DESC:FIELD OF THE INVENTION
The present application relates to an improved process for preparation of Lurbinectedin its intermediates, and pharmaceutical compositions thereof.

BACKGROUND OF THE INVENTION
The drug compound having the adopted name Lurbinectedin is a member of the ecteinascidin class of alkaloids, characterized by a densely functionalized pentacyclic structure. Lurbinectedin is an RNA Polymerase II inhibitor that binds to the minor groove of DNA and promote apoptosis for the potential treatment of solid tumors including lung cancer. Lurbinectedin is represented by the structure of formula I.

Lurbinectedin has been approved by the US FDA for the treatment of adult patients with metastatic small cell lung cancer (SCLC).
Lurbinectedin, its synthetic process and its pharmaceutical compositions are described in US patent No. 7,763,615 B2 (US ‘615). The final steps of the process described in US ‘615 are schematically represented below:

The compound of formula III is an advanced intermediate for the preparation of lurbinectedin and trabectedin, and was first reported in the literature by Corey et al (J. Am. Chem. Soc., 1996, 118, 9202-9203). This reported procedure uses the Rapoport method (J. Am. Chem. Soc., 1982, 104, 4446-4450) to convert the precursor primary amine to a carbonyl by forming an imine with 4-formyl-1-methylpyridinium iodide, treatment with a strong organic base (DBU) and then hydrolysis of the resulting product with aqueous oxalic acid to give the desired ketone. This procedure has been widely used by other groups involved in the synthesis of trabectedin and lurbinectedin as is perceived as the current ‘state of the art’ method for this transformation.
Despite this widespread usage, this method has significant drawbacks, primarily that the yield obtained is quite low, around 50-55% is typically reported. The process proceeds through several intermediates which cannot be readily monitored and the reaction itself is highly colored.
When evaluating the reported process to prepare the intermediate of formula III, the inventors of the present application found the reaction to be quite challenging to operate due to the lack of in-process analysis methods for the various intermediates, and were only able to get 35-40% yield of the desired product. Consequently, the inventors wanted to find an alternative process to make the intermediate of formula III which was more robust and reproducible, and gave better yields of the desired product.
There remains a need to provide commercially viable and advantageous processes to make the intermediate of formula III and Lurbinectedin.

SUMMARY OF THE INVENTION
The present application generally relates to process for preparation of Ecteinascidin derivatives (viz. Lurbinectedin and Trabectedin), their intermediates and pharmaceutical compositions thereof.
In a first aspect the present application provides a process for preparation of compound of Formula III, comprising reacting a compound of formula IV with a metal salt and a metal glyoxylate.

In a second aspect the present application provides a process for preparation of Lurbinectedin, comprising:
(a) reacting a compound of formula IV with a metal salt and a metal glyoxylate in presence of sodium acetate to form compound of formula III,

(b) reacting compound of formula III with a compound of formula V or a salt thereof to obtain a compound of formula II,

(c) converting compound of formula II into Lurbinectedin.

In a third aspect the present application provides a process for preparation of Lurbinectedin, comprising:
(a) reacting a compound of formula IV with a compound of formula VII, followed by hydrolysis of the intermediate species with an acid to form compound of formula III,

(b) reacting compound of formula III with a compound of formula V or a salt thereof to obtain a compound of formula II,

(c) converting compound of formula II into Lurbinectedin.

In another aspect, the present application provides pharmaceutical composition comprising Lurbinectedin prepared by the processes described in the present application and one or more pharmaceutically acceptable excipients.

DETAILED DESCRITPION
The present application generally relates to process for preparation of Lurbinectedin, its intermediates and pharmaceutical compositions thereof.
The present application provides a process for preparation of Lurbinectedin, comprising:
(a) reacting a compound of formula IV with a metal salt and a metal glyoxylate to form compound of formula III,

(b) reacting compound of formula III with a compound of formula V or a salt thereof to obtain a compound of formula II,

(c) converting compound of formula II into Lurbinectedin.

The step (a) of the process involves reaction of compound of formula IV with a metal sulfate or a metal chloride salt and a metal glyoxylate in presence of sodium acetate or potassium acetate to form compound of formula III.
The compound of formula IV can be prepared by the processes described in the art or the process of the present application. The metal salt can be a zinc sulfate, copper sulfate, zinc chloride or copper chloride. The metal glyoxylate can be calcium glyoxylate, magnesium glyoxylate or sodium glyoxylate. In one aspect the metal salt is zinc sulfate and metal glyoxylate is calcium glyoxylate.
The process involves reaction of compound of formula IV with sodium acetate or potassium acetate in presence of a suitable solvent such as acetic acid, acetonitrile, dichloromethane, DMF or mixtures thereof, followed by reacting the intermediate with metal salt and metal glyoxylate to from the compound of formula III.
The step (b) of the process involves reaction of compound of formula III with a compound of formula V, or a salt thereof, and sodium acetate in a suitable solvent such as acetic acid, ethanol, isopropanol or dichloromethane to obtain a compound of formula II.
The step (c) of the process involves reaction of compound of formula II with silver nitrate in a mixture of acetonitrile and water to form Lurbinectedin.
In another aspect the present application provides a process for preparation of compound of formula III, comprising reacting a compound of formula IV with a compound of formula VII, followed by hydrolysis of the intermediate species with an acid to form compound of formula III,

The process involves reaction of compound of formula IV with a compound of formula VII in presence of a suitable solvent such as methanol, followed by hydrolysis of the intermediate with an acid such as oxalic acid to form compound of formula III.
In another aspect, the present application provides a process for preparation of Lurbinectedin, comprising:
(a) converting compound of formula II into a suitable acid addition salt,

(b) reacting the acid addition salt of compound of formula II with silver nitrate to form an acid addition salt of lurbinectedin;

(c) adsorbing the acid addition salt of lurbinectedin onto an ion exchange resin;
(d) washing the resin with water;
(e) eluting the resin with a suitable solvent to isolate the acid addition salt of lurbinectedin from the resin;
(f) treating the acid addition salt of lurbinectedin with suitable base to form lurbinectedin; and
(g) optionally purifying the lurbinectedin obtained in step (f).
In another aspect, the present application provides a process for preparation of compound of formula IV, comprising:
(a) reacting compound of formula IX with a borane complex in presence of a palladium catalyst to form a compound of formula VIII
(b) without isolating reacting the compound of formula VIII with a suitable acid to form the compound of formula IV

In another aspect, the present application provides pharmaceutical composition comprising Lurbinectedin prepared by the processes described in the present application and one or more pharmaceutically acceptable excipients.
Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. Variations of the described procedures, as will be apparent to those skilled in the art, are intended to be within the scope of the present application.

DEFINITIONS
The following definitions are used in connection with the present application unless the context indicates otherwise.
The term "about" when used in the present application preceding a number and referring to it, is meant to designate any value which lies within the range of ±10%, preferably within a range of ±5%, more preferably within a range of ±2%, still more preferably within a range of ±1 % of its value. For example "about 10" should be construed as meaning within the range of 9 to 11, preferably within the range of 9.5 to 10.5, more preferably within the range of 9.8 to 10.2, and still more preferably within the range of 9.9 to 10.1.
All percentages and ratios used herein are by weight of the total composition and all measurements made are at about 25°C and about atmospheric pressure, unless otherwise designated. All temperatures are in degrees Celsius unless specified otherwise. As used herein, “comprising” means the elements recited, or their equivalents in structure or function, plus any other element or elements which are not recited. The terms “having” and “including” are also to be construed as open ended. All ranges recited herein include the endpoints, including those that recite a range “between” two values. Whether so indicated or not, all values recited herein are approximate as defined by the circumstances, including the degree of expected experimental error, technique error, and instrument error for a given technique used to measure a value.
Certain specific aspects and embodiments of the present application will be explained in greater detail with reference to the following examples, which are provided only for purposes of illustration and should not be construed as limiting the scope of the application in any manner. Reasonable variations of the described procedures are intended to be within the scope of the present invention. While particular aspects of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
EXAMPLES
Example-1: Preparation of compound of formula III

Compound of formula IV (61.9 mg), 3,5-di-tert-butylcyclohexa-3,5-diene-1,2-dione (compound of formula VII, 51 mg) and methanol (2 mL) were charged into a round bottom flask under nitrogen atmosphere. The reaction mixture was stirred for 10 hours at ambient temperature. Saturated aqueous oxalic acid (2 mL) was added to the reaction mixture and stirred for 10 minutes. Water (5 mL) and methanol (5 mL) were added to the mixture and stirred for 2 hours. Acetonitrile (5 mL) and saturated aqueous oxalic acid (2 mL) were added to the mixture and stirred for 2 hours. Ethyl acetate (10 mL) and brine (10 mL) were added to the mixture and stirred for 10 minutes. Layers separated and the aqueous layer was extracted with ethyl acetate (10 mL). The organic phases were combined and washed with brine (10 mL) and dried over sodium sulfate and concentrated in vacuo to afford a red oil. The crude product was purified via column chromatography using 40% ethyl acetate in heptane as eluent to afford 44.3 mg of compound of formula III as an off-white solid.

Example-2: Preparation of compound of formula III

NaOAc (1.66 g; 20.24 mmol) was dissolved in AcOH (95 ml). Separately, compound of formula IV (3.12 g; 5.01 mmol) was dissolved in MeCN (95 mL) and placed under a nitrogen atmosphere. The solution of sodium acetate in acetic acid was added to the solution of compound of formula IV in acetonitrile to give a yellow solution, which was stirred at 21°C under nitrogen. Zinc sulfate heptahydrate (2.88 g; 10.02 mmol) was added, followed by calcium glyoxylate (12.3 g; 11.05 mmol) and the resulting white suspension was stirred vigorously at 21°C under nitrogen for 17h. The mixture was then transferred to a separating funnel, washing the reaction flask with water (100 mL) and dichloromethane (100 mL), adding the washes to the separating funnel. The mixture was shaken and left to settle. The lower, orange dichloromethane phase was separated. The aqueous phase was extracted with dichloromethane (2 x 100 mL) and then discarded to waste. The combined organic phase was filtered through a pad of sodium sulfate into a suitable flask, washing with dichloromethane. The resulting solution was concentrated to low volume on a rotary evaporator, then the residue was co-distilled with heptane (3 x 50 mL) to give a viscous oil, which was purified by chromatography on silica gel, eluting with ethyl acetate/heptane mixtures to give the product (1.86 g).

Example-3: Preparation of compound of formula III

NaOAc (1.95 g) was dissolved in AcOH (110 ml). Separately, compound of formula IV (3.7 g) was dissolved in MeCN (110 mL) and placed under a nitrogen atmosphere. The solution of sodium acetate in acetic acid was added to the solution of compound of formula IV in acetonitrile to give a yellow solution, which was stirred at 21°C under nitrogen. Zinc sulfate heptahydrate (3.42 g) was added, followed by calcium glyoxylate (14.52 g) and the resulting white suspension was stirred vigorously at 21°C under nitrogen for 17h. The mixture was then transferred to a separating funnel, washing the reaction flask with water (110 mL) and dichloromethane (110 mL), adding the washes to the separating funnel. The mixture was shaken and left to settle. The lower, orange dichloromethane phase was separated. The aqueous phase was extracted with dichloromethane (2 x 120 mL) and then discarded to waste. The combined organic phase was filtered through pad of sodium sulfate into a suitable flask, washing with dichloromethane. The resulting solution was concentrated to low volume on a rotary evaporator, then the residue was co-distilled with heptane (3 x 60 mL) to give a viscous oil, which was purified by chromatography on silica gel, eluting with ethyl acetate/heptane mixtures to give the product (2.30 g). Purity: 99.65%.

Example-4: Preparation of compound of formula II

The compound of Formula III (2.3 g), 5-methoxytryptamine hydrochloride (2.60 g) and sodium acetate (1.52 g) were charged inti a suitable reaction vessel Acetic acid (50 mL) was added and the resulting mixture was stirred at 21°C under nitrogen for 18h. The mixture was then concentrated on a rotary evaporator, and the resulting residue was suspended in dichloromethane (50 mL) and water (20 mL). Saturated aqueous sodium bicarbonate (50 mL) was added slowly, followed by the addition of solid sodium bicarbonate (18 g) to adjust the pH of the aqueous solution to around 8. The mixture was transferred to a separating funnel, washing the reaction flask with dichloromethane (20 mL) and separated. The upper, aqueous layer was extracted with dichloromethane (2 × 50 mL). The combined dichloromethane extracts were filtered through a pad of sodium sulfate, washing with dichloromethane (2 x 15 mL). The dichloromethane solution was concentrated to a residue which was purified by chromatography on silica gel to give the product (3.05 g). Purity 99.5%.

Example-5: Preparation of Lurbinectedin

The Compound of Formula II (1.76 g) was charged to a suitable reaction flask. Dichloromethane (30 mL) and trifluoroacetic acid (1.8 mL) were added to give a clear solution. The mixture was concentrated on a rotary evaporator, n-heptane (20 mL) was added and the mixture was concentrated again. This was repeated with a second portion of n-heptane (20 mL). The residue was dissolved in acetonitrile (46 mL) to give a pale orange solution. Separately, silver nitrate (11.35 g) was charged to a suitable vessel, water (31 mL) was added and the mixture was agitated gently to give a clear solution. The silver nitrate solution was added to the acetonitrile solution of the compound of Formula II, the resulting pale orange solution was protected from light and stirred at 21°C for 21h. Dichloromethane (70 mL) was added, followed by saturated aqueous sodium chloride solution (70 mL). The resulting slurry was stirred at 21°C for 5 min, then saturated aqueous sodium bicarbonate solution (70 mL) was added and the resulting mixture was stirred at 21°C for approximately 10 min. The mixture was filtered through a pad of Celite to remove the precipitated solids. The reaction flask and filter cake were washed with methanol (2 x 15 mL) and water (20 mL), these washes were combined with the filtrate. The filtrate was transferred to a separating funnel and separated. The upper, aqueous phase was extracted with dichloromethane (2 x 70 mL). The combined dichloromethane extracts were concentrated to give a residue which was purified by chromatography on silica gel to give the product (1.30 g). Purity 99.25%.

Example-6: Preparation of Lurbinectedin

The Compound of Formula II (538 mg), dichloromethane (20 mL) and trifluoroacetic acid (1.0 mL) were charged to a suitable reaction flask and the mixture was concentrated on a rotary evaporator and the residue was dissolved in acetonitrile to give a pale orange solution. Separately, silver nitrate (3.46 g) was charged to a suitable vessel, water was added and the mixture was agitated gently to give a clear solution. The silver nitrate solution was added to the acetonitrile solution of the compound of Formula II, the resulting pale orange solution was protected from light and stirred at 21°C. While the reaction was underway, Amberlite XAD-16N resin (5.6 g) was weighed into a suitable vessel. The reaction mixture was filtered through cotton wool into the flask containing the resin, washing with 1:1 acetonitrile/water (1 mL). The resulting mixture was stirred at 20°C while water (60 mL) was added over ~1h. The mixture was stirred for a further 1h, then the resin was removed by filtration. Water (20 mL) was added and the mixture was stirred for 10 min, then filtered. The water treatment of the resin was repeated twice (20 mL water each time). The resin was then stirred with methanol (30 mL) for 10 min and filtered. This was repeated with 5 x 30 mL methanol, combining all the methanol solutions into a single portion. The combined methanol solution was concentrated to a residue on a rotary evaporator. This residue was suspended in a mixture of dichloromethane (20 mL), water (10 mL) and saturated aqueous sodium bicarbonate (10 mL) and stirred for 10 min. The phases were separated, and the upper aqueous phase was further extracted with dichloromethane (2 x 20 mL). The combined dichloromethane phase were concentrated to a residue which was purified by chromatography on silica gel to give the product (413 mg). Purity 99.55%.

Example-7: Preparation of compound of formula IV

Compound of formula IX (4.6 g), triphenylphosphine (65 mg) and dichloromethane (46 mL) were charged to a suitable vessel and placed under nitrogen and the mixture was stirred until a clear solution formed. Bis(triphenylphosphine)palladium(II) dichloride (11 mg) was added to the reaction mixture, followed by dimethylamine borane complex (1.808 g) and the resulting mixture was stirred at 20-25°C for 3.5 h, at which point TLC analysis showed reaction complete. Solid p toluenesulfonic acid monohydrate (11.65 g) was added in portions over ~15 min, and the resulting mixture was stirred at 20-25°C for 2.5 h, at which point TLC analysis showed reaction completion. Aqueous sodium bicarbonate (5% w/w; 50 mL) was added slowly, followed by the addition of solid sodium bicarbonate in portions until the pH of the aqueous phase was ~8. The mixture was transferred to a separating funnel and separated. The lower organic phase was washed with aqueous sodium bicarbonate, dried over sodium sulfate, filtered and concentrated to give crude compound of Formula IV (3.90 g). The crude compound of Formula IV used in the next step without further purification. ,CLAIMS:We claim
1. A process for preparation of Lurbinectedin, comprising:
(h) converting compound of formula II into a suitable acid addition salt,

(i) reacting the acid addition salt of compound of formula II with silver nitrate to form an acid addition salt of lurbinectedin;

(j) adsorbing the acid addition salt of lurbinectedin onto an ion exchange resin;
(k) washing the resin with water;
(l) eluting the resin with a suitable solvent to isolate the acid addition salt of lurbinectedin from the resin;
(m) treating the acid addition salt of lurbinectedin with suitable base to form lurbinectedin; and
(n) optionally purifying the lurbinectedin obtained in step (f).
2. The process according to claim 1, the suitable acid is acetic acid or trifluoroacetic acid.
3. The process according to claim 1, the ion exchange resin is Amberlite resin.
4. The process according to claim 1, the suitable solvent used to isolate the acid addition salt of lurbinectedin from the resin is selected from the group comprising methanol, ethanol, isopropanol, acetonitrile or a mixture thereof.
5. The process according to claim 1, the suitable base is sodium bicarbonate.
6. A process for preparation of compound of formula IV, comprising:
(c) reacting compound of formula IX with a borane complex in presence of a palladium catalyst to form a compound of formula VIII
(d) without isolating reacting the compound of formula VIII with a suitable acid to form the compound of formula IV

7. The process according to claim 6, the borane complex is dimethylamine borane complex, and palladium catalyst is Bis(triphenylphosphine)palladium(II) dichloride.
8. The process according to claim 6, the suitable acid is p-Toluene sulfonic acid.
9. A process for preparation of Lurbinectedin, comprising:
(a) reacting a compound of formula IV with zinc sulfate and calcium glyoxylate to form compound of formula III,

(b) reacting compound of formula III with a compound of formula V or a salt thereof to obtain a compound of formula II,

(c) converting compound of formula II into a suitable acid addition salt,

(d) reacting the acid addition salt of compound of formula II with silver nitrate to form an acid addition salt of lurbinectedin;

(e) adsorbing the acid addition salt of lurbinectedin onto an ion exchange resin;
(f) washing the resin with water;
(g) eluting the resin with a suitable solvent to isolate the acid addition salt of lurbinectedin from the resin;
(h) treating the acid addition salt of lurbinectedin with suitable base to form lurbinectedin; and
(i) optionally purifying the lurbinectedin obtained in step (f).
10. The process according to claim 9, the acid addition salt formed is trifluoro acetate salt.