MX2007015695A - An impurity of anastrozole intermediate, and uses thereof - Google Patents

Abstract

Reference markers and reference standards for the determination of impurities in Anastrozole are provided.

Description

AN INTERMEDIATE IMPURITY OF ANASTAZOL, AND USES OF THE Field of the Invention The present invention relates to an impurity of an Anastrozole intermediate, termed "Impurity A" and its uses.

BACKGROUND OF THE INVENTION Anastrozole, with the chemical name 1,3-benzenediacetonitrile-a, a, a ', a'-tetramethyl-5- (1H-1,2,4-triazol-ylmethyl) and having the following chemical structure : Anastrozole is a potent and selective non-spheroidal inhibitor of the aromatases system (estrogen synthetase), which converts adrenal androgens into estrogens in peripheral tissue. It is used in the treatment of advanced or locally advanced breast cancer, and as a coadjuvant treatment in early breast cancer, in postmenopausal women. This drug is commercially available for oral administration as ARIMIDEX® from AstraZeneca.

Like any synthetic compound, Anastrozole can contain foreign compounds or impurities that can come from many sources. They may be unreacted starting materials, byproducts of the reaction, products of side reactions, or degradation products. The impurities of Anastrozole or any other pharmaceutical ingredient (API) are undesirable and, in extreme cases, may still be harmful to a patient who is being treated with a dosage form containing the API.

It is also known in the art that the impurities of an API can arise from the degradation of the API itself, which is related to the stability of the pure API during storage, and the manufacturing process, which includes chemical synthesis. Process impurities include unreacted starting materials, chemical derivatives of impurities contained in initial materials, synthetic by-products, and degradation products.

In addition to the stability, which is a factor in API life, the purity of the API produced in the commercial manufacturing process is clearly a necessary condition for commercialization. Impurities introduced during commercial manufacturing processes should be limited to very small amounts, and preferably are substantially absent. For example, the ICH Q7A guide for API manufacturers requires process impurities to be kept below established limits by specifying the quality of the raw materials, controlling the parameters of the process, such as temperature, pressure, time and the stoichiometric ratios and including purification steps, such as crystallization, distillation and liquid-liquid extraction, in the manufacturing process.

The product mixture of a chemical reaction is rarely a single product with a purity sufficient to comply with pharmaceutical standards. The by-products and byproducts of the reaction and the additional reagents used in the reaction, in most cases, are also present in the product mix. At certain stages during the processing of an API, such as (S) -anastrozole, its purity must be analyzed, usually by HPLC or TLC analysis, to determine if it is suitable for continuous processing and, finally, for its use in a pharmaceutical product. The API does not need to be absolutely pure, since absolute purity is a theoretical ideal that is generally unattainable. Instead, the purity standards are set with the intention of ensuring that an API is as free of impurities as possible, and therefore, as safe as possible for chemical use. As discussed above, guidelines from the US Food and Drug Administration recommend that the amounts of some impurities be limited to less than 0.1 percent.

Generally, collateral products, byproducts, such as impurity A, and additional reagents (collectively "impurities") are identified spectroscopically and / or with another physical method, and then associated with a peak position, such as that of a chromatogram, or a spot on the TLC plate.

(Strobel p.953, Strobel, H.A., Heineman, W.R., Chemical Instrumentations: A Systematic Approach, 3rd dd. (Wiley &Sons, New York 1989)). Then, the impurity can be identified, for example, by its relative position on the TLC plate, where the position on the plate is measured in cm from the reference line on the plate or by its relative position on the chromatogram of the plate. HPLC, where the position in the chromatogram is measured conventionally in minutes between the injection of the sample into the column and the elution of the particular component through the detector. The relative position in the chromatogram is called the "retention time".

The retention time can vary an average value based on the condition of the instruments as well as many other factors.

To mitigate the effects of these variations on the precise identification of an impurity, practitioners use the "relative retention time" ("RRT") to identify impurities. (Strobel p.922). The RRT of an impurity is its retention time divided by the retention time of the reference marker. It may be advantageous to select a compound that is not the API that is added or is present in the mixture in an amount large enough to be detectable and sufficiently low to not saturate the column, and to use that compound as the reference marker for the determination of the RRT.

Those skilled in the art of drug manufacturing, research and development understand that a compound in a relatively pure state can be used as a "reference standard". A reference standard is similar to a reference marker, which is used for qualitative analysis only, but is also used to quantify the amount of the reference standard compound in an unknown mixture. A reference standard is an "external standard" when analyzing a solution of a known concentration of the reference standard and an unknown mixture using the same technique. (Strobel P. 924, Snyder P. 549, Snyder, L.R., Kirkland, J.J. Introduction to Modern Liquid Chromatography, 2nd ed. (John Wiley &Sons: New York, 1979)). The amount of the compound in the mixture can be determined by comparing the magnitude of the detector response. See also U.S. Patent No. 6,333,198, incorporated herein by reference.

The reference standard can also be used to quantify the amount of another compound in the mixture if a "reference factor" has been predetermined, which compensates for differences in detector sensitivity to the two compounds. (Strobel p.894). To this end, the reference standard is added directly to the mix, and is called the "internal standard". (Strobel P. 925, Snyder P. 552).

The reference standard can serve as an internal standard when, without deliberately adding the reference standard, an unknown mixture contains an amount that can be detected from the standard reference compound using the technique called "standard aggregate".

In the "standard aggregate technique", at least two samples are prepared by adding known and different amounts of the internal standard. (Strobel pp. 391-393, Snyder pp. 571, 572). The proportion of the detector response due to the reference standard present in the mixture without the aggregate can be determined by plotting the response of the detector against the amount of the reference standard added to each of the samples, and extrapolating the graph to zero concentration of the reference standard. (See, for example, Strobel, Fig. 11.4 p 392). The response of a detector to HPLC (eg, detection of ultraviolet radiation or refractive index detectors) can be and is generally different for each compound eluting from the HPLC column. The known response factors explain this difference in the detector response signal to different compounds eluting from the column.

As art experts know, the handling of process impurities is greatly improved by understanding their chemical structures and synthetic pathways, and by identifying the parameters that influence the amount of impurities in the final product.

The detection or quantification of the reference standard serves to establish the level of purity of the API or intermediates of it. The use of a compound as a standard requires recourse to a sample of a substantially pure compound.

EXAMPLE OF THE INVENTION In one aspect, the present invention provides a recently isolated impurity A, 2,3- 'Bis- [3- (cyano-dimethyl-methyl) -5-methyl-phenyl] -2-methyl-propionitrile of the following formula: In another aspect, the present invention provides a process for determining the presence of a compound in a sample comprising performing HPLC or TLC with an impurity A as a reference marker.

In still another aspect, the present invention provides a process for determining the presence of impurity A in a sample comprising performing HPLC or TLC with impurity A as a reference marker. Specifically, this process includes: (a) determining by HPLC or TLC the retention time corresponding to impurity A in a reference marker comprising impurity A; (b) determining by HPLC or TLC the retention time corresponding to impurity A in a sample comprising 3,5-bis (2-cyanoisopropyl) toluene and impurity A; Y (c) determining the presence of impurity A in the sample by comparing the retention time of step (a) with the retention time of step (b).

In one aspect, the present invention provides a process for determining the amount of a compound in a sample comprising performing HPLC or TLC with an impurity A as a reference standard. In another aspect, the present invention also provides a process for preparing anastrozole from 3,5-bis (2-cyanoisopropyl) toluene having less than 0.10% area by HPLC of the impurity A present, comprising the steps of: (a) obtaining one or more samples from one or more batches of 3,5-bis (2-cyanoisopropyl) toluene; (b) measuring the level of impurity A in each of the samples; (c) selecting a batch of step a) having a level of impurity A of less than 0.10% area by HPLC, based on the measurement of the batch samples; Y (d) use the selected batch to prepare anastrozole.

In still another aspect, the present invention provides an HPLC method used to determine the presence of impurity A in a sample of 5-bis (2-cyanoisopropyl) toluene comprising: combining a sample of 5-bis (2-cyanoisopropyl) toluene with water to obtain a solution; inject the solution obtained on a HYPERSIL BDS C18 (or similar) 100mmX4.6mm column; elute the sample from the column at 35 minutes using water (referred to herein as "eluent A") and acetonitrile (referred to herein as "eluent B") as the eluent, and measure the content of impurity A in the relevant sample with an ultraviolet radiation detector (preferably at a wavelength of 210 nm).

In one embodiment, the present invention provides a pharmaceutical composition comprising Anastrozole manufactured by the process of the invention and pharmaceutically acceptable excipients.

In another embodiment, the present invention provides a process for preparing a pharmaceutical formulation comprising admixing Anastrozole manufactured by the process of the invention and a pharmaceutically acceptable carrier.

Detailed Description of the Invention The term "substantially pure" with reference to 3, 5-bis (2-cyanoisopropyl) toluene refers to 3,5-bis (2-cyanoisopropyl) toluene containing less than 0.10% area by HPLC of impurity A.

The term "substantially pure" with reference to Anastrozole refers to Anastrozole that contains less than 0.10% area by HPLC of impurity B, defined below.

The present invention provides a recently isolated impurity, 2, 3-Bis- [3-cyano-dimethyl-methyl) -5-methyl-phenyl] -2-methyl-propionitrile of the following formula: This impurity, called "impurity A", contaminates an Anastrozole, 3, 5-bis (2-cyanoisopropyl) toluene intermediate of the formula I, It can be characterized by data selected from the group consisting of a RRT at 1.53 relative to 3,5-bis (2-cyanoisopropyl) toluene of formula I and / or an M / S spectrum with a peak of m / za 406.

Impurity A can be isolated by column chromatography using a mixture of heptane and ethyl acetate as eluent. Preferably, the eluent contains heptane and ethyl acetate in a ratio of 9: 1, respectively. Preferably, impurity A contains 0% to 10% area by HPLC of 3,5-bis (2-cyanoisopropyl) toluene of formula I.

The inventors of the present invention discovered that the impurity A is converted during the course of the reaction to prepare Anastrozole, 3,5-bis (2-cyanoisopropyl) toluene of the formula I into an impurity that contaminates Anastrozole, termed "impurity B". "of the following structure: wherein R and R 'can independently be H or or 1,2,4-triazole. The conversion of impurity A into impurity B is illustrated by the following scheme: IMPURITY A Where X and X "can be in. Independent image H or Br NaOH, triazole Doi.de R and R 'can, be imfedpendiente? Me? .te H or 1,2,4-iriazol IMPURITY S The conversion is such that the amount of impurity A is very similar to the amount of impurity B. Furthermore, since this impurity is characterized by a solubility similar to that of Anastrozole, it is difficult to separate it from Anastrozole, and therefore , use it as a marker and reference standard. Therefore, by combining the foregoing knowledge with the fact that the inventors of the present invention discovered that impurity A can be more easily and efficiently separated from the starting material, 3, 5-bis (2-cyanoisopropyl) toluene from Formula I makes its use more attractive as a reference marker and as a reference standard.

The present invention also provides a process for determining the presence of a compound in a sample comprising performing HPLC with impurity A as a reference marker.

The present invention also provides a process for determining the presence of impurity A in a sample comprising performing HPLC or TLC with impurity A as a reference marker. Specifically, this process comprises: (a) determining by HPLC or TLC the retention time corresponding to impurity A in a reference marker comprising impurity A; (b) determining by HPLC or TLC the retention time corresponding to impurity A in a sample comprising 3,5-bis (2-cyanoisopropyl) toluene and impurity A; and (c) determining the presence of impurity A in the sample by comparing the retention time of step (a) with the retention time of step (b).

The present invention provides a process for determining the amount of a compound in a sample comprising performing HPLC or TLC with an impurity A as a reference standard.

The present invention also provides a method for quantifying the amount of impurity A in a sample comprising performing HPLC or TLC, wherein the impurity is used as a reference standard. Specifically, this process comprises the steps of: (a) measuring, by HPLC or TLC, the area below a peak corresponding to impurity A in a reference standard comprising a known amount of impurity A; (b) measuring by HPLC or TLC, the area below a peak corresponding to impurity A in a sample comprising impurity A and 3, 5-bis (2-cyanoisopropyl) toluene; and (c) determining the amount of impurity A, in the sample by comparing the area of step (a) with the area of step (b).

The present invention also provides a process for preparing anastrozole from 3,5-bis (2-cyanoisopropyl) toluene having less than 0.10% area by HPLC of the impurity A present, comprising the steps of: (a) obtaining one or more samples of one or more batches of 3,5-bis (2-cyanoisopropyl) toluene; (b) measuring the level of impurity A in each of the samples; (c) selecting a batch of step a) having a level of impurity A less than 0.10% area by HPLC, based on the measurement of the batch samples; Y (d) use the selected batch to prepare anastrozole.

In a case where the level measured in step b) is greater than 0.10% area by HPLC, the process also comprises the purification step by any means known in the art, which includes the method disclosed in the Provisional Application U.S. Patent No. 60 / 694,528, wherein 3,5-bis (2-cyanoisopropyl) toluene is crystallized from a solvent selected from the group consisting of C6-9 aromatic hydrocarbons and C2-8 ethers.

The present invention provides an HPLC method used to determine the presence and amount of impurity A in a sample of 3,5-bis (2-cyanoisopropyl) toluene comprising: combining a sample of 5-bis (2-cyanoisopropyl) toluene with water to obtain a solution; inject the solution obtained on a HYPERSIL BDS C18 (or similar) column of 100mm X 4.6mm; elute the sample from the column at 35 minutes using water (referred to herein as "eluent A") and acetonitrile (referred to herein as "eluent B") as eluent, and measure the content of impurity A in a relevant sample with an ultraviolet radiation detector (preferably at a wavelength of 210 nm).

Preferably, the eluent used can be a mixture of the eluent A and the eluent B, wherein their ratio varies with time, i.e., a gradient eluent. At time 0 minutes, the eluent contains 80% of eluent A and 20% of eluent B. At 30 minutes, the eluent contains 40% of eluent A and 60% of eluent B. At 35 minutes, the eluent contains 20% of eluent A and 80% of eluent B, while at 36 minutes, the eluent contains 80% of eluent A and 20% of eluent B.

The present invention also provides a pharmaceutical composition comprising Anastrozole manufactured by the process of the invention and pharmaceutically acceptable excipients.

The present invention also provides a process for preparing a pharmaceutical formulation comprising mixing Anastrozole manufactured by the process of the invention and a pharmaceutically acceptable excipient.

Having described the invention with reference to certain preferred embodiments, other embodiments will become apparent to one skilled in the art from the analysis of the specification. The invention is also defined by reference to the following examples which describe in detail the preparation of the compound of the present invention. It will be apparent to those skilled in the art that many modifications can be made, both of materials and methods, without departing from the scope of the invention.

EXAMPLES The analysis of impurity A is carried out in crude 3, 5-bis (2-cyanisopropyl) toluene using the following HPLC: Column and Package: HYPERSIL BDS C18; 3 μm, 100 mm X 4.6 mm, category N ° 28103-104630 or equivalent Eluent A: Water Eluent B: Acetonitrile Gradient Time (min)% Eluent A% Eluent B 0 80 20 30 40 60 35 20 80 36 80 20 Stop time: 35 minutes Equilibrium time: 5 minutes Flow rate: 1.0 ml / minute Detector: ultraviolet radiation at 210 nm Column temperature: 60 ° C Injection: 5 μl Diluent: Acetonitrile The composition of the mobile phase and the flow rate can be varied to achieve this adaptation to the required system.

Mass spectrum analysis: Direct infusion in the ion source of ESI. The operating conditions used were the following: Instrument: LCQ Deca (Thermofinnigan), which operates in the positive ion mode Sample concentration: 10"6 M in Acetonitrile Spray Voltage: 4 kv Capillary Voltage: 13 V Capillary Temperature: 270 ° C Having described the invention with reference to certain preferred embodiments, other embodiments will become apparent to those skilled in the art from the analysis of the specification The invention is also defined by reference to the following examples which describe in detail the preparation of the composition and the methods of use of the invention. It is well known to those skilled in the art that many modifications can be made to both materials and methods, without departing from the scope of the invention.The examples given below describe unique crystallization experiments, which can be repeated to obtain the same. yields and improvements in the purification until the desired final purity is obtained.

Example 1; Crystallization of 3,5-bis (2-cyanoisopropyl) toluene from toluene A 4 g sample of 3, 5-bis (2-cyanoisopropyl) toluene, which has an initial content of impurity A of 1.93 area percent by HPLC, was suspended in 10 ml of toluene, and heated to 65 ° C, until the complete dissolution occurred. The solution was then allowed to cool to 25 ° C for a period of 1 hour, and then cooled to 0 ° C over a period of 2 hours. After 30 minutes at 0 ° C, the resulting suspension was filtered, and the filtrate was rinsed with 2.5 ml of toluene, precooled at 0 ° C. 3, 5-Bis (2-cyanisopropyl) toluene purified in an amount of 3.2 g, having an impurity content of 1.02 area percent was recovered by HPLC.

Example 3: Crystallization and Recrystallization of 3,5-bis (2-cyanoisopropyl) toluene from toluene 3, 5-bis (2-cyanoisopropyl) toluene (50 g), which contains 0.45% of impurity A, was dissolved in toluene (150 ml) and heated to 65 ° C-70 ° C until He obtained a complete dissolution. After 10 minutes, the solution was then allowed to cool to 25 ° C for 6 hours. After this time, the suspension was cooled to -20 ° C for 1 hour, stirred at the same temperature for 30 minutes and then filtered. The solid was then washed with toluene (25 ml) precooled at -20 ° C.

The wet solid was then analyzed by HPLC and showed a content of 0.24% of impurity A. Recrystallization of this solid another two times gave 3,5-bis (2-cyanoisopropyl) toluene having 0.07% impurity A. This solid was then dried in an oven at 50 ° C until all the solvent had been removed.

Example 4s Crystallization of 3,5-bis (2-cyanoisopropyl) toluene from 3 volumes of toluene A sample of 42 g of 3,5-bis (2-cyanoisopropyl) toluene, having an initial content of impurity A of 0.11 area percent by HPLC was suspended in 130 ml of toluene, and heated to 60 ° C. ° C, until the complete dissolution occurred. The solution was then allowed to cool to 25 ° C over a period of 3 hours and a suspension was obtained, and then cooled to -20 ° C over a period of 2 hours. After 30 minutes at -20 ° C, the resulting suspension was filtered and the filtrate was rinsed with 2.5 ml of toluene which was pre-cooled at -20 ° C. 3.5-bis (2-cyanoisopropyl) toluene purified in an amount of 40.1 g having an impurity content of 0.06 area percent was recovered by HPLC.

Example 4: Synthesis of Anastrozole A 30 g sample of 3, 5-bis (2-cyanoisopropyl) toluene having a 0.06% area by HPLC of impurity A, was dissolved in 150 ml of acetonitrile, and 24.8 g of N were added. -bromosuccinimide. The resulting suspension was heated at 50 ° C for 30 minutes, until a light yellow solution was obtained. Then, 0.5 g of 2,2'-azobis (2-methylpropionitrile) was added and the reaction was heated at 70 ° C for 6 hours. The solution was then allowed to cool to 20 ° C, and was poured into 150 ml of a 5 weight percent solution of sodium metabisulfite in water with vigorous stirring. The organic layer was then evaporated and washed with 100 ml of 5 weight percent of sodium carbonate solution in water before removing the organic solvent under reduced pressure, until a total volume of 90 ml was obtained. The resulting suspension was then heated to 50 ° C and 150 ml of heptane were slowly added over a period of 30 minutes, raising the temperature to 70 ° C. The suspension was then allowed to cool to 20 ° C, and filtered on a sintered glass funnel. Drying under reduced pressure gave 54 g of crude 85-percent pure l-bromo-3,5-bis (2-cyanoisopropyl) toluene (HPLC).

B; Anastrozole formation A sample of 16.7 g of 1,2,4-triazole was dissolved in 52 ml of NMP at 20 ° C and 9.7 g of NaOH were added in portions over 1 hour while maintaining the temperature at less than 35 ° C. The solution was stirred for 18 hours at 20 ° C and then cooled to -30 ° C. A solution of 40 g of alpha-bromo-3, Crude 5-bis (2-cyanisopropyl) toluene in 60 ml of NMP was added slowly for 6 hours, while keeping the temperature below -20 ° C. Upon completion of the addition, the suspension was stirred for 18 hours at -20 ° C, and during that time, the reaction was monitored by HPLC. When the amount of the starting material was less than 0.5 percent, acetic acid was added in an amount sufficient to provide a pH of 6.5 to 7. The mixture was allowed to slowly warm to 20 ° C, then 120 ml was added. of toluene, 240 of heptane and 170 ml of water. The biphasic system was vigorously stirred for 30 minutes, and the organic layer was then separated. Then, 240 ml of water, 60 ml of toluene, and 120 ml of heptane were added to the aqueous phase, and the system was stirred for 30 minutes before the organic phase was separated. Then, 400 ml of toluene and 240 ml of water were added to the aqueous portion, and the two-phase system was stirred for 1 hour. The organic layer was separated, and washed 3 times with 180 ml of a 0.05N solution of sulfuric acid in water. The final organic phase was concentrated under reduced pressure to a final volume of 150 ml at 40 ° C and 180 ml of heptane was added dropwise over a period of 1 hour. The suspension was cooled to 0 ° C, stirred for 1 hour and filtered. The crude solid was dissolved in 390 ml of 2-propanol at 50 ° C and 70 ml of heptane were added with stirring.

The solution was cooled to 0 ° C, stirred for 1 hour, and filtered. The solid was dried at 55 ° C under reduced pressure until a constant weight was reached; 23.5 g of the product with a purity greater than 99.4 area percent was produced by HPLC having 0.05% impurity B, and a melting point of 85 ° C, as measured by HPLC.

Example 5: Insulation of Impurity A A sample of 3,5-bis (2-cyanoisopropyl) toluene containing the impurity A was purified by flash column chromatography eluting with a 9: 1 mixture of heptane / ethyl acetate and analyzing the fractions with HPLC. Fractions containing impurity A with a purity > 90% were combined and the solvent was removed under vacuum to obtain the impurity A (2,3-Bis- [3- (cyano-dimethyl-methyl) -5-methyl-phenyl] -2-methyl-propionitrile) of the formula I.

Claims (21)

1. 2,3-Bis- [3- (cyano-dimethyl-methyl) -5-methyl-phenyl] -2-methyl-propionitrile isolated (impurity A), of the following formula:

2. The isolated impurity according to claim 1, containing 0% to 10% of 3,5-bis (2-cyanoisopropyl) toluene.

3. The isolated impurity according to claim 2, wherein it contaminates an Anastrozole, 3,5-bis (2-cyanoisopropyl) toluene intermediate of the formula I:

4. The isolated impurity according to any of claims 1 and 2, characterized by a RRT at 1.53 relative to 3,5-bis (2-cyanoisopropyl) toluene of the formula I.

5. The isolated impurity according to any of claims 1 to 3, characterized by M / S spectra with a peak of m / z to 406.

6. A process for determining the presence of a compound in a sample comprising performing HPLC or TLC with impurity A as a reference marker.

7. The process according to claim 6, wherein it is to determine the presence of impurity A in a sample comprising performing HPLC or TLC with impurity A as a reference marker.

8. The process according to any of claims 6 and 7, comprising: (a) determining by HPLC or TLC the retention time corresponding to impurity A in a reference marker comprising impurity A; (b) determining by HPLC or TLC the retention time corresponding to impurity A in a sample comprising 3,5-bis (2-cyanoisopropyl) toluene and impurity A; and (c) determining the presence of impurity A in the sample by comparing the retention time of step (a) with the retention time of step (b).

9. A process for determining the amount of a compound in a sample comprising performing HPLC or TLC with an impurity A as a reference standard.

10. The process according to any of claims 6 to 9, wherein the process is for quantifying the amount of impurity A in a sample comprising performing an HPLC or a TLC, wherein impurity A is used as the reference standard.

11. The process according to any of claims 6 to 10, comprising: (a) measuring by HPLC or TLC, the area below the peak corresponding to impurity A in a reference standard comprising a known amount of impurity A; (b) measuring by HPLC or TLC, the area below a peak corresponding to impurity A in a sample comprising impurity A and 3, 5-bis (2-cyanoisopropyl) toluene; and (c) determining the amount of impurity A, in the sample by comparing the area of step (a) with the area of step (b).

12. A process for preparing anastrozole from 3,5-bis (2-cyanoisopropyl) toluene having less than 0.10% area by HPLC of impurity A comprising the steps of: (a) obtaining one or more samples from one or more batches of 3, 5-bis (2-cyanoisopropyl) toluene; (b) measuring the level of impurity A in each of the samples; (c) selecting a batch of step (a) having a level of impurity A of less than 0.10% area by HPLC, based on the measurement of the batch samples; and (d) using the selected batch to prepare anastrozole.

13. The process according to claim 12, wherein the process also comprises, before step d, the purification of 3,5-bis (2-cyanoisopropyl) toluene when the level measured in step (b) is greater than 0, 10% area by HPLC.

14. The process according to any of claims 12 and 13, wherein the purification is performed by the crystallization of 3,5-bis (2-cyanoisopropyl) toluene from a solvent selected from the group consisting of C6-9 aromatic hydrocarbon and ether. of C2_8.

15. An HPLC method used to determine the presence and amount of impurity A in a 3,5-bis (2-cyanoisopropyl) toluene sample, comprising: (a) combining a sample of 3,5-bis (2-) cyanoisopropyl) toluene with water to obtain a solution; (b) injecting the obtained solution into a column; (c) eluting the sample from the column at 35 minutes using water, eluent A, acetonitrile, eluent B, as an eluent, and (d) measuring the content of impurity A in the relevant sample with a radiation detector. ultraviolet.

16. The method according to claim 15, wherein the ultraviolet radiation detector operates at a wavelength of 210 nm.

17. The process according to any of claims 15 and 16, wherein the eluent used is a mixture of the eluent A and the eluent B.

18. The method according to any of claims 15 to 17, wherein the ratio between the eluent A and the eluent B varies with time.

19. The method according to any of claims 15 to 18, wherein at 0 minutes, the eluent contains 80% of the eluent A and 20% of the eluent B; at 30 minutes, the eluent contains 40% of eluent A and 60% of eluent B; at 35 minutes, the eluent contains 20% of eluent A and 80% of eluent B; at 36 minutes, the eluent contains 80% of eluent A and 20% of eluent B.

20. A pharmaceutical composition comprising Anastrozole manufactured according to the process of any of claims 12 to 14 and pharmaceutically acceptable excipients.

21. A process for preparing a pharmaceutical formulation comprising mixing Anastrozole manufactured according to the process of any of claims 12 to 14, and a pharmaceutically acceptable carrier.