Method for producing hydroxyalkanoic acid crystals and crystalline polymorphs of hydroxyalkanoic acid

Abstract

To provide a method for obtaining solid crystal of hydroxyalkanoic acid in high yield.SOLUTION: A method for producing hydroxyalkanoic acid crystal includes the step of lyophilizing a solution containing hydroxyalkanoic acid. With the total amount of the hydroxyalkanoic acid as 100 mass%, (1) the content of an R body is at least 95-100 mass% or (2) the content of an S body is at least 95-100 mass%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing crystalline hydroxyalkanoic acid and a crystalline polymorph of hydroxyalkanoic acid. [Background technology]

[0002] Hydroxyalkanoic acids, such as 3-hydroxybutyric acid, are attracting attention as an innovative energy source that can replace carbohydrates. They are not only an energy source, but also have an excellent effect on cognitive function and long-term memory, and are therefore considered to be effective in preventing Alzheimer's disease.

[0003] For example, 3-hydroxybutyric acid (hereinafter simply referred to as "3HB") is taken into the bloodstream by ingesting and metabolizing medium-chain fatty acids (MCT) contained in coconut oil, etc., and is converted into energy. This process converts energy more quickly than carbohydrates obtained via the glycolysis pathway, and because it suppresses the absorption of fat and sugar into cells, it is expected to be applied as an energy substance for athletes, and in the field of diet and health foods.

[0004] However, 3HB is difficult to handle in an acidic state, and is generally provided as a powder in the form of a neutral salt such as a sodium salt, calcium salt, or magnesium salt.

[0005] This is because 3HB is difficult to isolate as a solid because it does not easily crystallize when water is removed from an aqueous solution and it easily forms a dimer when water is removed.

[0006] However, ingesting a large amount of such neutralized salts results in excess salt, which is undesirable from a health perspective. Therefore, there is a need for a method for providing hydroxyalkanoic acids, including 3HB, in the form of solid crystals.

[0007] Patent Document 1 discloses a method of extracting an aqueous solution containing 3HB with an organic solvent, followed by a reduced pressure concentration step, adding seed crystals of 3HB, and using ethyl acetate as a crystallization solvent to obtain solid crystals of 3HB.

[0008] However, this method does not provide a sufficient yield of isolated 3HB, and furthermore, because it requires the use of an organic solvent, it is not particularly suitable as a method for obtaining 3HB as a supplement raw material.

[0009] Thus, there is a need for a method for obtaining hydroxyalkanoic acids in high yield. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2018-73 A Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above circumstances, an object of the present invention is to provide a method for obtaining solid crystals of a hydroxyalkanoic acid in high yield. [Means for solving the problem]

[0012] As a result of intensive research conducted by the present inventors to solve the above problems, they found that hydroxyalkanoic acid crystals can be produced in high yields by freeze-drying hydroxyalkanoic acid that is only R-isomer or has a very high content of R-isomer, or hydroxyalkanoic acid that is only S-isomer or has a very high content of S-isomer. Based on this finding, the present inventors conducted further research and completed the present invention.

[0013] That is, the present invention provides the following method for producing a hydroxyalkanoic acid. Section 1. A method for producing hydroxyalkanoic acid crystals, comprising the steps of: freeze-drying a solution containing hydroxyalkanoic acid, The total amount of the hydroxyalkanoic acid is 100% by mass, (1) The R-isomer content is 95 to 100% by mass or more, or (2) A method characterized in that the S-form content is 95 to 100% by mass or more. Section 2. Item 2. The method according to item 1, wherein the solvent in the solution containing the hydroxyalkanoic acid is a polar solvent. Section 3. Item 3. The method according to item 1 or 2, wherein the polar solvent is water. Section 4. Item 4. The method according to any one of Items 1 to 3, wherein the hydroxyalkanoic acid is 3-hydroxybutyric acid. Section 5. A crystalline polymorph of hydroxyalkanoic acid having diffraction peaks at 2θ=11.9±0.2°, 12.1±0.2°, 15.0±0.2°, 18.8±0.2°, and 20.9±0.2° in a powder X-ray diffraction pattern. Section 6. Item 6. The crystalline polymorph according to item 5, wherein peak angle I is the largest at a diffraction angle 2θ=12.1±0.2°. Section 7. Item 5. The crystalline polymorph of item 5 or 6, wherein the hydroxyalkanoic acid is 3-hydroxybutyric acid. Effect of the Invention

[0014] According to the method for producing a hydroxyalkanoic acid of the present invention described above, solid crystals of a hydroxyalkanoic acid can be produced in high yield. [Brief description of the drawings]

[0015] [Figure 1] 1 is a photograph of 3-hydroxybutyric acid crystals of Example 1. [Diagram 2] 1 is a powder X-ray diffraction pattern of the 3-hydroxybutyric acid crystals of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] (1. Method for producing hydroxyalkanoic acid crystals) The method for producing hydroxyalkanoic acid crystals of the present invention includes a step of freeze-drying a solution containing a hydroxyalkanoic acid.

[0017] More specifically, hydroxyalkanoic acids include 3HB, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, and lactic acid, but are not limited to these.

[0018] In addition, the hydroxyalkanoic acid contained in the solution is such that, in a total amount of 100% by mass of the hydroxyalkanoic acid, the R-form of the hydroxyalkanoic acid is contained in an amount of 95% by mass or more, or the S-form of the hydroxyalkanoic acid is contained in an amount of 95% by mass or more. If either the R-form or the S-form does not reach the lower limit, the final target crystal cannot be obtained. Furthermore, the content of both the R-form and the S-form contained in the total amount of the hydroxyalkanoic acid is preferably 97% by mass or more, more preferably 99% by mass or more. The upper limit of these values ​​can be set to 100% by mass.

[0019] The solution containing hydroxyalkanoic acid may contain substances other than hydroxyalkanoic acid. However, from the viewpoint of obtaining hydroxyalkanoic acid crystals in high yield and high purity, it is preferable that the solution contains only hydroxyalkanoic acid.

[0020] The solvent used in the solution containing hydroxyalkanoic acid is preferably a polar solvent. As such polar solvent, known polar solvents such as water, ether solvents such as diethyl ether, tetrahydrofuran, and dioxane, alcohol solvents such as ethanol and butanol (preferably t-butanol), and amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide can be used. Only one of these may be used alone, or two or more may be mixed and used. However, considering that the final target hydroxyalkanoic acid crystals are used for applications such as supplements, it is preferable to use water and / or ethanol as the polar solvent.

[0021] The method for obtaining a solution containing hydroxyalkanoic acid is not particularly limited, and any known method can be widely adopted, and is not particularly limited. The solution may be obtained by dissolving hydroxyalkanoic acid in a solvent, or by chemical synthesis. Alternatively, the solution containing hydroxyalkanoic acid may be obtained by a microbiological method.

[0022] The content (concentration) of hydroxyalkanoic acid in the solution containing hydroxyalkanoic acid is preferably 1 to 60 mass%, and more preferably 10 to 40 mass%, in consideration of reducing the adverse effect of freezing point depression while ensuring good production efficiency.

[0023] In the step of freeze-drying a solution containing a hydroxyalkanoic acid, the temperature and pressure are not particularly limited, but the solution is first frozen at a temperature of preferably -80 to -5°C, more preferably -50 to -20°C, and then freeze-dried at a vacuum of preferably 10 to 110 Pa.

[0024] (2. Crystalline polymorphs of hydroxyalkanoic acids) The present invention includes an invention relating to a method for producing a crystalline polymorph of a hydroxyalkanoic acid.

[0025] Hydroxyalkanoic acids can specifically include 3HB, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, and lactic acid, and more specifically can include R-hydroxybutyric acid, but are not limited to these.

[0026] The crystalline polymorph of the present invention has diffraction peaks at 2θ=11.9±0.2°, 12.1±0.2°, 15.0±0.2°, 18.8±0.2°, and 20.9±0.2° in the powder X-ray diffraction pattern. Of these four peaks, it is preferred that the peak angle I at the diffraction angle 2θ=12.1±0.2° is the largest.

[0027] Specifically, such a powder X-ray diffraction pattern may be measured under conditions of a CuKα X-ray tube and a measurement angle of 5 to 85°.

[0028] Such a crystalline polymorph can be obtained, for example, by the above-mentioned method for producing a hydroxyalkanoic acid, and has the advantage of being less deliquescent than conventionally known crystalline forms. For example, a crystalline polymorph of 3-hydroxybutyric acid does not deliquesce even when left in the air for 3 days.

[0029] Although the embodiment of the present invention has been described above, the present invention is not limited to these examples, and it is needless to say that the present invention can be embodied in various forms without departing from the gist of the present invention. EXAMPLES

[0030] Hereinafter, the embodiments of the present invention will be described more specifically based on examples, but the present invention is not limited to these.

[0031] Preparation of hydroxyalkanoic acid aqueous solution The R-3-hydroxybutyric acid or S-3-hydroxybutyric acid used in the following examples or comparative examples was produced according to the method described in JP 2019-176839 A. The purity of the obtained R-isomer and S-isomer was 99% ee or more by HPLC measurement.

[0032] Example 1 2 g of R-3-hydroxybutyric acid (R-3HB) and 8 g of distilled water were mixed in a vial and heated in a 60°C water bath to completely dissolve the R-3HB. This was transferred to a 100 mL flask and completely frozen in a -30°C freezer. The mixture was then freeze-dried overnight at a pressure of 110 Pa or less in a room controlled at 25°C to obtain R-3HB crystals with a yield of 99% or more (Figure 1). A Tokyo Rikakikai FREEZEDRYER FD-1 freeze dryer was used.

[0033] The X-ray diffraction pattern of the R-3HB crystals obtained in Example 1 was measured using an X-ray diffraction measurement device (Rigaku Smart Lab) under conditions of an X-ray tube CuKα and a measurement angle of 5 to 85°, and is shown in Figure 2. Furthermore, even when 1 g of the crystals was placed on a petri dish and allowed to stand in a room at 35 to 40% RH for 3 days, no clear deliquescence was observed, confirming that the crystals obtained in Example 1 have low deliquescence.

[0034] Example 2 Crystals of S-3HB were obtained in a yield of 99% or more by the same method as in Example 1, except that R-3HB was replaced with S-3-hydroxybutyric acid (S-3HB).

[0035] Example 3 R-3HB crystals were obtained in a yield of 99% or more by the same method as in Example 1, except that the amount of R-3HB and the amount of distilled water were changed to 1 g and 9 g, respectively.

[0036] Example 4 R-3HB crystals were obtained in a yield of 99% or more by the same method as in Example 1, except that the amount of R-3HB and the amount of distilled water were changed to 3 g and 7 g, respectively.

[0037] Comparative Example 1 1 g of R-3HB, 1 g of S-3HB, and 8 g of distilled water were mixed in a vial and heated in a water bath at 60°C to completely dissolve R-3HB and S-3HB. The resulting solution was transferred to a 100 mL flask and completely frozen in a -30°C freezer, after which it was freeze-dried overnight at a pressure of 110 Pa or less in a room controlled at 25°C, but no crystallization occurred and the solution remained liquid.

[0038] Comparative Example 2 5 g of R-3HB and 1.5 g of ethyl acetate were mixed in a vial and heated in a 60°C water bath to completely dissolve the R-3HB. The mixture was returned to room temperature, one seed crystal of R-3HB was added, and the mixture was left to stand overnight in a 4°C refrigerator, whereupon R-3HB crystals precipitated. The crystals were isolated by filtration and weighed, revealing a yield of approximately 60%.

[0039] Comparative Example 3 100mL of an aqueous solution containing 10% by mass of R-3HB was concentrated using an evaporator at 70°C until no water was produced. High performance liquid chromatography (HPLC) revealed that this concentrated solution contained approximately 8% 3HB dimer by area ratio. When R-3HB seed crystals were added to this, it did not completely crystallize and remained in a semi-solid state. For the HPLC, a Hitachi High-Tech Science Chromaster was equipped with an Agilent Metacarb67H column, and 2.5mmol / L sulfuric acid aqueous solution was used as the mobile phase, and measurements were made using an RI detector.

Claims

1. A method for producing a crystal of 3-hydroxybutyric acid having diffraction peaks at 2θ=11.9±0.2°, 12.1±0.2°, 15.0±0.2°, 18.8±0.2°, and 20.9±0.2° in a powder X-ray diffraction pattern, comprising: The method includes a step of freezing a solution containing 3-hydroxybutyric acid at a temperature of −80 to −5° C. and then freeze-drying the solution at a vacuum of 10 to 110 Pa, The total amount of the 3-hydroxybutyric acid crystals is 100% by mass. (1) The R-isomer content is 95 to 100% by mass or more, or (2) The method, characterized in that the S-isomer content is 95 to 100% by mass or more.

2. The method according to claim 1, wherein the solvent in the solution containing 3-hydroxybutyric acid is a polar solvent.

3. The method according to claim 1 or 2, wherein the polar solvent is water.

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