Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D239/00—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings
  • C07D239/70—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings condensed with carbocyclic rings or ring systems
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/495—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with two or more nitrogen atoms as the only ring heteroatoms, e.g. piperazine or tetrazines
  • A61K31/505—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim
  • A61K31/519—Pyrimidines; Hydrogenated pyrimidines, e.g. trimethoprim ortho- or peri-condensed with heterocyclic rings
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P3/00—Drugs for disorders of the metabolism
  • A61P3/06—Antihyperlipidemics
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D239/00—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings
  • C07D239/70—Heterocyclic compounds containing 1,3-diazine or hydrogenated 1,3-diazine rings condensed with carbocyclic rings or ring systems
  • C07D239/72—Quinazolines; Hydrogenated quinazolines
  • C07D239/78—Quinazolines; Hydrogenated quinazolines with hetero atoms directly attached in position 2

Definitions

• the present invention relates to rosuvastatin degradation products and their use as a reference standard for analysis of rosuvastatin.
• Statins are currently the most therapeutically effective drugs available for reducing low-density lipoprotein (LDL) particle concentration in the blood stream of patients at risk for cardiovascular disease.
• LDL low-density lipoprotein
• statins are used in the treatment of hypercholesterolemia, hyperlipoproteinemia, and atherosclerosis.
• a high level of LDL in the bloodstream has been linked to the formation of coronary lesions that obstruct the flow of blood and can rupture and promote thrombosis.
• HMG-CoA 3-hydroxy-3-methyl-glutaryl-coenzyme A
• HMG-CoA reductase catalyzes the conversion of HMG to mevalonate, whicht is the rate-determining step in the biosynthesis of cholesterol. Decreased production of cholesterol causes an increase in the number of LDL receptors and corresponding reduction in the concentration of LDL particles in the bloodstream. Reduction in the LDL level in the bloodstream reduces the risk of coronary artery disease. J. .M. A. 1984, 251, 351-74.
• statins include lovastatin, simvastatin, pravastatin., fluvastatin, cerivastatin and atorvastatin. Lovastatin (disclosed in U.S. Pat. No.
• Rosuvastatin calcium (monocalcium bis (+) 7-[4-(4-fluorophenyl)-6- isopropyl-2-(N-methyl-N-methylsulfonylaminopyrimidin)-5-yl]-(3R,5S)-dihydroxy- (E)-6-heptenoate) is an HMG-CoA reductase inhibitor, developed by Shionogi for the once daily oral treatment of hyperlipidaemia (Ann Rep, Shionogi, 1996; Direct communications, Shionogi, 8 Feb 1999 & 25 Feb 2000). Rosuvastatin calcium is a superstatin, which can lower LDL-cholesterol and triglycerides more effectively than first generation drugs. Rosuvastatin calcium has the following chemical formula:
• Rosuvastatin calcium is marketed under the name CRESTOR for treatment of a mammal such as a human. According to the maker of CRESTOR, it is administered in a daily dose of from about 5mg to about 40 mg. For patients requiring less aggressive LDL-C reductions or who have pre-disposing factors for myopathy, the
• rosuvastatin by reacting 4-(4-fiuorophenyl)-6-isopropyl-2-(N-methyl-N-methylsulfonylamino)-5- pyrimidinecarbaldehyde with methyl (3R)-3-(tert-butyldimethylsilyloxy)-5-oxo-6- triphenylphosphoranylidene hexanate in acetonitrile under reflux.
• the silyl group is then cleaved with hydrogen fluoride, followed by reduction with NaBH 4 and diethylmethoxyborane in THF to obtain a methyl ester of rosuvastatin.
• the ester is then hydrolyzed with sodium hydroxide in ethanol at room temperature, followed by removal of ethanol and addition of ether, to obtain the sodium salt of rosuvastatin.
• the sodium salt is then converted to the calcium salt.
• the sodium salt is dissolved in water and maintained under a nitrogen atmosphere.
• Calcium chloride is then added to the solution, resulting in precipitation of rosuvastatin calcium (2:1).
• U.S. Pat. No. 6,316,460 discloses a pharmaceutical composition of rosuvastatin.
• the pharmaceutical compositions contain rosuvastatin or its salt and a multivalent tribasic phosphate salt.
• the product mixture of a reaction rarely is a single compound pure enough to comply with pharmaceutical standards. Side products and byproducts of the reaction and adjunct reagents used in the reaction will, in most cases, be present.
• the rosuvastatin must be analyzed for purity, typically by HPLC or GC analysis, to determine if it is suitable for continued processing or ultimately for use in a pharmaceutical product.
• the rosuvastatin does not need to be absolutely pure. Absolute purity is a theoretical ideal that is unattainable. Rather, there are purity standards intended to ensure that an API is not made less safe for clinical use because of the presence of impurities.
• impurities are identified spectroscopically and by other physical methods and then the impurities are associated with a peak position in a chromatogram (or a spot on a TLC plate). (Strobel p. 953) (Strobel, H.A.; Heineman, W.R., Chemical
• the impurity can be identified by its position in the chromatogram, which is conventionally measured in minutes between injection of the sample on the column and elution of the particular component through the detector, known as the "retention time.” This time period varies daily based upon the condition of the instrumentation and many other factors. To mitigate the effect that such variations have upon accurate identification of an impurity, practitioners use "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 some reference marker.
• rosuvastatin itself could be used as the reference marker, but as a practical matter it is present in such overwhelming proportion in the mixture that it tends to saturate the column, leading to irreproducible retention times, i.e., the maximum of the peak corresponding to rosuvastatin tends to wander (Strobel Fig. 24.8(b) p. 879, contains an illustration of the sort of asymmetric peak that is observed when a column is overloaded).
• a compound in a relatively pure state can be used as a "reference standard" (a "reference marker” is similar to a reference standard but it is used for qualitative analysis) to quantify the amount of the compound in an unknown mixture.
• a solution of a known concentration of the compound is analyzed by the same technique as the unknown mixture. (Strobel p. 924, Snyder p. 549) (Snyder, L.R.; Kirkland, JJ. 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.
• the reference standard compound also can be used to quantify the amount of another compound in the mixture if the "response factor," which compensates for differences in the sensitivity of the detector to the two compounds, has been predetermined.
• the reference standard compound may be added directly to the mixture, in which case it is called an "internal standard.”
• the reference standard compound can even be used as an internal standard when the unknown mixture contains some of the reference standard compound by using a technique called "standard addition,” wherein at least two samples are prepared by adding known and differing amounts of the internal standard. (Strobel pp. 391-393, Snyder pp.
• the proportion of detector response due to the reference standard compound that is originally in the mixture can be determined by extrapolation of a plot of detector response versus the amount of the reference standard compound that was added to each of the samples to zero. (e.g. Strobel, Fig. 11.4 p. 392).
• the present invention provides a rosuvastatin degradation product that can be used as a reference standard for analysis of rosuvastatin.
• the present invention provides a rosuvastatin degradation product having the following structure:
• the present invention provides a rosuvastatin degradation product having the following structure:
• the present invention provides a rosuvastatin degradation product having the following structure:
• the present invention provides a rosuvastatin degradation product having the following structure:
• M is an alkali or alkaline earth metal.
• M is calcium.
• the calcium salt may be converted to lactone form by combining acetonitrile, hydrochloric acid and the calcium salt to obtain the lactone; or to free acid comprising dissolving the calcium salt in a mixture of acetonitrile and water, and contacting the calcium salt with a silica column.
• the present invention provides a lactone form of a rosuvastatin degradation product having the following structure:
• the present invention provides a lactone form of a rosuvastatin degradation product having the following structure:
• the present invention provides a process for converting the lactone to a calcium salt comprising hydrolyzing the lactone under aqueous basic conditions, and reacting the hydrolyzed lactone with a source of calcium.
• the present invention provides a process for converting the lactone to free acid form comprising hydrolyzing the lactone under aqueous basic conditions to obtain a metal salt and contacting the metal salt with a silica column.
• the degradation product is about 95% free by weight of its corresponding stereoisomer at position 6.
• the rosuvastatin degradation product may be isolated or purified.
• the present invention provides a method for analyzing a sample of rosuvastatin comprising the steps of: a) performing chromatography on the sample to obtain data; and b) comparing the data with the chromatography data of the degradation product.
• the present invention provides a process for preparing the degradation product comprising the step of irradiating with visible light rosuvastatin acid, rosuvastatin alkali or alkaline earth metal salt or rosuvastatin lactone.
• the present invention provides a method for determining the retention time of a chromatography column for rosuvastatin, comprising the steps of carrying out chromatography with the following compound as a standard,
• Ri and R are independently hydrogen or a hydrolyzable protecting group; R is hydrogen, a C ⁇ to C 4 alkyl group, or an alkali or alkaline earth metal; or wherein C 1 and C 5 form a lactone.
• Figure 1 is an HPLC chromatogram of Compound VI.
• Figure 2 is an HPLC chromatogram of Compound NIL
• Figure 3 is an HPLC chromatogram of a mixture of rosuvastatin, Compound NI, and
• the term "reference standard” refers to a compound that may be used both for quantitative and qualitative analysis of an active pharmaceutical ingredient.
• the retention time of the compound in HPLC allows for setting a relative retention time, thus making qualitative analysis possible.
• the concentration of the compound in solution before injection into an HPLC column allows for comparison of the areas under the peaks in an HPLC chromatogram, thus making quantitative analysis possible.
• a “reference marker” is used in qualitative analysis to identify components of a mixture based upon their position, e.g. in a chromatogram or on a Thin Layer Chromatography (TLC) plate (Strobel pp. 921, 922, 953).
• TLC Thin Layer Chromatography
• a "reference marker” is used only for qualitative analysis, while a reference standard may be used for quantitative or qualitative analysis, or both. Hence, a reference marker is a subset of a reference standard, and is included within the definition of a reference standard.
• the detector response can be, for example, the peak heights or integrated peak areas of a chromatogram obtained, e.g. by UN or refractive index detection, from the eluent of an HPLC system or, e.g. flame ionization detection or thermal conductivity detection, from the eluent of a gas chromatograph, or other detector response, e.g.
• the position of the reference standard may be used to calculate the relative retention time for rosuvastatin and other impurities.
• rosuvastatin calcium is exposed to visible light irradiation, degradation products of rosuvastatin are obtained, which can be used as a reference standard.
• the two degradation products are diastereomeric cyclic products (II) and (III) with the creation of an additional asymmetric center in position 6 as follows:
• rosuvastatin calcium in addition to rosuvastatin calcium, other forms of rosuvastatin may be irradiated, including the lactone, free acid and salts such as sodium salt.
• the irradiation may be performed in solution or in solid state. When irradiating a solution, the irradiation may be performed at preferably from about room temperature up to about reflux temperature.
• the organic solvent used for dissolution may be either polar protonic (C ⁇ to C 4 alcohol such as methanol or ethanol) or aprotonic (acetonitrile, tefrahydrofuran) in a mixture with water.
• Visible light irradiation of about 750w at about 35°C of aqueous acetonitrile solution of rosuvastatin calcium for about 7 hours gives a mixture of compounds (II and III) in the ratio 1:1.
• the temperature is preferably from about 20EC to about 100EC.
• One of skill in the art may yet choose a narrow spectrum within these spectrums or a mixture of various spectrums. Based on the structural guidance provided herein of the various degradation products, one of skill in the art may prepare a synthetic route to obtain the degradation products.
• the corresponding lactone is obtained, either by irradiating the lactone form of rosuvastatin or by preparing the lactone from Compounds II and III to obtain the corresponding Compounds LV and N which can be used as a reference standard.
• Compound N has the following 1H ⁇ MR (300MHz, CDC1 3 ) ⁇ (ppm): 1.24, 1.29, 1.52, 1.70, 2.58, 3.02, 3.21, 3.27, 3.41, 3.55, 3.60, 4.26, 4.78, 7.05, 7.12, 8.34; FAB+m/z (MH + ): 464.
• the preparation of the corresponding lactone compounds IN and N from compound II and III includes dissolving compound II and III in a suitable solvent and forming a lactone ring for example with aqueous hydrochloric acid. Other acids may be used to form a lactone.
• a suitable solvent for preparation of the lactone from Compound II or III is dichloromethane, chloroform, acetonitrile or tetrahydrofuran.
• the suitable solvent is acetonitrile.
• the solvent may be removed by any conventional process, such as evaporation. Obtained compounds IN and N can be separated by methods such as column chromatography , and crystallization.
• the preparation of the corresponding lactone compounds LV and N from rosuvastatin lactone may also be performed by visible light irradiation in the same solvents. The irradiation characteristics are as described above.
• the lactone compounds IN and N may be hydrolyzed with an equivalent amount of an aqueous base such as sodium or calcium hydroxide to obtain the corresponding salts in the presence of a solvent.
• the solvent is acetonitrile.
• the lactones are hydrolyzed with an aqueous solution of sodium hydroxide in acetonitrile, followed by removal of acetonitrile and addition of a source of calcium such as calcium chloride.
• the lactone forms IN and N can be hydrolyzed with a base to obtain salts and thereafter converted to acid forms NI and NIL respectively, which can be used as a reference standard.
• the conversion of the lactones to salts maybe carried out by using a basic aqueous solution, h one embodiment, the lactone is dissolved in a mixture of acetonitrile and an aqueous ⁇ aOH solution. The acetonitrile is then removed and a source of calcium such as calcium chloride is added to precipitate the calcium salt.
• the acid forms are obtained after purifying the salt products by column chromatography on silica gel (as described in example 1). It is believed that the acidity of the silica column is responsible for the conversion.
• the various forms of the degradation product may be purified so that only one stereoisomer is present.
• the R stereoisomer at position 6 is preferably at least about 95% free of the S stereoisomer by weight.
• the S stereoisomer at position 6 is preferably at least about 95% free of the R stereoisomer by weight.
• Purification may be performed by column chromatography, TLC, HPLC, or other known purification methods. Instruments For chromatography, aluminum oxide or, preferably, silica gel may be used for packing. As for the eluent, different organic solvents or mixtures thereof may be used. Ethyl acetate is preferred.
• Compounds II and III, isolated as corresponding, acids (VI and Nil), lactones (IN and N) can be investigated with 1H ⁇ MR, 13 C ⁇ MR, COSY ⁇ MR and mass spectroscopic analyses to determine their structures.
• Example 1 Preparation of rosuvastatin degradation products by irradiation of rosuvastatin (Ca salt).
• Rosuvastatin (Ca-salt) (4.0g) was dissolved in a mixture acetonitrile-water (380ml- 140ml) and irradiated with visible light (750w, 35°C) for 7 hours. Acetonitrile and water were evaporated under vacuum.
• Lactone LV (0.8g) was dissolved in acetonitrile, and IN aqueous sodium hydroxide (4ml) was added. The mixture was stirred at room temperature overnight. After evaporation of acetonitrile and water, and drying under vacuum, the obtained product was purified by column chromatography on silica gel (eluent dichloromethane- methanol 65ml: 10ml), giving pure Compound NI (0.4g).
• Rosuvastatin lactone (2.0g) was dissolved in 200ml of acetonitrile and irradiated with visible light (750w, 35°C) for 7 hours. After evaporation of the acetonitrile, and drying under vacuum, the obtained products were separated by column chromatography on silica gel (eluent hexane-ethyl acetate 1 :2), giving lactone IN (l.lg) and lactone N (0.6g).
• Lactone IN (l.Og) was dissolved in 5ml of acetonitrile and 2ml of IN aqueous ⁇ aOH was added. The mixture was stirred at room temperature for 4 hours. After evaporation of acetonitrile, 1ml of 2 ⁇ aqueous CaCl 2 was added, and the mixture was stirred for 1 hour at room temperature. The precipitate was filtered and dried under vacuum giving Compound II. 3. Analogously, Compound III was obtained from lactone N.
• Example 3 HPLC impurity profile determination of rosuvastatin calcium The purity of Compounds IN, N, NI and Nil is determined by HPLC analysis.
• rosuvastatin calcium sample is weighed in a 20ml amber volumetric flask. The sample is dissolved with 10ml acetonitrile and diluted to volume with water.

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