CAS 1080028-80-3 BASE
1383828-47-4 OF HCL SALT
C21 H21 F2 N3 O S BASE
2H-Imidazole-2-thione, 1-[(3R)-6,8-difluoro-3,4-dihydro-2H- 1-benzopyran-3-yl]-1,3-dihydro-5-[2-[(phenylmethyl)amino] ethyl] -(R)-5-(2-(Benzylamino)ethyl)-1-(6,8-difluorochroman-3-yl)-1H-imidazole-2(3H)-thione
Molecular Weight, 401.47 BASE
- BIAL - PORTELA & CA., S.A. [PT/PT]; À Avenida da Siderurgia Nacional P-4745-457 S. Mamede do Coronado (PT)
- Zamicastat is a dopamine beta-monooxygenase inhibitor in phase I clinical studies at BIAL for the treatment of hypertension and heart failure.
- Zamicastat is a potent and selective dopamine β-mono-oxygenase inhibitor. Zamicastat Prevents the Deterioration of Cardiometabolic and Inflammatory Biomarkers in a Genetic Model of Salt-sensitive Hypertension. Chronic high salt intake deteriorates several cardiometabolic and inflammatory biomarkers in Dahl/SS rats, which can be prevented by dopamine β-hydroxylase inhibition with zamicastat.
forms of l-[(3R)-6,8-difluoro-
imidazole-2-thione, i.e. the Renantiomer of
Potent dopamines-hydroxylase inhibitors having high potency and significantly reduced brain access are disclosed in WO 2008/136695. WO 2008/136695 describes compounds of formula I:
Processes for the preparation of compounds of formula I, and in particular l-[(3R)-6,8- difluoro-3,4-dihydro-2H-l-benzopyran-3-yl]-l,3-dihydro-5-[2-[(phenylmethyl)amino] ethyl] -2H-Imidazole-2-thione, are described in WO 2008/136695 and are incorporated by reference herein. It is known that polymorphic forms of the same drug may have substantially different pharmaceutically important properties such as dissolution characteristics and bioavailability as well as stability of the drug. Furthermore, different forms may have different particle size, hardness and glass transition temperature. Thus, one form may provide significant advantages over other forms of the same drug in solid dosage form manufacture processes, such as accurate measurement of the active ingredients, easier filtration, or improved stability during granulation or storage. Furthermore, a particular process suitable for one form may also provide drug manufacturers several advantages such as economically or environmentally suitable solvents or processes, or higher purity or yield of the desired product.
Preparation of compound 2
 Six lots of compound 2 (designated as lots 1, 2, 3, 4, 5 and 6) were prepared. The starting materials were prepared according to the following experimental protocols.
Lot 1 (Form A)
To a suspension of (R)-5-(2-aminoethyl)-l-(6,8-difluorochroman-3-yl)-lH- imidazole-2(3H)-thione (6.23 g, 20 mmol) in a mixture of Dichloromethane (DCM - 40 ml) and Methanol (40.0 ml) was added BENZALDEHYDE (2.230 ml, 22.00 mmol). To the resulting clear solution SODIUM CYANOBOROHYDRIDE (1.9 g, 28.7 mmol) was added in portions at 20-25°C to avoid intensive foaming and the solution was stirred at 20- 25°C for 40 h. The solution was quenched at 20-25°C with IN HC1 (35 ml), neutralised with 3N NaOH (35 ml), the mixture was extracted with DCM (200 ml). The organic phase was washed with brine, dried (MgS04), evaporated to dryness. The oily residue crystallised from 2-propanol (40 ml) at 20-25°C over a week-end. The crystals were collected, washed with 2-propanol, dried to give 5.2 g of the crude product. Re- crystallisation from 2-propanol-DCM hasn't removed all impurities. Everything collected, evaporated with silica, applied on a column, eluted with Ethyl Acetate (EA)->EA-MeOH 9:1->4: 1, fractions 8-25 collected to give 3.8 g. Re-crystallised from 2-propanol (45 ml) and DCM (120 ml, removed on a rotavap) to give 2.77 g => initial lot (a) (HPLC 98.3% area) and 0.3 g of undissolved filtered off, by TLC right product. Initial lot (a) re- crystallised from 2-propanol (35 ml) and DCM (95 ml, removed on a rotavap) to give 2.51 g => initial lot (b) (HPLC 98.3% area). Combined with the above undissolved, re- crystallised from acetonitrile (200 ml, reflux to ice bath) to give 2.57 g => initial lot (c) (HPLC 98.8% area). Re-crystallised from acetonitrile (180 ml, reflux to 15°C) to give 2.25 g => Lot 1 (HPLC 99.2% area), mp 190-92°C. Lot 2 (Form A)
 (R)-5-(2-(benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole- 2(3H)-thione (12 g, 29.9 mmol) was dissolved with heating to reflux in Tetrahydrofuran (300 ml), the solution was cooled to 5-10°C, Water (510 ml) was added slowly (approx 10 min) with stirring. The mixture was stirred for 1 h, solid was collected, washed with water, dried to give 11.73 g of product, by HPLC 1% of (R)-5-(2-Aminoethyl)-l-(6,8- difluorochroman-3-yl)-l,3-dihydroimidazole-2-thione hydrochloride and 1% of less polar impurity. The product was dissolved in Tetrahydrofuran (300 ml) with heating to reflux, 2- Propanol (150 ml) was added, the solution was concentrated to approx 100 ml (crystallisation occured), stirred in ice for 1.5 h. Solid was collected, washed with 2- propanol, dried to give 11.2 g of product, by HPLC 0.8% of (R)-5-(2-aminoethyl)-l-(6,8- difluorochroman-3-yl)-lH-imidazole-2(3H)-thione hydrochloride and 0.5% of less polar impurity. The product was dissolved in Tetrahydrofuran (300 ml) with heating to reflux, 2- Propanol (150 ml) was added, the solution was concentrated to approx 100 ml (crystallisation occured), stirred at 20-25°C for 1 h. Solid was collected, washed with 2- propanol, dried to give (R)-5-(2-(benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH- imidazole-2(3H)-thione (10.22 g, 25.5 mmol, 85 % yield).,
Lot 3 (form B)
To (R)-5-(2-aminoethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole-2(3H)- thione (2.36 g, 7.58 mmol) in a mixture of Methanol (15.00 ml) and Dichloromethane (15 ml) was added BENZALDEHYDE (0.845 ml, 8.34 mmol). To the resulting clear solution SODIUM CYANOBOROHYDRIDE (0.702 g, 10.61 mmol) was added in portions at 20- 25°C to avoid intensive foaming and the solution was stirred at 20-25°C for 40 h. The solution was quenched at 20-25°C with IN HC1 (12 ml), neutralised with 3N NaOH (12 ml), the mixture was extracted with DCM (100 ml). The organic phase was washed with brine, dried (MgS04), evaporated to dryness. The residue was purified on a column with EA-MeOH 9: 1 as eluent, fractions collected, concentrated to approx 20 ml, cooled in ice. The precipitate collected, washed with Ethyl Acetate-Petroleum Ether 1 : 1, dried on air to give (R)-5-(2-(benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole-2(3H)- thione (1.55 g, 3.86 mmol, 50.9 % yield). Lot 4 (Form A)
To a 500 mL flask set up for atmospheric distillation was added (R)-5-(2- (benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole-2(3H)-thione (20 g, 49,8 mmol) and Tetrahydrofuran (400 ml) to afford a suspension. The suspension was heated until full dissolution was achieved (61°C) whereupon it was filtered. The resulting solution was then heated to 66°C in order to commence the distillation. A mixture of Water (125 ml) & 2-Propanol (125 ml) was added at the same rate as the distillate was collected. The distillation was continued until 400 mL of distillate was collected. Crystallisation commenced after ~320 mL of distillate was collected. The suspension was cooled to 20°C and aged for 45 min. before filtering and washing with additional 2- propanol (80 mL) and then dried under vacuum at 50°C overnight to give (R)-5-(2- (benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole-2(3H)-thione (18.79 g, 94%). Lot 5 (Form A)
To a mixture of Methanol (66 L) and Water (10 L) at 20°C was added purified (R)-5-(2-(benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH-imidazole-2(3H)-thione hydrochloride (4.37 kg, 9.98 mol) to afford a suspension. The reaction mixture was then heated to 67°C to affect complete dissolution, whereupon IN Sodium hydroxide (10.48 Ls 10.48 mol, 1.05 eq) was added in a single portion. The reaction mixture was adjusted back to 67°C and held at 67°C for 30 min. The reaction mixture was then cooled to 20°C and aged at 20°C for at least 30 min. The reaction was then filtered and the filter cake washed with aqueous Methanol (1 : 1 v/v, 20 L), sucked down for 15 min. and then dried at 45°C under vacuum, to afford (R)-5-(2-(benzylamino)ethyl)-l-(6,8-difluorochroman-3-yl)-lH- imidazole-2(3H)-thione (3.855 kg, 96%) as a pale tan crystalline solid.
(J?) -5- (2-Aminoethyl) -1- (6, 8-difluorochroman-3-yl) -1, 3-dihydroimidazole-2 -thione hydrochloride (the compound of formula 1, below) is a potent, non-toxic and peripherally selective inhibitor of ϋβΗ, which can be used for treatment of certain cardiovascular disorders. Compound 1 is disclosed in WO2004/033447 , along with processes for its preparation.
The process disclosed in WO2004/033447 involves the reaction of ( R) - 6 , 8 -difluorochroman-3 -ylamine hydrochloride (the structure of ( R) -6, 8-difluorochroman-3 -ylamine is shown below as compound QA) , [4 - ( tert-butyldimethylsilanyloxy) -3 -oxobutyl] carbamic acid tert-butyl ester and potassium thiocyanate .
(R) -6 , 8-difluorochroman- 3 -ylamine (compound QA) is a key intermediate in the synthesis of compound 1. The stereochemistry at the carbon atom to which the amine is attached gives rise to the stereochemistry of compound 1, so it is advantageous that compound QA is present in as pure enantiomeric form as possible. In other words, the (R) -enantiomer of compound QA should be in predominance, with little or no (S) enantiomer present. Thus, the process for preparing compound QA will advantageously produce compound QA with as high enantiomeric excess (ee) as possible.
Advantageous processes for preparing, for example, the compound of formula QA have now been found. In one aspect, the processes involve a biotransformation step. In another aspect, the processes involve chemical transformation. The processes may also be employed in the preparation of similar precursors useful in the production of other peripherally-selective inhibitors of dopamine -β -hydroxylase .
WO2008/136695 discloses a compound of formula YA, its (R) or (S) enantiomer, a mixture of its (R) and (S) enantiomers, or pharmaceutically acceptable salts thereof.
The (R) -enantiomer of the compound of formula YA has been found to be a potent dopamines-hydroxylase inhibitor having high potency and significantly reduced brain access.
As disclosed in WO2008/136695 , the compound of formula YA may be prepared by reacting the compound of formula 1 with benzaldehyde under reductive alkylation conditions. In particular, (R) -5- (2 -aminoethyl ) -1- (6 , 8-difluorochroman-3 -yl) - 1 , 3 -dihydroimidazole-2 -thione and benzaldehyde may be reacted in the presence of a solvent or mixture of solvents, and a reducing agent such as sodium cyanoborohydride or sodium triacetoxyborohydride .
process comprises the following steps:
The route from 2 , 4-difluorophenol may be as described 9/064210.
Preferably, the reagents and conditions are:
(i) H2S04, acetic acid
(ii) NaOCl, MeOH/water
(iii) Ru-based catalyst, H2, 30 bars, MeOH
(iv) aqueous KOH, MeOH, L-tartaric acid
(v) KSCN, AcOH/lPA
(vi) NaBH4, BF3.THF complex, THF then IPA
n one aspect, the process comprises the following steps
i. KOH, Thioglycolic acid or cysteine
According to an aspect of the present invention, there is provided the following 2 -part synthetic route from the starting material 2 , 4 -difluorophenol to (R) -5- (2 -aminoethyl ) -1- (6 , 8-difluorochroman-3 -yl) -1 , 3 -dihydroimidazole-2 - thione
Preferred reagents and conditions:
a) HMTA, CF3COOH, 115°C, 18 hours
b) CH2CHCN, DABCO, DMF, water, 70°C, 16 hours
c) H2S04, AcOH, 100°C, 1 hour
d) NaClO, NaOH, MeOH, 25°C, 24 hours
e) (R) -C3 -TunePhosRu (acac) 2 S/C 3000, 30 bar H2, MeOH, 80°C, 20 hours
f) Water, 2-propanol, reflux to 20°C
g) 40% KOH, MeOH, reflux, 24 hours
h) L-tartaric acid, ethanol, water, RT, 1 hour
Preferred reagents and conditions
a') methyl vinyl ketone, t-BuONa, EtOAc, EtOH, 40-50°C, 2-3 hours
Br2, MeOH, 20-25°C, 5 hours
water, reflux, 1 hour
KOH, AcOH, reflux, 1 hour
HCl, water, 2-propanol, 75 °C, 4 hours
KSCN, AcOH, 100°C, 2-4 hours
NaHC03, water, EtOH
NaBH4, 2-propanol, THF, water, 20-25°C, 16 hours
HCl, 2-propanol, water, reflux, 1-2 hours
The ( R ) -5- (2-Aminoethyl) -1- (6, 8-difluorochroman-3 -yl) -1,3-dihydroimidazole-2 - thione hydrochloride may then be used to
prepare (R) -5- (2- (benzylamino) ethyl) -1- (6, 8-difluorochroman-3 -yl) -lH-imidazole-2 (3H) -thione as follows.
Preferred reaction conditions/reagents:
q) NaBH(OAc)3, PhCHO, IPA;
t) NaOH, MeOH , H20
Either r) and s) :
r) HCI aq;
Or n) , o) and p) :
n) HCI aq;
o) MeOH, toluene;
Nitro chromene synthesis
To 3 , 5-difluoro-2-hydroxybenzaldehyde (lOg, 63mmol, leq) , di-n-butylamine (4.1g, 32mmol, 0.5eq) , phtalic anhydride (18.7g, 126mmol, 2eq) in toluene (500mL) was added nitroethanol (5.75g, 63mmol, leq) . The round bottomed flask fitted with a dean stark apparatus was refluxed for 18h. The mixture was cooled and nitroethanol (5.75g, 63mmol, leq) was added. The resulting reaction mixture was then reflux for 12h. After cooling, the solution was evaporated down to approximately 150mL and purified over silica gel (eluent ethyl acetate : hexane 1:1) this gave several fractions that contained only the product by TLC, these was evaporated under reduced pressure to yield 1.8g which was 100% pure by HPLC aera. Several more fractions were collected containing a mixture of product and starting material. These were combined and washed with 2% NaOH solution (2x50mL) to remove starting material. The organic layer was washed with water (50mL) , dried over sodium sulfate and evaporated under reduced pressure to give 2.49g of brown solid ( 100% pure by HPLC aera) . More fractions were collected. These were combined, washed with 2% NaOH solution (3xl00mL) , water (lOOmL) and dried over sodium sulfate. This was then filtered and evaporated down in vacuum to yield 6.14g of a brown solid which was 91.3% pure by HPLC aera. 6 , 8 -difluoro-3 -nitro-2H-chromene (9.90g, 73.4%) was obtained as a brown solid.
Nitro chromene synthesis with column purification
To a solution of isobenzofuran-1 , 3 -dione (4,68 g, 31,6 mmol) , 3 , 5-difluoro-2 -hydroxybenzaldehyde (2,5 g, 15,81 mmol) in Toluene (25 ml) was added 2 -nitroethanol (2,88 g, 31,6 mmol). The resulting mixture was heated to reflux overnight (Dean stark) .
The reaction conversion was checked by TLC (eluent PE/EtOAc 9:1) . A yellow spot was observed and corresponds to the expected product .
Reaction was cooled to room temperature and a plug of silica gel was performed. A pale brown solid (3.9g) was obtained. """H-NMR showed presence of product and starting material. The solid was dissolved in diethylether and the organic layer was washed with aqueous sodium carbonate, dried over Na2S04, filtered and concentrated under reduced pressure. A pale brown solid (1.7g,) was obtained. The 1H-NMR was indicated no starting material but still polymer from nitroethanol and residue of phtalic anhydride. A second silica plug (eluent: PE/EtOAc 95:5) was done. A pale yellow solid (1.5g) was obtained. 1H-NMR of solid showed only product and polymer. The solid was recrystallized from methanol/water . A pale yellow solid (1.05g, 31.2%) was obtained.
Nitro chromene synthesis without column purification
To a solution of isobenzofuran- 1 , 3 -dione (18,74 g, 127 mmol) , 3 , 5-difluoro-2 -hydroxybenzaldehyde (10 g, 63,3 mmol) in Toluene (100 ml) was added 2 -nitroethanol (6,86 ml, 95 mmol) . The resulting mixture was heated to reflux for 24h (Dean stark) .
The reaction conversion was checked by HPLC and by 1H-NMR. Only 50% conversion was obtained.
The reaction mixture was cooled to room temperature and diluted with DCM (lOOmL) and 1M NaOH solution (200mL) .
The biphasic system was stirred for 30 minutes and then separated (very difficult to see phase separation) . The aqueous layer was washed with DCM (50mL) and the combined organic layers were washed twice with water (2x50ml) , dried over sodium sulfate. The filtered organic layer was concentrated under reduced pressure. To the residue was added methanol (50mL) . The methanol was then removed by distillation under reduced pressure. A brown solution precipitated when most of the methanol was removed. More methanol was added and more solid crushed out then few drops of water was added to increase the product precipitation. The brown slurry was stirred for 30 minutes and filtered. The brown solid was washed with methanol/water (1:9, 5mL) and dried in a vacuum oven at 40°C for 12h.6, 8-difluoro-3 -nitro-2H-chroraene (4,9 g, 22,99 mmol,) was obtained as brown solid in 36.3% yield.
HPLC showed a purity of 98% and 1H-NMR confirmed the structure and purity around 95%
Reduction of nitro chromene to nitro-alkane (racemic mixture)
To a suspension of 6 , 8 -difluoro-3 -nitro-2H-chromene (213mg, 0,999 mmol) and silica (0,8 g, 0,999 mmol) in a mixture of CHC13 (10 ml) and IPA (3,4 ml) at 0°C was added portion wise sodium borohydride (95 mg, 2,498 mmol). The resulting mixture was stirred at 0°C for 45 minutes. Reaction conversion was checked by HPLC. 1 mL of acetic acid was added at 0°C and the resulting mixture was stirred for 30 minutes at room temperature. The slurry was filtered and the silica was washed with DCM. The filtrate was diluted with ethyl acetate and water and the biphasic system was separated. The aqueous layer was back extracted with ethyl acetate. The combined organic layers were washed with brine, dried over MgS04, filtered and concentrated under reduced pressure.
6 , 8-difluoro-3 -nitrochroman (196mg, 0,911 mmol, 91 % yield) was obtained as a pale yellow oil.
Preparation of 6 , 8 -difluorochroman-3 -one from nitro chromene
A solution of 6, 8-difluoro-3 -nitro-2H-chromene (lOOmg, 0,469 mmol) in acetic acid (0.5 ml) is added slowly to a stirred slurry of iron (262 mg, 4,69 mmol) in acetic acid (1 ml) at 60.deg. C. The reaction mixture is stirred at 60. °C for 2 hour then allowed to cool to room temperature and stirred overnight. The reaction mixture is poured onto ice-water (30 ml) and filtered through Celite. The solid was wash with dichloromethane (DCM) (50 ml) . The organic portion is separated and washed with water (2 x 30 ml) and brine (30 ml) , dried over MgS04, filtered and concentrated in vacuo to give a brown oil. 6,8-difluorochroman-3 -one (75 mg, 0,407 mmol, 87 % yield) was obtained as a brown oil.
Preparation of 6 , 8-difluorochroman-3 -one from methyl 6,8-difluoro-2H-chromen-3 -yl-carbamate
Methanol (1000m ml) was added to a slurry of methyl fluoro-2H-chromen-3 -yl -carbamate (250 g, 1.037 mol) hydrogen chloride 6N (2000 ml, 12 mol) at room temperature. The resulting mixture was reflux and stirred for 2 hours. Reaction monitored by HPLC.
Reaction was not complete but was stopped in order to avoid degradation of the product. The yellow solution was cooled to room temperature. A slurry (two type of solid) was observed and diluted with diethyl ether (300mL) . The resulting slurry was stirred at 5°C for 1 hour then filtered. The yellow solid was washed with water. The resulting wet yellow solid was suspended in diethylether (400mL) and petroleum ether (PE) (400mL) was added. Slight yellow solid was stirred at room temperature overnight, filtered and washed with PE (300mL) , dried in a vacuum oven at 30 °C for 4h. The wet sample was checked by NMR. No starting material was detected. A pale yellow solid (72.5g, solid 1) was obtained. The mother liquors were concentrated to dryness. A yellow solid was obtained, suspended in diethyl ether and PE. The slurry was then stirred for 4 hours, filtered, washed with PE . A dark yellow solid (4.5g, solid 2) was obtained. Solid 1 (2g) was diluted in DCM and washed with water (pH =6). The organic layer was then dried over Na2S04, filtered, concentrated to dryness. A crystalline pale yellow solid (1.9g, solid 3) was obtained. NMR showed the same purity for solid 3 as for solid 1. The remaining part of solid 1 was then diluted in DCM. The resulting organic layer was washed with water, dried over Na2S04, filtered and then concentrated to dryness. Slight yellow crystalline solid (68.5g, solid 4) was obtained. NMR confirmed high quality material.
Loss on Drying (LOD) : 1.03% .
Codexis transaminases ATA-025, ATA-251 and ATA-P2-A07 recognized 6 , 8 -difluorochroman-3 -one as the substrate and produced the corresponding 6 , 8 -difluorochroman-3 -amine .
International Journal of Pharmaceutics (Amsterdam, Netherlands) (2016), 501(1-2), 102-111.
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