SEPARATION OF CHIRAL ISOMERS BY SFC

Abstract

The present invention relates to the field of separating chiral isomers from each other. Particularly, it relates to the field of separating of chiral isomers of chromane or chromene compounds, particularly tocopherols, 3,4-dehydro-tocopherols and tocotrienols, as well as the protected forms thereof. It has been found that the use of supercritical carbon dioxide as mobile phase combined with the very specific chiral phase as stationary phase leads to a very efficient separation of the individual chiral isomers. As the method is very efficient and fast combined with advantageous in view of ecology it is of big industrial interest.

Claims

1. Process of separating chiral isomers of chromane or chromene compounds of formula (I-A) or (I-B) ##STR00010## wherein R.sup.1, R.sup.3 and R.sup.4 are independently from each other hydrogen or methyl groups; R.sup.2 represents hydrogen or a phenol protection group; R.sup.5 represents either a linear or branched completely saturated C.sub.6-25-alkyl group or a linear or branched C.sub.6-25-alkyl group comprising at least one carbon-carbon double bond; and wherein * represents a chiral center; comprising the steps of a) providing a mixture of isomers of formula (I-A) or (I-B) having different chiral configuration at the chiral centers represented by * in formula (I-A) or (I-B); b) chiral chromatographic separation of the mixture of isomers of step a) by means of supercritical fluid chromatography with supercritical carbon dioxide as a mobile phase and an amylose tris(3,5-dimethylphenylcarbamate) coated or immobilized on a silica support as a chiral stationary phase (CSP).

2. Process according to claim 1 wherein R.sup.1R.sup.3R.sup.4CH.sub.3.

3. Process according to claim 1, wherein R.sup.5 is of formula (III) ##STR00011## wherein m and p stand independently from each other for a value of 0 to 5 provided that the sum of m and p is 1 to 5, and where the substructures in formula (III) represented by s1 and s2 can be in any sequence; and the dotted line represents the bond by which the substituent of formula (III) is bound to the rest of formula (I-A) or (I-B); and wherein # represents a chiral center, obviously except in case where said center is linked to two methyl groups.

4. Process according to claim 1 wherein R.sup.5 is of formula (III-A), particularly (III-ARR), or (III-B) ##STR00012## wherein the dotted line represents the bond by which the substituent of formula (III-A) or (III-B) is bound to the rest of formula (I-A) or (I-B); and wherein # represents a chiral center.

5. Process according to claim 1, wherein the mobile phase comprises an alcohol particularly an alcohol being selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and 2-methyl-2-propanol.

6. Process according to claim 5 wherein the alcohol is used in a volume ratio of 1 to 30%, particularly of 1 to 25%, preferably of 5 to 20%, more preferably of 8 to 15%, relative to the supercritical carbon dioxide.

7. Process according to claim 1, wherein the chromatographic separation is done at a temperature in the range of between 31.3 C. and 80 C., preferably in the range of between 32 C. and 50 C., particularly between 35 C. and 45 C.

8. Process according to claim 1, wherein the chromatographic separation is done at a pressure in the range of between 73.9 to 200 bar, particularly between 74 to 150 bar, preferably between 75 and 100 bar, more preferably between 75 and 90 bar.

9. Process according to claim 1, wherein the chiral chromatographic separation of step b) yields a desired isomer (I.sub.des) and a residual (I) and further comprises the steps of c) isomerizing the chirality at the center in the ring indicated by * in formula (I-A) or (I-B) of the isomers of the residual (I) being separated in step b) yielding an isomerized product; e) collecting the desired isomer (I.sub.des).

10. Process according to step 9 wherein the process comprises a further step of d) introducing the isomerized product into the chromatographic separation of step b).

11. Process according to claim 1, wherein the mixture of chiral isomers of formula (I-B) is (all-rac)-tocopherol, particularly (all-rac)--tocopherol.

12. Process according to claim 1, wherein the mixture of chiral isomers of formula (I-B) is (2-ambo)-tocopherol, particularly (2-ambo)--tocopherol.

13. Process according to claim 1 wherein the chiral chromatographic separation uses Simulated Moving Bed (SMB) chromatography.

14. Use of supercritical fluid chromatography with supercritical carbon dioxide as a mobile phase and an amylose tris(3,5-dimethylphenylcarbamate) coated or immobilized on a silica support as a chiral stationary phase (CSP) for preparing a chromane or chromene which is selected from the group consisting of (2R, 4R, 8R)--tocopherol, (2R, 4R, 8R)--tocopherol, (2R, 4R, 8R)--tocopherol, (2R, 4R, 8R)--tocopherol; (2R, 4R, 8R)-3,4-dehydro--tocopherol, (2R, 4R, 8R)-3,4-dehydro--tocopherol, (2R, 4R, 8R)-3,4-dehydro--tocopherol, (2R, 4R, 8R)-3,4-dehydro--tocopherol, (2R)--tocotrienol, (2R)--tocotrienol, (2R)--tocotrienol and (2R)--tocotrienol; particularly selected from the group consisting of (2R, 4R, 8R)--tocopherol, (2R, 4R, 8R)-3,4-dehydro--tocopherol and (2R)--tocotrienol, in an isomeric purity of more than 95% by weight.

15. Process of manufacturing a food or a feed or a food supplement or a feed supplement or a pharmaceutical composition comprising the steps of i) preparing a compound of formula (I-A) or (I-B) having an isomeric purity of more than 95% by weight by a process according to claim 1; ##STR00013## wherein R.sup.1, R.sup.3 and R.sup.4 are independently from each other hydrogen or methyl groups; R.sup.2 represents hydrogen or a phenol protection group; R.sup.5 represents either a linear or branched completely saturated C.sub.6-25-alkyl group or a linear or branched C.sub.6-25-alkyl group comprising at least one carbon-carbon double bond; and wherein * represents a chiral center; ii) adding a compound of formula (I-A) or (I-B) of step i) to at least one food ingredient or at least one feed ingredient or at least one food supplement ingredient or at least one feed supplement ingredient or at least one ingredient for a pharmaceutical composition.

Description

FIGURES

[0200] FIGS. 1a) and 1) show a schematic representation of an equipment for chiral chromatographic separation and for supercritical fluid chromatography. FIG. 1b) shows the schematic representation of an embodiment preferred over the one depicted in FIG. 1a) where the equipment is rinsed with a solvent. FIG. 1c) shows schematically a process which comprises an isomerization step.

LIST OF REFERENCE SIGNS

[0201] 1 carbon dioxide cylinder [0202] 2 alcohol [0203] 3 chromatographic column [0204] 4 chiral stationary phase [0205] 5 SFC pump [0206] 6 mixture of isomers of formula (I-A)or (I-B) [0207] 7 heating device, SFC oven [0208] 8 eluate [0209] 9 detection means, diode array detector [0210] 10 computer [0211] 11 SFC equipment [0212] 11 modified SFC equipment [0213] 12 restrictor [0214] 13 supercritical carbon dioxide [0215] 14 gaseous carbon dioxide [0216] 15,15 separated isomers [0217] 16,16 vessels, first vessel, second vessel [0218] 17 valve [0219] 18 tube between restrictor 12 and valve 17 [0220] 19 residues [0221] 20 T-junction [0222] 21 Flushing/rinsing solvent [0223] 23 pump [0224] desired isomer (I.sub.des) [0225] 24 residual (I) [0226] 25 isomerized product

EXAMPLES

[0227] The present invention is further illustrated by the following experiments.

1. Chromatographic Separation

[0228] Starting Materials:

[0229] Solvents and reagents used as received were methanol (Merck Lichrosolv Reag Ph Eur, gradient grade for liquid chromatography, order no. 1.06007.2500), n-heptane (Merck Lichrosolv, for liquid chromatography, order no. 1.04390.1000), CO.sub.2 (Quality 4.8, Carbagas, Schweiz).

[0230] Chromatography:

[0231] The separations were performed on an Agilent Technologies 1260 Infinity Analytical SFC System comprising an Aurora SFC fusion A5 module, SFC binary pump (model G 4302A), Degasser, SFC autosampler, DAD (Diode Array Detector) (DAD SL, model G 1315C), Thermostatted Column Compartment and SFC Accessory Kit.

[0232] The DAD-detection range used and collected was 190-500 nm. Depending on the concentrations the signal at 210 nm, 290 nm, 295 nm has been used in the following.

[0233] The resulting chromatograms are shown in FIGS. 2 to 11. The x-axis of the chromatograms represents the retention time (t.sub.ret) in minutes. The y-axis of the chromatograms represents the absorbance (A) in arbitrary units (AU resp. mAU) by which the isomer distribution is detected.

[0234] Separation of (all-rac)--tocopherol

Example 1

[0235] A 50% by weight solution of (all-rac)--tocopherol (DSM Nutritional Products) in n-heptane was injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 150 bar back pressure; flow 3.0 ml/min; detection 295 nm, 5 l injection).

[0236] FIG. 2a) shows the obtained chromatogram of (all-rac)--tocopherol. From the 8 isomers of (all-rac)--tocopherol 3 isomers have been separated in a good baseline separation (3.57 min., 3.70 min. and 4.01 min). The peak with retention time at maximum of 3.70 min. could be identified as (2R, 4R, 8R)--tocopherol by a control experiment with a reference sample of (2R, 4R, 8R)--tocopherol with the same column and the same conditions. The chromatogram of this reference (2R, 4R, 8R)--tocopherol is shown in FIG. 2b).

[0237] Example 1 shows that the (all-rac)--tocopherol can be separated in less than 5 minutes by separation with supercritical fluid chromatography with supercritical carbon dioxide as a mobile phase and an amylose tris(3,5-dimethylphenyl-carbamate) coated or immobilized on a silica support as a chiral stationary phase (CSP). It further shows that the (2R, 4R, 8R)--tocopherol is a base-separated peak which can be easily isolated.

[0238] Separation of (all-rac)--tocopherol and 2-ambo--tocopherol by Two Columns in Sequence

Example 2

[0239] A solution of (all-rac)--tocopherol (DSM Nutritional Products) (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 210 nm, 5 l injection).

[0240] FIG. 3a) shows the obtained chromatogram of (all-rac)--tocopherol.

[0241] Furthermore, a solution of (2-ambo)--tocopherol (DSM Nutritional Products) (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 210 nm, 5 l injection).

[0242] FIG. 3b) shows the obtained chromatogram of 2-ambo--tocopherol.

[0243] From the 8 isomers of (all-rac)--tocopherol 4 isomers have been separated in a good baseline separation (t.sub.ret=9.56 min., 8.78 min., 8.52 min. and 8.17 min). Both isomers of 2-ambo--tocopherol have been separated in a good baseline separation (t.sub.ret=8.78 min. and 7.86 min.).

[0244] The peak with retention time at maximum of 8.78 min. of (all-rac)--tocopherol and 2-ambo--tocopherol could be identified as (2R, 4R, 8R)--tocopherol by a control experiment with a reference sample of (2R, 4R, 8R)--tocopherol with the same column and same conditions. The resulting chromatogram of this reference (2R, 4R, 8R)-tocopherol is shown in FIG. 3c).

[0245] The peak with retention time at maximum of 7.85 min. of 2-ambo--tocopherol could be, hence, identified as (2S, 4R, 8R)--tocopherol.

[0246] Compared to the experiment of example 1, the data of example 2 show that the coupling of 2 columns and use lower back pressure leads to an even better peak separation and the separation time is only extended to a minor extent, i.e. the whole chromatographic separation is achieved within a timeframe of less than 10 minutes.

Example 3

[0247] A solution of (all-rac)--tocopherol (DSM Nutritional Products) (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 35 C., 110 bar back pressure; flow 4.0 ml/min; detection 295 nm, 5 l injection).

[0248] FIG. 4a) shows the obtained chromatogram of (all-rac)--tocopherol. Furthermore, a solution of (2-ambo)--tocopherol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 35 C., 110 bar back pressure; flow 4.0 ml/min; detection 295 nm, 5 l injection).

[0249] FIG. 4b) shows the obtained chromatogram of (2-ambo)--tocopherol.

[0250] From the 8 isomers of (all-rac)--tocopherol 4 isomers have been separated in a good baseline separation (t.sub.ret=6.65 min., 6.05 min., 5.81 min. and 5.52 min). Both isomers of (2-ambo)--tocopherol have been separated in a good baseline separation (t.sub.ret=6.05 min. and 5.29 min.).

[0251] The peak with retention time at maximum of 6.05 min. of (all-rac)--tocopherol and (2-ambo)--tocopherol could be identified as (2R, 4R, 8R)--tocopherol by a control experiment with a reference sample of (2R, 4R, 8R)--tocopherol with the same column and same conditions. The chromatogram of this reference (2R, 4R, 8R)-tocopherol is shown in FIG. 4c).

[0252] The peak with retention time at maximum of 5.29 min. of (2-ambo)--tocopherol could be, hence, identified as (2S, 4R, 8R)--tocopherol.

[0253] Compared to the experiment of example 2, the data of example 3 show that despite the higher pressure used when lowering the temperature, a still excellent separation results at a very fast separation time of less than 7 minutes for the whole chromatographic separation.

[0254] Separation of (all-rac)--tocopherol and 2-ambo--tocopherol by Two Columns in Sequence

Example 4

[0255] A solution of (all-rac)--tocopherol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 210 nm, 15 l injection).

[0256] FIG. 5a) shows the obtained chromatogram of (all-rac)--tocopherol.

[0257] Furthermore, a solution of 2-ambo--tocopherol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 210 nm, 15 l injection).

[0258] FIG. 5b) shows the obtained chromatogram of (2-ambo)--tocopherol.

[0259] In case of (all-rac)--tocopherol 3 peaks have been separated in a good baseline separation (t.sub.ret=8.39 min., 8.85 min. and 9.36 min) (FIG. 5a).

[0260] Both isomers of (2-ambo)-tocopherol have been separated in a good baseline separation (t.sub.ret=8.86 min. and 9.36 min) (FIG. 5b).

[0261] The peak with retention time at maximum of 9.36 min. of (2-ambo)--tocopherol could be identified as (2R, 4R, 8R)--tocopherol by a control experiment with a reference sample of (2R, 4R, 8R)--tocopherol with the same column and same conditions. The chromatogram of this reference (2R, 4R, 8R)--tocopherol is shown in FIG. 5c).

[0262] The peak with retention time at maximum of 8.86 min. of (2-ambo)--tocopherol could be, hence, identified as (2S, 4R, 8R)--tocopherol.

[0263] Separation of (all-rac)-3,4-dehydro--tocopherol and (2-ambo)-3,4-dehydro--tocopherol by Two Columns in Sequence

Example 5

[0264] A solution of (all-rac)-3,4-dehydro--tocopherol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 295 nm, 15 l injection).

[0265] FIG. 6a) shows the obtained chromatogram of (all-rac)-3,4-dehydro--tocopherol.

[0266] Furthermore, a solution of (2-ambo)-3,4-dehydro--tocopherol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 295 nm, 15 l injection).

[0267] FIG. 6b) shows the obtained chromatogram of (2-ambo)-3,4-dehydro--tocopherol.

[0268] From the 8 isomers of (all-rac)-3,4-dehydro--tocopherol 3 isomers have been separated in a good baseline separation (t.sub.ret=6.60 min., 7.15 min. and 7.82 min). Furthermore, overlapping peaks leading to local maximums at t.sub.ret=6.81 min, 6.92 min. and 8.07 min. could been observed (FIG. 6a).

[0269] Both isomers of (2-ambo)-3,4-dehydro--tocopherol have been separated in a good baseline separation (t.sub.ret=6.60 min. and 7.82 min.)(FIG. 6b).

[0270] The peak with retention time at maximum of 7.82 min. of (all-rac)-3,4-dehydro--tocopherol and (2-ambo)-3,4-dehydro--tocopherol could be identified as (2R, 4R, 8R)-3,4-dehydro--tocopherol by a control experiment with a reference sample of (2R, 4R, 8R)-3,4-dehydro--tocopherol with the same column and same conditions.

[0271] The resulting chromatogram of this reference (2R, 4R, 8R)-3,4-dehydro--tocopherol is shown in FIG. 6c).

[0272] The peak with retention time at maximum of 6.60 min. of (2-ambo)-3,4-dehydro--tocopherol and (all-rac)-3,4-dehydro--tocopherol could be, hence, identified as (2S, 4R, 8R)-3,4-dehydro--tocopherol.

[0273] Separation of (rac)--tocotrienol by Two Columns in Sequence

Example 6

[0274] A solution of (rac)--tocotrienol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 295 nm, 15 l injection).

[0275] FIG. 7a) shows the obtained chromatogram of (rac)--tocotrienol.

[0276] The 2 isomers (=enantiomers) of-(rac)--tocotrienol could be observed as two slightly overlapping peaks (t.sub.ret=10.68 min. and 10.88 min.)(FIG. 7a).

[0277] The peak with retention time at maximum of 10.68 min. of (rac)--tocotrienol could be identified as (2R)--tocotrienol by a control experiment with a reference sample of (2R)--tocotrienol with the same column and same conditions.

[0278] The resulting chromatogram of this reference (2R)--tocotrienol is shown in FIG. 7b). The peak with retention time at maximum of 10.88 min. of 2-ambo--tocotrienol could be, hence, identified as (2S)--tocotrienol.

[0279] Separation of (rac)--tocotrienol by Two Columns in Sequence

Example 7

[0280] A solution of (rac)--tocotrienol (10 mg) in n-heptane (10 ml) was prepared, injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3.0 ml/min; detection 295 nm, 15 l injection).

[0281] FIG. 8a) shows the obtained chromatogram of (rac)--tocotrienol.

[0282] The 2 isomers of (rac)--tocotrienol could be separated in a good baseline separation (t.sub.ret=12.49 min. and 13.15 min.)(FIG. 8a).

[0283] The peak with retention time at maximum of 12.49 min. of (rac)--tocotrienol could be identified as (2R)--tocotrienol by a control experiment with a reference sample of (2R)--tocotrienol with the same column and same conditions.

[0284] The resulting chromatogram of this reference (2R)--tocotrienol is shown in FIG. 8b). The peak with retention time at maximum of 13.15 min. of (rac)--tocotrienol could be, hence, identified as (2S)--tocotrienol.

[0285] Separation of (2-ambo)--tocopherol in semi-preparative scale

Example 8

(No Rinsing/Flushing)

[0286] A 50% by weight solution of (2-ambo)--tocopherol in n-heptane was injected and separated on a chiral stationary phase (Daicel Chiralpak AD-3, 250 mm4.6 mm, 2 columns in sequence; eluent: supercritical CO.sub.2/10% by volume methanol, 40 C., 90 bar back pressure; flow 3 ml/min; detection 290nm, 5 l injection).

[0287] FIG. 9a) shows the chromatogram of (2-ambo)--tocopherol. As the amount of material separated is about a factor a factor 500 higher as in example 2, the peaks in the chromatogram are broader, however, are still separated.

[0288] The product leaving the outlet of the column was collected in a first glass vessel. At the detection of the local minimum at the retention time the valve at the outlet of the column was turned so that the substance eluted after the switch was collected in the second glass vessel.

[0289] The content of each glass vessel was dissolved in methanol to yield an analytical solution ready for injection. The solutions were injected again in the same manner as shown above (conditions of example 2, however, another column lot have been used which lead to the fact that the peaks elute a slightly earlier than in Example 2) with an injection of 5 l injection for analysis of identification and analysis of purity of the collected fractions.

[0290] The chromatogram of the first vessel is shown in FIG. 9b) and the chromatogram of the second vessel is shown in FIG. 9c)

[0291] These chromatograms show that the first glass vessel is pure (2S, 4R, 8R)--tocopherol (RRR-isomer is not detectable) whereas in the second glass vessel was (2R, 4R, 8R)--tocopherol and a small amount of (2S, 4R, 8R)--tocopherol. The isomeric purity of the (2R, 4R, 8R)--tocopherol was calculated from the area in the chromatogram (FIG. 9c) to be 89%.

Example 9

Rinsing/Flushing by N-Heptane

[0292] The example 9 was treated and measured identically to the example 8 except that between the detector and the restrictor a continuous flow (1 ml/min) of n-heptane was provided by means of a modular (stand-alone) HPLC pump according to the schematic diagram shown in FIG. 1b).

[0293] FIG. 10a) shows again the chromatogram during the high quantity separation.

[0294] FIG. 10b) shows the chromatogram of the sample from the first glass vessel. It could be identified to be pure (2S, 4R, 8R)--tocopherol (RRR is again not detectable).

[0295] FIG. 10c) shows the chromatogram of the sample from the second glass vessel. It shows that this sample is almost pure. Very pure (2R, 4R, 8R)--tocopherol with minor traces of fraction (2S, 4R, 8R)--tocopherol was collected. FIG. 10d) shows the chromatogram of FIG. 10c) in a representation where the y-axis is highly magnified. The isomeric purity of the (2R, 4R, 8R)--tocopherol was calculated from the area in the chromatogram (FIG. 10c, FIG. 10d) to be 99.7%.

Example 10

Rinsing/Flushing by Methanol

[0296] The example 10 was treated and measured identically to the example 9 except that methanol was used at flushing/rinsing solvent as well as solvent being part of the mobile phase, i.e. the alcohol being added to the carbon dioxide before entering the separation column. FIG. 11a) shows the chromatogram during the high quantity separation.

[0297] FIG. 11b) shows the chromatogram of the sample from the first glass vessel. It could be identified to be pure (2S, 4R, 8R)--tocopherol (RRR isomer is again not detectable).

[0298] FIG. 11c) shows the chromatogram of the sample from the second glass vessel. It shows that this sample is highly pure (2R, 4R, 8R)--tocopherol. No traces of (2S, 4R, 8R)--tocopherol could be detected as FIG. 11d) (being the chromatogram of FIG. 11c) in a representation where the y-axis is highly magnified) clearly shows.

[0299] Therefore, this example 4 shows that the disclosed process allows that, under optimal conditions, (2R, 4R, 8R)--tocopherol as well as (2S, 4R, 8R)--tocopherol can be obtained as absolutely isomerically pure (no other isomers detectable!) isomers from mixtures of said isomers.