This application claims the benefit of priority of our Indian patent application number 201641008562 filed on 11 ^th March 2016 which is incorporated herein by reference.

Field of the invention:

The present invention relates to an improved process for the preparation of l,3-bis(2- chloroethyl)urea compound of formula-2 which is useful intermediate in the preparation of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formual-1 and is represented by the following structural formula:

Formula- 1

Background of the invention:

l,3-bis(2-chloroethyl)-l -nitrosourea is known as Carmustine and is approved in USA under the brand names of BICNU for the treatment of chemotherapy of certain neoplastic diseases such as brain tumor, multiple myolema, Hodgkin's disease and non-Hodgkin's lymphomas & Gliadel for the treatment of newly-diagnosed high-grade-malignant glioma as an adjunct to surgery and radiation, recurrent glioblastoma multiforme as an adjunct to surgery.

Journal of Medicinal Chemistry 1963, 6, 669-681 firstly disclosed process for the preparation of l,3-bis(2-chloroethyl)-l-nitrosourea.

US2288178 patent disclosed the process for the preparation of the compound of formula-2 from aziridine and phosgene. J. Med. Chem., 1979, 22 (10), pp 1193-1198 disclosed the process for the preparation of the compound of formula-2 using 2- chloroethanamine and 2-chloroisocyanoethane.

Prior disclosed processes for the preparation of the compound of formula-2 are used hazardous reagents which were difficult to handle in the laboratory. The present inventors have developed an improved process for the preparation of the compound of formula-2 by using easily available raw materials and usage of that compound in the preparation of the compound of formula- 1 to get good yield and having high purity. Brief description of the invention:

The first aspect of the present invention is to provide an improved process for the preparation of l,3-bis(2-chloroethyl)urea compound of formula-2.

The second aspect of the present invention is to provide an improved process for the preparation of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula- 1.

Brief description of the drawings:

Figure 1: Illustrates the PXRD pattern of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1.

Figure 2: Illustrates the IR spectrum of 1, 3 -bis(2-chloroethyl)-l -nitrosourea compound of formula-1.

Figure 3: Illustrates the PXRD pattern of l,3-bis(2-chloroethyl)urea compound of formula-2. Advantages of the present invention:

• The preparation of the compound of formula-2 using CDI is having many advantages such as use of less expensive raw materials, improved yields. Further the purification of the compound of formula-2 using alcohol solvents provides highly pure compound of formula-2 which is more suitable for the synthesis of pure compound of formula-1.

Detailed description of the invention:

As used herein the term "suitable solvent" used in the present invention refers to "hydrocarbon solvents" such as n-hexane, n-heptane, cyclohexane, pet ether, benzene, toluene, pentane, cycloheptane, methylcyclohexane, ethylbenzene, m-, o-, or p-xylene and the like; "ether solvents" such as dimethoxymethane, tetrahydrofuran, 1,3-dioxane, 1,4- dioxane, furan, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, anisole, methyl tertiary butyl ether, 1,2-dimethoxy ethane and the like; "ester solvents" such as methyl acetate, ethyl acetate, isopropyl acetate, n-butyl acetate and the like; "polar- aprotic solvents such as dimethylacetamide (DMA), dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP) and the like; "chloro solvents" such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride and the like; "ketone solvents" such as acetone, methyl ethyl ketone, methyl isobutylketone and the like; "nitrile solvents" such as acetonitrile, propionitrile, isobutyronitrile and the like; "alcoholic solvents" such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t- butanol, 2-nitroethanol, 2-fluoroethanol, 2,2,2-trifluoroethanol, ethylene glycol, 2- methoxyethanol, 1, 2-ethoxyethanol, diethylene glycol, 1, 2, or 3-pentanol, neo-pentyl alcohol, t-pentyl alcohol, diethylene glycol monoethyl ether, cyclohexanol, benzyl alcohol, phenol, or glycerol and the like; "polar solvents" such as water; acid or mixtures thereof.

The term "pure" refers to the compounds prepared according to the present invention having purity greater than 95%; preferably >97%; more preferably >99% and most preferably >99.5%.

The term "suitable acid" used in the present invention refers to inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid; organic acids such as acetic acid, maleic acid, malic acid, oxalic acid, trifluoro acetic acid [TFA], etc., and mixtures thereof.

The first aspect of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)urea compound of formula-2

Formula-2

comprising of reacting 2-chloroethanamine compound of formula-3 or its salts

Formula-3 with carbonyldiimidazole [CDI] in a suitable solvent to provide l,3-bis(2-chloroethyl)urea compound of formula-2, optionally purifying the compound of formula-2 to get the pure compound of formula-2.

Wherein the suitable solvent is selected from chloro solvents, 'hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, nitrile solvents, polar solvents and mixtures thereof.

The preferred embodiment of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)urea compound of formula-2

Formula-2

comprising of reacting 2-chloroethanamine hydrochloride compound of formula-3a

CI

NH ₂

.HC1

Formula-3a

with carbonyldiimidazole [CDI] in tetrahydrofuran to provide l,3-bis(2-chloroethyl)urea compound of formula-2.

Wherein CDI is used in the molar ratio ranging between 0.3 to 0.6 moles with respect to the compound of formula-3a.

Another embodiment of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)urea compound of formula-2, comprising of :

a) Adding carbonyldiimidazole [CDI] to the mixture of 2-chloroethanamine hydrochloride compound of formula-3a and tetrahydrofuran at a suitable temperature, b) stirring the reaction mixture obtained in step-a) at a suitable temperature,

c) distilling off the solvent from the reaction mixture,

d) adding water to the compound obtained in step-c),

e) stirring the reaction mixture obtained in step-d),

f) filtering the solid obtained in step-e), g) optionally slurring the compound obtained in step-f) in water,

h) purifying the obtained compound in a suitable alcohol solvent to provide pure compound of formula-2.

Wherein the suitable alcohol solvent is selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol and the like; in step-a) the suitable temperature ranges from -25 to 25°C; in step-b) the suitable temperature ranges from 25°C to reflux temperature of the solvent used.

The second aspect of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula- 1

comprising of :

a) Reacting 2-chloroethanamine compound of formula-3 or its salts

CI . /\

Formula-3

with carbonyldiimidazole [CDI] in a suitable solvent to provide the compound of formula-2

O

CI . Jl I

N N H H

Formula-2,

b) optionally purifying the compound of formula-2 using a suitable solvent,

c) treating the compound of formula-2 with metal nitrite in presence of acid in a suitable solvent to provide the compound of formula- 1,

d) optionally purifying the obtained compound using a suitable solvent to get pure 1,3- bis(2-chloroethyl)- 1 -nitrosourea compound of formula- 1.

Wherein in step-a) to step-d) the suitable solvent is selected from chloro solvents, hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, nitrile solvents, polar solvents, acids and mixtures thereof;

in step-c) metal nitrite is preferably sodium nitrite and acid is selected from inorganic acid and organic acid.

The preferred embodiment of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)-l-nitrosourea compound of formula-1, comprising of :

a) Reacting 2-chloroethanamine hydrochloride compound of formula-3a with carbonyldiimidazole [CDI] in tetrahydrofuran to provide the compound of formula-2, b) purifying the compound of formula-2 using isopropanol,

c) treating the compound of formula-2 obtained in step-b) with sodium nitrite in the mixture of hydrochloric acid and acetic acid to provide the compound of formula-1, d) dissolving the compound obtained in step-c) in dichloromethane,

e) adding the solution obtained in step-d) to n-heptane,

f) filtering the obtained solid to get pure l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1.

Another preferred embodiment of the present invention provides an improved process for the preparation of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1 , comprising of :

a) Reacting 2-chloroethanamine hydrochloride compound of formula-3a with carbonyldiimidazole [CDI] in tetrahydrofuran to provide the compound of formula-2, b) treating the compound of formula-2 with sodium nitrite in the mixture of hydrochloric acid and acetic acid to provide the compound of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1.

An embodiment of the present invention provides an improved process for the purification of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1, comprising of : a) Dissolving the compound of formula-1 in chloro solvents at a suitable temperature, b) adding silicagel to the reaction mixture obtained in step-a),

c) filtering the reaction mixture,

d) distilling off the solvent from filtrate obtained in step-c), e) adding ether solvent to the compound obtained in step-d),

f) combining the reaction mixture with hydrocarbon solvent,

g) filtering the precipitated solid to get pure compound of formula-1.

Wherein in step-a) the suitable chloro solvent is selected from dichloromethane, dichloroethane, chloroform, carbon tetrachloride and the like; the suitable temperature is ranges from -10 to 25°C;

In step-e) the suitable ether solvent is selected from dimethoxymethane, tetrahydrofuran, 1,3- dioxane, 1,4-dioxane, furan, diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, anisole, methyl tertiary butyl ether, 1,2-dimethoxy ethane and the like; preferably methyl tertiary butyl ether;

In step-f) the hydrocarbon solvent is selected form n-hexane, n-heptane, cyclohexane, pet ether, benzene, toluene, pentane, cycloheptane, methylcyclohexane, ethylbenzene, m-, o-, or p-xylene and the like; preferably n-heptane.

The preferred embodiment of the present invention provides an improved process for the purification of l,3-bis(2-chloroethyl)-l -nitrosourea compound of formula-1, comprising of :

a) Dissolving the compound of formula-1 in dichloromethane,

b) adding silicagel to the reaction mixture,

c) filtering the reaction mixture obtained in step-b),

d) distilling off the solvent from the filtrate obtained in step-c),

e) adding methyl tertiary butyl ether to the compound obtained in step-d),

f) combining the reaction mixture with n-heptane,

g) filtering the precipitated solid to get pure compound of formula-1.

There are some unknown impurities formed during the synthesis of l ,3-bis(2- chloroethyl)-l -nitrosourea compound of formula-1 which are detected at R T's -0.08 & -0.13 which were difficult to control. However these impurities have been well controlled or completely washed out by the purification process described above.

An embodiment of the present invention provides crystalline l,3-bis(2-chloroethyl)-l- nitrosourea compound of formula- 1 characterized by its powder X-Ray diffraction pattern having peaks at 9.05, 18.64, 21.07, 22.92, 24.3, 25.06, 26.28, 27.8, 28.63, 29.59 and 32.97± 0.2 degrees of 2-theta. The said crystalline form is further characterized by its powder X-Ray diffraction pattern substantially in accordance with figure- 1 and by its IR spectrum shown in figure-2.

HPLC Method of Analysis:

l,3-bis(2-chloroethyl)-l -nitrosourea and its related substances were analyzed by HPLC with the following chromatographic conditions:

Apparatus: A liquid chromatographic system is to be equipped with variable wave length UV-detector; Column: Waters Spherisorb ODS2, 150X4.6 mm, 5 μπι or equivalent; Wave length: 200 nm, Column temperature: 25°C; Injection volume: 10 μί,; Diluent: Chilled acetonitrile; Needle wash: Diluent; Elution: Isocratic; Mobile phase: Acetonitrile.

PXRD analysis of l,3-bis(2-chloroethyl)-l -nitrosourea was carried out using BRUKER D8 ADVANCED/AXS X-Ray diffractometer using Cu a radiation of wavelength 1.5406 A° and continuous scan speed of 0.03 min. IR spectra were recorded on a Perkin- Elmer FT1R spectrometer.

The present invention is schematically represented in the scheme- 1.

Scheme-1

Formula-1

The present invention also provides an improved process for the preparation of the compound of formula- 1 and is schematically represented in schem-2.

Scheme-2;

O

O

NH ₂ ^{+ R} -0^ Solvent,

Base

.HC1 H H

Formula-3a Formula-4 Formula-2

Metal nitrite Acid

Wherein R= alky, aryl, aralkyl group

Formula-1 The process described in the present invention was demonstrated in examples illustrated below. These examples are provided as illustration only and therefore should not be construed as limitation of the scope of the invention.

Examples:

Example-1: Preparation of l,3-bis(2-chloroethyl)urea compound of formula-2

2-chloroethanamine hydrochloride (429.19 gm) was added to the mixture of carbonyldiimidazole (200 gm) and tetrahydrofuran (1000 ml) at 25-30°C and stirred the reaction mixture for 5 minutes. Heated the reaction mixture to 65-70°C and stirred for 14 hours at the same temperature. Cooled the reaction mixture to 25-30°C and water was added to the reaction mixture. Both the organic and aqueous layers were separated and the aqueous layer was extracted with ethyl acetate. Combined the organic layers and washed with aqueous sodium chloride solution. Distilled off the solvent from the organic layer completely under reduced pressure and co-distilled with isopropanol. Isopropanol (100 ml) was added to the obtained compound and stirred the reaction mixture at 25-30°C. Heated the reaction mixture to 80-85°C and stirred the reaction mixture for 10 minutes at the same temperature. Cooled the reaction mixture to 25-30°C and stirred for 2 hours at the same temperature. Filtered the precipitated solid, washed with isopropanol and dried to get the title compound. Yield: 1 10 gm; M.P: 121-125°C. Example-2: Preparation of l,3-bis(2-chloroethyl)-l-nitrosourea compound of formula-1 l,3-bis(2-chloroethyl)urea (50 gm) was added to the mixture of dilute hydrochloric acid (16 ml) and acetic acid (205 ml) at 25-30°C. Cooled the reaction mixture to 0-5°C and stirred for 1 hour at the same temperature. Sodium nitrite (46.6 gm) was added to the reaction mixture in lot-wise over the period of 3 hours at 0-5 °C and stirred the reaction mixture for 1 hour at the same temperature. The reaction mixture was quenched into pre-cooled water at 0-5°C and stirred it for 30 minutes at the same temperature. Filtered the precipitated solid and washed with water. Dissolved the obtained compound in dichloromethane (100 ml) at 0-5°C. The reaction mixture was added to pre-cooled n-heptane (250 ml) at 0-5°C and stirred for 1 ½ hour at the same temperature. Filtered the precipitated solid, washed with n-heptane and dried to get the title compound.

Yield: 28 gm.

Example-3: Preparation of l,3-bis(2-chloroethyl)urea compound of formuIa-2

Carbonyldiimidazole (8 kg) was slowly added to the pre-cooled mixture of 2- chloroethanamine hydrochloride (14.31 kg) and tetrahydrofuran (40 lit) at 0-5°C in lot-wise under nitrogen atmosphere and stirred the reaction mixture for 5 minutes. Raised the temperature of the reaction mixture to 25-30°C and stirred the reaction mixture for 36 hours at the same temperature. Distilled off the solvent completely from the reaction mixture under reduced pressure. Water was added to the obtained compound at 25-30°C and stirred it for I hour at the same temperature. Filtered the precipitated solid and washed with water. The obtained compound was slurried in water at 25-30°C, filtered and washed with water. Methanol was added to the obtained compound at 25-30°C and stirred it for 1 hour at the same temperature. Filtered the solid, washed with methanol and dried to get the title compound. Yield: 6 kg; PXRD of the obtained compound is shown in figure-3. Example-4: Preparation of l,3-bis(2-ch!oroethyl)-l-nitrosourea compound of formula-1 l,3-bis(2-chloroethyl)urea (6 kg) was added to the mixture of dilute hydrochloric acid (1.9 lit) and acetic acid (24.5 lit) at 25-30°C. Cooled the reaction mixture to 0-5°C, sodium nitrite (5.59 kg) was slowly added to the reaction mixture in lot-wise at 0-5°C and stirred the reaction mixture for 1 hour at the same temperature. The reaction mixture was quenched with pre-cooled water at 0-5°C. Cooled the reaction mixture to -15 to -10°C and stirred it for 1 hour at the same temperature. Filtered the precipitated solid and washed with water. Dissolved the obtained compound in dichloromethane (24 lit) at 5-10°C and stirred for 15 minutes at the same temperature. Both the organic and aqueous layers were separated. Silicagel (3 kg) was added to the organic layer at 5-10°C and stirred for 25 minutes at the same temperature. Filtered the reaction mixture through hyflow bed and washed with dichloromethane. Distilled off the solvent completely from the filtrate under reduced pressure and co-distilled with methyl tertiary butyl ether. Pre-cooled Methyl tertiary butyl ether (12 lit) was added to the obtained compound and stirred it for at 0-5°C. This reaction mixture was added to pre-cooled n-heptane (60 lit) at -15 to -10°C and stirred the reaction mixture for 1 hour at the same temperature. Filtered the precipitated solid and washed with chilled n- heptane. Dried the compound at 0-10°C under reduced pressure.

Yield: 4.5 kg; MR: 30-32°C;

Purity by HPLC: 99.97%; Impurity at RRT -0.08: 0.01%, Impurity at RRT -0.13: Not detected; l,3-bis(2-chloroethyl)urea: 0.02%

PXRD of the obtained compound is shown in figure- 1 and IR shown in figure-2.

Example-5: Preparation of l,3-bis(2-chloroethyl)-l-nitrosourea compound of formula-1 l,3-bis(2-chloroethyl)urea (150 gm) was added to the mixture of dilute hydrochloric acid (48 ml) and acetic acid (612 ml) at 25-30°C. Cooled the reaction mixture to 0-5°C, sodium nitrite (139.8 gm) was slowly added to the reaction mixture in lot-wise at 0-5°C and stirred the reaction mixture for 1 hour at the same temperature. The reaction mixture was quenched with pre-cooled water at 0-5°C. Cooled the reaction mixture to -15 to -10°C and stirred it for 1 hour at the same temperature. Filtered the precipitated solid and washed with water.

Purity by HPLC: 95.1 1%, Impurity at RRT -0.08: 4.17%, Impurity at RRT -0.13: 0.63%. Example 6: Purification of l,3-bis(2-chloroethyl)-l-nitrosourea compound of formula-1

Dissolved the compound of formula 1 obtained in example-5 in dichloromethane (600 ml) at 5-10°C and stirred for 15 minutes at the same temperature. Both the organic and aqueous layers were separated. Silicagel (75 gm) was added to the organic layer at 5-10°C and stirred for 25 minutes at the same temperature. Filtered the reaction mixture through hyflow bed and washed with dichloromethane. Distilled off the solvent completely from the filtrate under reduced pressure and co-distilled with methyl tertiary butyl ether. Pre-cooled Methyl tertiary butyl ether (300 ml) was added to the obtained compound and stirred it for 10-15 min at 0- 5°C. This reaction mixture was added to pre-cooled n-heptane (1500 ml) at -15 to -10°C and stirred the reaction mixture for 1 hour at the same temperature. Filtered the precipitated solid and washed with chilled n-heptane. Dried the compound at 0-10°C under reduced pressure. Yield: HO gm; MR: 30-32°C;

Purity by HPLC: 99.96%, Impurity at RRT -0.08: 0.02%, Impurity at RRT -0.13: Not detected; l,3-bis(2-chloroethyl)urea: 0.02%

PXPvD of the obtained compound is shown in figure-1 and IR shown in figure-2.