HRP921062A2 - Process for the preparation of calcium 2,5-dihydroxy-benzensulfonate - Google Patents

Description

Description of the invention

Background of the invention

This invention relates to a process for the preparation of N-formyl-L-aspartic acid anhydride (F-Asp=0), which is used for the preparation of peptide sweeteners, which contain the terminal residue of aspartic acid as methyl ester α-L-aspartyl-L-phenylalanine ( α-APM).

Dipeptides, which contain aspartyl, can be prepared in a coupling reaction in which aspartic acid is added to another amino acid or its derivatives, such as L-phenylalanine or its methyl ester. In these coupling reactions, an amino protecting group, attached to the residue of aspartic acid, such as formyl, acetyl, acetoacetyl, benzyl, substituted or unsubstituted carbo benzox, t-butoxy carbonyl and hydrogen halide salt is necessary. The amino protecting group, commonly referred to in the art as an N-protecting group, will be referred to as N-formyl for the purposes of this invention, as the formyl residue acts as a blocking agent. Formylated aspartic anhydride is used in bulk as a starting material and its process is described in more detail. Ch. US Patents 4,173,562, 3,933,781 and 3,962,207, which are incorporated herein by reference.

The joining reactions are carried out in a solvent and mainly represent protected procedures for the production of α-L-aspartyl-L-phenylalanine methyl ester (α-APM); Ch. US Patent 3,962,207, Uchiyama, US Patent 4,173,562, Bachman, and EPO Patent 127,411, Yaichi et al., which are incorporated herein by reference.

N-formyl-L-aspartic anhydride is usually prepared from a reaction mixture of aspartic acid with a large amount of formic anhydride and acetic acid. At a certain stage of the process, we have to remove the remaining formic acid by distillation and separate it from acetic acid, which all represents an additional cost for the final product. This invention excludes special distillation and separation procedures.

Summary of the invention

This invention relates to a process for the preparation of N-formyl-L-aspartic acid anhydride (F-Asp=0). The by-products of the reaction, which are formed during the formation of F-Asp=0, can serve as a solvent in the coupling reaction with another amino acid, for example L-phenylalanine, in a way that excludes separation problems, thus reducing preparation costs.

F-Asp=0 is prepared in the reaction of L-aspartic acid in the presence of effective amounts of acetic anhydride, under conditions sufficient for the formation of N-formyl-L-aspartic anhydride. After that, we add an effective amount of acetic anhydride and C3-C6 secondary alcohol to the reaction mixture, so that the rest of the formic acid is consumed. The resulting reaction mixture of N-formic anhydride-L-aspartic acid is suitable for further reactions without modification.

Formyl-L-aspartic anhydride is usually prepared by mixing aspartic acid with acetic anhydride and formic acid in a reaction process, which is known in the state of the art. Ch. US patent no. 3,933,781, 3,962,207 and 4,173,562. However, according to this invention, we use a minimal amount of formic acid (1.2-1.35 molar equivalents per mole of aspartic acid). It is particularly important to convert the remaining formic acid to isopropylformate by adding acetic anhydride and isopropyl alcohol to the reaction mixture.

Description of the invention

According to the process of this invention, L-aspartic acid is mixed with a minimum amount of formic acid (at least 1.2 molar equivalents per mole of aspartic acid) and acetic anhydride (at least about 2.0 molar equivalents per mole of aspartic acid), in the given case in the presence catalyst, eg magnesium oxide, which gives the anhydride of N-formyl-L-aspartic acid.

Suitable catalysts include metal oxides, hydroxides and salts, and are described in US Patents 4,508,912 and 4,550,180, which are incorporated herein by reference. We perform this reaction at temp. up to about 52°C. We preferentially mix the mixture at about 50°C for at least about 2.5 hours. After that, we add additional acetic anhydride (about 0.2 moles) to convert any remaining unreacted formic acid to formic-acetic anhydride, i.e. mixed anhydride. After an additional 2.5 hours, we add C3-C6-secondary alcohol, i.e. isopropyl alcohol (at least about 0.3 molar equivalents based on the total added formic acid) to the reaction mixture, so that all formic-acetic anhydride is converted into the corresponding ester, i.e. isopropylformate . The amount of formic acid used is preferably 1.3 to 1.35 molar equivalents per mole of aspartic acid.

Alternatively, we can add acetic anhydride to the reaction mixture all at once (2.3-2.9 moles per mole of aspartic acid), at the beginning of the reaction, and after that we can add secondary alcohol to consume the rest of the formic acid in the reaction with the mixed anhydride, which leads to the formation of the corresponding ester. We can also add a smaller amount of acetic anhydride in the same degree as secondary alcohol. But the formic acid, the main part of the acetic anhydride and the catalyst are preferably mixed for about 2-3 hours, followed by the addition of a smaller part of the acetic anhydride. The reaction is then stirred for the next 2-3 hours, after which secondary alcohol (isopropanol) is added. We preferentially mix this final reaction mixture for another 2-3 hours at 50°C until the end. The product, the anhydride of N-formyl-L-aspartic acid, can then be connected to another amino acid, eg L-phenylalanine or L-phenylalanine methyl ester in situ, which excludes any expensive and complicated separation techniques. The side products of the reaction serve as a co-solvent for the amino acid coupling reaction. The resulting dipeptides are intermediates in the preparation of aspartame.

The following examples are provided to clarify and illustrate the present invention, without in any way limiting it in any respect. Those skilled in the art are familiar with all materials and techniques of this invention.

Example 1

Dissolve 0.12 g (0.003 mol) of magnesium oxide, catalyst, in 16 mm (ml) (0.405 mol) of 95% formic acid. After that, add 60.2 ml of acetic anhydride and heat for 10-15 minutes at 35-40°C. After that, add 39.93 g (0.3 mol) of L-aspartic acid and stir for 2.5 hours at 50±2°C. At that point, add a further 8.6 ml of acetic anhydride and continue the reaction for a further 2.5 hours at 50±2°C. After that, add 9.2 ml (0.120 mol) of isopropyl alcohol and continue heating for another 2 hours. During this time, N-formyl-L-aspartic anhydride was formed, which was proven by high performance liquid chromatography (HPCL).

Example 2

Magnesium oxide (0.121 g; 0.003 mol) was dissolved in 16.4 ml (0.406 mol) of 93.4% formic acid under nitrogen. After that, we added 62.5 ml (0.655 mol) of acetic anhydride, and a white precipitate followed. We raised the temperature of the mixture to 37-38°C during the next 30 minutes. After that, L-aspartic acid (39.93 g; 0.30 mol) was added and the reaction mixture was heated at 48-50°C for 2.5 hours, after which additional acetic anhydride (8.6 ml; 0.09 mol) was added. and heated for the next 2.5 hours, after which we added 9.2 ml (0.120 mol) of isopropyl alcohol. We heated for another 2.0 hours at 50±2°C. The reaction mixture was then cooled to room temperature (22-27°C).

Example 3

Magnesium oxide (0.4 g; 0.01 mol) was dissolved in 53.3 ml (1.35 mol) of 95% formic acid and 200 ml (2.10 mol) of acetic anhydride. Due to the reaction, the temperature rose to 40°C (from 20-22°C) during 15 minutes. After that, we added L-aspartic acid (133.1 g, 1.0 mol) and heated the resulting suspension at 43-50°C for 2.5 hours, after which we added 28.9 ml (0.303 mol) of additional acetic anhydride. We continued the heating for the next 2.5 hours, after which we mixed in 30.7 ml (0.4 mol) of isopropyl alcohol. We stirred this mixture for 1.5 hours at 48-50°C and then allowed it to cool to room temperature (25±2°C). The resulting mixture without modifications is suitable for further reactions.

Example 4

Formic acid (95.7%, 16 ml, 0.405 mol) was added dropwise to 60.2 ml (0.631 mol) of acetic anhydride over 5 minutes, and the temperature rose to 40°C. The mixture was stirred for the next 55 minutes, after which 0.43 g (0.003 mol) of magnesium acetate and 39.93 g (0.3 mol) of L-aspartic acid were added. The resulting suspension was heated at 47-48°C for 2.5 hours, after which acetic anhydride (7.1 ml; 0.0744 mol) was added and heated for another 2.5 hours. After that, we added isopropyl alcohol (7.21 g, 0.120 mol) and heated for another 1.5 hours.

Example 5

Formic acid (16.0 ml; 0.405 mol) was added to 0.21 g (0.003 mol) of magnesium oxide under nitrogen and stirred until the solid dissolved. After that, acetic anhydride (60.2 ml; 0.631 mol) was added, during which a precipitate formed and the temperature rose to 40°C in 15 minutes. After that, we added L-aspartic acid (39.93 g; 0.3 mol) and heated the suspension to 48-50°C, then added acetic anhydride (9.3 g; 0.0974 mol) and heated another 1, 5 hours, after which we added isopropyl alcohol (11.9 ml; 0.155 mol) and heated the mixture for another 1.5 hours.

In similar operations, we used different secondary alcohols, and with the conditions from the procedures mentioned here, we obtained N-formyl-L-aspartic acids, and the final reaction mixture without modifications is suitable for further reactions.

Claims (14)

1. The procedure, characterized by the fact that it includes: (a) converting L-aspartic acid with formic acid in the presence of an effective amount of acetic anhydride, under conditions enabling the formation of N-formyl-L-aspartic anhydride; and, after that, adding k (a) (b) as an effective amount, the amount of C3-C6 secondary alcohol, which consumes the rest of the formic acid, and the resulting N-formyl-L-aspartic anhydride in the reaction mixture without modifications is suitable for further reactions. 2. The process according to claim 1, characterized in that the secondary alcohol is isopropanol and that the reaction is carried out in the presence of a catalyst. 3. The method according to claim 2, indicated by (i) adding formic acid to the reaction mixture in an amount of about 1.25 to about 1.35 molar equivalents per mole of L-aspartic acid and (ii) adding acetic anhydride in two stages, the main part in degree (a) and the minor part in degree (b). 4. The process according to claim 3, characterized in that acetic anhydride is added in step (a) in an amount of about 2.1 to about 2.5 molar equivalents per mole of L-aspartic acid. 5. The method according to claim 4, characterized in that acetic anhydride is added in step (b) in an amount of about 0.2 to about 0.4 molar equivalents per mole of L-aspartic acid. 6. The method according to claim 5, characterized in that isopropanol is added in an amount of about 0.25 to about 0.5 molar equivalents per mole of L-aspartic acid. 7. The process according to claim 6, characterized in that the reaction is performed at a temperature below about 52°C. 8. The method according to claim 7, characterized in that the temperature is about 50°C. 9. The procedure, characterized by the fact that it includes the following steps: (a) converting L-aspartic acid with formic acid in the presence of an effective amount of acetic anhydride and under conditions enabling the formation of N-formyl-L-aspartic anhydride; (b) adding a second portion of acetic anhydride and (c) adding an effective amount of C3-C6 secondary alcohol utilizing the remaining formic acid; and the resulting N-formyl-L-aspartic anhydride without modifications is suitable for further reactions. 10. The process according to claim 9, characterized in that the secondary alcohol is isopropanol and that the reaction is performed in the presence of a catalyst. 11. The method according to claim 10, characterized in that (i) add formic acid to the reaction mixture in an amount of about 1.25 to about 1.35 molar equivalents per mole of L-aspartic acid; (ii) add acetic anhydride in step (a) in an amount of about 2.1 to about 2.5 molar equivalents per mole of L-aspartic acid and add (or) acetic anhydride in step (b) in an amount of about 0.2 to about 0.4 molar equivalents per mole of L-aspartic acid. 12. The method according to claim 11, characterized in that isopropanol is added in an amount of about 0.25 to about 0.5 molar equivalents per mole of L-aspartic acid. 13. The method according to claim 12, characterized in that the reaction is carried out at a temperature below about 52°C. 14. The method according to claim 13, characterized in that the temperature is about 50°C.