Process for enantioselective enzymatic reduction of keto compounds
Chiral secondary alcohols may be produced enzymatically in high space-time yields while minimizing enzyme use, by reducing a keto compound in an aqueous reaction medium containing water, reducing agent, alcohol dehydrogenase and coenzyme, extracting the secondary alcohol formed by means of a further phase containing a water-immiscible organic solvent, and removing the phase used for extraction and reusing the aqueous reaction medium in step a).
1 . A process for preparing chiral secondary alcohols, comprising the steps of
a) enzymatically reducing a keto compound in an aqueous reaction medium containing water, reducing agent, alcohol dehydrogenase and coenzyme,
b) extracting the secondary alcohol formed by means of a further phase containing a water-immiscible organic solvent,
c) removing the phase used for extraction and reusing the aqueous reaction medium in step a).
2 . The process of claim 1 , wherein the reduction is carried out under reduced pressure and volatile components are removed from the reaction system.
3 . The process of claim 1 , wherein the reducing agent comprises isopropanol.
4 . The process of claim 2 , wherein the reducing agent comprises isopropanol.
5 . The process of claim 1 , wherein the reducing agent comprises formic acid or a salt of formic acid.
6 . The process of claim 2 , wherein the reducing agent comprises formic acid or a salt of formic acid.
7 . The process of claim 1 , wherein the phase used for extraction comprises methyl tert-butyl ether.
8 . The process of claim 2 , wherein the phase used for extraction comprises methyl tert-butyl ether.
9 . The process of claim 3 , wherein the phase used for extraction comprises methyl tert-butyl ether.
10 . The process of claim 1 , wherein the time of contact between the aqueous reaction medium and the organic extraction phase during extraction is from 1 min to 10 min.
11 . The process of claim 2 , wherein the time of contact between the aqueous reaction medium and the organic extraction phase during extraction is from 1 min to 10 min.
12 . The process of claim 3 , wherein the time of contact between the aqueous reaction medium and the organic extraction phase during extraction is from 1 min to 10 min.
13 . The process of claim 7 , wherein the time of contact between the aqueous reaction medium and the organic extraction phase during extraction is from 1 min to 10 min.
14 . The process of claim 1 , wherein the alcohol dehydrogenase comprises an alcohol dehydrogenase from yeast, equine liver, Rhodococcus erythropolis, Thermoanaerobium spec., Lactobacillus kefir or Lactobacillus brevis.
15 . The process of claim 1 , wherein the coenzyme comprises at least one of NADP, NADPH, NAD, NADH or salts thereof.
16 . The process of claim 1 , wherein the aqueous reaction mixture is contained in a first reaction vessel, and at least a portion of the aqueous reaction mixture is removed from the first reaction vessel, extracted with a further phase containing a water immiscible solvent, the aqueous phase and the further phase are phase separated, and the aqueous phase is returned to the first reaction vessel or to a further reaction vessel whereupon step a) is repeated.
17 . The process of claim 2 , wherein the aqueous reaction mixture is contained in a first reaction vessel, and at least a portion of the aqueous reaction mixture is removed from the first reaction vessel, extracted with a further phase containing a water immiscible solvent, the aqueous phase and the further phase are phase separated, and the aqueous phase is returned to the first reaction vessel or to a further reaction vessel whereupon step a) is repeated.
18 . The process of claim 16 , wherein the extraction is a batch extraction.
19 . The process of claim 16 , wherein the extraction is a continuous, countercurrent extraction.
20 . The process of claim 1 , wherein the keto compounds used are prochiral ketones of the general formula (I)
R 1 —C(O)—R 2 (I),
in which
R 1 and R 2 are selected independently of one another from the group consisting of C 1 -C 20 -alkyl, C 3 -C 20 -cycloalkyl, C 5 -C 20 -aryl, C 1 -C 20 -heteroaryl, C 2 -C 20 -alkenyl, C 5 -C 20 -aralkyl, C 5 -C 20 -alkylaryl, and rings formed from R 1 and R 2 ,
where R 1 and R 2 , independently of one another, are optionally substituted with one or more radicals Z, where
Z is selected from the group consisting of fluoro, chloro, bromo, iodo, —CN, —NO 2 , —NO, —NR 3 OR 3 , —CHO, —SO 3 H, —COOH, and —R 3 and
R 3 is R 1 or hydrogen, and
in R 1 and R 2 , independently of one another, one or more methylene groups may be replaced by identical or different groups Y, where
Y is selected from the group consisting of —CR 3 ═CR 3 —,
—C≡C—, —C(O)—, —C(O)O—, —OC(O)—, —C(O)OC(O)—, —O—,
—O—O—, —CR 3 ═N—, —C(O)—NR 3 —, —N═N—, —NR 3 —NR 3 —, —NR 3 —O—,
—NR 3 —, —P(O)(OR 3 )O—, —OP(O)(R 3 )O—, —P(R 3 )—, —P(O)(R 3 )—,
—S—, —S—S—, —S(O)O—, —S(O) 2 —, —S(O)NR 3 —, —S(O)(OR 3 )O—,
—Si(R 3 ) 2 —, —Si(R 3 ) 2 O—, —Si(R 3 )(OR 3 )—, —OSi(R 3 ) 2 O—,
—OSi(R 3 ) 2 —, and —Si(R 3 ) 2 OSi(R 3 ) 2 —.