A process for the production of finasteride

Abstract: Disclosed is a new process for producing finasteride which involves reacting the magnesium halide salt of 17β-carboalkoxy-4-aza-5α-androst-1-en-3-one with t-butylamino magnesium halide, present in at least a 2:1 molar ratio to the ester, formed from t-butyl amine and an aliphatic/aryl magnesium halide at ambient temperature in an inert organic solvent under an inert atmosphere followed by heating and recovering the product finasteride. Also disclosed are two polymorphic crystalline Forms I and II of finasteride, and methods of their production.

Description: Finasteride, marketed under the tradename of PROSCAR®, by Merck & Co., Inc. is 17β-(N-tert-butyl carbamoyl)-4-aza 5α-androst-1-en-3-one and is a 5α-reductase inhibitor for use in treating acne, female hirsulism, and particularly benign prostalic hyperplasia. See US Patent 4.760,071 (1988 ), the entire disclosure of which is incorporated herein by reference. The synthesis of finasteride in US Patent 4.760.071 involves reacting the 17β-(2-pyridylthio) carboxylate of 4-aza-5α-androst-1-ene-3-one with 1-butylamine. A further synthesis of finasteride is described in Synthetic Communications. 30 (17). p. 2683-2690 (1990 ), the entire disclosure of which is incorporated herein by reference, including the reacting of the 17-acylimidazole of 4-aza-5α-androst-1-en-3-one with 1-butylamine. However, both of these reactions require the use of heterocyclic aromatic amines which are expensive and give rise to environmental safety and toxicity considerations. Both of these intermediates are prepared from the 17β-carboxylic acid. McCauley. "Detection and Characterisation of Polymorphism in the Pharmaceutical Industry", AlChE Symposium Series, volume 87, No. 284 (1991) pp 58-63 describes two enantiotropic polymorphs of finasteride (PROSCAR®), but does not describe how to obtain either polymorph, except that, given the polymorph more stable at lower temperatures, it may be heated through a transition point and cooled to obtain the polymorph more stable at higher temperatures. Example 1 of EP 0 428 366 describes a method for obtaining crystalline finasteride which comprises dissolving finasteride in 10 ml of acetic acid, slowly adding 100 ml of water, ageing at room temperature and filtering and drying the crystalline solid obtained. Polymorphism can be defined as the ability of the same chemical substance to exist in different crystalline structures. The different structures are referred to as polymorphs, polymorphic modifications or forms. Finasteride has been found to exist in at least two polymorphic nonsolvated forms. Form I and Form II, each of which can be formed by careful control of the crystallization conditions. In one aspect of the present invention, there is provided a process for producing polymorphic Form I of finasteride, comprising the steps of: (1) crystallization from a mixture of finasteride in: (a) a mixture of ethyl acetate and water, wherein the amount of water in the solvent mixture is at most about 3.5 mg/ml; or (b) a mixture of iso-propyl acetate and water, wherein the amount of water in the solvent mixture is at most about 1.6 mg/ml: at an ambient temperature of about 25°C: (2) recovering the resultant solid phase, and (3) removing the solvent therefrom The crystallization examples above are to: procedures conducted at ambient temperature. As can be appreciated by those skilled in the art, the amount of water needed to produce Form I in any given organic solvent mixture will vary with temperature, since changes in temperature will alter the solubility of the solute For example, when using iso-propyl acetate to produce Form I, the following amounts of water may be present at the indicated temperatures: Temperature Amount of Water 1.4°C 0.8 mg/ml or less 6°C 0.9 mg/ml or less 12°C 1.0 mg/ml or less 18°C 1.3 mg/ml or less In another aspect, the present invention provides a process for producing polymorphic Form II of linasteride, comprising the steps of (1) crystallization from a mixture of finasteride in an organic solvent and water, wherein the organic solvent is glacial acetic acid, and the weight percentage of water in the solvent mixture is less than about 83%, or wherein the organic solvent is ethyl acetate and the amount of water in the solvent mixture is greater than about 3.5 mg/ml, or wherein the organic solvent is iso-propyl acetate, and the amount of water in the solvent mixture is greater than about 1.6 mg/ml, such that the amount of organic solvent and water in the mixture is sufficient to cause the solubility of the solvated form of finasteride to be exceeded and the solvated form of linasteride to be less soluble than any other form of finasteride in the mixture: (2) recovering the resultant solid phase: and (3) removing the solvent therefrom. When producing Form II from a water-miscible solvent, the weight percentage of water used in the solvent mixture will be less than that used to produce Form I from the same water-miscible solvent. For example, to produce Form II of finasteride from a glacial acetic acid/water mixture, the weight percentage of water in the solvent mixture is less than about 83%, at an ambient temperature of about 25°C. Furthermore, when a water-immiscible solvent such as ethyl acetate or iso-propyl acetate is used to produce Form II, then the amount of water used in the solvent mixture will be more than that used to produce Form I from the same organic solvent. For example, to produce Form II of finasteride from an ethyl acetate /water mixture, the amount of water used is greater than about 3.5 mg/ml, and from an iso-propyl acetate/water mixture, the amount of water used is greater than about 1.6 mg/ml, both at an ambient temperature of about 25°C. As explained above, those skilled in the art will appreciate that changes in temperature may affect the amount of water needed to produce Form II from any given solvent mixture. The following Examples illustrate methods for obtaining polymorphic Forms I and II of finasteride (Proscar®, MK 906) and some characterization data. The following examples are provided to further illustrate details for the preparation of the compounds of the present invention. The examples are not intended to be limitations on the scope of the instant invention in any way, and they should not be so construed. ILLUSTRATIVE EXAMPLE Finasteride Form I can be prepared by dissolving finasteride in glacial acetic acid (ca. 100 mg/ml) and adding water with stirring until the weight % of water equals or exceeds 84%. The resulting solid phase is collected by filtration and dried under vacuum and at about 50°C. The resulting Form I is characterized by a differential scanning calorimetry (DSC) curve, at heating rate of 20°C/min and in a closed cup, exhibiting a minor endotherm with a peak temperature of about 232°C, an extrapolated onset temperature of about 223°C with an associated heat of about 11 joules/gm and by a major melting endotherm with a peak temperature of about of 261°C, an extrapolated onset temperature of about 258°C with an associated heat of about 89 J/gm. The x-ray powder diffraction pattern is characterized by d-spacings of 6.44, 5.69, 5.36, 4.89, 4.55, 4.31, 3.85, 3.59 and 3.14. The FT-IR spectrum (in KBr) shows bands at 3431, 3237, 1692, 1666, 1602 and 688 cm-1. The solubilities in water and cyclohexane at 25°C are 0.05+0.02 and 0.27+0.05 mg/gm respectively. EXAMPLE 1 Form I of finasteride can be prepared by recrystallization from dry (H 2 O <1mg/ml) ethyl acetate and isopropyl acetate, at ambient temperature (~ 25°C) The isolated solids are dried under vacuum at about 50°C and have the same physical characterization data as given above. EXAMPLE 2 Form II of finasteride can be prepared by dissolving finasteride in glacial acetic acid (ca. 100 mg/ml) and adding water with stirring until the weight % of water equals about 75% but not in excess of 80%. The resulting solid phase is collected by filtration and dried under vacuum and at about 100°C. The resulting Form II is characterized by a DSC curve, at heating rate of 20°C/min and in a closed cup, exhibiting a single melting endotherm with a peak temperature of about of 261°C, an extrapolated onset temperature of about 258°C with an associated heat of about 89 J/gm. The x- ray powder diffraction pattern is characterized by d-spacings of 14.09, 10.36, 7.92, 7.18, 6.40, 5.93, 5.66, 5.31, 4.68. 3.90,3.60 and 3.25. The FT-IR spectrum (in KBr) shows bands at 3441, 3215, 1678, 1654, 1597, 1476 and 752 cm-1. The solubilities in water and cyclohexane at 25°C are 0.16+0.02 and 0.42+0.05 mg/gm respectively. In addition, Form II of finasteride can be prepared by recrystallization from ethyl acetate containing from about 3.5 to 30 mg/ml of water, or f rom isopropyl acetate containing from about 1.6 to 15 mg/ml of water, at ambient temperature (~ 25°C). The isolated solids are dried under vacuum at about 80°C and have the same physical characterization data as given above.

Claims: A process for producing polymorphic Form I of 17β-(N-tert-butyl carbamoyl)-4-aza-5α-androst-1-en-3-one, comprising the steps of: (1) crystallization from a mixture of finasteride in: (a) a mixture of ethyl acetate and water, wherein the amount of water in the solvent mixture is at most about 3.5 mg/ml: or (b) a mixture of iso-propyl acetate and water, wherein the amount of water in the solvent mixture is at most about 1.6 mg/ml: at an ambient temperature of about 25°C. (2) recovering the resultant solid phase; and (3) removing the solvent therefrom. A process for producing polymorphic Form II of 17β-(N-tert-butyl carbamoyl)-4-aza-5α-androst-1-en-3-one, comprising the steps of: (1) crystallization from a mixture of finasteride in an organic solvent and water, wherein the organic solvent is glacial acetic acid, and the weight percentage of water in the solvent mixture is less than about 83%, or wherein the organic solvent is ethyl acetate and the amount of water in the solvent mixture is greater than about 3.5 mg/ml, or wherein the organic solvent is iso-propyl acetate, and the amount of water in the solvent mixture is greater than about 1.6 mg/ml, such that the amount of organic solvent and water in the mixture is sufficient to cause the solubility of the solvated form of finasteride to be exceeded and the solvated form of finasteride to be less soluble than any other form of finasteride in the mixture; (2) recovering the resultant solid phase; and (3) removing the solvent therefrom.

Inventors: DOLLING ULF H, MCCAULEY JAMES A, VARSOLONA RICHARD J, DOLLING, ULF H., MCCAULEY, JAMES A., VARSOLONA, RICHARD J.
Applicants: MERCK & CO INC, MERCK & CO., INC.
Application year: 1993
Main classification: C07J73
IPC codes: C07J75, C07F3, C07J9, A61K31, C07J73, H04N5