JPS63101376A - Optical resolution of (+-)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxyl-ic acid - Google Patents

Abstract

PURPOSE:To subject (+ or -)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid useful as an intermediate for a benzofuran hypotensive diuretic to optical resolution by using an optically active menthol. CONSTITUTION:(+ or -)-6,7-Dichloro-2,3-dihydrobenzofuran-2-carboxylic acid shown by the formula is treated with an optically active menthol (l- or d-menthol) to form esters of enantiomer and the carboxylic acid is subjected to optical resolution in an extremely high yield and simply by using difference in solubility of the esters of by separating each enantiomer by chromatography. The separated menthyl ester is subjected to ester exchange by a conventional procedure and used for the following reaction or hydrolyzed to give carboxylic acid and the ester is preferably made into a lower alkyl ester once in order to carry out the following reaction efficiently.

Description

Detailed Description of the Invention (Objective of the Invention) Industrial Application Field The present invention relates to (±)-6,7-dichloro-
This invention relates to an optical resolution method for 2,3-dihydrobenzofuran-2-carboxylic acid (hereinafter referred to as racemic carboxylic acid).

Many useful benzofuran-based antihypertensive agents have been synthesized from this racemic carboxylic acid. In particular, there are many excellent compounds with a substituent at the 5-position, and it is known that they have both uric acid excretion and enrichment effects [Journal Medicinal Chemistry (J, Med, C
hem, 24.86!1r873 (1981)) and JP-A-61-63671.

For example, in the former document, (earth)-6,7-dichloro-
2,3-dihydro-5-(2-chenylcarbonyl)-
A racemic resolution method is disclosed in which 2-benzofurancarboxylic acid is reacted with (-) cinchonidine or d-(+)-α-methylbenzylamine to obtain the <+) enantiomer or the (-) enantiomer, respectively. It has also been disclosed that the ) enantiomer has a predominant natriuretic effect, and the (-) enantiomer has a predominant uric acid excretion effect.

Problems to be Solved However, this is a racemic resolution method for the target compound, and cannot be applied as is to other target compounds.

In particular, since the solubility tends to change depending on the type of substituent at the 5-position, there is a drawback that the resolution method must be considered for each compound. Furthermore, when only one of the enantiomers is used as the target compound, if optical resolution is performed in the final step, the other enantiomer is not required, which greatly affects production costs.

The racemic resolution method of the present invention is a simple method with very high yield, and because the resolution is performed at an early stage of synthesis, various optically active useful compounds can be efficiently synthesized. According to the method of the present invention, only useful enantiomers can be separated at an early stage, so it is particularly useful when producing only one enantiomer as a pharmaceutical product.

(Structure of the invention) Question 71. In view of the above points, the present inventors conducted intensive research on the optical resolution method of racemic carboxylic acid, which is an important intermediate for benzofuran-based antihypertensive diuretics. It has been found that by using this method, the racemic carboxylic acid can be easily optically resolved in high yield.

That is, the present invention utilizes the difference in solubility of (±)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid by reacting optically active menthol to form esters of enantiomers. , or a method of optical resolution using chromatography. The separated menthyl ester may be subjected to transesterification according to a conventional method and subjected to the next reaction, or may be hydrolyzed to form a carboxylic acid. Alternatively, the corresponding carboxylic acid may be obtained by directly alkali hydrolysis, but in order to carry out the subsequent reactions efficiently, it is preferable to first convert the ester into a lower alkyl ester.

In this specification, optically active menthol means cou or d-menthol, and commercially available menthol may be used.

In the menthyl ester production reaction, the amount of optically active menthol to be used is not particularly limited, but it is preferably in equimolar to a slight excess relative to the racemic carboxylic acid, allowing for high purity and effective optical resolution. The reaction is carried out in a solvent, and examples of the solvent used include halogenated solvents such as 1,2-dichloroethane, benzene, toluene, 1,2-dimethoxyethane, and tetrahydrofuran (THF), with benzene being particularly preferred. . Once the racemic carboxylic acid is converted into an acid chloride, it may be reacted with optically active menthol to form a menthyl ester,
Furthermore, the esterification reaction may be carried out in the presence of an acid catalyst. Examples of the acid catalyst used include hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, and p-toluenesulfonic acid, with p-toluenesulfonic acid being particularly preferred. The reaction may be carried out at room temperature or under heating, and is completed in a few minutes to several days. For example, in the reaction to obtain coumentyl ester, (R)-6,7-dichloro-2
, 3-dihydrobenzofuran-2-carribonic acid fist! −
Menthyl ester was separated as crystals, and from the mother liquor (
S) -2,3-dihydrobenzofuran-2-carboxylic acid cumentyl ester is separated as an oil.

Although chromatography may be used to separate each enantiomer, the recrystallization method is convenient and preferred because it can be obtained with the same yield. At this time, since the separation is efficient, the mother liquor can be directly used as a raw material for the corresponding enantiomer. The recrystallization solvent used is preferably a linear or branched aliphatic hydrogen ashing solvent, with n-hexane and n-pentane being particularly preferred. The amount of recrystallization solvent used is 0.5 to 3 parts by weight, more preferably 0.7 to 3 parts by weight, per 1 part by weight of the racemic menthyl ester.
2 parts by weight.

Menthyl esters of the separated enantiomers can be directly
Alternatively, after transesterification reaction, alkali hydrolysis may be performed to obtain the desired compound (+) or (-)-6,7-dichloro-2,
The hydrolysis reaction to form 3-dihydrobenzofuran-2-carboxylic acid (la or lb) is completed in several minutes to several hours. As the alkali, sodium hydroxide or the like is used in an equimolar to slight excess relative to the enantiomer, but it is preferable to use acetonitrile in an amount several times the amount of the alkali used, since the reaction rate increases.

For example, racemic carboxylic acid! - In the reaction with menthol, (R)-6,7-dichloro-2,3-dihydrohensefuran-2-carboxylic acid/coumentyl ester crystallizes and is separated. Due to its good separation ability, the mother liquor is rich in (S)-2,3-dihydrobenzofuran-2-carboxylic acid/gumenthyl ester, which can be directly hydrolyzed or transesterified to lower alkyl. Upon hydrolysis, (S)-2,3-dihydrobenzofuran-2-carboxylic acid can be obtained in high yield. However, the (S)-
If you want to obtain a carboxylic acid, it is recommended to perform a hydrolysis reaction and then react with d-menthol to form a d-menthyl ester, followed by hydrolysis.

In the reaction between racemic carboxylic acid and d-menthol, each enantiomer can be obtained in high yield in the same manner as described above. Either way! -Menthol or d-menthol is easily recovered with high purity and can be used as a raw material for the next reaction, which is industrially advantageous.

The invention will be explained in more detail with reference to examples and reference examples below, but these are not intended to limit the scope of the invention.

Example 1 Preparation of 2-menthyl ester (2a) (±)-6,7-cyclo2,3-dihydrobenzofuran-2-carboxylic acid 1)s, oog (21,4 mmo
1) in 50 ml of dry benzene and 1 thionyl chloride.
Add 2.7 g (0.107 mol) and heat under reflux for 3.5 hours. Benzene and excess thionyl chloride are distilled off under reduced pressure, and the residue is dissolved in 50 ml of benzene and cooled on an ice-water bath. ! - 3.68 g (23.5 mmol) of menthol
), 4-N, N-dimethylaminopyridine 261 m
g (2.14 mmol) and triethylamine 6°0
ml (42.8 mmol) was dissolved in benzene, and this was added dropwise to the above reaction solution for about 10 minutes or 1 hour, and after the dropwise addition was completed, the solution was stirred at room temperature for 2 hours. The reaction solution was diluted with ethyl ether, washed with dilute hydrochloric acid, water, and saturated brine, and the ether layer was dried over magnesium sulfate and then concentrated. Residue n-
Dilute with hexane and collect the precipitated crystals by filtration. The obtained crystals are dissolved in ethyl ether, washed with an aqueous sodium bicarbonate solution, the ether layer is dried over magnesium sulfate, and then concentrated. The residue was combined with the mother liquor and washing solution, and subjected to silica gel column chromatography (dichloromethane: n-
Coomentyl ester (2a
) is obtained as a yellow solid.

The obtained solid was recrystallized from n-hexane, collected by filtration, and then washed with pentane to obtain (R)-6,7-cyclo2,3-dihydrobenzofuran-2-carboxylic acid cumentyl ester (2a). 1.85 g of colorless crystals are obtained. After concentrating the mother liquor, it was cooled on a dry ice/acetone bath, and the precipitated crystals were quickly collected by filtration to obtain an additional 0.21 g of the desired comenthyl ester. Total acid: 12.06g (
Yield 37%) Melting point 111-116°C.

Elemental analysis (as C+ = H! I C1t Os)
Calculated values: C: 61.46, H: 6.52, at
19.10, Actual value: C: 61.53, H 6.43, C1; 19.38° [α] b”0+2.
4±0.4°(c=1.0.acetone)6IR(Nuj
ol)' 1740. 1600 am-1゜'H-N
MR (CDCIs): S 6.99 (2H, s),
5.27 <IH.

dd, J=10.0.6.9Hz), 4.76 (L
H, tdm, J40.0°4.5Hz), 3.63
(LH, dd, J: 16.0. 10.0Hz), 3
33 (LH, dd, J=16.0.6.9Hz), 2
．． 2-0.7 (18H, m).

Example 2 Separate method for producing coomentyl ester (2a) (±)-6
,7-dichloro-2,3-dihydrobenzofuran-2-
Carboxylic acid (1) 61.5g (0,264mol)!
- A catalytic amount of concentrated sulfuric acid (about 10 drops) was added to 49.5 g (0,316 m01) of menthol, heated under reflux in benzene, and azeotropically dehydrated. After 4.5 hours, the residue was diluted with 50% ethyl ether.
The mixture is diluted with 0ml and washed with an aqueous sodium bicarbonate solution, water, and then saturated saline. The ether layer is dried over magnesium sulfate and then concentrated. The residue was diluted with n-hexane 150
Dissolve the solution in m1 by heating and leave it at room temperature. The precipitated crystals were collected by filtration and recrystallized from n-hexane to give (R)-6,7
-:,Xchloro-2,3-dihydrobenzofuran-2-
Carboxylic acid/coumentyl ester (2a) 27.2g
is obtained as colorless crystals. Melting point: 111.5-113°C.

The mother liquor and washing liquid are treated with n-hexane in the same manner to obtain 13.41 g of ester (2a). Melting point 111
．． 5-1.13, 5°C. Total yield 40゜6g (51,4
%), melting point 112.5-113°C (n-nihexane).

[α, 21.5 +1.3±0.4° (c=1.0
．． acetone).

Example 3 Production of methyl ester (3a) Coomentyl ester (2a) obtained in Example 2 40.1
g (0,108 mol) is heated to reflux in methanol (400 ml) in the presence of a catalytic amount of p-toluenesulfonic acid. After 30 hours, the reaction solution was concentrated, the residue was diluted with ethyl acetate, and washed with water and then saturated brine. The organic layer is dried over magnesium sulfate and concentrated. The residue was heated and dissolved in 50 ml of n-hexane and cooled to room temperature to obtain crystals. Wash the crystals with n-hexane, (R)-(+)-6
,7-dichloro-2,3-dihydrohensifuran-2-
23.7 g of carboxylic acid methyl ester (3a) are obtained as colorless crystals. From the mother liquor having a melting point of 81.5 to 82°C and the solution, 1.76 g of ester (3a) is obtained by similarly treating with n-hexane.

Melting point: 81.5-81.5°C. Total yield 25.46g (95
%), melting point 81-82°C (benzene-n-hexane).

Sublimate the mother liquor again! - Menthol 16.0g (94,
8%) was recovered.

Elemental analysis (as C,.H*C1,○) Calculated value:
C; 48.61, +(; 3.26, CC28,70
, Actual value: C; 48.4 translation H; 33 translation C1; 2
8.56° [α] l11225”71.3±1.1°
(c=1.0.acetone).

IR(Nujol)' 1750.1600.1585
am-'.

'H-NMR (CDCIs)'l; 6.99 (2
H,s), 5.32 (LH.

dd, J:9.8.7.0Hz), 3.80 (38
, s), 3.63 (IH.

dd, J: 16.3.9.8Hz), 3.39 (L
H, dd, J=16.3°7.0Hz).

Example 4 Hydrolysis of methyl ester (3a) 170 mg (0
, 69 mnnol) was dissolved in acetonitrile (4 ml), and 0.3 ml of 10% aqueous sodium hydroxide solution (0,8
3 mmol) and stirred at room temperature for 3.5 hours. Concentrate the reaction solution, dissolve the residue in water, and wash with dichloromethane. The aqueous layer was made strongly acidic with 10% hydrochloric acid and extracted with ethyl acetate. The extract was washed with water and then with saturated saline, dried over magnesium sulfate, and the solvent was distilled off to obtain the desired (R)
-(+)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid (1a) as colorless crystals (153
+ng, 95%). Melting point: 173-174°C.

Elemental analysis (as C*H, C1, 0) Calculated value: C
; 46.3B, H; 2.59, C1; 30.43
゜Actual measurement value, C: 46.02, H: 2.72, C
1; 30.70° [α coD22.0 +77.9±1
．． 2@(c=1.0.acetone).

IR (Nujol): 3400=2700.1750
．． 1605.1585cm-1゜'H-NMR (CDC
1$): δ 10.4-9.2 (LH, b), 7.
20 (IH, dm, C8, IHz), 7.05
(IL d, J: 8.1Hz), 5.45 (LH, d
d, J=10.0. 6.8Hz), 3.76 (
LH, ddm, J=16.2. 10.0Hz),
3.45 (LH, ddm, J=16.2.6
．． 8Hz＞.

Example 5 Preparation of d-menthyl ester (2b) (±)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid (1)2. OOg (8,58mm
o 1 ) is heated and refluxed in benzene in the presence of a catalytic amount of p-)toluenesulfonic acid, and after 4 hours, a small amount of p-toluenesulfonic acid is added, and the mixture is further refluxed for 5 hours.

The reaction solution was washed with water and saturated saline, and 45% of the reaction solution was washed with water and saturated saline. The mixture was dried over magnesium sulfate and concentrated. The residue was subjected to silica gel column chromatography (dichloromethane:n-hexane-1=1) to obtain colorless crystals. This was recrystallized from n-hexane to obtain d-menthyl ester (2b) as colorless crystals (1.18 g). The mother liquor was cooled and filtered to obtain an additional 73 mg of d-menthyl ester (2b). Total yield 1°25g (39%). Melting point 111-112.
5℃.

Elemental analysis (as C,, H,, C1, O) Calculated values:
C; 61.46, n; 6.52, C1; 19.
10. Actual value: C; 61.34, old 6.36, C
1; 19.11° [α], 23.0-2.7±0.4
' (c=1.0.acetone).

Example 6 Production of methyl ester (3b) d-menthyl ester (2b) obtained in Example 5 512m
g (1.38 mmol) is heated to reflux in methanol in the presence of a catalytic amount of p-toluenesulfonic acid. After 27 hours, the reaction solution was concentrated, the residue was diluted with ethyl acetate, and washed with water and then saturated brine. The organic layer was dried over magnesium sulfate, concentrated, and the residue was purified by silica gel column chromatography (dichloromethane:rl-hexane-2:1
) to obtain (S ) -(-)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid.
Methyl ester (3b) was converted into colorless crystals (315 mg, 92
%). Melting point: 81.5-82°C.

Elemental analysis (as C,.HaCltOs) Calculated values:
C; 48.61, H; 3.26, C1; 28.70
, Actual value, C; 48.41, H; 3.32, C
1; 28.80° [α D23.0-72.3±1.
1° (c4.0.acetone).

Example 7 Hydrolysis of d-methyl ester (3b) Methyl ester (3b) obtained in Example 6 244 mg (0.99 mrn
ol) in acetonitrile (4 ml) and diluted with 1.19 ml (1.19 mmol) of IN-sodium hydroxide aqueous solution.
) and stirred at room temperature for 30 minutes. Concentrate the reaction solution,
Dissolve the residue in water and wash with dichloromethane. Hydrochloric acid is strongly acidified with 10% hydrochloric acid and extracted with ethyl acetate. The extract was washed with water and then with saturated saline, dried over magnesium sulfate, and the solvent was distilled off to obtain the desired (S)-(-)-
6,7-dichloro-2,3-dihydrobenzofuran-2
- Carvone # (lb) as colorless crystals (226 mg, 98%
). Melting point: 172.5-174°C.

Elemental analysis (as c tHs C1!Os) Calculated values:
(:; 46.38, H; 2.59, C1; 30
．． 43, Actual value: C: 46.15, l; 2.8
2, CL: 30.62° [α] D22=-78,3±
1.2° (c=1.0.acetone).

The optically active carboxylic acid obtained by the method of the present invention is
It is used as a synthetic intermediate for various pharmaceuticals. An example is shown below.

Reference example 1 (first step) (R)-(+)-6,7-dichloro- obtained in Example 3
1.5 g of chlorosulfonic acid was added to a solution of 2,3-dihydrobenzofuran-2-carboxylic acid methyl ester (3a) Ig (4.05 mmol) in dichloromethane (tOml).
(4,05 x 3 mmol) was added dropwise at room temperature, then thionyl chloride (t, zgi, osx2, 5 mmol) was added and stirred at 40°C for 1 hour. The reaction solution was placed in ice water and extracted with ethyl acetate.

The organic layer is washed with water, dried over magnesium sulfate, and the solvent is removed under reduced pressure to obtain an oil. 10ml of acetone for oily substance
The mixture was cooled to -30°C, 1.3 g of 50% dimethylamine aqueous solution was added, and the mixture was stirred for 2 hours. The reaction solution was concentrated and extracted with ethyl acetate/water. The organic layer is washed with water, dried over magnesium sulfate, and the solvent is distilled off under reduced pressure. The residue is subjected to silica gel column chromatography (dichloromethane) to obtain an oil. Recrystallized from ethyl ether (
R) -(+)-5-(N,N-dimethylsulfamoyl)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid methyl ester (4a)1.
262 g (8B. 3%) are obtained as colorless crystals. Melting point 9
9-100℃.

Elemental analysis (as C+tH+5NSOsC1t) Calculated values: Cf 40.69, l; 3.70, Ni 3.95
．． 5; 9.05, C1; 20.02, actual value:
(:; 40.56, Hl, 67, N; 3.85, S
; 8.95, C1; 20.02° [α] D”0+
16.7±0.3° (c=2.0.acetone).

(Second step) 708 mg of methyl ester (4a) was added to 5 mL of acetonitrile.
3 ml of sodium oxide in the solution IN7 dissolved in ml
was added dropwise under water cooling, and after the addition, the mixture was stirred at room temperature for 20 minutes. The reaction solution was concentrated, acidified with 2 ml of 10% hydrochloric acid, and extracted with ethyl acetate. The extract is washed three times with water, dried over magnesium sulfate, and the solvent is removed under reduced pressure. The residue was dissolved in a small amount of ethyl acetate, concentrated, and crystallized from n-hexane to obtain the desired (R)-(+)-5-(N,N
-dimethylsulfamoyl)-6,7-dichloro-2,
641 mg (94%) of 3-dihydrobenzofuran-2-carboxylic acid (hereinafter simply referred to as (+) compound) was obtained.

Melting point 135-136°C.

Elemental analysis (CI, Hl, NSO & C1, combined) calculated values: C; 38.84, H; 3.26, Ni 4.
12, S; 9.43, C1; 20.84, Actual value:
c; 38.93, H; 3.35, N; 4.03
, S; 9.25, ci; 20.92° [αko, 230" 18.9*0.3° (c: 2.0.
acetone).

Reference Example 2 Production of C-2-carboxylic acid (first step) (S)-(-)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid methyl ester obtained in Example 6 ( 3b) Add 1.5 chlorsulfonic acid to a solution of Ig (4.05 mmol) in dichloromethane (10 ml).
g (4,05×3 mmol) was added dropwise at room temperature, and then thionyl chloride 1.2 g (4,05×3 mmol) was added dropwise at room temperature.
9. Add and stir at 40"C for 1 hour. Place the reaction solution in ice water and extract with ethyl acetate.

The organic layer is washed with water, dried over magnesium sulfate, and the solvent is removed under reduced pressure to obtain an oil. 10ml of acetone for oily substance
was added and cooled to -30"C, and 1.3 g of 50% dimethylamine aqueous solution was added and stirred for 2 hours. Concentrate the reaction solution,
Ethyl acetate/water was added for extraction, the organic layer was washed with water, dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. Silica gel column chromatography (dichloromethane) of the residue
An oily substance is obtained. Recrystallized from n-hexane (
S)-(-)-5-(N, N-dimethylsulfamoyl)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid methyl ester (4b) t, 2s
sg (89.8%) is obtained as colorless crystals.

Melting point: 100-101°C.

Elemental analysis (as C,,H,,NS○,C1!) Calculated value: Ci 40.69, )l; 3.70, N; 3
．． 95.5; 9.05, C1; 20.02, actual value: C; 40.51, H; 3.69, N; 3.
88.5; 8.97, C1; 20.11° [αko,
”0-17.3±0°6° (c=1.0.acetone).

(Second step) 708 mg of methyl ester (4b) was added to 5 ml of acetonitrile.
3 liters of IN* sodium oxide in a solution dissolved in ml
Add dropwise under cooling and stir at room temperature for 20 minutes after dropping. Concentrate the reaction solution and acidify by adding 2ml of 10% hydrochloric acid.
Extract with ethyl acetate. The extract is washed three times with water, dried over magnesium sulfate, and the solvent is removed under reduced pressure. The residue was dissolved in a small amount of ethyl acetate, concentrated, and crystallized from n-hexane to obtain the desired (S)-(-)-5-(N,N-dimethylsulfamoyl)-6,7-dichloro- 2,3-
Dihydrobenzofuran-2-carboxylic acid (hereinafter simply referred to as (
-) Compound) 633 mg (93%) are obtained. Melting point 135-136°C.

Elemental analysis (c + l H, l N S Oa Cl
Calculated value: C; 38.84, H; 3.
26, N; 4. L2, Si 9.43, cl; 20
．． 84, Actual value: C; 39.07, Hi 3.2
9, N; 4.02.5; 9.37, C1; 20.
69° [α] o”0 (9,0±0.3° (c=2.0
．． acetone).

Experimental Example 1 (Na diuretic activity) (1) Benefit effect in rats 5lcj SD male rats (8 weeks old, weight 250 g)
was used. In the morning of the day before the experiment, the bait was replaced with sugar cubes, and in the evening (
4p, m, around) 5% glufus solution 20II+1/kg
Body weight was orally loaded. On the morning of the experiment, zoml/kg body weight of the specimen suspended or dissolved in 2% gum arabic was orally administered. The control group received 20 ml of 2% gum arabic solution/
kg body weight was administered orally. Immediately after administration of the sample, the animals were placed in plastic metabolic cages and urine was collected for 5 hours, and the amount of urine, sodium excretion in the bed, and potassium excretion in the urine were measured.

(2) Diuretic effect in mice Slc:ddy female mice (5 selections, weight approximately 20 g) were used. The animals were fasted from the day before the experiment and given water ad libitum. On the morning of the experiment, 30 ml/kg of the specimen suspended or dissolved in 2% gum arabic was orally administered.

To the control group, 30 ml/kg body weight of 2% gum arabic solution was orally administered. Immediately after administering the sample, five mice were placed in plastic metabolic cages, urine was collected for 4 hours, and urine volume, urinary sodium excretion, and urinary potassium excretion were measured.

The results are shown in Tables 1 and 2.

From the above results, it can be seen that the (-) compound has a significant natriuretic activity, while the (+) compound has almost no natriuretic activity.

(Left below) Experimental Example 2 (Uric acid excretion promoting effect) Male rats of appropriate age were used. To determine the oxonate clearance value and italin clearance value, 250 mg/kg body weight of potassium oxonate was administered intraperitoneally to rats, and within 2 hours after administration of potassium oxonate, the right thigh of the rat was anesthetized with bendoparbital Na. Cannulae for blood collection, drug injection, and urine collection were inserted into the artery, left venous vein, and bladder, respectively. Exactly 2 hours after the first dose, the same amount of potassium oxonate was administered again, followed by 2 m of 60% urethane.
1/kg body weight and inulin 4 ml/kg body weight were administered subcutaneously. Place the animal on a 30°C hot plate and add 4%
A mannitol-1,5% inulin-0,9% saline solution is administered at a flow rate of 0.1 ml/min. After equilibration for 40 minutes, 0.2 ml of arterial blood was collected six times at 20 minute intervals.
The 20 minute bed is sampled five times. The test drug was suspended in 1% Arabicum, and 2 ml/kg body weight of the drug was intraperitoneally administered immediately after the first urine collection. After blood collection, plasma was immediately separated and the plasma and urine were stored refrigerated.

Uric acid in plasma and urine was determined by Yonetani et al.
al.

Jpn, J, Pharmacol,, 30.82
9-840 (1980)). Inulin is basically Vur-ek and Pedalum.
gram) was measured by the method of (Vurek).
G, G,, Pegram S, E,, Anal,
Biochem.

Long, 409-419 (1966)), 0.1 ml of a diluted plasma protein-free solution for measuring uric acid or 1% dimedone-orthophosphoric acid solution is mixed with the solution and heated in a boiling pot for 5 minutes. After cooling in ice water, add 2.0 ml of acetic acid.
was added, excited at 360 nm, and fluorescence was measured at 410 nm. The results are shown in Table 3.

From the above results, it can be seen that the (+) compound has a significant uric acid excretion effect, while the (-) compound has almost no effect.

(Left below) Experimental Example 3 (Acute Toxicity) Acute toxicity (oral) to mice was investigated. The results are shown below.

(+) compound: 2878 mg/kg (-) compound: 2253 mg/kg Prior literature (Diuretics Chemistry:
Pharmacology and Medicine
, p., 254. Ed, by E, J, Crago
eJr.

John Wilay & 5ons, Inc.
Similar compounds (
±)-6,7-dichloro-2,3-dihydro-5-(2
-The acute toxicity of chenylcarbonylfurancarboxylic acid to mice is as follows.

Intravenous: 2 7 4 mg/kg Oral: 4 4 5 mg/kg As is clear from the above, both the (+) and (-) compounds synthesized using the method of the present invention are safe. It is a highly useful compound.

Claims (1)

[Claims] (±)-6,7-dichloro-2, characterized by reacting optically active menthol with (±)-6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acid;
Optical resolution method of 3-dihydrobenzofuran-2-carboxylic acid.