WO2004058711A1

WO2004058711A1 - Isolation of dihydropyridine derivative and preparation salts thereof

Info

Publication number: WO2004058711A1
Application number: PCT/TR2002/000078
Authority: WO
Inventors: Tuncer Aslan; Mustafa Adiyaman; Aycil Yurdakul; Filiz Sahpaz; Evren A. Ozarslan; Didem Guner; Nurten Ridvanoglu
Original assignee: Eos Eczacibasi Ozgun Kimyasal Urunler Sanayi Ve Ticaret A.S.
Priority date: 2002-12-30
Filing date: 2002-12-30
Publication date: 2004-07-15
Also published as: AU2002368531A1

Abstract

The title compound is isolated in pure form by using a crystallization process and converted to its pharmaceutically acceptable salts. The crystallization process affects stability and purity of the amlodipine salts. All known impurities and one unknown impurity, which forms during the synthesis of the amlodipine salts, were isolated, characterized, and synthesized. A new method allowing the quantitative HPLC analysis of all related impurities of amlodipine salts in a single chromatogram was developed.

Description

ISOLATION of DIHYDROPYRIDINE DERIVATIVE and PREPARATION SALTS THEREOF

BACKGROUND OF THE INVENTION

The invention enclosed here provides an improved industrial process for the isolation of 3-ethyl, 5-methyl (4RS) -2-[2-ammoemo^)methyl]-4-(2-chlorophenyl)-6-methyl 1,4- dihydropyridine-3₅5-dicarboxylate, hereafter named as amlodipine base, and preparation of pharmaceutically acceptable salts thereof.

There has been known methods for the preparation of amlodipine salts via in situ preparation of amlodipine base.

US Patent 4,572,909 encloses three different procedures for in situ preparation of the amlodipine base starting from 3-ethyl 5-methyl (4i?S)-4-(2-chlorophenyl)-2-[[2-(l,3-dioxo-l,3- dhydro-2H-isomdol-2-yl)emoxy]me yl]-6-memyl-l,4-dmy<kopyridιne-3,5-dicarboxylate, hereafter named as phthaloyl amlodipine. Phthalimido side chain of phthaloyl amlodipine is deprotected by using methylamine, hydrazine hydrate or potassium hydroxide, h any case the formed amlodipine base is not isolated but precipitated as maleate salt by adding maleic acid.

US Patent 5,438,145 describes another approach for the preparation of besylate salt of amlodipine base, in which the primary amino group is protected as trityl group by using triphenylmethyl chloride at the forth set of the synthesis. In this process again, amlodipine is not isolated as the free base but directly converted into the amlodipine besylate form.

EP 0 244 944 compares the stability, solubility, hygroscopicity and processability of the amlodipine salts. It was found that the most stable among all amlodipine salts is the amlodipine besylate. According to this patent, maleate salt is less stable than besylate, mesylate, tosylate, succinate and salicylate salts.

The present invention discloses here that the stability of the amlodipine salts depends strongly on the process that is followed through out the production of the active ingredient, particularly in the case of mesylate and maleate. The present invention solves the problems by isolating amlodipine base and provides products with a better quality and stability. SUMMARY OF THE INVENTION

The present invention provides a process for the isolation of 3-ethyl, 5-methyl (4i?5)- 2-[2-(am oemoxy)memyl]-4-(2-cMorophenyl)-l,4-dmydro-6-memylpyridine-3,5- dicarboxylate and salts thereof which comprises: (a) reacting phthaloyl amlodipine with 1 to 8 equivalent of hydrazine hydrate in a mixture of toluene and methanol at ranging temperatures from -10 to 80 °C;

(b) crystallizing the amlodipine base as a white solid by the addition of n-hexanes to the solution. This process improves the quality and stability of the final products; (c) identifying, characterizing and synthesizing a novel impurity which forms during the synthesis and particularly important in the case of amlodipine mesylate; and (d) developing a new HPLC method, which allows quantitative determination of all the impurities of amlodipine salts in a single chromatogram. DETAILED DESCRIPTION OF THE INVENTION Pharmaceutically acceptable salts of amlodipine are used as an antianginal and antihypertensive agent listed in EP 0 244 944. According to this patent pharmaceutically acceptable salts of amlodipine are besylate, mesylate, tosylate, succinate, maleate, salicylate acetate, and hydrochloride.

In the literature, amlodipine has not been isolated as the free base but directly converted into the corresponding salts starting from suitable precursor in all cases.

Initially, the inventors have conducted the experiment without isolating amlodipine base starting from phthaloyl amlodipine I. Three consecutive pilot batches, each about 2.3 kg were carried out to produce amlodipine maleate LT. The product of each batch was analyzed according to method given for amlodipine besylate in European Pharmacopoeia and the analysis showed that the product meets the specifications.

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Accelerated and normal stability tests of the active pharmaceutical intermediate (API) and the formulated product were initiated using samples from pilot batches. Although the products seemed to be stable initially, single and total impurity levels started to increase in time and the products were out of limits within the three months under accelerated stability conditions.

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Similar reactions have been attempted with unisolated base by using methanesulfonic acid to afford amlodipine mesylate HI, however it was observed by the inventors that the results were worse than amlodipine maleate case with respect to color, stability and impurity level. Since amlodipine base and the amlodipine salts have the similar impurity profile, it would be convenient to reduce the impurities by isolation of the base at the first step. This could improve the purity and stability of the final product. Phthaloyl group of amlodipine can be deprotected by the treatment with hydrazine hydrate, methylamine or potasium hydroxide and then the amlodipine base can be isolated in an organic solvent such as toluene, tetrahydrofuran, ethyl acetate, hexanes, isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile or mixture thereof, particularly in a toluene/hexane mixture. The reaction can be achieved at a temperature range of -10 to 80 °C. After deprotection of the phthaloyl group, formed phthalhydrazide precipitates as a yellow solid. The solid is removed by filtration, the organic phase is washed with water and dried over MgSO₄. The organic phase is reduced to one third of its original volume and the amlodipine base TV is crystallized out as a white powder by the addition of n-hexanes at 0 °C.

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The purity of the amlodipine base was measured by the HPLC analysis. The purity of crystallized amlodipine base is 99.47% based on the relative percent area whereas the purity of unisolated amlodipine base is 98.96%. As can be seen from these results, the isolation process reported in this invention have a great effect on the purity of the amlodipine base.

Amlodipine base is converted to the corresponding pharmaceutically acceptable salts using maleic acid, methanesulfonic acid, and benzenesulfonic acid. The inventors have performed the salt formation reaction with isolated base to solve above-mentioned purity and stability problems. In the case of amlodipine maleate, salt formation reaction can be carried out in an organic solvent such as, toluene, tetrahydrofuran, ethyl acetate, hexanes, isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, and mixture thereof, particularly in a toluene/mefhanol mixture.

IV π

In a typical procedure, amlodipine base is suspended in toluene and maleic acid is dissolved in methanol and was added to the above suspension. The resulting mixture was stirred at 21-24 °C temperatures for one hour. The solid product is taken out by filtration. Isolation of the base increases the purity of the amlodipine maleate π. Amlodipine maleate, which is prepared from isolated base, is stable under normal and accelerated stabihty conditions and stays within the limits. In the light of studies with amlodipine maleate above, similar experiments were carried out for the preparation of amlodipine mesylate HI. When the inventors initially obtained amlodipine mesylate from phthaloyl amlodipine without isolating amlodipine base as reported in US 4,572,909 patents the inventors have observed that the product was contaminated with an unknown impurity in amount that was exceeding the acceptable levels. As explained later in the text, the impurity is isolated, characterized and named as impurity E by the inventors.

Even amlodipine mesylate which is prepared from isolated base contains impurity E greater than 0.1% when analyzed according to amlodipine besylate method.

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After identification of the impurity, reactions were conducted by using more equivalents of deprotecting reagent. These reagents can be methylamine, KOH and particularly hydrazine hydrate. Increasing the equivalents of reagent during the preparation of the amlodipine base helps for reducing impurity E, but still not enough to drop to the acceptable level. The inventors have to add one more step to the process for the solution of the problem, all other attempts were unsatisfactory.

Further amlodipine mesylate ILT shows pseudo-polymorphism determined by using differential scanning caloiimetry. Either it catches an organic solvent or water. Thus amlodipine mesylate is converted to anhydrous mesylate salt and then to its stable form amlodipine mesylate monohydrate. The first step of the salt formation is a must to reduce impurity E level of the amlodipine mesylate. Organic solvents that can be used in the preparation of amlodipine mesylate anhydrous can be toluene, tetrahydrofuran, ethylacetate, hexanes, isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, and mixture thereof, particularly in a toluene/methanol mixture. In a typical reaction, amlodipine base TV is suspended into toluene and to this suspension methanesulfonic acid solution in methanol is added. After precipitation, the product is collected by filtration. The reaction can be performed between a temperature range of -10 to 80 °C, particularly between 0 to 30 °C.

Finally, amlodipine mesylate anhydrous IH is converted to the amlodipine mesylate monohydrate V in an organic solvent/water mixture. Organic solvents used in this reaction can be, such as toluene, tetrahydrofuran, ethylacetate, hexanes isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, and mixture thereof, particularly isopropanol/water mixture. In a typical reaction, amlodipine mesylate anhydrous is suspended into isopropanol/water mixture and heated gently until all the starting material is completely dissolved and then let to cool down to room temperature. This reaction can be done in a temperature range -10 to 80 °C.

Similar procedure is used for the preparation of amlodipine besylate as in the case of the amlodipine mesylate anhydrous starting from isolated base. In a typical procedure amlodipine base TV is suspended in toluene and to this suspension a solution of benzenesulfonic acid in methanol is added at room temperature. To remove the methanol in the mixture, 1/10 of the solvent was evaporated under high vacuum. The mixture was cooled down to 0-5 °C and stirred at this temperature for 2 hours. Formed crystals were filtered off and dried at 40 °C for 12h to yield amlodipine besylate VI in 87% yield as a white powder. Preparation of the amlodipine besylate starting from isolated amlodipine base reduces reaction time and provides an efficient process for the title compound. Synthesis of the Impurities

This invention provides a new HPLC method in order to detect and see all known amlodipine impurities in a single chromatogram as opposed to the method given in EP. The first step to develop an HPLC method requires an appreciable amount of the amlodipine impurities. These impurities are not commercially available and they have been prepared by organic synthesis.

3-Ethyl 5-methyl (4RS) -4-(2-chlorophenyl)-2-[[2-(l,3-dioxo-l,3-dhhydro-2fl-isoindol-2- yl)ethoxy] methyl]-6-methyl-l,4-dihydropyridine-3,5-dicarboxylate. Impurity A

This impurity known as phthaloyl amlodipine and chemical synthesis of the compound is given in US 4,572,909 patent.

3-Ethyl 5-methyl (4RS) -4-(2-chlorophenyI)-6-[[2-[[2-(methylcarbamoyl)benzoyl]amino] ethoxy]methyl]-l,4-dihydropyridine-3,5-dicarboxylate. Impurity B

Phthaloyl group of amlodipine can be deprotected by using three different reagents according to US patent 4,572,909. These reagents are methylamine, hydrazine hydrate and KOH. Impurity B forms during deprotection of phthaloyl group when methylamine is employed as the deprotecting agent. This impurity is reported in EP for amlodipine besylate as a side product.

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It was thought that impurity B could be obtained easily, if the deprotection reaction of phthaloyl group by using methylamine could be stopped at an early stage. Thus phthaloyl amlodipine is suspended into THF and aqueous methylamine solution is added to this suspension at room temperature. After 30 minutes, the mixture is concentrated under reduced pressure and impurity B is precipitated by adding diethylether as a white solid in 92 % yield. 3-Ethyl 5-methyl (4RS) 2,6-bis-[(2-aminoethoxy)methyI]-4-(2-chlorophenyl)-l,4-dihydro pyridine-3,5-dicarboxy!ate) Impurity C

Among all the impurities impurity C requires a special synthetic approach since it has two ethylamine side chains attached to the dihydropyridine functionality. Thus, accomplishment of the synthesis of impurity C requires a more difficult task than the synthesis of amlodipine itself.

In this invention, a convergent synthesis is employed to complete the synthesis of amlodipine impurity C. The first part of the synthesis involves the preparation of the ketoester iii as shown below. Firstly, phthalic anhydride is reacted with ethanol amine at varying temperatures from 90 °C to 135 °C to give N-(2-hydroxyethyl)ρhthalimide. Then, ethyl 4-[2- (phthalimido)ethoxy]acetoacetate is obtained by the reaction of N-(2-hydroxyethyi) phthalimide and ethyl 4-chloroacetoacetate in solvents such as THF or toluene using sodium hydride as the base at temperatures ranging from -15 °C to 30 °C. The ketoester XTIT is reacted with 2-chlorobenzaldehyde in an alcoholic solvent such as 2-propanol, ethanol, methanol in the presence of acetic acid and an organic base such as piperidine, pyrolidine, triethylamine at varying temperatures from 20 °C to 50 °C to give ethyl 2-(2-chlorobenzy Hα^e)-4-[2-(phmalimide)ethoxy]acetoacetate XVπi.

The second part of the synthesis involves the preparation of the enamine XVT. The reaction of methyl-4-chloroacetoacetate with N-(2-hydroxyethyl)phthalimide in solvents such as THF in the presence of a base such as sodium hydride at temperatures ranging from -15 °C to 30 °C afforded methyl 4-[2-(phthalimido)ethoxy]acetoacetate. The desired methyl (3- amino)-4-[2-(ph alimido)ethoxy]acetoacetate is obtained by the reaction of the ketoester XV and ammonium acetate in an alcoholic solvent such as methanol, ethanol, 2-propanol at varying temperatures from 20 °C to 60 °C. The Hantzsch reaction of the enone XVTJI and the enamine XVI in an alcoholic solvent such as methanol, ethanol, 2-propanol in the presence of acetic acid in varying amounts from 0.1 mole equivalent to 1 equivalent with respect to the mole of the enone XVHI at temperatures ranging from 40 °C to 85 °C gives the bis-phthalimido derivative IXX namely ethyl methyl 2,6-bis-[(2-phthalhnidoe oxy)methyl]-4-(2-cMorophenyl)-l,4-dmydropyri(l^ 3,5-dicarboxylate.

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Removal of phthaloyl groups was successfully accomplished by using hydrazine hydrate in a mixture of toluene/methanol with ranging ratios from 3:1 to 1:3, respectively to afford the amlodipine impurity C, namely ethyl methyl 2,6-bis-[(2-aminoethoxy)methyl]-4-(2- chlorophenyl)- 1 ,4-dihydropyridine-3 , 5-dicarboxylate XX. 3-Ethyl 5-methyl 2- [(2-aminoethoxy]methyl]-4-(2-chlorophenyl)-6-methylpyridine-3,5- dicarboxylate) Impurity D

Impurity D is the only degradation product among other impurities of the amlodipine salts. This product forms as a result of oxidation of dihydropyridine ring to substituted pyridine. The reaction can be achieved by using sulfur, tetrachlorochinone or KMnO .

XXII

At the beginning the inventors tried to oxidize amlodipine base with sulfur. But this reaction needs high temperature and at this temperature unprotected amino group causes degradation of the whole molecule. Then the inventors carried out oxidation reaction by using phthaloyl amlodipine as a starting material.

Thus sulfur and phthaloyl amlodipine are mixed and stirred at 170-180 °C for 30 minutes, and then cooled to 70 °C. Ethyl acetate is added at this temperature and the mixture is stirred for 10 minutes. The solid particles are removed by filtration. The organic phase is concentrated in vacuo and the residue is purified by using flash chromatography to give protected pyridine derivative XXI as a white solid in 62% yield. Phthaloyl group of the compound XXI is removed treating with hydrazine hydrate to give impurity D, namely 3- Ethyl -methyl 2-[(2-aminoethoxy]methyl]-4-(2-chlorophenyl)-6-methylpyridine-3,5- dicarboxylate) XXH as brown oil in 61 % yield. (4-(2-Chloro-phenyI)-2-[2-(3-{2-[3-(2-chloro-phenyl)-2-ethoxycarbonyl-4-methoxy carbonyl-5-methyl-cyclohexa-l,4-dienylmethoxy]-ethylcarbamoyl}-benzoylamino)- ethoxymethyl]-6-methyl-l,4-dihydro-pyridine-3,5-dicarboxyIic acid 3-ethylester 5- methylester) Impurity E

Detection of impurity E is specific to the amlodipine mesylate and currently used processes are not sufficient to prepare amlodipine mesylate in the pure form. Therefore the inventors decided to isolate amlodipine base by crystallization and eliminate the impurities at the first place. Indeed the inventors have achieved to bring the amount of impurity E in amlodipine mesylate within the acceptable limits. The inventors have isolated this unknown impurity by flash chromatography using EtOAc/hexanes as an eluent. The new compound was identified by using 1H, ¹³C, COSY, DEPT NMR and mass spectrometric techniques to be 4- (2-Chloro-phenyl)-2-[2-(3-{2-[3-(2-chloro-phenyl)-2-ethoxycarbonyl-4-methoxy carbonyl-5- methyl-cyclohexa-l,4-dienylmethoxy]-ethylcarbamoyl}-benzoylan ino)-ethoxymethyl]-6- methyl-l,4-dihydro-pyridine-3,5-dicarboxylic acid 3-ethylester 5-methylester as the inventors name it amlodipine impurity E. This is an unexpected result since impurity E has not been seen in appreciable amounts in the preparation of amlodipine besylate or amlodipine maleate salts.

XXIH The inventors have thought that Imp E must be formed in the synthesis by the reaction of phthaloyl amlodipine I and amlodipine base VI. In order to check this is the case and prepare Imp E in gram quantities, phthaloyl amlodipine is reacted with amlodipine base in ethanol at reflux temperature and obtained impurity E in pure form as an off-white solid. HPLC ANALYSIS OF AMLODIPINE RELATED MPTJRITIES

A test method is given in European Pharmacopoeia for the analysis of the amlodipine besylate and related impurities namely impurity A, B, C, and D.

However, according to EP monogram impurities can not be quantified in a single chromatogram by using an isocratic HPLC method. This method allows only quantification of impurity D. In addition to HPLC method a TLC method is also given for testing related substances. Then again TLC method can not be employed for the quantitative determination of the remaining impurities A, B, and C.

The inventors have a novel gradient system, which allows quantitative determination of the all related impurities of amlodipine salts in a single HPLC trace. In the present invention, a gradient system containing two mobile phases is used namely, mobile phase A and mobile phase B. Mobile phase A can be an organic solvent, such as d-C alkanol, acetonitrile and aqueous solution of phosphate salts with the formula

XH₂PO where X= Na, and K or mixture thereof. Mobile phase B can be methanol, ethanol and acetonitrile, particularly acetonitrile. A detailed explanation is given below.

Chromatographic System:

Column: Hypersil C18, 5μm, 150 x 4.6 mm Detector: UV, 237 nm

Flow Rate: 1 mL/min.

Inject volume: lOμL

Temperature: Ambient

Preparation of Mobil phases:

Mobile phase A: A mixture of 45 volume 0.03M KH₂PO₄ (4.08 g. KH₂PO₄ in IL water) and 30 volumes of acetonitrile, 25 volumes of methanol.

Mobile phase B: Acetonitrile

Preparation of sample solution:

Test solution: Dissolve 50.0 mg of the substance to be examined and dilute with 50.0 mL in the mobile phase A. Reference solution: Dilute 3 mL of Test solution to 100 mL with the mobile phase A and then again dilute 5 mL from this solution to 50 mL with mobile phase A. Reference solution (a): Dissolve 1 mg of Amlodipine Impurity E in 10 mL of mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A.

Reference solution (b): Dissolve 1 mg of Amlodipine Impurity A in 10 mL of mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A Reference solution (c): Dissolve 1 mg of Amlodipine Impurity B in 10 mL of mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A

Reference solution (d): Dissolve 1 mg of Amlodipine Impurity D in 10 mL of mobile phase A and dilute 3 mL from this solution to 100 mL with the mobile phase A In the chromatogram obtained with test solution: the area of any peak corresponding to impurity E is not greater than the area of the principal peak in the chromatogram obtained with the reference solution (a) (0.1 per cent)

In the chromatogram obtained with test solution: the area of any peak corresponding to impurity A is not greater than the area of the principal peak in the chromatogram obtained with the reference solution (b) (0.1 per cent) In the chromatogram obtained with test solution: the area of any peak corresponding to impurity B is not greater than the area of the principal peak in the chromatogram obtained with the reference solution (c) (0.1 per cent)

In the chromatogram obtained with test solution: the area of any peak corresponding to impurity D is not greater than the area of the principal peak in the chromatogram obtained with the reference solution (0.3 per cent)

The sum of the areas of all the peaks, apart from the principal peak and the peak corresponding to amlodipine impurity D, is not greater than the area of the principal peak in the chromatogram obtained with reference solution (0.3 per cent). Disregard any peak with an area less than 0.1 times the area of the principal peak in the chromatogram obtained with reference solution (0.03 per cent).

Gradient analysis is performed with a linear gradient using the following HPLC program in Table I.

TaWel

EXAMPLE 1

Preparation of

3-Ethyl, 5-methyl (4RS) 2-[(2-aminoethoxy)me%I]-4-(2-chIorophenyl)-6-methyl-l,4-dihydro pyridine-3,5-dicarboxylate (TV) A 100 L reactor was charged with 7.0 kg of phthaloyl amlodipine and 33.5 kg of toluene. Hydrazine hydrate 5.1 kg was mixed with 10.0 kg of methanol in a 25 L reactor and was added into the stirring suspension of phthaloyl amlodipine at 22-24 °C. The solution was stirred for 7h at this temperature. The solid material phthalhydrazide was filtered off. The organic phase was washed with 2 X 20 L of MgSO₄'7 H₂O. After separating the phases, organic phase dried over 1.28 kg of MgSO and filtered. The solution was concentrated to 1/3 of its original volume and 24 kg of n-hexanes was added. The mixture was cooled down to 0- 5 °C and kept at this temperature for 2h with stirring and then 12h without stirring. The product was filtered off and dried in oven under vacuum at 55 °C for 12h to give 4.6 kg of amlodipine base in 86.5% yield as a white powder. 1H-NMR (CDC1₃) δ 7.85(s, IH), 7.20(m, 4H), 5.38(s, IH), 4.78(d, IH), 4.70(d, IH), 3.95(m, 2H), 3.60(s, 3H), 3.57(d, 2H), 2.95(m, 2H), 2.34(s, 3H), 1.17(t, 3H). ¹³C-NMR (CDC1₃) δ 168.3, 167.4, 157.1, 146.2, 146.1, 144.6, 132.5, 131.7, 129.4, 127.5, 127.0, 104.0, 101.5, 73.5, 68.2, 60.0, 51.0, 41.3, 37.3, 19.4, 14.5.

EXAMPLE 2 Preparation of 3-Ethyl, 5-methyl (4RS) 2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-6-methyl 1,4- dihydropyridine-3,5-dicarboxylate maleate (H) Amlodipine base (80.0 g, 0.196 mol) was added into toluene (552 mL) at 21-24 °C. To dissolve the base methanol (65 mL) was added to above solution. Maleic acid (22.7 g, 0.196 mol) was disolved in MeOH (67 mL) and was added to above solution at 21-24 °C. The solution was stirred for lh at this temperature and the salt was filtered off. The crystals were washed with diethylether (100 mL) and ethyl acetate (100 mL) and dried to give 93.7 g of amlodipine maleate as a white solid in 91.2% yield. 1H-NMR (DMSO) δ 8.37(s, IH), 7.79(s, 3H), 7.20(m, 4H), 6.00(s, 2H), 5.38(s, IH) 4.68(d, IH), 4.55(d, IH), 3.95(m, 2H), 3.60(m, 2H), 3.48(s, 3H), 2.95(m, 2H), 2.28(s, 3H), 1.08(t, 3H). ¹³C-NMR (DMSO) δ 167.8, 167.7, 166.9, 146.3, 145.9, 145.2, 136.4, 131.8, 131.6, 129.7, 128.5, 128.1, 102.9, 102.6, 67.3, 67.2, 60.1, 51.2, 40.3, 37.3, 19.0, 14.7. EXAMPLE 3

Preparation of

3-Ethyl, 5-inethyl (4RS) 2-[(2-aminoethoxy)methyl]-4-(2-chloroρhenyl)-6-methyl -1,4- dihydropyridine-3,5-dicarboxy!ate methanesulfonate (HI) A 100 L reactor was charged with 27.5 kg of toluene and 4.6 kg of amlodipine base at

22-24 °C. To this solution was added 1.08 kg methanesulfonic acid in 1.6 L of methanol. The solution was stirred at 0-5 °C for 15 hours. Crystals were filtered off and washed with 2.8 kg of toluene, and 2.8 kg of ethyl acetate. The solid was dried in oven under vacuum at 55 °C for 1 h to give amlodipine mesylate 5.1 kg as a white powder in 90.0% yield. 1H-NMR (CDC1₃) δ 7.91 (s, 3H), 7.62 (s, IH), 7.01-7.40 (m, 4H), 5.38 (s, IH), 4.83 (d, IH), 4.74 (d, IH), 4.03 (q, 2H), 3.79 (m, 2H), 3.58 (s, 3H), 3.26 (m, 2H), 2.78 (s, 3H), 2.39 (s, 3H), 1.16 (t, 3H). ¹³C- j MR (CDCl₃) δ 169.5, 168.3, 146.4, 146.0, 145.2, 131.7, 131.3, 127.8, 127.5, 104.0, 102.6, 67.4, 66.6, 60.6, 50.8, 39.1, 38.5, 36.8, 18.1, 13.6.

EXAMPLE 4 Preparation of

3-Ethyl, 5-methyl (4RS) 2-(2-aminoethoxy)methyl)-4-(2-chlorophenyl)-6-methyl 1,4- dihydropyridine-3,5-dicarboxy!ate methanesulfonate monohydrate (V)

A 100 L reactor was charged with 24.3 kg of 2-propanol and 0.760 kg of water. To this solution was added 5.1 kg of amlodipine mesylate anhydrous. The mixture was heated to 55-60 °C to get a clear solution. The mixture was cooled down to 0-5 °C and stirred at this temperature for 2.5 hours. The crystals are filtered off under a nitrogen atmosphere and washed with 1.53 L of 2-propanol and dried under open air at 25-30 °C to give 5.02 kg of amlodipine mesylate monohydrate as a white powder in 95% yield. 1H-NMR (D₂O) δ 7.30 (d, IH), 7.28 (d, IH), 7.07 (t, IH), 6.97 (t, IH), 5.13 (s, IH), 4.52 (d, IH), 4.45 (d, IH), 3.87 (q, 2H), 3.64 (m, 2H), 3.40 (s, 3H), 3.09 (m, 2H), 2.62 (s, 3H), 2.11 (s, 3H), 0.95 (t, 3H). ¹³C- NMR (D₂O) δ 169.5, 168.3, 146.4, 146.0, 145.2, 131.7, 131.3, 127.8, 127.5, 102.6, 67.4, 66.6, 60.6, 50.8, 39.1, 38.5, 36.8, 18.1, 13.6.

EXAMPLE 5 Preparation of 3-Ethyl, 5-methyl (4RS) 2-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-6-methyl 1,4- dihydropyridine-3,5-dicarboxylate benzenesulfonate (VT) A 250 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 29.7 g of amlodipine base and 205.5 mL of toluene at room temperature. To this solution was added 11.5 g of benzenesulfonic acid in 10 mL of methanol. When the mixture was stirred at room temperature, 1/10 of the volume is distilled off under high vacuum. The mixture was cooled down to 0 °C and stirred at this temperature for 2 hours. The crystals were filtered and washed with toluene and diethylether 10 mL each. The product was dried at 40 °C for 12 hours and give 36.0 g of amlodipine besylate as a white solid in 87% yield. 1H-NMR(CD₃OD): δ 7.82 (m, 2H), 7.41 (m, 4H), 7.12 (m, 5H), 5.40 (s, IH), 4.89 (s, IH), 4.71 (dd, 2H), 4.03 (m, 2H), 3.77 (q, 2H), 3.57 (s, 3H), 3.25 (m, 4H), 2.32 (s, 3H), 1.15 (t, 3H), ¹³C-NMR (CDC1₃) δ 168.2, 167.6, 144.6, 143.5, 132.4, 131.6, 131.3, 129.3, 128.8, 127.5, 127.1, 125.8, 103.5, 102.3, 68.3, 66.8, 60.1, 50.9, 39.9, 37.1, 18.8, 14.4. EXAMPLE 6

Preparation of 3-Ethyl 5-methyl (4RS) -4-(2-chlorophenyl)-6-[[2-[[2-methylearbamoyl)benzoy]]amino] ethoxy]methyl]-l,4-dihydropyridine-3,5-dicarboxyIate (Vπ) A 250 mL one-necked flask, equipped with a magnetic stirrer was charged with 10 g phthaloyl amlodipine in 25 mL of THF. To this solution was added 3 mL of methyamine (40%). The solution was stirred at rt for 30 minutes. The solvent was evaporated in vacuo. The residue was precipitated by adding diethylether to give the title compound as a white solid 9.72 g (92%, with a relative purity> 96% based on area%). IR (cm^"1): 3340, 2341, 1699, 1670, 1636, 1540, 1487, 1286, 1205, 1100, 870, 668. EI-MS (70 eV): 569 [M]⁺ (3), 538 [M- C₂H₅]⁺ (12), 458 [M-C₆H₅C1]⁺ (45), 427 [M- Irø-OMe (91), 347 [Cι₈Hι₈ClNO₄]⁺ (100), 297 (66), 280 (7), 260 (13), 254 (18), 236 [C₁₂Hι₅N₂O₇]⁺ (10), 223 [CπHi_{4 2}O₃]⁺ (28), 208 (57), 174 (61), 162 (71), 148 (12), 130 (14), 105 (10), 76 (8). 1H-NMR (CDCI3) δ 7.83 (d, IH), 7.63-7.67 (m, 2H), 7.41-7.45 (m, 2H), 7.36 (d, IH), 7.20 (d, IH), 7.10 (q, IH), 7.00 (q, IH), 6.90 (q, IH), 5.37 (s, IH), 4.77 (d, IH), 4.67 (d, IH), 4.03 (q, 2H), 3.80-3.82 (m, 2H), 3.61 - 3.66 (m, 2H), 3.57 (s, 3H), 2.91 (d, 3H), 2.30 (s, 3H), 1.16 (t, 3H). ¹³C-NMR (CDCI₃) δ 170.9, 168.9, 168.3, 167.4, 146.1, 145.2, 145.1, 134.8, 134.2, 132.4, 131.6, 130.3, 129.5, 129.4, 127.9, 127.5, 127.0, 103.7, 101.9, 70.4, 70.3, 60.0, 50.9, 39.8, 37.2, 27.2, 19.2, 14.4.

EXAMPLE 7 Preparation of N-(2-Hydroxyethyl)phthalimide (XT)

A 100 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 20 g (135 mmol) of phthalic anhydride and 9.1 g (148.5 mmol) of ethanol amine. The mixture was heated from 115 °C to 125 °C in 20 minutes and then stirred at 125 °C for an additional 10 minutes. The resulting light yellow solution was cooled to 50 °C and then 50 mL of methanol was added. While cooling the reaction mixture to room temperature, the product was precipitated out. 50 mL of water was added and the resulting mixture was vigorously stirred for 10 min and then the product was filtered off to give 18.8 g of N-(2- hydroxyethyl) phthalimide as a white solid product. The methanolic aqueous layer was extracted with 80 mL of ethyl acetate. After separating the phases, the organic phase dried over 3 g of MgSO₄. MgSO₄ was filtered off and the filtrate was concentrated in vacuo to give 1.65 g of white solid product which was combined with 18.8 g of product (yield 77%, rel. compound purity > 99%).IR (KBr, cm^-1): 3467 and 1683. M.p.: 127.9-128.5. 1H-NMR (CDC1₃) δ 7.79 (dd, 2H), 7.68 (dd, 2H), 3.84 (t, 4H), 2.70 (br, IH). ¹³C-NMR (CDCI3) δ 169.1, 134.3, 132.1, 123.6, 61.0, 40.9.

EXAMPLE 8

Preparation of

Ethyl 4-[2-(phthalimido)ethoxy]acetoacetate (Xm) A 250 mL two-necked flask, equipped with a magnetic stirring bar, thermometer and a pressure equalized addition funnel was charged with 75 mL of tetrahydrofuran under nitrogen atmosphere. 7.53 g Sodium hydride (60% dispersed in oil) was added and the resulting suspension was cooled to -10 °C and 20 g of N-(2-hydroxyethyl)phthalimide was added slowly over 5 minutes. The resulting slurry was stirred at -10 °C for 30 minutes. To this mixture a solution of 16.35 g ethyl 4-chloroacetoacetate in 30 mL of tetrahydrafuran was added at -10 °C in 40 minutes. The reaction mixture was warmed to room temperature and then stirred at room temperature for 18 hours. The reaction mixture was placed in an ice bath and quenched by dropwise addition of 10 mL ethanol. The mixture was then poured into 150 mL of IN hydrochloric acid solution in crushed ice and 200 mL of ethyl acetate was added. The resulting mixture was transferred into a separatory funnel and the aqueous phase was separated. The organic phase was first washed with 70 mL of ethyl acetate was added. The resulting mixture was transferred into a separatory funnel and the aqueous phase was separated. The organic phase was first washed with 70 mL of 5 wt.% of NaHCO₃ solution, then with 150 mL of water, dried over 5 g of MgSO . MgSO was filtered off and the filtrate was concentrated in vacuo to give a light brown oily product. The oil was washed with 15 mL of hexane to remove the mineral oil to give 17.2 g of ethyl 4- [2- (phthalimido)ethoxy]acetoacetate light brown product, (yield 51%, rel. compound purity > 80%).IR (KBr, cm^"1): 2995 and 1716. 1H-NMR (CDCI3) δ 7.76 (dd, 2H), 7.65 (dd, 2H), 4.11 (s, 2H), 4.02 (q, 2H), 3.80 (t, 2H), 3.70 (t, 2H), 3.37 (s, 2H), 1.16 (t, 3H). ¹³C-NMR (CDC1₃) δ 201.7, 168.4, 167.2, 134.3, 132.2, 123.5, 75.6, 68.7, 61.6, 46.0, 37.4, 14.3.

EXAMPLE 9 Preparation of Methyl 4-[2-(phthalimido)ethoxy]acetoacetate (XV)

A 250 mL two-necked flask, equipped with a magnetic stirring bar, thermometer and a pressure equalized addition funnel was charged with 60 mL of tetrahydrofuran under nitrogen atmosphere. 3.14 g sodium hydride (60% dispersed in oil) was added and the resulting suspension was cooled to -10 °C and 10 g of N-(2-hydroxyethyl)phthalimide was added slowly over 5 minutes. The resulting slurry was stirred at -10 °C for 30 minutes. To this mixture a solution of 7.48 g ethyl 4-chloroacetoacetate in 25 mL of tetrahydrafuran was added at -10 °C in 40 minutes. The reaction mixture was warmed to room temperature and then stirred at room temperature for 18 hours. The reaction mixture was placed in an ice bath and quenched by dropwise addition of 5 mL ethanol. The mixture was then poured into 100 mL of IN hydrochloric acid solution in crushed ice and 150 mL of ethyl acetate was added. The resulting mixture was transferred into a separatory funnel and the aqueous phase was separated. The organic phase was first washed with 50 mL of 5 wt.% of NHCO₃ solution, then with 100 mL of water, dried over 5 g of MgSO . MgSO₄ was filtered off and the filtrate was concentrated in vacuo to give a light brown oily product. The oil was washed with 10 mL of hexane to remove the mineral oil to give 8.87 g of methyl 4-[2-(phthalimido)ethoxy]aceto acetate as a light brown product (yield 55%, rel. compound purity > 95%).TR (KBr. cm^"1): 2995 and 1716.-1H-NMR (CDCI3) δ 7.80 (dd, 2H), 7.70 (dd, 2H), 4.11 (s, 2H), 3.87 (t, 2H), 3.75 (t, 2H), 3.61 (s, 3H), 3.44 (s, 2H). ¹³C-NMR (CDCI3) δ 201.7, 168.4, 167.2, 134.3, 132.2, 123.5, 75.6, 68.7, 52.8, 46.0, 37.4.

EXAMPLE 10

Preparation of

Methyl 3-amino-4-[2-(phthalimido)ethoxy]acetoacetate (XVI) A 250 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 10 g of methyl 4-[2-(phthalimido)ethoxy]acetoacetate and 2.52 g ammonium acetate and 80 mL of methanol under nitrogen atmosphere. The reaction mixture was heated to 41 °C and stirred at this temperature for 20 minutes. The mixture was cooled to room temperature and stirred at room temperature for 18 hours. The precipitated product was filtered off to give 6.23 g of methyl (3-ammo)-4-[2- hthalimido)ethoxy]acetoacetate as a white to light yellow powder. (60%, rel. compound purity > 98%). 1H-NMR (CDC1₃) δ 7.81 (dd, 2H), 7.70 (dd, 2H), 4.46 (s, 2H), 4.01 (s, 2H), 3.88 (t, 2H), 3.70 (t, 2H), 3.60 (s, 3H). ¹³C- J MR (CDC1₃) δ 168.4, 167.2, 158.1,134.3, 132.2, 123.5, 80.1, 70.1, 68.7, 52.8, 37.4.

EXAMPLE 11 Preparation of Ethyl 2-(2-chlorobenzyIidine)-4- [2-(phthalimide)ethoxy] acetoacetate (XVTJI) A 250 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 10 g of ethyl 4-[2-(phthalimido)ethoxy]acetoacetate and 3.96 g 2- chlorobenzaldehyde and 100 mL isopropanol under nitrogen atmosphere. To the resulting mixture was added 0.188 mL of acetic acid and 0.223 mL pyrolidine. The reaction mixture was heated to 37 °C and stirred at this temperature for 5 hours. The solvent was removed in vacuo and the residue was dissolved in 100 mL of methylene chloride. The resulting solution was washed with 100 mL of sat. aHCO3 and 100 mL of water, dried over 5 g of MgSO₄. MgSO was filtered off, the filtrate was concentrated in vacuo. The residue was purified by flash chromatography using ethyl acetate/hexane (20/80) as an eluent to give 7.72 g of ethyl 2-(2-cWorobenzyUdme)-4-[2-(phthalimide)ethoxy]acetoacetate as an light brown oil (yield 56%, rel. compound purity > 98%). 1H-NMR (CDC1₃) δ 7.89 (s, IH), 7.78 (dd, 2H), 7.69 (dd, 2H), 7.35 (m, IH), 7.28 (m, 2H), 7.17 (m, IH), 4.44 (s, 2H), 4.05 (q, 2H), 3.76 (t, 2H), 3.64 (t, 2H), 1.20 (t, 3H). ¹³C-NMR (CDCl₃) δ 203.2, 168.4, 164.0, 140.0, 134.0, 133.9, 132.3, 131.5, 130.4, 129.8, 127.3, 126.8, 123.4, 77.7, 68.5, 62.0, 37.4, 14.3.

EXAMPLE 12 Preparation of Ethyl methyl 2,6-bis-[(2-phthalimidoethoxy)methyl]-4-(2-chlorophenyl)-l,4-dihydro pyridine-3,5-dicarboxy!ate (JLXX)

A 250 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 7.72 g of ethyl 2-(2-chlorobenzylidine)-4-[2-(phthalimide) ethoxy] acetoacetate and 5.56 g methyl (3-an no)-4-[2-(phthalimido)ethoxy]acetoacetate and 80 mL isopropanol. The reaction mixture was refluxed for 18 hours. The solvent was removed in vacuo. The residue was purified by flash chromatography using ethyl acetate/hexane (40/60) as an eluent to give 7.513 g of ethyl methyl 2,6-bis-[(2-phthalimidoethoxy)methyl]-4-(2- cUorophenyl)-l,4-dihydropyridine-3,5-dicarboxylate as a light thick oil (yield 59%, rel. compound purity > 99%)._1H-NMR (CDC1₃) δ 8.18 (br, IH), 7.83 (dd, 4H), 7.70 (dd, 4H), 7.25 (d, IH), 7.19 (d, IH), 7.12 (t, IH), 7.05 (t, 2H), 5.38 (s, IH), 4.76 (dd, IH), 4.61 (dd, IH), 4.10 (dd, IH), 3.95 (dd, IH), 3.88 (m, 4H), 3.77 (m, 4H), 3.58 (s, 3H), 1.60 (t, 3H). ¹³C- JNMR (CDC1₃) δ 168.0, 167.7, 146.5, 145.8, 145.3, 135.0, 132.3, 131.7, 131.6, 129.5, 128.3, 128.0, 123.6, 102.9, 102.4, 68.1, 67.9, 60.0, 51.2, 37.8, 37.3, 14.6.

EXAMPLE 13 Preparation of

Ethyl methyl 2,6-bis-[(2-aminoethoxy)methyl]-4-(2-chlorophenyl)-l,4-dihydro pyridine-

3,5-dicarboxylate (XX) A 250 mL one-necked flask, equipped with a magnetic stirring bar was charged with 7.5 g of ethyl methyl 2,6-bis-[(2-phthaiimidoethoxy)methyl]-4-(2-chlorophenyl)-l,4- dihydropyridine-3,5-dicarboxylate and 75 mL of toluene under nitrogen atmosphere. 5 mL of hydrazine hydrate (80%) was dissolved in 5 mL of methanol and was added to the stirring solution of diphthaloil amlodipine impurity C at room temperature under nitrogen atmosphere. The reaction mixture was stirred at room temperature for 18 hours. The precipitated phthalhydrazide was filtered off and the solid residue was washed with 9 mL of toluene/methanol (3:1). The filtrate was washed with 75 mL of brine solution. The organic phase was dried with 4 g of MgSO . MgSO was filtered off The filtrate was concentrated under vacuum up to 10 mL. To this was added 15 mL of ethyl acetate/hexane (1:9) and the product was precipitated out. The solvent was decanted and the solid residue was dried under reduced pressure to give 3.2 g of ethyl methyl 2,6-bis-[(2-aminoethoxy)methyl]-4-(2- chlorophenyl)-l,4-dihydropyridine-3,5-dicarboxylate yellowish white powder (yield 66%, rel. compound purity > 98%). IR (cm ): 2342, 1687, 1486, 1278, 1208, 1102. EI-MS (eV): 468 [M+Hf (100), 406 [M-C₂H₅O₂]⁺ (30), 356 (75), 297 (5). 1H-NMR (CDCI3) δ 8.46 (br, IH), 7.37 (d, IH), 7.20 (d, IH), 7.12 (t, IH), 7.02 (t, IH), 5.40 (s, IH), 4.80 (dd, 2H), 4.69 (dd, 2H), 4.03 (q, 2H), 3.60 (brs, 7H), 2.95 (t, 4H), 1.85 (brs, 2H), 1.16 (t, 3H). ¹³C-NMR (CDCI3) δ 168.1, 166.8, 146.5, 145.8, 145.5, 132.9, 130.4, 129.2, 128.4, 126.3, 102.9, 102.9, 102.2, 72.5, 68.3, 60.0, 51.1, 41.0, 37.3, 14.6. EXAMPLE 14

Preparation of

3-Ethyl 5-methyl -2-[[(phthalimido)ethoxy]methyl]-4-(2-chlorophenyl) -6-methyl pyridine-3, 5-dicarboxylate (XXI) A 300 mL one-necked flask, equipped with a magnetic stirrer was charged with 10 g

(0.018 mol) Phthaloyl amlodipine and with 5 g sulfur . The mixture was heated and stirred at 170-180 °C for 50 minutes. The solution was cooled to the 70 °C and was added 100 mL of ethyl acetate. The suspension was stirred for 10 minutes. The solid particle was removed by filtration and the solvent was removed under reduced pressure, the residue was purified by flash-chromatopraphy eluting with ethyacetate/hexane 1:3 to give 6.25 g of pyridine derivative in 62% yield as a white solid. 1H-NMR (CDC1₃) δ 7.59-7.76 (d, 4H), 7.04-7.32 (m, 4H), 4.78 (d, IH), 4.74 (d, IH), 3.93 (q, 2H), 3.78 (s, 2H), 3.62 (s, 2H), 3.44 (s, 3H), 2.52 (s, 3H), 0.82 (t, 3H). ¹³C-NMR (CDCl₃) δ 167.1, 166.3, 165.2, 155.1, 155.0, 143.8, 133.8, 133.0, 132.8, 131.0, 130.9, 129.2, 128.7, 128.0, 122.2, 122.1, 71.7, 66.5, 60.3, 59.7, 51.2, 36.2, 22.1, 12.4.

EXAMPLE 15

Preparation of

3-Ethyl 5-methyl 2- [ [(2-aminoethyl)-oxy] methyl] -4-(2-cMorophenyl)-6-methyIpy ridine-

3,5-dicarboxylate) (XXH) A 250 mL one-necked flask, equipped with a magnetic stirrer was charged with 100 mL of toluene and 6.25 g (0.012 mol) dihydropyridine derivative. To this solution was added, hydrazine hydrate 3.75 mL in methanol 7 mL The solution was stirred at rt for 4h. The progress of the reaction was checked by TLC. The solid particle was filtered off. To the filtrate was added 40 mL of water and the phase were separated. The organic phase was dried over MgSO and concentrated in vacuo to give the title compound as a brown oil 2.9 g (61%, relative compound purity >97%). TR (cm^-1): 2342, 1731, 1558, 1436, 1295, 1231, 1108, 1042, 757. EI-MS (70 eV): 406 [M] ⁺, 389 [(M-NH₃] ⁺, 375 [-OCH₃] ⁺, 364 [M- CCH₂O] ⁺, 347 [M- OCH₂CH₂ Γ 318 [(M- CO2CH2CH3, CH₃] ⁺, 295 [M- CβHLjCTJ ⁺, 260 [M- CH₂OCH₂CH₂NH, CO₂CH₂CH₃]⁺. 1H-TMMR (CDC13) δ 7.39 (dd, IH), 7.28 (m, 2H), 7.14 (dd, IH), 4.81 (d, IH), 4.79 (d, IH), 3.97 (q, 2H), 3.78 (m, 2H), 3.50 (s, 3H), 3.22 (s, 2H), 2.60 (s, 3H), 0.83 (t, 3H). ¹³C-NMR (CDCl₃) δ 167.3, 166.6, 156.7, 156.0, 145.2, 135.1, 132.9, 130.4, 130.0, 129.9, 129.2, 128.4, 126.3, 72.4, 68.4, 61.8, 52.4, 40.0, 23.3, 13.6. EXAMPLE 16

Preparation of

(4-(2-Chloro-phenyl)-2-[2-(3-{2-[3-(2-chloro-phenyl)-2-ethoxycarbonyl-4-methoxy carbonyl-5-methyl-cyclohexa-l,4-dienylmethoxy]-ethylcarbamoyl}-benzoylamino)- ethoxymethyl]-6-methyl-l,4-dihydro-pyridine-3,5-dicarboxyIic acid 3-ethylester 5- methylester) (XXIH) A 250 mL two-necked flask, equipped with a magnetic stirring bar and thermometer was charged with 10 g (186 mmol) of phthaloil amlodipine, 8.36 g (204 mmol) of amlodipine base, 100 mL of isopropanol and 3 mL of water. The resulting mixture was refluxed for two days. The reaction mixture was cooled to room temperature and the unreacted phthaloil amlodipine and amlodipine base solidified out. The solid mixture was filtered off and the filtrate was concentrated in vacuo. The residue was purified by flash chromatography using ethyl acetate/hexane (80:20) as an eluent to give 2.87 g of amlodipine as a white to off white powder (yield 16%, rel. compound purity >99%). TR (cm-1): 2342, 1687, 1486, 1278, 1208, 1102, 1042. EI-MS (70 eV): 969 [M+Na]⁺, 947 [M] ⁺, 919 [M-CO] ⁺, 598 [M- CH₃- C=C(CO₂Et)-CH(C₆H₄Cl)-C(CO₂Me)=C(CH₂)NH]⁺, 347 [[M- CH₃-C=C(CO₂Et)- CH(C₆H₄Cl)-C(CO₂Me)=C(CH₂)NΗ ]-OCH₂CH2-NH-CO-C₆H₄-CO-NH-CH₂CH₂O]⁺, 174 [[[M- CH₃-C=C(CO₂Et)-CH(C₆H₄Cl)-C(CO₂Me)=C(CH2)]SlH

CO-NH-CH₂CH₂O]- (C6H4Cl-CH₃O-CO)]. 1H-NMR (CDC1₃) δ 7.60 (dd, 2H), 7.49 (dd, 2H), 7.35 (d, IH), 7.21 (d, IH), 7.10 (t, IH), 7.04 (t, IH), 4.88 (s, IH), 4.75 (dd, 2H), 4.05 (dd, IH), 4.00 (dd, IH), 3.68 (m, 4H), 3.60 (s, 3H), 2.60 (s, 3H), 1.18 (t, 3H). ¹³C-NMR (CDCI3) δ 169.3, 168.0, 166.8, 146.0, 145.7, 144.5, 132.0, 131.9, 131.3, 130.2, 128.3, 127.5, 126.6, 126.3, 104.0, 102.0, 70.0, 68.0, 60.1, 51.9, 40.0, 37.6, 18.7, 14.6.

Claims

What claimed is:

1. A process for the crystallizing the compound with the formula:

comprises dissolving compound with the formula in a solvent, and crystallizing said compound by adding another solvent or by varying the temperature, the said solvent can be toluene, tefrahydrofuran, ethyl acetate, hexane, pentane, diethylether, isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, acetone or mixture thereof, particularly in atoluene hexanes mixture, the said temperature can be at a range of-10 °C to 100 °C.

2. A process for preparing acid salts of isolated compound in claim 1 by using maleic acid, methanesulfonic acid and benzenesulfonic acids.

3. A process for the preparation of the compound with the formula:

4. A process for the preparation of the compound with the formula:

5. A process for the preparation of the compound with the formula:

6. A novel compound with the formula and process for the preparation of the compound:

7. A HPLC method including quantitative testing of related impurities of amlodipine salts in a 5 single chromatogram by using a gradient system containing two different mobile phases, the mobile phases can be methanol, ethanol, isopropanol, an aqueous solution of KH₂P0₄ and NaH₂P0₄ or mixtures thereof.

8. A process for producing a compound as defined in claim 3, which comprises: (i) reacting phthaloyl amlodipine with memylamine in an solvent; and l o (ϋ) precipitating by adding another solvent to the mixture, the solvent used in this process can be toluene, tefrahydrofuran, ethylacetate, hexanes isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, acetone and mixture thereof, particularly in a tetiahydrofuran/water/diethylether mixture.

9. A process for producing a compound as defined in claim 4, which comprises:

15 (i) reacting methyl 4-[2-φhmalimido)ethoxy]acetoacetate with ammonium acetate affording methyl (3-aιιrmo)-4-[2- hthalimido)ethoxy]acetoacetate in an alcoholic solvent such as methanol, ethanol, isopropanol, at varying temperature from 0 °C to

85 °C; (ii) coupling between methyl (3-ammo)-4-[2-(phtnalimido)ethoxy]acetoacetate and ethyl 20 2-(2-chlorobenzylidine)-4-[2-(phthalimide)ethoxy]acetoacetate to give 3-ethyl 5- memyl 2,6-bis-[(2-phthalinndoethoxy)methyl]-4-(2-chlorophenyl)-l,4-dihydro pyridine-3,5-dicarboxylate; and (iii) removing phthalimido groups of 3-ethyl 5-methyl 2,6-bis-[(2- phthalimidoethoxy)methyl]-4-(2-chlorophenyl)- 1 ,4-dihydro pyridine-3 ,5 - 25 dicarboxylate by using memylamine, KOH or hydrazine hydrate affords compound in claim 4.

10. A process for producing a compound as defined in claim 5, which comprises: (i) treating phthaloyl amlodipine alone or in an organic solvent, with an oxidizing agent such as tetrachlorochinone, sulfur or KMn0 at a temperature range of 0-180 °C gives 3-Ethyl 5-methyl -2-[[( hmdimido)ethoxy]methyl]-4-(2-chlorophenyl)-6- methyl pyridine-3, 5-dicarboxylate; and (ii) reacting this compound with a reagent such as methylamine, KOH or particularly with hydriazine hydrate affords the compound in claim 5.

11. A process for producing a compound as defined in claim 6, which comprises:

(i) reacting amlodipine base with phthaloyl amlodipine in a solvent such as be toluene, tetrahydrofuran, ethylacetate, hexanes isopropanol, ethanol, methanol, dioxane, dichloromethane, acetonitrile, and mixture thereof, particularly in isopropanol/water mixture and in a temperature range of 0-120 °C affords compound defined in claim 6.

12. A method according to claim 7, which includes the step of:

(i) dissolving 50.0 mg of the substance to be examined in the 50.0 mL of mobile phase A to produce a test solution;

(ϋ) diluting 3 mL of test solution to 100 mL with the mobile phase A and dilute 5 mL from this solution to 50 mL with mobile phase A to produce a reference solution; (ϋi) dissolving 1 mg of amlodipine impurity E in 10 mL mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A to produce a reference solution for impurity E;

(iv) dissolving 1 mg of amlodipine impurity A in 10 mL mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A to produce a reference solution for impurity A; (v) dissolving 1 mg of amlodipine impurity B in 10 mL mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A to produce a reference solution for impurity B; (vi) dissolving 1 mg of amlodipine impurity D in 10 mL mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A to produce a reference solution for impurity D; (vii) dissolving 1 mg of amlodipine impurity C in 10 mL mobile phase A and dilute 1 mL from this solution to 100 mL with the mobile phase A to produce a reference solution for impurity C; (viii) injecting test solution of compound to be examined and impurities reference solutions on o an HPLC column; and (ix) determining main peak areas of each solution and calculating these results to see how much the sample to be tested contains each impurity.