This application claims priority to Indian patent applications numbered 1274/CHE/2011 filed on April 12, 2011 the contents which are incorporated by reference in their entity.

FIELD OF THE INVENTION

The present invention relates to a novel biocatalytic process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester of formula (II) and its further conversion into (S)-N-Ethy1-N-methy1-3-[1-(dimethylamino)ethyl]-pheny1-carbamate of formula (I) with enhanced yield.

BACKGROUND OF THE INVENTION
Rivastigmine, (S)-N-Ethy1-N-methy1-3-[ 1 -(dimethylamino)ethyl]-phenyl carbamate, marketed in the form of its tartarate salt, is a reversible cholinesterase inhibitor, prescribed for the treatment of mild to moderate Alzheimer's disease.

Rivastigmine in its tartarate form, i.e. (S)-N-Ethy1-N-methy1-3-[1-(dimethylamino)ethyl]-phenyl carbamate hydrogen-(2R,3R)-tartarate is marketed under the brand name of Exelon in the form of capsules and oral solution by Novartis. Exelon Capsules contain Rivastigmine tartarate, equivalent to 1.5, 3, 4.5 and 6 mg of Rivastigmine base for oral administration. Exelon Oral Solution is supplied as a solution containing
Rivastigmine tartarate, equivalent to 2 mg/mL of Rivastigmine base for oral administration.

Rivastigmine and its pharmaceutical activity are first disclosed in US 4,948,807, wherein racemic Rivastigmine is prepared by reacting a-m-hydroxyphenyl ethyldimethylamine with carbamoyl chloride in the presence of NaH.

In J. Org. Chem. 2009, 74, 5304-5310, Rivastigmine is also synthesized by reverse hydrolysis method using lipase from Candida antartica B as well as Ru-cat using vinyl acetate or isoprenyl acetate as acyl donar.
In US20060122417, Rivastigmine is also synthesized by reverse hydrolysis method using lipase from Candida antartica B using vinyl acetate as acyl donar.

The present invention relates to a novel biocatalytic process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester of formula (II), which is & useful intermediate for the preparation of Rivastigmine.

OBJECT OF THE INVENTION:

Principle object of the present invention is to provide a novel biocatalytic process for the preparation of (S) CrC4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester.

SUMMARY OF THE INVENTION:
Main aspect of the present invention is to provide a novel biocatalytic process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester and its further conversion into (S)-N-Ethy1-N-methy1-3-[ 1 -(dimethylamino)ethyl]-pheny1-carbamate.

In one aspect, the present invention provides a novel process for the preparation of (S) d-C4 carboxylic acid, 1 -(3-methoxy-phenyl)-ethyl ester comprising:

a) suspending racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester in a buffer or organic solvents or mixtures thereof;

b) treating above reaction mixture with an enzyme: and

c) isolating (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a novel biocatalytic process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester, which is an intermediate for the preparation of Rivastigmine and its further conversion into Rivastigmine.

The schematic representation of the present invention is given in the scheme-I.

In one aspect, the present invention provides a novel biocatalytic process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester comprising:

a) suspending racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester in a buffer or an organic solvent or mixtures thereof;

b) treating above reaction mixture with an enzyme: and

c) isolating (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester.

In one embodiment of the present invention, the racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester is suspened in a buffer or an organic solvent or mixtures thereof, wherein the buffer is selected from inorganic or organic weak acid and conjugate base; wherein the organic solvent is selected from polar protic solvents, polar aprotic solvents and non polar solvents.

In another embodiment of the present invention, the polar protic solvents are selected from isopropanol, methanol, ethanol, butnaol, formic acid, acetic acid; , polar aprotic solvents selected from dimethyl sulfoxide, dimethyl formamide, acetonitrile, acetone, tetrahydrofiiran, 1,4 dioxane; non polar solvents selcted from n-hexane, n-heptane, benzene, toluene, diethyl ether, chloroform, ethyl acetate and chloroform.

In one more embodiment of the present invention, the suspended C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester reaction mixture is treated with an enzyme, wherein the enzyme is selected from Lipase from Candida antartica B, Novozyme 435, Lipolase L, Amano lipase PS, Lipase from Candida antartica A, Protex 6L from Genencor, Lipase from Candida rugosa, Amano lipase AK, Amano lipase PS-D-1, Amano lipase IM and Lipase from hog pancreas to isolate (S) C1-C4 Carboxylic acid 1-(3-methoxy-phenyl)-ethyl ester.

In one more embodiment of the present invention, lipase or protease or esterase selected is not only confined to above mentioned enzymes but also from native or Immobilized or genetically modified organisms such as Candida rugosa, Candida antartica, Candida species, Bacilllus licheniformis, BasicUus subtilis, Psudomonas species, Saccharomyces species, Rhizopus sp., Rhizomucor sp., Aspergillus sp., Procine pancrease, Chromobacterium sp. Rhodococcus sp., Penicillium sp., Burkholderia cepacia, Thermomyces languinosa and hog pancreas.

In one embodiment of the present invention, R is ethyl, methyl, propyl, preferably methyl i.e (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester is (S) Acetic acid, 1-(3-methoxy-phenyl)-ethyl ester.

In one more embodiment of the present invention, Deacylation using lipase is not only confined to above mentioned ester but also to other acylated products like Isoprenyl acetic acid ester and Methoxyacetic acid ester and so on.

According to the present invention, racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester is suspened in a buffer selected from inorganic or organic weak acid and conjugate base or optionally in a mixture of buffer and an organic solvent, wherein the organic solvent is selected from polar protic solvents, polar aprotic solvents and non polar solvents. The polar protic solvents are selected from isopropanol, methanol, ethanol, butnaol, formic acid, acetic acid; , polar aprotic solvents selected from dimethyl sulfoxide, dimethyl formamide, acetonitrile, acetone, tetrahydrofuran, 1,4 dioxane; non polar solvents selcted from n-hexane, n-heptane, benzene, toluene, diethyl ether, chloroform, ethyl acetate and chloroform . The above suspened racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester reaction mixture was treated with an enzyme, wherein the enzyme is selected from Lipase from Candida antartica B, Novozyme 435, Lipolase L, Amano lipase PS, Lipase from Candida antartica A, Protex 6L from Genencor, Lipase from Candida rugosa, Amano lipase AK, Amano lipase PS-D-1, Amano lipase IM and Lipase from hog pancreas to isolate (S) Acetic acid 1-(3-methoxy-phenyl)-ethyl ester.

According to the present invention, the racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester is suspened in an organic solvent, wherein the organic solvent is selcted from polar aprotic solvents selected from dimethyl sulfoxide, dimethyl formamide, acetonitrile, acetone, tetrahydrofuran, 1,4 dioxane; preferably dimethyl sulfoxide and the obtained reaction mixture is treated with an enzyme selcted from Lipase from Candida antartica B, Novozyme 435, Lipolase L, Amano lipase PS, Lipase from Candida antartica A, Protex 6L from Genencor, Protex 6L, Lipase from Candida rugosa, Amano lipase AK, Amano lipase PS-D-1, Amano lipase IM and Lipase from hog pancreas to isolate (S) Acetic acid 1 -(3-methoxy-phenyl)-ethyl ester.

In another embodiment of the present invention, racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester is prepared comprising reduction and acylation of 1-(3-Methoxy-phenyl)-ethanone.
Yet another embodiment of the present invention, the (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester of formula (II) can be converted into Rivastigmine or pharmaceutically acceptable sahs thereof as per the process described in literature.

The following non-limiting examples illustrate specific embodiments of the present invention. The examples are not intended to be limiting the scope of present invention in any way.

Examples:
Example 1. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer. To the mixture was added Lipase from Candida antartica B and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 88 %ee, R- alcohol - 45%ee.

Example 2. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended buffer to the mixture was added Novozyme 435 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 85 %ee, R- alcohol - 83%ee.

Example 3. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Lipolase L and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 90 %ee, R- alcohol - 81% ee.

Example 4. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Amano lipase PS and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 100 %ee, S- alcohol - 25 % ee.

Example 5. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Lipase from Candida antartica A and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 90 %ee, S- alcohol - 50 % ee .

Example 6. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in 10% IPA in buffer. To the mixture was added 20% w/w of Lipase from Candida antartica B and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 98 %ee, R- alcohol - 81% ee.

Example 7. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Lipase from Candida antartica B and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 90 %ee, R- alcohol - 81% ee.

Example 8. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in DMSO in buffer to the mixture was added 20% w/w of Lipase from Candida antartica B and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC.

HPLC: S- ester - 94 %ee, R- alcohol - 89% ee.
Example 9. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Novozyme 435 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 99.99 %ee, R- alcohol - 84% ee.

Example 10. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Novozyme 435 and stirred at 30 °C for 24 hrs. Tlie reaction mixture was monitored by chiral HPLC. PffLC: S- ester - 95 %ee, R- alcohol - 97% ee.

Example 11. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in dimethyl sulfoxide in buffer to the mixture was added Novozyme 435 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 94 %ee, R- alcohol - 92 % ee.

Example 12. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended buffer to the mixture was added Protex 6L from Genencor and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 95 % ee, S- alcohol - 65 % ee

Example 13. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA to the mixture was added Protex 6L and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 50 %ee, S- alcohol - 50 % ee

Example 14. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Lipase from Candida rugosa and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 95 %ee, R- alcohol - 30 % ee

Example 15. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Lipase from Candida rugosa and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 50 %ee, R- alcohol - 35 % ee

Example 16. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Candida antartica lipase A (IMMCALA-T2-150) and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 95 %ee, R- alcohol - 22 % ee.

Example 17. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in DMSO in buffer to the mixture was added Candida antartica lipase B (IMMCALB-T2-150) and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 93 % ee.

Example 18. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Candida antartica lipase B (IMMCALB-T2-150) and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 96%ee, R- alcohol - 97 % ee.

Example 19. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Candida antartica lipase A (IMMCALA-T2-150) and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 95%ee, R- alcohol - 22 % ee.

Example 20. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Amano lipase PS and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 99.9 %ee, R- alcohol - 82 % ee.

Example 21. Racemic Acetic acid 1-(3-methoxy-plienyl)-ethyI ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Amano lipase PS and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 99.7 %ee, R- alcohol - 96 % ee.

Example 22. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in DMSO in buffer to the mixture was added Amano lipase PS and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 96 %ee, R- alcohol - 92 % ee.

Example 23. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Amano lipase AK and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 92 %ee, R- alcohol - 74 % ee.

Example 24. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added Amano lipase AK and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 82 % ee.

Example 25. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in DMSO in buffer to the mixture was added Amano lipase AK and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 96 % ee, R- alcohol - 93 % ee.

Example 26. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Amano lipase AK and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 97 % ee.

Example 27. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added 20% w/w of Amano lipase PS-D-1 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 90 %ee, R- alcohol - 79 % ee.

Example 28. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in IPA in buffer to the mixture was added 20% w/w of Amano lipase PS-D-1 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 83 % ee.

Example 29. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in n-hexane in buffer to the mixture was added Amano lipase PS-D-1 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 97 % ee.

Example 30. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Amano lipase IM and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 100 %ee, S- alcohol - 60 % ee

Example 31. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in buffer to the mixture was added Lipase from hog pancreas and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: R- ester - 100 %ee, R- alcohol - 90 % ee

Example 32. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyl ester (100 mg) was suspended in DMSO to the mixture was added Amano lipase PS-D-1 and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. HPLC: S- ester - 97 %ee, R- alcohol - 92 % ee.

Example 33. Racemic Acetic acid 1-(3-methoxy-phenyl)-ethyI ester (100 mg) was suspended in 10-30% of IPA/n-hexane to the mixture was Lipase from Candida antartica A and stirred at 30 °C for 24 hrs. The reaction mixture was monitored by chiral HPLC. No selectivity was observed. HPLC: S- ester - 100 %ee, R- alcohol - 50 % ee

We Claim:

1. A process for the preparation of (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-
ethyl ester comprising:

a) reacting racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester with an enzyme; and

b) isolating (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester.

2. The process according to the claim 1, wherein the reaction of racemic C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester with an enzyme is carried out in presence of buffer or an organic solvent or mixtures thereof

3. The process according to the claim 2, wherein the buffer is selected from inorganic or organic weak acid and conjugate base.

4. The process according to the claim 2, wherein the organic solvent is selected from polar protic solvents, polar aprotic solvents and non polar solvents.

5. The process according to the claim 2, wherein the enzyme is selected from Lipase.

6. The process according to the claim 5, wherein the Lipase enzyme is selected from Candida antartica B, Novozyme 435, Lipolase L, Amano lipase PS, Lipase from Candida antartica A, Protex 6L from Genencor, Lipase from Candida rugosa, Amano lipase AK, Amano lipase PS-D-1, Amano lipase IM and Lipase from hog pancreas.

7. The process according to the claim 1, wherein the (S) C1-C4 carboxylic acid, 1-(3-methoxy-phenyl)-ethyl ester is further converted into (S) Rivastigmine.

8. A process for the preparation of (S) Acetic acid 1-(3-methoxy-phenyl)-ethyl ester

a) reacting racemic acetic acid, 1-(3-methoxy-phenyl)-ethyl ester with an enzyme: and
b) isolating (S) Acetic acid, 1-(3-metlioxy-phenyl)-ethyl ester.

9. The process according to the claim 8, wherein (S) Acetic acid 1-(3-methoxy-phenyl)-ethyl ester is further converted into (S)-Rivastigmine.