CS227527B1 - Method of preparing l-galactose - Google Patents

Description

The invention relates to a process for the preparation of L-galactose from crystalline 1-deoxy-1-nitro-L-galactitol or from a mixture of 1-deoxy-1-nitro-L-galactitol and 1-decxy-1-nitro-L-talitol.

L-galactose is a scarce rare carbohydrate that occurs in nature, but its isolation from natural material is challenging, (C.Araki, K.Arai Methods Carbohyd.Chem. 1, 122 (1962)). It can be prepared synthetically from L-galactonolactone by sodium amalgam reduction, but the yield is low. A. Frush, HSIsbell: Methods Carbohyd.Chem. 1, 127 (1962). ^more preferred is the synthesis of L-galactose from L-lyxose and nitromethane in the presence of sodium methylate. jfv.Bilik: Coll, Czech.Chem.Commun.

39, 1621 (1974). This reaction produces a mixture of 1-deoxy-1-nitro-L-galactitol and 1-deoxy-1-nitro-L-talitol. L-galactose and L-talose are obtained from these by the action of sulfuric acid or hydrogen peroxide under the catalytic action of molybdate ions. A disadvantage of this method is that the obtained mixture of sugars always contains a considerable amount of L-lyxose. As a result, the yields are reduced and the separation and cleaning of the products becomes more difficult.

These disadvantages are overcome by the process for the preparation of L-galactose according to the invention, which consists in the fact that 1-deoxy-1-nitro-L-galactitol, respectively, is used. decompose 1-deoxy-1-nitro-L-galactitol and 1-deoxy-1-nitro-L-talitol with sulfuric acid at 15-20 ° C for 3 to 5 min., remove the inorganic from the reaction mixture with methanol the salts and their residue are collected on a column by means of a cation and anion exchanger, concentrated to a syrup and crystallized from methanol, or crystallized from L-galactose and L-talose using p-toluidine isolated by filtration, and the solution from l-galactose is isolated. of methanol crystallized.

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As we have found, 1-deoxy-1-nitro-L-galactitol as well as a mixture of 1-deoxy-1-nitro-L-galactitol and 1-deoxy-1-nitro-L-talitol is not stable in an alkaline® environment, but decomposes to give the starting 1-lyxose. When preparing an aqueous solution of 1-deoxy-1-nitro-L-galactitol sodium salt, respectively. the above citric acid mixture begins to decompose immediately and continues until all of the solution is added to the sulfuric acid or reacted with hydrogen peroxide. To prevent the decomposition of 1-deoxy-1-nitro-L-galactitol, respectively. of the above-mentioned mixture, it is necessary to add the solution of its sodium salt to the sulfuric acid as quickly as possible, preferably in 3-5 minutes. When working with a higher amount of substance, it is advantageous to prepare this solution in portions so that it can always be processed in the prescribed time. Following this procedure, the resulting product contains only traces of L-lyxose and pure L-galactose is obtained in high yield.

For the preparation of L-galactose, it is not necessary to start from pure 1-deoxy-1-nitro-L-galkatitol, but it is also possible to use a mixture thereof with 1-deoxy-1-nitro-L-talitol which contains no L-lyxose and it can be prepared from L-lyxose, nitromethane and sodium methylate. In this case, a mixture of L-galactose and L-talose is obtained from which the major part of L-galactose is isolated by crystallization, and from the remaining sugar mixture Ltalose is prepared after conversion to N-p-tolyl-L-talozylamine.

Example 1

1-Deoxy-1-nitro-L-galactitol (21.1 g) is dissolved in small portions in sodium hydroxide solution (4.0 g) in water (80 ml). Each portion of the solution is added dropwise over 5 min. to sulfuric acid (20 ml) diluted with water (25 ml) at

227 527 at 20 ° C. The reaction mixture was stirred for a further 30 min, neutralized with sodium carbonate solution (35 g) in water (150 ml) and diluted with methanol (1000 ml) to remove more sodium sulfate. After filtration, the solution is concentrated to a volume of 230 ml and deionized by percolation through a cation and anion exchanger column having dimensions of 40 cm in length and 2 cm in diameter. A solution containing only traces of L-lyxose in addition to L-galactose is concentrated to a syrup which is dissolved in methanol (100 ml). 14.5 g of L-galactose are crystallized. melting point l69 ° C, - 79.5 °, yield 80%

Example 2

A mixture of 1-deoxy-1-nitro-L-galactitol and 1-deoxy-1-nitroL-talitol prepared from L-lyxose, nitromethane and sodium methylate (21.1 g) is dissolved in small portions in sodium hydroxide solution (4), 0 g (in water (80 ml)). Each portion of the solution was added dropwise over 5 min. Sulfuric acid (20 ml) was diluted with water (25 ml) at 20 ° C. The reaction mixture was stirred for a further 30 min, neutralized with sodium carbonate solution (35 g) in water (150 ml) and diluted with methanol (1000 ml) to remove more sodium sulfate. After filtration, the solution is concentrated to a volume of 250 ml and deionized by percolation through a 40 cm long, 2 cm diameter cation and anion exchanger column. The solution containing L-galactose next to L-talcose and only traces of L-lyxose is concentrated to a syrup which is dissolved in methanol (80 ml). 9.0 g of L-galactose crystallize in 50% yield. A solution of p-toluidine (6 g) in 96-ethanol (25 ml) and (0.5 ml) 10% acetic acid was added to the mother liquor after crystallization of L-galactose (35 ml).

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N-p-tolyl-L-talozylamine crystallizes, which is filtered off and washed with (200 ml) 50% ethanol. The solution is purified by adding (10 g) of activated carbon to a syrup which is dissolved in methanol (50 ml), and crystallizes 5.5 g of L-galactose. Mp 168 ° C, -79.3 ° · Yield 69%.

The invention has extensive application in the study of biochemical processes as a model substance in medicine. L-galactose is a rare and hardly available carbohydrate.

Claims (1)

OBJECT OF THE INVENTION 227 527 Process for the preparation of L-galactose, characterized in that 1-deoxy-1-nitro-L-galactitol or a mixture of 1-deoxy-1-nitro-L-galactitol and 1-deoxy-1-nitro-L-talitol are dissolved in an aqueous solution sodium hydroxide and decomposed with sulfuric acid at 15 to 20 ° C for 3 to 5 min. and after removal of the inorganic salts or isolation of L-talose with p-toluidine in the form of crystalline N-p-tolyl-L-talozylate, it is crystallized from the methanol solution.