JPH05186497A - Crystallization of alpha-l-aspartyl-l-phenylalanine methyl ester - Google Patents

Abstract

PURPOSE:To precipitate and collect the crystals of alpha-L-aspartyl-L-phenylalanine methyl ester from a solution of alpha-L-aspartyl-L-phenylalanine methyl ester. CONSTITUTION:alpha-L-aspartyl-L-phenylalanine methyl ester solution is brought into direct contact with ice to cool the solution whereby the peptide can be crystallized out. The crystals has excellent filtrability, large size, high hardness and high purity.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for crystallizing α-L-aspartyl-L-phenylalanine methyl ester.

[0002]

2. Description of the Related Art α-L-Aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as APM) exhibits high-quality sweetness and has a sweetness of about 200 times that of sugar. It is a useful substance that is expected to be widely used as an agent.

APM is synthesized by various methods,
As a method for industrially manufacturing, for example, there is the following method.

That is, a method in which N-substituted aspartic acid and phenylalanine methyl ester are condensed in the presence of an enzyme, and then the protecting group is eliminated (JP-A-55-13559).
5), a method of condensing an N-substituted aspartic acid anhydride and phenylalanine methyl ester in an organic solvent to remove the protecting group by a conventional method (USP 3,786,03).
9), etc. are known.

In any of the production methods, the crystallization step is indispensable in order to isolate APM from the reaction solution and finally make it a product. In this crystallization step, the APM solution that has undergone the synthesis and purification steps is usually cooled and precipitated, or the crude product is redissolved in water, an organic solvent or an aqueous solution containing an organic solvent, and cooled to precipitate APM crystals. Ordinarily, this is performed by solid-liquid separation with a centrifuge or the like, dehydration, and drying to obtain a product.

As the crystallization method, a stirring crystallization tank having a cooling heat transfer surface or a crystallization tank having an external circulation heat exchanger is usually used. There is also a method of performing crystallization by cooling by heat conduction without giving forced flow for the purpose of improving the crystal grain size (JP-A-58-177952).

[0007]

[Problems to be Solved by the Invention] However, AP
When M is cooled and crystallized in a crystallization tank accompanied by forced flow such as normal stirring or external circulation, crystals having relatively poor solid-liquid separation and dehydration properties are obtained. Further, in this case, crystals are easily deposited on the cooling heat transfer surface, so-called scaling occurs, and heat transfer efficiency is rapidly deteriorated. Therefore, it was necessary to interrupt the crystallization operation and remove the scale from time to time. Furthermore, since the crystals are fine and have a high water content, various problems occur. For example, in the drying process, the mother liquor containing impurities is APM
By adhering to crystals, it is associated with unwanted impurities in the product. Further, the dried product contains a large amount of fine powder, which causes problems such as scattering in the form of fine powder.

As a method for avoiding such a problem, in the above-mentioned Japanese Patent Laid-Open No. 58-177952, the APM aqueous solution is cooled by conduction heat transfer without giving forced flow such as mechanical stirring to form a pseudo solid phase. Then, a method of further cooling if necessary is disclosed.

According to this method, APM crystals having improved solid-liquid separation and dehydration properties can be obtained. However, since it is cooled by conduction heat transfer without giving a forced flow, and further after forming the pseudo solid phase,
Cooling efficiency is extremely poor. Therefore, it is necessary to reduce the volume of the crystallization tank and increase the number, to cool for a long time, or to use a special crystallization tank as disclosed in the publication.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling and crystallization method for APM crystals, which have large crystals and are hard, that is, have good filterability and dryability and which are excellent in production, quality and handling. To provide.

[0011]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors of the present invention have conducted earnest researches for improving the properties of APM, and as a result of various investigations, as a result, a truly surprising new fact, that is, APM solution. It was found that a large and hard APM crystal can be obtained by contacting ice with ice and direct cooling to crystallize APM, and that crystallization can be completed within a short time, and the present invention has been achieved. did.

That is, the present invention resides in a crystallization method of APM characterized in that the APM solution is brought into contact with ice and directly cooled to crystallize APM. Hereinafter, the present invention will be described in detail.

The APM solution may be water, an organic solvent or an aqueous solution containing an organic solvent.
However, from the crystal growth, operation and handling of APM,
It is preferably substantially an APM aqueous solution. In such an APM aqueous solution, usually at least 85% or more by weight of the total solution is water.

The size of ice to be used is not particularly limited, but it is desirable that one piece is 100 g or less in view of the melting rate of ice (cooling rate by ice), ice production cost, handleability and the like.

The shape of ice may be cubic, spherical, or any shape. Also, a crystallization tank having an ice layer produced by cooling water at the bottom and / or wall of the APM crystallization tank may be used.

Although ice made from water is usually used as ice, it may be made from a dilute aqueous solution of APM. The APM concentration at that time is preferably 2 wt% or less.

The amount of ice used can be determined by the amount of APM deposited. That is, it is set by the cooling temperature of the APM solution. APM cooled directly with ice
The amount of APM precipitation and the temperature at that time when crystallization is performed can be calculated from the solubility of APM with respect to temperature.

When ice is used for cooling, the ice melts into water and the APM concentration decreases, but since the ice cooling capacity is large and the temperature can be effectively lowered with a small amount, the APM concentration at that time is reduced. Is small. Therefore, the amount of APM precipitation usually increases as the amount of ice used increases. Further, the crystal growth of APM increases as the temperature increases. Therefore, APM
From the aspect of crystal growth and precipitation amount, the cooling temperature is 0 to 30 ° C.
Is preferable, and further 3 to 20 ° C. is preferable.

Further, the cooling of the APM solution may be combined with the direct cooling with ice and the cooling generally used, or the indirect cooling using a coolant such as cold water or brine.

The direct cooling of the APM solution with ice may be carried out by adding the APM solution to the ice or vice versa. In addition, ice and the APM solution may be added simultaneously to the crystallization tank.

The operation may be either continuous type or batch type, but the batch type is easy to operate.

The mixture of the APM solution and ice may or may not be stirred. If large APM crystals are desired, no agitation is desirable. Even if stirring is carried out, it is desirable to carry out lightly.

When the APM solution comes into contact with ice, the temperature of the APM solution is lowered and APM crystals are precipitated. The crystals are
Large and hard. The size varies depending on the conditions, but the length is usually 50 μm or more and 1000 μm or more, and the width thereof is a columnar shape having 5 μm or more and 50 μm or more.

Precipitation of APM continues until it becomes close to the saturated concentration of APM at that temperature, but the crystallization time is short and is completed in 10 to 120 minutes even without stirring. or,
Without stirring, there is a slight temperature difference between the upper part and the lower part of the crystallization tank, and there is some supersaturation, but it does not matter. In this case, it is preferable to perform stirring at the time when the APM precipitation is almost completed (equal to the time when the ice is almost melted) to eliminate the supersaturation. Also, after directly cooling with ice, stirring or
Alternatively, without performing, it may be indirectly cooled with cold water, brine, or the like. The temperature is preferably 3 to 10 ° C.

In the indirect cooling, the APM precipitation starts near the cooling surface, but in the direct cooling by the ice of the present invention, it starts at a site slightly away from the ice and spreads throughout the solution.
There is almost no scale problem like the conventional method. This is also a great feature of the present invention.

The pH of the APM solution used in the present invention is not limited, but a pH of 3 to 6 is preferable, and a pH of 3 to 4 is particularly preferable because it increases the precipitation amount of APM crystals and further increases crystal growth.
5 is desirable.

Filtration of the resulting slurry of APM crystals
Either a batch system or a continuous system may be used, and a high dehydration rate can be achieved in a short time. As the filter, any centrifugal filter, a filter press, a belt filter, a drum filter, or the like which is normally used industrially can be applied. Moreover, you may wash with water or an APM solution as needed. Cleaning is easy, and the attached mother liquor can be further removed by cleaning, which leads to improvement in quality. The obtained wet cake may be dried after granulation or may be dried as it is. Any kind of dryer can be used as the dryer. For example, a flash dryer, a fluidized dryer, a rotary dryer, etc. can be used.

[0028]

[Action] Why is it so large when it is directly cooled with ice and crystallized?
Whether or not a hard APM crystal having good filterability can be obtained cannot be clearly explained, but it is estimated as follows from careful observation of the crystallization state of the APM crystal.

At the same time as adding ice to the APM solution (
The same is true when the PM solution is added), but the ice begins to melt and the temperature of the APM solution drops. The part of the solution where the temperature becomes the lowest is around the ice, but the precipitation of APM starts from a part slightly away from the ice. The precipitated APM crystals are columnar, large and hard. Also, the ice melts into water and becomes APM
The solution concentration drops slightly. That is, the closer to ice, the lower the APM concentration.

That is, the temperature of the APM solution becomes lower as it approaches ice, and the APM concentration becomes lower as it approaches ice. A
The higher the APM concentration and the lower the temperature of the crystallization of PM, the faster the crystallization starts and the higher the crystallization rate. When directly cooled with ice, the relationship between temperature and APM concentration becomes appropriate.
The number of PM crystal nuclei is appropriate, the growth rate is high,
As a result, it is considered that a large and hard APM crystal can be obtained.

We performed direct cooling of the APM solution using dry ice instead of ice. As a result, the obtained APM crystals were extremely fine and were difficult to filter.

This is because the temperature near the dry ice rapidly decreased, and crystallization of APM started near the surface of the dry ice, and APM crystals were formed at an extremely high rate.
It is considered that this is the reason why the crystal growth did not proceed and became a fine APM crystal.

We also packed ice cubes one by one in a polyethylene bag, put them in an APM solution, and indirectly cooled them with ice. As a result, APM crystals began to precipitate from the surface of the polyethylene bag, and the precipitation rate was high.
The obtained APM crystal was small. This is also
It seems to be related to temperature and APM concentration.

That is, the large and hard APM having good filterability, which is shown in the present invention only by directly cooling with ice that melts into water and slightly reduces the APM concentration.
Crystals are obtained.

In Example 5 of JP-A-3-72497, a method is described in which cold water at 5 ° C. is added to a hot aqueous solution of APM at 50 ° C. However, the properties of the crystals obtained by this method do not reach the properties of the crystals obtained by the present invention.

[0036]

As described above, according to the present invention, it is possible to obtain a hard APM crystal having a large grain size and growing in the diameter direction in a short time. As a result, many important effects are obtained as follows. (1) Since the crystallization can be completed within a short time because of the simple operation and the direct cooling, the productivity is improved, the operation becomes easy, and the economical effect is high. (2) The APM crystal slurry obtained by crystallization can be easily filtered and washed, and an APM wet cake with low water content and few impurities can be obtained within a short time. (3) APM wet cake has a small amount of adhering water content, so that it can be easily dried, and can be dried at a low temperature and a low temperature in a short time to obtain a product. Furthermore, it is possible to obtain high-quality APM without product deterioration during drying. In addition, there is little generation of fine powder in the drying process, which is beneficial in operation. (4) Dried product, that is, less powdering of the product, is extremely advantageous in handling. (5) The APM crystals obtained in the present invention can be improved by wet pulverizing them if necessary, and then using these as seed crystals in addition to the conventional APM precipitation method to precipitate crystals.

[0037]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto.

In the following examples and comparative examples,
The filtration rate of crystals was measured by the following method.

Slurry 500 containing crystallized APM crystals
Weigh out ml and aeration rate 5ml / cm ² · sec (12m
(mH ₂ O) A polypropylene filter cloth equipped with a suction filter (leaf tester) was used to filter at -400 mmHg while pouring the slurry so as not to run out of liquid on the filter cloth. From the time from the start of filtration until the end of pouring the whole amount until the liquid no longer exists on the filter cloth and the amount of filtrate at that time,
The filtration rate was calculated. Further, the specific resistance (α) was calculated by the following formula based on the change with time of the amount of filtrate.

[0040] However, t = filtration time (s) V = amount of filtrate (m ³ ) α = specific resistance of filter cake (m / Kg) η = kinematic viscosity of filtrate (Pa.s) ΔP = differential pressure of filtrate (Pa) C = mass of precipitated crystals per unit liquid volume of the obtained filtrate (K
g / m ³ ) Rm = resistance of filter cloth material (1 / m) A = filtration area (m ² ) where: ΔP = 53329 Pa, A = 1/127 m ² Example 1 with an internal volume of 2.0 liters In a glass flask,
1 kg of 3.5 wt% APM aqueous solution (pH = 4.5) was added. Next, 3 cm x 3 cm x made with pure water
500 g of 2.5 cm ice cubes were added to the flask at once. Approximately 5 seconds after the addition of the ice cubes, crystallization of APM started at a lower portion slightly apart from the ice layer. After 55 minutes, the ice was almost completely melted and the crystallization of APM was almost completed, so the slurry was stirred with a stirring blade. The stirring was easy and there was no scale. The temperature was 16.5 ° C., the APM crystals were columnar with a width of 5 to 35 μm and a length of 100 μm or more, and the slurry filtration rate was 439 liter / m ² · mi.
n. The specific resistance α was 3.44 × 10 ⁹ m / Kg, and the filtration was extremely good. Example 2 A glass flask having an internal volume of 2.0 liters was charged with Example 1
Add 400g of ice cubes same as the above, and then add 60g to the flask.
1 kg of APM solution of 4.0 wt% at pH 4.5 and 4.5 was added all at once. Approximately 4 seconds after the addition of the APM aqueous solution, crystallization of APM started in the lower portion slightly apart from the ice layer.

After 40 minutes, the ice had almost completely melted and the APM
Since the crystallization was almost completed, the slurry was stirred with a stirring blade. The stirring was easy and there was no scale. The temperature is 19.5 ° C., and the APM crystal has a width of 5 to 30 μm.
m, a columnar shape having a length of 100 μm or more, and a filtration rate of 427 liter / m ² · min. , The specific resistance α is 4.
27 × 10 ⁹ m / Kg), and the filtration was extremely good. Example 3 In a glass flask having an internal volume of 2.5 liters and having an external cooling jacket, the same ice cubes as in Example 1 were shaved and an ice maker (Tiger Thermos Industry Co., Ltd., Rakuwari ASC-2
643 g of coarse ice obtained by crushing at 000) was added, and then 1360 g of an APM aqueous solution having a pH of 4.5 and 4.0 wt% at 60 ° C. was added at once to the flask.

A few minutes after the addition of the APM aqueous solution, crystallization of APM started from a site slightly away from the ice.

After 30 minutes, the ice has almost completely melted and the APM
Since the crystallization of was almost completed, the flask was equipped with a stirring blade and the slurry was stirred. The stirring was easy and there was no scale. The temperature was 16.5 ° C., and the APM crystal was in the shape of a rod having a width of 3 to 25 μm and a length of 100 μm or more.

Next, the slurry was cooled by passing cold water through the outer jacket of the flask at a stirring speed of 300 rpm.

After 50 minutes, the slurry temperature reached 5 ° C., so cooling was stopped and the slurry was taken out. By this cooling, some small APM crystals were deposited, but most of them had a slightly grown rod shape, and the filtration rate was 35.
9 liter / m ² · min. , The specific resistance α is 7.42 × 1
A 0 ⁸ m / Kg, filtration was very good. or,
There was no scale on the flask wall. Example 4 Using a glass cylindrical crystallizer having an inner diameter of 5 cm and a length of 53 cm with a cooling jacket, a refrigerant of -7 ° C was passed through the crystallizer jacket, and then water of about 2 ° C was added. 50 minutes later, about 5m
Since m-thick ice formed on the vessel wall, excess water was drained. The amount of ice was 330 g (calculated from the balance of water), and immediately, 666 g of a 3.5 wt% APM aqueous solution at 60 ° C. and pH 4.5 was introduced into the crystallizer. A few minutes later, crystallization of APM started from a site slightly away from the ice layer, and 15 minutes later,
Since the ice was almost completely melted and the crystallization of APM was almost completed, the APM slurry was extracted from the lower part of the crystallizer using gravity. It is easy to pull out the slurry, and the scale
There was no le.

The slurry temperature is 15 ° C., the APM crystals are columnar with a width of 5 to 20 μm and a length of 100 μm or more, and the slurry filtration rate is 419 liters / m ^2.
・ Min. The specific resistance α was 3.70 × 10 ⁹ m / Kg, and the filtration was extremely good. Example 5 In a glass flask having an internal volume of 2.0 liters, 0.5 w
3cm x 3cm x 2.5c manufactured with t% APM aqueous solution
474 g of ice cubes of m, then 60 ° C., pH 4.5,
1 kg of 3.5 wt% APM aqueous solution was added at once. AP
Crystallization of APM started 1 to 2 seconds after the addition of the M aqueous solution.

After 80 minutes, the ice had almost completely melted and the APM
Since the crystallization of was almost completed, the slurry was stirred with a stirring blade. The stirring was easy and there was no scale. The temperature is 13.5 ° C. and the APM crystal has a width of 2 to 20 μm.
m, a columnar shape having a length of 100 μm or more, and a filtration rate of 369 liter / m ² · min. , The specific resistance α is 4.
It was 94 × 10 ⁹ m / Kg, and the filtration was extremely good.

The APM crystal was slightly smaller than that in Example 2. Comparative Example 1 A glass flask having an internal volume of 2.5 liters equipped with an external cooling jacket and a stirrer was placed at 60 ° C., pH 4.5, 3.
Add 2 liters of 5 wt% APM aqueous solution, 300r
1 at a cooling rate of 15 ° C per hour with a stirring speed of pm
It was set to 0 ° C. The obtained APM crystal has a width of 10 μm or less and a length of 30 to 100 μm, and its filtration rate is 8 μm.
8 liter / m ² · min. , The specific resistance α is 3.24 × 1
The filtration was difficult at 0 ¹⁰ m / Kg. Also, the scale was quite visible.

Comparative Example 2 In the method of Example 2, 360 g of dry ice was used instead of ice cubes in a 3 liter beaker. APM
Aqueous solution (60 ° C., pH 4.5, 3.5 wt%) 2 liters of APM aqueous solution was added, and the stirring rate was 300 rpm and the cooling rate was 15 ° C. per hour to 10 ° C. The obtained APM crystal has a width of 10 μm or less and a length of 30 to 1
And the filtration rate is 88 liters / m ² ·
min. The specific resistance α was 3.24 × 10 ¹⁰ m / Kg, which was difficult to filter. Also, the scale was quite visible.

Next, the slurry was stirred little by little with a stirring blade to sublimate dry ice. The temperature of the slurry is
20.5 ° C., the filtration rate is 75 liter / m ²
・ Min. The specific resistance α was 5.08 × 10 ¹⁰ m / Kg, which was difficult to filter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Takeshima 3-chome, Ogami 12-50-102, Shinnanyo, Yamaguchi Prefecture

Claims (1)

[Claims] 1. From a solution of α-L-aspartyl-L-phenylalanine methyl ester, α-L-aspartyl-
In precipitating the crystal of L-phenylalanine methyl ester, the solution of α-L-aspartyl-L-phenylalanine methyl ester was directly contacted with ice to cool the solution, and α-L-aspartyl-L-phenylalanine methyl ester was obtained. A method for crystallizing α-L-aspartyl-L-phenylalanine methyl ester, which comprises crystallizing the ester.