DESC:FIELD OF THE INVENTION
The invention relates to a cost effective commercially viable chemical process for the preparation of the Z-isomer of Eicosapentaenoic acid of formula (1) with desired impurity profile, purity, and improved overall yield in mild conditions.

BACKGROUND OF THE INVENTION
Omega-3 unsaturated fatty acids (HUFAs) like EPA and docosahexaenoic acid (DHA), found in fish oil supplements up to 20-30%, have gained significant commercial interest as they have been found to be important dietary compounds for preventing arteriosclerosis and coronary heart disease, for alleviating inflammatory conditions and for retarding the growth of tumor cells.

The all cis-5,8,11,14,17-Eicosapentaenoic acid (EPA) is an omega-3 polyunsaturated fatty acid with 20 carbon atoms and 5 unconjugated double bonds in Z configuration. It exists in a multitude of organisms ranging from microscopic bacteria to humans and is present in the animal body in the form of an acyl chain of membrane phospholipids for altering the physicochemical properties of membranes such as elasticity, permeability, and fluidity. EPA exhibits its physiological action on the nervous system for signal transduction by getting converted to an anti-inflammatory lipid mediator in the body.

Eicosapentaenoic acid (1)

Icosapent ethyl, the ethyl ester of Eicosapentaenoic acid (EPA) was approved by USFDA under the trade name VASCEPA. The approved drug product is a lipid-regulating agent indicated as an adjunct to maximally tolerated statin therapy and as an adjunct to diet to reduce TG levels in adult patients with severe (= 500 mg/dL) hypertriglyceridemia.

Icosapent ethyl

Omega-3 unsaturated fatty acids although found in fish oil supplements, however, has significant problems for administration in human beings, as the oil also contains bio accumulated fat-soluble vitamins and high levels of saturated and omega-6 fatty acids, both of which have deleterious health effects. Eicosapentaenoic acid (EPA) and omega-3 fatty acids can also be obtained by fermentation process from microorganism but there are extremely few instances of synthetic EPA manufacturing for human consumption due to the several complexities in the synthetic manufacturing processes. Therefore, due to the scarcity of EPA, the formulations containing either synthetic EPA or DHA have exorbitant costs, which restricts its reach to the target population.

The presence of multiple Z-oriented double bonds in these natural products presents another synthetic challenge. The frequently utilized methods for preparing the (Z,Z)-1,4-diene systems present in polyunsaturated natural products, PUFAs and derivatives are based on any of the following methods:
(1) Cu(I)-catalyzed reaction of a propargyl halide and acetylide followed by stereoselective partial reduction,
(2) Z-selective Wittig, Ando or Still–Gennari reactions,
(3) alkyne metathesis followed by Z-stereoselective partial hydrogenation,
(4) Pd mediated (Suzuki and Migita–Kosugi–Stille) or (Sonogashira) reactions.

The Lindlar reduction is also employed sometimes during the total synthesis of PUFAs and polyunsaturated natural products. However, despite employing a wide variety of reducing agents and processes, problems with catalyst reproducibility, variable selectivity and over-reductions are invariably observed, especially for obtaining (Z,Z)-1,4-dienes.

Further, for achieving high Z-stereoselectivity, a strong base, low temperatures, avoiding lithium salts, dilute conditions, and in many cases the addition of a co-solvent like HMPA, was also tried. However, strong basic conditions invariably induce isomerization of the skipped Z-olefins into mixtures of conjugated E,E or E,Z-olefins. Pd-Catalyzed reactions have mostly been used for the synthesis of PUFAs that contain conjugated double bonds.

EP0460917B1 discloses a method for isolating eicosapentaenoic acid or an ester with a purity of at least 80%, by continuous distillation of a mixture of fatty acids and/or esters thereof obtained from natural fats and oils, with a fractionating column into a polar solvent containing urea for adduct formation, which is isolated by adding a non-polar solvent. The process leads to a lot of material loss due to polymerization of the higher boiling fractions, during distillation.

Journal of Organic Chemistry 1995, 60, 6627-6630 discloses a method for preparation of EPA and DHA from (Z)-l,l,6,6-Tetraisopropoxy-2-hexene, using Wittig reaction in multiple stages at -50 to -70°C with a reducing agent like LiAlH4 requiring absolute anhydrous conditions for obtaining Z isomer of Eicosapentaenoic acid. However, the reference is silent about the % of the Z isomer obtained.

Chemistry of Natural Compounds, 2015, 51 (6), 1038-1041 discloses preparation of Eicosatetraenoic Acid and Octadecatetraenoic acid via stereoselective reduction of triple bonds in polyacetylene precursors using Brown catalyst (P2-Ni) and sodium borohydride, which is then purified by column chromatography using diethyl ether and hexane. However, the document is silent about the % of the Z isomer and the yield of Eicosatetraenoic Acid and octadecatetraenoic acid.

Angew. Chem. Int. Ed. 2016, 55(40), 12300-12305, discloses the synthesis of bis(alkyne) derivatives from protected propargyl alcohol by coupling with different aliphatic bromides in the presence of n-butyl lithium (n-BuLi) and HMPA (hexamethylphosphoramide) at -78?. The process has commercial limitations due to the use of hazardous reagents like n-butyl lithium, very low temperature and stringent anhydrous conditions.

Journal of Chemical Society Perkin Trans., 2000, 1(3), 253–273, discloses a review of various synthetic approaches for the preparation of polyunsaturated fatty acids and its derivatives including (all-Z)-eicosa-5,8,11,14,17-pentaenoic acid (timnodonic acid), Eicosa-5,8,11,14-tetraynoic acid, Eicosa-8,11,14-trienoic acids. Various routes have been disclosed along with their yields, but the reference does not make even a remote mention about the problems or advantages associated with these routes and is also silent about the impurity profiles which would motivate any chemist to utilize these synthetic methods on a commercial scale.

Journal of Labelled Compounds and Radiopharmaceuticals, 1998, 41, 411-421, discloses the synthesis of methyl ester of Eicosapentaenoic acid by utilizing an aldehyde intermediate in presence of a moisture sensitive and hazardous reagent like n-butyl lithium (n-BuLi) and HMPA at a low temperature of -78?. The isomeric purity obtained is quite low ˜ 94%, necessitating elaborate purifications for improving isomeric purity. The use of a hazardous reagent like n-butyl lithium is a deterrence for employing the method on a commercial scale.

Journal of Organic Chemistry 1995, 60, 139-142 discloses synthesis of Ethyl Docosa-4,7,10,13,16,19 hexanoate wherein the desired geometric isomer purity is obtained by the formation of phosphonium salt of the geometric isomer mixture. It is pertinent to mention that this method utilizes an extremely hazardous reagent like Osmium tetroxide (OsO4), which affects the eyes and is avoided on a commercial scale. Also, the method involves periodate oxidation, which is normally avoided on a commercial scale.

Journal of Biotechnology, 1993, 30(2), 161-183 summarizes the preparations of Eicosapentaenoic acid (EPA) from various microorganisms. The pathway generally followed for such synthesis is chain elongation followed by unsaturation. EPA production using microorganisms is dependent qualitatively and quantitatively on the media composition, temperature, aeration, pH of the reaction medium. Since these parameters are quite sensitive, any minor change in these parameters affects the biosynthesis and the nature of the yield.

Tetrahedron Letters, 1992, 33(34), 4897-4900 describes the total stereospecific synthesis of all cis-5,8,11,14,17-Eicosapentaenoic Acid (EPA) starting from 2,5-dihydroanisole. The disclosed process utilizes academically relevant methods such as ozonolysis, and hazardous reagents such as lithium aluminium hydride and n-butyl lithium (n-BuLi) at -70?, which are not practical on a commercial scale.

Tetrahedron Letters, 2011, 52, 1057–1059 discloses synthesis of methyl (5Z,8Z,10E,12E,14Z) eicosapentaenoate in seven steps with 16% overall yield. Hydrolysis of the methyl ester leads to isomerization of the sensitive Z, E, E, Z – tetraene moiety along with partially polymerized material.

Tetrahedron Letters, 2012, 53, 5837–5839 discloses preparation of polyunsaturated fatty acids using hazardous reagents like n-butyl lithium. However, there is no mention about an alternate method with mild bases for preparing EPA.

Organic Biomolecular Chemistry 2018, 16, 9319-9333 discloses various synthetic routes involving Z-selective reduction methods for Eicosapentaenoic acid (EPA). The synthesis of (Z, Z)-1,4-dienes, is generally associated with problems of catalyst reproducibility, variable selectivity, and over-reductions. Further, to achieve a high Z-stereoselectivity, the use of a mild base, low temperature, avoiding lithium salts, dilute conditions and in many cases, the addition of a co-solvent like HMPA, are necessary. The strong basic conditions are likely to induce isomerization of the skipped Z-olefins into mixtures of conjugated E, E or E, Z-olefins.

The availability of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is currently limited since the availability is mainly from marine fisheries which are unable to meet the demands of the ever-expanding market.

The synthetic methods/processes currently used for commercial purposes either have low overall yields or have impurity profiles not matching pharmacoepial regulations/ specifications. The existing routes have been evaluated by the present inventors and it was found that although the routes are different, the presence of impurities having structural similarities to the intermediates, or the products made with rigorous purification make these procedures quite elaborate and costly. Also, reductions of internal alkynes were found to be quite challenging due to diminished Z-selectivity, poor catalyst reproducibility and over-reductions. All these factors led to the development of a new route, which was found to have an advantage over prior art methods, in terms of better yields, impurity profile, and less purification steps. The developed process avoided the use of hazardous reagents like n-butyl lithium and low temperatures of around -50 to -70°C temperatures, thereby leading to better economics for employing on a commercial scale.

OBJECT OF THE INVENTION
An objective of the present invention is to avoid hazardous reagents, strong bases, rigorous conditions (low temperatures ˜ -70°C), anhydrous conditions and repeated purifications of Eicosapentaenoic acid (1) and its intermediates.

Another objective of the present invention is to reduce the number of synthetic steps, utilize mild reagents, reaction conditions and avoid repeated purification for providing a robust, cost-effective process for preparation of Eicosapentaenoic acid of Formula (1) and intermediates thereof.

Eicosapentaenoic acid (1)

A further objective of the instant invention is to improve the Z isomer selectivity, the impurity profile and thereby the purity of Eicosapentaenoic acid of Formula (1) and intermediates thereof.

SUMMARY OF THE INVENTION
An aspect of the invention relates to a process for preparation of Eicosapentaenoic acid of Formula (1) comprising,
reaction of methyl-hex-5-ynoate of formula (2) with 3-bromo-1-(trimethylsilyl)-1-propyne of formula (3) in presence of a base, metal iodides, to provide methyl-9-(trimethylsilyl)nona-5,8-diynoate of formula (4) which on treatment with an acid, optionally without a phase transfer catalyst, provides methyl nona-5,8-diynoate of formula (5), further reaction with undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) in presence of a base and metal iodide, provides compound of formula (7), subsequent reduction with a hydrogenating agent in presence of hydrogen gas followed by hydrolysis yields (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoic acid of formula (1).

A further aspect of the present invention relates to a process for the preparation compound of Formula (6) comprising,
reaction of 1-bromo-2-pentyne of formula (6A) with propargyl alcohol in presence of a base, tetra alkyl ammonium halide, optionally with a phase transfer catalyst to provide octa-2,5-diyn-1-ol of formula (6B), which was then reacted with methanesulfonyl chloride in presence of an organic base, to give octa-2,5-diyn-1-yl methanesulfonate of formula (6C), further treatment with propargyl alcohol in presence of a base, a metal iodide, optionally with a phase transfer catalyst gave undeca-2,5,8-triyn-1-ol of formula (6D), which after further reaction with methanesulfonyl chloride in presence of organic base, provided undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6).

Yet another aspect of the present invention relates to a process for the preparation of compound of formula (7) by reaction of undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) with tetrahydropyran protected propargyl alcohol in presence of a base, tetraalkyl ammonium iodide in a aprotic solvent, with or without phase transfer catalyst to provide 2-(tetradeca-2,5,8,11-tetrayn-1-yloxy)tetrahydro-2H-pyran of formula (7A), which was then deprotected with an acid, to provide tetradeca-2,5,8,11-tetrayn-1-ol of formula (7B), further treatment with methanesulfonyl chloride in presence of organic base, provided tetradeca-2,5,8,11-tetrayn-1-yl methanesulfonate of formula (7C), subsequent reaction with Methyl-hex-5-ynoate of formula (2) in presence of a base and a metal iodide gave methyl icosa-5,8,11,14,17-pentaynoate of formula (7).

The objectives of the present invention will become more apparent from the detailed description.

DETAILED DESCRIPTION OF THE INVENTION
The invention is embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the disclosures satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms “a”, “an”, “the”, include plural referents unless the context clearly indicates otherwise.

Abbreviations used for the following terms:
Dimethylformamide: DMF / Tetrahydrofuran: THF / Grams: “gms” OR “g”.
Tetrahydropyran: THP

The term solvent used herein refers either to a single solvent or a mixture of solvents.

The present inventors, while working on the development of a commercially viable, cost-effective process for Eicosapentaenoic acid, have tried out various synthetic sequences disclosed in prior art. The inventors have resolved perennial problems associated with Z-selectivity, impurity profile, rigorous reaction conditions and the overall reaction yield. Purifications which reduced the overall yield have been avoided or significantly reduced to increase regulatory compliance and commercial viability.

After reviewing the impurity profiles of various synthetic sequences, the present inventors developed a synthetic route and process for preparation of Eicosapentaenoic acid (1) based on the reaction sequence disclosed in Scheme 1 Scheme 2 and Scheme 3. The reaction sequence disclosed in the latter scheme is related to the preparation of intermediate used in Scheme 1.

The major advantages of instant invention over the prior art processes are listed below.
1. Stereoselectivity of the process for providing only the Z-isomer instead of the undesired E-isomer (impurity).
2. The synthetic route avoided strong bases like n-BuLi, low temperatures ˜-70°C, and rigorous anhydrous conditions which drastically increased the cost and the time required for a single batch,
3. Reactions were facile, leading to low impurity formation and higher yield. Repeated purifications were not required. Therefore, improved yields were obtained, with overall yield around 35%, which was about 15-20% higher than prior art yields of around 15-20%.

Scheme-1: Method for preparation of Eicosapentaenoic acid (1)

Scheme-2: Method for preparation of compound of formula (6)

Scheme-3: Method for preparation of compound of formula (7)
In an embodiment, the present invention disclosed in Scheme 1, relates to a process for the preparation Eicosapentaenoic acid of Formula (1) which comprises:
reaction of methyl-hex-5-ynoate of formula (2) with 3-bromo-1-(trimethylsilyl)-1-propyne of formula (3) in presence of a base, metal iodides, to provide methyl-9-(trimethylsilyl)nona-5,8-diynoate of formula (4) which on treatment with an acid, optionally without a phase transfer catalyst, provides methyl nona-5,8-diynoate of formula (5), further reaction with Undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) in presence of a base and metal iodides, provides compound of formula (7), subsequent reduction with a hydrogenating agent in presence of hydrogen gas followed by hydrolysis of the resultant compound provides (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoic acid of formula (1).

In a related embodiment, the present invention as disclosed in Scheme 2, relates to a process for the preparation compound of Formula (6), a key intermediate of Eicosapentaenoic acid of Formula (1), which comprises,
reaction of 1-bromo-2-pentyne of formula (6A) with propargyl alcohol in presence of a base, tetra alkyl ammonium halide, optionally with a phase transfer catalyst to provide octa-2,5-diyn-1-ol of formula (6B), which was then reacted with methanesulfonyl chloride in presence of an organic base, to provide octa-2,5-diyn-1-yl methanesulfonate of formula (6C), further treatment with propargyl alcohol in presence of a base, a metal iodide, with or without phase transfer catalyst gave undeca-2,5,8-triyn-1-ol of formula (6D), which after further reaction with methanesulfonyl chloride in presence of organic base, provided undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6).

In a further embodiment, the scheme disclosed in Scheme 3, relates to an process for the preparation compound of Formula (7), a key intermediate of Eicosapentaenoic acid of Formula (1), starting from propargyl alcohol which comprises:
reaction of undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) with tetrahydropyran protected propargyl alcohol in presence of a base, tetraalkyl ammonium iodide in a aprotic solvent, with or without phase transfer catalyst to provide 2-(tetradeca-2,5,8,11-tetrayn-1-yloxy)tetrahydro-2H-pyran of formula (7A), which was then deprotected with an acid, to provide tetradeca-2,5,8,11-tetrayn-1-ol of formula (7B), further treatment with methanesulfonyl chloride in presence of organic base, to provide tetradeca-2,5,8,11-tetrayn-1-yl methanesulfonate of formula (7C), subsequent reaction with Methyl-hex-5-ynoate of formula (2) in presence of a base, metal iodides, gave methyl icosa-5,8,11,14,17-pentaynoate of formula (7).

In an embodiment of the present invention, the base is selected from sodium carbonate, potassium carbonate, cesium carbonate.

In another embodiment of the present invention, the metal iodide is selected from potassium iodide, sodium iodide, copper(I) iodide.

In another embodiment of the present invention, wherein the phase transfer catalyst is a tetraalkyl ammonium halide selected from the group comprising of tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), tetrabutylammonium chloride (TBACl), tetrabutylammonium fluoride (TBAF); methyl trialkyl ammonium halides such as methyltricaprylammonium chloride, methyltributylammonium chloride, methyl trioctylammonium chloride and tetra butyl ammonium hydrogensulphate (TBAHS), benzyltriethylammonium chloride, Aliquat 336 and potassium iodide (KI).

In another embodiment of the present invention, wherein the solvent used for the preparation of compound of formula (4), (5), (7) is an aprotic solvent selected from dimethyl formamide (DMF) and tetrahydrofuran (THF).

In another embodiment of the present invention, wherein the reduction of compound of formula (7) is carried out with a hydrogenating agent selected from Lindlar catalyst, palladium, nickel acetate + sodium borohydride + ethylene diamine and potassium borohydride.

In another embodiment of the present invention, wherein reduction of compound of formula (7) is carried out in a solvent selected from the group comprising of methanol, ethanol, and isopropanol.

In another embodiment of the present invention, the hydrolysis reaction is carried out with a base selected from lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH).

In another embodiment of the present invention, the solvent used for hydrolysis reaction is carried out in a solvent selected from methanol, ethanol, and isopropanol.

In another embodiment of the present invention, wherein the solvent used for deprotection of alcohol reaction is carried out in a solvent selected from methanol, ethanol and isopropanol and the acid is selected from para toluene sulfonic acid, camphor sulfonic acid, acetic acid, sulfuric acid, hydrochloric acid or hydrobromic acid.

In another embodiment of the present invention, wherein the solvent used for the preparation of compound of formula (6B), (6D), (7A), (7) is an aprotic solvent selected from the group of dimethylformamide (DMF), tetrahydrofuran (THF) while the solvent used for the preparation of compound of formula (6C), (6), is selected from dichloromethane and dichloroethane.

In another embodiment of the present invention, the organic base is selected from triethylamine and trimethylamine.

The following examples are meant to be illustrative of the present invention. These examples exemplify the invention and are not to be construed as limiting the scope of the invention.

EXAMPLES

Example 1: Preparation of octa-2,5-diyn-1-ol [Compound 6B]

Copper iodide (6.45 g) and tetrabutylammonium iodide (12.56 g) were added to a cooled and stirred solution of dimethylformamide (500 ml), propargyl alcohol (20.90 g) and potassium carbonate (70.36g), at 0oC in nitrogen atmosphere. 1-Bromo-2-pentyne (6A) (50 g) was added to the reaction mixture at 0oC, and stirring was continued at 25 to 30oC till completion of reaction, as monitored by TLC. The reaction mixture was quenched with water (1000ml) and methyl-tert-butyl ether (1000ml). The reaction mixture was then filtered, and the organic layer was separated and concentrated to obtain compound 6B.
Yield: 37.31gms (90%).
1H NMR: (400 MHz, CDCl3) ? 4.26 (s,2H), 3.19 (s,2H), 2.19-2.13 (m,2H), 1.11 (t, 3H)

Example 2: Preparation of Octa-2,5-diyn-1-yl methanesulfonate [Compound 6C]

Triethyl amine (46.20 g) was added to a solution of octa-2,5-diyn-1-ol (6B) (37.31 g) in dichloromethane (373ml) and the reaction mixture stirred at 0°C under nitrogen atmosphere. Methanesulfonyl chloride (34.86 gms) was added to the reaction mixture at same temperature and stirred till completion of reaction, as monitored by TLC. The reaction mixture was quenched with water (500ml) and extracted with dichloromethane (500ml). The organic layer was separated and concentrated to yield compound 6C, which was used in the next reaction without any further purification.
Yield: 61.19gms
1H NMR: (400 MHz, CDCl3) ? 4.85 (s, 2H), 3.20 (s, 2H), 3.13 (s, 3H), 2.19-2.13 (m, 2H), 1.12 (t, 3H).

Example 3: Preparation of undeca-2,5,8-triyn-1-ol [Compound 6D]

Propargyl alcohol (18.80 g) was added to a cooled solution of dimethylformamide (373 ml), cesium carbonate (109.03 g), copper iodide (58.08g), and sodium iodide (45.44g) at 0°C under nitrogen atmosphere. Octa-2,5-diyn-1-yl methanesulfonate (6C) (61.19 g) in DMF solution was then added to the reaction mixture at 0oC and stirred further at 25 to 30°C till completion of reaction as monitored by TLC. The reaction mixture was diluted with water (1000ml) and methyl-tert-butyl ether (1000ml) and filtered. The organic layer was separated and concentrated to obtain compound 6D.
Yield: 39.14 gms (80%).
1H NMR: (400 MHz, CDCl3) ? 4.25 (s, 2H), 3.20 (s, 2H), 3.13 (s, 2H), 2.20-2.13 (m, 2H), 1.11 (t, 3H)

Example 4: Preparation of undeca-2,5,8-triyn-1-yl methanesulfonate [Compound 6]

Undeca-2,5,8-triyn-1-ol (6D; 39.14 g) was dissolved in dichloromethane (391 ml) and triethyl amine (36.96 g) was added with stirring at 0°C under nitrogen atmosphere. Methane sulfonyl chloride (27.88 g) was added to the reaction mixture and stirred at same temperature till completion of reaction as monitored by TLC. After reaction completion, the mixture was diluted with water (500ml) and extracted with dichloromethane (500ml). The organic layer was concentrated to yield undeca-2,5,8-triyn-1-yl methanesulfonate (Compound 6) and used further without any purification.
Yield: 58.24gms
1H NMR (400 MHz, CDCl3) ? 4.84 (s,2H), 3.22 (s,2H), 3.13 (s,2H), 3.11 (s,3H), 2.17-2.14 (m,2H), 1.11 (t,3H)

Example 5: Preparation of 2-(tetradeca-2,5,8,11-tetrayn-1-yloxy)tetrahydro-2H-pyran [compound of formula (7A)]

THP protected propargyl alcohol (37.35gms) was added to dimethylformamide (391 ml) at 0°C, followed by gradual addition of cesium carbonate (87.23 gms), copper iodide (46.46 gms), sodium iodide (36.35 gms) and stirred further at 0°C for 30 minutes under nitrogen atmosphere. Undeca-2,5,8-triyn-1-yl methanesulfonate (6, 58.24 g) obtained from the previous step was dissolved in DMF (100ml) and added to the reaction mass at 0°C with stirring. The reaction was then stirred at 25 to 30°C till completion of reaction as monitored by TLC. After reaction completion, the mixture was quenched with water (1500ml) and methyl-tert-butyl ether (1500ml). The reaction mass was filtered, and the organic layer was concentrated to obtain compound 7A, which was used without further purification for the next reaction.
1H NMR (400 MHz, CDCl3) ? 4.82-4.78 (m,1H), 4.32-4.17 (m,2H), 3.85-3.80 (m,2H), 3.74-3.51 (m,2H), 3.19-3.12 (m,6H), 2.19-2.13 (m,2H),1.64-1.59 (m,4H), 1.11 (t,3H).
Yield: 41.45 gms (60%)

Example 6: Preparation of tetradeca-2,5,8,11-tetrayn-1-ol [compound of formula (7B)]

2-(Tetradeca-2,5,8,11-tetrayn-1-yloxy)tetrahydro-2H-pyran (7A, 41.45gms), obtained from Example 5 was added to methanol (500 ml) with stirring. p-Toluene sulfonic acid (PTSA) (500 mg) was added to the reaction mixture at 0°C till completion of reaction as monitored by TLC. The reaction mass was diluted with an aqueous solution of sodium bicarbonate (2000ml) and extracted with ethyl acetate (2000ml). The organic layer was concentrated to yield compound 7B and carried forward for the next reaction without purification.
Yield: 26.18gms (90%).
1H NMR (400 MHz, CDCl3) ? 4.26 (s,2H), 3.20 (s,2H), 3.15 (s,2H), 3.13 (s,2H), 2.19-2.14 (m,2H), 1.11 (t,3H)

Example 7: Preparation of tetradeca-2,5,8,11-tetrayn-1-yl methanesulfonate [compound of formula (7C)]

Tetradeca-2,5,8,11-tetrayn-1-ol (7B, 26.18 gms) was dissolved in dichloromethane (261 ml) and triethylamine (19.99 gms) was added to the mixture at 0°C under nitrogen atmosphere. Methane sulfonyl chloride (15.04 g) was then added to the reaction mass at same temperature and the reaction mixture stirred till completion of reaction as monitored by TLC. The reaction mass was quenched with water (500ml) and extracted with dichloromethane (500ml). The organic layer was separated and concentrated to yield compound 7C and carried forward for the next reaction without any further purification.
Yield: 36.49gms
1H NMR (400 MHz, CDCl3) ? 4.85 (s, 2H), 3.13 (s, 6H), 2.96 (s, 3H), 2.19-2.11 (m, 2H), 1.13 (t, 3H)

Example 8: Preparation of methyl icosa-5,8,11,14,17-pentaynoate [compound of formula (7) (Scheme 3)]

Methyl-hex-5-ynoate (2, 16.64 g) was dissolved in dimethylformamide (261 ml) and cooled to 0°C. Cesium carbonate (47.19 g), copper Iodide (25.13 g), sodium iodide (19.66 g) and were gradually at 0°C and stirred under nitrogen atmosphere. Tetradeca-2,5,8,11-tetrayn-1-yl methanesulfonate (7C, 36.49 g) obtained from Example 7, was dissolved in dimethylformamide (150ml) and added to the reaction mass at 0oC and stirred at 25 to 30°C till completion of reaction as monitored by TLC. The reaction mixture was diluted with water (1500ml) and ethyl acetate (1500ml) and filtered. The organic layer was separated and concentrated to obtain crude compound 7. Crude compound was then purified by column chromatography using neutral alumina and eluted with 4% ethyl acetate in n-hexane to obtain compound 7.
Yield: 38.01gms (90%).
1H NMR (400 MHz, CDCl3) ? 3.67 (s,3H), 3.21 (s,8H), 2.42 (t,2H), 2.23 (t,2H), 2.17-2.13 (m,2H), 1.84-1.77 (m,2H), 1.11 (t,3H)

Example 9: Preparation of Methyl-hex-5-ynoate [compound of formula (2)]

Sulfuric acid (0.5 ml) was added dropwise to a solution of 5-hexynoic acid (3.33 g) in methanol (33 ml) at 0°C and stirred at same temperature for 30 minutes under nitrogen atmosphere. The temperature was raised to 25 to 30°C and stirred till completion of reaction as monitored by TLC. An aqueous solution of sodium bicarbonate (250 ml) was added to the reaction mixture and extracted with methyl tert-butyl ether (250 ml). The organic layer was separated and concentrated to yield compound 2 and used for the next reaction without any further purification.
Yield: 3.38gms (90%).
1H NMR (400 MHz, CDCl3) ? 3.67 (s, 3H), 2.45 (t, 2H), 2.26 (t, 2H), 1.97 (s, 1H), 1.88-1.81 (m, 2H)

Example 10: Preparation of Methyl-9-(trimethylsilyl)nona-5,8-diynoate [compound of formula (4)]

3-Bromo-1-(trimethylsilyl)-1-propyne (3) (4.96 g) dissolved in dimethylformamide (10ml) was added to a cooled mixture of Methyl-hex-5-ynoate (2) (3.38 g) in dimethylformamide (33.8 ml) stirred with cesium carbonate (9.29 g), copper iodide (5.33 g), and sodium iodide (4.17g) at 0°C and stirred for 30 minutes under nitrogen atmosphere. The temperature was raised to 25 to 30°C and stirred till completion of reaction as monitored by TLC. The reaction mixture was diluted with water (500 ml) and methyl tert-butyl ether (500 ml). The reaction mixture was then filtered, the organic layer was separated and concentrated to obtain compound 4.
Yield: 4.03gms (60%)
1H NMR (400 MHz, CDCl3) ? 3.67 (s,3H), 3.17 (s,2H), 2.43 (s,2H), 2.23 (t,2H), 1.83-1.79 (m,2H), 0.15 (s,9H)

Example 11: Preparation of methyl nona-5,8-diynoate [compound of formula (5)]

Methyl-9-(trimethylsilyl)nona-5,8-diynoate (4; 4.03g) dissolved in tetrahydrofuran (THF) was added to a mixture of tetra-N-butylammonium fluoride (5.87 g; 1M solution). Acetic acid (0.76 g) dissolved in THF (20ml) was then added at 0°C and stirred till completion of reaction as monitored by TLC. The reaction mixture was concentrated to provide crude compound 5. Crude compound was then purified by column chromatography with silica gel and eluted with 10% ethyl acetate in n-hexane to obtain compound 5.
Yield: 1.57gms (60%).
1H NMR (400 MHz, CDCl3) ? 3.67 (s,3H), 3.14 (s,2H), 2.43 (s,2H), 2.24 (t,2H), 2.05 (s,1H),1.80 (q,2H)

Example 12: Preparation of Methyl icosa-5,8,11,14,17-pentaynoate [compound of formula (7) (Scheme 1)]

Undeca-2,5,8-triyn-1-yl methanesulfonate (6) (2.26 g) was added to a cooled solution of dimethylformamide (15.7 ml) stirred with cesium carbonate (3.39 g), copper iodide (1.98 g) and sodium iodide (1.54 g) at 0°C under nitrogen atmosphere. Methyl nona-5,8-diynoate (5) (1.57 g) in DMF solution, was added to the reaction mixture at same temperature and stirred further 25 to 30°C till completion of reaction as monitored by TLC. The reaction mixture was diluted with water (250 ml) and methyl tert-butyl ether (250 ml) and filtered. The organic layer was separated and concentrated to obtain crude compound 7. The crude compound was then purified by column chromatography on neutral alumina and eluted with 4% ethyl acetate in n-hexane to obtain compound 7.
Yield: 2.45gms (80%).
1H NMR (400 MHz, CDCl3) ? 3.67 (s, 3H), 3.21 (s, 8H), 2.42 (t, 2H), 2.23 (t, 2H), 2.17-2.13 (m, 2H), 1.84-1.77 (m, 2H), 1.11 (t, 3H).

Example 13: Preparation of (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoic acid [compound of formula (1), EPA]

Methyl icosa-5,8,11,14,17-pentaynoate (7) (2.45 g) dissolved in a mixture of tetrahydrofuran (24.5 ml) and ethanol (24.5 ml) solution was added to a mixture of nickel acetate (1.20 g), sodium borohydride (0.398 g) and ethylene diamine (3.28 g) in ethanol (30ml) with stirring at 25oC to 30oC under nitrogen atmosphere. Hydrogen gas was bubbled into the mixture at same temperature till completion of reaction as monitored by TLC. The reaction mixture was diluted with ethyl acetate (200 ml) and filtered, and the filtrate concentrated to obtain a residue, which was then diluted with THF (5 ml) and stirred with a solution of lithium hydroxide (0.14 g) in water (5 ml) at 25°C to 30°C till complete hydrolysis based on TLC monitoring. After completion of reaction, the reaction mixture was acidified with 0.1N HCl and extracted with ethyl acetate (100 ml). The organic layer was concentrated to yield compound 1.
Yield: 1.45 g (80%)
Purity: 98.97% (HPLC)
1H NMR (400 MHz, CDCl3) ? 5.36 (t, 10H), 2.82 (t, 8H), 2.38 (t, 2H), 2.15-2.04 (m, 2H), (m, 2H), 1.74-1.67 (m,2H), 0.98 (t, 3H)

Example 14: Preparation of methyl nona-5,8-diynoate [compound of formula (5)]

Methyl-9-(trimethylsilyl)nona-5,8-diynoate (4; 5g) dissolved in a solution of 35 ml dichloromethane (MDC), 20 ml methanol and 5 ml water. The resulting reaction mixture was stirred for 10 minutes. Silver nitrate (0.350 gms) was added, and the reaction mixture stirred at room temperature for 4 hours. Progress of the reaction mixture was confirmed by TLC. The reaction mixture was quenched with 50 ml water, the organic layer separated, dried over sodium sulphate, and concentrated under vacuum to obtain compound (5).
Yield: 3.36 g; (97% yield).
1H NMR (400 MHz, CDCl3) d 3.67 (s,3H), 3.14 (s,2H), 2.43 (s,2H), 2.24 (t,2H), 2.05 (s,1H),1.80 (q,2H).
,CLAIMS:Claims:

We claim,
1) A process for preparation of Eicosapentaenoic acid of Formula (1) comprising, reaction of methyl-hex-5-ynoate of formula (2) with 3-bromo-1-(trimethylsilyl)-1-propyne of formula (3) in presence of a base, metal iodides, to provide methyl-9-(trimethylsilyl)nona-5,8-diynoate of formula (4) which on treatment with an acid or its salt, optionally without a phase transfer catalyst, provides methyl nona-5,8-diynoate of formula (5), further reaction with undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) in presence of a base and metal iodide, provides compound of formula (7), subsequent reduction with a hydrogenating agent in presence of hydrogen gas followed by hydrolysis yields (5Z,8Z,11Z,14Z,17Z)-icosa-5,8,11,14,17-pentaenoic acid of formula (1).

2) A process as claimed in claim 1, wherein the compound of Formula (6) is prepared by a process comprising reaction of 1-bromo-2-pentyne of formula (6A) with propargyl alcohol in presence of a base, tetraalkyl ammonium halide, optionally with a phase transfer catalyst to provide octa-2,5-diyn-1-ol of formula (6B), which was then reacted with methanesulfonyl chloride in presence of an organic base, to give octa-2,5-diyn-1-yl methanesulfonate of formula (6C), further treatment with propargyl alcohol in presence of a base, a metal iodide, optionally with a phase transfer catalyst gave undeca-2,5,8-triyn-1-ol of formula (6D), which after further reaction with methanesulfonyl chloride in presence of organic base, provided undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6).

3) A process as claimed in claim 1, wherein the compound of Formula (7) is prepared by a process comprising reaction of undeca-2,5,8-triyn-1-yl methanesulfonate of formula (6) with tetrahydropyran protected propargyl alcohol in presence of a base, tetraalkyl ammonium iodide in a aprotic solvent, with or without phase transfer catalyst to provide 2-(tetradeca-2,5,8,11-tetrayn-1-yloxy)tetrahydro-2H-pyran of formula (7A), which was then deprotected with an acid, to provide tetradeca-2,5,8,11-tetrayn-1-ol of formula (7B), further treatment with methanesulfonyl chloride in presence of organic base, provided tetradeca-2,5,8,11-tetrayn-1-yl methanesulfonate of formula (7C), subsequent reaction with methylhex-5-ynoate of formula (2) in presence of a base and a metal iodide gave methyl icosa-5,8,11,14,17-pentaynoate of formula (7).

4) A process as claimed in claim 1, wherein the metal iodide is selected from the group comprising of potassium iodide, sodium iodide, copper(I) iodide.

5) A process as claimed in claim 1 and 2, wherein the phase transfer catalyst is a tetraalkyl ammonium halide selected from the group comprising of tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI), tetrabutylammonium chloride (TBACl), tetrabutylammonium fluoride (TBAF); methyl trialkyl ammonium halides such as methyltricaprylammonium chloride, methyltributylammonium chloride, methyl trioctylammonium chloride and tetra butyl ammonium hydrogensulphate (TBAHS), benzyl triethylammonium chloride, Aliquot 336 and potassium iodide (KI).

6) A process as claimed in claim 1, wherein the solvent used for the preparation of compound of formula (4), (5), (7) is an aprotic solvent selected from dimethyl formamide (DMF) and tetrahydrofuran (THF).

7) A process as claimed in claim 1 and 3, wherein the hydrogenating agent is selected from the group of Lindlar catalyst, palladium, nickel acetate + sodium borohydride + ethylene diamine and potassium borohydride.

8) A process as claimed in claim 1, wherein the compound of formula 4 is treated with silver nitrate in a solvent mixture of dichloromethane, methanol and water at room temperature for 4 hours and after quenching with water followed by concentration of the organic layer gave compound of formula 5.