CS225526B1 - Preparation of l-manose - Google Patents

Description

The present invention relates to a process for the preparation of L-mannose from crystalline 1-deoxy-1-nitro-L-mannitol.

L-mannose is a six-carbon rare carbohydrate that cannot be prepared from natural material and must therefore be prepared synthetically. The most suitable method for the preparation of L-mannose is the condensation of L-arabinose with nitromethane in the presence of sodium methylate. In this reaction, a mixture of sodium salts of 1-deoxy-1-nitro-L-mannitol and 1-deoxy-1-nitro-L-glucitol is formed which is decomposed by the action of sulfuric acid / J. Sowden, H.O.L. Fischer; Soc. 67,1963 (1947j)]

Methods Carbohyd.Chem. 1. 132 (1962) or with hydrogen peroxide under catalysis with molybdate ions. Commun. 39, 1621 (1974)] to form L-mannose and L-glucose. The mixture of 1-deoxy-1-nitro-1-mannitol and 1-deoxy-1-nitro-L-glucitol can be separated by fractional crystallization, but usually decomposes into L-mannose and L-glucose starting from a mixture of sodium salts. , which is obtained by condensing L-arabinose with nitromethane. The sugar mixture obtained, from which L-mannose is isolated as insoluble phenylhydrazone, always contains a considerable amount of L-arabinose. As a result, satisfactory yields are not achieved and it is difficult to separate the mixture of sugars.

These disadvantages of the prior art are eliminated by the process for the preparation of L-mannose according to the invention, which consists in that 1-deoxy-1-nitro-L-mannitol is decomposed with sulfuric acid at a temperature of 15 to 20 ° C for 3 to 5 The inorganic salts are removed from the reaction mixture with methanol and the residue is collected on a column using a cation and ariion exchanger, concentrated to a syrup and crystallized from methanol.

-t, 225 526

As we have found, 1-deoxy-1-nitro-L-mannitol is not stable in an alkaline environment, but decomposes to form an exit! L-arabinose. When an aqueous solution of 1-deoxy-1-nitro-L-mannitol sodium is prepared prior to processing into L-mannose, the decomposition to L-arabinose begins immediately and continues until all of the solution is added to the sulfuric acid. up to 2 hours, depending on how much substance is processed. In order to prevent the decomposition of 1-deoxy-1-nitro-L-mannitol into L-arabinose, it is necessary to add the sodium salt solution to the sulfuric acid as quickly as possible, at most within 5 minutes. When working with a higher amount of substance, it is advantageous to prepare this solution in portions so that it can be processed in the prescribed time. In such a case, the resulting product contains only traces of L-arabinose and L-mannose can be isolated by crystallization. There is no need to isolate it as phenylhydrazone and do not use phenylhydrazine, which is harmful to health.

Example 1

1-Deoxy-1-rfitro-L-mannitol (21.1 g) is dissolved in a solution of sodium hydroxide (4.0 g) in water (80 ml) by dividing into 5 equal portions and each portion of the solution is added dropwise into sulfuric acid (20 mL) diluted with water (25 mL) for 5 min, at a rate such that the temperature did not exceed 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 most of the sodium sulfate. After filtration, the solution is concentrated to a volume of 25 ml and deionized by percolation through a 40 cm long and 2 cm diameter exchanger-anion exchanger knee. A solution containing only traces of L-arabinose in addition to L-mannose is added

5,225,526 is concentrated to a syrup which is dissolved in a mixture of methanol (30 ml) and 96% ethanol (70 ml). 13.6-14.5 g of L-raanose crystallize, m.p. 132 ° C, - 13.9 °. Yield 76-81%.

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

Claims (1)

OBJECT OF THE INVENTION 225 526 Process for preparing L-mannose, characterized in that 1-deoxy-1-nitro-L-mannitol is decomposed in sulfuric acid solution at 15 to 20 ° C for 5 to 5 minutes after dissolution in sodium hydroxide solution. The inorganic salts and their residue are deionized on a column using a cation and anion exchanger, concentrated to a syrup and crystallized from methanol.