DE19937825B4 - Process for the reduction of hydroxyketo-carboxylic acids and their esters - Google Patents

Abstract

The present invention relates to a process for the reduction of diketocarboxylic acids or hydroxyketocarboxylic acids or their esters, in which at least one keto group is converted to a hydroxy group in the presence of Lactobacillus species.

Description

The The present invention relates to a process for the reduction of hydroxyketocarboxylic acids or their esters to hydroxy compounds.

optical active hydroxy compounds are valuable chiral building blocks. So Chiral diols are important ingredients for a variety of drugs in pharmacy and crop protection as well as for catalysts.

to Production of chiral compounds can be biotechnological processes be applied either using whole microorganism cells or by means of isolated enzymes work.

Suitable enzymes for the synthesis of alcohols include oxidoreductases, which are known in the EP 0456107 A2 (obtained from Lactobacillus kefir), the EP 0796914 A2 and PCT / DE 99/00848 (from Lactobacillus brevis). However, the syntheses require accessibility to the appropriate enzymes, the addition of a soluble coenzyme (NADH, NADPH) and a coenzyme regeneration system. Likewise, WO 97/00968 describes the use of reductases for the reduction of keto groups.

Furthermore, in the U.S. Patent 5,342,767 a method is described in which a reduction is carried out using alcohol dehydrogenase from Lactobacillus kefir.

In the DE 196 10 984 A1 Also, a method is described in which an alcohol dehydrogenase is used. In addition to the purified enzymes, whole cells can also be used. However, the subject of this invention is not the reaction of compounds having two or more keto groups. Likewise, the method does not relate to the reaction of keto carboxylic acids and. their esters.

microorganisms make a cost-effective Alternative to enzymes. However, these methods often yield low Yields (F. Aragazzini et al., Appl. Microbiol. Biotechnol. (1986). 24, 175-177). Furthermore occur frequently yield-reducing side reactions and possess the products not always sufficient enantiomeric purity. The product yield and quality hang strongly depending on the strain used and the conditions of cultivation.

From the EP 0569 998 A2 Finally, a method is known in which various microorganisms are used for the reduction of ether-containing diketo esters. The microorganisms usable in the description of this invention include many yeasts and bacteria, but not Lactobacillus species.

object The present invention accordingly provides a method of reduction of hydroxyketocarboxylic acids or their esters, which no longer has the described disadvantages. Hydroxy groups are also here masked with protective groups To understand hydroxy groups.

The The invention is characterized by a method for the reduction of Hydroxyketocarbonsäuren or their esters in the presence of Lactobacillus species the keto group is converted to a hydroxy group.

A, B = C=O oder CHOΣ, wobei A ≠ B und Σ = H oder Schutzgruppe für die Hydroxyfunktion.
R¹, R² = H oder eine Komponente aus der Gruppe Alkyl, Alkenyl, Alkinyl, Cycloalkyl, Cycloalkenyl, Aryl, Aralkyl, Cycloalkylalkyl, wobei die Komponenten auch einfach oder mehrfach mit den Heteroatomen Si, N, P, O, S, F, Cl, Br oder I substituiert oder vollständig durch Heteroatome ersetzt sein können.
R³ = H, Metallkationen oder eine Komponente aus der Gruppe Alkyl, Alkenyl, Alkinyl, Cycloalkyl, Cycloalkenyl, Aryl, Aralkyl, Cycloalkylalkyl, wobei die Komponenten auch einfach oder mehrfach mit den Heteroatomen Si, N, P, O, S, F, Cl, Br oder I substituiert sein können.
Y = eine Komponente aus der Gruppe Alkyl, Alkenyl, Alkinyl, Cycloalkyl, Cycloalkenyl, Aryl, Aralkyl, Cycloalkylalkyl, wobei die Komponenten auch einfach oder mehrfach mit den Heteroatomen Si, N, P, O, S, F, Cl, Br oder I substituiert sein können. Ausgeschlossen wird X-CH₂-O-CH₂-, wobei X = Alkyl, Aryl, Cycloalkyl, Aralkyl oder Cycloalkylalkyl sein kann. Unter den Halogenen sind Fluor und Chlor besonders bevorzugt.
n = 0-10.The process according to the present invention comprises, in particular, the catalytic reduction of the prochiral 3,5-dioxocarboxylic acid derivatives according to formula 1:

A, B = C = O or CHOΣ, where A ≠ B and Σ = H or protective group for the hydroxy function.
R ¹ , R ² = H or a component from the group alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also monosubstituted or polysubstituted by the heteroatoms Si, N, P, O, S, F , Cl, Br or I can be substituted or completely replaced by heteroatoms.
R ³ = H, metal cations or a component from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also mono- or polysubstituted by the heteroatoms Si, N, P, O, S, F, Cl, Br or I can be substituted.
Y = a component from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also monosubstituted or polysubstituted by the heteroatoms Si, N, P, O, S, F, Cl, Br or I. may be substituted. Excluded is X-CH ₂ -O-CH ₂ -, where X = alkyl, aryl, cycloalkyl, aralkyl or cycloalkylalkyl may be. Among the halogens, fluorine and chlorine are particularly preferred.
n = 0-10.

Under Alkyl is both straight-chain and branched saturated carbon To understand chains. By way of example, methyl, ethyl, n-propyl, i-propyl, t-butyl, pentyl, i-pentyl, n-hexyl, i-hexyl.

With Alkenyl are called straight-chain and branched unsaturated hydrocarbons, for the exemplified by vinyl, 1-propenyl, allyl, butenyl, i-butenyl can be.

With Alkynyl is called straight-chain and branched unsaturated hydrocarbons, the at least one -C≡C- Contain binding, such as ethynyl or propynyl.

From The term cycloalkyl will be saturated, annular hydrocarbon chains comprises those from three, four, five, consist of six or seven hydrocarbon atoms.

cycloalkenyl denotes unsaturated, annular Hydrocarbons, with five, six, seven or eight carbon atoms. Aryl is aromatic Systems, including heteroaromatic and substituted aromatic Systems, such. As phenyl, p-methylphenyl or furanyl to understand.

Under Aralkyl are aryl radicals linked via alkyl groups are, for. B. a benzyl radical.

Under the term cycloalkylalkyl includes cycloalkyl radicals which are via alkyl groups are bound.

As well reactions of the compounds according to formulas 2 and 3 are possible.

Here, R ¹ , R ² , R ³ and Y have the same meaning as in formula 1.
Σ = H or protective groups for the hydroxy functions.

Hierbei haben R¹, R², R³ und Y dieselbe Bedeutung wie in Formel 1.
Σ = H oder Schutzgruppe für die Hydroxyfunktion.Accordingly, in particular 3,5-dihydroxycarboxylic acid derivatives of the formula 4 shown below can be produced by the process according to the invention:

Here, R ¹ , R ² , R ³ and Y have the same meaning as in formula 1.
Σ = H or protective group for the hydroxy function.

Especially can with the method according to the invention, in contrast to the prior art, compounds according to the formulas 2 and 3 are reacted as substrates.

ever after configuration at the stereocenters C-3 and C-5, the 3,5-dihydroxycarboxylic acid derivatives prepared according to the invention of Formula 4 in the synthesis of chiral natural products, Pharmaceutical and agroactive agents, catalysts and inhibitors used become. Examples of this are HMG-CoA reductase inhibitors of the mevinic acid type and lipase inhibitors of the lipstatin type.

Other Natural or active ingredients require different stereogenic configurations Centers in positions C-3 and C-5. Again, this is with the present Invention possible.

Before carrying out the process according to the invention, reduction of 3,5-dioxocarboxylic acid derivatives can be effected by regioselective introduction of a hydroxy group in position C-3 or C-5, giving a product of r-configuration. For the term r-configuration, the following is an example of formula 2:
In Formula 2, the OΣ group emerges at the 5-position from the paper plane, while Y and the carbon atoms of the carbon backbone are in the paper plane:

These Configuration will be independent of Y as r configuration below designated.

In the reduction of 3,5-Dioxocarbonsäurederivaten targeted determination of the stereocenters in the position C-2 and C-4 is possible. This is especially true in the case where R ¹ and R ² are different from H and R ^{1 is,} for example, a methyl group. Both the enantiomeric purity and the diastereomeric purity are very high (> 95%).

According to the invention, the reduction process can also be used to prepare mixtures which have compounds with different hydroxyl group contents. Examples thereof are mixtures consisting of compounds of formulas 2, 3 and 4, wherein R ¹ , R ² = H; Y = -CH ₃ or -CH ₂ Cl and R ³ = C (CH ₃ ) ₃ . The method according to the invention is carried out with Lactobacillus species. In principle, all Lactobacillus species come into consideration. However, particularly preferred is the use of Lactobacillus kefir and Lactobacillus brevis.

The inventive method can be under usual Fermentation conditions and be carried out in the usual reactors.

When Cosubstrate can be an easily metabolizable carbonaceous material Substrate, e.g. Glucose can be used. This will be the case Reduction equivalents consumed in the implementation.

The Reactions according to the invention at temperatures from 10 to 50 ° C, preferably from 15 to 40 ° C carried out.

Of the pH is 2 to 10, preferably between 4 and 8. To ensure A suitable pH can be any buffer substance customary in fermentation technology be used. These are z. Triethanolamine, phosphate buffer, phosphate citrate buffer, 2-amino-2- (hydroxymethyl) -1,3-propanediol buffer, 2- [N-morpholino] ethanesulfonic acid buffer (MES) or Tris buffer. The concentration ranges for the buffers are advantageously between 50 and 500 mmol / l.

When Reactors can also find all known reactor types use. So both conventional stirred reactors as well as fixed bed reactors are used.

When using the method according to the invention, especially cost-intensive and environmentally harmful racemate or diastereomer separations are eliminated. Required in a diastereoselective synthesis Connection and removal of a stoichiometric amount of a homochiral auxiliary group is avoided. Furthermore, the carbon skeleton of the Dihydroxycarbonsäureester in the starting compounds is already complete, that is, the stereocenters are introduced at a later date in the overall synthesis sequence. This keeps the loss of homochiral material low. At the same time very high stereoselectivities are achieved with the method according to the invention. The use of whole cells also eliminates the need to include additional costly coenzymes and coenzyme regeneration systems in the reactions.

The produced according to the invention Compounds according to formula 4 can especially for the production of chiral natural products, pharmaceuticals and agroactive agents, catalysts and inhibitors. Examples of this For example, HMG-CoA reductase inhibitors are mevinic acid-type and lipase inhibitors are lipstatin-type.

in the The invention is described in more detail below with reference to examples:

Example 1: Preparation of Lactobacillus cells (Lactobacillus kefir)

Cells for reduction can be obtained by propagating a stock culture of Lactobacillus kefir (eg DSM 20587) in the following medium:
Per 1 L: 10 g of casein peptone, tryptically digested; 10 g meat extract; 5 g of yeast extract, 20 g of glucose; 1 g Tween 80; 2 g K ₂ HPO ₄ ; 5 g of Na acetate; 2 g of diammonium citrate; 0.2 g of MgSO ₄ .7H ₂ O; 0.05 g of MnSO ₄ .H ₂ O; pH = 6.2-6.5. After 24 hours of growth, the cells are harvested by centrifugation. They can be stored by freezing.

The Example 2 below shows the preparation of 3,5-dihydroxycarboxylic acid derivatives IV by the inventive method with the possibility an upstream reduction (not according to the invention) of 3,5-Diketocarbonsäurederivaten with Lactobacillus kefir.

Example 2:

Synthesis of secondary alcohols (S) -II, (R) -III and (3R, 5S) -IV (Scheme I)

The whole cell transformations described below are carried out at room temperature with cells of Lactobacillus kefir obtained as described in Example 1. Diketo compound I is prepared as described in M. Wolberg, W. Hummel, M. Müller, DE 19847302 A , 1998.

Carrying out the microbial reduction

In To a 50 ml beaker add 0.61 g of wet cell mass in 0.5 ml of phosphate-citrate buffer (250 ml.) mM, pH 5.5) with stirring suspended. 0.9 ml of this cell suspension are mixed with 1 ml of glucose solution (5 M, autoclaved), 8 ml of phosphate-citrate buffer (250 mM, pH 5.5) and 50 μl of 6-chloro-3,5-dioxo-hexanoic acid tert-butyl ester (I) offset. The reaction mixture is stirred with a magnetic stirrer.

reaction monitoring

After 1 h, 2 h, 6.5 h and 10.5 h, samples are taken. To this is added 40 .mu.l of the reaction solution to 200 .mu.l of ethyl acetate, shaken out and analyzed the organic phase by gas chromatography, using a quadrupole mass spectrometer with electron impact ionization (70 eV) as a detector (GC-MS coupling).
GC capillary column: HP-5MS (5% phenyl-methyl-siloxane; 30.0 m × 250 μm × 0.25 μm nominal)
Temperature program: 1 min 60 ° C, then to 280 ° C (15 ° C / min)
Gas flow: 1.0 ml / min helium
Injection: split 50: 1 retention times: I: 8.21 min (S) -II: 8.10 and 8.84 min (see below) (R) -III: 9:06 min (3R, 5S) -IV: 9:26 min

The Diketo compound I is detected as furanone, as is the hydroxyketoester (R) III (HCl elimination in the injector, see also formula scheme IV). The hydroxyketoester (S) -II is produced by partial thermal lactone formation in the GC injector two signals.

Based The chromatograms can be followed by the course of the microbial reduction become: In the first two samples can be growing proportions of the hydroxyketones (S) -II and (R) -III, while in the later stages taken samples the signal for the dihydroxy compound (3R, 5S) -IV gains in intensity. At the same time the signals for the hydroxyketones (S) -II and (R) -III lose intensity again, it can be assumed that the dihydroxy compound (3R, 5S) -IV by microbial reduction of the intermediately occurring hydroxyketones (S) -II and (R) -III is formed.

Work-up:

To 12.5 h, the reaction is stopped by centrifuging the cells. The cell pellets and the centrifugation supernatant are separated twice with ethyl acetate extracted. After drying the combined organic phases with Sodium sulfate and concentration on a rotary evaporator are 44 mg of crude product receive.

product analysis

a) Determination of shares the reaction products in the crude product

For a decay-free Gas chromatographic analysis (GC-MS, method s o.) Are in one 1.5 ml of GC glass vial 1.5 mg of the crude product of the microbial reduction taken up in 0.5 ml dichloromethane and with 10 ul trifluoroacetic anhydride (TFAA) and 10 μl Pyridine added. Subsequently the glass vial is sealed with a septum and stored at 40 ° C for 30 min (Water bath).

The subsequent GC-MS analysis gives four main signals, which are based on the associated Mass spectra of the derivatization products (3R, 5S) -V, (S) -VI, (S) -VII, and VIII can be assigned (formula scheme II).

Derivative (3R, 5S) -V is formed from the microbial reduction product (3R, 5S) -IV, while the hydroxyketone (S) -II reacts to the two stereoisomeric bisacylation products (S) -VI and (S) -VII. The cyclic derivative VIII is formed from the furanone IX, whose formation from the diketo compound I during the microbial reaction is known (by-product by intramolecular alkylation, see M. Wolberg, W. Hummel, M. Müller, DE 19857302 A , 1998). A derivative of the hydroxyketoester (R) -III can not be found in the crude product. This intermediately occurring compound is completely converted to the dihydroxy compound (3R, 5S) -IV in the reaction procedure chosen here (termination of the reaction after 12.5 h).

The integration of the four main sinals in the gas chromatogram yields the following relative intensities ((S) -VI and (S) -VII summarized, retention times in parentheses): (3R, 5S) -V: 34% (8.14 min) (S) -VI / (S) -VII: 61% (8.30 / 7.84 min) VIII: 5% (6.85 min)

at the reaction of microbial reduction described here receives one thus a crude product, mainly from the hydroxy ketone (S) -II exists. This result is confirmed by NMR spectroscopy (s. u.).

It is undoubtedly possible by variations of the reaction regime to influence the composition of the crude product.

The just described derivatization and GC-MS analysis was with the racemic hydroxyketoester rac-II and the diastereomeric mixture the dihydroxy compounds syn- / anti-IV, which by an independent synthesis were obtained (formula scheme III), checked.

The Retention times and mass spectra of these racemic samples are correct with the retention times and mass spectra of the products of the microbial Reduction match. The same applies to the respective TFA derivatives (formula scheme II).

The Furanone IX was also synthesized in an independent synthesis (Formula scheme IV).

Also Here, the retention times and mass spectra agree with the analog Signals in the spectra of the crude product of the microbial reduction match.

b) Determination of the Diastereomeric Ratio

The Diastereomers syn-IV and anti-IV are used with the gas chromatographic Method not separated. A baseline separation, however, can can be achieved after derivatization with TFAA / pyridine (formula scheme V).

The more polar isomer anti-V has a longer retention time compared to the syn isomer on. Both signals show identical mass spectra.

Applied to the crude product of the microbial reduction, this method gives a ratio of 135: 1 for the diastereomers syn-V and anti-V. The microbial reduction thus gives the syn isomer in very high excess. This result is confirmed by NMR spectroscopy (see below). For the TFA derivatives of the products of the almost unselective NaBH ₄ reduction (formula scheme III), the integration of the GC signals gives a ratio of 1.4: 1.0.

c) NMR spectroscopy

The NMR spectra of the crude microbial reduction product confirm the results of the GC-MS analyzes. The ¹ H NMR spectrum shows a superposition of the individual spectra of the compounds (S) -II, (3R, 5S) -IV- and IX, with the signals of the hydroxyketone (S) -II clearly dominating, while the signals of furanone IX are only weak to see.

Hydroxyketoester (S) -II:

¹ H-NMR (300 MHz, CDCl ₃ , 22 ° C, only the signals of the keto form are given) δ: 4.31 (m, 1H, CHOH), 3.6 (m, fine structure not detectable by overlay with multiplet of compound (3R , 5S) -IV, 2 × H6), 3.41 (s, 2H, H2), 2.90 (dd, J = 17.5, 5.0 Hz, 1H, H4), 2.83 (dd, J = 17.5, 7.3 Hz, 1H, H4 ), 1.46 (s, 3 × CH ₃ , overlay with analog signal of compounds (3R, 5S) -IV and IX). Keto: Enol = approx. 95: 5. ¹³ C-NMR (75.5 MHz, CDCl ₃ , only the signals of the ketoform are given) δ: 28.13 (OC (CH ₃ ) ₃ ), 46.57, 48.43, (C4, C6), 51.31 (C2), 67.58 (C5 ), 82.73 (OC (CH ₃ ) ₃ ), 166.22 (COOtBu), 202.93 (C3).

Dihydroxy compound (3R, 5S) -IV:

¹ H-NMR (300 MHz, _CDCl3, 22 ° C) δ: 4.22 (m, 1H, H5), 4:05 (m, 1H, H3), 3.6 (m, fine structure not recognized by superimposing a multiplet of compound (S ) -II; 2 x H6), 2:43 (d, J = 6.3 Hz, 2H, H2), 1.70 (m, 2H, H4), 1:46 (s, 3 x CH _3, superimposed on the analog signal of the compounds (S) -II and IX). ¹³ C-NMR (75.5 MHz, CDCl ₃₎ δ: 28.27 (OC (CH _{3) 3),} 39.45, 42.47 (C2, C4), 49.17 (C6), 68.35 (C3), 71.57 (C5), 81.90 (OC (CH ₃ ) ₃ ), 172.21 (COOtBu).

Furanone IX:

¹ H-NMR (300 MHz, _CDCl3, 22 ° C) δ: 5.69 (s, 1H, H3), 4:54 (s, 2H, H5), 3:48 (s 2H, H6.), 1:47 (s, 3 x CH ₃ , overlay with analog signal of compounds (S) -II and (3R, 5S) -IV).

The displacements given refer to CHCl ₃ in CDCl ₃ ( ¹ H NMR: δ = 7.27, ¹³ C NMR: δ = 77.23) and agree with the data for the independently synthesized comparative compounds rac-II, syn / anti-IV and IX (formula scheme III).

The signals of the dihydroxy compound anti-IV, which differ from those of the stereoisomeric compound syn-IV, can not be observed in the ¹³ C-NMR spectrum of the crude product of the microbial reduction. This is further proof of the very high proportion of the syn isomer (see above).

Dihydroxy anti-IV (from an independent synthesis, see Formelschem III): ¹³ C-NMR (75.5 MHz, CDCl ₃₎ δ: 28.27 (OC (CH _{3) 3),} 39.33, 42.22 (C2, C4), 49.60 (C6) , 65.46 (C3), 68.94 (C5), 81.87 (OC (CH _{3) 3),} 172.54 (COOtBu).

The assignment of the signal sets in the ¹³ C-NMR spectrum of the isomeric mixture syn- / anti-IV to the diastereomers is based on the characteristic chemical shift of the carbon atoms C-3 and C-5 (formula scheme VI).

• a) F. G. Kathawala et al., Helv. Chim. Acta 1986, 69, 803–805
• b) K.-M. Chen et al., Tetrahedron Lett. 1987, 28, 155–158
• c) C. Bonini et al., Gazz. Chem. Ital. 1991, 121, 75–80

In the present class of compounds (1,3-diols), the signals of the hydroxyl-bearing carbon atoms of the syn isomer relative to the analog signals of the anti-isomer usually have a downfield shift. Compare:

• a) FG Kathawala et al., Helv. Chim. Acta 1986, 69, 803-805
• b) K.-M. Chen et al., Tetrahedron Lett. 1987, 28, 155-158
• c) C. Bonini et al., Gazz. Chem. Ital. 1991, 121, 75-80

The ¹³ C NMR spectrum of the crude product thus shows that the syn isomer is formed in the microbial reduction described here.

d) Determination of absolute Configuration and enantiomeric purity

Since the stereochemistry of the C-3 stereocenter relative to the stereocenter C-5 has already been clarified by ¹³ C NMR spectroscopy, further analysis is confined to determining the configuration of the stereocenter C-5. For this purpose, the crude product of the microbial reduction is converted into the cyclic derivative (S) -X (formula scheme VII).

The racemic derivative rac-X (formula scheme VIII), which bears the same Method is obtained from the hydroxyketoester rac-II, can be by HPLC with chiral stationary Separate phase.

HPLC conditions: Chiracel OB (DAISO); 25 ° C; 1 ml / min i-hexane / i-propanol (80-20); Detection at 210 nm. Retention times: (S) -X: 24.7 min (R) -X: 21.5 min

The assignment of the absolute configuration of the separated enantiomers is made by comparison with the retention time of an authentic sample of the lactone (S) -X, which is prepared analogously to the racemic derivative rac-X from the hydroxyketone (S) -II (> 99% ee) ( Formula scheme VIII). The enantiomerically pure hydroxyketone (S) -II is obtained according to a known procedure (M. Wolberg, W. Hummel, M. Müller, DE 19857302 A , 1998).

By Integration of the signals of the derivative (S) -X, which consists of the crude product the microbial reduction was prepared (formula scheme VII), calculates an enantiomeric excess of 99.4%.

Claims (7)

Process for the reduction of hydroxyketocarboxylic acids or their esters with whole cells of Lactobacillus, with the keto group is converted to a hydroxy group. Process according to Claim 1, characterized in that compounds of the formula 1

where A = C =O, CHOΣ, B =C = O, CHOΣ, with A≠B and Σ =H or protecting group for the hydroxy function, R 1, R 2 = H or a component from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also monosubstituted or polysubstituted by the heteroatoms Si, N, P, O, S, F, Cl , Br or I can be substituted or completely replaced by heteroatoms. R3 = H, metal cations or a component from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also mono- or polysubstituted by the heteroatoms Si, N, P, O, S, F, Cl , Br or I can be substituted. Y = a component from the group consisting of alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, aralkyl, cycloalkylalkyl, where the components are also monosubstituted or polysubstituted by the heteroatoms Si, N, P, O, S, F, Cl, Br or I. may be substituted. Excluded is X-CH ₂ -O-CH ₂ -, where X = alkyl, aryl, cycloalkyl, aralkyl or cycloalkylalkyl may be. n = 0-10. Process according to Claim 1, characterized in that compounds of the formula 2

or their enantiomers are used, wherein R1, R2, R3 and Y have the same meaning as in formula 1. Σ = H or protective groups for the hydroxy functions. Process according to Claim 1, characterized in that compounds of the formula 3

or their enantiomers are used, wherein R1, R2, R3 and Y have the same meaning as in formula 1. Σ = H or protective groups for the hydroxy functions. Method according to one of Claims 1 to 4, characterized that Lactobacillus kefir or Lactobacillus brevis or a mixed culture of these microorganisms is used. Method according to one of claims 1 to 5, characterized that it is carried out at a pH of 2 to 10. Method according to one of claims 1 to 5, characterized that it at a pH of 4 to 8 is performed.