Method for producing α-hydroxyesters by Grignard coupling reaction and thiolation reaction

Abstract

The present disclosure provides methods for preparing α-hydroxy esters by adding a vinyl Grignard reagent to an oxalate ester and thiolating the resulting double bond. Also provided are α-hydroxy esters and synthetic intermediates prepared according to the methods disclosed herein, as well as compositions containing the α-hydroxy esters.

Description

[Technical Field]

[0001] Related applications This application claims priority to International Application PCT / CN2019 / 120393, filed on 22 November 2019, which is incorporated herein by reference in its entirety for any purpose.

[0002] This disclosure provides a method for producing α-hydroxyesters by adding a vinyl Grignard reagent to an oxalic acid ester and thiolation of the resulting double bond. Also provided herein are α-hydroxyesters and synthetic intermediates produced according to the method disclosed herein, compositions containing the α-hydroxyester, and methods for using the compositions. [Background technology]

[0003] Alpha-hydroxy ester analogs of natural amino acids are useful as nutritional supplements and in the study of enzymatic processes and protein function. The synthesis of such esters typically involves acid-catalyzed Fischer esterification of the corresponding acid with an alcohol in the presence of a strong acid such as H2SO4 or Amberlyst® cation exchange resin; acid-mediated hydrolysis of the corresponding nitrile in the presence of a strong acid; or enzymatically mediated methods. However, acid-catalyzed methods result in the decomposition of starting materials and products, as well as contamination of the product with dimeric and oligomeric components. These methods generally yield low yields, and complex purification techniques are required to isolate the target compound from polymer by-products. Enzymatic methods require expensive and unstable reagents and special reaction conditions.

[0004] A particularly important α-hydroxy ester is isopropyl 2-hydroxy-4-(methylthio)butyrate (HMBi). HMBi is the isopropyl ester of 2-hydroxy-4-(methylthio)butyric acid (HMBA), a hydroxy analog of methionine. HMBi is used to help supplement methionine in ruminant animals such as cattle. Achieving adequate levels of methionine in dairy cows helps maintain desirable levels of milk protein synthesis and, by extension, desirable levels of milk production. However, the methionine content in animal feed is significantly insufficient and is a major limiting factor in the diet of dairy cows. HMBi is a chemical derivative of methionine that diffuses easily and rapidly through the rumen wall and avoids degradation by rumen microorganisms. Once it passes through the rumen wall, HMBi is metabolized in the liver and becomes available for milk protein synthesis in dairy cows.

[0005] There is a need for additional methods for synthesizing α-hydroxy esters such as HMBi that use inexpensive and non-toxic reagents and mild reaction conditions and provide the ester product in high yield and high purity. SUMMARY OF THE INVENTION

[0006] In one aspect, the present disclosure provides Formula (I):

Chemical formula

Chemical formula

[0007] In one embodiment, the present disclosure relates to a method for producing a compound of formula (I), Formula (II): [ka] The above method includes reducing the compound with a reducing agent to form the compound of formula (I).

[0008] In some embodiments, the compound of formula (I) above is of formula (IA): [ka] It is a compound of [the compound].

[0009] In another embodiment, this disclosure relates to formula (IA): [ka] A method for producing the compound, Esterilizing oxalic acid with isopropanol to form diisopropyl oxalate, Diisopropyl oxalate is coupled with vinyl magnesium bromide to form formula (III-A): [ka] To form the compound, The compound of formula (III-A) above is thiolated with CH3SH to obtain formula (II-A): [ka] To form the compound, The compound of formula (II-A) above is reduced to form the compound of formula (IA) above. The above methods, including those mentioned above, are included.

[0010] In another embodiment, this disclosure covers compounds of formula (I) or formula (IA) prepared as in any of the methods described herein.

[0011] In another embodiment, this disclosure relates to isopropyl 2-oxobuta-3-enoate.

[0012] In another embodiment, this disclosure relates to animal feed compositions comprising a compound of formula (I) or formula (IA) as described herein. In some embodiments, the animal feed is cattle feed, such as dairy cow feed.

[0013] In another embodiment, the disclosure relates to a method for supplying bioavailable methionine to dairy cows, comprising administering to the cows a compound of formula (I) or formula (IA) or an animal feed composition as described herein. In another embodiment, the disclosure relates to a method for supplying at least about 50% bioavailable methionine to dairy cows, comprising administering to the cows a compound of formula (I) or formula (IA) or an animal feed composition as described herein. In another embodiment, the disclosure relates to a method for improving milk obtained from dairy cows, comprising administering to the cows a compound of formula (I) or formula (IA) or an animal feed composition as described herein.

[0014] In another embodiment, the present disclosure relates to a method for improving the condition of cattle, which comprises supplying the cattle with a compound of formula (I) or formula (IA) described herein or an animal feed composition.

Brief Description of the Drawings

[0015] [Figure 1A] Figure 1A is the 13C NMR spectrum of diisopropyl oxalate described in Example 1. [Figure 1B] Figure 1B is the 1H NMR spectrum of diisopropyl oxalate described in Example 1. [Figure 2A] Figure 2A is the 13C NMR spectrum of isopropyl 2-oxo-4-methylthiobutanoate described in Example 3. <​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0018] In this specification, the terms "2-hydroxy-4-(methylthio)butanoate," "2-hydroxy-4-(methylthio)butanoic acid," and "HMBA" refer to compounds having the following structure. [ka]

[0019] The compounds described herein may exist in racemic form, as a single enantiomer, or as a mixture of enantiomers. Therefore, for example, HMBi refers to racemic HMBi (i.e., "DL-HMBi"), or D-HMBi or L-HMBi, or a mixture thereof.

[0020] The compounds described herein may also exist in salt form. The chemical formulas shown herein should be understood to encompass both the shown structure and their salt forms. For example, if a compound contains a carboxylic acid, the formula also encompasses the salt form of its conjugate base (carboxylate salt), such as a sodium salt, potassium salt, magnesium salt, or calcium salt. If a compound contains an indole group or an imidazole group, the formula also encompasses the salt of its conjugate acid, such as an HCl salt.

[0021] "Alkyl" refers to linear, saturated, monovalent hydrocarbon radicals with 1 to 8 carbon atoms (e.g., 1 to 6 carbon atoms, 1 to 4 carbon atoms, or 1 to 3 carbon atoms), or branched, saturated, monovalent hydrocarbon radicals with 3 to 8 carbon atoms (e.g., 3 to 6 carbon atoms, 3 to 4 carbon atoms, or 3 carbon atoms), such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl (including all isomers).

[0022] "Cycloalkyl" refers to a cyclic, saturated, monovalent hydrocarbon radical with 3 to 10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, or cyclohexyl.

[0023] "Optional" or "optionally" means that the event or situation described thereafter may occur, but is not necessarily required, and that the above description encompasses both cases in which the event or situation occurs and cases in which it does not. For example, "optionally -OH-substituted alkyl group" means that -OH may be present, but is not necessarily required, and that the above description encompasses both the situation in which the alkyl group is substituted with an -OH group and the situation in which the alkyl group is not substituted with an -OH group.

[0024] The term "reaction solvent" refers to an organic liquid used as a carrier for the dissolved reactants. In some embodiments, one of the reactants in the reaction functions as both a reactant and a reaction solvent. In other embodiments, the reactant is diluted with a different reaction solvent.

[0025] The term "acid catalyst" refers to an acid added to a reaction in a substoichiometric amount that has the function of catalyzing the reaction. The acid catalyst may be a Brønsted acid (an acid with a pKa of less than 7, such as HCl, H2SO4, KHSO4, acetic acid, etc.) or a Lewis acid (such as a boronic acid). In some embodiments, the above acid is produced in situ, for example, by the reaction of acetyl chloride or TMSCl with water or an alcohol.

[0026] The term "concentration" refers to the amount of solute in a solvent. In this specification, concentration may be expressed in weight percent, molar concentration (M), or normality (N).

[0027] The term "heptane" or "n-heptane" refers to pure n-heptane or n-heptane in a mixture with other C7 isomers (e.g., at least 90% n-heptane and at least 95% total C7 isomers).

[0028] The term "reflux temperature" or "reflux" refers to the temperature at which a reaction solvent boils. Typically, a condenser is used to cool and condense the solvent vapor, which is then returned to the reactor. The exact temperature at which a given solvent reaches reflux may vary depending on environmental factors.

[0029] The term "approximately" refers to numerical values, including integers, fractions, and percentages, whether or not explicitly indicated. Generally, "approximately" refers to a range of numerical values ​​(e.g., ±5 to 10% of the stated value) that a person skilled in the art would consider equivalent to (e.g., having a similar function or result) the stated value. When terms such as "at least" and "approximately" precede an enumeration of numerical values ​​or ranges, those terms modify all values ​​or ranges shown in the enumeration. In some cases, the term "approximately" may include rounded numerical values.

[0030] The terms “extract,” “extraction,” or “extracting” refer to the process of distributing a substance between an organic phase and an aqueous phase. In some embodiments, the extraction is performed on a reaction mixture or a concentrated residue of a reaction mixture. The “extract” is the organic phase that has been separated from the aqueous phase. In this specification, extraction does not include purification methods performed on crude reaction products, such as simple distillation, vacuum distillation, azeotropic distillation, fractional distillation, continuous distillation, flash chromatography, HPLC, or recrystallization.

[0031] In this specification, "purification" or "purification" means a method for isolating the product of a reaction after the completion of the reaction. Purification methods include simple distillation, vacuum distillation, azeotropic distillation, fractional distillation, continuous distillation, flash chromatography, HPLC, or recrystallization.

[0032] The term "substantially," for example, "substantially in monomeric form," refers to the purity of the compound of formula (I) with respect to its dimer analogs and / or oligomer analogs.

[0033] In this specification, the terms “dimer” or “dimeric compound” refer to a compound obtained by condensing two molecules of a given monomeric structure, or one molecule each of two different monomeric structures, into a single molecule. In this specification, the terms “oligomer” or “oligomeric compound” refer to a compound obtained by condensing three or more molecules of a given monomeric structure, or three or more molecules of at least two different monomeric structures, into a single polymeric structure. HMBi may form homooligomers or heteroHMBi oligomers (containing at least one HMBi monomer unit).

[0034] The term "purity" or the expression "percentage of a compound" (e.g., x% HMBi) refers to the purity of a compound in a sample, measured by weight, by GC analysis, and / or by HPLC analysis. In some embodiments, the purity by weight is measured by GC or HPLC analysis using UV detection.

[0035] The term "purity by weight" refers to the purity of a compound in a sample relative to other components in the sample, expressed as a percentage, where the ratio of the mass of the compound to the mass of the sample is expressed as such.

[0036] In the context of gas chromatography (GC) purity or HPLC purity, "purity" refers to the calculated purity (expressed as a percentage) of the peak area of ​​the compound in question relative to the sum of all peak areas in the chromatogram. In some embodiments, purity is measured by HPLC with UV detection.

[0037] In some embodiments, purity is the purity required in accordance with the sales regulations for the regulated product. For example, in the case of HMBi, the water content of the compound is 0.5% or less (measured, for example, by Karl Fischer analysis). (See Commission Implementing Regulation (EU) No. 469 / 2013 of 22 May 2013).

[0038] The terms "crude," "crude product," and "crude compound" refer to samples of compounds obtained from a reaction mixture after concentration of the reaction mixture, and / or after extraction of the reaction mixture into an organic solvent and concentration of the organic extract.

[0039] The term "animal feed composition" refers to a product suitable for use in supplementing animal nutrition. In some embodiments, the animal feed composition is an animal feed (e.g., food or drinking water containing nutritional supplements), and in some embodiments, the animal feed composition is a feed additive. The feed additive is suitable for mixing with animal feed or drinking water.

[0040] The term "carrier" refers to a carrier suitable for animal feed additives. Suitable carriers include water (in the case of liquid or solid feed additives) or silica (in the case of solid feed additives). In some embodiments, the carrier is silica (silicon dioxide). In some embodiments, the feed additive contains the compound and silica in a ratio of 3:2.

[0041] In some embodiments, the animal feed comprises granulated, protein-rich feed (e.g., peanut-based, rapeseed meal-based, and / or soybean meal-based) supplemented with 2.5% by weight or 1% by weight of HMBi. In some embodiments, the animal feed comprises about 45% and about 50% grain (corn, barley, wheat, and / or wheat by-products) supplemented with 0.5% by weight or 3.0% by weight of HMBi. In some embodiments, the animal feed comprises powdered or granulated feed containing molasses, each supplemented with 2.5% by weight or 1% by weight of HMBi.

[0042] The term "administering" refers to giving a nutritional supplement to the target animal. Administration may be carried out, for example, through the ingestion of food or drinking water containing the above compound, or orally by injection or other means of administration.

[0043] In this specification, “improving milk” means an improvement in the quality and / or quantity of milk produced by a treated cow or herd of treated cows compared to milk produced by an untreated control animal. Examples of milk improvements include an increase in the protein content of the milk (e.g., an increase in α, β, and / or κ proteins), an increase in the fat content of the milk, and / or an increase in the volume of milk produced.

[0044] In this specification, “improving the condition of cattle” means improving the health indicators of treated cattle or a herd of treated cattle compared to health indicators of untreated control animals. Improvement in the condition of cattle may also refer to several characteristics compared to untreated animals, such as weight gain.

[0045] In this specification, "improvement of fertility" includes, for example, shortening the interval between birth and reproduction, and / or increasing the fertilization rate during insemination.

[0046] In this specification, "improvement of liver function" includes, for example, a reduction in metabolic problems, an improvement in very low-density lipoprotein levels, a reduction in hyperketonemia, and / or a reduction in the incidence of fatty liver.

[0047] In this specification, “increase in energy” means, for example, an increase in digestible organic matter, and consequently, stimulation of the fermentation process in the rumen, which leads to more energy for the animal.

[0048] Synthesis process This disclosure relates to a method for producing compounds of formula (I) or formula (IA) and / or intermediates, comprising the following reaction, namely: a) Oxalyl chloride or oxalic acid R 2 Formation of oxalic acid diesters by esterification at -OH, b) Formation of alkenyl-substituted α-ketoesters (2-oxobuta-3-enoic acid esters) by coupling the above oxalate diester with an alkenyl Grignard reagent. c) Formation of 4-alkylthio-2-oxobutanoic acid esters by thiolation of the above alkenyl-substituted α-ketoesters, and d) Formation of a compound of formula (I) or formula (IA) by reduction of the above 4-alkylthio-2-oxobutanoic acid ester. The above method involves one or more of the above. Oxalic acid can be used, for example, as oxalic acid or oxalic acid dihydrate.

[0049] In some embodiments, this disclosure is, Equation (I): [ka] (In the formula, R 1 is C 1~4 It is alkyl, R 2 is C 1~8 Alkyl or C 4~7 It is a cycloalkyl, R 3 and R 4 (Each of these is independently selected from H, methyl, and ethyl.) A method for producing the compound, Formula (IV): [ka] The compound of formula (A): [ka] (In the formula, X is either Br or Cl) When coupled with the vinyl Grignard reagent, equation (III) is obtained: [ka] To form the compound, Converting the compound of formula (III) above into the compound of formula (I) above The above method, including the above method.

[0050] In some embodiments, the present disclosure relates to a method for producing a compound of formula (III), comprising coupling a compound of formula (IV) with a vinyl Grignard reagent of formula (A).

[0051] In some embodiments, R 1 It is methyl.

[0052] In some embodiments, each R 2 R is selected from methyl, ethyl, and isopropyl. In some embodiments, each R 2 It is isopropyl.

[0053] In some embodiments, R 3 and R 4 These are H.

[0054] In some embodiments, the compound of formula (I) is of formula (IA): [ka] It is a compound of [the compound].

[0055] In some embodiments, the compound of formula (III) is of formula (III-A): [ka] It is a compound of [the compound].

[0056] In some embodiments, the vinyl Grignard reagent of formula (A) is vinyl-MgCl. In some embodiments, X is Cl. In some embodiments, the Grignard coupling is carried out in the presence of a salt additive such as LiCl or ZnCl2. In some embodiments, the salt additive is LiCl.

[0057] In some embodiments, the coupling involves mixing the compound of formula (IV) with a vinyl Grignard reagent of formula (A) in an amount of about 0.8 to about 2.0 molar equivalents, or about 1.0 to about 1.75 molar equivalents, or about 1.0 to about 1.5 molar equivalents, or about 1.2 to about 1.75 molar equivalents, or about 1.4 to about 1.6 molar equivalents, or about 1.5 molar equivalents.

[0058] In some embodiments, the coupling is carried out at a temperature in the range of about -80°C to about 10°C, or about -80°C to about -70°C, or about -50°C to about 10°C, or about -40°C to about 5°C, or about -50°C to about -20°C, or about -30°C to about -20°C, or at a temperature of about -78°C, or about -20°C, or about 0°C. In some embodiments, the coupling is carried out at a temperature of about -50°C to about -20°C, or about -30°C to about -20°C, with about 1.5 molar equivalents of the vinyl Grignard reagent of formula (A). In some embodiments, the vinyl Grignard reagent is added to the compound of formula (IV) slowly and / or in several portions.

[0059] In some embodiments, the coupling is carried out in an aprotic solvent. In some embodiments, the aprotic solvent is an ether such as MTBE, THF, or Et2O, optionally mixed with a nonpolar solvent such as heptane or hexane. In some embodiments, the aprotic solvent is MTBE or THF, optionally mixed with heptane. In some embodiments, the concentration of the coupling reaction is about 0.25 M to about 1.3 M (moles of the compound of formula (IV) above per liter of reaction solvent), or about 0.4 M to about 1.1 M, or about 0.4 M to about 0.5 M, or about 0.9 M to about 1.0 M, or about 0.5 M, or about 1 M.

[0060] In some embodiments, the above coupling is performed with the compound of formula (III) and formula (III-Z): [ka] A mixture of the compound is produced, the mixture having a ratio of (III):(III-Z) of at least 5:1, or at least 6:1, or at least 7:1, or at least 8:1, or at least 9:1, or at least 10:1, or at least 15:1, or at least 20:1.

[0061] In some embodiments, the conversion of the compound of formula (III) to the compound of formula (I) is as follows: formula (B) or formula (C): R 1 -SH (B) R 1 -S - M + (C) (In the formula, M + (It is a metal cation.) The compound of formula (III) above is thiolated with the thioling agent to obtain formula (II): [ka] To form the compound, The compound of formula (II) above is reduced to form the compound of formula (I) above. Includes.

[0062] In some embodiments, the disclosure relates to a method for producing a compound of formula (II), comprising thioling a compound of formula (III) with a thioling agent of formula (B) or formula (C).

[0063] In some embodiments, the thiolation is carried out with the thioling agent of formula (B) in the presence of an additive. In some embodiments, the additive is an amine base such as triethylamine, diethylamine, pentylamine, or hexylamine; a phosphine such as dimethylphenylphosphine (DMPP) or tris(2-carboxyethyl)phosphine (TCEP); a basic salt such as NaHCO3 or Na2CO3; a Lewis acid such as scandium(III) triflate or anhydrous cerium(III) chloride; or an N-heterocyclic carbene (NHC) complex (e.g., Au-NHC complex). In some embodiments, the additive is triethylamine.

[0064] In some embodiments, the method further comprises generating a thioling agent of formula (B) from a thioling agent of formula (C). In some embodiments, the generation is carried out in the presence of an acid catalyst. In some embodiments, the acid catalyst is acetic acid, p-toluenesulfonic acid, or H2SO4. In some embodiments, the thiolation is carried out at a temperature in the range of about -40°C to about 10°C, or about -35°C to about 5°C, or about -30°C to about -20°C, or about 0°C.

[0065] In some embodiments, the thioling agent is of formula (C), and the thioling is carried out at a temperature in the range of about -80°C to about 35°C, or about 15°C to about 35°C.

[0066] In some embodiments, M + is Na + or K + That is the case.

[0067] In some embodiments, the coupling includes extracting the compound of formula (III) into an organic solvent to form an extract of formula (III), and the thiolation includes adding the thioling agent to the extract of formula (III). Thus, the thiolation reaction is carried out without purifying the intermediate of formula (III) derived from the coupling reaction before the thiolation reaction. In some embodiments, the above procedure is as follows. [ka]

[0068] In some embodiments, the reduction of the compound of formula (II) is carried out in the presence of a reducing agent selected from NaBH4, LiBH4, and Al(O-iPr)3 / iPrOH. In some embodiments, the reducing agent is NaBH4. In some embodiments, the thiolation involves extracting the compound of formula (II) into an organic solvent to form an extract of formula (II), and the reduction involves adding the reducing agent to the extract of formula (II). Thus, the reduction is carried out without purifying the compound of formula (II) before the reduction. In some embodiments, the coupling involves extracting the compound of formula (III) into an organic solvent to form an extract of formula (III), the thiolation involves adding the thioling agent to the extract of formula (III) and extracting the compound of formula (II) into an organic solvent to form an extract of formula (II), and the reduction involves adding the reducing agent to the extract of formula (II). Thus, as shown in the following scheme, the coupling, thiolation, and reduction described above are carried out without purifying the intermediates of formulas (II) and (III). [ka]

[0069] In some embodiments, the above reduction is performed (a) in an alcohol solvent such as methanol, ethanol, or isopropanol, and / or (b) Using approximately 0.25 to 1.0 molar equivalent of reducing agent, and / or (c) At temperatures ranging from approximately -10°C to approximately 30°C, or at approximately 0°C, This procedure is performed using NaBH4 or LiBH4.

[0070] In some embodiments, the reduction is carried out using Al(O-iPr)3 / iPrOH at a temperature in the range of about 50°C to about 90°C, or at about 80°C.

[0071] In some embodiments, the above method involves using oxalyl chloride as R 2 The method further includes esterification with -OH to form the compound of formula (IV) above. In some embodiments, the esterification is carried out in the presence of at least one amine base such as N,N-dimethylpyridine, pyridine, or triethylamine. In some embodiments, the esterification is carried out at a temperature in the range of about -5°C to about 30°C.

[0072] In some embodiments, the above method is performed in the presence of an optional dehydrating agent such as an acid catalyst and azeotropic water removal, molecular sieves, or a combination thereof, R 2The process further includes esterifying oxalic acid with -OH to form the compound of formula (IV) above. In some embodiments, the acid catalyst is selected from p-TsOH; H2SO4; macroporous sulfonic acid resin catalysts such as Amberlyst®-15, Dowex®, or M32; aluminates; phosphoric acid; boronic acid; acetyl chloride; and acids with a pKa of less than 3. In some embodiments, the acid catalyst is p-TsOH or H2SO4. In some embodiments, the acid catalyst is about 0.01 to about 0.1 molar equivalents or about 0.025 to about 0.05 molar equivalents of p-TsOH, or about 1 to about 3 molar equivalents or about 2 molar equivalents of H2SO4. In some embodiments, the esterification is carried out at reflux temperature of the reaction solvent. In some embodiments, the esterification is carried out in a reaction solvent selected from toluene, CHCl3, and isopropanol.

[0073] In some embodiments, this disclosure relates to formula (I): [ka] (In the formula, R 1 is C 1~4 It is alkyl, R 2 is C 1~8 Alkyl or C 4~7 It is a cycloalkyl, R 3 and R 4 (Each of these is independently selected from H, methyl, and ethyl.) A method for producing the compound, Formula (II): [ka] The present invention relates to a method comprising reducing a compound with a reducing agent to form a compound of formula (I). In some embodiments, the compound of formula (I) is the compound of formula (IA). In some embodiments, the compound of formula (II) is the compound of formula (II-A): [ka] It is a compound of [the compound].

[0074] In some embodiments, the reduction of the compound of formula (II) is carried out in the presence of a reducing agent selected from NaBH4, LiBH4, and Al(O-iPr)3 / iPrOH. In some embodiments, the reducing agent is NaBH4.

[0075] In some embodiments, the above reduction is performed (a) in an alcohol solvent such as methanol, ethanol, or isopropanol, and / or (b) Using approximately 0.25 to 1.0 molar equivalent of reducing agent, and / or (c) At temperatures ranging from approximately -10°C to approximately 30°C, or at approximately 0°C, This procedure is performed using NaBH4 or LiBH4.

[0076] In some embodiments, the reduction is carried out using Al(O-iPr)3 / iPrOH at a temperature in the range of about 50°C to about 90°C, or at about 80°C.

[0077] In some embodiments, the above method is expressed by formula (III): [ka] (In the formula, R 3 and R 4 (Each of these is independently selected from H, methyl, and ethyl.) The compound of formula (B) or formula (C): R 1 -SH (B) R 1 -S - M + (C) (In the formula, M + (It is a metal cation.) The further step involves thiolation with a thioling agent to form the compound of formula (II). In some embodiments, the compound of formula (II) is the compound of formula (II-A), and the compound of formula (III) is the compound of formula (III-A): [ka] It is a compound of [the compound].

[0078] In some embodiments, this disclosure relates to formula (IA): [ka] A method for producing the compound, Esterilizing oxalic acid with isopropanol to form diisopropyl oxalate, Diisopropyl oxalate is coupled with vinyl magnesium bromide to form formula (III-A): [ka] To form the compound, The compound of formula (III-A) above is thiolated with CH3SH to obtain formula (II-A): [ka] To form the compound, The compound of formula (II-A) above is reduced to form the compound of formula (IA) above. The above method, including the above method.

[0079] In some embodiments, the method described herein yields the compound of formula (I) or formula (IA) with a purity of at least about 95% by GC, HPLC, and / or by weight. In some embodiments, the method yields the crude compound of formula (I) or formula (IA) which is unpurified or purified only by fractional distillation, with a purity of at least about 95%, at least about 96%, at least about 97%, or at least about 98% by weight, GC, and / or HPLC. In some embodiments, the method yields the crude compound of formula (I) or formula (IA) which is substantially in monomeric form, or with a content of less than about 5% by weight, or less than about 3% by weight, of dimer compounds and / or oligomer compounds, which is unpurified or purified only by fractional distillation.

[0080] compound products In some embodiments, the reaction yields a crude compound of formula (I) having a purity by weight (and / or by GC or HPLC) of at least about 80%, at least about 90%, at least about 95%, at least about 96%, at least about 97%, or at least about 98%, which is either unpurified or purified only by fractional distillation. In some embodiments, the reaction yields a crude compound of formula (I) or formula (IA) having a substantially monomeric form or a content of less than about 5% by weight, or less than about 3% by weight, which is either unpurified or purified only by fractional distillation.

[0081] In some embodiments, the disclosure relates to compounds of formula (I) or formula (IA) prepared as described herein. In some embodiments, the disclosure relates to compounds of formula (I) or formula (IA) that are unpurified or purified only by fractional distillation, having a purity by weight (and / or by GC or HPLC) of at least about 80%, at least about 90%, at least about 95%, at least about 96%, at least about 97%, or at least about 98%. In some embodiments, the compounds are substantially in monomeric form, or the mixed amount of dimeric compounds and / or oligomeric compounds is less than about 5% by weight, or less than 3% by weight.

[0082] In some embodiments, the HMBi (formula (IA)) product has one or more of the following specifications: (a) an HMBi monomer content and chemical purity of at least about 95% by weight or HPLC analysis; (b) a water content of less than about 0.5% by Karl Fischer analysis; and (c) a pH lower than about 6.0 (measured in water at a 1% concentration).

[0083] This specification also discloses compounds of formula (I) or formula (IA) prepared by any of the methods described herein. In some embodiments, there are compounds of formula (I) or formula (IA) that are crude compounds, unpurified and / or purified only by fractional distillation, with a purity by weight (and / or by GC or HPLC) of at least about 95%, at least about 96%, at least about 97%, or at least about 98%. In some embodiments, the above compounds are R 1 is -CH2CH2-S-CH3, and R 2 The compound is of formula (I) in which isopropyl, or the compound is of formula (IA). In some embodiments, the compound is substantially in monomeric form, or the amount of the dimeric compound and / or oligomeric compound mixed is less than about 5% by weight, or less than about 3% by weight.

[0084] Animal feed composition and use In some embodiments, this disclosure relates to animal feed compositions comprising compounds of formula (I) or formula (IA) as described herein. In some embodiments, the animal feed compositions are suitable for administration to ruminants such as cattle, cows, sheep, antelopes, deer, giraffes, Bovids (e.g., bison, buffalo, or yak), goats, and / or gazelles. In some embodiments, the animal feed compositions are cattle feed compositions such as dairy cattle feed compositions, or additives for cattle feed such as dairy cattle feed. In some embodiments, the animal feed compositions are dairy cattle feed compositions.

[0085] In some embodiments, the animal feed composition is an animal feed or an animal feed additive. In some embodiments, the animal feed additive is in liquid or solid form, the liquid form comprising the compound and optionally a liquid carrier, the solid form comprising the compound mixed with a solid carrier, optionally the solid carrier being silica (silicon dioxide), and optionally the ratio of the compound to the solid carrier being about 5:1 to about 1:5 or about 3:2. In some embodiments, the feed composition is a liquid feed additive or a solid feed additive. In some embodiments, the animal feed composition is a drinking water additive. In some embodiments, the pH of the liquid feed additive or drinking water additive is in the range of about 4.0 to about 7.5.

[0086] In some embodiments of the above animal feed composition, R 1 is -CH2CH2-S-CH3, and R 2 isopropyl. In some embodiments, the above compound is a compound of formula (IA).

[0087] In some embodiments, the Disclosure relates to a method for supplying bioavailable methionine to dairy cows, comprising administering the cows a compound or animal feed composition described herein. In some embodiments, administration comprises feeding the cows a feed composition containing the compound. In some embodiments, the Disclosure relates to a method for supplying at least about 50% bioavailable methionine to dairy cows, comprising administering the cows a compound or animal feed composition described herein. In some embodiments, the Disclosure relates to a method for improving milk obtained from dairy cows, comprising supplying the cows a compound or animal feed composition described herein. In some embodiments, the improvement of the milk includes an increase in the protein content of the milk. In some embodiments, the improvement of the milk includes an increase in the fat content of the milk. In some embodiments, the Disclosure relates to a method for improving the condition of cows, comprising supplying the cows a compound or animal feed composition described herein. In some embodiments, the improvement of the condition of cows includes an improvement in fertility. In some embodiments, the improvement of the condition of cows includes an improvement in liver function. In some embodiments, the improvement of the condition of cows includes an increase in energy.

[0088] In some embodiments, any of the reactions described herein may be carried out using a continuous flow apparatus. [Examples]

[0089] Apparatus: All millimolar-scale experiments were carried out using 100 mL or 250 mL three-necked round-bottom flasks equipped with a magnetic stirrer, dropping funnel, and thermometer. These reaction flasks were fitted with a condenser and a thermometer for monitoring the reaction temperature. When the reaction was carried out under reflux, the reaction mixture was heated using a silicone oil bath. For experiments at temperatures below room temperature, a liquid nitrogen bath or a salt / ice mixture bath was used. All kilogram-scale experiments were carried out using a 5 L jacketed reactor. Concentration and / or purification of intermediates and crude products were carried out using laboratory-scale vacuum distillation apparatus, rotary evaporator, or column chromatography, or by other methods as indicated in the following examples.

[0090] Example 1: Synthesis of diisopropyl oxalate from oxalic acid [ka]

[0091] In a 5 L laboratory reactor, oxalic acid (1 kg, 11.1 mol) was added to isopropyl alcohol (1700 mL) under stirring. A clear solution was formed. Subsequently, a solution of p-toluenesulfonic acid monohydrate (47.67 g, 2.5 mol%) in toluene (200 mL) was slowly added to the above solution. The reaction mixture was heated and stirred under reflux for 24 hours. The water produced was continuously removed by azeotropy using a Dean-Stark trap to complete the reaction. The reaction mixture was cooled, neutralized with 500 mL of saturated NaHCO3 aqueous solution, and partitioned between 400 mL of toluene and 1 L of water (twice). The combined organic phase was dehydrated with 1 L of saturated NaCl aqueous solution. The organic phase was separated, and the solvent was removed under reduced pressure. The crude substance was purified by heating under high vacuum and distillation to obtain 1740 g (90%) of diisopropyl oxalate as a colorless oil. 13 C NMR (100 MHz, CDCl3) δ (ppm) 157.96, 71.44, 21.63 (Fig. 1A); 1HNMR (400 MHz, CDCl3)δ 5.13 (hept, J = 6.3 Hz, 2 H), 1.33 (d, J = 6.2 Hz, 12 H) (Fig. 1B).

[0092] As shown in Table 1, various other suitable reaction conditions were investigated using oxalic acid dihydrate (serial numbers 1-5) or oxalic acid (serial numbers 6-7) as the starting material. A 4 Å molecular sieve (1-2 g per 5 g of starting material) was added to the reaction mixture, and water was further removed during the reaction. Workup included diluting the reaction mixture with ethyl acetate, neutralizing to pH 7 with saturated aqueous solution of NaHCO3, separating the layers, washing the organic extract with saturated aqueous solution of NaHCO3 and saturated aqueous solution of NaCl, and concentrating to obtain the crude residue. [Table 1]

[0093] Example 2: Synthesis of diisopropyl oxalate from oxalyl chloride [ka]

[0094] To a 3L sample of isopropyl alcohol at 0°C in a 5L glass-lined laboratory reactor, 1019g of oxalyl chloride was slowly added in several portions under stirring while maintaining the temperature at 0-5°C. After the addition was complete, the reaction mixture was gradually and naturally warmed to room temperature and stirred for 12 hours. The mixture was concentrated by distillation and high vacuum using a rotary evaporator to obtain the crude product. This crude product was diluted with dichloromethane (1000mL) and washed with saturated aqueous solution of NaHCO3 (3×500mL) to obtain an organic extract. The first two aqueous washes were back-extracted with dichloromethane (1L each) to obtain two further organic extracts. These three organic extracts were dehydrated with saturated aqueous solution of NaCl (3×500mL), combined, concentrated, and purified by distillation to obtain diisopropyl oxalate in 86% yield. 1H NMR (400 MHz, CDCl3) δ 5.13 (hept, J = 6.3 Hz, 2 H), 1.33 (d, J = 6.2 Hz, 12 H).

[0095] As shown in Table 2, various other suitable reaction conditions were investigated. [Table 2]

[0096] Example 3: Synthesis of isopropyl 2-oxo-4-methylthiobutanoate (small-scale experiment) [ka]

[0097] Step 1: A mixture of diisopropyl oxalate (1.4 g, 8 mmol, 1.0 equivalent), 16 mL of solvent (MTBE, MTBE / heptane mixture, or THF), and 2 equivalents of LiCl (0.68 g, 16 mmol, if used) was cooled to the test temperature (shown in Table 3) under either a liquid nitrogen bath or a salt bath. A solution of vinyl magnesium chloride (1.6 M THF solution) was slowly added, and the resulting mixture was stirred until the starting material was consumed (see Table 3). This reaction mixture was quenched by washing with saturated aqueous solution of NH4Cl (2 × 100 mL). The product was extracted with SiO2SO4 (2 × 100 mL), dehydrated over Na2SO4, and filtered. The yield of isopropyl 2-oxo-3-butenoate was measured by GC / MS. This extract was used directly in the next step without purification. [Table 3]

[0098] Step 2, Thiolation reaction

[0099] Procedure 1: As shown in Table 4, CH3SH gas was generated by treating a 20% w / v aqueous solution of CH3SNa with an acid catalyst (AcOH (12 mmol) or TsOH (12 mmol)) at -30 to -20°C, or with H2SO4 (2 equivalents relative to CH3SNa) at 50°C for 15 to 30 minutes. The generated CH3SH was bubbling under stirring into a solution of MTBE (20 mL) containing triethylamine (0.1 mL) at 0°C. The resulting MTBE solution of CH3SH was added to the MTBE solution of the crude product derived from Step 1, Table 3, serial number 14, at 0°C or -30 to -20°C, as shown in Table 4, and the reaction mixture was stirred for 15 to 30 minutes. The reaction mixture was quenched with 2 M HCl, extracted with ethyl acetate, dehydrated (Na2SO4), filtered, and concentrated. This crude substance was then used in the next reaction step.

[0100] In Table 4, for serial numbers 1-5, CH3SH gas was generated using acetic acid or p-toluenesulfonic acid. For serial numbers 1-3, the yield is the isolation yield after column chromatography. For serial numbers 4-5, the yield is the isolation yield after distillation of the product. For serial numbers 6-9, CH3SH gas was generated by heating a 20% aqueous solution of CH3SNa with H2SO4 at 50°C. [Table 4]

[0101] Procedure 2: To a THF solution of the crude product from Step 1, Table 3, serial number 11, at -78°C, 1 equivalent of a 20% w / v aqueous solution of CH3SNa and 2 equivalents of H2SO4 were added. The reaction mixture was allowed to rise naturally to room temperature and stirred for 16 hours. The reaction mixture was quenched with 2M HCl, extracted with ethyl acetate (2 × 50 mL), dehydrated (Na2SO4), filtered, and concentrated. This crude product was then used in the next reaction step. The product was isolated to obtain the product in 33% yield. 1H NMR (400 MHz, CDCl3) δ 5.12 (hept, J = 6.2 Hz, 1 H), 3.13 (t, J = 7.2 Hz, 2 H), 2.76 (t, J = 7.2 Hz, 2 H), 2.11 (s, 3 H), 1.33 (d, J = 6.3 Hz, 6 H).

[0102] Procedure 3, Continuous Flow Reactor: Instead of the above, a mixture of isopropyl 2-oxo-3-butenoate and 10 mL of triethylamine is supplied to the reactor at a controlled flow rate by a pump. The outlet is further connected to the inlet of a Y-shaped mixer, in which MeSH gas (at a controlled flow rate) is supplied to another inlet. The two components are then mixed and further stirred in the batch reactor while maintaining the reaction temperature at 0°C. When the reaction is shown to be complete by GC monitoring, 1N HCl is added and the mixture is post-treated as described above.

[0103] Example 4: Synthesis of isopropyl 2-oxo-4-methylthiobutanoate (kilogram-scale synthesis) Step 1, Grignard reaction: In a 20 L laboratory reactor, at -30 to -20°C, 7 L of vinyl magnesium chloride (1.6 M solution in THF) was added dropwise to a 3.4 L solution of diisopropyl oxalate (1.7 kg, 10 mol) in anhydrous MTBE under stirring. The temperature was maintained at -30 to 20°C. Once the vinyl addition was confirmed by gas chromatography, the reaction mixture was quenched by adding 1 L of saturated aqueous NH4Cl solution at room temperature. The organic phase was separated and washed with 500 mL of water, and the aqueous phase was back-extracted with 400 mL of MTBE. These MTBE extracts were combined to obtain isopropyl 2-oxo-3-butenoate with a conversion rate of over 90%, which was used directly in the next step without further purification or distillation.

[0104] Step 2: The MTBE extract from Step 1 was cooled to 0°C in the reactor and treated with triethylamine (10 mL). MeSH gas was generated in-situ by reacting a solution of CH3SNa (1.0 equivalent; 20% aqueous solution) with H2SO4 (2 equivalents) at 50°C for 30 minutes. The generated CH3SH gas was bubbling into the reaction solution at 0°C under stirring, and stirring was continued at 0°C. When GC monitoring indicated that the above intermediate had been converted to isopropyl 2-oxo-4-methylthiobutanoate, 1N HCl (780 mL) was added to the reactor to quench the reaction mixture. The organic layer was separated from the aqueous phase, washed with 500 mL of water, and the aqueous phase was extracted with 650 mL of MTBE (2×). The combined organic extract was concentrated by distillation under reduced pressure, and the product was purified by distillation under reduced pressure to obtain 1021 g (55%) of isopropyl 2-oxo-4-methylthiobutanoate as a colorless oil. 13 C NMR (100 MHz, CDCl3) δ(ppm) 193.21, 160.25, 70.95, 39.33, 27.32, 21.63, 15.74 (Figure 2A); 1 HNMR (400 MHz, CDCl3)δ 5.12 (hept, J = 6.2 Hz, 1 H), 3.13 (t, J = 7.2 Hz, 2 H), 2.76 (t, J = 7.2 Hz, 2 H), 2.11 (s, 3 H), 1.33 (d, J = 6.3 Hz, 6 H) (Figure 2B).

[0105] Example 5: Synthesis of isopropyl 2-hydroxy-4-methylthiobutanoate (HMBi) [ka]

[0106] In a 5 L reactor, NaBH4 (99 g, 2.6 mol) was added in several portions to a methanol (2 L) solution of isopropyl 2-oxo-4-methylthiobutanoate (1 kg, 5.25 mol) at 0-5°C. The resulting reaction mixture was maintained at 0-5°C and stirred for 1 hour. The reaction mixture was washed with a saturated aqueous solution of NH4Cl (500 mL). The organic phase was separated, the solvent was removed by vacuum distillation, and the crude product was purified by distillation to obtain HMBi (859 g, yield 85%, monomer ester with 97% yield) as a pale yellow oil. 13 C NMR (100 MHz, CDCl3) δ (ppm) 174.52, 69.85, 69.34, 33.76, 29.69, 21.87, 21.83, 15.60 (Figure 3A); 1 HNMR (400 MHz, CDCl3)δ 5.08 (hept, J = 6.3 Hz, 1 H), 4.24 (dd, J = 7.9, 3.8 Hz, 1 H), 2.97 (br, 1 H), 2.67-2.55 (m, 2 H), 2.10-2.01 (m, 4 H), 1.93-1.84 (m, 1 H), 1.27 (d, J = 1.9 Hz, 3 H), 1.26 (d, J = 2.2 Hz, 3 H) (Figure 3B).

[0107] Alternative method for the synthesis of 2-hydroxy-4-(methylthio)butanoate isopropyl ester (HMBi) from 2-oxo-4-methylthiobutanoate isopropyl ester (OMBi) [ka]

[0108] For the production of HMBi from 2-oxo-4-methylthiobutanoate isopropyl, various reagents and conditions, including NaBH4, transition metal-catalyzed hydrogenation, and keto reduction, were screened. Several reaction temperatures, times, reagents, and solvents were tested. The conversion rate to the product and the yield of the isolated product were measured for each combination of conditions, and the results are shown in Table 5. [Table 5]

Claims

1. Equation (I): 【Chemistry 1】 (In the formula, R １ is C １～４ It is alkyl, R ２ is C １～８ Alkyl or C ４～７ It is a cycloalkyl, R ３ and R ４ (Each of these is independently selected from H, methyl, and ethyl.) A method for producing the compound, Formula (IV): 【Chemistry 2】 The compound of formula (A): 【Transformation 3】 (In the formula, X is either Br or Cl) When coupled with the vinyl Grignard reagent, formula (III) is obtained: 【Chemistry 4】 To form the compound, The compound of formula (III) is formula (B) or formula (C): R １ -SH (B) R １ -S － M ＋ (C) (In the formula, M ＋ (It is a metal cation.) Thiolation with the thioling agent results in formula (II): 【Transformation 5】 To form a compound, and The compound of formula (II) above is NaBH ４ LiBH ４ , and Al(O-iPr) ３ The compound of formula (I) is formed by reduction with a reducing agent selected from iProOH, The method, including the method described above.

2. Each R ２ The method according to claim 1, wherein the compound is selected from methyl, ethyl, and isopropyl.

3. R １ is methyl, and / or each R ２ is isopropyl and / or R ３ and R ４ The method according to claim 1, wherein each of them is H.

4. The compound of formula (I) is formula (I-A): 【Transformation 6】 The method according to claim 1, wherein the compound is [the compound].

5. The compound of formula (III) is formula (III-A): 【Transformation 7】 The method according to claim 1, wherein the compound is [the compound].

6. The method according to any one of claims 1 to 5, wherein the vinyl Grignard reagent of formula (A) is vinyl-MgCl.

7. The method according to any one of claims 1 to 5, wherein X is Cl.

8. The coupling of LiCl and ZnCl ２ The method according to claim 7, carried out in the presence of a salt additive selected from the following.

9. The method according to any one of claims 1 to 8, wherein the coupling comprises mixing the compound of formula (IV) with 0.8 to 2.0 molar equivalents, or 1.0 to 1.75 molar equivalents, or 1.0 to 1.5 molar equivalents, or 1.2 to 1.75 molar equivalents, or 1.4 to 1.6 molar equivalents, or 1.5 molar equivalents of the vinyl Grignard reagent of formula (A).

10. The method according to any one of claims 1 to 9, wherein the coupling is performed at a temperature in the range of -80°C to 10°C, or -80°C to -70°C, or -50°C to 10°C, or -40°C to 5°C, or -50°C to -20°C, or -30°C to -20°C, or at a temperature of -78°C, -20°C, or 0°C.

11. The method according to any one of claims 1 to 10, wherein the coupling is performed in an aprotic solvent.

12. The method according to claim 1, wherein the thiolation is carried out by a thioling agent of formula (B) in the presence of an additive.

13. The aforementioned additive Amine base selected from triethylamine, diethylamine, pentylamine, and hexylamine, A phosphine selected from dimethylphenylphosphine (DMPP) and tris(2-carboxyethyl)phosphine (TCEP), NaHCO ３ and Na ２ CO ３ A basic salt selected from, A Lewis acid selected from scandium(III) triflate and cerium(III) anhydrous chloride, or Au-NHC complex The method according to claim 12.

14. The method according to claim 12, wherein the additive is triethylamine.

15. The method according to any one of claims 1 to 14, further comprising generating a thioling agent of formula (B) from a thioling agent of formula (C).

16. The method according to claim 15, wherein the above-mentioned production is carried out in the presence of an acid catalyst.

17. The acid catalyst is acetic acid, p-toluenesulfonic acid, or H ２ SO ４ The method according to claim 16.

18. M ＋ Na ＋ or K ＋ The method according to any one of claims 1 to 17.

19. To reduce, (a) in an alcohol solvent selected from methanol, ethanol, and isopropanol, and / or (b) Using 0.25 to 1.0 molar equivalent of a reducing agent, and / or (c) The reducing agent is Al(O-iPr) ３ If it is not iPrOH, the temperature should be in the range of -10°C to 30°C, or at 0°C, or the reducing agent should be Al(O-iPr) ３ If it is iProOH, the temperature range is 50°C to 90°C, or 80°C. The method according to any one of claims 1 to 18.

20. The method according to any one of claims 1 to 19, wherein the thiolation comprises extracting the compound of formula (II) into an organic solvent to form an extract of formula (II), and the reduction comprises adding the reducing agent to the extract of formula (II).

21. Oxalyl chloride R ２ The method according to any one of claims 1 to 20, further comprising esterification with -OH to form a compound of formula (IV).

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