N-[(Phenylmethoxy)carbonyl]-L-valine 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy]-3-hydroxypropyl ester

White Solid

ganciclovir phosphate diester 60g, 600ml 1000ml of methanol was added to the reaction flask, through appropriate amount of concentrated hydrochloric acid, and then heated at 50-60 C for 4 hours, then500mL of methanol was distilled off at atmospheric pressure, cooled to room temperature, water was added764.4mL stirred cooled to 0-5 C, filtration, and drying in vacuo to afford N- benzyloxycarbonyl -L- valineganciclovir monoester 35.3g, yield 90 %, a purity of 98.5%.Example 9PREPARATION OF MONO-(Cbz-L-VALYL)-ESTER OF GANCICLOVIR (FORMULA X). Bis-(Cbz-L-valyl)-ester of ganciclovir of Formula IX (100 g) and methanol (200 mL) are charged into round bottom flask and stirred for 5 minutes. n-Propylamine (13.6 mL) is added to the reaction mass at 27 C. and maintained at 27 for 30 hours. Acetic acid (9.5 mL) is slowly added and the mass and cooled to 16 C. Acetic acid (390.5 mL) is added to the reaction mass at 15-20 C. and maintained reaction mass at 12 C. for 1 hour. The resultant reaction mass is slowly added to water (2000 mL) at 12 C. and maintained at 12 C. for 1 hour. The separated solid is collected by filtration, washed with pre-cooled (10-15 C.) water (1000 mL), and dried at 45 C. for 12 hours under reduced pressure. The obtained dry compound (80 g) and acetic acid (320 mL) is charged into round bottom flask and stirred for 1 hour. The resultant reaction mass is slowly added to water (1600 mL) at 12 C. and stirred for 1 hour. The separated solid is collected by filtration and washed with pre-cooled (10-15 C.) water (1600 mL). The obtained wet compound and ethyl acetate (600 mL) are charged into round bottom flask and stirred at 62 C. for 8 minutes. Reaction mass is cooled to 26 C. and stirred for 1 hour. The separated solid is collected by filtration and washed with ethyl acetate (60 mL). The obtained wet compound, ethyl acetate (750 mL), and water (22.5 mL) are charged into round bottom flask and stirred at 62 C. for 75 minutes. The reaction mass is cooled to 26 C. and stirred for 80 minutes. The separated solid is collected by filtration and washed with ethyl acetate (45 mL). The obtained wet compound, ethyl acetate (270 mL), and water (18 mL) are charged into round bottom flask and stirred at 62 C. for 1 hour. Reaction mass is cooled to 6 C. and stirred for 1 hour 30 minutes. The separated solid is collected by filtration and washed with ethyl acetate (36 mL). The obtained wet compound, ethyl acetate (216 mL), and water (14.4 mL) are charged into round bottom flask and stirred at 62 C. for 1 hour 30 minutes. Reaction mass is cooled to 26 C. and stirred for 70 minutes. The separated solid is collected by filtration, washed with ethyl acetate (28.8 mL), and dried at 45-50 C. for 10 hours under reduced pressure. Dry compound is milled and further dried at 45-50 C. for 24 hours to afford 28.0 g of the title compound. Purity by HPLC: 99.59%; ganciclovir: 0.37%; bis-(Cbz-L-valyl)-ester of ganciclovir of Formula IX: 0.22%.Step (c) Preparation of 2-(2-amino 1, 6 dihydro-6oxo-purine-9-yl)-methoxy-3 hydroxy-1-propyl-N-(benzyloxy carbonyl 1-L-valinate. Step (b) product (34 gms) and piperidine (68 ml) were stirred at 25 C for 48 hours . After completion of reaction, Isopropyl alcohol (136 ml) was added, stirred and further Hexane (340 ml) was added and stirred for 15 min and allowed to settle. Hexane layer was decanted and oil was further stirred in a mixture of isopropyl alcohol and hexane for 1 hour. The resulting solid was filtered and washed with hexane and dried under vacuum at 50 C to get 29gms of the titled compound purified using conventional acid base purification method.Step (c) Preparation of 2-(2-amino 1, 6 dihydro-6oxo-purine-9-yl)-methoxy-3 hydroxy-1-propyl-N-(benzyloxy carbonyl)-L-valinate. Step (b) product (34 gms) and piperidine (68 ml) were stirred at 25 C. for 48 hours. After completion of reaction, Isopropyl alcohol (136 ml) was added, stirred and further Hexane (340 ml) was added and stirred for 15 min and allowed to settle. Hexane layer was decanted and oil was further stirred in a mixture of isopropyl alcohol and hexane for 1 hour. The resulting solid was filtered and washed with hexane and dried under vacuum at 50 C. to get 29 gms of the titled compound purified using conventional acid base purification method.Step (d) Preparation of2-(2-amino 1, 6 dihydro-6oxo-purine-9-yl)-methoxy-3 hydroxy-1- propyl- Lvalinate hydrochloride. Product from Step (c) (29 gms) was added to mixture of ethyl alcohol (700 ml) and water 170 ml. 10% Palladium on carbon (5.8 gms) was added followed by conc.HCL (5.8 ml). Reaction mass was stirred at 25 -30 C. Hydrogen gas was bubbled through the reaction mass for 12 to 20 hours. After completion of reaction, the reaction mass was filtered typically using a diatomaceous earth filter. (for example : Hyflo) filtrate was concentrated to redisue. The residue was dissolved in 50 ml water under stirring and further 600 ml of isoproyl alcohol was charged slowly in 2 hrs. at 25-30C. The resulting suspension was stirred at 25-30C for 30 minutes, and was filtered and washed with 50 ml isopropyl alcohol. The solid was dried under vacuum at 50C to get 20gms of 2- (2-amino 1, 6 dihydro 6-oxo- purine 9-yl) - methoxy 3 acetoxy -1-propyl-N -(bezyloxy carbonyl)- L valinate hydrochloride (Valganciclovir Hydrochloride)Step (b) Preparation of 2-(2-amino 1, 6 dihydro-6oxo-purine-9-yl)-methoxy-3 acetoxy-1-propyl-N-(benzyloxy carbonyl)-Lvalinate. N-CBZ-L-valine(170 gms), dicyclohexyl carbodiimide (130gms) were stirred in dichloromethane (2 litres). Product from step (a) (70 gms) was added to the reaction mass and stirred for 3 - 4 hours. Dimethyl formamide (140 ml) and dimethyl amino pyridine (0.82gms) were added to the reaction mass and stirred at 25 C for 12 hours. Reaction mass was filtered, typically using a diatomaceous earth filter. (for example: Hyflo). Clear filtrate was concentrated under vacuum to remove DMF. Oily residue was dissolved in isopropyl alcohol (180ml) and hexane (700 ml) was added and stirred for 30 minutes and allowed to settle. The upper hexane layer was decanted. Oily layer was further stirred in a mixture of isopropyl alcohol and hexane for 1 hour, resulting solid was filtered and washed with hexane and dried under vacuum at 50 C to get 34gms of the titled compound.Example 4N- benzyloxycarbonyl -L- valine ganciclovir monoester 45.6g, palladium on carbon catalyst Pd-C3.0g, chilled methanol, 365 ml, 8.4 mL of concentrated hydrochloric acid, and turn to the high pressure into thebottle, evacuated to -0.08Mpa, filled with hydrogen to 0.2Mpa, room temperature for 18 hours, filtered, and thefiltrate was concentrated under reduced pressure to 45 C dry, pure water was added 36.5mL, isopropanol36.5mL, clear solution was stirred heated, filtered, and the filtrate control temperature 60 ~ 70 C solution ofisopropanol 164.3mL, dropwise slow cooling, the precipitated white solid was cooled to -11 C suctionfiltration, the filter cake was dried under reduced pressure to 50 C valganciclovir hydrochloride 30g, yield:82%, purity: 99.4%.Preparation of Valganciclovir Hydrochloride Using Iso-PropanolHydrochloric acid (13 g) and 10% palladium on carbon (5.5 g) was added to a solution of The pure CBZ-protected mono L-valyl ester of ganciclovir (100 g) was suspended in 20% aqueous ethanol (1200 ml) and to this suspension was added concentrated hydrochloric acid (21 ml, 35% w/w) and palladium on carbon (10%, 50% wet, 1 lg). The suspension was stirred at 0.5-1. 0 Kg hydrogen pressure at 20-40C. After completion of reaction, catalyst was filtered through celite bed and the bed was washed with 10% aqueous ethanol. The filtrate obtained was concentrated completely at 35-38C under vacuum and the residue was crystallized using water (0.8 times) and isopropyl alcohol (6.5 times). The crystalline product was washed with isopropyl alcohol and dried under vacuum at 55-60C to get substantially pure mono L-valyl ester of ganciclovir as its hydrochloride salt. Yield: 60-65 g. Purity (by HPLC) : greater than 99%; Bis L-valyl ester of ganciclovir less than 1% ; Ganciclovir less than 1%.PREPARATION OF ENATIOMERICALLY PURE HYDROCHLORIDE SALT OF MONO L-VALYL ESTER OF GANCICLOVIR The pure CBZ-protected mono L-valyl ester of ganciclovir (100 g) was suspended in 20% aqueous ethanol (1200 ml) and to this suspension was added concentrated hydrochloric acid (21 ml, 35% w/w) and palladium on carbon (10%, 50% wet, 1 lg). The suspension was stirred at 0.5-1. 0 Kg hydrogen pressure at 20-40C. After completion of reaction, catalyst was filtered through celite bed and the bed was washed with 10% aqueous ethanol. The filtrate obtained was concentrated completely at 35-38C under vacuum and the residue was crystallized using water (0.8 times) and isopropyl alcohol (6.5 times). The crystalline product was washed with isopropyl alcohol and dried under vacuum at 55-60C to get enantiomerically pure mono L-valyl ester of ganciclovir as its hydrochloride salt. Yield: 60 g. Purity (by HPLC) : greater than 99%; Bis L-valyl ester of ganciclovir less than 1%; Ganciclovir less than 1 %. Enantiomeric Purity: L-Mono-VGNC: 99.64% D-Mono-VGNC : 0.36%Step (d) Preparation of 2-(2-amino 1, 6 dihydro-6oxo-purine-9-yl)-methoxy-3 hydroxy-1-propyl-Lvalinate hydrochloride Product from Step (c) (29 gms) was added to mixture of ethyl alcohol (700 ml) and water 170 ml. 10% Palladium on carbon (5.8 gms) was added followed by conc.HCL (5.8 ml). Reaction mass was stirred at 25-30 C. Hydrogen gas was bubbled through the reaction mass for 12 to 20 hours. After completion of reaction, the reaction mass was filtered typically using a diatomaceous earth filter. (for example: Hyflo) filtrate was concentrated to redisue. The residue was dissolved in 50 ml water under stirring and further 600 ml of isoproyl alcohol was charged slowly in 2 hrs. at 25-30 C. The resulting suspension was stirred at 25-30 C. for 30 minutes, and was filtered and washed with 50 ml isopropyl alcohol. The solid was dried under vacuum at 50 C. to get 20 gms of 2-(2-amino 1, 6 dihydro 6-oxo-purine 9-yl)-methoxy 3 acetoxy-1-propyl-N-(bezyloxy carbonyl)-L valinate hydrochloride (Valganciclovir Hydrochloride)Example 7 PREPARATION OF VALGANCICLOVIR HYDROCHLORIDE SALT. To a solution of mono-(Cbz-L-valyl)-ester of ganciclovir of Formula X (10 g) in methanol (320 mL) in an autoclave vessel is added aqueous HCl (2.33 mL) and 10% palladium on carbon (50% wet, 1.0 g), and a hydrogen pressure of 0.7-1 kg/cm2 is maintained for 17-18 hours at 25-30 C. The mass is filtered and the collected solid is washed with methanol (46 mL). To the filtrate is added triphenylphosphine (25 mg) and charcoal. The reaction mass is maintained for 1-2 hours at 25-30 C. The mass is filtered and the collected solid is washed with methanol (30 mL). To the filtrate is added water (10 mL), the mixture is evaporated below 40 C. to remove methanol, and the volume is adjusted to 13.5 mL with water. The aqueous layer is washed with toluene (3*18 mL) and 1-butanol (2*18 mL) at 25-30 C. Isopropyl alcohol (100 mL) is added to the mixture and maintained for 15-18 hours for solid formation at 25-30 C. Cyclohexane (45 mL) is added to the reaction mass. Reaction mass is cooled and maintained for 1-2 hours at 0 to -15 C. The formed solid is collected by filtration at -10 to -15 C., washed with chilled isopropyl alcohol (18 mL), and dried under reduced pressure at 40-50 C. to afford the title compound. Yield: 5.0 g.To the filtrate obtained in was added ethyl acetate (1.0 L) and the resultant mixture was stirred at 20-30C for 10 minutes. Water (1.5 L) was added at 30-35C and stirred for 30 minutes, the separated solids were filtered and washed with ethyl acetate (200 ml). Analysis of the wet solids showed: Desired product-CBZ- protected mono-L-valyl ester of ganciclovir about 65%; Ganciclovir about 30%; and CBZ-protected Bis L-valyl ester of ganciclovir about 5%. The wet solids obtained above were suspended in ethyl acetate (1.0 Lit) and heated to 50C, cooled to 20-25C and separated solids were filtered to get mono L-valyl ester of ganciclovir contaminated with ganciclovir. The ethyl acetate layers were combined and used for recovery of CBZ-protected bis L-valyl ester of ganciclovir. Analysis of the solid obtained showed: Desired product-To a solution of methanol (200 ml) and water (500 ml) was added the wet solid obtained in and the resultant mass was cooled to 0C. Trifluoroacetic acid (105 ml) was then slowly added at 0-5C. The resultant solution was extracted with dichloromethane (3 x 500 ml). The combined organic layer was washed with water (400 ml) containing trifluoroacetic acid (35 ml) at 0-10C. The organic layer is concentrated at 35-40C under vacuum and the concentrated mass was crystallized using IPA and hexane. The combined aqueous layer was kept separately for ganciclovir recovery. The product was dried to get pure CBZ-protected mono L-valyl ester of ganciclovir. Yield: 35 g Purity: 99. 3% (by HPLC) Enantiomeric Purity: L-enantiomer 99.8%, D-enantiomer 0.2% Melting point : 122-124C.The wet solids obtained in Example 3 were suspended in methanol (540 ml) and the suspension is cooled to about 2C. Trifluoroacetic acid (100 ml) was added to the suspension and the resultant mass is stirred to get clear solution. The solution was further diluted with water (1.5 L) and the product is extracted using dichloromethane (3 x 100 ml). The organic layer was separated and concentrated to dryness under vacuum. The residue was crystallized from isopropanol or mixture of isopropanol and hexane and dried under vacuum to get 28-30 g product. Purity: more than 98% (by HPLC) Melting point : 176-178C.The ethyl acetate filtrates obtained in Example 3 were combined and evaporated to dryness. To the residue was added methanol (200 ml) and aqueous sodium hydroxide solution (100 ml, 40% w/v). The resultant mixture was stirred till TLC showed absence of bis L-valyl ester of ganciclovir. The pH of the solution was adjusted to 6.5-7. 0 using aqueous hydrochloric acid. The solids started to separate which were filtered and washed with water. The wet solid was suspended in water and heated to 70-80C to get a clear solution. The solution was cooled to 0-5C, filtered and dried to get ganciclovir. This recovered ganciclovir was recycled in the process as exemplified in Example 1. Yield: 8 g.To the aqueous layer obtained in Example 4 was further diluted with water (500 ml) and the resultant mixture neutralized to pH of about 6.7 using aqueous sodium hydroxide solution (20% w/v). The reaction mass was cooled to 2-5C and further maintained at the same temperature for 3 hours. The separated solids were filtered and washed with water (2 x 250 ml), the wet material (100 gm) was dissolved in water (600 ml) at 75-80C. The clear solution obtained was cooled to 5-10C and further maintained at 5-10C for 3 hours. The separated solids were filtered and washed with water (100 ml). The recovered ganciclovir was then dried at 50-55C. The recovered ganciclovir was recycled in the process as exemplified in Example 1.Trifluoroacetic acid (400 ml) was cooled to 5C and to it was added wet solids obtained in Example 3. The clear solution was obtained after stirring for 10-20 minutes. To this solution was added water (1.0 L) slowly at 5-10C and the resultant mixture was extracted with dichloromethane (3 x 500 ml). The aqueous layer was stored separately for recovery of ganciclovir. The combined organic layers were washed with water (500 ml) and concentrated at 35-40C under vacuum and the residue was recrystallized using denatured spirit. The product is dried to get pure CBZ-protected mono L-valyl ester of ganciclovir. Yield: 35-40 g Purity: more than 98% (by HPLC) Melting point : 176-178C.To a solution of CBZ-L-valine (88. 4 g) in dimethylsulphoxide (350 ml) at 18-20C was added dicyclohexylcarbidiimide (105 g), followed by the addition of 4-dimethylamino pyridine (2. 8 g). The reaction mixer was stirred for 10 minutes and was added to a solution of anhydrous ganciclovir (100 g) in dimethylsulphoxide (650 ml) in one lot at 20- 25C. The reaction mass was stirred at 20-25C for 60 minutes and then quenched by adding water (400 ml) slowly at 20-30C. The reaction mixture was stirred at 20-25C for 3 0 minutes. The separated solids were filtered and washed with a solution of dimethylsulphoxide (60 ml) in water (40 ml). Analysis of the filtrate showed: Desired product-