SPECIFICATION
Methods for producing carboxylic acid chloride compounds
Technical Field of the Invention
The present invention relates to methods for producing carboxylic acid chloride compounds which are useful as an intermediate for producing D-phenylalanine derivatives which have the hypoglycemic action and are used as agents for treating diabetes. The present invention also relates to the production of D-phenylalanine derivatives using the carboxylic acid chloride compound(s).
Background of the Invention
Patent Literature 1 has already disclosed that D-phenylalanine derivatives including N-(trans-4-isopropylcyclohexylcarbonyl) -D-phenylalanine (nateglinide) have the hypoglycemic action and are useful as agents for treating diabetes-
Further, Patent Literature 2 discloses methods for synthesizing phenylalanine derivatives which include Schotten-Baumann reaction comprising the step of reacting trans-4-isopropylcyclohexanecarbonyl chloride hereinafter referred to as ICCC) with phenylalanine (Phe). According to it, nateglinide can be synthesized as follows-

Namely> carboxyhc acid chlorides including ICCC are useful as an intermediate of D-phenylalanine derivatives which are useful as agents for treating diabetes.
There are various known methods for synthesizing trans-4-isopropylcyclohexanecarbonyl chloride (ICCC) which is used as a raw

material in the above synthesis of nateglinide. Patent Literature 3 discloses the following method comprising the step of making phosphorus chlorides such as phosphorous pentachloride and phosphorous trichloride or thionyl chloride act on trans-4-isopropylcyclohexanecaxboxylic acid (hereinafter referred to as ICC), which is a corresponding carboxylic acid-

Disclosure of the Invention
The object of the present invention is to provide methods for producing a carboxyhc acid chloride compound which has high reaction speed, and whose product has high purity or high yield.
The further object of the present invention is to provide methods for effectively producing D-phenylalanine derivatives such as nateglinide, which comprise the above method for producing a carboxyhc acid chloride compound.
The inventors thoroughly studied to solve the above problems and found that the problems can be solved by the method comprising the step of reacting a carboxyhc acid compound with a chlorinating agent such as thionyl chloride in the presence of a compound having a specific urea structure, since the compound having a specific urea structure acts as a catalyst of the chlorination. The

present invention has been completed based on this finding.
Namely, the present invention provides a method for producing a carboxylic acid chloride compound of the following formula (III), which comprises the step of
reflrtinp" a rarbnyvlir, acid nnmnminrl nf tViP fni-mnla (lY.
wherein R1, R3, R5 and R6 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; and R5 and R6 may bind to each other and, in such a case, -R°-R6- represents an ethylene, trimethylene, or tetramethylene group, to synthesize said carboxyhc acid chloride compound of the formula (III)'

wherein Riag A and R1 are the same as those in the above formula (I).
The present invention also provides a method for producing a D-phenylalanine derivative of the following formula (V), which comprises the steps of producing the carboxyhc acid chloride compound of the formula (in) in accordance with the above production method:
wherein Ring A and R1' are the same as those in the above formula (I)' and then reacting a D-phenylalanine compound of the formula (IV) therewith


wherein Ring A, R1 and R* are the same as those mentioned in above.
According to the present invention, a carboxyhc acid chloride compound which is an objective substance can be promptly obtained since the reaction quickly proceeds by using a specific urea compound.
Further, according to the preferable embodiments of the present invention, there is the advantage that, even in the case of a sohd carboxylic acid compound, the carboxylic acid compound promptly changes into a liquid after the reaction starts, and therefore, it becomes easier to handle the compound such as stirring and to control the reaction. Besides, when thionyl chloride is used as a chlorinating agent, it is possible to lessen the usage amount thereof, and therefore, it is economical and good for the environment, and also makes it easier to remove thionyl chloride. Further, the carboxylic acid chloride compomids obtained by the present invention have fewer impurities such as geometric isomers.
Best Mode for Carruying out the Invention
In the carboxyhc acid compound of the formula (1) used in the present invention, Ring A represents a cyclohexane ring or a benzene ring, and a cyclohexane ring is preferable. R1 is a straight or branched alkyl group having 1 to G carbon atoms, preferably an alkyl group having 2 to 5 carbon atoms, more preferably a branched alkyl group having 3 to 5 carbon atoms, and particularly

preferably an isopropj'l group. R1 may be located at the o-, m- or p-position to the carboxyl group, and preferably at the p-position thereto. A particularly preferable example of the carboxylic acid compound of the formula (I) is trans-4-isopropylcyclohexanecarboxylic acid.
The present invention comprises the step of using the urea compound of the formula (II) as a catalyst when reacting the carboxylic acid compound of the formula (I) with the chlorinating agent such as thionyl chloride. Examples of the urea compound of the formula (11) include urea itself, dialkylurea, trialkylurea and tetraalkylurea, and tetraalkylurea is preferable. It is particularly preferable that, in the formula (11), R1, R3, R5 and R1 each independently represents an alkyl group having 1 to 3 carbon atoms; and R° and R1 may bind, to each other and, in such a case, -R1-R1- represents an ethylene, trimethylene, or tetramethylene group. Especially, it is preferable to use l,3-diaLkyl-2-imidazolidinone wherein, in the formula (11), W' and R1 are binding to each other £ind -R1-R1- is an ethylene group, and further more preferable to use l,3-dimethyl-2-imidazohdinone (DMI) wherein both R1 and R1 are a methyl group in addition to the above conditions. Since DMI is relatively stable in a strong acid, has thermostability and generates fewer decomposed materials, it is preferable in terms of control of impurities as well as the catalyst activity. Meanwhile, in the formula (II), both R1 and R1 may be a hydrogen atom or a methyl group and both R1 and R1 may be a hydrogen atom, or all of R1, R3, R5 and R6 may be a methyl group.
Examples of the chlorinating agent used in the present invention include at least one kind of the chlorinating agent selected from the group consisting of thionyl chloride, oxalyl chloride, phosgene, phosphorous pentachloride, phosphorous trichloride and phosphoryl chloride. Thionyl chloride is preferable among them.
When the chlorinating' agent is thionyl chloride, 0.8 to 5 mol of thionyl chloride is preferably industrially used per 1 mol of the carboxylic acid compound

of the formula (I), more preferably 0.8 to 2 mol thereof, and further more preferably 1 to 1.2 mol thereof is used. The urea compound of the formula (II) is preferably used in a catalytic amount thereof. For example, 0.001 to 5 parts by weight of the urea compound is preferably used per 100 parts by weight of the carboxylic acid compound of the formula (I), more preferably 0.01 to 3 parts by weight thereof, and particularly preferably 0.01 to 1 parts by weight thereof is used. Meanwhile, the urea compound may be used in larger amounts as a solvent.
This chlorination is preferably conducted without any solvent, but can be conducted with a solvent(s). It is preferable that the reaction is conducted at the temperature ranging from room temperature to around 80 °C, and more preferably from 30 to 60°C. Further, it is preferable to conduct the reaction under atmospheric pressure; and after the reaction completes, to remove acidic gases such as sulfur dioxide and chlorine gas under reduced pressure, each of which is dissolved in a reaction solution. It is further more preferable to remove unreacted thionyl chloride under reduced pressure.
When the chlorinating agent is oxalyl chloride, phosgene, phosphorous pentachloride, phosphorous trichloride, phosphoryl chloride or the like, each can be used in the present invention under the same conditions as those of thionyl chloride and, if necessary, making changes to said conditions, which would be easy for those skilled in the art.
In the present invention, the carboxyHc acid chloride compound of the formula (III) is particularly preferably trans-4-isopropylcyclohexanecarbonyl chloride.
It is possible to produce the D-phenylalanine derivative of the formula (V) by the method comprising the steps of producing the carboxyhc acid chloride compound of the formula (III) in accordance with the above production method; and converting said carboxyhc acid chloride compound. More specifically, it is possible to produce nateghnide by the method comprising the steps of producing

ICCC in accordance with the above production method; and converting said ICCC.
In the present invention, the D-phenylalanine derivative of the formula (V) is produced by the method comprising the steps of producing the carboxyUc acid chloride compound of the formula (ill) in accordance with the above production method; and reacting the D-phenylalanine compound of the formula (TV) thereto in accordance with Schotten-Baumann reaction. In the formula (JV), R1 is preferably a hydrogen atom. Nateglinide is a particularly preferable example of the D-phenylalanine derivative of the formula (V).
The above reaction is preferably conducted in accordance with the conditions described in Patent Literature 2 (WO02/32853). The description of Patent Literature 2 is incorporated into the present specification.
More specifically, it is preferable to react the carboxylic acid chloride compound of the formula (ill) and the phenylalanine compound of the formula (IV) in a mixed solvent of an organic solvent and water with keeping said mixed solvent in the alkaline condition by using potassium hydroxide, and preferably keeping said mixed solvent in pH 12.5 or more, and more preferably pH 13.5 or more. However, since the reaction solution is sometimes colored when the pH is over 14, the value of pH needs to be taken into account if coloring is to be avoided. When controlling pH, though the value thereof may depart from the above range, there is no problem since such departure does not exert a harmful influence if temporarily. Meanwhile, the value of pH herein mentioned is an instrument reading of a pH meter with glass electrodes. Though the concentration of an aqueous solution of potassium hydroxide is not particularly limited, it is usually 2 to 50% by weight and preferably 5 to 25% by weight.
As for an organic solvent, those which mix with water are used. Examples thereof include acetone, methyl ethyl ketone, dioxane, tetrahydroiuran, acetonitxile, methanol, ethanol, propanol and isoprpanol. Acetone is particularly preferable among them.

As for the mixture ratio of the organic solvent and water, though it differs depending on a used carboxyhc acid chloride and cannot be uniformly defined, it is 10:90 to 80:20 and preferably 15:85 to 40:60.
As for the temperature and the concentration of the reaction, though they also differ depending on a used acid chloride and a reaction solvent and cannot be uniformly defined, the reaction temperature is usually -5 to 25''C and preferably 0 to 15 °C, and the reaction concentration is usually 1 to 20 weight% and preferably 2 to 10 weight%. The suitable conditions thereof can be determined based on jdeld, operabOity, productivity, and the hhe.
As for the reaction method, it is possible to adopt the method which comprises the steps of dissolving a phenylalanine compound in water by using about the same molar amount of an aqueous solution of potassium hydroxide; adding an organic solventCs) thereto, and then adding an aqueous solution of potassium hydroxide to control pH; and adding dropwise a carboxyhc acid chloride compound thereto with stirring. The drop time is preferably 15 minutes to 2 hours. The molar ratio of the phenylalanine compound and the carboxyhc acid chloride compound such as trans-4-isopropylcyclohexylcarbonyl chloride used in the reaction is 0.5:1 to 2:1 and preferably 0.9:1 to 1.5:1. The concentration of the phenylalanine compound and the acid chloride compound such as trans-4-isopropylcyclohexylcarbonyl chloride in the reaction is, when each compound is mthin the above ratio, preferably 2 to 15wt% in terms of the concentration of the phenylalanine compound. The generated acylphenylalanine derivative can be taken out by the steps of acidifying the reaction solution with a hydrochloric acid or the hke to precipitate crystals thereo:P and filtering them out and washing them with water
According to the above production methods, it is possible to easily produce the D-phenylalanine derivative such as nategHnide in high purity by Schotten-Baumann reaction, which is an industrially superior reaction.
In addition, when the D-phenylalanine derivative of the formula (V) wherein

R* represents an alkyl group having 1 to 3 carbon atoms or a benzyl group is obtained by the method comprising the steps of producing the carboxylic acid chloride compound of the formula (III); and then converting said compound, a D-phenylalanme derivative of the formula (V-2) can be obtained by deesterifying said D-phenylalanine derivative of the formula (V)-
pi COOH

wherein Ring A and Ri are the same as those mentioned in above.
More specifically, examples of deesterification include hydrolysis in the presence of an acid, alkali, or the like if necessary, and when R'* represents a benzyl group, also include catalytic hydrogenation.
Next, Examples will further iQustrate the present invention.
Examples
Example 1 (usage of DMI: 2wt%)
O.Slg (2%) of l,3-dimethyl-2-imidazolidinoiie (DMI) was added to 30g (l76mmol) of trans-4-isopropylcyclohexanecarboxylic acid (ICC), and 21.6g (l82mmoI, 1.03 equivalent) of thionyl chloride was added dropwise thereto at 40°C in 3 hours (ICC residue upon completion of the drop: 1.1%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases (sulfur dioxide and hydrogen chloride) at 40°C under reduced pressure of 30kPa (XCC residue 0.4%; thionyl chloride residue 0.49wt%). Further, thionyl chloride was removed under 5kPa at 40 °C for 3 hours to obtain 33.6g of trans-4-isopropylcyclohexanecarbonyl chloride (ICCC) (content^ 96.8wt%) as a concentrated residue. ICC residue in this ICCC was 0.3%, and thionyl chloride residue therein was less than 0.01wt%. Example 2 (usage of DMI: 0.05wt%)
0.014g(0.05wt%) of DMI was added to 30g (l76mmoD of ICC, and 21.6g

(l82mmol, 1.03 equivalent) of thionyl chloride was added dropwise thereto at 40°C in 3 hours (ICC residue upon completion of the drop: 5.1%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases at 40°C under reduced pressure of SOkPa (ICC residue- 1.5%; thionyl chloride residue: 0.33wt%). Further, thionyl chloride was removed under 5kPa at 40°C for 3 hours to obtain 32.9g of ICCC (content: 98.5wt%) as a concentrated residue. ICC residue in this ICCC was 1.3%, and thionyl chloride residue therein was 0.13wt%. Comparative Example 1 (no use of DM1)
21.6g (182mniol, 1.03 equivalent) of thionyl chloride was added dropwise to 30g of ICC (l76mmol) at 40°C in 3 hours (ICC residue upon completion of the drop: 31.7%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases at 40°C,under reduced pressure of SOkPa QCC residue: 18.9%). Further, thionyl chloride was removed under 5kPa at 40''C for 3 hours to obtain 32.6g of a concentrated residue containing ICCC (content: 88.3%). ICC residue in this concentrated residue was 12.1%, and thionyl chloride residue therein was 0.39wt%.
The comparison between the result of Example 1 and that of Comparative Example 1 has clarified that, when DMI is not used (Comparative Example l), the reaction stops in the middle though thionyl chloride is used in the same amount as that in the case of using DMI (Example l). Comparative Example 2 (no use of DML thionyl chloride: 1.5 equivalent)
31.5g (265mmol, 1.5 equivalent) of thionyl chloride was added dropwise to 30g of ICC (iTGmmol) at 40''C in 3 hours (ICC residue upon completion of the drop: 15.0%). Then, the reaction was continued for 4 hours with removing dissolved acidic gases at 40°C under reduced pressure of 30kPa (ICC residue 1 hour later: 3.9%; and 4 hours later: 1.6%). Next, thionyl chloride was removed under 5kPa at 40°C for 3 hours. At that time, ICC residue in the residue containing ICCC was 1.6%, and thionyl chloride residue therein was 9.7wt%.

From the above, ICCC reaches a usable level by using thionyl chloride in an amount of 1.5 equivalent, because ICG residue is 2.0% or less. However, the residual amount of thionyl chloride is 9.7wt% and high in quantity, and therefore, it has been clarified that it does not reach a usable level of 0.2wt% or less in the same conditions as those in the case of using DMI.
Therefore, thionyl chloride was further removed under 5kPa at 40°C for 7 hours to obtain 33.4g of a concentrated residue containing ICCC. ICC residue in this ICCC was 1.4%, and thionyl chloride therein was 2.0wt%. Thus, it has been clarified that, when DMI is not used, the compound does not reach a desired quality (thionyl chloride: 0.2wt% or less) though thionyl chloride was removed in three times as long as the case of using DMI,
Meanwhile, in above Examples and Comparative Examples, a content rate of each component was calculated as follows.
(1) ICC in the reaction solution or in the concentrated residue
ICCC contained in the reaction solution or in the concentrated residue was derivatized to a coxxesponding ICC methyl ester by pretxeating said reaction solution or concentrated residue. This pretreated test substance was analyzed with HPLC (detection: UV, 210nm). The area of the detected ICC was divided by the area of ICC methyl ester to calculate the content rate of ICC (ICC/ICCC%).
(2) Thionyl chloride in the reaction solution or in the concentrated residue:
Thionyl chloride contained in the reaction solution or in the concentrated
residue was derivatized to diethyl sulfite by pretreating said reaction solution or concentrated residue. This pretreated test substance was analyzed with GC. The content rate of thionyl chloride (wt%) was calculated by quantitating the detected diethyl sulfite with a standard preparation.
(3) ICCC in the concentrated residue:
ICCC was derivatized to a corresponding amide by reacting the concentrated residue with isobutylamine in the pretreatment. This pretreated test substance was analyzed with HPLC (detection: uv, 210nm). The content rate of ICCC

(wt%) was calculated by quantitating- the detected amide with a standard preparation-Table 1 shows results of Examples 1 and 2, and Comparative Examples 1 and 2.

residue o£4 hours later is 1.6%.
As for the quahty of ICCC, it is required that ICC residue is 2.0% or less and thionyl chloride residue is 0.2wt% or less. However, in the case of conducting the reaction without using DMI, ICC is left when using l.03eq of SOCb, and, on the other hand, the residual amount of thionyl chloride becomes larger when increasing the amount of SOCI2. Thus, the results shown in Table 1 clarify that ICCC having a desired quality cannot be promptly obtained. Example 3 (1,1,3,3-tetramethylurea: 0.05%)
O.OlSg (0.05%) of 1,1,3,3-tetramethylurea was added to 30g (l76mmol) of ICC, and 21.6g (182mmol, 1.03 equivalent) of thionyl chloride was added dropwise thereto at 40°C in 3 hours (ICC residue upon completion of the drop-1.8%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases at 40 °C under reduced pressure of SOkPa (ICC residue: 2.1%). Further, thionyl chloride was removed under 5kPa at 40°C for 3 hours to obtain 32.4g of ICCC as a concentrated residue. ICC residue in this ICCC was 2.0%. Example 4 (l,3-dimethylurea: 0.05%)

0.016g CO.05%) of DMI was added to 30^ (l76mmol} of ICC, and 21.6g (l82mmoI, 1.03 equivalent) of thionyl chloride was added dropwise thereto at 40°C in 3 hours (ICC residue upon completion of the drop^ 10.4%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases at 40°C under reduced pressure of 30kPa (IGC residue 3.9%). Further, thiouyl chloride was removed under 5kPa at 40°C for 3 hours to obtain 30.6g of ICCC as a concentrated residue. ICC residue in this ICCC was 4.7%. Example 5 (urea: 0.05%)
O.Gl6g (0.05%) of DMI was added to 30g (l76mmol) of ICC, and 21.6g (l82mmol, 1.03 equivalent) of thionyl chloride was added dropwise thereto at 40°C in 3 hours (ICC residue upon completion of the drop: 16.3%). Then, the reaction was continued for 1 hour with removing dissolved acidic gases at 40°C under reduced pressure of 30kPa (ICC residue: 7.1%). Further, thionyl chloride was removed luider 5kPa at 40°C for 3 hours to obtain 31.7g of ICCC as a concentrated residue. ICC residue in this ICCC was 6.6% and thionyl chloride residue therein was less than 0.01wt%.
Table 2 shows results of Examples 3 to 5.


The results of Table 2 clarify that ICCC can be more promptly obtained by using a specific urea compound as compared with Comparative Example 1 in Table 1. Example 6 Production of nateglinide
143mL of water and 77mL of an aqueous solution of 10% potassium hydroxide were added to 19.3g of D-phenylalanine and dissolved. 82mL of acetone was added thereto and cooled down to about 10°C. Then, 20.Og (about 99% purity) of trans-4-isopropylcyclohexylcarbonyl chloride obtained by the same method as that of Example 2 was added dropwise thereto. Simultaneously the pH was controlled to 13.5 to 14.0 with an aqueous solution of 10% potassium hydroxide, and the reaction was conducted to obtain an objective compound (trans-4-isopropylcyclohexylcarbonyl-D-phenylalanine).

What is claimed is-
1. A method for producing a carboxylic acid chloride compound of the following
formula (III), which comprises the step of reacting a carboxylic acid compound of
■fVl /^ ■T/\1*»TTI'il 1 ill"
wherein R^, R^, R^ and R^ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atomsi and Yi? and R^ may bind to each other and, in such a case, -R5-R6- represents an ethylene, trimethylene, or tetramethylene group, to synthesize said carboxyhc acid chloride compound of the formula (III)-

wherein Ring A and R1 are the same as those in the above formula (I),
2. The method for producing the carboxylic acid chloride compound according to claim 1, wherein, the urea compound of the formula (II) is tetraalkylurea; and R2, W, W and R5 each independently represents an alkyl group having 1 to 3 carbon atoms.
3. The method for producing the carboxyhc acid chloride compound according to claim 1, wherein, in the formula dl), both R2 and R3 are a methyl group; and R5 and R5 bind to each other and -R5-R6- represents an ethylene group.
4. The method for producing the carboxyhc acid chloride compound according to

any one of claims 1 to 3, wherein O.S to 5 mol of the chlorinating agent is used per 1 mol of the carboxylic acid compound of the formula (I); and the urea compound of the formula (II) is used in a catalytic amount thereof.
5. The method for producing" the carboxylic acid chloride compoimd according to
any one of claims 1 to 4, wherein the reaction is conducted without any solvent
and at the temperature ranging from room temperature to 80°C.
6. The method for producing the carboxylic acid chloride compound according to
any one of claims 1 to 5, wherein the chlorinating agent is thionyl chloride.
7. A method for producing a D-phenylalanine derivative of the following
formula (V), which comprises the steps of producing the carboxyHc acid chloride
compound of the formula (III) in accordance with the production method of claim
i:
I
1
i
wherein R^ represents a hydrogen atom, an alkyl group having 1 to 3 carbon
atoms or a benzyl group,
to synthesize a D-phenylalanine derivative of the formula (V):

wherein Ring A, R1 and R4 are the same as those mentioned above.
8. The method for producing the D-phenylalanine derivative according to claim
7, wherein R4 is a hydrogen atom.
9. A method for producing a D-phenylalanine derivative of the following

formula (V-2), which comprises the step of deesterifying the D-phenylalanine derivative of the formula (V) obtained by the production method of daim 7, wherein R4 is an alkyl group having 1 to 3 carbon atoms or a benzyl group, to synthesize said D-phenvlalanine derivative of the formula (V-2):
i.
10. The production method according to any one of claims 1 to 9, wherein Ring A
represents a cyclohexane ring.
11. The production method according to any one of claims 1 to 10, wherein R1
represents a branched alkyl group having 3 to 5 carbon atoms.
12. The production method according to any one of claims 1 to 11, wherein the
carboxylic acid compound of the formula Ct) represents
trans-4-isopropyicyclohexanecarboxylic acid.