ZILPATEROL

Originator

Zilpaterol hydrochloride,LONZA LTD.

Uses

Zilpaterol is a β-Adrenergic agonist. Growth promotant.

Definition

ChEBI: Zilpaterol is a benzazepine.

Manufacturing Process

7.6 g of sodium hydride as a 50% suspension in oil were added over 30 min with stirring to a mixture of 29.6 g of 1,3-dihydro-1-benzyl-2H-benzimidazol- 2-one [described in Helv., Vol. 44 (1961), p. 1278] in 296 ml of dimethylformamide and the mixture was stirred for another 30 min and was cooled to 5°C. 33.9 g of ethyl 4-bromobutyrate were added dropwise to the mixture over 30 min and the mixture was stirred at room temperature for 3 h and was poured into 900 ml of iced water. The mixture was extracted with ether and the organic phase was washed with water, dried and evaporated to dryness. The oil residue was dissolved in 50 ml of isopropyl ether and the solution was allowed to crystallize for 16 h and was then vacuum filtered to obtain 22.6 g of ethyl 1,3-dihydro-2-oxo-3-benzyl-1H-benzimidazol-1- butanoate, melting point 52°C (crystallization from cyclohexane).
A mixture of 40.6 g of the ethyl 1,3-dihydro-2-oxo-3-benzyl-1H-benzimidazol- 1-butanoate and 400 ml of 1 N methanolic sodium hydroxide was refluxed for 3 h under an inert atmosphere and was then concentrated to 0.5 its value and was poured into 1 L of iced water. The pH was adjusted to 2 by addition of concentrated hydrochloric acid and the mixture was vacuum filtered. The product was washed and dried to obtain 35.2 g of 1,3-dihydro-2-oxo-3- benzyl-1H-benzimidazol-1-butanoic acid, melting point 168°C (crystallization from ethyl acetate).
21.5 ml of thionyl chloride were added to a suspension of 21.5 g of the product of 1,3-dihydro-2-oxo-3-benzyl-1H-benzimidazol-1-butanoic acid in 430 ml of chloroform and the mixture was refluxed for 75 min and was evaporated to dryness under reduced pressure. The residue was dissolved in 860 ml of dichloroethane under an inert atmosphere and after cooling the mixture to 15°C, 18.67 g of aluminum chloride were added thereto. The mixture was stirred at 20°C for 4 h and was poured into 1 L of iced water. 43 ml of concentrated hydrochloric acid were added thereto and the mixture was stirred for 10 min and was filtered. The decanted aqueous phase was extracted with methylene chloride and the combined organic phases were washed with aqueous 10% potassium carbonate to a pH of 6 and were dried and evaporated to dryness under reduced pressure. The residue was crystallized from ethyl acetate and dried to give 8.7 g of 5,6-dihydro-1- benzyl-imidazo[4,5,1-j-k][1]benzazepin-2,7-[1H,4H]-dione, melting point 135°C (crystallization from isopropanol).
A mixture of 29.2 g of the 5,6-dihydro-1-benzyl-imidazo[4,5,1-j- k][1]benzazepin-2,7-[1H,4H]-dione, 292.0 g of o-phosphoric acid and 14.1 g of phenol were heated at 150°C under an inert atmosphere for 2 h, was cooled to about 35°C and was poured into 1200 ml of iced water with stirring. 2 L of methylene chloride were added to the mixture which was then made alkaline with sodium hydroxide. The mixture was filtered and the solids were washed with methylene chloride. The combined organic phases were washed, dried and evaporated to dryness under reduced pressure. The residue was crystallized and was chromatographed over silica gel. Elution with a 90:2:2 ethyl acetate-methanol-triethylamine mixture yielded 9.7 g of 5,6-dihydro- imidazo[4,5,1-j-k][1]benzazepin-2,7-[1H,4H]-dione, melting point 235°C.
42.5 ml of 1.8 N ethanolic hydrochloric acid and 10.5 ml of tert-butyl nitrite were added at 5°C under an inert atmosphere to a suspension of 15.5 g of the 5,6-dihydro-imidazo[4,5,1-j-k][1]benzazepin-2,7-[1H,4H]-dione in 620 ml of tetrahydrofuran and the mixture was stirred at 5°C for 3 h and was vacuum filtered. The product was washed with tetrahydrofuran and with a 1:1 chloroform-methanol mixture to obtain 16.5 g of 6-oxime of 4,5- dihydroimidazo[4,5,1-j-k][1]benzazepin-2,6,7[1H]-trione, melting point >280°C.
A suspension of 4.0 g of the 6-oxime of 4,5-dihydroimidazo[4,5,l-j- k][1]benzazepin-2,6,7[1H]-trione 2.0 g of 10% palladium carbon and 150 ml of methanol was stirred under hydrogen for 2,5 h and was then filtered. The filtrate was cooled in an ice bath while slowly adding with mild stirring 0.66 g of sodium borohydride and the mixture was stirred at 5°C for 90 min. The mixture was evaporated to dryness under reduced pressure at 30°C and the residue was dissolved in 15 ml of methanol. The solution was acidified to a pH of 1-2 by addition of hydrogen chloride in ethyl acetate and the mixture was vacuum filtered to obtain 3.6 g of (6RS, trans)-6-amino-7-hydroxy-4,5,6,7- tetrahydro-imidazo[4,5,l-j-k][1]benzazepin-2[1H]-one hydrochloride melting at >260°C (crystallization from methanol and then from ethanol). The base (6RS, trans)-6-amino-7-hydroxy-4,5,6,7-tetrahydro-imidazo[4,5,l-j- k][1]benzazepin-2[1H]-one may be produced from (6RS,trans)-6-amino-7- hydroxy-4,5,6,7-tetrahydro-imidazo[4,5,l-j-k][1]benzazepin-2[1H]-one hydrochloride by treatment of salt with sodium hydroxide.
3.0 g of sodium cyanoborohydride were added over 15 min at 0-5°C to a mixture of 6.0 g of (6RS, trans)-6-amino-7-hydroxy-4,5,6,7-tetrahydro-imidazo[4,5,l-j-k][1]-benzazepin-2(1H)-one, 60 ml of methanol and 30 ml of acetone and the mixture was stirred at room temperature for 3 h and was evaporated to dryness under reduced pressure. The residue was added to 60 ml of water and the mixture was extracted with chloroform. The organic phase was dried and evaporated to dryness to obtain 3.6 g of (6RS,trans)-6- isopropylamino-7-hydroxy-4,5,6,7-tetrahydro-imidazo[4,5,l-j-k][1]- benzazepin-2(1H)-one, melting point 166°C.

Therapeutic Function

Beta-adrenergic blocker, Cardiac stimulant

Raw materials

Preparation Products