INTERMEDIATE FOR THE SYNTHESIS OF AMLODIPINE, PREPARATION PROCESS AND CORRESPONDING UTILIZATION

Abstract: An intermediate for the synthesis of amlodipine, a process for the preparation thereof and the corresponding use are disclosed. The intermediate is ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate and is of formula III The process for the preparation thereof comprises reacting the acetoacetate of formula with ammonium acetate; and the use thereof is for the preparation of the compound of formula the process being conducted by reacting ethyl 3-amino-4-[2-(phthalimido)ethoxy]crotonate with a benzylidene derivative.

Description: The present invention relates to an intermediate for the synthesis of amlodipine, to a process for the preparation thereof and to a use of the intermediate. The invention belongs to the field of heterocyclic chemistry and, as indicated, it relates to a chemical intermediate, ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate, to the process for the preparation thereof, and to the use thereof for the synthesis of 2-((2-aminoethoxy)methyl)-4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-1,4-dihydropyridine, generically known as amlodipine, a product having a therapeutical activity used as an antiischaemic and antihypertensive agent. Patent EP 0 089 167 discloses the use of 1,4-dihydropyridines of formula I, as immediate precursors of amlodipine of formula II Patent EP 0 060 674 discloses two processes for the preparation of 1,4-dihydropyridines containing in the 2 position a substituent having an amino group and having antiischaemic and antihypertensive utility. In both cases, the yields indicated are very low (≈15%) and the products have to be purified by chromatography, making the industrial application thereof difficult. Patent EP 0 089 167 discloses the preparation of various 1,4-dihydropyridines of formula I, precursors of amlodipine, following the same processes as indicated in patent EP 0 060 674: (a) where the aminoprotector groups are benzyl, azido or phthalimido, by reacting 2-chlorobenzaldehyde (IV) with ethyl acetoacetate (V) and methyl 3-aminocrotonate (VI) (b) Alternatively, where the aminoprotector groups are benzyl and azido, by reacting the benzylidene derivative (VII) with the aminocrotonate (VIII), this latter being prepared "in situ" from the corresponding ethyl acetoacetate (V) and ammonium acetate. In both processes the yields obtained are very low (30% and 11% respectively where the protector group is azido, NR 1 R 2 =N 3 ). On the other hand, the intermediate aminocrotonates (VIII) are not isolated or characterized, since they are prepared "in situ" from the corresponding ethyl acetoacetate (V) prior to the reaction with the benzylidene derivative (VII). No description has been found in the literature for the isolation or characterisation of these aminocrotonates (VIII). The present inventors have unsuccessfully tried to isolate the formula VIII compound disclosed in patent EP 0 089 167, where R 1 = R 2 = Bn. This patent discloses these compounds as prepared "in situ" (page 8), without any experimental check of their characteristics or chemical structure. Since the acetoacetates (V) and the benzylidene derivative (VII) are oils, it was fundamental to have a solid intermediate allowing formula (I) compounds to be prepared with a high yield and purity. The present invention relates to a new compound, ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate, of formula III It has been possible to isolate the new compound of formula III in solid state, thereby allowing for the purification, identification and characterisation thereof. This compound has turned out to be very useful as an intermediate for the synthesis of 4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-(2-phthalimidoethoxy)methyl-1,4-dihydropyridine (of formula I, where NR 1 R 2 = phthalimido), the immediate precursor of amlodipine. The process of preparation of III consists of reacting ethyl 4-[2-(phthalimido)ethoxy]acetoacetate (V, NR 1 R 2 = phthalimido) with ammonium acetate in a reaction medium, which is preferably an organic solvent (ethanol, isopropanol, toluene, etc.) and the desired product is isolated in solid form by crystallisation, with good yield and a high degree of purity. The reaction is conducted at a temperature ranging from 10°C to the reflux temperature, preferably from 50 to 70°C. When the reaction is conducted in toluene, a Dean-Stark device can be used, in order to remove the formed water. Optionally, in this case, at the end of the reaction the toluene can be distilled off and replaced by an alcohol, preferably ethanol or isopropanol, in order to reach a higher yield. One use of interest of the solid ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate (of formula III) is achieved by reacting it with methyl 2-(2-chloro-benzylidene)acetoacetate (of formula VII) in a organic solvent (methanol, ethanol, isopropanol, toluene, xylene), preferably ethanol, at a temperature ranging from 10°C and the reflux temperature, preferably from 60 to 80°C. The reaction was held for 12 to 24 hours, after which, it was cooled, whereby the 4-(3-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-(2-phthalimidoethoxy)methyl-1,4-dihydropyridine (I; NR 1 R 2 = phthalimido) crystallised, and was isolated with a high degree of purity and yield, superior to those described in the literature. Certain examples illustrating the invention are described hereinafter. EXAMPLE 1 Ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate (III) 32 g (100 mmoles) of ethyl 4-[2-(phthalimido)ethoxy]acetoacetate in 200 ml of toluene were reacted with 8.1 g (105 mmoles) of ammonium acetate at 65°C for 4 hours, the water formed in the reaction being removed with a Dean-Stark apparatus. The toluene was evaporated to dryness and the distillation residue was crystallised from isopropanol to give 24.5 g (yield 77%) of a beige coloured solid, corresponding to ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate. m.p.: 90-92°C. 1 H NMR (300 MHz, DMSO) δ 7.8 (m, 4H, ar), 7.5 (s, 1H, NH 2 ), 6.7 (s, 1H, NH 2 ), 4.4 (s,1H, -CH=), 3.9 (m, 4H, -COCH 2 -, =C-CH 2 O-), 3.8 (t, 2H, -OCH 2 -), 3.6 (t, 2H, -CH 2 N), 1.1 (t, 3H, CH 3 ) EXAMPLE 2 4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-(2-phthalimidoethoxy)methyl-1,4-dihydropyridine. 24.0 g (75.4 mmoles) of ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate and 18.9 g (79.2 mmoles) of methyl 2-(2-chlorobenzylidene)acetoacetate in 64 ml of ethanol were heated under reflux for 20 hours. The reaction mixture was diluted with 56 ml of ethanol and was cooled to crystallise the product. 14.2 g (yield 70%) of 4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-(2-phthalimidoethoxy)methyl-1,4-dihydropyridine were obtained. m.p.: 150-151°C. IR (KBr): 3370, 1712, 1489, 1422, 1392, 1287, 1201, 1122, 1102, 1024 cm -1

Claims: An intermediate for the synthesis of amlodipine, said intermediate being known as ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate, of formula III A process for the preparation of an intermediate known as ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate of formula III comprising reacting the acetoacetate of formula with ammonium acetate, at a temperature ranging from 10°C to the reflux temperature, to prepare said intermediate, which is isolated in solid form by crystallisation in the same reaction medium. The process of claim 2, wherein said reaction medium is an organic solvent. The process of claim 3, wherein said organic solvent is ethanol, isopropanol or toluene. A process of use of ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate of formula III for the preparation of the compound of formula comprising reacting said ethyl 3-amino-4-(2-(phthalimido)ethoxy)crotonate with a benzylidene derivative of formula VII at a temperature ranging from 10°C to the reflux temperature.

Inventors: CAMPON PARDO JULIO, COPPI LAURA, GASANZ GUILLEN YOLANDA, CAMPON PARDO, JULIO, COPPI, LAURA, GASANZ GUILLEN, YOLANDA
Applicants: ESTEVE QUIMICA SA, ESTEVE QUIMICA, S.A.
Application year: 1999
Main classification: C07D209
IPC codes: C07D401, A61K31, C07D209, A61P9