CA2066689A1

CA2066689A1 - Enantioselective, enzymatic synthesis of s(-) and r(+)esters of 4-hydroxy-cyclopentene-1-one and its 2'-2'-dimethylpropane-1,3'-diol-ketal

Info

Publication number: CA2066689A1
Application number: CA 2066689
Authority: CA
Inventors: Stefan B. Schapoehler; Thomas Scheper; Karl Schuegerl
Original assignee: Individual
Current assignee: EUROPAEISCHE WIRTSCHAFTSGEMEINSCHAFT (EWG)
Priority date: 1989-09-25
Filing date: 1990-09-27
Publication date: 1991-03-26
Also published as: DK37392A; DK37392D0; PT95404A; WO1991004337A1; JPH06500458A; LU87593A1; EP0419988A1; IE903437A1

Abstract

The S(-) and R(+) esters of 4-hydroxy-cyclopentene-1-one and its 2',2'-dimethylpropane 1',3'-diol-ketal are produced by direct, enantioselective, enzymatic synthesis by reacting the corresponding 4-hydroxy compounds with an ester as acyl donor in the presence of an enzyme. The esters obtained are valuable intermediate products for stereospecific synthesis, in particular for the stereoselective synthesis of chemical compounds, in particular stable, storable, chiral prostaglandin derivatives, especially storable chiral prostaglandinsynthone.

Description

Fo 2256 2~ 9 Enantioselective enzymatic synthe~i~ of S(-)- and R(+)-esters of 4-hydro~y-2-cyclopenten-1-one and its ketal formed with 2',~'dimethylpropane-1',3-diol .. .. ~
The invention relates to the enantioselective enzymatic synthesi~ of S(-)- and R(+)-esters of 4-hydroxy-2-cyclopenten-1-one and its ketal formed with

2',2'dimethylpropane-1',3'diol, and it particularly relates to a process for the enantioselective preparation of the said S(-)- and (R(~)-esters of the general formula (Ia) and (Ib), respectively, indicated below ,~ .
.
.
H3 I~C~

OAc~,l OAcy~

, (Ia) - (Ib) which are valuable intermediate for the targeted, that is to say stereo- and enantioselective, synthesis of chemical compounds, especially chiral pro~taglandin derivatives which are table on storag-.

~ .

..
. ' - 2 - 2~?~ 39 j,'~ !~ German Offenlegungsschrift 37 24 721 ha~ di~-closed the preparation from racemic ketal acetate by hydrolytîc ester cl2avage in the presence of an enzyme, that is to say by enzymatic hydrolysis, of the corres-ponding S(-)-alcohol, with the R(+)-e~ter being left behind. However, the S(-)-alcohol contained in the reaction mi~ture (pH 7) i~ unstable in the aqueous-reaction system and the further processing thereof to the S(-)-ester by chemical esterification is extremely technically complicated, and the desired final product i~
obtdined in only relatively low yield~. ' Hence the ob;ect of the invention was to find a way for qelectively preparing the S(-)- and R(~)-esters of 4-hydroxy-2-cyclopenten-1-one and its ketal formed with 2~,2'-dimethylpropane-1',3'diol, which is indu~trially straightforward and provide~ the desired final product in high purity and yleld.
' It has now been found that this ob~ect can be achieved according to the invention by preparing in a reversal of the already disclosed enantioselective' enzymatic cleavage of the racemic ketal acetate in an aqueous medium buffered to pH 7 the S(-)- and R(+)-esters of 4-hydroxy-2-cyclopenten-1-one and its ketal formed with 2',2'dimethylpropane-1',3-diol by targeted, that is to 25 say stereo- and enantioselective, enzymatic ~ynthesis from the corre ponding racemic hydroxyl compound and from an acid ester as acyl donor in the presence of an enzyme in an organic solvent.
The invention relates to a process for the .

, ~ ' .

.

. . .
. ~ . .

~ 3 ~ 2~ 9 . . .
enantio~elective preparation of S(-)- and R(+)-esters o 4-hydroxy-~-cyclopenten-1-one and it~ ketal formed with 2',2-dimethylpropane-1~,~-diol, of the general formula (Ia) and (Ib) respectively ~I~,C C~3 ~3C CH3 ~ ~ ,.
0~0 , [o~o .
OAcyl O A cyl (Ia) (Ib) .

which i~ characterized in that a) a racemic mixture of 4-hydroxy-2-cyclopenten-1-one or its ketal formed with 2',2'-dimethylpropane-1',3 diol, of the formula (II), i~ reacted in the pre sence of an enzyme with an e~ter of the general formula (III) a acyl donor in organic phase, ~ preferably in anhydrous organic pha~e, at room ; temperature or ~elevated temperature, with the : formation of the S(-)-e~ter tIa) and with the R(~)-alcohol o~ the formula (IIb) being left behind, in ~ccordance with the re~Ftlon equation:

.; ,.

~ . .

;21~ 3 .. . .

Ac~l-OR ~C ~ C~ H3C ~ CH3

3 + O ~ O

O Ac OH
(~

(II) (Ia) (IIb) + R - OH

(IV) in which acyl denotes any desired acid residue, preferably the residue of an organic C~-C~-carboxyIic acid, and R denotes an optionally sub-stituted, unbranched or branched alXyl, alkenyl or alkynyl group with 1 to 22, preferably 1 to 12, in particular 1 to 6, carbon atoms, an optionally sub~tituted aryl group with 6 to 12, preferably 6 to 10, carbon atoms, or an optionally substituted heterocyclic group with S to 10, preferabLy 5 to 7, ring atoms, which contain~ at least one nitrogen, oxygen and/or sulphur-atom as hetero atom(-s),-ànd in which the enzyme is chosen from the group comprising lipases obtained from Pseudomonas fluorescens, Candida cylindracea, Porcins pancreas, Mucor miehei, . .
b) the product mixture obtained in stage ~a) is frac-~ . i tionated by chromatography or extxàc~ion into the : S(-)-ester of the formula (Ia), which is obtained as first final product, and into the R(+)-alcohol of the formula ~IIb), which . .

:

. :. , , , :.

. .. . . ..

~: 2~ 9 c) is converted by chemical or enzymatic esterification with the ester of the formula (III) into the R(~)-e~ter of the formula (Ib) which in turn i~ obtained . by chromatography or extraction in pure form as second final product, in accordance with the reac-tion equation: .

~C><;CH3 H3C C~
~ Acyl-OR o~o OAcyl' (IIb) - (III) (Ib) + R - OH
(IV) It i~ possible by the process according to the invention to prepare in an industrially straightforward and economic manner, by direct enantioselective enzymatic synthesis, avoiding the un table S(-)-hydroxy compound, ; the S(-)- and R(~)-esterq of 4-hydroxy-2-cyclopenten-1-one and its ketal foxmed with 2',2'dimethylpropane 1',3-diol, which are valuable intermediate~ for the synthesis : of a chiral prostaglandin synthon which is stable on storage. In particular, 4-acetoxycyclopentenone and its ketal are key substances in the synthesis of cyclo-: pentanoid natural~ubstance~ (compare German ~ .
.

, , ~ ' ' ' :

. ` - 6 - 2~ 9 Offenlegungs~chrift 37 24 721, R. Noyori et al, ~Angewandte Chemie~, 96, 854 (1984), and E. Winterfeldt et al, ~Angewandte Chemie~, 94, 496 (1982)).
When carrying out the process according to the invention, the desired final products are obtained in stable form and extremely high purity and yield. Further-more, the process according to the invention has the following industrial advantages over the process dis~
closed in German Offenlegungsschrift 37 24 721: besides the smaller number of synthetic steps, there is a dis-tinct reduction in the solvent requirement; the reaction takes place in very small volumes; it is unnecessary to use toxic or carcinogenic extracting solvent~ because direct wor~ing up is po~ible, which is also a~sociated with an energ~ saving; the enzyme can easily be removed (for example by filtration) and no immobilization is necessary; continuou~ use with an enzyme cartridge (fixed bed) i~ directly possible; and no use of solubilizers is necessary.
When carrying out the process according to the invention, the acyl donor which i preferably used is an ester of the general formula O
R1 ~ C ~ OR2 V

in which R1 and R2, which can be identical or different, each have the meanings indicated above for R.
It is very particularly preferred to use the ethyl ester of acetic acid ~ethyl acetate) and a glycerol ,.

.

:: , . , ... . ~ .:
~ ~ , ,. . ., . , -:~ .,: .: ' ' , ~ 7 - 2~
triester of an organic acid with 1 to 22 carbon atomq, especially triacetin, tributyrin and the like, aq acyl donor, the latter being distinguished by their non-toxicity and their high reaction rate.
When carrying out the process according to the invention, conventional flaqh column chromatography is prefera~le to extractive working up (compare Still et al, ~'J. Org. Chem~", 43, 2 923 (1978)), a3 has also been uqed in the examples hereinafter. When carrying out stage (c) of the process according to the invention, the enzymatic esterification is preferable to qtandard chemical esteri-fication (with an acid chloride/acid anhydride and pyridine and an alcohol). The procedure for this proces~
corresponds to the procedure for the enantioselective esterification. Direct enantioselecti~e enzymatic esteri-fication according to the present invention i8 particu-larly advantageous for the ketalized compound, it being possible to achieve complete separation of the enantio-mers with the ketal formed with 2',2'dimethylpropane-1',3'-diol (= ketal alcohol)l in which case it is easy to obtain, by ~ubsequent deketalization, the enantiomeri-cally pure ester of non-ketalized 4-hydroxycyclopentenone (- keto alcohol) (for example with addition of catalytic acetic acid or formic acid at room temperature by shaking for I hour or lea~ing to stand for 48 hour~ on Merck silica gel No. 9385).
Wherea~ in the case of the keto ~ubstrate of the formula (II) in stage (a) of the process according to the invention the enzyme which is preferably used i3 pig ..

.

: . ,: , :

~ - 8 - Z~ 9 .,- ` .
liver esterase, in the case of the ketal sub~trate of the formula ~II) the enzyme which is preferably used i5 lipase, in particular a lipase which ha~ been obtained from Pseudomonas fluorescens (Amano lipase P, batch no.
LPL 05518).
A 60 ~ enantioselective enzymatic esterification of the keto substrate is achieved according to the invention with Pseudomonas fluorescens lipase (for example Amano lipase P, batch no. LPL 05518 or Rohm, EL
220-88). In the case of the ketalized compound, complete separation of enantiomers can be achieved with the following lipases: lipases from Pseudomonas fluorescens (for example Amano lipase P, batch no. LPL 05518 or R~hm, EL 220-88), Candida cylindracea (manufacturer, inter alia, Amano lipase AY, batch no. LAY MO 3517 or Sigma, cat. no. L-1754, batch no. 34F-0621), porcine pancreas (manufacturer, inter alia, Rohm, batch no. 7023 C, Sigma, cat. no. L-3126, batch no. 74F-0470) and Muco~ miehei (Gist-Brocades, batch no. 0282).
The enzymes are preferably employed in excess.
Enzyme/alcohol ratios of from 0.5:1 to 10:1 by mass have proved advantageou~, depending on the activity (U) of the enzyme (reference reaction~ hydrolysis of a triglyceride or solvent ester, U - ~mol of fatty acid equivalent per minute at constant pH in aqueous emulsion, also in accordance with the statements of the enzyme manufac-~ ~turers). The immobilized Pseudomonas lipase from Rohm has, for example, a 6-time~ lower specific activity, and thus a correspondingly higher dose is necessary.

~ , .

-, : :
.

2~ g ~ hen carrying out the proces~ according to the invention, the organic solvent preferably used in stage (a) is a hydrocarbon such as n-heptane, i-octane etc., or an ester, especially cyclohexyl acetate, specifically the ester employed as acyl donor, especially tributyrin.
The transesterification carried out in stage (a) of the process according to the invention can be carried out at room temperature or elevated temperature, prefer-ably at a temperature in the range from 40 to 75C, in particular 58 to 62C, specifically at 60C.
The organic solvent and the alcohol of the formula (II) are preferably employed in stage (a) of the process according to the invention in a ratio of from 4:1 to 100:1, in particular from 5:1 to 10:1, by mass, with the ratio of solvent to alcohol also being crucially determined by the solubility of the alcohol used.
The enzyme and the alcohol of the formula (II) are preferably employed in stage (a) of the process according to the invention in a ratio of from 0.5:1 to 10~ pecifically 0.5:1 to 1.5:1, in particular 0.7:1 to 0.9:1, by mas~.
According to a particularly preferred embodiment of the procèss according to the invention it is possible, in place of the esterification of the R(~)-alcohol of the formula (IIb) in ~tage (c), to carry out a racemization of the alcohol and recycling thereof to stage (a), which makes it po~sible to achieve complete enantioselective esterification of the racemic hydroxy compound of the formula tII~ to the S(-)-e~ter of the formula (Ia).

, , .
.
'; ' , ' 0 - 2~ 9 The course of the reaction and the enantiomer ratio can be determined by use of high-pressure liquid chromatography ~HPLC with ~he chiral Daicel OA HPLC
column, eluent n-hexane/isopropanol 10:1) or capillary gas chromatography (Lipodex' A column from Macherey h Nagel). The details of the~e processes correspond to the general laboratory standard (taking account of the manufacturers' manuals). Finally, the enantiomer ratio and the absolute configuration can be confirmed in a standard way by H-NMR of the Mosher ester3 (compare J.A. Dale et al, "JACS~, 95, 512-519 (1973), and German Offenlegungsschrift 37 2~ 721).
The enzyme used according to the invention can be employed in free form, that is to say~dissolved or suspended in-the organic reaction medium, or in immobil-ized form, for example in a form entrapped in a polymer substrate.
The formulae Ia, Ib, II and IIb indicated above represent combined formulae in which the structural formulae of 4-hydroxy-2-cyclopenten-1-one and it~ ester derivatives on the one hand, and its ketal formed with : 2~,2'dimethylpropane-1',3'-diol and its ester derivatives on the-other hand, are combined in order to simplify the reaction equations. Thus, for example, the formula (II) 2S represents a combination of formulae (II') and (II"):

..
..
.: . . . .

.

Z~ 'ti~39 ,, ~ ,~ .

~;;; = ~, p><;

OH ~

(II) (II') (IIn) .
Taking into account the above definition, the course of the proce~ according to the invention when ethyl acetate is used as acyl donor for the two startin~
compounds 4-hydroxy-2-cyclopenten-1-one (A) and its ketal ormed with 2',2'-dimethylpropane-1',3'diol (~) can be represented diagrammatically as follows (Ac = acetyl): -':
-.

:: ::
- :: , ~ - 12 - 2~ 9 A) O O O
Esterase +Ac-GR y OH70~ conversiOn after 0AC OH
. 20 h or alkaline/acid reracemization + AC-OR
__ __ _ _ ____ l O
~>

C~c ~ ~ C~ C ~ C~3 ~C ~ C~
0~0 L 0~0 +
0~0 70% conver ion after OH 20 h OAC
OH

I or alkaline~acid rexacemization ~Ac-OR

. .
~ C ~ C~3 X
oAc .. , . - .. . . ., - . ~ . ... .. ~ ... ..
. ;. ~ " -. ~ ~ ,.. ~ ., . , -~, . - .
..
, , , ,. ,. ~ , ". , , ., . ., :, : . , .
.~ . . . , ~, ' - 13 - 2~ 9 .- The reaction parameters suitable for the acetyl-ation by the proces~ according to the invention depend on the varying marginal conditions, for example on the ratios by ma~s or the particular activity of the enzyme 5 used in each case, on the choice of the desired acid residue (for example acetic acid, butyric acid or oleic acid residue) and the like. The optimal parameters for the acetylation by the process according to the invention are the following, in particular:
Enzyme: Pig liver esterase or lipase from P3eudomonas fluorescens (Amano llpase P, batch no.
LPL 05518) Solvent (S): Triacetin (glycerol tri-. acetate, completely environ-mentally neutral because a natural substance) Dried ester (S)/ketal i alcohol ratio by ma s: 6:1 Enzyme/ketal alcohol ratio by mass: 1:1 Reaction temperature: 40C ~ 1C
-Water content of the 3.17 ~ (lyophilized enzyme,enzyme: ~ employed for tho reaction directly from the manufac-turer) The invention i~ explained in more detail by the examples which follow, without being limited to them.

. .

.

- 14 - 2~ 9 . , .
Example 1 521.3 mg (- 2.83 mmol) of ketal alcohol, 511.3 mg of Amano lipase P (batch no. LPL 05518) in 3 ml (= 3.1 g = 9 mmol) of tributyrin were reacted in a 10 ml round-bottomed flask in an oil bath at 40C on a magnetic stirrer.
After 45 h, the reaction was qtopped, the enzyme was filtered off and washed with acetone, and the entire filtrate was fractionated on a 50 g silica column ~Merc~
flash silica gel 60, No. 9385) with 2:1 petroleum ether/
ether as mobile phase.
240.1 mg (= 0.98 mmol) of S(-)-Xetal butyrate (enantiomeric purity ~ 95 ~ee, according to HPLC) and 281.2 mg (= 1.53 mmol) of R(+)-ketal alcohol (> 95 ~ee according to HPLC) were obtained.
Example 2 2 ml of dri`ed cyclohexyl acetate (13.6 mmol), 250 mg of Amano lipase P (as in Example 1) and 308.0 mg (- 1.68 INmol) of ketal alcohol were reacted in a 10 ml round-bottomed flasX in an oil bath at 60C on a magnetic stirrer.
After 20 h, the reaction wa~ qtopped, the enzyme wa~ filtered off and washed with acetone, and the filt-rate was fractionated on a 50 g silica column ~Merck, No.
9385), with a petroleum ether/ether (1:1) mixture.
Yield: 140.2 mg (0.76 mmol) of R(+)-ketal alcohol (> 95 %ee according to HPLC and H-NMR of the Mosher ester) and 203.4 mg (= 0.83 mmol) of S(-)-ketal butyrate (> 95 ~ee according to HPLC).

: ~ , - .,:
, . , : . :
- - ~
:
, . .
,

Claims

Enantioselective enzymatic synthesis of S(-)- and R(+)-esters of 4-hydroxy-2-cyclopenten-1-one and its ketal formed with 2,2-dimethylpropane-1,3-diol P a t e n t C l a i m s

1. Process for the enantioselective preparation of S(-)- and R(+)-esters of 4-hydroxy-2-cyclopenten-1-one and its ketal formed with 2',2'-dimethylpropane-1',3'-diol of the general formula (Ia) and (Ib) respectively (Ia) (Ib) characterized in that a) a racemic mixture of 4-hydroxy-2-cyclopenten-1-one or its ketal formed with 2',2'-dimethylpropane-1',3'-diol, of the formula (II) below, is reacted in the presence of an enzyme with an ester of the general formula (III) below as acyl donor in organic phase, with the formation of the corresponding S(-)-ester of the general formula (Ia) and with the R(+)-alcohol of the formula (IIb) being left behind, in accordance with the reaction equation:

(II) (III) (Ia) (IIb) (IV) in which acyl denotes any desired acid residue, preferably the residue of an organic C1-C22-carboxylic acid, and R denotes an optionally sub-stituted, unbranched or branched alkyl, alkenyl or alkynyl group with 1 to 22, preferably 1 to 12, in particular 1 to 6, carbon atoms, an optionally substituted aryl group with 6 to 12, preferably 6 to 10, carbon atoms, or an optionally substituted heterocyclic group with 5 to 10, preferably 5 to 7, ring atoms, which contains at least one nitrogen, oxygen and/or sulphur atom a hetero atom(s), and in which the enzyme is chosen from the group comprising lipases obtained from Pseudomonas fluorescens, Candida cylindracea, Porcine pancreas, Mucor miehei, b) the product mixture obtained in stage (a) is frac-tionated by chromatography or extraction into the S(-)-ester of the formula (Ia), which is obtained as first final product, and into the R(+)-alcohol of the formula (IIb), which c) is converted by chemical or enzymatic esterification with the ester of the formula (III) into the R(+)-ester of the formula (Ib) which in turn is obtained by chromatography or extraction in pure form as second final product, in accordance with the reac-tion equation:

(IIb) (III) (Ib) (IV)

2. Process according to Claim 1, characterized in that the acyl donor used is an ester of the general formula:

V

in which R1 and R2, which can be identical or different, each have the meanings indicated for R in Claim 1.

3. Process according to Claim 1 or 2, characterized in that the ethyl ester of acetic acid (ethyl acetate) or a glycerol triester of an organic acid with up to 22 car-bon atoms, especially triacetin or tributyrin, is used as acyl donor.

4. Process according to one of Claims 1 to 3, characterized in that pig liver esterase is used as enzyme in the case of the keto substrate of the formula (II).

5. Process according to one of Claims 1 to 3, characterized in that lipase from Pseudomonas fluorescens is used as enzyme in the case of the ketal substrate of the formula (II).

6. Process according to one of Claims 1 to 5, characterized in that a hydrocarbon and/or an ester, preferably the ester employed as acyl donor, is used as organic solvent in stage (a).

7. Process according to one of Claims. 1 to 6, characterized in that the transesterification in stage (a) is carried out at room temperature or elevated temperature, preferably at a temperature in the range from 40 to 75°C, in particular 58 to 62°C, specifically at 60°C.

8. Process according to one of Claims 1 to 7, characterized in that the organic solvent and the alcohol of the formula (III) are employed in stage (a) in a ratio of from 4:1 to 100:1, preferably 5:1 to 10:1, by mass.

9. Process according to one of Claims 1 to 8, characterized in that the enzyme and the alcohol of the formula (III) are employed in stage (a) in a ratio of from 0.5:1 to 10:1, specifically 0.5:1 to 1.5:1, in particular 0.7 2 1 to 0.9:1, by mass.

10. Process according to one of Claims 1 to 9, characterized in that in place of the esterification of the R(+)-alcohol of the formula (IIb) in stage (c), a racemization of the R(+)-alcohol and a recycling thereof to stage (a) are carried out for complete enantioselec-tive conversion of the racemic compound of the formula (II) into the S(-)-ester of the formula (Ia).