RU2435779C1 - Method of producing betulin 28-hemisuccinate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to an improved method of producing betulin 28-hemisuccinate from mother solutions from crystallising betulin from birch bark extracts. Method involves hydrolysis of mother solutions in an alkaline alcohol solution, concentrating and washing the organic extract with calcium chloride solution, treating the obtained mixture with succinic anhydride with selective acylation of betulin on the primary alcohol group in the presence of organic bases (pyridine, triethylamine) while heating to not more than 40°C. Purification is carried out by washing off impurity compounds with an organic solvent.

EFFECT: efficient method.

1 cl, 3 ex, 1 tbl

Description

The invention relates to the field of pharmaceutical industry, specifically to a method for producing betulin 28-hemisuccinate (4 - (((1R, 3aS, 5aR, 5bR, 7aR, 11aR, 11bR, 13aS, 13bS) -9-hydroxy-5a, 5b, 8, 8,11a-pentamethyl-1- (prop-1-en-2-yl) eicosahydro-1H-cyclopenta [a] chrysen-3a-yl) methoxy) -4-oxobutanoic acid) of the formula 1:

Betulin 28-Hemisuccinate is of interest as an intermediate for synthesis, as well as a biologically active compound. Betulin 28-hemisuccinate is active, in particular, as an inhibitor of leukocyte elastase, as well as fungicidal activity [US 6458834].

Known methods for the selective preparation of 28-acylated derivatives of betulin using cyclic dibasic anhydrides, in particular substituted glutaral anhydrides [I-Chen Sun, Hui-Kang Wang, Yoshiki Kashiwada, Jing-Kang Shen, L. Mark Cosentino, Chin-HoChen, Li -MingYang, and Kuo-Hsiung Lee, J.Med. Chem. 1998, 41, 4648 4657] (Scheme 1). A solution of betulin, 4-dimethylaminopridine and cyclic anhydride in pyridine is heated at 40 ° C until completion of the reaction, the pyridine bases are separated by treatment with an aqueous acid solution, and the product is purified by chromatography. The disadvantages of the method is the use of pyridine as a solvent, the use of chromatography for the purification of products.

Scheme 1

The closest analogue (prototype) to the claimed method is the method [US 6458834], in which pure betulin is acylated with succinic anhydride in the presence of imidazole at room temperature, while betulin 28-hemisuccinate is obtained as the only reaction product (Scheme 2). At a higher temperature (70 ° C), betulin acylation proceeds quantitatively for both alcohol groups.

Scheme 2

The disadvantage of the prototype method is the need to use pure betulin to obtain Betulin 28-hemisuccinate 1.

Betulin is obtained from extracts of birch bark, which is a waste of woodworking. Various solvents are used for extraction [V.A. Levdansky, N.I. Polezhaeva, A.V. Levdansky, B.N. Kuznetsov. Chemistry of Plant Raw Materials. 2004. No2. S.17-20]. Betulin with a purity of 90-98% is obtained by crystallization of extracts (aliphatic alcohols, for example isopropanol, or ethanol are used for crystallization [S. Ohara, Y. Hayashi, M. Yatagai. Utilization of bark extractives. Henkan Keikaku Kenkyu Hokoku. 1990. V.24. P.12-35 (S.A. 1994, V.120, 301339f]), however, some of the betulin and readily soluble impurities remain in the mother liquors.The problem of processing waste from the separation of betulin to produce chemically pure products with biological activity is relevant.

Along with betulin, mother liquors from crystallization of betulin contain impurities of other triterpene compounds: lupeol, oleanolic acid, phytosterols. Most of these compounds, with the exception of betulin, contain a secondary alcohol group, but do not contain a primary one. In addition, the mother liquors contain aliphatic acids, phenolic acids, “bound” acids, which are impurities of polyesters (suberin), impurities of hydrocarbons.

The present invention is to develop a method for producing pure 28-betulin hemisuccinate from waste from the extraction of birch bark, resulting from the production of pure betulin.

The problem is solved by the method of obtaining betulin 28-hemisuccinate from waste from the extraction of birch bark, resulting from the production of pure betulin. The mother liquor from crystallization of the extract of birch bark is purified from impurities of acids and polyesters and acylated with succinic anhydride in the presence of organic bases (pyridine, triethylamine) with heating not higher than 40 ° С followed by washing of the target product with an organic solvent.

The solution to the task of cleaning the mother liquors from impurities of acids, phenols and polyesters is achieved by alkaline hydrolysis of the mother liquors from crystallization of betulin, the conversion of surface-active salts of fatty acids into sparingly soluble calcium salts, followed by the separation of acid salts.

Obtaining of betulin 28-hemisuccinate is achieved by selective acylation of the primary alcohol group of betulin, which is present in purified mother liquors, with succinic anhydride in the presence of organic bases (pyridine, triethylamine) at a temperature not exceeding 40 ° С. Under these conditions, the secondary alcohol groups of betulin 2, lupeol 5, sterols (in particular, lanosterol 6) are not affected (Scheme 3). The resulting 28-hemisuccinate betulin 1 is a polar crystalline compound, poorly soluble in low-polar solvents. Impurity compounds are separated from the target product by washing with a solvent.

The inventive method for producing 28-hemisuccinate betulin is illustrated by the following examples.

Example 1. Purification of mother solutions containing betulin from free and bound acids.

The concentrate of the mother liquor from crystallization of the birch bark extract is a departure from betulin crystallization - (20 g), [C. Eckerman, R. Ekman, Pap.ja puu, 3 (1985) 100] are dissolved in 200 ml of isopropanol and 10 g of KOH are added. The mixture is boiled for 6 hours, the solution is decanted and filtered. The resulting filtrate was concentrated to constant weight by evaporation in vacuo. The concentrate was extracted with methyl tertiary butyl ether (MTBE) (3 × 50 ml) with stirring.

The resulting extract was washed with a solution of CaCl ₂ to clean from surface-active acid salts (2x20 ml of 10% CaCl ₂ ). The organic layer was filtered, dried (Na ₂ SO ₄ ), evaporated to give 7.2 g of a yellow solid after concentration.

According to chromatography-mass spectrometry, the mixture contains betulin, lupeol, minor impurities of lanosterol, taraxasterol, terpene hydrocarbons (bergamotene, santalen).

Example 2. Obtaining of 28-betulin hemisuccinate from mother liquor concentrate after separation of free and bound acids.

5 g of the concentrate obtained according to example 1 is dissolved in 50 ml of MTBE, 5 ml of pyridine and 5 g of succinic anhydride are added and heated with stirring (30-35 ° C, 20 hours).

Water (5 ml) was added to the mixture, the mixture was stirred for 2 hours under heating (40-50 ° C). The aqueous layer was separated, the organic layer was washed with 5% H ₂ SO ₄ (2 × 30 ml), dried (Na ₂ SO ₄ ), concentrated, and 5.2 g of the product mixture were obtained in the form of a solid powder containing 28-betulin hemisuccinate and a mixture triterpene secondary alcohols, hydrocarbon impurities. The resulting product was washed with petroleum ether (50 ml), MTBE (2 × 5 ml), dried, and 28 betulin hemisuccinate was obtained in the form of a white powder (1.8 g).

The content of the basic substance 95% + (HPLC).

¹ H NMR spectrum (Py-d ₅ ) (300.13 MHz, δ _H , ppm): 4.79 (s, 1H), 4.65 (s, 1H), 4.49 (d, J = 11.1 Hz, 1 N), 4.06 (d, J = 11.1 Hz, 1 H), 3.37 (m, 1H), 2.87 (m 4H), 2.44 m (1H), 1.65 (s, 3H), 1.15 (s, 3H), 0.95 (s, 3H), 0.91 (s, 6H), 0.78 (s, 3H) 0.6-2.1 (signal set, 28 N) ¹³ C NMR spectrum (Py-d ₅ ) (75.48 MHz, δ _C , ppm)

174.78 s, 173.22 s, 150.44 s, 110.11 t, 77.99 d, 62.85 t, 55.71 d, 50.57 d, 49.01 d, 47.83 d, 46.75 s, 42.79 t, 41.01 s, 39.39 t, 39.15 s, 37.68 d, 37.32 t , 34.77 s, 34.41 s, 29.97 t, 29.85 t, 28.54 sq.

28.16 t, 27.33 t, 25.48 t, 20.81 t, 19.19 q, 18.62 t, 16.28 q, 16.23 q, 14.79 q

Example 3

Obtaining 28-betulin hemisuccinate from the mother liquor concentrate after separation of free and bound acids. Specific conditions and outputs are indicated in the table.

5 g of the concentrate obtained according to example 1 are dissolved in 50 ml of solvent (MTBE, CH ₂ Cl ₂ ), 5 ml of base (pyridine, triethylamine) and 5 g of succinic anhydride are added and stirred for 20 hours with heating.

Water (5 ml) was added to the mixture, the mixture was stirred for 2 hours under heating (40-50 ° C). The aqueous layer was separated, the organic layer was washed with 5% H ₂ SO ₄ (2 × 30 ml), dried (Na ₂ SO ₄ ), concentrated, and 5.2 g of product mixture were obtained in the form of a solid powder containing 28-betulin hemisuccinate and a mixture triterpene secondary alcohols, hydrocarbon impurities. The resulting product was washed with MTBE (2 × 5 ml), dried, and 28 betulin hemisuccinate was obtained in the form of a white powder.

The content of the basic substance 95% + (HPLC).

From the data presented in the table, it is seen that the best yield is achieved by carrying out the reaction in the presence of pyridine.

Table Note
R Loading of betulin containing mother liquor purified from acids and polyesters Solvent Base The temperature of the reaction, ° C The yield of compound 1, g 3 5 g MTBE Et ₃ N 30-35 1.3 four 5 g CH ₂ Cl ₂ pyridine 40 1.7 5 5 g CH ₂ Cl ₂ Et ₃ N 40 1,5

Claims (1)

A method of obtaining a 28-betis hemisuccinate of formula 1:

by acylation of betulin with succinic anhydride, characterized in that betulin-containing mother liquors obtained by crystallization of birch bark extracts in aliphatic alcohol, previously purified from impurities of acids and polyesters by alkaline hydrolysis in a solution of aliphatic alcohol, followed by concentrated organic solution with washing, are used as betulin. calcium chloride, and acylation is carried out with an excess of succinic anhydride in the presence of organic bases (pyridine, triethylamine) when heated not higher than 40 ° C, followed by washing the target product with an organic solvent.