WO2018158697A1 - A process for the preparation of ixazomib citrate - Google Patents

A process for the preparation of ixazomib citrate Download PDF

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WO2018158697A1
WO2018158697A1 PCT/IB2018/051268 IB2018051268W WO2018158697A1 WO 2018158697 A1 WO2018158697 A1 WO 2018158697A1 IB 2018051268 W IB2018051268 W IB 2018051268W WO 2018158697 A1 WO2018158697 A1 WO 2018158697A1
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Prior art keywords
formula
compound
ilia
reacting
ila
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PCT/IB2018/051268
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French (fr)
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Maneesh Kumar PANDEY
Sonu Prasad Shukla
Raj Narayan TIWARI
Sarbjot Singh Sokhi
Govind Singh
Saswata Lahiri
Walter Cabri
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Fresenius Kabi Oncology Limited
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic System
    • C07F5/02—Boron compounds
    • C07F5/025—Boronic and borinic acid compounds
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
    • C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
    • C07D233/56—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring carbon atoms
    • C07D233/60—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring carbon atoms with hydrocarbon radicals, substituted by oxygen or sulfur atoms, attached to ring nitrogen atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07B—GENERAL METHODS OF ORGANIC CHEMISTRY; APPARATUS THEREFOR
    • C07B2200/00—Indexing scheme relating to specific properties of organic compounds
    • C07B2200/13—Crystalline forms, e.g. polymorphs

Definitions

  • the present invention relates to a process for the preparation of compound formula I,
  • R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid.
  • the present process relates to preparation of Ixazomib citrate of compound of formula la,
  • the process comprises the use of diimidazole or ditriazole based coupling reagent for amide and peptide bond formation.
  • the present process is more economical and less time consuming than processes described in the literature due to easier isolation of intermediates and Ixazomib of compound of formula,
  • the present invention also relates to preparation and isolation of an amorphous form of Ixazomib citrate of formula la.
  • Ixazomib citrate is boronic ester compound and marketed as Ninlaro ® , it is structurally known as compound of formula la,
  • the Ixazomib citrate is an antineoplastic agent and works as pro drug. After oral administration it rapidly hydrolyzes to its biologically active form, Ixazomib of formula,
  • the ixazomib citrate is R- stereoisomer and chemically known as 1,3,2- dioxaborolane-4,4-diacetic acid, 2-[(lR)-l-[[2-
  • WO2009/154737A1 The boronic ester compounds, particularly the Ixazomib citrate as represented by formula la, is disclosed in WO2009/154737A1 (hereinafter referred as WO 737).
  • the synthetic scheme described in WO2009/154737A1 is depicted below as scheme - 1 :
  • the amide bond is formed by reacting 2,5-dichlorobenzoyl chloride with glycine under basic environment at 0+1 °C.
  • the preparation of 2,5- dichlorobenzoyl chloride is not disclosed in WO 37; however, commonly known reagents like thionyl chloride or oxalyl choride are extensively used in industry for the formation of acid chloride from their acid precursors.
  • the reagents like thionyl chloride or oxalyl choride are hazardous and not advisable at large scale production.
  • the peptide bond is formed by reacting 2,5- [(dichlorobenzoyl)amino] acetic acid with trifluoroacetic acid salt of (lR)-3- methyl- l-[(3aS,4S,6S,7aR)-3a,5,5-trimethylhexahydro-4,6-methano- 1,3,2- benodioxaborol-2-yl]butan-l-amine in presence of coupling reagent O- (Benzotriazol-l-yl)-N,N,N N-tetramethyluronium tetrafluoroborate (TBTU) and diisopropylethylamine (DIPEA) base in dimethylformamide. After completion of the reaction the mixture is diluted with ethyl acetate then washed multiple times, with sodium chloride, potassium carbonate and phosphoric acid.
  • TTU Triazol-l-yl
  • DIPEA diisopropylethylamine
  • the obtained benzamide compound is further dissolved in methanol/hexane mixture and stirred overnight in presence of (2-methylpropyl)boronic acid ((iBuB(OH) 2 ) to form Ixazomib (a free boronic acid derivative) or its boroxine derivative.
  • (2-methylpropyl)boronic acid ((iBuB(OH) 2 )
  • Ixazomib a free boronic acid derivative
  • the isolation of these derivatives requires long acid-base processing of the reaction mixture, which is tedious and time consuming.
  • the isolated Ixazomib or its boroxine derivative is further reacted with citric acid in ethyl acetate (EtOAc) to form Ixazomib citrate, which is isolated in two different crystalline forms I and II by controlling the process of cooling of the reaction mixture.
  • EtOAc ethyl acetate
  • the WO ⁇ 677 further discloses the process of preparation of amorphous form of Ixazomib citrate by lyophilisation of a freeze- dried solution.
  • the inventors of the present application have developed a process which preferably involves a diimidazole or ditriazole based coupling reagent for the formation of amide and peptide bonds to prepare Ixazomib citrate of compound of formula la.
  • the use of a diimidazole or ditriazole based coupling reagent is advantageous, which devoid the use of hazardous reagent, use of low temperature condition and reduces the long processing time of the reaction mixture for the isolation of intermediates and Ixazomib.
  • the process of present invention is cleaner, more economical, less time consuming and does not require any special instrument as compared to processes described in the literature.
  • the present invention relates to a process for the preparation compound of formula I,
  • R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the steps of: a) reacting a compound of formula Ila,
  • X is imidazole or triazole c) reacting the compound of formula III or formula Ilia with a compound of formula IV or its salt in suitable solvent,
  • R 1 and R 2 are same as defined for the compound of formula I
  • Another aspect of the present invention relates to a process for the preparation of compound of formula I,
  • R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the reaction of a compound of formula Ilia,
  • X is imidazole or triazole with a compound of formula IV or its salt in suitable solvent
  • R 1 and R 2 are same as defined for the compound of formula I
  • Another aspect of the present invention relates to a process for the preparation of a compound of formula Ila,
  • X is imidazole or triazole by reacting a compound of formula II,
  • Another aspect of the present invention relates to a process for the preparation of a compound of formula Ilia,
  • X is imidazole or triazole by reacting a compound of formula III,
  • Another aspect of the present invention relates to use of compound of formula Ila and/or Ilia,
  • Yet another aspect of the present invention relates to an amorphous
  • Formula la Still yet another aspect of the present invention relates to preparation amorphous form of compound of formula la,
  • FIG. 1 is an illustration of an X-ray powder diffraction (PXRD) pattern of an amorphous form of compound of formula la
  • FIG. 2 is an illustration of a Differential Scanning Calorimetry (DSC) of an amorphous form of compound of formula la
  • FIG. 3 is an illustration of a Thermogravimetric analysis (TGA) of an amorphous form of compound of formula la
  • FIG. 4 is a schematic representation of preferred embodiments of the process of preparation of a compound of formula I and la
  • Amorphous _ refers to a solid state form of a compound of formula la wherein the three dimensional structure positions of the molecules relative to one another are essentially random, [for example, see Hancock et al. "Characteristics and significance of the amorphous state in pharmaceutical systems" J. Pharm. Sci. Vol. 86, pp. 1-12 (1997)].
  • amorphous material will have only liquid-like short range order, and, when examined by X-ray diffraction (XRPD), will generally produce broad, diffuse scattering will result in peak intensity sometimes centered on one or more amorphous halos.
  • XRPD analysis of amorphous material will provide a 2-theta pattern with one or more broad bands with no distinctive peaks.
  • the " Amorphous _ compound of formula la may sometimes be characterized by its glass transition temperature (Tg), which defines a pseudo second order phase transition in which a super cooled melt of formula la yields, on cooling, a glassy structure with properties similar to those of crystalline compound of formula la.
  • Tg glass transition temperature
  • Tg is a kinetic parameter, its value will be dependent on the melt cooling rate and the measurement conditions used for its determination (e.g., the slower the melt cooling rate, the lower Tg will be).
  • the glass transition temperature (Tg) for a sample of amorphous form of compound of formula la may be obtained by differential scanning calorimetry (DSC).
  • amide bond and peptide bond _ are distinguish in the context that amide bond results in amide derivative, which is any derivative of oxoacid in which the hydroxyl group has been replaced with an amino or substituted amino group while peptide bond results in a derivative of at least two amino acids in which the amine of one is reacted with the carboxylic acid of the next to form a peptide bond.
  • alpha-hydro xy carboxylic acid compound _ refers to a compound which contains a carboxylic acid functional group and hydroxy functional group separated by one carbon atom.
  • beta-hydro xy carboxylic acid compound _ refers to a compound which contains a carboxylic acid functional group and hydroxy functional group separated by two carbon atoms.
  • alpha- hydroxy carboxylic acid compound _ and beta-hydroxy carboxylic acid compound _ are not intended to be limited to compounds having only one hydroxyl group and one carboxylic acid group.
  • moiety derived from an alpha-hydroxy carboxylic acid compound refers to a moiety formed by condensation of carboxylic acid and hydroxyl group of an alpha-hydroxy carboxylic acid compound, wherein hydroxyl group of an alpha-hydroxy carboxylic acid compound is present in an alpha position relative to the carboxylic acid group.
  • moiety derived from a beta-hydroxy carboxylic acid compound refers to a moiety formed by condensation of carboxylic acid and hydroxyl group of a beta-hydroxy carboxylic acid compound, wherein hydroxyl group of a beta- hydroxy carboxylic acid compound is present in a beta position relative to the carboxylic acid group.
  • One aspect of the present invention relates to a process for organic synthesis, more particularly for the synthesis of amide and peptide bonds, and new intermediates of compound of formula I,
  • R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or derived from a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R together form the boronate esters of boronic acid.
  • the boronate esters of boronic acid of formula I contain a derivative which may be formed by reacting the acid groups of the boronic acid with a hydroxy compound.
  • Preferred hydroxy compounds are dihydroxy compounds, especially pinacol, perfluoropinacol, pinanediol, ethylene glycol, diethylene glycol, 1,2-cyclohexanediol, 1,3-propanediol, 2,3-butanediol, glycerol or diethanolamine.
  • the present invention involves efficient methods for formation of amide and peptide bonds to prepare compound of formula I.
  • the amide bond is formed by reacting a compound of formula Ila,
  • X is imidazole or triazole with glycine to form a compound of formula III;
  • the peptide bond is formed by reacting a compound of formula Ilia,
  • X is imidazole or triazole with compound of formula IV or its salt to obtain a compound of formula I.
  • the compound of formula Ila and Ilia are activated carboxylic acid derivatives. These derivatives are typically formed by reacting their corresponding acid compound of formula II or III,
  • the present process resides in a novel and improved method of producing activated carboxylic acid group with diimidazole or ditriazole based coupling reagent.
  • the diimidazole or ditriazole based coupling reagent may be selected from the group consisting of 1,1 " carbonyldiimidazole (CDI), 1,1 " -carbonyldi- (1,2,4-triazole), 1,1 " thiocarbonyldiimidazole and 1,1 " oxalyldiimidazole.
  • CDI carbonyldiimidazole
  • thiocarbonyldiimidazole 1,1 " oxalyldiimidazole.
  • diimidazole based coupling reagents Particular preference is given to 1,1 " carbonyldiimidazole (CDI).
  • the other coupling reagents may also be utilized for producing the activated carboxylic acid group of the compounds of present invention.
  • These coupling reagent may be selected from the group consisting of carbodiimide such as ⁇ , ⁇ '- dicyclohexylcarbodiimide (DCC), ⁇ , ⁇ '-diisopropylcarbodiimide (DIC), 1-ethyl- 3-(3-dimethylaminopropyl)carbodiimide (EDC) and the like.
  • the compounds II or III of the present invention react readily with diimidazole or ditriazole based coupling reagent to form carbon dioxide and imidazole or triazole as by-products.
  • the carbon dioxide is gaseous by-product, which is easily removed from the reaction mixture wherein imidazole or triazole is soluble in water hence does not require any cumbersome methods such as multiple washings with sodium chloride, potassium carbonate and phosphoric acid to remove them from the reaction mixture.
  • diimidazole or ditriazole based coupling reagent for the preparation of activated carboxylic acid compound of formula Ila also avoids the use of hazardous chlorinating reagent such as thionyl chloride or oxalyl chloride for the preparation of acid chloride derivative, 2,5-dichlorobenzoyl chloride.
  • hazardous chlorinating reagent such as thionyl chloride or oxalyl chloride for the preparation of acid chloride derivative, 2,5-dichlorobenzoyl chloride.
  • the problem of handling liquid 2,5-dichlorobenzoyl chloride and maintaining reaction temperature at 0+1 °C during its reaction with glycine are also solved by the process of the present invention.
  • the activation of carboxylic acid group of formula II is typically performed by reacting it with diimidazole or ditriazole based coupling reagent at suitable temperature in suitable solvent, optionally isolating the compound of formula Ila, then reacting it with glycine, preferably for 30 minutes to 5 hours at 0°C to 20°C, particularly preferably for 1 to 2 hours at 0°C to 10°C. It is advantageous to use aqueous alkaline solution of glycine, preferably aqueous sodium hydroxide solution of glycine. After completion of the reaction compound of formula III can be isolated by any known methods of the art.
  • the compound of formula III can be converted to compound of formula I as per the disclosed method of ⁇ * 737.
  • R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid.
  • the boronate esters of boronic acid of formula IV may be formed by reacting the acid groups of the boronic acid with a hydroxy compound.
  • Preferred hydroxy compounds are dihydroxy compounds, especially pinacol, perfluoropinacol, pinanediol, ethylene glycol, diethylene glycol, 1,2-cyclohexanediol, 1,3- propanediol, 2,3-butanediol, glycerol or diethanolamine.
  • the salt of compound of formula IV is trifluoro acetic acid salt of pinanediol derivative of boro leucine of compound of formula IVa,
  • reaction mixture of compound of formula Ilia and IV or IVa is preferably stirred for 30 minutes to 5 hours at 0°C to 20°C, particularly preferably for 1 to 2 hours at 0°C to 10°C.
  • the compound of formula I can be isolated by any known methods of the art.
  • the isolation of resulting compound I, compound of formula Ila and Ilia may be achieved by filtration of precipitated solid by gravity or by suction, distillation, centrifugation, cooling, crystallization, anti-solvent addition, removal of solvent by evaporation or the like.
  • the preparation of compound of formula I may be achieved by filtration of precipitated solid by gravity or by suction, distillation, centrifugation, cooling, crystallization, anti-solvent addition, removal of solvent by evaporation or the like.
  • R 1 and R 2 are other than hydroxyl group or compound of formula I is not a compound of formula la, the resulting compound of formula I may be further hydro lysed with suitable reagent based on the nature of R 1 and R 2.
  • the resulting compound of formula I is pinanediol boronate ester of compound of formula lb,
  • the suitable acid for the hydrolysis may be selected from the group consisting of hydrochloric acid, boric acid, isobutyl boronic acid, paratoluenesulphonic acid (PTSA), phosphoric acid; and mixtures thereof.
  • the strength and concentration of the acids may be varied as per the hydrolysis condition to achieve the desired result.
  • the Ixazomib or its boroxine derivative is further reacted with citric acid in suitable solvent to obtain Ixazomib citrate of formula la.
  • the suitable solvent may be selected from the group consisting of acetone, methyl ethyl ketone, isobutyl methyl ketone; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxyethane; methanol, ethanol, propanol, isopropyl alcohol, n-butanol; ethyl acetate; acetonitrile, propionitrile; dimethylformamide, dimethylacetamide, dimethyl sulfoxide or mixtures thereof.
  • the solvent is acetonitrile during the activation of the carboxylic acid group of compound of formula II or III.
  • the hydrolysis of pinanediol boronate ester of formula lb is preferably carried out in acetonitrile or diisopropyl ether or mixture thereof.
  • the formation of citrate salt of Ixazomib is preferably carried out in acetone.
  • a further aspect of the present invention relates to an amorphous form of Ixazomib citrate of formula la and process of preparation thereof.
  • the amorphous form of Ixazomib citrate of formula la is characterized by the X- ray powder diffraction (PXRD) pattern as shown in Fig. l and/or characterized by the Differential scanning calorimetry (DSC) as shown in Fig.2 and/or characterized by the Thermogravimetric analysis (TGA) as shown in Fig.3.
  • PXRD X- ray powder diffraction
  • DSC Differential scanning calorimetry
  • TGA Thermogravimetric analysis
  • the preparation of an amorphous form of Ixazomib citrate of formula la comprising steps of: a) dissolving a compound of formula la in suitable solvent, b) removing the solvent to isolate the amorphous form of compound of formula la.
  • the suitable solvent for the preparation of amorphous form of a compound of formula la may be selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol, n-butanol; acetone, methyl ethyl ketone, methyl iso butyl ketone (MIBK); ethyl acetate; dichloromethane, chloroform; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxyethane; acetonitrile, propionitrile or mixtures thereof.
  • the solvent is methanol or its mixture with dichloromethane or acetone or ethyl acetate.
  • the solvent is methanol or a methanol/dichloromethane mixture or a methanol/acetone mixture.
  • step a) optionally undissolved particles, if any, may be removed suitably by filtration, centrifugation, decantation, and any other known techniques.
  • the solution can be filtered by passing through paper, glass fiber, or other membrane material, or a clarifying agent such as celite.
  • the filtration apparatus may need to be preheated to avoid premature isolation.
  • step b) the removal of the solvent from solution can be performed by suitable techniques which may be selected from the group consisting of evaporation, evaporation under vacuum, flash evaporation, simple evaporation, rotational drying, agitated nutsche filter drying, pressure nutsche filter drying or any other technique known in the art.
  • the resulting amorphous compound may be optionally further dried. Drying can be carried out in a tray dryer, vacuum oven, air oven, cone vacuum dryer, rotary vacuum dryer, fluidized bed dryer, spin flash dryer, flash dryer, or the like. The drying can be carried out at temperatures of less than about 70°C, or any other suitable temperatures; at atmospheric pressure or under a reduced pressure; as long as the amorphous Ixazomib citrate is not degraded in its quality. The drying can be carried out for any desired times until the required product quality is achieved.
  • XRPD X-ray Powder Diffraction
  • thermogram is recorded from 25°C to 250°C under nitrogen atmosphere of 50 mL/min by using following methodology, a) Equilibrate at 25 °C b) Modulate (+) 1°C every 60 seconds c) Isothermal for 5 minutes d) Ramp 5°C/minutes to 250°C
  • the glass transition temperature (Tg) is observed at 112.06°C.
  • the corresponding thermogram is shown in Fig.2.
  • the thermal gravimetric analysis (TGA Q-500) of amorphous Ixazomib citrate of formula la is conducted on TA Instruments model Q-500.
  • the sample (about 10- 30 mg) is placed in a platinum pan previously tared.
  • the weight loss of the sample is determined by heating the sample from room temperature to 300°C at a heating rate of 10°C/minutes under nitrogen atmosphere of 60 mL/min.
  • the weight loss of Ixazomib citrate of formula la from RT to ⁇ 150°C is found to be 2.52 % w/w and the corresponding thermogram is shown in Fig.3.
  • the Ixazomib (5 g) was added in a solution of citric acid (2.93 g) in acetone (100 mL) at ambient temperature. The reaction mixture was stirred for 30 minutes and filtered. The filtrate was stirred for 4-5 hours. The solid was collected by filtration and dried to give Ixazomib citrate. (Yield- 95 %)
  • Example 5 Preparation of amorphous form of Ixazomib citrate
  • the Ixazomib citrate (2 g) was dissolved in methanol (30 mL) at ambient temperature. The solvent was removed under vacuum at 50-55°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.
  • the Ixazomib citrate (2 g) was dissolved in methanol (15 mL) and dichloromethane (55 mL) at ambient temperature. The solvent was removed under vacuum at 40-50°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.
  • the Ixazomib citrate (2 g) was dissolved in methanol (4 mL) and acetone (40 mL) at ambient temperature. The solvent was removed under vacuum at 50-55°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.

Abstract

The present invention relates to a process for the preparation of compound of formula (I), wherein, R1 and R2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R1 and R2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R1 and R2 together form the boronate esters of boronic acid.

Description

A PROCESS FOR THE PREPARATION OF IXAZOMIB CITRATE
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of compound formula I,
Figure imgf000003_0001
Formula I
wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid.
More particularly, the present process relates to preparation of Ixazomib citrate of compound of formula la,
Figure imgf000003_0002
Formula la
Preferably, the process comprises the use of diimidazole or ditriazole based coupling reagent for amide and peptide bond formation. The present process is more economical and less time consuming than processes described in the literature due to easier isolation of intermediates and Ixazomib of compound of formula,
Figure imgf000004_0001
Ixazomib
The present invention also relates to preparation and isolation of an amorphous form of Ixazomib citrate of formula la.
BACKGROUND OF THE INVENTION
Ixazomib citrate is boronic ester compound and marketed as Ninlaro®, it is structurally known as compound of formula la,
Figure imgf000004_0002
The Ixazomib citrate is an antineoplastic agent and works as pro drug. After oral administration it rapidly hydrolyzes to its biologically active form, Ixazomib of formula,
Figure imgf000004_0003
Ixazomib
The ixazomib citrate is R- stereoisomer and chemically known as 1,3,2- dioxaborolane-4,4-diacetic acid, 2-[(lR)-l-[[2-
[(2,5dichlorobenzoyl)amino]acetyl]amino]-3-methylbutyl]-5-oxo. It is indicated in combination with lenalidomide and dexamethasone for the treatment of patients having multiple myeloma and who have received at least one prior therapy.
The boronic ester compounds, particularly the Ixazomib citrate as represented by formula la, is disclosed in WO2009/154737A1 (hereinafter referred as WO 737). The synthetic scheme described in WO2009/154737A1 is depicted below as scheme - 1 :
Figure imgf000005_0001
Scheme -1 In first step, the amide bond is formed by reacting 2,5-dichlorobenzoyl chloride with glycine under basic environment at 0+1 °C. The preparation of 2,5- dichlorobenzoyl chloride is not disclosed in WO 37; however, commonly known reagents like thionyl chloride or oxalyl choride are extensively used in industry for the formation of acid chloride from their acid precursors. The reagents like thionyl chloride or oxalyl choride are hazardous and not advisable at large scale production.
In second step, the peptide bond is formed by reacting 2,5- [(dichlorobenzoyl)amino] acetic acid with trifluoroacetic acid salt of (lR)-3- methyl- l-[(3aS,4S,6S,7aR)-3a,5,5-trimethylhexahydro-4,6-methano- 1,3,2- benodioxaborol-2-yl]butan-l-amine in presence of coupling reagent O- (Benzotriazol-l-yl)-N,N,N N-tetramethyluronium tetrafluoroborate (TBTU) and diisopropylethylamine (DIPEA) base in dimethylformamide. After completion of the reaction the mixture is diluted with ethyl acetate then washed multiple times, with sodium chloride, potassium carbonate and phosphoric acid.
The resulting organic layer is concentrated to a thick oil, diluted with heptane and evaporated to yield 2,5-dichloro-N-[2-({(lR)-3-methyl-l-[(3aS,4S,6S,7aR)- 3a,5,5- trimethylhexahydro-4,6-methano-l,3,2-benzodioxaborol-2- yl]butyl}amino)-2-oxoethyl]benzamide. The obtained benzamide compound is further dissolved in methanol/hexane mixture and stirred overnight in presence of (2-methylpropyl)boronic acid ((iBuB(OH)2) to form Ixazomib (a free boronic acid derivative) or its boroxine derivative. The isolation of these derivatives requires long acid-base processing of the reaction mixture, which is tedious and time consuming. The isolated Ixazomib or its boroxine derivative is further reacted with citric acid in ethyl acetate (EtOAc) to form Ixazomib citrate, which is isolated in two different crystalline forms I and II by controlling the process of cooling of the reaction mixture.
The process disclosed in \νθ 737 suffers from following disadvantages;
1) The 2,5-dichlorobenzoyl chloride is liquid above 30°C, which is difficult to handle at large scale production.
2) The reaction of 2,5-dichlorobenzoyl chloride with glycine is performed at 0+1 °C, which is tedious to maintain at large scale production. 3) The use of coupling reagent such as 0-(Benzotriazol-l-yl)-N,N,N N→ tetramethyluronium tetrafluoroborate (TBTU) during the peptide bond formation is not advisable, the TBTU and its by-products such as hydroxybenzotriazole (HOBt) are not water soluble. Hence removal of these from the reaction mixture requires very long and tedious processing steps like multiple washings with sodium chloride, potassium carbonate and phosphoric acid, which is time consuming and equally not economical.
4) The use of costly reagents such as (2-methylpropyl)boronic acid ((iBuB(OH)2) for the hydrolysis to form Ixazomib is also not advisable. The use of (2-methylpropyl)boronic acid requires long acid-base treatment of the reaction mixture before the isolation of Ixazomib.
WO2016/165677A1 (hereinafter referred as WO "677) discloses an amorphous form of Ixazomib citrate characterized by an X-ray pattern and glass transition temperature Tg=104.1°C. The WO~677 further discloses the process of preparation of amorphous form of Ixazomib citrate by lyophilisation of a freeze- dried solution.
The process disclosed in WO "677 involves the use of special instrument for lyophilisation of the freeze-dried solution, which is difficult to use and not viable at industrial scale production.
As evident from the above discussion the disclosed processes of WO*737 and WO "677 suffer from many disadvantages; hence, there is a need to develop a process for the preparation of boronic ester compound such as Ixazomib citrate and its amorphous form.
The inventors of the present application have developed a process which preferably involves a diimidazole or ditriazole based coupling reagent for the formation of amide and peptide bonds to prepare Ixazomib citrate of compound of formula la. The use of a diimidazole or ditriazole based coupling reagent is advantageous, which devoid the use of hazardous reagent, use of low temperature condition and reduces the long processing time of the reaction mixture for the isolation of intermediates and Ixazomib. Further, the process of present invention is cleaner, more economical, less time consuming and does not require any special instrument as compared to processes described in the literature.
SUMMARY OF THE INVENTION
In a first aspect, the present invention relates to a process for the preparation compound of formula I,
Figure imgf000008_0001
Formula I wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the steps of: a) reacting a compound of formula Ila,
Figure imgf000008_0002
Formula Ila wherein, X is imidazole or triazole with glycine in suitable solvent to obtain a compound of formula III,
Figure imgf000009_0001
Formula III
b) optionally, converting the compound of formula III to a compound of formula Ilia,
Figure imgf000009_0002
Formula Ilia
wherein, X is imidazole or triazole c) reacting the compound of formula III or formula Ilia with a compound of formula IV or its salt in suitable solvent,
Figure imgf000009_0003
Formula IV
wherein, R 1 and R 2 are same as defined for the compound of formula I
to obtain the compound of formula I. Another aspect of the present invention relates to a process for the preparation of compound of formula I,
Figure imgf000010_0001
Formula I
wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the reaction of a compound of formula Ilia,
Figure imgf000010_0002
Formula Ilia
wherein, X is imidazole or triazole with a compound of formula IV or its salt in suitable solvent,
Figure imgf000010_0003
Formula IV
wherein, R 1 and R 2 are same as defined for the compound of formula I
to obtain the compound of formula I. Another aspect of the present invention relates to a process for the preparation of a compound of formula Ila,
Figure imgf000011_0001
Formula Ila
wherein, X is imidazole or triazole by reacting a compound of formula II,
Figure imgf000011_0002
Formula II
with diimidazole or ditriazole based coupling reagent in suitable solvent.
Another aspect of the present invention relates to a process for the preparation of a compound of formula Ilia,
Figure imgf000011_0003
Formula Ilia
wherein, X is imidazole or triazole by reacting a compound of formula III,
Figure imgf000012_0001
Formula III
with diimidazole or ditriazole based coupling reagent in suitable solvent.
Another aspect of the present invention relates to use of compound of formula Ila and/or Ilia,
Figure imgf000012_0002
Formula Ila Formula Ilia wherein, X is imidazole or triazole
for the preparation of the compound of formula I.
Yet another aspect of the present invention relates to an amorphous
Ixazomib citrate of a compound of formula la,
Figure imgf000012_0003
Formula la Still yet another aspect of the present invention relates to preparation amorphous form of compound of formula la,
Figure imgf000013_0001
Formula la
comprising the steps of: a) dissolving a compound of formula la in suitable solvent, b) removing the solvent to isolate the amorphous form of compound of formula la.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of an X-ray powder diffraction (PXRD) pattern of an amorphous form of compound of formula la
FIG. 2 is an illustration of a Differential Scanning Calorimetry (DSC) of an amorphous form of compound of formula la FIG. 3 is an illustration of a Thermogravimetric analysis (TGA) of an amorphous form of compound of formula la
FIG. 4 is a schematic representation of preferred embodiments of the process of preparation of a compound of formula I and la
DETAILED DESCRIPTION OF THE INVENTION
DEFINITIONS
The following definitions are used in connection with the present invention unless the context indicates otherwise. The term "Amorphous _ as used herein, refers to a solid state form of a compound of formula la wherein the three dimensional structure positions of the molecules relative to one another are essentially random, [for example, see Hancock et al. "Characteristics and significance of the amorphous state in pharmaceutical systems" J. Pharm. Sci. Vol. 86, pp. 1-12 (1997)]. As a result, amorphous material will have only liquid-like short range order, and, when examined by X-ray diffraction (XRPD), will generally produce broad, diffuse scattering will result in peak intensity sometimes centered on one or more amorphous halos. Thus, XRPD analysis of amorphous material will provide a 2-theta pattern with one or more broad bands with no distinctive peaks.
The "Amorphous _ compound of formula la may sometimes be characterized by its glass transition temperature (Tg), which defines a pseudo second order phase transition in which a super cooled melt of formula la yields, on cooling, a glassy structure with properties similar to those of crystalline compound of formula la. However, since Tg is a kinetic parameter, its value will be dependent on the melt cooling rate and the measurement conditions used for its determination (e.g., the slower the melt cooling rate, the lower Tg will be).
The glass transition temperature (Tg) for a sample of amorphous form of compound of formula la may be obtained by differential scanning calorimetry (DSC).
The terms "amide bond and peptide bond _ are distinguish in the context that amide bond results in amide derivative, which is any derivative of oxoacid in which the hydroxyl group has been replaced with an amino or substituted amino group while peptide bond results in a derivative of at least two amino acids in which the amine of one is reacted with the carboxylic acid of the next to form a peptide bond. The term "alpha-hydro xy carboxylic acid compound _ refers to a compound which contains a carboxylic acid functional group and hydroxy functional group separated by one carbon atom.
The term "beta-hydro xy carboxylic acid compound _ refers to a compound which contains a carboxylic acid functional group and hydroxy functional group separated by two carbon atoms.
The terms "alpha- hydroxy carboxylic acid compound _ and "beta-hydroxy carboxylic acid compound _ are not intended to be limited to compounds having only one hydroxyl group and one carboxylic acid group.
The term "moiety derived from an alpha-hydroxy carboxylic acid compound" refers to a moiety formed by condensation of carboxylic acid and hydroxyl group of an alpha-hydroxy carboxylic acid compound, wherein hydroxyl group of an alpha-hydroxy carboxylic acid compound is present in an alpha position relative to the carboxylic acid group.
The term "moiety derived from a beta-hydroxy carboxylic acid compound" refers to a moiety formed by condensation of carboxylic acid and hydroxyl group of a beta-hydroxy carboxylic acid compound, wherein hydroxyl group of a beta- hydroxy carboxylic acid compound is present in a beta position relative to the carboxylic acid group.
The terms "about, general, generally _ and the like are to be construed as modifying a term or value such that it is not an absolute. Such terms will be defined by the circumstances and the terms that they modify, as those terms are understood by those skilled in the art. This includes, at very least, the degree of expected experimental error, technique error and instrument error for a given technique used to measure a value. As used herein, the terms "comprising _ and "comprises _ mean 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.
The term "optional _ or "optionally _ is taken to mean that the event or circumstance described in the specification may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
One aspect of the present invention relates to a process for organic synthesis, more particularly for the synthesis of amide and peptide bonds, and new intermediates of compound of formula I,
Figure imgf000016_0001
Formula I
wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or derived from a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R1 and R together form the boronate esters of boronic acid. Preferably, the boronate esters of boronic acid of formula I contain a derivative which may be formed by reacting the acid groups of the boronic acid with a hydroxy compound. Preferred hydroxy compounds are dihydroxy compounds, especially pinacol, perfluoropinacol, pinanediol, ethylene glycol, diethylene glycol, 1,2-cyclohexanediol, 1,3-propanediol, 2,3-butanediol, glycerol or diethanolamine.
The present invention involves efficient methods for formation of amide and peptide bonds to prepare compound of formula I.
In first stage, the amide bond is formed by reacting a compound of formula Ila,
Figure imgf000017_0001
wherein, X is imidazole or triazole with glycine to form a compound of formula III; Preferably, in second stage, the peptide bond is formed by reacting a compound of formula Ilia,
Figure imgf000017_0002
Formula Ilia
wherein, X is imidazole or triazole with compound of formula IV or its salt to obtain a compound of formula I. The compound of formula Ila and Ilia are activated carboxylic acid derivatives. These derivatives are typically formed by reacting their corresponding acid compound of formula II or III,
Figure imgf000018_0001
Formula II Formula III with diimidazole or ditriazole based coupling reagent in suitable solvent.
The activation of carboxylic acid group of compound of formula II or compound of formula III with a suitable diimidazole or ditriazole based coupling reagent forms following derivatives,
Figure imgf000018_0002
These derivatives may be isolated before subjecting to formation of amide or peptide bond, which is also a part of preferred aspect of the present invention. The present process resides in a novel and improved method of producing activated carboxylic acid group with diimidazole or ditriazole based coupling reagent. The diimidazole or ditriazole based coupling reagent may be selected from the group consisting of 1,1 " carbonyldiimidazole (CDI), 1,1 "-carbonyldi- (1,2,4-triazole), 1,1 " thiocarbonyldiimidazole and 1,1 " oxalyldiimidazole. Preference is given to diimidazole based coupling reagents. Particular preference is given to 1,1 " carbonyldiimidazole (CDI).
The other coupling reagents may also be utilized for producing the activated carboxylic acid group of the compounds of present invention. These coupling reagent may be selected from the group consisting of carbodiimide such as Ν,Ν'- dicyclohexylcarbodiimide (DCC), Ν,Ν'-diisopropylcarbodiimide (DIC), 1-ethyl- 3-(3-dimethylaminopropyl)carbodiimide (EDC) and the like.
The compounds II or III of the present invention react readily with diimidazole or ditriazole based coupling reagent to form carbon dioxide and imidazole or triazole as by-products. The carbon dioxide is gaseous by-product, which is easily removed from the reaction mixture wherein imidazole or triazole is soluble in water hence does not require any cumbersome methods such as multiple washings with sodium chloride, potassium carbonate and phosphoric acid to remove them from the reaction mixture.
The use of diimidazole or ditriazole based coupling reagent for the preparation of activated carboxylic acid compound of formula Ila also avoids the use of hazardous chlorinating reagent such as thionyl chloride or oxalyl chloride for the preparation of acid chloride derivative, 2,5-dichlorobenzoyl chloride. The problem of handling liquid 2,5-dichlorobenzoyl chloride and maintaining reaction temperature at 0+1 °C during its reaction with glycine are also solved by the process of the present invention. The activation of carboxylic acid group of formula II is typically performed by reacting it with diimidazole or ditriazole based coupling reagent at suitable temperature in suitable solvent, optionally isolating the compound of formula Ila, then reacting it with glycine, preferably for 30 minutes to 5 hours at 0°C to 20°C, particularly preferably for 1 to 2 hours at 0°C to 10°C. It is advantageous to use aqueous alkaline solution of glycine, preferably aqueous sodium hydroxide solution of glycine. After completion of the reaction compound of formula III can be isolated by any known methods of the art.
The compound of formula III can be converted to compound of formula I as per the disclosed method of \νθ *737.
Preferably, the carboxylic acid group of compound of formula III,
Figure imgf000020_0001
Formula III
is further activated by reacting it with diimidazole or ditriazole based coupling reagent at suitable temperature in suitable solvent, optionally isolating the compound of formula Ilia, then reacting it with compound of formula IV or its salt such as hydrochloric acid salt, hydrobromic acid salt, p-toluene sulfonic acid salt, phosphoric acid salt or trifluoro acetic acid salt or the like,
Figure imgf000020_0002
Formula IV wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid.
The boronate esters of boronic acid of formula IV may be formed by reacting the acid groups of the boronic acid with a hydroxy compound. Preferred hydroxy compounds are dihydroxy compounds, especially pinacol, perfluoropinacol, pinanediol, ethylene glycol, diethylene glycol, 1,2-cyclohexanediol, 1,3- propanediol, 2,3-butanediol, glycerol or diethanolamine.
Preferably, the salt of compound of formula IV is trifluoro acetic acid salt of pinanediol derivative of boro leucine of compound of formula IVa,
Figure imgf000021_0001
Formula IVa
The reaction mixture of compound of formula Ilia and IV or IVa is preferably stirred for 30 minutes to 5 hours at 0°C to 20°C, particularly preferably for 1 to 2 hours at 0°C to 10°C. After completion of the reaction, the compound of formula I can be isolated by any known methods of the art.
Preferably, the isolation of resulting compound I, compound of formula Ila and Ilia may be achieved by filtration of precipitated solid by gravity or by suction, distillation, centrifugation, cooling, crystallization, anti-solvent addition, removal of solvent by evaporation or the like. During the preparation of compound of formula I,
Figure imgf000022_0001
Formula I
wherein, R 1 and R 2 are other than hydroxyl group or compound of formula I is not a compound of formula la, the resulting compound of formula I may be further hydro lysed with suitable reagent based on the nature of R 1 and R 2.
Preferably, the resulting compound of formula I is pinanediol boronate ester of compound of formula lb,
Figure imgf000022_0002
Formula lb
which may be hydrolysed by acid in suitable solvent to obtain Ixazomib or its boroxine derivative,
Figure imgf000022_0003
Boroxine derivative
The suitable acid for the hydrolysis may be selected from the group consisting of hydrochloric acid, boric acid, isobutyl boronic acid, paratoluenesulphonic acid (PTSA), phosphoric acid; and mixtures thereof. The strength and concentration of the acids may be varied as per the hydrolysis condition to achieve the desired result.
Preferably, the Ixazomib or its boroxine derivative is further reacted with citric acid in suitable solvent to obtain Ixazomib citrate of formula la.
The suitable solvent may be selected from the group consisting of acetone, methyl ethyl ketone, isobutyl methyl ketone; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxyethane; methanol, ethanol, propanol, isopropyl alcohol, n-butanol; ethyl acetate; acetonitrile, propionitrile; dimethylformamide, dimethylacetamide, dimethyl sulfoxide or mixtures thereof.
Preferably, the solvent is acetonitrile during the activation of the carboxylic acid group of compound of formula II or III. The hydrolysis of pinanediol boronate ester of formula lb is preferably carried out in acetonitrile or diisopropyl ether or mixture thereof. The formation of citrate salt of Ixazomib is preferably carried out in acetone.
A further aspect of the present invention relates to an amorphous form of Ixazomib citrate of formula la and process of preparation thereof. The amorphous form of Ixazomib citrate of formula la is characterized by the X- ray powder diffraction (PXRD) pattern as shown in Fig. l and/or characterized by the Differential scanning calorimetry (DSC) as shown in Fig.2 and/or characterized by the Thermogravimetric analysis (TGA) as shown in Fig.3.
The amorphous form of Ixazomib citrate of formula la is further characterized by glass transition temperature Tg = 112.06°C.
The preparation of an amorphous form of Ixazomib citrate of formula la comprising steps of: a) dissolving a compound of formula la in suitable solvent, b) removing the solvent to isolate the amorphous form of compound of formula la.
The suitable solvent for the preparation of amorphous form of a compound of formula la may be selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol, n-butanol; acetone, methyl ethyl ketone, methyl iso butyl ketone (MIBK); ethyl acetate; dichloromethane, chloroform; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxyethane; acetonitrile, propionitrile or mixtures thereof. Preferably, the solvent is methanol or its mixture with dichloromethane or acetone or ethyl acetate. Particularly preferably, the solvent is methanol or a methanol/dichloromethane mixture or a methanol/acetone mixture.
In step a), optionally undissolved particles, if any, may be removed suitably by filtration, centrifugation, decantation, and any other known techniques. The solution can be filtered by passing through paper, glass fiber, or other membrane material, or a clarifying agent such as celite. Depending upon the equipment used and the concentration and temperature of the solution, the filtration apparatus may need to be preheated to avoid premature isolation.
In step b), the removal of the solvent from solution can be performed by suitable techniques which may be selected from the group consisting of evaporation, evaporation under vacuum, flash evaporation, simple evaporation, rotational drying, agitated nutsche filter drying, pressure nutsche filter drying or any other technique known in the art.
The resulting amorphous compound may be optionally further dried. Drying can be carried out in a tray dryer, vacuum oven, air oven, cone vacuum dryer, rotary vacuum dryer, fluidized bed dryer, spin flash dryer, flash dryer, or the like. The drying can be carried out at temperatures of less than about 70°C, or any other suitable temperatures; at atmospheric pressure or under a reduced pressure; as long as the amorphous Ixazomib citrate is not degraded in its quality. The drying can be carried out for any desired times until the required product quality is achieved.
The X-ray Powder Diffraction (XRPD): XRPD analysis of amorphous Ixazomib citrate of formula la is conducted on a Panalytical, Model-Empyrean X-Ray powder diffractometer. The instrumental parameters are mentioned below, and graph XRPD graph is shown in Fig. 1:
Start position [ 2Theta] 3.0 End position [ 2Theta] 40.0 Step size [ 2Theta] 0.013 Scan step time (s) 39.27 Anode material Cu Generator setting 40mA, 45 KV Spinning Yes Goniometer theta: theta Sample stage Reflection-transmission spinner Sample mode Reflection
Sample specimen preparation Sample back loading technique
The thermal analysis of amorphous Ixazomib citrate of formula la is conducted by differential scanning calorimetry (DSC) (TA Instruments- DSC Q-2000) equipped with refrigerated cooling system (RCS90). Analysis is performed by taking 2 to 3 mg of sample encapsulated into aluminum sample pan with crimped lid. The thermogram is recorded from 25°C to 250°C under nitrogen atmosphere of 50 mL/min by using following methodology, a) Equilibrate at 25 °C b) Modulate (+) 1°C every 60 seconds c) Isothermal for 5 minutes d) Ramp 5°C/minutes to 250°C
The glass transition temperature (Tg) is observed at 112.06°C. The corresponding thermogram is shown in Fig.2.
The thermal gravimetric analysis (TGA Q-500) of amorphous Ixazomib citrate of formula la is conducted on TA Instruments model Q-500. The sample (about 10- 30 mg) is placed in a platinum pan previously tared. The weight loss of the sample is determined by heating the sample from room temperature to 300°C at a heating rate of 10°C/minutes under nitrogen atmosphere of 60 mL/min. The weight loss of Ixazomib citrate of formula la from RT to ~150°C is found to be 2.52 % w/w and the corresponding thermogram is shown in Fig.3.
EXPERIMENTAL
Detailed experimental parameters according to the present invention are provided by the following examples, which are intended to be illustrative and not limiting of all possible aspects of the invention. EXAMPLES
PREPARATION OF IXAZOMIB CITRATE
Example 1: Synthesis for N-(2,5-dichlorobenzoyl)glycine (Formula III)
1,1 " Carbonyldiimidazole (CDI) (127.3 g) was added to a mixture of 2,5- dichlorobenzoic acid (100 g) in acetonitrile (500 mL) under nitrogen atmosphere at ambient temperature. The reaction mixture was stirred for 1 hour at the same temperature to obtain compound of formula Ila1. After stirring, the reaction mass was added to a mixture of water (1500 mL), sodium hydroxide (NaOH; 31.4 g) and glycine (58.9 g) at 0-10°C. The obtained reaction mass was stirred for 1 hour at 0-10°C. After completion of the reaction, the reaction mixture was maintained at pH 2-3 with hydrochloric acid solution to obtain a solid residue. The solid residue was filtered to obtain N-(2,5-dichlorobenzoyl)glycine. (Yield: 97.7 %)
Example 2: Synthesis of 2,5-dichloro-N-[2-({(lR)-3-methyl-l-[(3aS,4^,6^,7a/?)- 3a,5,5-trimethylhexa- hydro-2H-4,6-methano-l,3,2-benzodioxaborol-2- yl]butyl}amino)-2-oxoethyl]benzamide (Formula lb)
1,1 "-Carbonyldiimidazole (CDI) (15.7 g) was added to a mixture of N-(2,5- dichlorobenzoyl)glycine (20 g) in acetonitrile (100 mL) at 20-30°C to obtain compound of formula Ilia1. The reaction mixture was cooled to 0-10°C then added trifluoro acetic acid salt of pinanediol derivative of boroleucine of formula IVa (29.0 g). The reaction mixture was stirred for 1 hour at the same temperature. After completion of the reaction, methanol (100 mL) and demineralised water (300 mL) was added to the reaction mass and stirred for 3 hours at 20-30°C. The solid was collected by filtration to obtain the title compound. (Yield: 93.7 %)
Example 3: Synthesis of Ixazomib
The pinanediol boronate ester (5 g) of compound of formula lb was mixed with a mixture of concentrated hydrochloric acid (5 mL) and boric acid (1.9 g) in diisopropyl ether (100 mL) at ambient temperature. The reaction mixture was stirred for 5 hours and solid was filtered and washed with diisopropyl ether (25 mL). The isolated solid was dried under vacuum to obtain Ixazomib. (Yield: 86.5 %)
Example 4: Synthesis of Ixazomib citrate of formula la
The Ixazomib (5 g) was added in a solution of citric acid (2.93 g) in acetone (100 mL) at ambient temperature. The reaction mixture was stirred for 30 minutes and filtered. The filtrate was stirred for 4-5 hours. The solid was collected by filtration and dried to give Ixazomib citrate. (Yield- 95 %)
Example 5: Preparation of amorphous form of Ixazomib citrate The Ixazomib citrate (2 g) was dissolved in methanol (30 mL) at ambient temperature. The solvent was removed under vacuum at 50-55°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.
Example 6: Preparation of amorphous form of Ixazomib citrate
The Ixazomib citrate (2 g) was dissolved in methanol (15 mL) and dichloromethane (55 mL) at ambient temperature. The solvent was removed under vacuum at 40-50°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.
Example 7: Preparation of amorphous form of Ixazomib citrate
The Ixazomib citrate (2 g) was dissolved in methanol (4 mL) and acetone (40 mL) at ambient temperature. The solvent was removed under vacuum at 50-55°C and further degassed for 2-3 hours at the same temperature to obtain amorphous form of Ixazomib citrate.

Claims

Claims
1. A process for preparation of a compound of formula I,
Figure imgf000029_0001
Formula I wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the steps of, a) reacting a compound of formula Ila,
Figure imgf000029_0002
Formula Ila
wherein, X is imidazole or triazole with glycine in suitable solvent to obtain a compound of formula III,
Figure imgf000029_0003
Formula III b) optionally, converting the compound of formula III to a compound of formula Ilia,
Figure imgf000030_0001
Formula Ilia
wherein, X is imidazole or triazole c) reacting the compound of formula III or formula Ilia with a compound formula IV or its salt in suitable solvent,
Figure imgf000030_0002
Formula IV
wherein, R 1 and R 2 are same as defined for the compound of formula I
to obtain the compound of formula I.
2. A process for the preparation of a compound of formula Ila,
Figure imgf000030_0003
Formula Ila
wherein, X is imidazole or triazole comprising the reaction of a compound of formula II,
Figure imgf000031_0001
Formula II
with diimidazole or ditriazole based coupling reagent in suitable solvent to obtain the compound of formula Ila.
3. The process for the preparation of the compound of formula I, according to claim 1, wherein the conversion of step b) comprises the steps of, reacting a compound of formula III,
Figure imgf000031_0002
Formula III
with diimidazole or ditriazole based coupling reagent in suitable solvent to obtain a compound of formula Ilia,
Figure imgf000031_0003
Formula Ilia wherein, X is imidazole or triazole
4. A process for the preparation of a compound of formula I,
Figure imgf000032_0001
Formula I
wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the steps of: reacting a compound of formula Ilia,
Figure imgf000032_0002
Formula Ilia
wherein, X is imidazole or triazole with a compound of formula IV or its salt in suitable solvent,
Figure imgf000032_0003
Formula IV
wherein, R 1 and R 2 are same as defined for the compound of formula I
to obtain the compound of formula I.
5. A process for the preparation of a compound of formula I,
Figure imgf000033_0001
Formula I
wherein, R 1 and R 2 are each independently hydroxy, alkoxy, aryloxy, or aralkoxy; or R 1 and R 2 together form a moiety derived from an alpha-hydroxy carboxylic acid compound or a beta-hydroxy carboxylic acid compound, wherein the atom attached to boron in each case is an oxygen atom; or R 1 and R 2 together form the boronate esters of boronic acid comprising the steps of: a) reacting a compound of formula II,
Figure imgf000033_0002
Formula II
with diimidazole or ditriazole based coupling reagent in suitable solvent to obtain a compound of formula Ila,
Figure imgf000033_0003
Formula Ila
wherein, X is imidazole or triazole b) reacting the compound of formula Ila with glycine in suitable solvent to obtain a compound of formula III,
Figure imgf000034_0001
Formula III
c) reacting the compound of formula III with diimidazole or ditriazole based coupling reagent in suitable solvent to obtain a compound of formula Ilia,
Figure imgf000034_0002
Formula Ilia
wherein, X is imidazole or triazole d) reacting the compound of formula Ilia with a compound of formula IV its salt in suitable solvent,
Figure imgf000034_0003
Formula IV wherein, R 1 and R 2 are same as defined for the compound of formula I
to obtain the compound of formula I.
6. The process according to any of claims 1 to 5, wherein the diimidazole or ditriazole based coupling reagent is selected from the group consisting of 1,1 " carbonyldiimidazole (CDI), 1,1 ~-carbonyldi-(l,2,4-triazole), 1,1 " thiocarbonyldiimidazole and 1,1 " oxalyldiimidazole, preferably carbonyldiimidazole (CDI).
7. The process according to any of claims 1 to 5, wherein the suitable solvent is selected from the group consisting of acetone, methyl ethyl ketone, isobutyl methyl ketone; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxy ethane; methanol, ethanol, propanol, isopropyl alcohol, n-butanol; ethyl acetate; acetonitrile, propionitrile; dimethylformamide, dimethylacetamide, dimethyl sulfoxide or mixtures thereof.
8. The process according to any of claims 1 to 5, wherein the compound of formula I is a compound of formula lb,
Figure imgf000035_0001
Formula lb
9. The process according to any of claims 1 to 5, wherein the compound of formula I is a compound of formula la,
Figure imgf000035_0002
Formula la
10. A process for the preparation of a compound of formula lb,
Figure imgf000036_0001
Formula lb comprising the steps of: a) reacting a compound of formula II,
Figure imgf000036_0002
Formula II
with 1,1 " carbonyldiimidazole (CDI) in acetonitrile to obtain a compound of formula Ila1,
Figure imgf000036_0003
Formula Ila1 b) reacting the compound of formula Ila1 with glycine to obtain a compound of formula III,
Figure imgf000036_0004
Formula III c) reacting the compound of formula III with 1,1 " carbonyldiimidazole (CDI) in acetonitrile to obtain a compound of formula Ilia1,
Figure imgf000037_0001
Formula Ilia1 d) reacting the compound of formula Ilia1 with trifluoro acetic acid salt compound of formula IVa,
Figure imgf000037_0002
Formula IVa
to obtain the compound of formula lb.
11. The process according to claim 10, further comprising converting the compound of formula lb to a compound of formula la, a) hydrolysing the compound of formula lb with boric acid and hydrochloric acid, preferably in diisopropyl ether, to obtain Ixazomib of a compound of formula,
Figure imgf000037_0003
b) treating the Ixazomib with citric acid in acetone to obtain a compound of formula la,
Figure imgf000038_0001
Formula la
A compound of formula Ila,
Figure imgf000038_0002
Formula Ila
wherein, X is imidazole or triazole
13. A compound of formula Ilia,
Figure imgf000038_0003
Formula Ilia
wherein, X is imidazole or triazole
14. An amorphous form of compound of formula la, which is characterized by the X-ray pattern as shown in Fig. 1.
15. An amorphous form of compound of formula la with the glass transition temperature Tg = 112.06°C. A process for preparation of amorphous form of a compound of formula
Figure imgf000039_0001
Formula la comprising the steps of: a) dissolving the compound of formula la in suitable solvent, b) removing the solvent to isolate amorphous form of the compound of formula la.
17. The process according to claim 16, wherein the suitable solvent is selected from the group consisting of methanol, ethanol, propanol, isopropyl alcohol, n- butanol; acetone, methyl ethyl ketone, methyl iso butyl ketone (MIBK); ethyl acetate; dichloromethane, chloroform; dimethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxy ethane; acetonitrile, propionitrile.
18. The process according to claim 16, wherein the removal of solvent is selected from the group consisting of evaporation, evaporation under vacuum, flash evaporation, simple evaporation, rotational drying, agitated nutsche filter drying, pressure nutsche filter drying.
19. The process according to claim 16, wherein preparation of amorphous form of a compound of formula la,
Figure imgf000040_0001
Formula la
comprises the steps of: a) dissolving the compound of formula la in methanol or its mixture with dichloromethane or acetone or ethyl acetate, b) evaporating the solvent to isolate amorphous form of the compound of formula la.
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