CN112575042A - Novel method for preparing ethambutol hydrochloride - Google Patents

Abstract

The invention takes cheap and easily obtained L-threonine as a raw material to synthesize L-2-aminobutyric acid, and then uses the L-2-aminobutyric acid as an intermediate to synthesize ethambutol hydrochloride. Firstly, using an enzyme catalysis method, taking L-threonine as a raw material, preparing L-2-aminobutyric acid (D-2-aminobutanol and L-2-aminobutyrate are both in S configuration) by a one-pot method, reacting the intermediate with oxalyl chloride to generate a dicarboxylic acid compound containing a diamide group, then obtaining ethambutol by cobalt catalytic hydrogenation reduction, and then introducing hydrogen chloride gas to generate ethambutol hydrochloride. The process has the characteristics of low cost, simple and convenient operation, environmental protection, high conversion rate and high optical purity of the product.

Description

Novel method for preparing ethambutol hydrochloride

Technical Field

The invention relates to a technology for preparing ethambutol hydrochloride.

Background

Tuberculosis is a chronic infectious disease which seriously harms the health of people, about 20 hundred million people infect tuberculosis worldwide at present, about 850-1000 million tuberculosis patients appear each year, and about 250 million deaths are caused by tuberculosis each year. China is one of 22 countries with serious prevalence of tuberculosis in the world and is also one of 27 countries with serious prevalence of multi-drug resistant tuberculosis in the world, and the number of tuberculosis patients occupies the second place in the world and is only second to India. The number of tuberculosis in China is about 140 thousands, and the number of tuberculosis deaths reaches 15 thousands every year, which exceeds the sum of the number of deaths caused by other infectious diseases. Therefore, tuberculosis is one of the major diseases which are mainly controlled in China.

Ethambutol hydrochloride is a first-line medicine of antituberculosis drugs, belongs to an arabinose analogue, is mainly used for treating patients with common primary treatment and secondary treatment tuberculosis, is discovered in 1961 due to the effect of inhibiting human and bovine tuberculosis bacilli, acts on mycobacterium arabinosyltransferase, and exerts antibacterial effect by inhibiting the polymerization of arabinosyl into arabinogalactan and influencing the formation of cell wall mycolic acid-arabinogalactan-proteoglycan complex. Ethambutol hydrochloride is a first-line medicine recommended by the world health organization, and has extremely important clinical significance in the field of antituberculosis drugs.

Ethambutol hydrochloride is chemically named as [2R,2[ S- (R, R) ] -S ] - (+) -2,2' - (1, 2-ethanediyldiimino) -bis-1-butanol dihydrochloride. The ethambutol hydrochloride has two chiral centers, so the ethambutol hydrochloride has optical activity, 3 isomers of levorotatory isomer, dextrorotatory isomer and meso isomer, the clinically used ethambutol hydrochloride is the dextrorotatory isomer, and the activity of the dextrorotatory isomer is 500 times that of the levorotatory isomer and 12 times that of the meso isomer. Therefore, the optical purity of ethambutol hydrochloride determines the clinical efficacy of the product.

At present, the industrial production of ethambutol hydrochloride at home and abroad is basically carried out by a process of reacting an intermediate D-2-aminobutanol with 1, 2-dichloroethane (methods for preparing ethambutol and ethambutol hydrochloride [ P ] CN 201210413254.7, 2012-10-25 ]. The existing process has been developed for a long time, so that the reaction efficiency and the optical purity are greatly improved, but the synthetic route has inherent defects. Firstly, the synthetic intermediate D-2-aminobutanol adopts a chemical method, raw materials are not easy to obtain, the reaction selectivity is not high, manual resolution is involved, and the process is complex and the raw materials are wasted; secondly, the problems of excessive consumption of D-2-aminobutanol and more byproducts exist in the D-2-aminobutanol and the 1, 2-dichloroethane, so that the reaction efficiency is low and the separation is difficult. Therefore, the development of a new route method has great significance for overcoming the defects of the existing process route. In addition, in the process of producing ethambutol by using D-2-aminobutanol and 1, 2-dichloroethane, the expensive D-2-aminobutanol needs to be greatly excessive to inhibit the N-polyalkyl substitution reaction, and even if the N-polyalkyl substitution reaction is generated, more byproducts are produced, which brings troubles for separation and purification. Therefore, the existing method for preparing ethambutol hydrochloride has many defects, and a new method with good selectivity, high yield, small environmental pollution and simple and convenient operation needs to be found.

Disclosure of Invention

In order to solve the problems, the invention takes the natural product L-2-aminobutyric acid as an intermediate to synthesize the ethambutol hydrochloride, realizes kilogram-level production of the intermediate L-2-aminobutyric acid by using an enzyme catalysis method and taking the L-threonine as a raw material, realizes one-step reduction of carboxylic acid and amide by using metal cobalt catalysis, and has the total yield of 70 percent.

The specific technical route of the invention is as follows:

1. the efficient industrial production of L-2-aminobutyric acid is realized by a 'one-pot method' by using L-threonine as a substrate and utilizing coenzyme regeneration cycle (figure 2).

The optimized technical scheme is that genetic engineering bacteria for simultaneously expressing Formate Dehydrogenase (FDH) and leucine dehydrogenase (FDH) are constructed by utilizing a gene recombination technology, and FDH/FDH co-expression crude enzyme liquid containing FDH and FDH is prepared by fermentation; preparing a reaction system containing threonine, ammonium formate, TD enzyme solution, FDH/FDH co-expression crude enzyme solution, NAD + and pyridoxal phosphate in a buffer solution, and carrying out a biocatalytic reaction to prepare the L-2-aminobutyric acid.

2. And then L-2-aminobutyric acid reacts with oxalyl chloride under the condition that triethylamine and dichloromethane serve as solvents, and the amidation reaction is carried out by heating to obtain the diamide dicarboxylic acid. The byproduct triethylamine hydrochloride is recycled and reused after neutralization.

3. Adding methanol, diamide dicarboxylic acid, a cobalt catalyst and an equimolar amount of tridentate phosphine ligand into a high-pressure kettle, introducing hydrogen to a certain pressure, heating to perform catalytic hydrogenation reaction, and obtaining the ethambutol.

Preferably, the cobalt catalyst is Co (CH)₃COO)₂·4H₂O，Co(BF₄)₂·6H₂O, and more preferably Co as the catalyst is Co (BF)₄)₂·6H₂O；

Preferably, the tridentate phosphine ligand is 1,1, 1-tris (diphenylphosphinomethyl) ethane, (4S, 5S) -4, 5-bis (diphenylphosphinomethyl) -2- (6-diphenylphosphino) n-hexyl-1, 3-dioxolane, and more preferably, the tridentate phosphine ligand is 1,1, 1-tris (diphenylphosphinomethyl) ethane.

4. Slowly introducing hydrogen chloride gas into the ethanol solution of ethambutol, stirring, controlling the temperature at 45-55 ℃ and the pH value at 3.0-4.0, stopping introducing the hydrogen chloride gas when the pH value is stable and unchanged, continuing to keep the temperature and stirring for half an hour, cooling to 15 ℃ after the pH value is unchanged, keeping the temperature for half an hour, and filtering to obtain the ethambutol hydrochloride product.

Drawings

FIG. 1 is a synthetic route for ethambutol hydrochloride;

FIG. 2 shows the principle of a route for synthesizing L-2-aminobutyric acid from L-threonine;

FIG. 3 is a nuclear magnetic spectrum of ethambutol hydrochloride¹HNMR；

FIG. 4 is a nuclear magnetic spectrum of ethambutol hydrochloride¹CNMR。

Detailed Description

Example 1: synthesis of L-2-aminobutyric acid

2382.4g L-threonine (20 mol), 1261.2g ammonium formate (1mol), 1L TD enzyme solution, 1L FDH/FDH co-expression crude enzyme solution, 2L mixed solution of NAD + and pyridoxal phosphate are added into 5L phosphate buffer solution, reaction is carried out for 24h at 40 ℃, after macromolecular impurities are adsorbed by macroporous resin, the product is concentrated, ethanol is added to dissolve the impurities, and the obtained solid product is filtered and dried to be used for the next reaction. The dried product was 1959.2g of L-2-aminobutyric acid with a purity of 96% in a yield of 91%.

Example 2: synthesis of diamide dicarboxylic acids

200 ml of methylene chloride, 103.12g L-2-aminobutyric acid (1mol), 76.16g of oxalyl chloride (0.6mol) and 200 ml of triethylamine were charged into the reaction vessel, and amidation reaction was carried out at 100 ℃ for 12 hours to obtain (2S, 2S ') -N, N' -bis (2-butyric acid) -oxamide, i.e., diamide dicarboxylic acid. After the completion of the reaction, excess low-boiling solvent was removed by rotary evaporation, and the remaining solid was recrystallized from an aqueous solution and dried to obtain 213.4g of bisamide dicarboxylic acid in 82% yield.

Example 3: synthesis of ethambutol

1L of methanol, 130.13g of diamide dicarboxylic acid (0.5mol), 22.17g of Co (BF4) 2.6H 2O (0.025mol) and 15.62g of tridentate phosphine ligand 1,1, 1-tri (diphenylphosphinomethyl) ethane in equal molar amount are added into an autoclave, hydrogen is introduced, the pressure is maintained at 0.5MPa, and catalytic hydrogenation reaction is carried out at 150 ℃ for 2H to obtain 183.88g of ethambutol, wherein the yield is 90%.

Example 4: synthesis of ethambutol hydrochloride

Slowly introducing hydrogen chloride gas into ethanol solution of 183.88 ethambutol, stirring, controlling temperature at 45-55 deg.C, pH value at 3.0-4.0, stopping introducing hydrogen chloride gas when pH is stable, stirring for half an hour, cooling to 15 deg.C when pH is not stable, maintaining temperature for half an hour, filtering to obtain ethambutol hydrochloride product with equivalent weight¹H NMR (400 MHz, D₂O) δ 4.02 – 3.89 (m, 1H), 3.82 (ddd, J = 13.1, 5.1, 2.1 Hz, 1H), 3.57 (s, 2H), 3.42 – 3.28 (m, 1H), 1.90 – 1.65 (m, 2H), 1.02 (ddd, J = 9.9, 5.0, 2.4 Hz, 3H)，¹³C NMR (100 MHz, D₂O) δ 61.46, 57.89, 40.82, 20.42, 9.09. [α]²⁵ _D = +4.7 (c = 2, H₂O) optical purity 99%.

Claims (4)

1. A process for the preparation of ethambutol comprising the steps of:

s1, producing L-2-aminobutyric acid by using a coenzyme regeneration circulation method by using L-threonine as a substrate;

s2, heating L-2-aminobutyric acid and oxalyl chloride under the condition that triethylamine and dichloromethane serve as solvents to perform amidation reaction to obtain diamide dicarboxylic acid;

s3, hydrogenating and reducing the diamide dicarboxylic acid under the conditions of cobalt catalysis and the existence of tridentate phosphine ligand to obtain the ethambutol.

2. A process for the preparation of ethambutol hydrochloride comprising the steps of:

s1, producing L-2-aminobutyric acid by using a coenzyme regeneration circulation method by using L-threonine as a substrate;

s2, heating L-2-aminobutyric acid and oxalyl chloride under the condition that triethylamine and dichloromethane serve as solvents to perform amidation reaction to obtain diamide dicarboxylic acid;

s3, under the condition of cobalt catalysis and the existence of tridentate phosphine ligand, the diamido dicarboxylic acid is hydrogenated and reduced to obtain ethambutol, and then hydrogen chloride gas is introduced to generate ethambutol hydrochloride.

3. The process according to claim 2, the cobalt catalyst used is preferably Co (BF)₄)₂·6H₂O。

4. The process according to claim 2, wherein the tridentate phosphine ligand is 1,1, 1-tris (diphenylphosphinomethyl) ethane, (4S, 5S) -4, 5-bis (diphenylphosphinomethyl) -2- (6-diphenylphosphino) n-hexyl-1, 3-dioxolane.

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