JPS6055063B2 - Optical separation method of DL-cysteine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for optically resolving DL-cysteine, and in particular, converts DL-cysteine into a hydrochloride hydrate, and then optically resolves this to obtain L-(or D-)cysteine hydrochloride. The present invention relates to a method for preferentially obtaining salt hydrates and a method for fractionating them or simultaneously producing them as crystals with different particle sizes.

Cysteine is one of the sulfur-containing amino acids, and there are three types: optically active monomer, L-form, and optically inactive L-form (racemic), which is a mixture of equal amounts thereof.
Industrially, currently mainly natural products (e.g. hair, wool, etc.)
Because it is produced by extraction from the hydrolyzate of
- Cysteine is the main ingredient, and is used in pharmaceuticals, food additives, cosmetics, feed, etc. However, because it relies on natural products for raw materials, the problem is that supply is unstable. Therefore, various methods of synthesizing by chemical means are being considered, using easily available chemicals as raw materials, but no matter which known methods are used, cysteine synthesized by chemical means is It is a DL-form, and an optical splitting operation is required to selectively obtain only the L-form. D-cysteine, on the other hand, has recently been discovered to be effective as a drug and has attracted attention, but it is difficult to find it naturally, so the L-form from the natural product is racemized to form the DL-form, or There is no suitable method other than to separately synthesize the DL-form by chemical means and obtain it by optical resolution. In general, various methods are known for the optical resolution of racemic organic compounds, including physicochemical methods, chemical methods, biological methods, and enzymatic methods.Many attempts have also been made for amino acids, mainly for glutamic acid. being done.

Among the optical resolution methods that have been proposed so far, the most industrially advantageous one is the so-called seed crystallization method, which can preferentially isolate the L-isomer or D-isomer directly from an aqueous solution of the racemate. However, for many amino acids, DL as a whole forms a molecular compound, so it is impossible to resolve them as they are by seeding crystallization. Therefore, various attempts have been made to find divisible crystal forms such as salts with organic acids and inorganic acids, metal salts, N-acylation, and other derivatives, but it has not been possible to predict the composition of divisible crystals for individual amino acids. The possible laws are not yet known, so the reality is that we have to narrow down our focus empirically from among the vast number of possible combinations and conduct numerous experiments to find them. Regarding cysteine, N
There are some reports on chemical methods such as converting into -acyl-S-benzyl derivatives, adding an optically active resolving agent to this, and resolving using the difference in solubility of the resulting diastereomers. Until now, no method has been known of directly physicochemically optically resolving cysteine.

That is, not only does cysteine have a relatively low solubility in a neutral aqueous solution, but it is also easily oxidized to cysteine by dissolved oxygen, and in particular, the presence of trace amounts of metals such as iron and copper significantly accelerates the oxidation to cysteine. Furthermore, DL-integrated cysteine forms a molecular compound and has a lower solubility than L-integrated (or D-integrated), so it is considered impossible to divide the cysteine by inoculation.
The present inventors have completed the method of the present invention as a result of extensive research into a method that can industrially advantageously carry out the optical resolution of cysteine. The solution is converted into an aqueous solution, and the solution is saturated or permeated. Crystals of optically active cysteine hydrochloride hydrate are inoculated in a saturated state, or optically active cysteine hydrochloride hydrate present in an excess amount of either D- or L- is crystallized in a supersaturated state, and the inoculation or crystallization is performed. The same kind of light as this using a crystal as a seed crystal! The present invention aims to provide a method for optical resolution of DL-cysteine, which is characterized by preferentially crystallizing the chemically active form and separating it from the mother liquor.

That is, by converting DL-cysteine into DL-cysteine hydrochloride monohydrate crystals, it has high solubility in water, which is advantageous for inoculation and division, and is no longer oxidized to cystine by dissolved oxygen. It was discovered that it was possible to separate L-cysteine hydrochloride hydrate crystals and D-cysteine hydrochloride hydrate crystals by an inoculation method. The present invention provides a method for supplying D-cysteine after racemizing 4 natural products L-cysteine at an industrially low cost.
- It provides a method for supplying cysteine, and the racemization method includes converting cysteine to cystine and then boiling it in concentrated mineral acid, or adding a large excess of acetic anhydride to perform acetylation. Any method may be used, such as simultaneous racemization, deacetylation, etc. to obtain optically inactive cystine, and then reduction of this to DL-cysteine. For example, those synthesized from one serine, those synthesized by hydrolyzing two thiazoline ring derivatives, those synthesized by hydrolyzing three thiazole ring derivatives, those derived from 4β-chloroalanine, etc. can be mentioned.

DL-cysteine hydrochloride hydrate can be easily produced. It is obtained as crystals by dissolving DL-cysteine in a hydrochloric acid aqueous solution at a ratio of 1 mole or less to hydrogen chloride and then concentrating the solution. The crystals can be stored in a dry state by drying them with warm air at 40°C or by washing them with an ethanol-ether-hydrochloric acid mixture.

Various means are possible to bring this aqueous solution of DL-cysteine hydrochloride hydrate into a saturated state and further into a supersaturated state.

Cooling and concentration are the most common methods, but methods such as gradually dissolving a saturated solution of the DL compound at a high temperature or adjusting the amount of hydrochloric acid may also be used. There is no particular limit to the degree of supersaturation, but considering the nature of this method, it is important to keep the degree of supersaturation to a low level if high optical purity is to be obtained.

The mother liquor after splitting can be used repeatedly by replenishing the DL form, so how much active form to take out in one split is determined by setting the degree of supersaturation in consideration of the desired optical purity. All you have to do is decide. There is no particular limit to the dividing temperature, but since the melting point of DL-cysteine hydrochloride hydrate crystals is relatively low, there is a natural limit, and the temperature is preferably 45°C.
It is carried out below ℃.

Even at low temperatures, the viscosity of the solution increases and the crystal growth rate slows down, so it is desirably carried out at a temperature of 10° C. or higher. There are no particular limitations on the crystals of optically active cysteine hydrochloride hydrate to be inoculated.

The larger the amount of adhesion, the faster the dividing operation will proceed, but in order to stir uniformly, a crystal concentration of 30% or less is desirable. On the small side, inoculation of 0.5% or more is sufficient. If the amount of inoculation is the same, the smaller the particle size, the larger the surface area, and therefore the faster the crystal growth, but since the set supersaturation degree is determined by expecting a certain crystal growth rate,
A particle size so small as to cause growth far exceeding the expected degree is not preferred because it may reduce optical purity. It is sufficient that the particle size is such that it causes no problems in terms of filtration, drying, and handling. The same applies to particles with a large particle size; if the particle size is too large, the surface area will be reduced, so a large amount must be inoculated, making it difficult to achieve a uniform stirring operation. Desirably, one with a mesh size of 20 mesh or less is used. Incidentally, from the beginning, crystals of optically active cysteine hydrochloride hydrate of both L-integrated and D-integrated with different particle sizes were inoculated at the same time, and the L-integrated and D-integrated crystals with different particle sizes were precipitated using each crystal as a nucleus. A screening method (see Japanese Patent Publication No. 37-906 Wani) can also be used. Of course, it is desirable that the optically active substance to be inoculated be pure, but optically impure substances may also be used. In other words, if the seed crystal is impure, after inoculating it into a saturated liquid, the temperature of the liquid is raised in a small range and stirred for a while to dissolve the DL form in the seed crystal and increase the optical purity of the seed crystal. I can do it. This operation can also be applied to the optically active material after splitting. That is, if the optical purity of the split optically active form does not reach the desired level, the optically active cysteine hydrochloride hydrate crystals are immersed in a saturated solution of the DL form, and the crystals are purified in a minute range while stirring. The temperature of the liquid is raised to make it unsaturated. The DL form in the optically active substance crystal begins to dissolve, and the liquid becomes a saturated solution, and the pure optically active substance remains as a crystal, which can be separated by furnace. In the mother liquor that has been split by the above operations, the other optically active form is present in excess, so either the DL form is replenished or without replenishment, seed crystals of the one which is present in excess are inoculated and the same process is carried out. Do the split.

In this case, it is also possible to spontaneously crystallize the excess active substance in a supersaturated state without inoculation and use this as a seed crystal for division. After dividing DL-cysteine hydrochloride hydrate into D-form and L-form, if necessary, the unnecessary optically active form is neutralized by a known method, oxidized and converted to cystine, and then converted to cystine by a known method. Racemize with DL-
As cysteine, it can be returned to the raw material for this splitting operation.

According to the present invention, unlike many other methods, there is no need to further neutralize or ion-exchange the optically active substance taken out after separation to remove or replace the salt.
Although it can be divided as it is in the form of L-cysteine hydrochloride hydrate crystals, which meets food additive standards, and delivered to products, it is not easy to convert the cysteine hydrochloride to cysteine if necessary. The desired cysteine can be obtained, for example, by dehydrochlorination with triethylamine or the like in an organic solvent, or by neutralization with a weak base in an aqueous solution.

Hereinafter, typical examples of the method of the present invention will be shown and explained in more detail, but these are merely illustrative examples to facilitate understanding of the present invention, and the present invention is therefore limited only to these examples. Needless to say, there is no limitation in any way.

Example 1 128 g of DL-cysteine hydrochloride hydrate crystals and 37 y of water
was added and heated to 35°C to completely dissolve, and then gradually cooled.

When the liquid temperature reached 31 DEG C., 1.0 y of 40 to 60 mesh crystals of L-cysteine hydrochloride hydrate was inoculated, and the mixture was cooled to 27.5 DEG C. over 7 times while stirring. Here, 1.0 ml of supernatant liquid was collected and IN
When diluted to 10ml with hydrochloric acid water and measured the optical rotation, α
= -0.016°C, and it was confirmed that splitting had occurred, so the grown crystals were promptly cut off. Dry weight 5.4f(7) L-cysteine hydrochloride hydrate crystals were obtained, and the specific optical rotation of this was [α] 0 = +5.6
7 (C=8, NHCl).

This is the specific optical rotation a of pure L-cysteine hydrochloride hydrate.
[α]→=6.30 Compared to the salt, the optical purity was 90.0%. 4.0 y of DL-cysteine hydrochloride hydrate crystals are added to the above-mentioned divided mother liquor, heated again to 35° C., completely dissolved, and then gradually cooled. When the temperature reached 31, D-cysteine hydrochloride hydrate crystal 1.
0' is inoculated and the same operation is performed thereafter.

A D-cysteine hydrochloride hydrate crystal with a dry weight of 8.0y was obtained, and the specific optical rotation of this crystal was [α] 0 = -5.04
0 (C=8, NHC content. Example 2 128f of an aqueous solution containing 77.5% by weight of DL-cysteine hydrochloride hydrate was gradually cooled from 35°C to 30.5°C.
When it reaches L-cysteine hydrochloride hydrate crystal 1
y was inoculated and cooled to 29°C in 10 increments while stirring.

The grown crystals were collected and a dry weight of 2.0y(7)L-cysteine hydrochloride hydrate was obtained, which had an optical purity of 100%. Example 3 DL-cysteine hydrochloride hydrate 128f<5 L-To the crystals containing cysteine hydrochloride hydrate 6f, 37f of water was added and completely dissolved at 40°C, and then 1. It was cooled at a rate of (1).

Since the generation of nucleation particles reaching 2 (generations) was observed, cooling was stopped and stirring was continued for 2 (3 generations) using FC.

The crystallization was quickly stopped and the dry weight was 16.0f (
7) L-cysteine hydrochloride hydrate was obtained. The optical purity of this product was 77.0%. Comparative Example DL-cysteine 11f was added to 100 y of water, heated to 40° C. to completely dissolve it, and then gradually cooled.

When the temperature reached 31°C, 0.5y of L-cysteine was inoculated with stirring, and the mixture was cooled to 27°C in 2 hours, and the grown crystals were separated to obtain 2f crystals.

Claims (1)

[Claims] 1 DL-cysteine is converted into hydrochloride hydrate to form an aqueous solution, and this solution is inoculated with crystals of optically active cysteine hydrochloride hydrate in a saturated or supersaturated state, or an excess amount of either D- or L- is added in a supersaturated state. crystallizes optically active cysteine hydrochloride hydrate present in
A method for optical resolution of DL-cysteine, which comprises using the inoculated or crystallized crystal as a seed crystal to preferentially crystallize an optically active substance of the same type as the seed crystal and separate it from the mother liquor.