ACETONE SOLVATE OF PHTHALOYL AMLODIPINE

FIELD OF THE INVENTION

The present invention is directed to an acetone solvate of phthaloyl amlodipine, a process for its preparation and its use in the synthesis of amlodipine.

BACKGROUND OF THE INVENTION

Amlodipine besylate, also known as 2-{(2-aminoethoxy)-methyl-4-(2- chlorophenyO-S-ethoxycarbonyl-S-methoxycarbonyl-ό-methyl-l^ -dihydropyridine} benzene sulphonate or 3-ethyl, 5-methyl 2-((2-aminoethoxy)methyl)-4-(2- chlorophenyl)-l ,4-dihydro-6-methylpyridine-3,5-dicarboxylate benzene sulphonate, is an anti-ischemic and anti-hypertensive drug.

Amlodipine besylate

A number of synthesis have been described for the synthesis of amlodipine besylate in which the key intermediate is phthaloyl amlodipine, also known as 4-(2- chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2- (2-phtalimidoethoxy)- methyl- 1 ,4-dihydropyridine or 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4-dihydro-6- methyl-2-[(2-phthalimidoethoxy)methyl]-3,5-pyridinedicarboxy late.

Phthaloyl amlodipine

Thus, providing phthaloyl amlodipine in good yield and high purity is a central issue in the synthesis amlodipine, especially for the synthesis of amlodipine besylate.

In US 4,572,909 phthaloyl amlodipine is obtained by condensation of phthalic anhydride with the corresponding free amine or condensation of 2-chlorobenzaldehyde, 4-[2-(phthalimido)ethoxy]acetoacetate and methyl 3-aminocrotonate. Purification of phthaloyl amlodipine is carried out by precipitation from acetic acid, followed by resuspension in methanol.

In WO00/24714 phthaloyl amlodipine is obtained by condensation between ethyl 3-amino-4-(2-phthalimidoetoxi)crotonate and methyl 2-(2- chlorobenzyliden)acetoacetate. Purification is carried out by recrystallization in methanol, ethanol, isopropanol, toluene or xylene.

In JP20001002677 phthaloyl amlodipine is purified by recrystallization in an organic solvent in the presence of acetic acid. In WO02053135 phthaloyl amlodipine is purified by a first recrystallizing in acetic acid, resuspending in methanol and finally by recrystallization from ethyl acetate.

US 6,784,297 describes a process for the synthesis of amlodipine besylate starting from phthalic anhydride and comprising phthaloyl amlodipine as intermediate (step d)). Phthaloyl amlodipine is subsequently purified in step e) in a two step sequence which comprises (i) dissolving it in an organic solvent in the ratio 1 :2-1:5 w/v followed by (ii) precipitation by the addition of water at 35-60 ⁰ C. According to a preferred embodiment, the solvent in step (i) is acetone. The free phthaloyl amlodipine obtained is then transformed into its base and then into amlodipine besylate.

The purification methods of the prior art required complicated purification methods and are not capable of removing all the impurities to the levels required by regulator.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows an X-ray powder diffractogram of the acetone solvate of the invention. The abscissa axis shows the 2θ angles and the ordinate axis shows the intensity.

Figure 2 shows an Infrared Spectrum of the acetone solvate of the invention. The abscissa axis shows the frequency (cm ⁴ ) and the ordinate axis shows the transmittance (%T).

SUMMARY OF THE INVENTION

The inventors have now surprisingly found that the provision of an acetone solvate of phthaloyl amlodipine provides an excellent method for the purification of phthaloyl amlodipine.

Recrystallization of phthaloyl amlodipine from acetone and further cooling provides an acetone solvate of phthaloyl amlodipine with high purity and yield, and without the need of using complicated work-up methods. Additionally, said acetone solvate of phthaloyl amlodipine shows a high degree of crystallinity, which makes it easy to manipulate and store. The acetone solvate of phthaloyl amlodipine of the invention has excellent solubility and may be used to obtain amlodipine with high purity.

Thus, according to a first aspect, the present invention is directed to an acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4-dihydro-6-methyl-2-[(2- phthalimidoethoxy)methyl]-3,5-pyridinedicarboxylate.

Acetone solvate of Phthaloyl amlodipine

According to a second aspect, the present invention is directed to a process for the synthesis of said acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)- 1 ,4- dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5-pyridin edicarboxylate which comprises

a) dissolving 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4-dihydro-6-methyl-2-[(2- phthalimidoethoxy)methyl]-3,5-pyridinedicarboxylate in acetone at a temperature comprised between above 2O ⁰ C and reflux; and b) cooling the mixture to a temperature comprised between -10° C and 20 ⁰ C in order to precipitate the acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)- l ,4-dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5- pyridinedicarboxylate.

According to a third aspect, the present invention is directed to the use of said acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4-dihydro-6-methyl-2-[(2- phthalimidoethoxy)methyl]-3,5-pyridinedicarboxylate for the synthesis of 3-ethyl, 5- methyl 2-((2-aminoethoxy)methyl)-4-(2-chlorophenyl)- 1 ,4-dihydro-6-methylpyridine- 3,5-dicarboxylate , its salts or solvates thereof, preferably its benzene sulphonate salt (amlodipine besylate).

DETAILED DESCRIPTION OF THE INVENTION

Synthesis of the acetone solvate of phthaloyl amlodipine

Contrary to the method described in US 6,784,297, the method of the invention does not comprise the addition of water. Instead, once the phthaloyl amlodipine is dissolved in acetone, the mixture is allowed to cool to a temperature comprised between -10° C and 20 ⁰ C. The inventors have found that in this range of temperatures, the desired acetone solvate of phthaloyl amlodipine is readily obtained in good yields and high purity. According to a preferred embodiment, the mixture is cooled in step b) at a temperature comprised between -5°C and 5°C.

It has been observed that excellent results are obtained when cooling in step b) is performed in two steps. According to a preferred embodiment, cooling in step b) is performed in two steps: a first cooling to a temperature comprised between above 5°C and 20 ⁰ C and a second cooling to a temperature comprised between -10 ⁰ C and 5°C.

According to a preferred embodiment, said first cooling comprises a temperature between 7°C and 15 ⁰ C. According to a preferred embodiment, said first cooling comprises a temperature between 1O ⁰ C and 15 ⁰ C.

According to a preferred embodiment, said first cooling comprises a temperature between 8 ⁰ C and 12°C.

According to a preferred embodiment, said second cooling comprises a temperature between 0 ⁰ C and 5 ⁰ C. The temperature to which phthaloyl amlodipine is heated or the concentration of phthaloyl amlodipine in step a) of the process is not critical. The only requirement is that phthaloyl amlodipine is dissolved. Therefore, the higher the temperature and/or the lower the concentration, the more readily, phthaloyl amlodipine is dissolved.

According to a preferred embodiment, the temperature in step a) is comprised between 30 ⁰ C and reflux. According to another preferred embodiment, the temperature in step a) is comprised between 40 ⁰ C and reflux.

According to a preferred embodiment, the concentration of phthaloyl amolodipine in step a) is comprised between 0.02 and 0.3 g/ml, preferably between 0.04 and 0.2 g/ml. The above mentioned process requires no seeding with preformed crystals of the acetone solvate of phthaloyl amlodipine. However, the process of the invention may also include such possibility. Thus, according to a preferred embodiment, the process of the invention comprises the additional step, between step a) and step b), of seeding the mixture with a crystal of an acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)- l,4-dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5-pyr idinedicarboxylate. Such preferred embodiment comprises the following steps: a) dissolving 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4-dihydro-6-methyl-2-[(2- phthalimidoethoxy)methyl]-3,5-pyridinedicarboxylate in acetone at a temperature comprised between above 20 ⁰ C and reflux; b) seeding the mixture with a crystal of an acetone solvate of 3-ethyl, 5-methyl 4-

(2-chlorophenyl)-l,4-dihydro-6-methyl-2-[(2-phthalimidoethox y)methyl]-3,5- pyridinedicarboxylate in order to precipitate the acetone solvate; and c) cooling the mixture to a temperature comprised between -10° C and 20 ⁰ C in order to isolate the acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4- dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5-pyridin edicarboxylate.

According to another preferred embodiment, the process comprises

a) dissolving 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l ,4-dihydro-6-methyl-2-[(2- phthalimidoethoxy)methyl]-3,5-pyridinedicarboxylate in acetone at a temperature comprised between 50 ⁰ C and reflux; b) cooling the mixture to a temperature comprised between 30 ⁰ C and 45°C; c) seeding the mixture with a crystal of the acetone solvate of 3-ethyl, 5-methyl 4-

(2-chlorophenyl)-l ,4-dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5- pyridinedicarboxylate in order to precipitate the acetone solvate; and d) cooling the mixture to a temperature comprised between -10° C and 20 ⁰ C in order to isolate the acetone solvate of 3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4- dihydro-6-methyl-2-[(2-phthalimidoethoxy)methyl]-3,5-pyridin edicarboxylate.

The process of the invention provides phthaloyl amlodipine with high purity, even with regard to impurities which are difficult to remove with other purification methods. For example, in the process described example 1 below, phthaloyl amlodipine is obtained in 70% yield and a purity of 98.6%. Said process comprises the steps of a) condensation between (Z)-methyl 2-(2-chlorobenzylidene)-3-oxobutanoate and ethyl 3- amino-4-[2-(phthalimido)ethoxy]crotonate, and b) isolation of phthaloyl amlodipine. One of the main impurities obtained is impurity HA

impurity HA that is, 4-(2-Chloro-phenyl)-2,6-bis-[2-(l,3-dioxo-l,3-dihydro-isoind ol-2-yl)- ethoxymethyl]-l,4-dihydro-pyridine-3,5-dicarboxylic acid diethyl ester or ethyl 2,6- bis[2-(phthalimidoethoxy)methyl]-4-(2-chlorophenyl)-l,4-dihy dro-3,5-pyridine dicarboxylate (named "impurity HA" for the purposes of the present invention). As shown in examples 4 to 10, the provision of the acetone solvate of phthaloyl amlodipine significantly reduces the levels of impurity HA.

The concentration of other impurities is also significantly reduced when forming the acetone solvate of phthaloyl amlodipine.

Characterization of the acetone solvate of phthaloyl amlodipine

The acetone solvate of phthaloyl amlodipine obtainable by the process of the invention was characterized by X-ray powder diffractogram, thermogravi metric analysis (TG), differential scanning calorimetry (DSC) and infrared spectrum (IR).

X-Ray diffractograms were obtained using a PANalytycak X'Pert PRO MPD diffractometer with a goniometer θ/θ, radiation CuKa, λ = 1.5406A

The DSC measurements were carried out at a scan rate of 2 °C/minute from 40 ⁰ C to 170 ⁰ C with a Mettler Toledo DSC822 ^e

Thermogravimetric analysis measurements were carried out at a scan rate of 5 ^o C/minute from 25 ⁰ C to 200 ⁰ C with a Mettler Toledo TGA/STDA 85 l ^e .

Fourier transform infrared spectra were acquired on a Perkin Elmer Spectrum One. Sample preparations were performed as KBr disk.

X-ray powder diffractogram

The acetone solvate of phthaloyl amlodipine shows an X-ray powder diffractogram having relevant peaks expressed as 2θ angles at about 10.2, 12.1, 13.0, 13.9, 15.3, 17.5, 19.7, 20.6, 22.7, 23.5 and 24.4°. A complete X-ray powder diffractogram is shown in figure 1 and a complete peak pattern is shown in table 1 (peaks with an intensity below 5% are not shown).

Table 1

Differential Scanning Calorimetry (DSC)

The acetone solvate of phthaloyl amlodipine obtainable by the process of the invention shows an endothermal peak around 80 ⁰ C, between 75°C and 85 ⁰ C.

Thermogravimetric analysis The acetone solvate of phthaloyl amlodipine obtainable by the process of the invention shows a total weight loss of about 10.4%, between 7 and 12% w/w. The theoretical acetone content of a sample is 9.7%.

Infrared Spectrum (IR) The acetone solvate of phthaloyl amlodipine showed an IR spectrum having relevant peaks expressed in cm ^"1 at about 3361, 2949, 1769, 1714, 1693, 1644, 1601, 1484, 1433, 1421, 1394, 1363, 1343, 131 1, 1287, 1213, 1 1 18, 1 102, 1042, 1025, 727, 530 cm-1. A complete IR is shown in figure 2.

Use of the acetone solvate of phthaloyl amlodipine

As mentioned above, the acetone solvate of phthaloyl amlodipine is obtained in high yields and excellent purity. The acetone solvate can then be readily liberated in order to obtain free phthaloyl amlodipine or it can be used directly.

Therefore, the acetone solvate of phthaloyl amlodipine is an excellent intermediate for the synthesis of amlodipine [3-ethyl, 5-methyl 4-(2-chlorophenyl)-l,4- dihydro-6-methyl-2-(2-amino-ethoxymethyl)-3,5-pyridinedicarb oxylate], its salts or solvates thereof.

Amlodipine

According to a preferred embodiment, phthaloyl amlodipine is used for the synthesis of 3-ethyl, 5-methyl 2-((2-aminoethoxy)methyl)-4-(2-chlorophenyl)- 1 ,4-

dihydro-6-methylpyridine-3,5-dicarboxylate benzene sulphonate, that is, amlodipine besylate.

For example, the acetone solvate of phthaloyl amlodipine may be used as the starting material in the synthesis of amlodipine following any of the methods described in the prior art. For example, amlodipine besylate may be obtained using the acetone solvate of phthaloyl amlodipine by the method described US 6,784,297.

EXAMPLES

Example 1; Preparation of phthaloyl amlodipine

Methyl 2-(2-chlorobenzyliden)acetoacetate (40.6 g; 169.9 mmol) was condensed with ethyl 3-amino-4-[2-(phthalimido)ethoxy]crotonate (51.5 g; 161.8 mmol) in 2-propanol (160 ml) under reflux for 11 hours. Methanol (103 ml) was added and mixture was cooled to 5/0 ⁰ C. The solid was filtered off and dried at 40 ⁰ C. Phthaloyl Amlodipine (60.7 g, purity: 98.6%; 0.86% of impurity HA) was obtained.

Preparation of the acetone solvate of phthaloyl amlodipine

Examples 2 and 3 illustrate the method of synthesis of the acetone solvate of phthaloyl amlodipine.

Example 2 (Preparation of solvate without seeding) Phthaloyl amlodipine (10 g, purity: 95.4%) was dissolved in 50 ml of acetone under reflux. Once solution was complete, it was cooled slowly to 15/10 ⁰ C. Then the solution was cooled to 5/0 ⁰ C and the solid was filtered off and washed with cold acetone. The product was dried under vacuum. Yield of Phthaloyl amlodipine acetone solvate: 9.2 g. Purity: 98.9%.

¹ H-NMR (400 MHz, DMSOd ₆ ) δ(ppm): 8.29 (broad singlet, I H); 7.85 (m, 4H); 7.27 (dd, J: 7.7 Hz, J': 1.8 Hz, IH); 7.24 (dd, J: 7.7 Hz, J': 1.3 Hz, IH); 7.20 (dt, J: 7.2 Hz, J': 1.3 Hz, I H); 7.10 (dt, J: 7.2 Hz, J': 1.8 Hz, I H); 5.23 (s, IH); 4.63 (d, J: 14.2 Hz, I H); 4.50 (d, J: 14.2 Hz, IH); 3.92 (m, 2H); 3.82 (m, 2H); 3.70 (m, 2H); 3.47 (s, 3H); 2.19 (s, 3H); 2.08 (s, 6H); 1.07 (t, J: 7.1 Hz, 3H).

IR 3361, 2949, 1769, 1714, 1693, 1644, 1601 , 1484, 1433, 1421, 1394, 1363, 1343, 131 1, 1287, 1213, 1 1 18, 1 102, 1042, 1025, 727, 530 cm- ¹

Example 3 (solvate with seed) Phthaloyl amlodipine (1O g, purity: 98.6%) was dissolved in 60 ml of acetone under reflux. Then the solution is cooled to 45/30 ⁰ C and seeded with Phthaloyl amlodipine acetone solvate to allow precipitation. The suspension was then cooled to 5/0 °C, filtered off and washed with cold acetone. The solid was dried under vacuum. Yield of Phthaloyl amlodipine acetone solvate: 10.5 g. Purity: 99.9%.

Examples 4 to 10

The following examples 4 to 6 further illustrate the method of synthesis of the acetone solvate of phthaloyl amlodipine. The comparative examples (examples 7 to 10) correspond to examples 1 to 4 of US 6,784,297, respectively, and have been prepared for comparative purposes. As shown in examples 7 to 10 below, the process according to US 6,784,297 does not provide the acetone solvate of phthaloyl amlodipine. In order to compare the purity of the compounds obtained by the method of the invention, the levels of impurity HA have been measured in examples 4 to 10. As shown below, the provision of the acetone solvate of phthaloyl amlodipine according to the present invention yields a final product with higher levels of purity compared to the method disclosed in US 6,784,297. A similar trend has been observed with other impurities.

Example 4 (Preparation of solvate without seed) Phthaloyl amlodipine (1O g, purity: 95.4%; 1.06% of impurity HA) was dissolved in 50 ml of acetone under reflux. Once solution was complete, it was cooled slowly to 15/10 ⁰ C. Then the solution was cooled to 5/0 ⁰ C and the solid was filtered off and washed with cold acetone.

The product was dried under vacuum at room temperature.

Yield of Phthaloyl amlodipine acetone solvate: 9.2 g.

DSC peak: 79.3 ⁰ C.

Purity: 98.9%; 0.08% of impurity HA.

Example 5 (Preparation of solvate without seed)

Phthaloyl amlodipine ( 1O g, purity: 92.8%; 1.90% of impurity HA) was dissolved in

173 ml of acetone at 32 ⁰ C. Once solution was complete, it was cooled to 12/8 ⁰ C until precipitation. Then the slurry was cooled to 5/0 ⁰ C and the solid was filtered off and washed with cold acetone.

The product was dried under vacuum at room temperature.

Yield of Phthaloyl amlodipine acetone solvate: 8.2 g.

DSC peak: 79.1 ⁰ C.

Purity: 99.5%; 0.14% of impurity HA.

Example 6 (Preparation of solvate with seed)

Phthaloyl amlodipine (1O g, purity: 98.6%; 0.86% of impurity HA) was dissolved in 60 ml of acetone under reflux. Then the solution is cooled to 45/30 ⁰ C and seeded with

Phthaloyl amlodipine acetone solvate to allow precipitation. The suspension was then cooled to 5/0 ⁰ C and water (5 ml) was added. The solid was filtered off, washed with acetone and dried under vacuum at room temperature.

Yield of Phthaloyl amlodipine acetone solvate: 10.4 g (8.1% w/w of acetone).

DSC peak: 81.3 ⁰ C.

Purity: 99.94%; 0.01% of impurity HA.

Comparative Examples

Example 7 (Example 1 of US6784297)

Phthaloyl amlodipine ( 10 g, purity: 98.6%; 0.86% of impurity HA) was dissolved in 35 ml of acetone at reflux and cooled to 45 ⁰ C. Water (10 ml) was slowly added to precipitate the product which was cooled to 5/0 ⁰ C and dried under vacuum at room temperature.

Yield: 9.3 g (<0.3% w/w of acetone).

DSC peak: 135.8 ⁰ C.

Purity: 99.0%. 0.83% of impurity HA

Example 8 (Example 2 of US6784297)

Phthaloyl amlodipine (10 g, purity: 98.6%; 0.86% of impurity HA) was dissolved in 50 ml of acetone at 45 ⁰ C and 14 ml of water was slowly added to precipitate the product which was cooled to 5/0 ⁰ C and dried under vacuum.

Yield: 9.5 g (<0.3% w/w of acetone).

DSC peak: 135.5 ⁰ C.

Purity: 98.9%. 0.84% of impurity HA

Example 9 (Example 3 of US6784297)

Phthaloyl amlodipine (1 O g, purity: 98.6%; 0.86% of impurity HA) was slurried in 25 ml of acetone, heated to reflux for 15 min and cooled to 45 ⁰ C. Water (9 ml) was slowly added to precipitate the product which was cooled to 5/0 ⁰ C and dried under vacuum at room temperature.

Yield: 9.5 g (<0.3% w/w of acetone).

DSC peak: 136.3 ⁰ C.

Purity: 99.2%. 0.60% of impurity HA

Example 10 (Example 4 of US6784297)

Phthaloyl amlodipine (1O g, purity: 98.6%; 0.86% of impurity HA) was dissolved in 50 ml of acetone at 45 ⁰ C and 15 ml of water was slowly added to precipitate the product which was cooled to 5/0 ⁰ C and dried under vacuum at room temperature. Yield: 8.7 g (<0.3% w/w of acetone). DSC peak: 135.5 ⁰ C.

Purity: 99.0%. 0.83% of impurity HA

Results obtained in example 4 to 10 are summarized in table 1

Table 1