WO1996020910A1

WO1996020910A1 - Method for optical resolution of (r,s)-1,2-phenylethanediol using enzymes

Info

Publication number: WO1996020910A1
Application number: PCT/KR1996/000001
Authority: WO
Inventors: Yong Moon Choi; Min Woo Kim; Kwang Hyouk Lee
Original assignee: Yukong Limited
Priority date: 1995-01-03
Filing date: 1996-01-03
Publication date: 1996-07-11
Also published as: KR960029463A; KR0150592B1

Abstract

There is disclosed a method for optical resolution of 1,2-phenylethanediol, comprising the reaction of a racemic mixture of (R,S)-1,2-phenylethanediol, represented by formula (I), with an acetyl donor in the presence of an enzyme, to produce optically active diesters, whereby the racemic mixture can be separated into respective optical isomers within a short time. The method is also very advantageous in that it is carried out under mild conditions while producing enantiomers of 1,2-phenylethanediol in high optical purity. In addition, the post-reaction treatment is very simple.

Description

METHOD FOR OPTICAL RESOLUTION OF (R.S.-1.2- PHENYLETHANEDIOL USING ENZYMES

BACKGROUND OF THE INVENTION

Field of the invention The present invention relates to a method for optical resolution of (R,S)-l,2-phenylethanediol and, more particularly, to a method for separating a racemic mixture of (R,S)-1,2-phenylethanediol into respective optical isomers using an enzyme.

Description of the Prior Art

1,2-Phenylethanediol, represented by the following formula I;

has a chiral center and its enantiometically pure forms are useful intermediates in preparing various pharmaceuticals, agricultural chemicals and liquid crystal polymers. There has been extensive research for the development of production processes for pure enantiomers of 1,2-phenylethanediol.

For example, pure enantiomers of 1,2-phenylethanediol has been prepared chemically either by a reduction of optically pure mandelic acid (J. Org. Chem. , 44, 1729 (1979)) or by a multiple step modification of optically pure mannitol (J. Org. Chem., 43, 4876 (1978)). However, these methods do not provide industrially useful manufacturing process due either to the use of large quantity of catalyst (e.g. lead tetraacetylate) or to the lengthy synthetic procedures.

In EP A 317998, it has been disclosed that an optically active form of 1,2-phenylethanediol can be prepared from its racemic mixture by a selective metabolism of one enantiomer with a biocatalyst. This method provides only one form of 1,2-phenylethanediol enantiomers in low yield.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the problems encountered in prior arts and to provide a method for separating optical isomers of 1,2- phenylethanediol.

It is another object of the present invention to provide a simple method for separating optical isomers of 1,2-phenylethanediol in high optical purity.

It is a further object of the present invention to provide an industrially useful enzymatic method for separating optical isomers of 1,2-phenylethanediol.

The present invention provides a biochemical optical resolution method for 1,2-phenylethanediol in which a racemicmixture of (R,S)-l,2-phenylethanediol, represented by the following formula I;

is reacted with an acetyl donor in the presence of an enzyme, producing the mixture of monoesters and diesters thereof.

According to the method of the present invention, the optical resolution can be completed within a short period and under mild conditions while producing monoesters and diesters of 1,2-phenylethanediol in high optical purity. The present invention also provides a method that requires a simple post-reaction treatment. DETAILED DESCRIPTION OF THE INVENTION '

In the present invention, vinyl acetate is used as the acetyl donor in the optical resolution of 1,2- phenylethanediol. Acetyl group is sequentially transferred from vinyl acetate to 1,2-phenylethanediol in the presence of an enzyme, producing optically active diester of 1,2-phenylethanediol. In detail, when vinyl acetate is reacted with 1,2-phenylethanediol under an ambient pressure in the presence of an enzyme, typically a lipase derived from various microorganisms, an acetyl group is first transferred to either one of the hydroxyl groups of 1,2-phenylethanediol to give a mixture of two regioisomeric forms of monoacetate of 1,2- phenylethanediol, represented by the following formulas II and III respectively:

I]

Acetylation of the mixture of the monoacetates produces the diester, represented by the following formula IV in high optical purity:

It is obvious that the high optical purity of the diester is the result of the enzymatic catalysis during the sequential transfer of two acetyl groups from vinyl acetate to 1,2-phenylethanediol. In the transfer of the first acetyl group, the enzymatic optical selectivity is none or very low, if there is any, while in the transfer of the second acetyl group, the enzymatic optical is essentially high. The monoacetates mixture and the diacetate of 1,2-phenγlethanediol can be separated by column chromatography from the reaction mixture containing the compounds represented by the formulas II, III and IV.

According to the method presented by the invention, the reaction mixture consisting essentially of 1,2- phenylethanediol, vinyl acetate, solvent and either free or immobilized form of an enzyme, is subjected to esterification with vigorous stirring at a ' temperature between 0 to 50 ^*C and preferably between 20 to 30 ^*C.

At the completion of the reaction, excessive reagent is removed and the diester represented by the formula IV is obtained by column chromatography and is converted to 1,2- phenylethanediol by various chemical methods.

Various organic solvents, such as vinyl acetate, ethyl acetate, n-hexane, butyl acetate, and diethyl ether, may be used as the reaction media for the acetylation of the present invention. It is preferred to use vinyl acetate, which is the acetyl donor in the present invention, as the reaction medium.

The molar ratio of 1,2-phenylethanediol to the acetyl donor is in the range of 1:1.6 to 1:15 and preferably in the range of 1:2.5 to 1:3. When vinyl acetate is used as the solvent, the molar ratio of 1,2-phenγlethanediol to the vinyl acetate is 1:25 or higher.

The concentration of 1,2-phenylethanediol in various solvent is from 0.01M to 2M, and preferably from 0.05M to 1M. The ratio (w/w) of 1,2-phenylethanediol to the enzyme is from 1:0.2 to 1:100.

After the transesterification, the used enzyme is recovered by a filtration and can be reused because the activity and selectivity of the enzyme are maintained substantially. The enzyme used in the present invention is a lipase derived from microorganisms and can be employed as free or immobilized state. The microorganisms comprise yeast such as Candida and Torulopsis, molds such as Rhizopus, Penicillium, Aspergillus, Geotrichum, and Mucor, and bacteria such as Pseudomonas, Achromobacter and Staphylococcus. In general, immobilized forms of enzymes show enhanced and constant activity with better stability. In addition, immobilized forms of enzymes are easier to recover, hence easier to reuse. Immobilization of an enzyme can be appropriately made on porous carriers with large surface areas, such as celite, porous glass and silica. Immobilization can be easily achieved by stirring an enzyme and a selected carrier in a phosphate buffer, filtration and drying the immobilized enzyme at ambient temperature.

A better understanding of the present invention may be obtained in light of following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE I

Immobilization of Enzyme 40 g of pseudomonas lipase was suspended in 240 ml of 10 mM phosphate buffer (pH 7) and sufficiently dissolved by stirring for 30 minutes at ambient temperature. In 600 ml of the same buffer 80 g of celite (545) was added and stirred at ambient temperature for 30 minutes. This solution was filtered by passing through a filter with a pore size of 0.45 μm. The filtered celite solution was added in the enzyme suspension and sufficiently mixed by stirring for 30 minutes. The resulting solution was poured into prechilled (-20 ^ΦC) 1.2 liter of acetone, stirred for 30 minutes, filtered with a membrane and dried in vacuo.

EXAMPLE II

Optical Resolution of (R,S)-l,2-Phenylethanediol

In 12.5 ml of vinylacetate, 0.25 g of the immobilized pseudomonas lipase prepared in Example I was added together with 0.25 g of (R,S)-l,2-phenylethanediol. The reaction mixture was vigorously stirred at 25 ^*C and the progress of reaction was monitored by gas chromatography. After 25 hours, the products of reaction consisted of 50 % of diester and 50% of monoesters respectively. At the moment the enzyme was removed by filtration. Thereafter, the organic solvent layer was washed with 5 % sodium carbonate solution, dried over magnesium sulfate and concentrated in vacuo to give colorless oil. This concentrate was subjected to column chromatography (mobile phase, n-hexane:ethylacetate = 9:1 v/v), to separate into respective optical isomers: (S)-l,2-propanoyloxy- phenylethane (optical purity 93%) and (R)-l-propanoγloxy- 2-phenylethanol (optical purity 89%).

^•Physical properties of (S)-l,2-propanoyloxy- phenylethane:

[α] = +59.4^* (c=1.0, acetone), ee=93% ^-NMRfCDC^, 200 MHz), ppm (δ); 1.2(t,3H), 2.4(q,lH), 4.4(m,2H), 6.1(m,lH), 7.4(s,5H) ^•Physical properties of (R)-l-propanoyloxγ-2- phenylethanol:

[α] = -15.2^* (C=1.0, acetone), ee=89% ¹H-NMR(CDC1_3/ 200 MHz), ppm (6); 1.2(t,3H),

2.4(q,lH), 2.9(s,lH), 4.2(m,2H), 4.95(m,lH),

7.4(s,5H) Optical purity of the diesters produced was assayed by gas chromatography (Chiraldex G-TA column. Astech) during the reaction. The diesters were removed and converted into diols by use of methanol, the optical purity of which was again assayed by high pressure liquid chromatography (Chiralcel OB-H column, Dicell). Other features, advantages and embodiments of the present invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosures. In this regard, while specific embodiments of the invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed.

Claims

WHAT IS CLAIMED IS:

1. A method for optical resolution of 1,2- phenylethanediol, comprising the reaction of a racemic mixture of (R,S)-l,2-phenylethanediol, represented by the following formula I:

with an acetyl donor in the presence of an enzyme, to produce a mixture of monoesters and diesters.

2. The method in accordance with claim 1, wherein said acetyl donor is vinylacetate.

3. The method in accordance with claim 1, wherein said enzyme is a lipase derived from microorganisms.

4. The method in accordance with claim 3, wherein said enzyme is free or immobilized on a carrier.

5. The method in accordance with claim 1, wherein the ratio (w/w) of 1,2-phenylethanediol to the enzyme is from 1:0.2 to 1:100.

6. The method in accordance with claim 1, wherein the molar ratio of said diol to acetyl group donor is in the range of 1:1.6 to 1:15.

7. The method in accordance with claim 1, wherein said reaction is carried out at a temperature of 0 to 50

^•c

8. The method in accordance with claim 1, which further comprises isolating said diesters from the mixture by column chromatography and converting the isolated diesters into optically pure 1,2-phenylethanediol by a chemical process.