Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07J—STEROIDS
  • C07J31/00—Normal steroids containing one or more sulfur atoms not belonging to a hetero ring
  • C07J31/006—Normal steroids containing one or more sulfur atoms not belonging to a hetero ring not covered by C07J31/003
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07J—STEROIDS
  • C07J1/00—Normal steroids containing carbon, hydrogen, halogen or oxygen, not substituted in position 17 beta by a carbon atom, e.g. estrane, androstane
  • C07J1/0003—Androstane derivatives
  • C07J1/0011—Androstane derivatives substituted in position 17 by a keto group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07J—STEROIDS
  • C07J43/00—Normal steroids having a nitrogen-containing hetero ring spiro-condensed or not condensed with the cyclopenta(a)hydrophenanthrene skeleton
  • C07J43/003—Normal steroids having a nitrogen-containing hetero ring spiro-condensed or not condensed with the cyclopenta(a)hydrophenanthrene skeleton not condensed

Definitions

• the basic process for making abiraterone-3 -acetate disclosed in WO 93/20097 comprises
• DHEA acetate replacing the enol-form of the 17-oxo group in dehydroepiandrosterone- 3 -acetate (DHEA acetate) of formula (2)
• a leaving group L which is capable of being replaced by a 3-pyridyl group in a palladium(O) complex-catalyzed cross-coupling reaction with a 3-pyridinyl (dialkyl/ dialkoxy) -boron compound (so called Suzuki coupling reaction)
• the palladium complex in Suzuki coupling reaction is preferably a palladium(O) complex such as tetrakis(triphenylphosphine)palladium(0) or a complex reducible in situ to such palladium(0)phosphine species.
• the leaving groups L actually used in prior art documents were an iodo group and a trifluoromethanesulfonate (triflate) group.
• the 3-acetate group may be introduced only after introducing the 17-(3-pyridyl)- group, thus the actual starting material is not the compound of formula (2) but dehydroepiandrosterone (DHEA) of formula (3).
• DHEA dehydroepiandrosterone
• the compound of formula (3) is converted to the corresponding iodo-compound of formula (4) in two steps; subsequently, after performing the Suzuki coupling reaction on compound (4), abiraterone of formula (1A) is obtained.
• abiraterone (1A) is acetylated to the desired abiraterone-3 -acetate.
• the second known route employing the triflate leaving group L is two steps shorter and thus more advantageous.
• diethyl(3-pyridyl)borane was added to the isolated triflate compound of formula (5) in THF containing a catalytic amount of
• WO 2006/021776 and WO 2006/021777 suggest two improvements in the original process.
• the triflating step is advantageously conducted in the presence of an organic base comprising a tertiary or heterocyclic amine having a pKa value of the conjugate acid at 25°C within the range of 5.21 (i.e. pyridine) to 12 (i.e DBU, a diazabicycloundecene).
• an organic base comprising a tertiary or heterocyclic amine having a pKa value of the conjugate acid at 25°C within the range of 5.21 (i.e. pyridine) to 12 (i.e DBU, a diazabicycloundecene).
• DBU diazabicycloundecene
• this starting material may be removed from the reaction mixture by converting the product (1) to an acid addition salt, separating the salt in solid state and recrystallizing the salt.
• the mesylate salt of (1) was described to be the most advantageous salt in WO'776.
• Such salt may be obtained from a solution of the free base of (1) in a suitable solvent, e.g.
• the present invention relates to an improved process for making the compound 3 ⁇ - acetoxy-androsta-5,16-dien-17-yl trifluoromethanesulfonate of formula (5), which is an important intermediate in making abiraterone-3 -acetate of formula (1).
• the invention provides a process for making the compound of formula (5)
• a inflating agent preferably trifluoromethanesulfonic anhydride, in an inert solvent in the absence of an organic base.
• the inert solvent comprises an aliphatic acid ester, preferably having 2 to 10 carbon atoms, an aliphatic or aromatic hydrocarbon, preferably having 5 to 8 carbon atoms or a chlorinated aliphatic or aromatic hydrocarbon, preferably having 1 to 8 carbon atoms, and mixtures thereof.
• concentration of the compound (2) in the solvent is higher than 0.3M, preferably higher than 1.5M.
• reaction temperature is lower than 0°C, preferably from -5 to -30°C, most preferably from -10 to -20°C.
• the dehydroepiandrosterone-3 -acetate of formula (2) is prepared by reaction of dehydroepiandrosterone of formula (3) with acetic anhydride, and the so-obtained crude reaction mixture is used as the starting material for the reaction with the triflating agent.
• the reaction is carried out either in the absence of a base or in the presence of an inorganic base, preferably sodium or potassium carbonate.
• the triflate of formula (5) may be advantageously isolated from the reaction mixture, and the crude triflate may be purified by crystallization from a suitable solvent.
• a suitable crystallization solvent is an aliphatic alcohol, e.g. methanol or isopropanol, acetic acid, acetic anhydride or any mixture thereof with water.
• the invention provides a process for purification of the compound of formula (5), comprising crystallizing the compound of formula (5) from a solvent comprising an aliphatic alcohol, acetic acid or acetic anhydride or any mixture thereof with water.
• the triflate compound of formula (5) prepared by the above process is converted to crude abiraterone-3 -acetate of formula (1) under conditions of Suzuki coupling reaction, preferably by reaction with a dialkyl(3-pyridyl)borane in an inert solvent in the presence of a catalytic amount of bis(triphenylphosphine)palladium(II)chloride.
• the present invention relates to a process for making abiraterone-3 -acetate of formula (1) starting from dehydroepiandrosterone-3-acetate (DHEA) of formula (2).
• DHEA dehydroepiandrosterone-3-acetate
• Any of the known processes for making the compound of formula (5) comprises reaction of dehydroepiandrosterone-3 -acetate (DHEA) of formula (2) with a triflating agent such as trifluoromethanesulfonic anhydride in the presence of an organic base.
• the reaction of the compound of formula (2) with a triflating agent may proceed even without a base or in the presence of an inorganic base.
• the triflation reaction may even proceed under acidic conditions, e.g. in the presence of formic acid, acetic acid or acetanhydride.
• the reaction of compound (2) with triflic anhydride in the absence of an organic base often exhibits a high degree of conversion without considerable formation of the elimination and deacetylation byproducts.
• the present invention accordingly provides an improved process for making abiraterone-3 -acetate of formula (1), which includes a process for making the triflate compound of formula (5) in which dehydroepiandrosterone- 3 -acetate (DHEA- 3 -acetate) of formula (2) reacts with a triflating agent, preferably trifluoromethanesulfonic anhydride.
• a triflating agent preferably trifluoromethanesulfonic anhydride
• absence of an organic base means that no organic base is present in any starting material nor is added to the reaction mixture before, during or after the reactive contact between dehydroepiandrosterone-3 -acetate and triflating agent. The absence of an organic base does not preclude the presence of an inorganic base.
• the starting material dehydroepiandrosterone- 3 -acetate of formula (2) is commercially available or may be produced by processes known in the art.
• the compound of formula (2) may be prepared from dehydroepiandrosterone of formula (3) by reaction thereof with an acetylation agent, e.g. with acetic anhydride or an acetyl halide.
• an acetylation agent e.g. with acetic anhydride or an acetyl halide.
• the acetylation reaction may be performed using acetic anhydride, which also serves as the solvent, without need of any other inert solvent and/or diluent.
• the compound of formula (2) does not need to be purified after acetylation of dehydroepiandrosterone of formula (3) with acetic anhydride, but may advantageously be used as a crude reaction mixture in the triflation process in accordance with the present invention.
• a suitable inert solvent to be used in accordance with the process of the present invention typically is an aprotic organic solvent and preferably comprises, without limitation, an aliphatic acid ester, preferably having 2 to 10 carbon atoms; an aliphatic or aromatic hydrocarbon, preferably having 5 to 8 carbon atoms; or a chlorinated aliphatic or aromatic hydrocarbon, preferably having 1 to 8 carbon atoms, and mixtures thereof.
• Suitable solvents include ethyl acetate, isopropyl acetate, dichloromethane, 1 ,2-dichloroethane, toluene, and mixtures thereof.
• the preferred triflating agent is trifluoromethanesulfonic anhydride (triflic anhydride), which is commercially available. Preferably, it is used in a molar excess (5-150 molar excess) with respect to the compound of formula (2).
• the concentration of the compound of formula (2) in the inert solvent is preferably higher than 0.3M, more preferably higher than 0.4M, and most preferably higher than 1.5M.
• the triflation reaction typically proceeds at a lower than ambient temperature.
• the reaction temperature is lower than 0°C, more preferably from -5 to -30°C, most preferably from -10 to -20°C.
• the triflating agent is advantageously added slowly, e.g. portionwise, under temperature control, to the well-stirred mixture comprising the compound (2) in the inert solvent to avoid local overheating.
• the course of reaction may be monitored by a suitable analytical technique, for instance by HPLC.
• an inorganic base such as sodium or potassium carbonate or sodium or potassium acetate
• an inorganic base may optionally be added to the reaction mixture, before and/or during the triflation reaction, in particular in the case when the above (crude) acidic reaction mixture comprising DHEA-3acetate is used as the starting material for the triflation reaction.
• an inorganic base may react with the acetic acid or triflic acid arising from the reaction and neutralize the acid, it does neither react with the starting material nor with the desired end-product.
• the relative molar amount of the inorganic base is advantageously at least equivalent to the molar amount of the acidic components in the reaction mixture such as acetate or trifluoromethanesulfonate moieties.
• the reaction mixture is advantageously elaborated with the aim to remove side-products, particularly the resulting triflic acid.
• the mixture is extracted with water, which may be optionally alkalinized, and the traces of water are removed by drying the organic phase.
• the extractions may be performed at ambient or lower than ambient temperature.
• the so-obtained solution of the crude triflate compound of formula (5) may be used in the next step as such if desired, or advantageously the triflate may be isolated therefrom by evaporation of the solvent.
• the obtained triflate compound of formula (5) may be purified.
• the purification is performed without using chromatographic separation.
• the inert organic solvent is removed by evaporation and the residual material is crystallized from a suitable solvent, which may be an aliphatic alcohol having from 1 to 5 carbon atoms, e.g. methanol or, preferably, isopropanol, acetic acid, or acetic anhydride.
• a suitable solvent which may be an aliphatic alcohol having from 1 to 5 carbon atoms, e.g. methanol or, preferably, isopropanol, acetic acid, or acetic anhydride.
• the crude compound of formula (5) is dissolved in the crystallization solvent at an elevated temperature, which advantageously is a temperature from 40°C up to the boiling point of the solvent, the solution is optionally treated with a surface active material and/or filtered, and the hot solution is cooled to ambient or lower than ambient temperature.
• seed crystals of compound (5) may be added.
• an anti-solvent may be added to decrease the solubility of the product.
• the obtained solid, typically crystalline triflate is isolated by filtration or centrifugation, and optionally dried.
• the triflate compound of formula (5) or a solution comprising it is used in the next step without delay; otherwise it may be stored for certain time in a closed container protected from light and, preferably, at a temperature well below 0°C.
• the triflate compound of formula (5) prepared by the above process is converted into crude abiraterone-3 -acetate of formula (1) under conditions of the Suzuki coupling reaction.
• the conditions of the Suzuki coupling reaction on the compound of formula (5) are well- known in the art and were disclosed in the prior art documents cited above.
• diethyl(3-pyridyl)borane is added to the isolated triflate compound (5) in a suitable solvent, e.g. in tetrahydrofuran, containing a catalytic amount of bis(triphenylphosphine)- palladium(II) dichloride and sodium carbonate as a nucleophilic activator.
• the reaction proceeds by stirring the mixture at an elevated temperature (typically at 60-90°C) and may be followed by a suitable analytical technique, for instance by HPLC. After termination of the reaction, the reaction mixture is worked-up with the aim to isolate crude abiraterone-3 - acetate. Typically, the mixture is partitioned between ethyl acetate and water; the organic layer is separated, and the solvent is evaporated.
• an elevated temperature typically at 60-90°C
• HPLC HPLC
• the resulting crude abiraterone-3 -acetate still comprises some unreacted starting material (typically less than 10%) and traces of other impurities. It may be purified by converting it to an acid addition salt. While the prior art documents suggest using methanesulfonic acid as the best acid for said purposes, in the context of the present invention the use of ethanesulfonic (esylic) acid is preferred. This acid forms the esylate salt of abiraterone-3 -acetate in a good yield and superior purity. Such salt is insoluble in non-polar or low polar organic solvents and may be easily separated by precipitation and filtration.
• the salt of abiraterone-3 -acetate with ethanesulfonic acid is obtained in an isolated, solid state.
• Impurities, which do not comprise the pyridine moiety, such as the starting material or the intermediate, unreacted triflate, remain dissolved.
• the crude abiraterone-3 -acetate is dissolved in a suitable solvent, which preferably is an aliphatic ester, such as ethyl acetate, an ether, such as methyl tert-butyl ether, and mixtures thereof.
• a suitable solvent which preferably is an aliphatic ester, such as ethyl acetate, an ether, such as methyl tert-butyl ether, and mixtures thereof.
• ethanesulfonic acid is added upon stirring, typically at ambient temperature.
• the ethanesulfonate (esylate) salt precipitates from the solution and may be easily isolated by filtration.
• the esylate salt may be recrystallized from a suitable solvent, for instance from acetonitrile or an aliphatic alcohol, such as isopropanol.
• the purity of the esylate salt may reach at least 97% (HPLC, internal normalization (IN)), advantageously at least 98%, and in some embodiments at least 99%.
• pure abiraterone- 3 -acetate is made starting from the esylate salt.
• the esylate salt is dissolved or suspended in a solvent which is not miscible with water, such as a chlorinated hydrocarbon, for instance
• aqueous base for instance saturated aqueous sodium carbonate or saturated aqueous sodium acetate.
• aqueous phase is then removed.
• Concentration of the organic phase and triturating the residue with a useful liquid vehicle such as with an aliphatic hydrocarbon, for instance a hexane or a heptane, or with an ethanol/water mixture, gives a suspension of the desired product.
• the solid is separated by ordinary techniques, e.g. by filtration or centrifugation, washed, and dried.
• the process of forming the salt and liberating the compound (1) from the salt may be repeated until the desired purity is obtained.
• reaction mixture was diluted with dichloromethane (100 ml) and was extracted two times with 1M aqueous solution of sodium carbonate (2x 200 ml). The reaction mixture was allowed to heat to ambient temperature during extractions.
• Trifluoromethanesulfonic anhydride (0.544 ml, 3.78 mmol) was added portionwise to the reaction mixture over 20 minutes at -15°C. The mixture was stirred at -15°C for 1.5 hours, and then diluted with 2 ml of dichloromethane. The mixture was extracted with 2 x 7 ml of 1M sodium carbonate, 2x 10 ml of wate,r and 10 ml of brine. The organic layer was dried with magnesium sulfate, filtered, and concentrated to dryness on rotavap to constant weight. Yield: 1.35 g (85%), conversion 86% (HPLC).
• Dehydroepiandrosterone-3-acetate (10 g, 30.3 mmol) was diluted with toluene (40 ml) and benzene (1 ml). Potassium carbonate (8.36 g, 60.5 mmol) was added, and the mixture was stirred for 0.5 h at 25°C. The mixture was cooled to -15°C, trifluoromethanesulfonic anhydride (7.17 ml, 42.4 mmol) was dosed over 20 min, and the whole mixture was stirred at -15 to -18°C for 20 h. The reaction mixture was diluted with water (70 ml), and then with toluene (40 ml).
• Dehydroepiandrosterone-3-acetate (1 g, 3.03 mmol) was diluted with dichloromethane (8 ml) and toluene (0.1 ml). Potassium carbonate (1.673 g, 12.10 mmol) and acetic acid (0.207 ml, 3.63 mmol) were added, and the mixture was stirred for 0.5 h at 25°C. The mixture was cooled to -15°C and trifluoromethanesulfonic anhydride (1.739 ml, 10.3 mmol) was added in 3 portions. The mixture was stirred at -15 to -18°C for 11 h. The reaction mixture was diluted with water (7 ml), and then with toluene (7 ml).
• Dehydroepiandrosterone-3-acetate (1 g, 3.03 mmol) was diluted with dichloromethane (6 ml) and toluene (0.1 ml). Potassium carbonate (1.673 g, 12.10 mmol) and acetic anhydride (0.286 ml, 3.03 mmol) were added, and the mixture was stirred for 0.5 h at 25°C. The mixture was cooled to -15°C and trifluoromethanesulfonic anhydride (1.739 ml, 10.3 mmol) was added in 3 portions. The mixture was stirred at -15 to -18°C for 11 h. The reaction mixture was diluted with water (7 ml) and then with toluene (7 ml).

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