This application claims priority to Indian patent application no 3105/CHE/2009 filed on Dec 16, 2009 the contents of which are incorporated by reference in their entirety.

FIELD OF INVENTION:

The present invention relates to impurities of Valgancyclovir hydrochloride and the
process for their preparation thereof.

The present invention further relates to a process for the preparation of Valgancyclovir
hydrochloride.

BACKGROUND OF THE INVENTION:

Valcyte (Valgancyclovir HC1 tablets) contains Valgancyclovir hydrochloride, a hydrochloride salt of the L-valyl ester of ganciclovir that exist as a mixture of two diastereomers. Ganciclovir is a synthetic guanine derivative active against cytomegalovirus (CMV). The chemical name for Valgancyclovir hydrochloride is L-valine, 2-(2-amino-1,6-dihydro-6-oxo-purin-9-yl)-methoxy-3-hydroxy-1 -propany 1 ester monohydrochloride. The chemical structure of Valgancyclovir hydrochloride is represented as the formula I shown below

European patent No. 375329 discloses ester prodrugs of Ganciclovir i.e. Valgancyclovir and its physiologically acceptable salts thereof having advantageous bioavailability when administered by an oral route. The patent however, teaches about the process for the preparation of Valgancyclovir.

Valgancyclovir is prepared in various ways. PCT Patent application WO 94/ 29311 disclosed a process for the preparation of amino esters of a nucleoside analogue, including acyclovir and Ganciclovir. This process comprises reacting a nucleoside analogue having a esterifiable hydroxyl group in its linear or cyclic ether moiety, with a 2-oxa-4-aza-cycloalkane-l,3-dione of the formula (II)

Wherein R1 may represent hydrogen, a C1-4 alkyl or alkenyl group or other amino acid side chain, and R2 may represent hydrogen or a group COOR3 where R3 is a benzyl, t-butyl, fluorenylmethyl or an optionally halo substituted linear or branched C|.g alkyl group. Preferred R1 groups include hydrogen, methyl, iso-propyl and isobutyl, yielding respectively the glycine, alanine, valine and isoleucine esters of acyclovir or ganciclovir. Examples 1-3 of the PCT patent application WO 94/029311 discloses only the condensation of acyclovir with the valine-substituted 2-oxa-4-aza-cycloalkane-l,3-dione (Z-valine-N-carboxy anhydride) by conventional procedures. While the amino acid esters of the PCT application include both the acyclovir and ganciclovir esters, the application does not disclose how to prepare the ganciclovir esters, much less the mono-esters of ganciclovir.

WO 1997/27194 describes process for the preparation of Valgancyclovir. The process
includes the reaction of ganciclovir with N-Boc-Valine-NCA in presence of silylating
agent and base for 72 hours at lower temperature it gives 2-(2-amino-l,6-dihydro-6-oxo-
purin-9-yl)-methoxy-3-hydroxy-l-propyl-N-(benzyloxycarbonyl)-L-valinate i.e.
protected Valgancyclovir. This process takes more time for completion of the reaction.

U.S. Patent Nos. 5,700,936, 5,756,736, 5,840,890, 5,856,481 discloses process for the preparation of Valgancyclovir, which involve divalinate, N, O-bistrityl,
monocarboxylate-monovalinate, bis(L-valinate) intermediates and U.S. Patent. Nos. 6,040,446, 6,215,017 & 6,218,568, involve persilyl guanine or glycerol derivatives as intermediates.

The present invention relates to impurities of valgancyclovir hydrochloride formed during the process of making valgancyclovir hydrochloride. The present invention relates to novel 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate, 2-[2-Amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinyl valinate (impurities of Valgancyclovir), and process for the preparation thereof.

OBJECT AND SUMMARY OF THE INVENTION:

The main object of the present invention relates to 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate, a novel impurity of Valgancyclovir hydrochloride and its diastereomers. The present invention also relates to process for the preparation 2-[(2-amino-6-oxo-l ,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate.
In one aspect, the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate comprising the steps of a) dissolving 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-hydroxy-l-propryl-N-(benzyloxycarbonyl)-L-valinate in organic solvent(s) b) adding thionyl chloride c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-l-propryl-N-(benzyloxycarbonyl)-L-valinate. d) deprotecting 2-[(2-amino-6-oxo-1,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-1 -propryl-N-(benzyloxycarbonyl)-L-valinate and e) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate.

In another aspect, the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl) methoxy]-3-chloropropyl valinate comprising
the steps of a) dissolving Valgancyclovir hydrochloride in organic solvent b) adding thionyl chloride c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate.

In yet another aspect, the present invention relates to process for the preparation of 2-[(2-amino-6-oxo-l, 6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate and its diastereomers.

Another object of the present invention relates to process for the preparation of 2-[(2-
amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate
comprising the steps of a) dissolving Valgancyclovir hydrochloride in a alcoholic
solvent b) adding Z-valine NCA c) isolating protected 2-[(2-amino-6-oxo-l,6-dihydro-
9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate d) deprotecting protected 2-[(2-
amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate and e)
isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl
vinylvalinate.

In one aspect, the present invention relates to process for the preparation valgancyclovir hydrochloride.

In another aspect, the present invention relates to a process for the preparation of valgancyclovir hydrochloride by controlling the given impurities to less than 0.1%.

Yet another object of the present invention relates to a process for the preparation of valgancyclovir hydrochloride by controlling the given impurities to less than 0.1%.

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to impurities of Valgancyclovir hydrochloride and process for their preparation thereof.

"As used herein, the term "isolated" refers to separate or remove a chemical substance out of a combined mixture."

In one embodiment, the present invention relates to a 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate, an impurity of Valgancyclovir hydrochloride, represented by formula C, its diastereomers and its preparation process thereof.

In another embodiment, the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l, 6-dihydro-9H-purin -9yl) methoxy]-3-chloropropyl valinate as illustrated in Scheme 1 below:

In another embodiment, the present invention relates to a process for the preparation of 2-
[(2-amino-6-oxo-l ,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate
comprising the steps of a) dissolving 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-hydroxy-l-propryl-N-(benzyloxycarbonyl)-L-valinate in organic solvent b) adding thionyl chloride c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-l-propryl-N-(benzyloxycarbonyl)-L-valinate. d) deprotecting 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-l-propryl-N-(benzyloxycarbonyl)-L-valinate and e) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate.

In yet another embodiment, the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l, 6-dihydro-9H-purin -9yl) methoxy]-3-chloropropyl valinate as illustrated in Scheme 2 below:

In another embodiment, the present invention relates to a process for the preparation of 2-
[(2-amino-6-oxo-l ,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate
comprising the steps of a) dissolving Valgancyclovir hydrochloride in organic solvent b) . adding thionyl chloride c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate may be illustrated by the following Scheme.

In yet another embodiment, the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate and its diastereomers as illustrated in Scheme 3

In another embodiment, the present invention relates to process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate comprising the steps of a) dissolving Valgancyclovir hydrochloride in organic solvent b) adding Z-valine NCA c) isolating protected 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate d) deprotecting protected 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate and e) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate. Another embodiment of the present invention relates to a process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate comprising the steps of a) dissolving Valgancyclovir hydrochloride in a organic solvent b) adding Z-valine NCA c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.

According to the present invention the organic solvent is selected from dimethyl formamide, methylene dichloride and the alcoholic solvents are selected from methanol, ethanol, isopropanol or butanol.

According to the present invention deprotection is carried out in presence of catalyst is selected from Pd/C under hydrogen pressure.

In yet another embodiment, the present invention relates to dimmer impurity having the following structure formed during the process of making valganciclovir hydrochloride

In yet another embodiment, the present invention relates to methylated impurity having the following structure formed during the process of making valganciclovir hydrochloride
In yet another embodiment, the present invention relates to dimmer and methylated impurities of valganciclovir hydrochloride formed during the process of making valgancyclovir hydrochloride as depicted in scheme 4 below:

In yet another embodiment, the present invention relates to a process for the preparation of valgancyclovir hydrochloride as illustrated by scheme 5 below:

The following non-limiting examples illustrate specific embodiments of the present invention. They should not construe it as limiting the scope of present invention in any way.

EXAMPLES:
Example 1: Preparation of 2-(2-amino-l, 6-dihydro-6-oxopurin-9yl)methoxy-3-chloro-l-propryl-n-(benzyloxy carbonyl)-l-valinate

2-(2-amino-l,6-dihydro-6-oxopurin-9yl)methoxy-3 -hydroxy- 1-propryl-n-(benzyloxycarbonyl)-I-valinate (10 g,) was dissolved in methylene chloride (250 ml) and dimthylformamide (50 ml) to get clear solution, added to this slowly thionyl chloride (lOg). Stirred the reaction mass at 30-50°C till there is no starting material. Reaction mass was evaporated under reduced pressure residue is purified by column chromatography to get pure 2-(2-amino-l,6-dihydro-6-oxopurin-9yl)methoxy-3-chloro-l-propryl-n-(benzyIoxy carbonyl)-l-valinate 5 g.

Example 2: Preparation of 2-(2-amino-l,6-dihydro-6-oxopurin-9yi)methoxy-3-chloro-l-propryl-n-(benzyloxy carbonyl)-l-valinate
2-(2-amino-l,6-dihydro-6-oxopurin-9yl)methoxy-3-hydroxy-l-propryl-n-(benzyloxy-carbonyl)-l-valinate (10g,) was dissolved in methylene chloride (250 ml) and dimthylformamide (50 ml) to get clear solution and added to this slowly thionyl chloride (lOg). Stirred the reaction mass at 30-50°C till there is no starting material. Reaction mass was evaporated under reduced pressure residue is purified by column chromatography to get pure 2-(2-amino-l,6-dihydro-6-oxopurin-9yl)methoxy-3-chloro-l-propryl-n-(benzyloxy carbonyl)-l-valinate 5 g (vi).Added to the solution Pd/C (5 g ) reaction mass purge hydrogen till starting material disappear evaporated under reduced pressure residue was purified by column chromatography to get pure 2-[(2-amino-6-oxo-l,6-dihydro-9h-purin-9yl)methoxy] -3-chloropropyl valinate 2 g .

Example 3: Preparation of 2-(2-amino-l,6-dihydro-6-oxopurin-9yl)methoxy-3-chloro-1 -propryl-n-(benzyloxy carbonyl)-l-valinate
Valgancyclovir hydrochloride (10 g,) was dissolved in dimethyl formamide (50 ml) to get clear solution and added to this thonyl chloride (7g). Stirred the reaction mass at 30-40°C till there is no starting material. Reaction mass was evaporated under reduced pressure, residue was purified by column chromatography to get pure 2-[(2-amino-6-oxo-l,6-dihydro-9h-purin-9yl)methoxy] -3-chloropropyl valinate 5 g

Example 4: Preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.

Valgancyclovir hydrochloride (10 g,) was dissolved in methanol (250 ml) to get clear solution and added to this Z-valine NCA (10g,). Stirred the reaction mass at 30-50°C till there was no starting material. Reaction mass was evaporated under reduced pressure, residue was purified by column chromatography to get pure 5 g of compound

Example 5: Preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.
Valgancyclovir hydrochloride (10 g,) was dissolved in methanol (250 ml) to get clear solution and added Z-valine NCA (lOg). Stirred the reaction mass at 30-50°C till there was no starting material. Added Palladium/carbon (5 g), purged hydrogen till starting material disappeared. Evaporated the solution under reduced pressure and the residue was purified by column chromatography to get 3g of pure 2-[(2-amino-6-oxo-1.6-dihydro-9h-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.

Example 6: Preparation of Valgancyclovir Hydrochloride Stage 1: Preparation of Monoprotected Valgancyclovir
To N, N- Dimethylformamide (500ml) was added Ganciclovir (100 g) and ditilled under vacuunm to get moisture free ganciclovir. Added N,N- Dimethylformamide (500ml) and cooled the reaction mass to -10°C. Added trimethyl chlorosilane (53 g) and stirred at 5 to -10°C to get clear solution. To the solution, added imidazole (38 g) and stirred for one hour at the same temperature and added Z-Valine NCA (lOOg). Raised the temperature to 50 - 70°C and stirred at 50-70°C for 5-10 hours and cooled and added methylene chloride containing hexamethyldisiloxane in presence of hexamethyldisiloxane (1100 ml) and dilute hydrochloric acid (700ml). Separated the layers. Stored the methylene chloride layer. The product is precipitated from aqueous layer by adjusting pH slowly between 1 to 2.5 with dilute ammonia 5 -10°C. Filtered the solid and washed with water. To the combined methylene chloride layer containing hexamethyldisiloxane and product was added dilute hydrochloric acid and methanol. Stirred & separated the layers. To the aqueous methanolic layer was added wet solid obtained at pH 1 to 2.5. Stirred the solution and washed with methylene chloride containing hexamethyldisiloxane (3x 600 ml). The aqueous ammonia was added slowly to the aqueous layer in order to isolate the product between pH 5 - 6.5 and temperature of below 10-25°C. Filtered and washed with water. Dried the wet mass to get monoprotected valgancyclovir product 70g

Stage 2: Preparation of Valgancyclovir hydrochloride

Taken methanol (1400 ml), water (450 ml) and cooled to 10 ± 5°C. To the solution was added hydrochloric acid (30ml) and monoprotected valgancyclovir (lOOg). Stirred the mixture to get clear solution. Added Palladium/Carbon and passed bubbling hydrogen till the starting material converts to the product. Filtered, washed with methanol and concentrated the mass under reduced pressure of below 20 mm/Hg and 40°C. Added methanol and distilled and degassed the mass under reduced pressure of NMT 20 mm/Hg and 40°C. To the residue was added 200 ml water and stirred to get a solution. The solution was filtered and isopropyl alcohol (700ml) was added, cooled to 5-10°C and left to obtain precipitate. Further cooled the precipitate to 0-10°C and added another lot of isopropyl alcohol (700ml). Filtered and washed with mixture of isopropyl alcohol & water. Dried the wet mass under reduced pressure of below 20 mm/Hg between 45 -55°C to get 65g pure valgancyclovir hydrochloride.

Stage 3: Purification of Valgancyclovir hydrochloride
200 ml water is added to impure Valgancyclovir hydrochloride (lOOg) to get a clear solution. Washed the solution with ethyl acetate (2x100) and filtered followed by addition of isopropyl alcohol (700ml). Cooled the reaction mixture to 5-10°C thus precipitating the solid. Further cooled to 0-10°C and added another lot of isopropyl alcohol (700ml). Filtered and washed with isopropyl alcohol & water. Dried the wet mass under reduced pressure of below 20 mm/Hg between 45-55°C to get 85g pure Valgancyclovir Hydrochloride.

Example 7: Preparation of Valgancyclovir hydrochloride with dimmer dimmer, other impurities and its isomers.
Taken methanol (1400 ml), water (450 ml) and cooled to 10 ± 5°C. To the solution was added hydrochloric acid (30ml) and monoprotected valgancyclovir (lOOg). Stirred the mixture to get clear solution. Added Palladium/Carbon and passed bubbling hydrogen till the starting material converts to the product. Filtered, washed with methanol and concentrated the mass under without vacuum / using low vacuum i.e., reduced pressure of more than 20 mm/Hg (500 to 20 mm/Hg) and above 40°C. Added methanol and distilled and degassed the mass under reduced pressure of without vacuum / using low vacuum i.e., reduced pressure of more than 20 mm/Hg (500 to 20 mm/Hg) and above 40°C. To the residue was added 200 ml water and stirred to get a solution. The solution was filtered and isopropyl alcohol (700ml) was added, cooled to 5-10°C and left to obtain precipitate. Further cooled the precipitate to 0-10°C and added another lot of isopropyl alcohol (700ml). Filtered and washed with mixture of isopropyl alcohol & water. Dried the wet mass under reduced pressure of above 20 mm/Hg between 45 -55°C to get 60 g valgancyclovir hydrochloride with Valgancyclovir hydrochloride dimmer and other impurities.

We claim:

1. 2-[(2-amino-6-oxo-l ,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate.

2. A process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate comprising the steps of

a) dissolving 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-hydroxy-l-propryl-N-(benzyloxycarbonyl)-L-valinate in organic solvent

b) adding thionyl chloride

c) isolating2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-l-propryl-N-(benzyloxycarbonyl)-L-valinate.

d) deprotecting 2-[(2-amino-6-oxo-l ,6-dihydro-9H-purin-9yl)methoxy]-3-chloro-1 -propryl-N-(benzyloxycarbonyl)-L-valinate and

e) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-chloropropyl valinate

3. A process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -
9yl)methoxy]-3-chloropropyl valinate comprising the steps of

a) dissolving Valgancyclovir hydrochloride in organic solvent
b) adding thionyl chloride
c) isolating 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin -9yl)methoxy]-3-
chloropropyl valinate.

4. A process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-
9yl)methoxy]-3-hydroxypropyl vinylvalinate comprising the steps of

a) dissolving Valgancyclovir hydrochloride in organic solvent
b) adding Z-valine NCA
c) isolating protected 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate
d) deprotecting protected 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate and
e) isolating2-[(2-amino-6-oxo-1,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.

5. A process for the preparation of 2-[(2-amino-6-oxo-l,6-dihydro-9H-purin-
9yl)methoxy]-3-hydroxypropyl vinylvalinate comprising the steps of

a) dissolving Valgancyclovir hydrochloride in a organic solvent
b) adding Z-valine NCA
c) isolating2-[(2-amino-6-oxo-1,6-dihydro-9H-purin-9yl)methoxy]-3-hydroxypropyl vinylvalinate.

6. The process according to any of the preceding claims, wherein the organic solvent is selected from dimethyl formamide, methylene dichloride, methanol, ethanol, isopropanol or butanol.

7. The process according to any of the preceding claims, wherein deprotection is carried out by hydrogenation in presence of Pd/C.

8. An Isolated impurity compound of formula C, or diastereomers thereof.

9. An isolated impurity compound of formula F, or a salt thereof.

10. An isolated impurity compound of formula G, or a salt thereof.