FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of Micafungin sodium of a Structural Compound of Formula (I).
BACKGROUND OF THE INVENTION
Micafungin sodium is chemically known as Pneumocandin AO, 1-[(4R,5R)-4,5-dihydroxy-N2-[4-[5-[4-(pentyloxy)phenyl]-3-isoxazolyl]benzoyl]-Lornithine]-4-[(4S)-4-hydroxy-4-[4-hydroxy-3-(sulfooxy)phenyl]-L-threonine]-, monosodium salt. Micafungin sodium is a light-sensitive, hygroscopic white powder that is freely soluble in water, isotonic sodium chloride solution, N,N-dimethylformamide and dimethylsulfoxide, slightly soluble in methyl alcohol, and practically insoluble in acetonitrile, ethyl alcohol (95%), acetone, diethyl ether and n-hexane. Micafungin sodium is a semisynthetic lipopeptide (echinocandin) synthesized by a chemical modification of a fermentation product of Coleophoma empetri F-11899. Micafungin inhibits the synthesis of 1, 3-beta-D-glucan, an integral component of the fungal cell wall. Micafungin sodium is marketed under the brand name MYCAMINE®. Micafungin sodium is an echinocandin indicated in adult and pediatric

patients 4 months and older for the Treatment of Patients with Candidemia, Acute Disseminated Candidiasis, Candida Peritonitis and Abscesses.
Micafungin sodium (1) was disclosed first time in LIS 6107458. This patent reported a process of Micafungin sodium from a natural product of FR-901379 (Compound of Formula III) isolated from the fungus Coleophoma empetri F-l 1899. By removing the N-acyl group side chain of precursor FR-901379 through an enzymatic deacylation to obtain a Compound of Formula II (FR-179642). The Compound of Formula II is further reacted with 4-[5-(4-Pentyloxyphenyl)isoxazolyl-3-yl]benzoic acid (Compound of Formula IV) or its reactive derivative to obtain Micafungin.

The above disclosed process for obtaining 4-[5-(4-pentyloxyphenyl)isoxazot-
3-yl]benzoic acid as a starting compound for a lipopeptide antifungal agent and a
process for preparing an excellent antifungal agent from the said starting compound.
However, 5-(4-pentyloxyphenyl)-3-[4-[5-(4-pentyloxyphenyl)isoxazol-3-
yl]pheny]]isoxazole was produced as a by-product in an initial step. It was difficult to isolate the 4-[5-(4-pentyloxyphenyl)isoxazol-3-yl]benzoic acid (IV) from the by-product. For this reason, the process was not preferable as a process for preparing the starting compound for a pharmaceutical product required having particularly high purity.
And also the above reported method for obtaining the sodium salt by using cation exchange resin. It is difficult to control the pH value of the product using said method. In addition, this method only applies to small-scale preparation. It is not suitable for large scale of production and quality of products thereof is unmanageable.
US 7,199,248 also discloses variant process for the preparation of Micafungin
sodium (I). The process involves condensing FR-179642 (II) with l-[4-[5-(4-
Pentyloxyphenyl)isoxazol-3-yl]benzoyl]benzotriazole-3-oxide (HOBT-Isoxazole
adduct) of a Compound of Formula V in the presence of DIPEA (N,N-Diisopropylethylamine) and N,N-Dimethylformamide (DMF) to obtain Micafungin DIPEA salt. Later conversion of Micafungin DIPEA salt to Micafungin sodium using aqueous sodium hydroxide. The process as shown in Scheme-II below:

US '248 discloses a process wherein a crude DIPEA salt of Micafungin is purified by filtration and chromatographic separation using a regenerated y Alumina in a 1350-L column and eluting Micafungin DIPEA with methanol. The Micafungin containing fraction is further purified using ion exchange resin UBK510L. Sodium salt of micafungin was prepared by treatment of aqueous sodium hydroxide followed by precipitation using acetone and ethyl acetate mixture. Inventors found that, the above reported methods for obtaining the sodium salt by using aqueous sodium hydroxide which is a strong base. It is difficult to control the pH value of the product using said method. This method using 0.1 mol/L NaOH solution to adjust pH value to 6-8. The Inventors have performed multiple experiments using methods reported in the literature anqUia^eTjij$c.orv.ere^^

leads to a significant rise in the content of impurity from Micafungin degradation, thereby considerably increasing the difficulty in the subsequent separation and purification and it is difficult to prepare Micafungin sodium of high purity. Hence, the method cannot suitable for commercial manufacturing.
The process use mixture of aqueous and organic solvents resulting in joss of polar micafungin sodium. Another disadvantage of the process' is use of two successive column chromatography is required for purification.
International PCT Publication WO 2013/034670 also discloses process for the preparation of Micafungin sodium (I). The process involves condensing FR-179642 (II) with 4-[5-(4-Pentyloxyphenyl)isoxazolyl-3-yl]benzoic acid of a Compound of Formula IV in the presence of TEA (Triethylamine), pivalic acid chloride and DMF to obtain Micafungin TEA salt. Conversion of Micafungin TEA salt to Micafungin sodium using ion exchange resin (CG 120 I; counter ion sodium).

The process require ion exchange column to prepare sodium salt using a mixture of organic and aqueous eluent. Yield of the process is low.
US 8,981,055 reported a one-pot process for the manufacturing of Micafungin or a salt thereof, wherein activated derivative of Isoxazole carboxylic acid compound of Formula IV is in situ condensed with FR 179642.
US 9,115.177 reported a method for the preparation of Micafungin sodium. wherein said method comprises: mixing a weak base solution with a water solution containing Micafungin or a mixture solution of water and organic solvent(s) containing Micafungin to obtain Micafungin sodium, wherein said weak base is selected from the group consisting of disodium hydrogen citrate, sodium citrate, sodium acetate, sodium propionate, sodium butyrate, sodium isobutyrate, sodium tartrate, sodium oxalate, sodium benzoate, sodium sorbate, sodium malate, monosodium succinate, disodium succinate, sodium bicarbonate, sodium carbonate, disodium hydrogen phosphate, sodium borate, sodium sulfite or sodium hydrosulfide.
However, Applicant found that the use of water during preparation of Micafungin sodium was reducing yield of final product. Water wash is required to wash out access polar base which lead to lose of yield.
IN 201621007136 reported a process for the preparation of Micafungin sodium, the process comprises: treating sodium source with one or more solvents to obtain a mixture, reacting the obtained mixture with FR-179642 and a compound of Formula V in one or more solvents, wherein said sodium source is selected from one or more of disodium hydrogen citrate, sodium citrate, sodium acetate, sodium propionate, sodium butyrate, sodium isobutyrate, sodium tartrate, sodium oxalate, sodium benzoate, sodium sorbate, sodium malate, monosodium succinate, disodium succinate, sodium bicarbonate, sodium carbonate, disodium hydrogen phosphate, sodium borate, sodium sulfite or sodium hydrosulfide.

However, inventors found thai the use of water during preparation of Micafungin sodium was reducing yield of final product. Water is required to wash out excess of polar sodium source which lead to lose of yield.
Considering the importance of Micafungin sodium, there is always a need for an alternative preparative routes, which for example, involve fewer steps, use reagents that are less expensive and/or easier to handle, consume smaller amounts of reagents, provide a higher yield of product, have smaller and/or more eco-friendly waste products, and/or provide a product of higher purity. In view.of this our inventors have developed the present invention, related to a process for the preparation of Micafungin sodium (1) with good yield and high purity.
OBJECTIVE OF INVENTION
The main objective of the present invention is to provide a simple and cost effective process for the preparation of Micafungin sodium (I) with high purity and good yield on commercial scale.
SUMMARY OF THE INVENTION
In one embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (I):

(a) reacting compound FR.-179642 of a Compound of Formula (II);
or its reactive derivative, wherein R is hydrogen or protecting group;
to produce Micafungin or its base addition salt of a Compound of formula (la);
(b) treating Micafungin or its base addition salt obtained in Step (a) with fatty acid
sodium salt;

(c) isolating Micafungin sodium of a Compound of Formula (]).
In another embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (I):
wherein said process comprises; (a) reacting compound FR-179642 of a Compound of Formula (II);
with Isoxazole adduct of a Compound of formula (V);

in presence of a base selected from DIPEA;
to produce Micafungin DIPEA salt of a Compound of formula (lb);
(b) treating Micafungin DIPEA salt obtained in Step (a) with resin followed by
treatment with fatty acid sodium salt, selected from sodium hexanoate or sodium salt
longer fatty acids, preferably sodium decanoate;
(c) isolating Micafungin sodium of a Compound of Formula (I).
In another embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (I):

wherein said process comprises;
(a) treating Micafungin DIPEA salt of a Compound of formula (lb);
with resin followed by treatment with fatty acid sodium salt, selected from sodium hexanoate or sodium salt longer fatty acids, preferably sodium decanoate;
(b) isolating Micafungin sodium of a Compound of Formula (I).
In another embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (I):

wherein said process comprises; mixing a fatty acid sodium salt, selected from sodium hexanoate or sodium salt longer fatty acids, like sodium decanoate with an organic solvent or mixture of organic solvents containing the Micafungin of a compound of formula la or a salt thereof;
to produce Micafungin sodium of a Compound of Formula (I).
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment, the present invention provides an improved process for the
prg^atiftn^f-^na-ftTr^infsKfliiHii ofta 'Sompound Of rofrrrula (1):

which comprises; (a) reacting compound FR-179642 of a Compound of Formula (II);
with Isoxazole carboxylic acid of a Compound of formula (VI);
or its reactive derivative, wherein R is hydrogen or protecting group selected from Hydroxybenzotriazole (HOBt) in presence of a base;

to produce MicafunRin or its base addition salt of a Compound of formula (la);
(b) treating Micafungin obtained in Step (a) with fatty acid sodium salt;
(c) isolating Micafungin sodium of a Compound of Formula (I).
In another embodiment of the invention, Compound of formula (II) is obtained by removing the N-acyl group side chain of precursor Compound of Formula III (FR-901379) through an enzymatic deacylation. FR-901379 is a natural product isolated from the fungus Coleophoma empetri F-l 1899.
In still another embodiment, in a Compound of Formula (VI), R is selected from hydrogen or Hydroxybenzotriazole (HOBt).
In still another embodiment, R is specifically selected from Hydroxybenzotriazole (HOBt).
In still another embodiment, reactive derivative of Isoxazole carboxylic acid of a Compound of formula (VI) is HOBt Isoxazole adduct of a Compound of formula (V).

In still another embodiment, the reaction of a Compound of Formula (II) with Compound of formula (VI) in step (a) is carried out in the presence of a base and a solvent.
In still another embodiment, the base is organic base such as tri(lower)alkylamine (e.g., N,N-diisopropylethylamine, triethylamine etc.), pyridine, di(lower)alkylaminopyridine (e.g., 4-dimethylaminopyridine, etc.) N,N-di(lower)alkylbenzyiamine, or the like.
In still another embodiment, the base is preferably N,N-diisopropylethylamine (DIPEA).
In still another embodiment, the solvent used in the reaction step comprises polar aprotic solvent or non-polar solvents and/or mixtures thereof.
In another embodiment, polar aprotic solvent comprises dimethylformamide (DMF), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), acetonitrile, acetone, ethyl acetate, N-methylpyrrolidone and/or mixtures thereof; and non-polar solvents comprises hexane, benzene, toluene, 1,4-dioxane, chloroform, diethyl ether, methylene chloride (CH2C12) and/or mixtures thereof.
In still another embodiment, the solvent is preferably N,N-dimethylforrnamide (DMF).
The reaction is usually carried out at low temperature or room temperature. The temperature is preferably -10 to 10°C, and more preferably -5 to 0°C.

The compounds obtained by the process of the present invention can be isolated and purified by a conventional method such as pulverization, recrystallization, column-chromatography, reprecipitation or the like.
In still another embodiment of the invention, treating Micafungin obtained in Step (a) with fatty acid sodium salt.
]n still another embodiment of the invention, fatty acid sodium salt is selected from the group consisting of Sodium hexanoate, sodium decanoate or Sodium oleate or Sodium palmitate or Sodium stearate.
In still another embodiment, the fatty acid sodium salt is preferably sodium decanoate.
In still another embodiment, the reaction of step (b) is usually carried out in the presence of an organic solvent or mixture of organic solvents.
This organic solvent is alcohol (e.g. methanol, ethanol, propanol, etc.), ether (diethyl ether, diisopropyl ether, methyl tert-butyl ether (MTBE)), N,N-dimethylformamide, tetrahydrofuran, toluene, methylene chloride, ethylene dichloride, chloroform, 1,2-dimethoxy ethane, dioxane, ethyl acetate, etc., or the mixture thereof.
In still another embodiment of the invention, before treating with fatty acid sodium salt, Micafungin is treated with sulphonic acid resin.
In still another embodiment of the invention, sulphonic acid resin is selected from DIAION SKI 04H.
In still another embodiment, inventors are using long chain fatty acid salt like sodium decanoate in non-aqueous solvent like methanol. Unreacted fatty acid sodium salt can be washed out using less polar organic solvent without losing Micafungin sodium.
The reaction temperature is not critical, and the reaction is usually carried out under cooling to heating.

The temperature is preferably 10 to 25° C.: and more preferably 5 to 10° C for a time period of 1 -5 hours.
One advantage of using sodium salt of long chain fatty acid is that unreacted fatty acid sodium salt can be washed out using less polar organic solvent in which micafungin sodium is insoluble thereby avoiding loss of the product during washing.
In another embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (1):
wherein said process comprises; (a) reacting compound FR-179642 of a Compound of Formula (II);

with HOBt Isoxazole adduct of a Compound of formula (V):
in presence of a base selected from DIPEA;
to produce Micafungin DIPEA salt of a Compound of formula (lb);
(b) treating Micafungin DIPEA salt obtained in Step (a) with resin followed by fatty acid sodium salt, selected from sodium hexanoate or sodium salt longer fatty acids, preferably sodium decanoate;
(c) isolating Micafungin sodium of a Compound of Formula (I).
In still another embodiment, the reaction of a Compound of Formula (II) with Compound of formula (V) in step (a) is carried out in the presence of a base selected from DIPEA and a solvent.
In still another embodiment, the solvent in step (a) is mentioned as above.

In still another embodiment, treating Micafungin DIPEA salt obtained in Step (a) with fatty acid sodium salt, selected from sodium decanoate.
In still another embodiment, the reaction of step (b) is usually carried out in the presence of an organic solvent or mixture of organic solvents.
In still another embodiment, the organic solvent in step (b) is mentioned as above.
In still another embodiment of the invention, before treating with fatty acid sodium salt, Micafungin is treated with sulphonic acid resin.
In still another embodiment of the invention, the resin is sulphonic acid resin is selected from DIAION SK104H.
In still another embodiment, inventors are using long chain fatty acid salt like sodium decanoate in non-aqueous solvent like methanol. Unreacted fatty acid sodium salt can be washed out using less polar organic solvent without losing Micafungin sodium.
The reaction temperature is not critical, and the reaction is usually carried out under cooling to heating.
The temperature is preferably 0 to 20° C, and more preferably 5 to 10 C for a time period of 1 -5 hours.
In another embodiment, the present invention provides an improved process for the preparation of Micafungin sodium of a Compound of Formula (I):

wherein said process comprises; mixing a fatty acid sodium salt, selected from sodium hexanoate* or long chain fatty acid sodium salt like sodium decanoate with an organic solvent or mixture of organic solvents containing the Micafungin of a compound of formula la or Micafungin DIPEA salt of a Compound of formula (lb);

to produce Micafungin sodium of a Compound of Formula (I).
In still another embodiment, organic solvent is mentioned as above.
One advantage of using sodium salt of long chain fatty acid is that unreacted fatty acid sodium salt can be washed out using less polar organic solvent in which micafungin sodium is insoluble. As micafungin sodium is soluble in water use of less polar organic solvent avoid loss during washing.
In still another embodiment, inventors are using long chain fatty acid salt like sodium decanoate in non-aqueous solvent like methanol. Unreacted fatty acid sodium salt can be washed out using less polar organic solvent without losing Micafungin sodium.
The reaction temperature is not critical, and the reaction is usually carried out under cooling to heating.
The temperature is preferably 0 to 20° C, and more preferably 5 to 10° C for a time period of 1-5 hours.
Generally, there are two ways for preparing Micafungin acid into Micafungin
__ sodium salt. One is exchange using cationic resin; the other is via adjusting pH value.

Preparing sodium salt by adjusting pH value is a process of neutralization reaction between acid and base. It includes two types of reactions, i.e. the reaction between strong acid and strong base, and the reaction between strong acid and weak base. If strong base solution is added into strong acid solution for adjusting pH value, there is a sharp change in the pH value of the solution and the pH value will be instantly altered by 8. Therefore, in the practical production, it is hard to control the pH value and a slightest mistake could lead to an overregulated pH value. In.US 7,199,248, a 0.1 mol/L NaOH solution was used to adjust pH value to 6-8 for obtaining Micafungin sodium. It was actually a reaction between strong acid and strong base. Micafungin contains benzene sulfonic acid groups and pKa values of benzene sulfonic acid compounds are generally less than 1, therefore, the compound is strong acid compound. Therefore, theoretically, the method using NaOH solution to adjust pH values for obtaining sodium salt is unsuitable for preparation of formula II compound.
The inventors have repeated the method reported in US 7,199,248 for multiple times and analyzed and validated the reported method from the point of view of local pH value. The inventors have found that during the course of pH adjusting, regarding the whole solution system, 0.1 mol/L NaOH solution has a relatively low concentration and the overall pH value can be managed at 6-8, however, during the course of adding NaOH solution dropwise, the local base concentration gets too high, i.e. local pH value in the solution gets overly high, therefore, partial degradation occurred in Micafungin.
In order to avoid the aforesaid defects, the inventors have conducted further and intensive researches and have unexpectedly found that by using fatty acid sodium salt in an organic media, organic, compound of formula I (Micafungin sodium) can be obtained without generating extra impurities.
In another embodiment, after completion of the reaction, Compound (1) is isolated by conventional methods such as by removing the solvent under reduced pressure.

In another embodiment, Compound (1) is optionally purified by conventional methods.
In another embodiment, purification is carried out by crystallization using a solvent or mixture of solvents.
The following examples illustrate the nature of the invention and are provided for illustrative purposes only and should not be construed to limit the scope of the invention.
EXAMPLES:
EXAMPLE 1:
PREPARATION OF MICAFUNGIN DIPEA SALT
In a 2L RBF, a solution of FR-179642 (1 g, 0.8 g) in DMF (13 mL) were suspended at 25-30°C. The reaction mass was stirred and cooled to -3°C. To this solution diisopropylethyl amine (DIPEA) (230 mg, 1.77 mmol) and l-[[4-[5-(4-pentyloxyphenyl) isoxazol-3-yl] benzoyl] oxy]-lH-l,2,3-benzotriazole (Compound of Formula V) (536 mg, 1.14 mmol) was added and stirred at -3°C for 4.5 hrs. The reaction mass was diluted with ethyl acetate (65 mL) and stirred at 0-5°C for 1 hr. Resulted precipitate was filtered and washed with ethyl acetate (10 mL) and acetone (10 mL). Product was dried at 20-25°C for 12 hrs. to afford Micafungin DIPEA salt (1.05 g, yield: 92%).
'H NMR (MICA.Na, 300 MHz, DMSO-d6): 8 = 8.90 (m, 2H), 8.28 (br d, J = 8.0 Hz, 1 H), 7.99 - 8.15 (m, 5H), 7.89 (d, J = 8.7 Hz, 2H), 7.59 (s, 1 H), 7.29 - 7.50 (series of m, 3H), 7.16 (d, J = 8.9 Hz, 2H), 7.09 (m, 1 H), 6.76 - 6.90 (series of m, 3H), 5.58 (d, J = 5.7 Hz, 1 H), 5.29 (d, J = 4.2 Hz, 1 H), 4.82 - 5.21 (series of m, 9H), 3.72 - 4.54 (series of m, 16H), 3.23 (m, 1 H), 1 .88 - 2.61 (series of m, 7H), 1 .79 (m, 2H), 1 .42 (m, 4H), 1 .13 (d, J = 5.8 Hz, 3H), 1 .01 (d, J = 6.7 Hz, 3H), 0.95 (t, J - 7.1 Hz, 3H).

PREPARATION OF MICAFUNGIN SODIUM:
In a 1L RBF, a solution of Micafungin DIPEA salt (0.5 g) in methanol (250 mL) was cooled to 5°C. Sulphonic acid resin SK-104F (4.0 mL) was added to this and stirred at 0-5°C for 30 min. The reaction mass was filtered and resin was washed with cold (0-5°C) methanol (3mL). Combined filtrate was taken in a round bottomed flask precooled to 0-5°C. A solution of sodium decanoate (0.152 g) in methanol (6 mL) was added at maintaining temperature of 0-5°C. The mass was stirred at 0-5°C for 2 hrs. Slowly added MTBE (50 mL) to this reaction mixture, and stirred at same temperature for lhr. the mass was filtered and solid was washed with 4 mL of MTBE-methanol mixture (50%). The product was dried under high vacuum at 20-25°C for 12 hrs. to obtain Micafungin sodium (0.39 g, 84% yield).
1H NMR (DMSO-d6): 5 = 8.90 (m, 2H), 8.28 (br d, J = 8.0 Hz, 1 H), 7.99 -
8.15 (m, 5H), 7.89 (d, J = 8.7 Hz, 2H), 7.59 (s, 1 H), 7.29 - 7.50 (series of m, 3H),
7.15 (d, J = 8.9 Hz, 2H), 7.09 (m, 1 H), 6.76 - 6.90 (series of m, 3H), 5.58 (d, J = 5.7 Hz, 1 H), 5.29 (d, J = 4.2 Hz, 1 H), 4.82 - 5.21 (series of m, 9H), 3.72 - 4.54 (series of m, 16H), 3.23 (m, 1 H), 1 .88 - 2.61 (series of m, 7H), 1 .79 (m, 2H), 1 .42 (m, 4H), 1 .13 (d, J = 5.8 Hz, 3H), 1 .01 (d, J = 6.7 Hz, 3H), 0.95 (t, J - 7.1 Hz, 3H).
HPLC Purity: 99.51%