New astaxanthin synthesis

Abstract

The present invention relates to a new process for producing astaxanthin.

Description

[0001] Confidential Case 34619-WO-PCT New Astaxanthin Synthesis The present invention relates to a new process for producing astaxanthin. Astaxanthin, which is the compound of the following formula (I), is a keto-carotenoid within a group of chemical compounds known as terpenes. It is a lipid- soluble pigment with red coloring properties, which result from the extended chain of conjugated (alternating double and single) double bonds at the center of the compound. Astaxanthin is a natural pigment which is used for coloring foodstuffs, salmon and trout. Astaxanthin can be sourced from natural sources (by extraction / isolation). Alternatively, astaxanthin can be synthesised (bio)chemically. Accordingly, a large number of methods is known for the isolation or synthesis of astaxanthin. Thus, for example, the isolation of astaxanthin by extraction from crustacean shells is known from the prior art (i.e. from WO8606082 A1). Alternatively, astaxanthin can be obtained by fermentation processes or from micro- algae. Furthermore, it is possible to produce astaxanthin by chemical synthesis. A very common and widely described way to produce astaxanthin is shown in the following reaction scheme Confidential 34619-WO-PCT . The disadvantage of the process according to the prior art (e.g., in Widmer et al. Helvetica Chimica Acta, Vol 64, no.7, 1981; 2436-2446) is that one or more of the steps of the process (step (i), step (ii) and / or step (iii)) is / are carried out in a halogenated solvent. Most halogenated solvents are persistent in air and / or sediment, are ozone-depleting chemicals and / or contribute to the generation of greenhouse gases. Due to these concerns, stricter regulations have been enforced, leading many halogenated solvent users to investigate possible alternatives. Confidential 34619-WO-PCT Although in chemical syntheses, halogenated solvents have several advantages over non-halogenated solvents, as they have relatively low boiling points and are inert, thus can be used in highly reactive reactions, there is an urgent need to avoid such halogenated solvents. However, it is difficult to replace halogenated solvents by non-halogenated solvents, particularly in the above-mentioned optimised reactions, due to its harsh conditions such as described in Widmer et al. The goal of the present invention is to achieve a process, wherein all steps are carried out in a non-halogenated solvent and wherein the yield of astaxanthin is as good as reported in the prior art using the halogenated solvents. Surprisingly, it was found that when, contrary to the recommendations of Widmer et al., instead of HBr – HCl is used in the first step (i) then it becomes possible to carry out all steps in non-halogenated solvents (see following reaction scheme):

[0002] Confidential 34619-WO-PCT , Furthermore, another advantage of the present invention lies therein that the compound of formula (III), contrary to the corresponding compound with a bromine substituent, is stable and can be isolated. Only the fact that the compound of formula (III) can be isolated allows the required solvent change after step (i), which is required if a non-inert solvent must be used in at least one of the steps. This would not have been the case if HBr was used instead of HCl in step (i). The change of solvent is necessary because there is no non-halogenated solvent having the same properties that halogenated solvents offer to optimise the conditions of this reaction and that could be used in both, step (i) and (ii) of Confidential 34619-WO-PCT the reaction scheme above. The boiling points of the non-halogenated solvent should be as low as possible, preferably below 100°C, more preferably below 80°C. Therefore, the present invention relates to a process (P) for producing the compound of formula (I) , wherein a first step (i), the compound of formula (II) is reacted with HCl in at least one solvent chosen from the group consisting of hydrocarbons and carbonates, and afterwards in step (ii) the reaction product of step (i), which is the compound of formula (III) Confidential 34619-WO-PCT is reacted with triphenylphosphine in at least one solvent chosen from the group consisting of acetonitrile and C1-C8-alcohols, thereof preferably methanol, ethanol, n-propanol and isopropanol, and afterwards in step (iii) the reaction product of step (ii), which is the compound of formula (IV) is reacted with the compound of formula (V) in at least one solvent chosen from the group consisting of toluene and C1-C8-alcohols, thereof preferably methanol, ethanol, n-propanol and isopropanol, in the presence of at least one base. As stated above the present invention is carried in solvents, which are non-halogenated. In the following, the various steps of the present invention are discussed in more details. Step (i) The reaction process of step (i) is the following . Confidential 34619-WO-PCT As stated above this process step is carried out in at least one solvent chosen from the group consisting of hydrocarbons and carbonates. The hydrocarbons can be aliphatic as well as aromatic. The hydrocarbons can be linear or branched as well as cyclic. Preferably, the hydrocarbons are chosen from the group consisting of n-hexane, n- heptane and toluene. Also preferred are carbonates, such as dialkyl carbonates, preferably diethyl carbonate. Therefore, the present invention also relates to a process, wherein the at least one solvent is chosen from the group consisting of aliphatic hydrocarbons, aromatic hydrocarbons and dialkyl carbonates. Therefore, the present invention also relates to a process, wherein the at least one solvent is chosen from the group consisting of n-hexane, n-heptane, toluene and diethyl carbonate. The reaction process of step (i) is carried by reacting the compound of formula (II) with HCl. HCl can be added as gas and / or as an aqueous solution. Preferably, HCl is added as an aqueous solution. HCl is added in an at least equimolar amount (in regard of the compound of formula (II)). Usually and preferably HCl is added in a molar excess in regard to the compound of formula (II). Usually and preferably the molar ratio of HCl to the compound of formula (II) is at least 1.2:1. Usually and preferably, the molar ratio of HCl to the compound of formula (II) is up 15:1. A preferred range of the molar ratio of HCl to the compound of formula (II) is 1.2:1 to 15:1, more preferred, 1.2:1 to 10:1. Confidential 34619-WO-PCT Therefore, the present invention also relates to a process, wherein HCl is added in gaseous form to the reaction mixture of step (i). Therefore, the present invention also relates to a process, wherein HCl is added as an aqueous solution to the reaction mixture of step (i). Therefore, the present invention also relates to a process, wherein HCl is added in an equimolar ratio (in regard to the compound of formula (II)) to the reaction mixture of step (i). Therefore, the present invention also relates to a process, wherein the molar ratio of HCl to the compound of formula (II) is at least 1.2:1 in step (i). Therefore, the present invention also relates to a process, wherein the molar ratio of HCl to the compound of formula (II) is up 15:1 in step (i). Therefore, the present invention also relates to a process, wherein the molar ratio of HCl to the compound of formula (II) is 1.2:1 to 15:1 in step (i). Therefore, the present invention also relates to a process, wherein the molar ratio of HCl to the compound of formula (II) is 1.2:1 to 10:1 in step (i). The reaction process of step (i) is usually carried out at lower temperature. Usually, the reaction process of step (i) is carried out at a temperature of -20°C to 10°C. Preferably, the reaction process of step (i) is carried out at a temperature of -10°C to 5°C. Therefore, the present invention also relates to a process, wherein the reaction process of step (i) is carried out at a temperature of -20°C to 10°C, preferably -10°C to 5°C. The reaction time of the reaction process of step (i) is usually from 30 minutes up to several hours. After the reaction process of the step (i) the reaction product, which is the compound of formula (III) can be isolated from the reaction mixture. Confidential 34619-WO-PCT This can be done by using commonly known processes. The compound of formula (III) can also be further purified. As stated above the compound of formula (III) is a stable compound and can be isolated easily. This is not possible with the compound of the prior art of the following formula . This compound of the prior art is not stable and therefore, it is not possible to isolate it in a sufficient manner. Without isolating this compound, the required exchange of the solvent is not easy to achieve. Furthermore, the compound of formula (III) is a new compound. Therefore, a further embodiment of the present invention is the compound of formula (III) . If step (ii) is carried out in the same solvent (or mixture of solvents) as step (i) the isolation step could be skipped. Step (ii) Confidential 34619-WO-PCT The reaction process of step (ii) is carried out in at least one solvent chosen from the group consisting of acetonitrile and C1-C8-alcohols, thereof preferably methanol, ethanol, n-propanol and isopropanol. The reaction process of step (ii) is carried by reacting the compound of formula (III) with triphenylphosphine. Usually, triphenylphosphine is added in about an equimolar amount (in regard of the compound of formula (III)). Usually, triphenylphosphine is added in a slight molar excess in regard to the compound of formula (III). Usually and preferably the molar ratio of triphenylphosphine to the compound of formula (III) is 1:1 to 2:1. Therefore, the present invention also relates to a process, wherein triphenylphosphine is added in an equimolar ratio (in regard to the compound of formula (III)) to the reaction mixture of step (ii). Therefore, the present invention also relates to a process, wherein the molar ratio of triphenylphosphine to the compound of formula (III) is 1:1 to 2:1 in step (ii). The reaction process of step (ii) is usually carried out at a temperature of 10°C to 80°C. Usually, the reaction process of step (ii) is carried out at a temperature of 20°C to 60°C. Preferably, the reaction process of step (ii) is carried out at a temperature of 30°C to 60°C. Confidential 34619-WO-PCT Therefore, the present invention also relates to a process, wherein the reaction process of step (ii) is carried out at a temperature of 10°C to 80°C. Therefore, the present invention also relates to a process, wherein the reaction process of step (ii) is carried out at a temperature of 20°C to 60°C. Therefore, the present invention also relates to a process, wherein the reaction process of step (ii) is carried out at a temperature of 30°C to 60°C. The reaction time of the reaction process of step (ii) is usually from 60 minutes up to several hours. Usually, after this reaction has been carried out (after 60 minutes up to several hours) a solvent change is carried out and the so-obtained reaction mixture is applied to an elevated temperature (50°C – 100°C). Afterwards, the reaction product, which is the compound of formula (IV) can be isolated from the reaction mixture. This can be done by using commonly known processes. The compound of formula (IV) can also be further purified. If step (iii) is carried out in the same solvent (or mixture of solvents) as step (ii) the isolation step could be skipped. Step (iii)

[0003] Confidential 34619-WO-PCT The reaction process of step (iii) is carried out in at least one solvent chosen from the group consisting of toluene and C1-C8-alcohols, thereof preferably methanol, ethanol, n- propanol and isopropanol. The reaction process of step (iii) is carried by reacting the compound of formula (IV) with the compound of formula (V) to get astaxanthin (compound of formula (I)). Usually, the compound of formula (IV) is added in a molar excess in regard to the compound of formula (V). Usually and preferably the molar ratio of triphenylphosphine to the compound of formula (III) is 2:1 to 4:1. Therefore, the present invention also relates to a process, wherein the molar ratio of the compound of formula (IV) to the compound of formula (V) is 1:1 to 4:1 in step (iii). Step (iii) is carried out in the presence of at least one base. Suitable bases are solutions of alkali metal or alkaline earth metal alkoxides or alkali metal or alkaline earth metal hydroxides in methanol or ethanol, alkali metal or alkaline earth metal hydroxides, ammonia, triethylamine, and alkali metal or alkaline earth metal carbonates. More preferred bases are aqueous solution of NaOH or KOH, a methanolic sodium methoxide solution or an ethanolic sodium ethoxide solution. Confidential 34619-WO-PCT Therefore, the present invention also relates to a process, wherein the at least one base is chosen from the group consisting of solutions of alkali metal, solutions of alkaline earth metal alkoxides, solutions of alkali meta, solutions of alkaline earth metal hydroxides in methanol or ethanol, alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, triethylamine, alkali metal carbonates and alkaline earth metal carbonates. Therefore, the present invention also relates to a process, wherein the at least on base is chosen from the group consisting of aqueous solution of NaOH, aqueous solution of KOH, a methanolic sodium methoxide solution and an ethanolic sodium ethoxide solution. The molar ratio of the at least one base to the compound of formula (IV) is 1 to 1.5 preferably 1 to 1.2. Therefore, the present invention also relates to a process, wherein the molar ratio of the at least one base to the compound of formula (IV) is 1 to 1.5. Therefore, the present invention also relates to a process, wherein the molar ratio of the at least one base to the compound of formula (IV) is 1 to 1.2. The reaction process of step (iii) is usually carried out at a temperature of -10°C to 20°C, preferably at a temperature of -10°C to 10°C, more preferably at a temperature of -5°C to 10°C, when the at least one base is added to the reaction mixture. The reaction mixture is stirred for about 30 minutes to a few hours at this temperature range. Afterwards (after having reaction at a temperature of -10°C to 20°C) the reaction mixture is heated up to elevated temperature for a few hours. The temperature range is 30°C to 120°C. Therefore, the present invention also relates to a process, wherein the reaction process of step (iii) is first carried out at a temperature of -10°C to 20°C. Therefore, the present invention also relates to a process, wherein the reaction process of step (iii) is first carried out at a temperature of -10°C to 10°C. Confidential 34619-WO-PCT Therefore, the present invention also relates to a process, wherein the reaction process of step (iii) is first carried out at a temperature of -5°C to 10°C. Therefore, the present invention also relates to a process, wherein the reaction mixture of step (iii) is heated up to 30°C to 120°C after the reaction of step (iii) has been carried out at -10°C to 20°C. After the reaction process of the step (iii) the reaction product, which is the compound of formula (I) can be isolated from the reaction mixture. This can be done by using commonly known processes. The compound of formula (I) can also be further purified. The following Examples illustrate the invention further without limiting it. All percentages and parts, which are given, are related to the weight and the temperatures are given in °C, and the pressures are absolute pressures when not otherwise stated. The details, examples and preferences provided in relation to any particular one or more of the stated aspects of the present invention further described herein apply equally to all aspects of the present invention. Any combination of the embodiments, examples and preferences described herein in all possible variations thereof is encompassed by the present invention unless otherwise indicated herein, or otherwise clearly contradicted by context.

[0004] Confidential 34619-WO-PCT EXAMPLES Example 1 Step (i) Under inert gas atmosphere, ketolyl dienol (KDL; compound of formula (II)) (289.2 mmol) was suspended in toluene (188 mL) and cooled to 1°C. Within 60 min, aqueous HCl (37%) (4.32 eq., 1249 mmol) were added, so that the temperature did not exceed 2°C. After stirring the brown solution at 0°C for another 30 min. Water (200 mL) was added. The organic layer was separated and washed with water to neutral pH. The aqueous layers were re-extracted with toluene (100 mL). The organic layers were combined, dried over sodium sulphate, filtered and concentrated under reduced pressure (rotavap at 25°C water-bath temperature) and in high vacuum (15 min). KDL chloride was obtained as dark-brown oil in 94.4 % yield. The reaction of step (i) was also carried out in methanol, tert-butyl methyl ether, cyclohexane, and acetic acid, wherein the yield of KDL chloride was very low. Step (ii) Under argon atmosphere, the freshly prepared KDL chloride of step (i) (compound of formula (III)) was dissolved in 1-propanol (378 mL), and triphenylphosphine (84.95 g, 1.11 eq., 320.64 mmol) was added. After stirring at 40°C for 20 hours. The dark-orange solution (503.77 g) was concentrated on a rotavap at 35°C to 243.7 g. Then, ethyl acetate (150 mL) was added to dissolve the viscous oil. Another portion of ethyl acetate (350 mL) was added to crystallise the product (fine, yellow crystals). The slurry was heated to reflux and stirred for 1 hour. After that, the suspension was cooled to room temperature and then cooled to 0°C. The suspension was filtered, and the filter cake was rinsed with ethyl acetate (2x 50 mL). The crystalline material was dried in vacuum at 50°C overnight. The phosphonium salt (compound of formula (IV)) was obtained as pale-yellow crystals (121.48 g) in 75.5% yield. Another 10.9% yield were detected in the mother liquor. This corresponds to 86.4% total yield (based on KDL). Confidential 34619-WO-PCT The following table shows the yields of step (ii), wherein the reaction of step (ii) was carried out in the same way as described above but in different solvents. Solvent yield methanol 83.0 ethanol 81.4 isopropanol 73.7 1-pentanol 77 1-butanol 60.0 toluene 0.7 Diethyl carbonate --- THF --- tert-butyl methyl ether --- n-heptane --- ethyl acetate --- As can be seen, the reaction of step (ii) is not working in toluene, diethyl carbonate, THF, tert-butyl methyl ether, n-heptane and ethyl acetate as a solvent. Step (iii) Under inert gas atmosphere, the astenyl salt obtained in step (ii) (compound of formula (IV) (86.18 g, 2.04 eq.155.0 mmol) was dissolved in 1-propanol (300 mL) and cooled to 0°C. Then, C10-dialdehyde (compound of formula (V) (12.94 g, 1.00 eq., 75.98 mmol) was added. To the yellow suspension was added sodium ethoxide (55.9 mL, 21.5% in ethanol, 2.04 eq.155.0 mmol) drop wise over 5 hours. After addition was complete, stirring was continued for another 2 hours at 0°C. Formic acid (3.07 mL, 1.05 eq., 79.78 mmol) was added drop wise. The reaction mixture was heated to reflux and part of the solvent (80 mL) was removed by distillation and replaced by 1-propanol (80 mL). The dark-red suspension was heated to 97°C for 17 hours, then cooled to room temperature, stirred for another 1 hour, and filtered. The filter cake was rinsed with 1-propanol (2x 60 mL) and water (3x 60 mL). The obtained crystalline material was dried in vacuum at 60°C for 16 hours. The crude astaxanthin (compound of formula (I)) (40.59 g, 93.19 wt%) was obtained as dark-purple crystals in 83.4% yield. Confidential 34619-WO-PCT After extraction and removal of solvent, another 1.56% yield were detected in the mother liquor. This corresponds to a total yield of 85.0% (based on C10- dialdehyde). The crude astaxanthin was recrystallized from acetone / methanol / water 70:25:5 in an autoclave at 96°C for 5 hours, followed by another 1 hour at room temperature. After filtration and drying (60°C, 14 hours) the purified product was obtained in 98.4% crystallisation yield (based on the crude material) and high purity of 96.45 wt%. The reaction of step (iii) was also carried out in methanol, ethanol, THF and 1- butanol, wherein the yields were similar to those achieved in 1-propanol.

Claims

Confidential 34619-WO-PCT CLAIMS 1. Process for producing the compound of formula (I), wherein a first step (i), the compound of formula (II) is reacted with HCl in at least one solvent chosen from the group consisting of hydrocarbons and carbonates, and afterwards in step (ii) the reaction product of step (i), which is the compound of formula (III)is reacted with triphenylphosphine in at least one solvent chosen from the group consisting of acetonitrile and C1-C8-alcohols, thereof preferably methanol, ethanol, n-Confidential 34619-WO-PCT propanol and isopropanol, and afterwards in step (iii) the reaction product of step (ii), which is the compound of formula (IV)is reacted with the compound of formula (V)in at least one solvent chosen from the group consisting of toluene and C1-C8- alcohols, thereof preferably methanol, ethanol, n-propanol and isopropanol, in the presence of at least one base.

2. Process according to claim 1, wherein HCl is added in gaseous form to the reaction mixture of step (i).

3. Process according to claim 1, wherein HCl is added as an aqueous solution to the reaction mixture of step (i).

4. Process according to any of the preceding claims, wherein HCl is added in an equimolar ratio (in regard to the compound of formula (II)).

5. Process according to any of claims 1 – 3, wherein the molar ratio of HCl to the compound of formula (II) is 2:1 to 15:1 in step (i).

6. Process according to any of the preceding claims, wherein the reaction process of step (i) is carried out at a temperature of -20°C to 10°C.

7. Process according to any of the preceding claims, wherein triphenylphosphine is added in an equimolar ratio (in regard to the compound of formula (III)) to the reaction mixture of step (ii).Confidential 34619-WO-PCT 8. Process according to any of claims 1 – 6, wherein the molar ratio of triphenylphosphine to the compound of formula (III) is 1:1 to 2:1 in step (ii).

9. Process according to any of the preceding claims, wherein the reaction process of step (ii) is usually carried out at a temperature of 10°C to 80°C.

10. Process according to any of the preceding claims, wherein the compound of formula (IV) is added in an equimolar ratio (in regard to the compound of formula (V)) to the reaction mixture of step (iii).

11. Process according to any of claims 1 – 9, wherein the molar ratio of the compound of formula (IV) to the compound of formula (V) is a1:1 to 4:1 in step (i).

12. Process according to any of the preceding claims, wherein the at least one base in step (iii) is chosen from the group consisting of solutions of alkali metal, solutions of alkaline earth metal alkoxides, solutions of alkali meta, solutions of alkaline earth metal hydroxides in methanol or ethanol, alkali metal hydroxides, alkaline earth metal hydroxides, ammonia, triethylamine, alkali metal carbonates and alkaline earth metal carbonates.

13. Compound of formula (III).

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