7,8,3',4'- heptamethoxyflavone. In such a case the corresponding compounds of formula (I) are 5-desmethyl-isosinensetin (5-hydroxy-3',4',7,8-tetramethoxyflavone), 5-desmethyl- sinensetin (5-hydroxy-3',4',6,7-tetramethoxyflavone), 5-desmethyl-nobiletin (5-hydroxy- 3',4',6,7,8-pentamethoxyflavone), 5-desmethyl-tangeretin (5-hydroxy-4', 6,7,8- tetramethoxyflavone), 5-desmethyl-TOM-scutellarein (5-hydroxy-4' ,6,7- trimethoxyflavone), 5-desmethyl-HOM-quercetagenin (5-hydroxy-3',4', 3,6,7- pentamethoxyflavone) or 5-hydroxy-3,6,7,8,3' ,4'-hexamethoxyflavone.

According to a particular embodiment, the invention's process is particularly suitable for obtaining 5-desmethyl-tangeretin, from the corresponding compounds of formula (II).

As mentioned above, the invention's process is carried out by reacting a compound of formula (II) with an alcoholic HCl solution, i.e. a solution obtained by dissolving gaseous HCl in an alcohol. According to a particular embodiment of the invention, the alcohol is practically neutral from a flavor point of view, i.e. it does not significantly alter the organoleptic properties of flavoring ingredients, for example an alcohol of current use in the flavor industry.

According to an embodiment of the invention, the water content of the alcoholic solution is preferably lower, e.g. lower than 30% or of 20%, or even below 5% or 2%. Of course suitable alcohol should be in a liquid form at the reaction temperature. Non- limiting examples of alcohols are propylene glycol, benzylic alcohol or the Ci-C₄ alcohols, such as ethanol, propanol, isopropanol. In particular ethanol can be used. The HCl concentration of the HCl solution can be comprised between 0.2 N and saturation, preferably between 0.5 N and 3 N.

The process of the invention is carried out at a temperature above 5O⁰C. Advantageously, the temperature can be comprised between 7O⁰C and the reflux temperature of the medium, more preferably in the range of between 7O⁰C and 12O⁰C. However, it is also understood that the reaction could also be carried out in an autoclave at higher temperature to speed up the process, as the skilled person in the art can easily understand.

In order to obtain a compound of formula (I) which can be used as food ingredient or additive, the invention's process may also need an additional step in order to eliminate the HCl. Therefore, the invention concerns also a process as described above further comprising, at the end of the reaction, the following steps: i) elimination, by evaporation or distillation under vacuum or not, of the alcoholic HCl solution, i.e. of the alcohol and of HCl (which is a gas); and subsequently ii) optionally, the addition of a solvent of current use in the flavor industry and then, optionally, elimination by the same means of said flavor- less solvent.

Non-limiting examples of solvents currently used in the flavor industry are propylene glycol, triacetine, triethyl citrate, benzylic alcohol, ethanol, vegetal oils or terpenes. The invention's process allows to obtain the desired compound with high yields, such as at least 80% or even 90-95%. Furthermore, the product thus obtained can be food- grade and used as such, since it does not present any unsuitable off-notes, such as acetic notes.

According to an embodiment of the invention, the reaction can be carried out up to completion, so as to transform all the starting PMF in the desired product, or stopped at a desired rate of conversion so as to fine tune the organoleptic properties of the final product, which would be composed of a mixture of compounds (I) and (II). According to a particular embodiment, the invention's process can be carried out over between 2 to 100 hours, or between 5 to 100 hours or even between 10 to 90 hours. It is important to say that the invention's process can also be carried out using as starting material a mixture of compounds of formula (II) to obtain mixtures of compounds of formula (II). More surprisingly, the invention's process can also be carried out using as starting material natural extracts or fractions, such as orange oil distillation residues, which contain preferably more than 50 % w/w of compounds of formula (II).

In this way it is therefore possible to use natural products or extracts as starting materials as well as to improve their organoleptic properties. Therefore a further object of the present invention concerns a process as described above wherein the compound of formula (II) is in the form of a natural product or extract.

According to a particular embodiment of the invention, the natural extract or fraction contains up to 70% w/w or even 90% w/w of compounds of formula (II).

As can be seen in the examples, surprisingly, this method works well even using natural extract, despite the fact that such starting material may contain other natural ingredients, i.e. which are not of formula (II), which can degrade during the acidic treatment and thus produce unsuitable off-notes rendering the final product unsuitable for food applications.

Non-limiting examples of natural extracts or fractions suitable for such method or the process mentioned above are polymethoxyflavone rich fractions obtained from citrus cold press oils or other citrus by-products, such as citrus molasses extracts or citrus leaves extracts. In particular one may cite the extracts or fractions previously mentioned and obtained from oranges, tangerines and/or mandarins.

Examples

The invention will now be described in further detail by way of the following examples, wherein the abbreviations have the usual meaning in the art, the temperatures are indicated in degrees centigrade (⁰C).

Example 1

Preparation of 5-desmethylsinensetin using the invention's process

20 mg of sinensetin (synthetic sample) were refluxed in 3 ml of a HCl in ethanol (1.25 M, Fluka) for 72 hours. The ethanol was evaporated. Then fresh ethanol (3 ml) was added and evaporated. This operation was repeated two times to ensure that the product contained no remaining HCl. The product was obtained with a nearly quantitative yield. HPLC-UV-MS and ¹H and ¹³C-NMR analyses showed that it contained 91.6 % of 5-desmethylsinensetin and 2.8 % of non-reacted sinensetin (based on UV at 214 nm). Example 2

Preparation of 5-desmethyltangeretin using the invention's process 20 mg of tangeretin (synthetic sample) were refluxed in 3 ml of a HCl solution in ethanol (1.25 M, Fluka) for 130 h. The ethanol was evaporated. Then fresh ethanol (3 ml) was added and evaporated. This operation was repeated two times to ensure that the product contained no remaining HCl. The product was obtained with a nearly quantitative yield. HPLC-UV-MS and ¹H and ¹³C-NMR analyses showed that it contained 85.4 % of 5-desmethyltangeretin and 2.5 % of non-reacted tangeretin (based on UV at 214 nm).

Example 3

Preparation of a mixture of 5-desmethylpolvmethoxyflavones from a natural polymethoxyflavones-rich extract using the invention's process

Obtention of a polymethoxyflavone-rich extract

1 kg of orange cold pressed oil distillation residues (Firmenich) and dissolved in 1.5 1 of ethanol. Deionized water (3.5 1) was added under vigourous stirring. Then 1 liter of cyclohexane was added and the mixture was stirred for 30 minutes. The organic phase was decanted and further centrifuged at 4000 rpm. This process was repeated two times with 1 1 of fresh cyclohexane. After the last decantation/centrifugation step, the hydroalcoholic phase was evaporated to dryness to yield 115 g of polymethoxyflavone- rich fraction (11.5 %). This mixture contained the 6 major polymethoxyflavones known to be present in orange: sinensetin, nobiletin, tangeretin, TOM-scutellarein, HOM- quercetagenin and 3,5,6,7,8,3',4'-heptamethoxyflavone. These 6 compounds represented more than 80% of the total weight. Other minor compounds (less than 15%) were also present, in particular 5-hydroxy-polymethoxyflavones that are known to occur naturally in orange oil.

Improvement of the organoleptic properties of a polymethoxyflavone-rich extract -A)

54 g of the above obtained fraction were refluxed in 500 ml of a HCl solution in ethanol (1.25 M, Fluka) for 70 h. The ethanol was evaporated. About 100 ml of fresh ethanol were added and evaporated to dryness. This was repeated two times. 46.5 g of 5-hydroxy polymethoxyflavones-rich fraction were obtained. This fraction contained at least 85% w/w of 5-desmethyl polymethoxyflavones, relative to total flavone fraction (HPLC- UV-MS). Further HPLC purification work and NMR analyses showed the presence of 5-desmethylsinensetin, 5-desmethylnobiletin, 5-desmethyltangeretin, 5-desmethyl-TOM- scutellarein, 5-desmethyl-HOM-quercetagenin and 5-hydroxy-3,6,7,8,3\4'- hexamethoxyflavone.

Improvement of the organoleptic properties of a polymethoxy flavone -rich extract -B) 165 mg of the PMF rich fraction were refluxed over 24 hours in 1.8 ml of ethanol and 0.2 ml of concentrated aqueous. About 15 ml of water were added and the mixture was extracted two times with 5 ml of dichloromethane. The organic phase was dried over Na2SO4 and the solvent was evaporated. 124 mg (yield: 75%) of 5-hydroxy polymethoxyflavones-rich fraction were obtained. This fraction contained a proportion of 5-desmethyl polymethoxyflavones, relative to total flavones, higher than 95 % (HPLC- UV-MS).

The same result was obtained in 1.6 ml of ethanol and 0.4 ml of concentrated HCl.

Example 4

Influence of the water contents of the reacting medium

300 mg of a polymethoxyflavone-rich extract obtained in Example 3 were reacted at 8O⁰C in the presence of ethanolic HCl solutions having different amounts of water. All the different experiments were analysed by HPLC after 18 hours of reaction to monitor the progression. The results (UV-peak area) are shown in Table 1 hereinbelow:

PMF: polymethoxyflavone

As it can be seen easily, if the water content of the alcoholic HCl solution is above 50% w/w, the yield of conversion is very low and preferably said water content should be below 33% or 20%.

Example 5

A beverage base containing artificial sweeteners (BB) was prepared by admixing the following ingredients:

0.33% w/w of aspartame

0.12% sodium benzoate

0.90% citric acid

0.31% sodium citrate

98,34% water

100,00%

Then the following beverages were prepared:

BB-I: comprises BB and 20 ppm of PMF (from fraction not treated) BB-2: comprises BB and 2 ppm of 5-OH-PMF (from the fraction treated according to te invention and as disclosed in Example 3)

The attenuation of the sweet lingering taste of aspartame, compared to that of the beverage base, was evaluated for the two new beverages obtained and the best effect was observed for BB-2, despite the lower dosage. Furthermore, BB-I presented also bitter notes, to the contrary of BB-2.

If, instead of the natural extracts, were used pure tangeretin (20 ppm in the beverage base described above) or the 5-desmethyltangeretin (produced as described in example 2 and added at 20 ppm in the beverage base described above), the results indicated the same trend. The attenuation of the lingering aftertaste of aspartame was more pronounced in the case of the 5-desmethyltangeretin obtained according to the invention's process.

Claims

1. A process for making a compound of formula

wherein each R, R' or R" has the same meaning as defined in formula (I); characterized in that the compound of formula (II) is reacted with an alcoholic HCl solution at a temperature above 5O⁰C; said alcoholic HCl solution containing less than 50%, relative to its total weight, of water

2. A process according to claim 1, characterized in that two or three R are OMe groups.

3. A process according to claim 1, characterized in that the compound of formula (I) is 5-desmethyl-isosinensetin (5-hydroxy-3',4',7,8-tetramethoxyflavone), 5-desmethyl-sinensetin (5-hydroxy-3 ' ,4' ,6,7-tetramethoxyflavone), 5-desmethyl-nobiletin (5-hydroxy-3',4',6,7,8-pentamethoxyflavone), 5-desmethyl-tangeretin (5-hydroxy- 4',6,7,8-tetramethoxyflavone), 5-desmethyl-TOM-scutellarein (5-hydroxy-4',6,7- trimethoxyflavone), 5-desmethyl-HOM-quercetagenin (5-hydroxy-3',4', 3,6,7- pentamethoxyflavone) or 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone.

4 A process according to claim 1, characterized in that the water content of the alcoholic solution is lower than 30%.

5. A process according to claim 4, characterized in that the HCl concentration of the alcoholic HCl solution is comprised between 0.2 N and saturation.

6. A process according to claim 4, characterized in that the temperature is comprised between 7O⁰C and the reflux temperature of the medium.

7. A process according to claim 6, characterized in that it further comprises the following steps: i) elimination, by evaporation or distillation under vacuum or not, of the alcoholic HCl solution, i.e. of the alcohol and of HCl (which is a gas); and subsequently ii) optionally, the addition of a solvent of current use in the flavor industry and then, optionally, elimination by the same means of said flavor- less solvent.

8. A process according to claim 1, characterized in that said compound of formula (II) is in the form of a natural products or extract.

9. A process according to claim 8, characterized in that said natural product or extract is a polymethoxyflavone rich fraction obtained from citrus cold press oils.

10. A process according to claim 8, characterized in that said natural extract or fraction contains up to 70% or even 90% of compounds of formula (II).