WO2011095990A2

WO2011095990A2 - Process for the purification of prostaglandins and analogues thereof

Info

Publication number: WO2011095990A2
Application number: PCT/IN2011/000076
Authority: WO
Inventors: Mohan Anand Chandavarkar; Ramakrishnan Ramachandran Iyer; Vikas Vasant Nawathye; Gajanan Jalindar Chavan; Sandeep Laxman Nawale
Original assignee: CHACHAD KALPESH CHINTAMANI; FDC Ltd
Current assignee: CHACHAD KALPESH CHINTAMANI; FDC Ltd
Priority date: 2010-02-03
Filing date: 2011-02-02
Publication date: 2011-08-11
Anticipated expiration: 2012-08-03
Also published as: WO2011095990A3

Abstract

The present invention discloses a process for purification of prostaglandins of formula (1) into enantiomerically pure isomer of formula (2) by reverse phase preparative HPLC, and converting said isomer into prostaglandin derivative of formula (3). The prostaglandin derivative in this invention relates to PGF_2α analogues

Description

"PROCESS FOR THE PURIFICATION OF PROSTAGLANDINS AND

ANALOGUES THEREOF"

Technical field:

The present invention relates to a process for purification of prostaglandins of formula 1 into enantiomerically pure isomer of formula 2 by reverse phase preparative HPLC, and converting said isomer into prostaglandin derivatives of formula 3. Prostaglandin derivatives in this invention relates to PGF_2a analogues.

formula 3

Wherein R_\ is selected from benzyl or phenoxy group substituted with alkyl, halo or haloalkyl, R₂ is selected from branched or linear chain alkoxy and alkylamino, preferably R₂ is selected from group consisting of Ci to C₆ alkoxy groups and C\ to C₆ alkylamino and represents either single or double bond.

Background and prior art:

Prostaglandin!^ (PGF_2a) is known to be a very potent vasoconstrictor and oxytoxic agent. A prostaglandin is a member of a group of lipid compounds which are derived enzymatically from fatty acids and have important functions in the animal body. Prostaglandin is characterized by the substituents on the cyclopentyl ring. They are mediators and have a variety of strong physiological effects, such as regulating the contraction and relaxation of smooth muscle tissue.

Prostaglandin analogues such as Latanoprost, Bimatoprost and Travoprost have been used in the management of open-angle glaucoma. They reduce intra-ocular pressure by enhancing uveoscleral outflow, and may also have some effect on the trabecular meshwork as well.

US 5422368 discloses preparation of prostaglandins and their analogues by oxidation of protected-Corey lactone, followed by Emmons condensation reaction, reduction, deprotection, DIBAL reduction, Wittig reaction and esterification. Further, prostaglandins were purified by column chromatography on silica gel-60 using ethyl acetate as eluant.

US 7498458 discloses process for the synthesis and purification of prostaglandins and analogues especially analogues of PGF_2a. The synthesis of prostaglandin analogues involves oxidation of protected-Corey lactone, followed by modified Homer- Wadsworth- Emmons reaction to yield the desired enone. Reduction followed by deprotection, and hydrogenation gives the corresponding diol which is protected as its silyl ether. Reduction of the lactone along with Wittig reaction, esterification and deprotection provided the desired Latanoprost This patent specifically discloses purification of Latanoprost by normal phase HPLC.

US 7166730 discloses process for the preparation of prostaglandins wherein it involves stereoselective reduction of the carbonyl group of a substituted Corey lactone followed by isolation. The undesired isomer formed during the reduction was oxidized back to the substituted Corey lactone. The desired isomer was further processed to form respective prostaglandin derivative, where the penultimate intermediate of prostaglandin derivative was purified by column chromatography on silica gel.

US 3962312 discloses purification of 9a-hydroxy-l l a, 15 a-ditetrahydropyranyloxy- prost-cis-5-enoic acid by column chromatography on silica gel.

US 6689901 discloses preparation of 15(S)-prostaglandin intermediates by contacting corresponding enone with (-)-chlorodiisopinocampheylborane at -50 to 0°C, followed by reacting with a boron complexing agent. The said intermediate is used to prepare Latanoprost that is purified by column chromatography on silica gel.

EP1891005 discloses process for preparation of prostaglandins especially Latanoprost, by anion generation from sulfone, followed by alkylation, reductive desulfonation, hydroxyl group deprotection, conversion and esterification. Latanoprost was purified by chromatography on LiChroprep column, followed by preparative HPLC.

None of the above prior art explains purification of penultimate intermediate of prostaglandin derivatives by reverse phase HPLC. Most of the prior art teaches purification of prostaglandin derivatives either by column chromatography or normal phase HPLC. During chromatographic purification, one of the eluants used is selected from hydrocarbons, which is costly and flammable and may not be applicable for industrial scale preparation.

Therefore, the present invention provides a process for purification of penultimate intermediate of prostaglandin derivative by reverse phase preparative HPLC that reduces the purification time by providing easy separation of impurities of the prostaglandins.

Object of the invention:

The primary objective of the present invention is to provide a process for purification of prostaglandins of formula 1 using reverse phase preparative HPLC. Another objective of the present invention is to provide a process for purification of prostaglandins of formula 1 using inexpensive and non-hazardous eluant system, which will not only make the purification process cost effective, but will also increase the efficiency of purification.

Yet another objective of the present invention is to provide easy and excellent separation of prostaglandins from undesired trans-impurity.

Summary of the invention:

In accordance with the above objectives, the present invention discloses a process for purification, of prostaglandins of formula 1 into enantiomerically pure isomer of formula 2 by reverse phase preparative HPLC, and converting said isomer into prostaglandin derivative of formula 3. The prostaglandin derivative in this invention relates to PGF_2a analogues.

formula 2

formula 3

Wherein, Ri is selected from benzyl or phenoxy group substituted with alkyl, halo or haloalkyl, R₂ is selected from branched or linear chain alkoxy and alkylamino, preferably R₂ is selected from a group consisting

to C₆ alkoxy groups and Ci to C₆ alkylamino and represents either single or double bond.

Detailed description of the invention:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

As used herein the term "RP-HPLC" refers to reverse phase HPLC, which is a well developed method for separating substances on the basis of hydrophobicity. In normal phase (NP-HPLC), the mobile phase is non-polar and the stationary phase is polar. In reverse-phase (RP-HPLC), polarities of the stationary and mobile phases are reversed, allowing only hydrophobic interactions with the analytes. Polar analytes elute first followed by non-polar. In RP-HPLC hydrophobic packings such as octadecyl- or octylsilane phases bonded to silica or neutral polymeric beads are used, and the mobile phase used is usually water and a water-miscible organic solvent.

In accordance with the above objectives, the present invention provides the process for purification of prostaglandins of formula 1 into enantiomerically pure isomer of formula 2 by RP-HPLC (reverse phase preparative HPLC), and converting the said isomers into prostaglandin derivative of formula 3.

Prostaglandin derivatives in this invention relate to PGF_2a analogues including Latanoprost, Travoprost and Bimatoprost. To illustrate the process of the invention, the detailed description is provided herein as depicted below in Scheme 1.

formula 1

formula 2 haloalkyl or

alkyl amine

formula 3

Scheme 1 wherein R_\ is selected from benzyl or phenoxy group substituted with alkyl, halo or haloalkyl; R₂ is selected from branched or linear chain alkoxy and alkylamino, preferably R₂ is selected from group consisting of Q to C₆ alkoxy groups and Q to C₆ alkylamino; and represents single or double bond.

Starting prostaglandin of formula 1 is riot only racemic at 15-position but also has 5-trans as a geometrical isomeric impurity present in it. This prostaglandin is produced by general processes known in the art.

The present invention discloses purification process^" of penultimate intermediate of prostaglandin derivatives using reverse phase HPLC in order to separate the undesired trans-impurity from the desired prostaglandin. The reverse phase HPLC is performed using a non-chiral preparative HPLC column and an eluant system. According to the invention, the non-chiral preparative HPLC column is selected from C4, C8 and CI 8 columns and the eluant system comprises a mixture of inexpensive and non- hazardous solvents out of which one solvent is water whose pH has been adjusted between 2.0-5.0 using trifluoro acetic acid. The water as used above is selected from plain water, 0.0 IM ammonium formate in water, 0.0 IM ammonium acetate in water or 0.01M D-tartaric acid in water, whose pH has been adjusted between 2.0-5.0 using trifluoro acetic acid.

Hereafter, 'water' is referred to as 'water whose pH has been adjusted between 2.0-5.0 using trifluoro acetic acid'. For the purpose of this invention, the water as used above is selected from plain water, 0.0 IM ammonium formate in water, 0.0 IM ammonium acetate in water or 0.0 IM D-tartaric acid in water.

In the preferred embodiment of the present invention, the eluant system comprises of water and at least one organic solvent selected from acetonitrile, alcohol and THF. The said alcohol is selected from a group consisting of methanol, ethanol, propan-l-ol, propan-2-ol, butan-l-ol, butan-2-ol, tert-butanol, 3-methyl-l-butanoI, 2-methyl-l- propanol, 2-methoxyethanoI and 2-ethoxyethanol.

The ratio of water in the mobile phase of the eluant system ranges from 30% to 80% and the ratio of other solvent (s) ranges from 18% to 70%.

The preferred eluant system with their volume percentage ranges are as follows:

Eluant system Volume % range

Water: acetonitrile : alcohol (s) 50% - 75% : 20% - 38% : 2% - 16%

Water : acetonitrile : THF 55% - 75% : 22% - 35% : 1% - 10%

Water : alcohol 30% - 80% : 20% - 70%

Water : acetonitrile 55% - 75% : 25% - 45%

Water : THF 55%-75% : 25%-45%,

Water : acetonitrile + THF 40% - 70% : 30%- 60%

Water : acetonitrile : THF: alcohol 65%-75% : 5%-15% : 10%-20% : 3%-10% By using the above purification process, it has been found that prostaglandin is substantially free of the undesired trans-isomer.

The term "substantially free" of the undesired trans-isomer refers to less than 1%, preferably less than 0.5%, more preferably less than 0.3% and even more preferably less than 0.2% of the trans-isomer impurity.

Thus, preferably the desired cis-isomer is greater than 98.5 %., and the trans-isomer impurity is less than 0.5 %.

The pure cis-isomer form of prostaglandin of formula 2 as obtained according to the process of present invention is converted into corresponding prostaglandin derivative of formula 3 by processes known in the prior art.

The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Examples

Purification of Latanoprost acid:

Example 1

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises of water (adjusted with trifluoro acetic acid to a pH of 3): acetonitrile : ethanol in the volume percent ratio of 65% : 30% : 5%.

The relative retention times of Latanoprost acid and trans-impurity of Latanoprost acid are observed as follows: Product Relative Retention Time Amount

Latanoprost acid 1.00 99.7 %

Trans-impurity 0.88 0.30 %

Example 2

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3) : acetonitrile : isopropanol in the volume percent ratios of 65%: 30%: 5%.

The relative retention times of Latanoprost acid and trans- impurity of Latanoprost acid are observed as follows:

Example 3

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3) : acetonitrile : tetrahydrofuran in the volume percent ratios of 65%: 30%: 5%.

Product Relative Retention Time Amount

Latanoprost acid 1.00 99.4 %

Trans-impurity 0.90 0.60 % Example 4

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3) : acetonitrile in the volume percent ratios of 65%: 35%

The relative retention times of Latanoprost acid and trans-impurity of Latanoprost acid are observed as follows:

Example 5

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3) : isopropanol in the volume percent ratios of 70%:30%

Example 6

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 2): acetonitrile : ethanol in the volume percent ratios of 65%: 30%: 5%.

Latanoprost acid 1.00 99.7 %

Trans-impurity 0.88 0.30 %

Example 7

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 5): acetonitrile : ethanol in the volume percent ratios of 65%: 30%: 5%.

Example 8

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3): acetonitrile : tetrahydrofuran : isopropanol in the volume percent ratios of 70%: 10%: 15%: 5%.

Product Relative Retention Time Amount

Latanoprost acid 1.00 99.6 %

Trans-impurity 0.89 0.40 % Example 9

HPLC separation of Latanoprost acid was carried out using a C-8 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3):acetonitrile : ethanol : isopropanol in the volume percent ratios of 60%: 30%: 5%: 5%.

Example 10

HPLC separation of Latanoprost acid was carried out using a C-4 column. The isocratic eluant system comprises water (adjusted with trifluoro acetic acid to a pH of 3): acetonitrile : ethanol in the volume percent ratios of 65%: 30%: 5%.

Example 11

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises 0.01M D-tartaric acid in water (adjusted with trifluoro acetic acid to a pH of 3) : methanol in the volume percent ratios of 40%: 60% The relative retention times of Latanoprost acid and trans-impurity of Latanoprost acid are observed as follows:

Example 12

HPLC separation of Latanoprost acid was carried out using a C-18 column. The isocratic eluant system comprises 0.01 M ammonium formate in water (adjusted with trifluoro acetic acid to a pH of 3) : acetonitrile : ethanol in the volume percent ratios of 65%: 30%: 5%

The relative retention times of Latanoprost acid and. trans-impurity of Latanoprost acid are observed as follows:

The pure Lantanoprost acid thus obtained is converted into Lantanoprost by conventional methods. Similarly, the other prostaglandins of formula I such as Travoprost acid and Bimatoprost acids are purified by adopting the reverse phase preparative HPLC by employing the non-chiral columns and eluent systems as exemplified above to obtain desired cis-isomers that are substantially free from its 'trans-isomer'. These acids are subsequently converted into Travoprost and Bimatoprost.

Claims

We claim,

1. A process for purification of prostaglandins of formula 1 into enantiomerically pure isomers of formula 2, by using reverse phase preparative HPLC using a non- chiral preparative HPLC column and an eluant system that comprises water and at least one organic solvent.

formula 1 formula 2 wherein Ri is selected from benzyl or phenoxy group substituted with alkyl, halo or haloalkyl, and represents a single or double bond .

2. The purification process of prostaglandins as claimed in claim 1, wherein the water in the eluant system is the water whose pH has been adjusted between 2.0- 5.0 using trifluoro acetic acid.

3. The purification process of prostaglandins as claimed in claim 2, wherein the water is selected from plain water, 0.01M ammonium formate in water, 0.01M ammonium acetate in water or 0.01M D-tartaric acid in water.

4. The purification process of prostaglandins as claimed in claim 1 wherein the water in the eluant system is present in an amount of 30 - 80 %.

5. The purification process of prostaglandins as claimed in claim 1, wherein the organic solvent in the eluant system is present in an amount of 18 - 70 %.

6. The purification process of prostaglandins as claimed in claim 1, wherein the organic solvent used in the eluant system is selected from acetonitrile, an alcohol or THF.

7. The purification process of prostaglandins as claimed in claim 6, wherein the alcohol is selected from methanol, ethanol, propan-l-ol, propan-2-ol, butan-l-ol, butan-2-ol, tert-butanol, 3-methyl-l-butanol, 2-methyl-l-propanol, 2- methoxyethanol or 2-ethoxyethanol.

8. The purification process of prostaglandins as claimed in claim 1, wherein the non-chiral preparative HPLC column is selected from C4, C8 or CI 8 column.

9. The purification process of prostaglandins as claimed in claim 1, wherein the purification process by reverse phase HPLC yields less than 0.5 % of undesired trans-isomer impurity, and greater than 98.5 % of desired enantiomerically pure cis isomers.

10. The purification process of prostaglandins as claimed in claim 1, wherein the enantiomerically pure isomers obtained from the purification process, are further converted into prostaglandin analogues such as Latanoprost, Travoprost and Bimatoprost.