WO2019186522A1

WO2019186522A1 - An improved process for preparation of lopinavir and its intermediates thereof

Info

Publication number: WO2019186522A1
Application number: PCT/IB2019/052666
Authority: WO
Inventors: Ravindra Babu Bollu; DalaSingh PRASANTA; Narendra Babu TALLURI; Pedda Reddiah BASINENI; Prasant Kumar BARIK; Uma Maheswer Rao VASIREDDI
Original assignee: Laurus Labs Limited
Priority date: 2018-03-30
Filing date: 2019-04-01
Publication date: 2019-10-03

Abstract

The present invention generally relates to an improved process for preparation of lopinavir and its intermediates through formation of tartrate salt of compound of Formula (III).

Description

“An improved process for preparation of lopinavir and its intermediates thereof’

PRIORITY:

This application claims the benefit under Indian Provisional Application No. 201811012127 filed on March 30, 2018 entitled“An improved process for preparation of lopinavir and its intermediates thereof’, the content of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an improved process for preparation of lopinavir and its intermediates thereof.

BACKGROUND OF THE INVENTION

Lopinavir, also known as [lS-[lR,(R),3R,4R]]-N-[4-[[(2, 6-dimethyl phenoxy) acetyl] amino] -3 -hydroxy- 5-phenyl- 1 -(phenylmethyl)pentyl] tetrahydro alpha-( 1 - methylethyl)-2-oxo-l(2H)-pyrimidine acetamide of Formula I:

Formula I

Lopinavir is an HIV-l protease inhibitor and marketed by Abbvie under the trade name Kaletra^® in combination with Ritonavir for the treatment of HIV-l infection in adults and pediatric patients.

U.S. Patent No. 5914332 (“the‘332 patent”) discloses a variety of retroviral protease inhibiting compounds such as lopinavir and processes for preparation thereof. The processes disclosed in the‘332 patent is schematically represented as follows: Scheme- 1:

Compound of Formula III, chemically known as (2S,3S,5S)-2-N,N-dibcnzylamino-3- hydroxy-5-amino-l,6-diphenylhexane, is an important intermediate in the preparation of lopinavir. The process disclosed in the‘332 patent scheme-2 involves preparation of compound of Formula III as an oily mass and the oily mass was proceeds to next step without any purification. U.S. Patent No. 6372905 (“the ‘905 patent”) disclosed an improved process for preparation of lopinavir. The processes disclosed in the‘905 patent is schematically represented as follows:

U.S. Patent No. 8236991 (“the‘991 patent”) disclosed a process for preparation of lopinavir, which is similar to the‘332 patent but through formation of the compound of Formula III as its L-pyroglutamic acid salt instead of as an oily compound.

The ‘991 patent disclosed comparative examples for preparation of compound of Formula III by the‘332 patent process and reported that the HPLC purity of the obtained Formula III oily mass was 86% with contamination of undesired impurities, which are carry forward to the finished product. Removal of these impurities in the final stage is often proved to be difficult and requires repeated crystallizations, which finally results in the low yield of final API. To avoid this,‘991 patent process involves purification of Formula III by formation of L-pyroglutamic acid salt.

The preparation process of lopinavir as disclosed in the ‘991 patent has certain drawbacks as it involves: i) isolation of compound of Formula III involves contamination with unreacted Formula II and its intermediatery enaminone reduced compound, which are not easily removed even after purification by formation of L-pyroglutamic acid salt of Formula III. Further, HPLC purity of obtained L-pyroglutamic acid salt of Formula III was 93% only; ii) reduction of Formula II to Formula III involves formation of diastereomer of diastereomer-l ((2S,3R,5S)-5-amino-2-dibenzylamino-3-hydroxy-l, 6-diphenyl hexane), diastereomer-2 ((2S,3S,5R)-5-amino-2-dibenzylamino-3-hydroxy-l,6- diphenyl hexane) and diastereomer-3 ((2S,3R,5R)-5-amino-2-dibenzylamino-3- hydroxy-l, 6-diphenyl hexane), which are present after purification of Formula III by formation of L-pyroglutamic acid salt in an amount of diastereomer-l: 5.5%, diastereomer-2: 1.2% and diastereomer-3: 1.5% by HPLC; iii) disclosed process involves use of ethyl acetate in neutralization of L- pyroglutamic acid salt of Formula III, which process prone to form N-acetyl impurity of Formula A by acetylation of free amine present in Formula III with the aid of ethyl acetate in basic conditions used in the process,

Formula A iv) during the debenzylation of Formula V due to the presence of impurity of Formula A and unreacted Formula II, debenzylated impurities of acetylated Formula B and Formula C are formed, followed by Formula D and dimer impurity of Formula E in subsequent step with the reaction of Formula VII, and

Formula D Formula E v) further the reported processes involves reaction of compound of Formula VI or a salt thereof with a compound of Formula VII, which process yields lopinavir along with substantial amount of dimer impurity of Formula F. The impurity of Formula F is difficult to separate by normal purifications techniques.

Formula F

Based on the drawbacks mentioned above, there is a vital need to develop a process for the preparation of lopinavir and its intermediates, which is readily amenable to large scale production.

The present inventors focused research on preparation of pure compound of Formula III by formation of its salt and converting it in to lopinavir, thereby avoiding the aforementioned problems. The present inventors surprisingly found that isolation of compound of Formula III as its tartarate salt and use of ether solvents in place of ethyl acetate in the salt neutralization step, getting the lopinavir with improved purity and avoiding the formation of undesired impurities when compared to the same process as disclosed under the‘991 patent that having the compound of Formula III isolated as L- pyroglutamic acid. SUMMARY OF THE INVENTION

In accordance with one embodiment, the present invention provides a process for preparation of lopinavir of Formula I:

Formula I

comprising:

a) reducing a compound of Formula II in presence of a suitable reducing agent in a suitable solvent to obtain a compound of Formula III,

Formula II Formula III

b) treating the compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain a compound of Formula III. Tartrate,

Formula III. Tartrate

c) reacting the compound of Formula III. Tartrate with a compound of Formula IV in presence of a suitable coupling agent and a suitable base in an ether solvent to obtain a compound of Formula V,

Formula IV Formula V d) debenzylating the compound of Formula V in presence of suitable debenzylating agent to obtain a compound of Formula VI or a salt thereof, and

Formula VI

e) reacting the compound of Formula VI or a salt thereof with a compound of Formula VII, where in the“Lg” represents suitable leaving group, to obtain lopinavir.

Formula VII

In accordance with another embodiment, the present invention provides a process for preparation of lopinavir of Formula I, comprising:

a) treating a compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain a compound of Formula III.Tartrate,

Formula III Formula III.Tartrate b) treating the compound of Formula III.Tartrate with a suitable base to obtain a compound of Formula

Formula III c) reacting the compound of Formula III with a compound of Formula IV in presence of a suitable coupling agent in an ether solvent to obtain a compound of Formula V, and

Formula IV Formula V

d) converting the compound of Formula V in to lopinavir.

Formula II Formula III

b) treating the compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain a compound of Formula III.Tartrate,

Formula III.Tartrate

c) treating the compound of Formula III.Tartrate with a suitable base to obtain a compound of Formula III,

Formula III

d) reacting the compound of Formula III with a compound of Formula IV in presence of a suitable coupling agent in an ether solvent to obtain a compound of Formula V, and

Formula IV Formula V

e) converting the compound of Formula V in to lopinavir. In accordance with another embodiment, the present invention provides a process for preparation of lopinavir of Formula I: comprising:

a) preparing the compound of Formula V according to above embodiment,

Formula V

b) debenzylating the compound of Formula V in presence of suitable debenzylating agent to obtain a compound of Formula VI or a salt thereof, and

Formula VI c) reacting the compound of Formula VI or a salt thereof with a compound of Formula VII, where in the“Lg” represents suitable leaving group, to obtain lopinavir.

Formula VII

In accordance with another embodiment, the present invention provides a process for preparation of lopinavir of Formula I: comprising:

Formula III

comprising:

a) reacting a compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain Formula III. Tartrate, and

Formula III. Tartrate

b) treating the Formula III. Tartrate with a suitable base to obtain a compound of Formula III, and

c) converting the compound of Formula III to lopinavir. In accordance with another embodiment, the present invention provides a compound of Formula III. Tartrate

Formula III. Tartrate

In accordance with another embodiment, the present invention provides crystalline compound of Formula III.Tartrate characterized by a powder X-Ray diffraction (PXRD) pattern substantially in accordance with Figure 1.

In accordance with another embodiment, the present invention provides crystalline compound of Formula III.Tartrate characterized by differential scanning calorimetry (DSC) substantially in accordance with Figure 2.

In accordance with another embodiment, the present invention provides a process for preparation of lopinavir of Formula I substantially free of a compound of Formula F, comprising: reacting lopinavir and a compound of Formula F with a suitable base in a suitable solvent to obtain lopinavir.

Formula F

In accordance with another embodiment, the present invention provides a process for preparation of lopinavir of Formula I substantially free of a compound of Formula F, comprising:

i) reacting lopinavir and a compound of Formula F with a suitable base in a suitable solvent at a temperature of about ambient to reflux to obtain a reaction mixture,

ii) evaporating the reaction mixture to obtain a residue,

iii) treating the residue with a mixture of suitable water immiscible organic solvent and water,

iv) separating the water immiscible organic solvent, and

v) isolating the lopinavir of Formula I.

In accordance with another embodiment, the present invention provides an improved process for preparation of lopinavir of Formula I, comprising:

c) reacting the compound of Formula III. Tartrate with a compound of Formula IV in presence of a suitable coupling agent and a suitable base in an ether solvent to obtain a compound of Formula V, d) debenzylating the compound of Formula V in presence of suitable debenzylating agent to obtain a compound of Formula VI or a salt thereof,

e) reacting the compound of Formula VI or a salt thereof with a compound of Formula VII, where in the“Lg” represents suitable leaving group to obtain lopinavir, and

f) reacting the lopinavir with a suitable base in a suitable solvent to obtain lopinavir.

In accordance with another embodiment, the present invention provides a pharmaceutical composition, comprising lopinavir prepared by the processes of the present invention and at least one pharmaceutically acceptable excipient.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

Figure 1 is the characteristic powder X-ray diffraction (XRD) pattern of compound of Formula III. Tartrate.

Figure 2 is the characteristic differential scanning calorimetric (DSC) thermogram of compound of Formula III. Tartrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention encompasses an improved process for the preparation of lopinavir by formation of compound of Formula III. Tartrate to obviate reported processes problems. Further, the present invention avoids reported acetate solvents in neutralization of salt of Formula III and in subsequent coupling reaction with Formula IV, thereby avoiding the formation of undesired impurities as compared to the reported process.

Formula I

comprising: a) reducing a compound of Formula II in presence of a suitable reducing agent in a suitable solvent to obtain a compound of Formula III,

Formula II Formula III

Formula III. Tartrate

Formula IV Formula V

d) debenzylating the compound of Formula V in presence of suitable debenzylating agent to obtain a compound of Formula VI or a salt thereof, and

Formula VI e) reacting the compound of Formula VI or a salt thereof with a compound of Formula VII, where in the“Lg” represents suitable leaving group, to obtain lopinavir.

Formula VII

The starting compound of Formula II and intermediates of Formula IV and Formula VII (where in the “Lg” represents chloro) are known in the art and are available commercially from various sources or can be prepared by the processes known in the art, for example: US5914332.

The step a) of reduction of a compound of Formula II to Formula III is known in the art and can be carried out by following the processes known in the art for example: US6372905 or may be by following the process described in the below examples using reducing agent sodium borohydride in a mixture of solvents l,2-dimethoxy ethane and isopropanol.

The‘991 patent reported process of isolation of compound of Formula III involves contamination with unreacted Formula II and its intermediatery enaminone reduced compound, which are not easily removed even after purification by formation of L- pyroglutamic acid salt of Formula III. Further, HPLC purity of obtained L-pyroglutamic acid salt of Formula III was 93% only. Also the reduction of Formula II to Formula III involves formation of diastereomer- 1 ((2S,3i?,5S)-5-amino-2-dibenzylamino-3-hydroxy- 1, 6-diphenyl hexane), diastereomer-2 ((2S,3S,5i?)-5-amino-2-dibenzylamino-3-hydroxy- 1, 6-diphenyl hexane) and diastereomer-3 ((2S,3i?,5i?)-5-amino-2-dibenzylamino-3- hydroxy-l, 6-diphenyl hexane), which are present after purification of Formula III by formation of L-pyroglutamic acid salt in an amount of diastereomer- 1: 5.5%, diastereomer-2: 1.2% and diastereomer-3: 1.5% by HPLC. Further,‘991 process involves use of ethyl acetate in neutralization of L-pyroglutamic acid salt of Formula III, which process prone to form N-acetyl impurity of Formula A by acetylation of free amine present in Formula III with the aid of ethyl acetate in basic conditions used in the process.

To overcome the difficulties associated with the processes described above, the inventors of the present invention have developed an improved process for preparation of lopinavir, which involves purification of Formula III by formation of its tartarate salt, which substantially removed the unreacted starting material and impurities when compared to the reported process. Purification of Formula III by formation of its tartarate salt also substantially minimized the unwanted diastereomers of diastereomer- 1, diastereomer-2 and diastereomer-3. The present inventors also tried to purify the compound of Formula III by formation of other than tartarate salt which includes di-benzoyl-tartrate, fumarate salts, succinic acid, oxalic acid and citric acid. However, the purity of the Formula III was not achieved when compared to the tartarate salt. Even the compound of Formula III does not forming solid salt with some of the acids like succinic acid, oxalic acid and citric acid.

Step b) of aforementioned process involves purification of compound of Formula III by treating the compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain a compound of Formula III. Tartarate.

The suitable organic solvent used herein in for formation of tartarate salt includes, but are not limited to alcohols, ethers, halogenated hydrocarbons, ketones or mixtures thereof. The alcohols include, but are not limited to methanol, ethanol, propanol, isopropanol and the like; ethers include, but are not limited to methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, l,4-dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane and the like and mixtures thereof; halogenated hydrocarbons include, but are not limited to methylene chloride, ethylene chloride and the like; ketones include, but are not limited to acetone, methyl isobutyl ketone, methyl ethyl ketone and the like and mixtures thereof. Preferably the solvent is ether and more preferably methyl tertiary butyl ether.

The treating the compound of Formula III with L-tartaric acid is carried out at a temperature of about 25 °C to about reflux temperature; preferably at a temperature of about 35°C to about 60°C.

After completion of the salt formation, the temperature of the reaction mass may be cool to less than l5°C and then the resultant compound of Formula III. Tartarate salt may be isolated by conventional techniques known in the art such as precipitation by cooling the reaction mass, isolated by solvent precipitation, crystallization, concentrated by subjecting the solution to heating, decantation or filtration; preferably by filtration. Typically, if stirring is involved, the temperature during stirring can range from about 0°C to about l5°C.

The present invention provides a compound of Formula III. Tartarate prepared by the process described as above having a purity of at least about 97%, as measured by HPLC, preferably at least about 98% as measured by HPLC, and more preferably at least about 99.5%, as measured by HPLC; and content of diastereomer-l or diastereomer-2 or diastereomer-3 are less than about 0.5%, as measured by HPLC, more preferably less than about 0.3% as measured by HPLC.

HPLC purity comparison table for Formula III Tartrate salt and other salts:

From the above table, it is evident that the tartrate salt of the present invention provides Formula III in higher purity as compared to the‘991 patent L-pyroglutamate salt and other salts.

In another embodiment, the present invention provides a compound of Formula III. Tartrate:

Formula III. Tartrate

In another embodiment, the present invention provides crystalline compound of Formula III.Tartrate characterized by a powder X-Ray diffraction (PXRD) pattern substantially in accordance with Figure 1.

In another embodiment, the present invention provides crystalline compound of Formula III.Tartrate characterized by differential scanning calorimetry (DSC) substantially in accordance with Figure 2.

In another embodiment, the present invention provides a process for the preparation of lopinavir, comprising providing a compound of Formula III.Tartrate as obtained by the process described above, as a starting material or as an intermediate by the process known in the art or by the process described in the present specification.

In an embodiment, the step c) of the aforementioned process involves reaction of the compound of Formula III. Tartrate with a compound of Formula IV in presence of a suitable coupling agent in an ether solvent to obtain a compound of Formula V. Wherein the step c) process first involves neutralization of compound of Formula III. Tartrate by treating the compound of Formula III.Tartrate with a suitable base in an ether solvent to obtain a compound of Formula III.

The‘991 patent reported process involves use of ethyl acetate in neutralization of L- pyroglutamic acid salt of Formula III, which process prone to form N-acetyl impurity of Formula A about 0.5% to 1% as measured by HPLC, by acetylation of free amine present in Formula III with the aid of ethyl acetate in basic conditions used in the process. To avoid the formation of N-acetyl impurity of Formula A the present inventors have avoided the use of acetate solvents in neutralization of Formula III salt. The present inventors have surprisingly found that use of ether solvents in neutralization of Formula III salt avoids formation of N-acetyl impurity of Formula A.

The suitable base used herein for neutralization of compound of Formula III.Tartrate include but is not limited to inorganic bases selected from alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and the like; alkali metal alkoxides such as sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert-butoxide and the like; alkali metal carbonates such as sodium carbonate, potassium carbonate, cesium carbonate and the like; alkali metal bicarbonates such as sodium bicarbonate, potassium bicarbonate and the like; and organic bases selected from the group consisting of triethylamine, isopropyl ethylamine, diisopropyl amine, diisopropyl ethylamine, N-methyl morpholine, piperidine, pyridine and the like and mixtures thereof. Preferably the base is sodium bicarbonate.

The neutralization of Formula III.Tartrate is advantageously carried out in water and ether solvent include but is not limited to methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, l,4-dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane and the like and mixtures thereof; preferably methyl tertiary butyl ether. The neutralization step is carried out at a temperature of about 25°C to about 50°C.

After neutralization of Formula III.Tartrate, the product containing organic layer may be separated and as such may be used for next reaction with a compound of Formula IV in presence of a suitable coupling agent without isolating the Formula III.

The suitable coupling agent used herein for reaction of the compound of Formula III with a compound of Formula IV includes, but is not limited to N-(3-dimethylaminopropyl)- N’-ethylcarbodiimide,l,l'-carbonyldiimidazole, carbonyl di imidazole, diisopropyl carbodiimide, dicyclohexyl carbodiimide and the like and mixture thereof. Preferably the coupling agent is carbonyl di imidazole.

The ether solvent used herein for reaction of the compound of Formula III with a compound of Formula IV is may be the same solvent used for neutralization step or may be include but is not limited to methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, l,4-dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane and the like and mixtures thereof. Preferably, the solvent is a mixture of methyl tertiary butyl ether, tetrahydrofuran.

The reaction of the compound of Formula III with a compound of Formula IV is carried out at a temperature of about 25°C to reflux temperature. Preferably the reaction is carried out at about 45 °C to about 65 °C. After completion of the reaction, reaction mass is treated with water and the product containing organic layer may be separated and as such may be used for further step without isolating Formula V.

The present invention provides a compound of Formula V prepared by the process described as above having a purity of at least about 97%, as measured by HPLC, preferably at least about 98% as measured by HPLC, and more preferably at least about 99.5%, as measured by HPLC; and content of N-acetyl impurity of Formula A is less than about 0.1%, as measured by HPLC, preferably less than about 0.05%, more preferably less than about 0.03% as measured by HPLC.

The step d) of debenzylating the compound of Formula V and further convertion in to lopinavir is carried out by following the processes known in the art. For example: US6372905 or may be by following the process described in the below examples.

Further, the reported processes of lopinavir involve isolation of lopinavir along with 4 to 5 % of dimer impurity of Formula F, as measured by HPLC. Due to less polarity difference, the dimer impurity of Formula F is difficult to separate from lopinavir by normal purifications techniques.

The present inventors have surprisingly found that treating the lopinavir containing substantial amount of dimer impurity of Formula F with a suitable base converts the impurity of Formula F in to lopinavir.

In another embodiment, the present invention provides a process for preparation of lopinavir of Formula I substantially free of a compound of Formula F, comprising: reacting lopinavir and a compound of Formula F with a suitable base in a suitable solvent to obtain lopinavir.

Formula F

The suitable base used herein for preparation of lopinavir of Formula I substantially free of a compound of Formula F include but is not limited to ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert-butoxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, triethylamine, isopropyl ethylamine, diisopropyl amine, diisopropyl ethylamine, N-methyl morpholine, piperidine, pyridine and the like and mixtures thereof. Preferably the base is ammonia. The suitable solvent used herein for preparation of lopinavir of Formula I substantially free of a compound of Formula F include but is not limited to alcohols, ethers, halogenated hydrocarbons, esters, ketones or mixtures thereof. The alcohols include, but are not limited to methanol, ethanol, propanol, isopropanol and the like; ethers include, but are not limited to tetrahydrofuran, dimethoxyethane, dimethyl ether, diisopropyl ether, methyl tertiary butyl ether, l,4-dioxane and the like; halogenated hydrocarbons include, but are not limited to methylene chloride, ethylene chloride and the like; esters include, but are not limited to ethyl acetate, methyl acetate, isopropyl acetate and the like; ketones include, but are not limited to acetone, methyl isobutyl ketone, methyl ethyl ketone and the like and mixtures thereof. Preferably the solvent is alcohol and more preferably methanol.

The reaction of a mixture of lopinavir and a compound of Formula F with a suitable base is carried out at a temperature of about 25 °C to about 60°C. Preferably the reaction is carried out at about 35°C to about 50°C

After completion of the reaction, the reaction mass may be subjected to evaporation under vacuum at below 60°C and treating the residue with a mixture of suitable water immiscible organic solvent; preferably methyl tertiary butyl ether, diethyl ether, ethyl acetate, methylene chloride, chloroform toluene, xylene and the like; more preferably methyl tertiary butyl ether and water. Then the product containing organic layer may be separated and the lopinavir can be isolated by conventional techniques known in the art, for example, precipitation, evaporation and the resultant product may optionally be further dried.

In another embodiment, lopinavir obtained by the processes described as above, having purity of at least about 99% as measured by HPLC, preferably at least about 99.9% as measured by HPLC and substantially free of impurity of Formula A or Formula B or Formula C or Formula D or Formula E or Formula F; wherein the word "substantially free" refers to lopinavir having less than about 0.15% of Formula A or Formula B or Formula C or Formula D or Formula E or Formula F as measured by HPLC, preferably less than about 0.1% of Formula A or Formula B or Formula C or Formula D or Formula E or Formula F as measured by HPLC; more preferably less than about 0.05% of Formula A or Formula B or Formula C or Formula D or Formula E or Formula F as measured by HPLC; still more preferably less than about 0.02% of Formula A or Formula B or Formula C or Formula D or Formula E or Formula F as measured by HPLC.

In another embodiment, the present invention provides a pharmaceutical composition, comprising lopinavir prepared by the processes of the present invention and at least one pharmaceutically acceptable excipient. Advantageous of the present invention:

• Provides a simple and efficient process for the preparation of pure lopinavir and its intermediates.

• Provides a process for purification of Formula III by formation of tartarate salt, which substantially removed the unreacted starting material and impurities including diastereomers, which are otherwise not removable by methods known in the art.

• Provides a process for preparation of Formula III free from N-acetyl impurity of Formula A, by replacing the acetate solvents with ether solvents during neutralization Formula IILsalt.

• Provides a process for preparation of lopinavir free from dimer impurity of Formula F, by treating a mixture of lopinavir and dimer impurity of Formula F with a suitable base.

The X-Ray powder diffraction can be measured using PANalytical X’per pro X-ray powder Diffractometer equipped with a Cu-anode ([l] =1.54 Angstrom), X-ray source operated at 45kV, 40 mA. Two-theta calibration is performed using an NIST SRM 640c Si standard. The sample was analyzed using the following instrument parameters: measuring range=3-45°20; step size=0.0l°; and Time per step=50 sec.

The DSC data reported herein is analyzed in hermitically sealed aluminium pan, with a blank hermitically sealed aluminium pan as the reference and were obtained using DSC (DSC Q200, TA instrumentation, Waters) at a scan rate of l0°C per minute with an Indium standard.

The present invention provides lopinavir and its intermediates, obtained by the above process, as analyzed using high performance liquid chromatography (“HPLC”) with the conditions are tabulated below:

EXAMPLES

The present invention is further illustrated by the following examples, which are provided by way of illustration only and should not be construed to limit the scope of the invention.

EXAMPLE 1:

Preparation of Formula III. Tartrate

In a round bottom flask, sodium borohydride (78g) and l,2-dimethoxy ethane (1650 mL) were charged and a solution of methane sulphonic acid (468 g) in l,2-dimethoxy ethane (420 mL) was added at -l2±3°C. Further, a solution of Formula II (300g) in a mixture of l,2-dimethoxy ethane (630 mL) and isopropanol (375 mL) was added to the reaction mass at 20-25°C and stirred for 6hrs at same temperature. After completion of reaction, a solution of triethanolamine (318g), in l,2-dimethoxy ethane (375 mL) was added to the reaction mass dropwise, and the mixture stirred for 1 hr at l5-20°C. A solution of sodium borohydride (54.3g), in l,2-dimethoxy ethane (600 mL), was added and the mixture stirred for 3h. After completion of reaction, water (3000 mL) was added to the reaction mass and stirred for 45 min and then the reaction mass extracted with methyl tert-butyl ether (3000 mL). The organic layer was subjected to multiple aqueous washings, and then the combined organic layer temperature was raised to 43±3°C, L-Tartaric acid (88g) was added and the temperature of the mixture was further raised to mild reflux. The mixture was seeded (0.6g), maintained for 2h, cooled to 20±3°C and slurred for another 5h. Precipitated solid was filtered and dried at 60-65°C under vacuum to get the title compound. Yield: 315 g; HPLC purity: 99.0%; diastereomer- 1 by HPLC: 0.24%; diastereomer-2 by HPLC: 0.16%; diastereomer-3 by HPLC: 0.38%; Formula II by HPLC: Not detected; PXRD: Fig. 1; DSC: Fig. 2.

EXAMPLE 2:

Preparation of pyroglutamic acid salt of Formula VI

In a round bottom flask, Formula III. Tartrate (300 g), 8% aq sodium bicarbonate (1500 mL) and methyl tert-butyl ether (1500 mL) were charged at 25-35°C and stir for 60 min at same temperature. After completion of neutralization, organic layer was separated and transferred in to another reaction flask and heated to 45-50°C. To the reaction mass added a solution of compound of Formula IV (124 g) and carbonyl di-imidazole (109 g) in a mixture of tetrahydrofuran (300 mL), methyl tert-butyl ether (600 mL) and water (3 mL) at 55-60°C and stir for 5-6 hrs at same temperature. After completion of reaction, reaction mass allowed to cool to 25-35°C and washed the reaction mass with water. Then the organic layer was separated and concentrated under vacuum at below 55°C to obtain residue. Then the residue was dissolved in methanol (1500 mL) and to the reaction mass ammonium formate (95.4 g), 5% Pd/C (30 g) were charged at same temperature and allowed to stir for 6-8 hrs at 50-55°C. After completion of reaction, reaction mass was filtered through hyflo bed and concentrated the solvent under vacuum at below 60°C to obtain residue. Then the residue was dissolved in dimethyl formamide (300 mL) and ethyl acetate (1500 mL) at 50-55°C. To the reaction mass a solution of L-pyroglutamic acid (60 g) in dimethyl formamide (300 mL) was added at 50-55°C and stir for 60 min at same temperature. Reaction mass temperature was cool to 20-25°C and stir for 5-6 hrs at same temperature. Precipitated solid was filtered and dried at 60-65°C under vacuum to get the title compound. Yield: 285 g; HPLC purity: 99.0%; Formula A by HPLC: 0.03%; Formula B by HPLC: 0.03%; and Formula C by HPLC: 0.03%.

EXAMPLE 3:

Preparation of lopinavir

2,6-dimethylphenoxyacetic acid (28.7 g), ethyl acetate (100 mL), thionyl chloride (25 g) and dimethyl formamide (1 mL) were charged in reaction flask at 25-35°C. Reaction mass was heated to 50-55°C and stirred for 2-3 hrs at same temperature, and then added to a mixture of pyroglutamic acid salt of Formula VI (100 g), ethyl acetate (750 mL), water (750 mL) and sodium bicarbonate (82.5 g) at 25-35°C and stir for 60 min at same temperature. After completion of the reaction, organic layer was separated and treated with 5% sodium bicarbonate solution (25 g dissolved in 500 mL). Then the organic layer was separated and concentrated under vacuum at below 60°C to get the title compound as a residue. Yield: 100 g; HPLC purity: 99%; Formula D by HPLC: 0.15%; Formula E by HPLC: Not detected; and Formula F by HPLC: 0.8%.

The above lopinavir (100 g) was dissolved in methanol (300 mL) and ammonia (100 mL) was charged and the reaction mass was heated to 40-45°C for 1-2 hrs at same temperature. After completion of the reaction, solvent was concentrated under vacuum at below 60°C to obtain residue. To the obtained residue methylene chloride (400 mL) and water (200 mL) were charged at 25-35°C. Then the product containing organic layer was speared and concentrated under vacuum at below 45°C. The obtained solid was dissolved in acetone (200 mL) at 50-55°C for 30-60 min. Reaction mass was gradually cool to 0- 5°C and the precipitated solid was filtered and washed with chilled acetone (100 mL) and dried at 30-35°C under vacuum to get the title compound. Yield: 90 g; HPLC purity: 99.9%; Formula A by HPLC: Not detected; Formula B by HPLC: Not detected; Formula C by HPLC: Not detected; Formula D by HPLC: 0.02%; Formula E by HPLC: Not detected; and Formula F by HPLC: Not detected.

EXAMPLE 4:

Preparation of di-benzoyl-tartaric acid salt of Formula III

Sodium borohydride (2.6 g) and l,2-dimethoxy ethane (55 mL) were charged in to a reaction flask and cool to -10 to -15°C. To the reaction mass, solution of methane sulphonic acid (10.6 mL) in l,2-dimethoxy ethane (14 mL), a solution of compound of Formula II (10 g) in a mixture of l,2-dimethoxy ethane (21 mL) and isopropanol (12.5 mL) were charged at 25 °C and allowed to stir for 6 hrs at 20°C to 25 °C. After completion of the reaction, temperature was allowed to cool -5°C and charged a solution of triethanolamine (10.6 g) in l,2-dimethoxy ethane (10 mL) and sodium borohydride (1.8 g) in dimethyl acetamide (20 mL) at below l0°C and stirred for 4 hrs at l5°C to 20°C. After completion of the reaction, water (100 mL) and the product was extracted with methyl tert-butyl ether (100 mL). The organic layer was treated with 10% sodium hydroxide solution (50 mL), 10% sodium chloride solution (50 mL) and water (50 mL). To the organic layer charged di-benzoyl-tartaric acid (6.6 g) at 25°C to 30°C and stirred for 30 min at same temperature. Precipitated solid was filtered and washed with methyl tert-butyl ether (20 mL) and dried at 50-55°C under vacuum to get the title compound. Yield: 8.2 g; HPLC purity: 91.6 %; diastereomer- 1 by HPLC: 1.6 %; diastereomer-2 by HPLC: 4.2%; diastereomer- 3 by HPLC: 0.6%.

EXAMPLE 5:

Preparation of fumaric acid salt of Formula III

Sodium borohydride (2.6 g) and l,2-dimethoxy ethane (55 mL) were charged in to a reaction flask and cool to -10 to -l5°C. To the reaction mass, solution of methane sulphonic acid (10.6 mL) in l,2-dimethoxy ethane (14 mL), a solution of compound of Formula II (10 g) in a mixture of l,2-dimethoxy ethane (21 mL) and isopropanol (12.5 mL) were charged at 25 °C and allowed to stir for 6 hrs at 20°C to 25 °C. After completion of the reaction, temperature was allowed to cool -5°C and charged a solution of triethanolamine (10.6 g) in l,2-dimethoxy ethane (10 mL) and sodium borohydride (1.8 g) in dimethyl acetamide (20 mL) at below l0°C and stirred for 4 hrs at l5°C to 20°C. After completion of the reaction, water (100 mL) and the product was extracted with methyl tert-butyl ether (100 mL). The organic layer was treated with 10% sodium hydroxide solution (50 mL), 10% sodium chloride solution (50 mL) and water (50 mL). To the organic layer charged fumaric acid (1 g) at 25°C to 30°C and stirred for 30 min at same temperature. Precipitated solid was filtered and washed with methyl tert-butyl ether (20 mL) and dried at 50-55°C under vacuum to get the title compound. Yield: 6.2 g; HPLC purity: 84.1 %; diastereomer- 1 by HPLC: 6.5 %; diastereomer-2 by HPLC: 3.3 %; diastereomer-3 by HPLC: 1.4%; and Formula II by HPLC: 0.8%.

COMPARATIVE EXAMPLE 1:

Preparation of L-pyroglutamic acid of Formula III

Sodium borohydride (28 g) and l,2-dimethoxy ethane (550 mL) were charged in to a reaction flask and cool to -10 to -l5°C. To the reaction mass, solution of methane sulphonic acid (105.5 mL) in l,2-dimethoxy ethane (140 mL), a solution of compound of Formula II (100 g) in a mixture of l,2-dimethoxy ethane (210 mL) and isopropanol (125 mL) were charged at 25 °C and allowed to stir for 6 hrs at 20°C to 25 °C. After completion of the reaction, temperature was allowed to cool -5°C and charged a solution of triethanolamine (106 g) in l,2-dimethoxy ethane (100 mL) and sodium borohydride (18 g) in dimethyl acetamide (200 mL) at below l0°C and stirred for 4 hrs at l5°C to 20°C. After completion of the reaction, water (1 lit) and the product was extracted with methyl tert-butyl ether (1 lit). The organic layer was treated with 10% sodium hydroxide solution (500 mL), 10% sodium chloride solution (500 mL) and water (500 mL). The product containing organic layer was concentrated under vacuum at below 50°C to obtain residue. The obtained residue was dissolved in ethyl acetate (1 lit) at 55-60°C and L- pyroglutamic acid (25 g) was added to the reaction mass and stir for 1 hrs at same temperature for 2 hrs. Then the temperature was cool to 25-35°C and the precipitated solid was filtered and washed with ethyl acetate (200 mL) and dried at 50-60°C under vacuum to get the title compound. Yield: 95 g; HPLC purity: 90.2 %; diastereomer-l by HPLC: 5.5 %; diastereomer-2 by HPLC: 1.2 %; diastereomer-3 by HPLC: 1.5 %.

COMPARATIVE EXAMPLE 2:

Preparation of pyroglutamic acid salt of Formula VI

Sodium bicarbonate (13.7 g), pyroglutamic acid salt of Formula III (95 g), ethyl acetate (475 mL) and water (475 mL) were charged in to a reaction flask at 25-35°C and stir for 60 min at same temperature. After completion of neutralization, organic layer was separated and transferred in to another reaction flask and heated to 70-75°C. To the reaction mass added a solution of compound of Formula IV (36.9 g) and carbonyl di imidazole (32.4 g) in a mixture of ethyl acetate (190 mL) and water (1 mL) at 70-75°C and stir for 1 hr at 50-55°C. After completion of reaction, reaction mass allowed to cool to 25-35°C and washed the reaction mass with water. Then the organic layer was separated and concentrated under vacuum at below 55°C to obtain residue. Then the residue was dissolved in methanol (500 mL) at 50-55°C. Reaction mass was cool to 30- 35°C, ammonium formate (30.3 g), 5% Pd/C (9.5 g) were charged at same temperature and allowed to stir for 6-8 hrs at 30-35°C. After completion of reaction, reaction mass was filtered through hyflo bed and concentrated the solvent under vacuum at below 50°C to obtain solid as foam. Then the foam was dissolved in dimethyl formamide (95 mL) and ethyl acetate (475 mL) at 50-55°C. To the reaction mass a solution of L- pyroglutamic acid (18.4 g) in dimethyl formamide (95 mL) was added at 50-55°C and stir for 60 min at same temperature. Reaction mass temperature was cool to 30-35°C and stir for 5-6 hrs at same temperature. Precipitated solid was filtered and washed with a mixture of dimethyl formamide (95 mL), ethyl acetate (190 mL) and dried at 55-60°C under vacuum to get the title compound. Yield: 91 g; HPLC purity: 98.5%; Formula A by HPLC: 0.5%; Formula B by HPLC: 0.5%; and Formula C by HPLC: 0.3%.

COMPARATIVE EXAMPLE 3:

Preparation of lopinavir 2,6-dimethylphenoxyacetic acid (15.13 g), ethyl acetate (50 mL), thionyl chloride (12.48 g) and dimethyl formamide (0.5 mL) were charged in reaction flask at 25-35°C. Reaction mass was heated to 50-55°C and stirred for 2-3 hrs at same temperature. Then the reaction mass was allowed cool to 20-25 °C and added to the separately prepared bi- phasic mixture of pyroglutamic acid salt of Formula VI (50 g) in ethyl acetate (375 mL), water (375 mL) and sodium bicarbonate (41.2 g) at 20-25°C and stirred for 1 hour at same temperature. Organic layer was separated and washed with 5% sodium bicarbonate (250 mL) and 5% sodium chloride (250 mL). Then the organic layer was separated and concentrated at below 50°C to obtain foam solid. To the solid ethyl acetate (100 mL) was charged at 25-30°C and heated to 55-60°C and charged n-heptane (200 mL) at 55-60°C and stirred for 1 hour at same temperature. Reaction mass was allowed to cool 20-25°C and stirred for 8 hrs at same temperature. Precipitated solid was filtered washed with a mixture of ethyl acetate and n-heptane (1:1, 50mL), dryed under vacuum at 50-55°C to get the title compound. Yield: 39 g; HPLC purity: 94%; Formula D by HPLC: 0.5%; Formula E by HPLC: 0.2%; and Formula F by HPLC: 3%.

It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore the above description should not be constructed as limiting, but merely as exemplifications of preferred embodiments. For example, the functions described above and implemented as the best mode for operating the present invention are for illustration purposes only. Other arrangements and methods may be implemented by those skilled in the art without departing from the scope and spirit of this invention. Moreover, those skilled in the art will envision other modifications within the scope and spirit of the specification appended hereto.

Claims

WE CLAIM

1. A process for preparation of lopinavir of Formula I,

Formula I

comprising:

Formula II Formula III

Formula III.Tartrate

c) treating the compound of Formula III.Tartrate with a suitable base to obtain a compound of Formula

Formula III d) reacting the compound of Formula III with a compound of Formula IV in presence of a suitable coupling agent in an ether solvent to obtain a compound of Formula V, and

Formula IV Formula V

e) converting the compound of Formula V in to lopinavir.

2. The process as claimed in claim 1, wherein the reducing agent of step a) is sodium borohydride and the solvent is a mixture of l,2-dimethoxy ethane and isopropanol.

3. The process as claimed in claim 1, wherein the organic solvent of step b) is selected from the group consisting of methanol, ethanol, propanol, isopropanol, methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2- methyltetrahydrofuran, l,4-dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane, methylene chloride, ethylene chloride, acetone, methyl isobutyl ketone, methyl ethyl ketone and mixtures thereof.

4. The process as claimed in claim 1, wherein the base of step c) is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert- butoxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, triethylamine, isopropyl ethylamine, diisopropyl amine, diisopropyl ethylamine, N-methyl morpholine, piperidine, pyridine and mixtures thereof.

5. The process as claimed in claim 1, wherein the step b) is carried out in methyl tertiary butyl ether at a temperature of about 25°C to reflux.

6. The process as claimed in claim 1, wherein the step c) is carried out with sodium bicarbonate at a temperature of about 25°C to about 50°C.

7. The process as claimed in claim 1, wherein the coupling agent of step d) is selected from the group consisting of N-(3-dimethylaminopropyl)-N’- ethylcarbodiimide, 1,1 '-carbonyl diimidazole, carbonyl di imidazole, diisopropyl carbodiimide, dicyclohexyl carbodiimide and mixture thereof.

8. The process as claimed in claim 1, wherein the ether solvent of step d) is selected from the group consisting of methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, l,4-dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane and mixtures thereof.

9. The process as claimed in claim 1, wherein the coupling agent is carbonyl di imidazole, ether solvent is a mixture of methyl tertiary butyl ether, tetrahydrofuran.

10. The process as claimed in claim 1, wherein the step d) is carried out at a temperature of at a temperature of about 25 °C to reflux.

11. A process for preparation of lopinavir of Formula I substantially free of a compound of Formula F, comprising: reacting lopinavir and a compound of Formula F with a suitable base in a suitable solvent to obtain lopinavir.

Formula F

12. The process as claimed in claim 11, wherein the base is selected from the group consisting of ammonia, lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert-butoxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, triethylamine, isopropyl ethylamine, diisopropyl amine, diisopropyl ethylamine, N-methyl morpholine, piperidine, pyridine and mixtures thereof.

13. The process as claimed in claim 11, wherein the solvent is selected from the group consisting of methanol, ethanol, propanol, isopropanol, tetrahydrofuran, dimethoxyethane, dimethyl ether, diisopropyl ether, methyl tertiary butyl ether, l,4-dioxane, methylene chloride, ethylene chloride, ethyl acetate, methyl acetate, isopropyl acetate, acetone, methyl isobutyl ketone, methyl ethyl ketone and mixtures thereof.

14. The process as claimed in claim 11, wherein the base is ammonia and solvent is methanol.

15. The process as claimed in claim 11, wherein the reaction is carried out at a temperature of at a temperature of about 25 °C to about 60°C.

16. The process as claimed in claim 11, wherein the process further comprises:

i) evaporating the reaction mixture obtained by the process of claim 11 to obtain a residue,

ii) treating the residue with a mixture of suitable water immiscible organic solvent and water,

iii) separating the water immiscible organic solvent, and

iv) isolating the lopinavir of Formula I.

17. The process as claimed in claim 16, wherein the evaporation is carried out at below 60°C under vacuum.

18. The process of claim 16, wherein the water immiscible organic solvent is selected from the group consisting of methyl tertiary butyl ether, diethyl ether, ethyl acetate, methylene chloride, chloroform, toluene, xylene.

19. A process for preparation of lopinavir of Formula I: comprising:

a) reacting a compound of Formula III with L-tartaric acid in a suitable organic solvent to obtain Formula III. Tartrate,

c) converting the compound of Formula III to lopinavir.

20. The process as claimed in claim 19, wherein the organic solvent is selected from the group consisting of methanol, ethanol, propanol, isopropanol, methyl ethyl ether, methyl tertiary butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4- dioxane, cyclopentyl methyl ether, dimethoxymethane, di-tert-butyl ether, methoxyethane, methylene chloride, ethylene chloride, acetone, methyl isobutyl ketone, methyl ethyl ketone and mixtures thereof.

21. The process as claimed in claim 19, wherein the base is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium tert-butoxide, sodium carbonate, potassium carbonate, cesium carbonate, sodium bicarbonate, potassium bicarbonate, triethylamine, isopropyl ethylamine, diisopropyl amine, diisopropyl ethylamine, N-methyl morpholine, piperidine, pyridine and mixtures thereof.

22. The process as claimed in claim 19, wherein the organic solvent is methyl tertiary butyl ether and the base is sodium bicarbonate.

23. A compound of Formula III. Tartrate.

Formula III. Tartrate

24. The compound as claimed in claim 23, wherein the compound of Formula III.

Tartrate is characterized by a powder X-Ray diffraction (PXRD) pattern substantially in accordance with Figure 1.

25. The compound as claimed in claim 23, wherein the compound of Formula III.

Tartrate is characterized by differential scanning calorimetry (DSC) substantially in accordance with Figure 2.