Analysis method for detecting beclomethasone propionate related substances by high performance liquid chromatography

Abstract

The invention discloses an analysis method for detecting beclomethasone propionate related substances by high performance liquid chromatography, which comprises the following steps: preparation of a test solution: dissolving beclomethasone propionate in tetrahydrofuran-acetonitrile-methanol, and diluting with a monopotassium phosphate aqueous solution to prepare the test solution; the determination method comprises the following steps: taking a test solution, taking a monopotassium phosphate aqueous solution as a mobile phase A, taking a tetrahydrofuran-acetonitrile-methanol solution as a mobile phase B, and carrying out high performance liquid chromatography detection, the high performance liquid chromatography is isocratic elution; in the isocratic elution process, the volume ratio of the mobile phase A to the mobile phase B is (40-44): (56-60). The method is used for solving the technical problem that the detection accuracy of the beclosone propionate related substances is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of pharmaceutical analysis and detection, and particularly relates to an analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography. Background Art

[0002] Beclomethasone dipropionate is a potent topical glucocorticoid drug, which has anti-inflammatory, anti-allergic and antipruritic effects. It can inhibit bronchial exudation, eliminate bronchial mucosal swelling, relieve bronchospasm. Its vasoconstrictive effect on the skin is much stronger than that of hydrocortisone, and its local anti-inflammatory effect is 5 times that of fluocinonide and triamcinolone acetonide. It has strong lipophilicity and is easy to penetrate, and can take effect 30 minutes after being applied to the affected area. It can be used topically to treat various inflammatory skin diseases, such as eczema, allergic dermatitis, neurodermatitis, contact dermatitis, psoriasis, pruritus, etc. The aerosol can be used for chronic and allergic asthma, allergic rhinitis, etc.

[0003] Beclometasone 17-monopropionate is a metabolite after the prodrug of beclomethasone dipropionate enters the human body. Qualitative detection and control of impurities in the prodrug are crucial for the accuracy and controllability of clinical drug administration. It is included in the Chinese Pharmacopoeia 2015 edition, but the related substances are not controlled. The quality standards of "Beclomethasone Dipropionate Bulk Drug" are included in the Chinese Pharmacopoeia 2015 edition, USP41, and EP9.0. For the related substances, the Chinese Pharmacopoeia 2015 edition and USP41 both use thin layer chromatography, which cannot accurately quantify, and EP9.0 uses the HPLC method, but the resolution between the impurity and the main peak is poor. Therefore, there is a need to provide an accurate and sensitive high performance liquid chromatography method. Summary of the Invention

[0004] The present invention provides an analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography to solve the technical problem of low accuracy in detecting impurities of beclomethasone dipropionate.

[0005] In view of this, an analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography provided by the present invention includes the following steps:

[0006] Preparation of the test solution: Take beclomethasone dipropionate, dissolve it in tetrahydrofuran - acetonitrile - methanol, and then dilute it with potassium dihydrogen phosphate aqueous solution to obtain the test solution;

[0007] Determination method: Take the test solution, use potassium dihydrogen phosphate aqueous solution as mobile phase A and tetrahydrofuran - acetonitrile - methanol solution as mobile phase B for high performance liquid chromatography detection;

[0008] The high performance liquid chromatography is performed with isocratic elution;

[0009] During the isocratic elution process, the volume ratio of mobile phase A to mobile phase B is (40 - 44):(56 - 60).

[0010] Further, an analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography includes the following steps:

[0011] Preparation of test solution: Take 20 - 30 mg of beclomethasone dipropionate, accurately weigh it, place it in a 20 - 30 mL volumetric flask, dissolve it with tetrahydrofuran - acetonitrile - methanol, and then dilute it with an aqueous solution of potassium dihydrogen phosphate to a solution containing 0.8 - 1.2 mg of beclomethasone dipropionate per 1 mL as the test solution; wherein, the volume ratio of beclomethasone dipropionate to the tetrahydrofuran - acetonitrile - methanol solution is 1:(0.52 - 0.65);

[0012] Determination method: Take the test solution, use the aqueous solution of potassium dihydrogen phosphate as mobile phase A and the tetrahydrofuran - acetonitrile - methanol solution as mobile phase B for high performance liquid chromatography detection;

[0013] The high performance liquid chromatography is performed with isocratic elution;

[0014] During the isocratic elution process, the volume ratio of mobile phase A to mobile phase B is (40 - 44):(56 - 60);

[0015] Further, the volume ratio of the aqueous solution of potassium dihydrogen phosphate - (tetrahydrofuran - acetonitrile - methanol) is 42:58.

[0016] Optionally, during the high performance liquid chromatography detection process, the chromatographic column is YMC - Triart C18, 4.6 mm×250 mm, 3 μm.

[0017] Optionally, the concentration of the aqueous solution of potassium dihydrogen phosphate is 2.7 - 2.75 g / L, and the pH value is adjusted to 2 - 2.5 with phosphoric acid.

[0018] Further, the concentration of the aqueous solution of potassium dihydrogen phosphate is 2.72 g / L, and the pH value is adjusted to 2.35 with phosphoric acid.

[0019] Optionally, in the tetrahydrofuran - acetonitrile - methanol, the volume ratio of tetrahydrofuran - acetonitrile - methanol is (2 - 8):(20 - 25):(20 - 30).

[0020] Further, in the tetrahydrofuran - acetonitrile - methanol, the volume ratio of tetrahydrofuran - acetonitrile - methanol is 5:23:25.

[0021] Optionally, during the high performance liquid chromatography detection process, the flow rate is 0.8 - 1.2 mL / min.

[0022] Further, during the high performance liquid chromatography detection process, the flow rate is 1.0 mL / min.

[0023] Optionally, during the high performance liquid chromatography (HPLC) detection, the column temperature is 45 - 55 °C.

[0024] Further, during the high performance liquid chromatography (HPLC) detection, the column temperature is 50 °C.

[0025] Optionally, during the high performance liquid chromatography (HPLC) detection, the detection wavelength is 250 - 260 nm, and the injection volume is 18 - 23 μL.

[0026] Further, during the high performance liquid chromatography (HPLC) detection, the detection wavelength is 254 nm, and the injection volume is 20 μL.

[0027] Optionally, the analysis method further includes performing high performance liquid chromatography (HPLC) detection on a blank solvent;

[0028] The blank solvent is prepared by mixing an aqueous solution of potassium dihydrogen phosphate with tetrahydrofuran - acetonitrile - methanol.

[0029] Optionally, 18 impurities in beclomethasone dipropionate are detected at one time using the analysis method.

[0030] Optionally, the 18 impurities are respectively 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-21-propionate, denoted as impurity A; 21-(acetyloxy)-9-chloro-11β-hydroxy-16β-methyl-3,20-dione pregn-1,4-diene-17-propionate, denoted as impurity B; 9-chloro-11β-hydroxy-16β-methyl-3,20-dione-17-(propionyloxy)-pregn-1,4-diene-21-butyrate, denoted as impurity C; 16β-methyl-11β,17α,21-trihydroxy-9α-bromopregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity D; 16β-methyl-11β,17α,21-trihydroxy-6α,9α-dichloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity E; 16β-methyl-11β,17α,21-trihydroxy-6α-bromo-9α-chloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity F; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-17-propionate, denoted as impurity H; 16β-methyl-17α,21-dihydroxypregn-1,4,9(11)-triene-3,20-dione-17,21-dipropionate, denoted as impurity I; 16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity J; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-4-ene-3,20-dione-17,21-dipropionate, denoted as impurity L; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-4,6-diene-3,20-dione-17,21-dipropionate, denoted as impurity M; 16β-methyl-11β,17α,21-trihydroxy-2-bromo-9α-chloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity N; 16β-methyl-17α,21-dihydroxy-11β,9α-dichloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity O; 16β-methyl-17α,21-dihydroxypregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity Q; 9β,11β-epoxy-17α,21-diol-16β-methylpregn-1,4-diene-3,20-dione, denoted as impurity R; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-11,17,21-tripropionate, denoted as impurity S;16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-17-propionate, denoted as impurity U; 16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-21-propionate, denoted as impurity V.

[0031] Furthermore, the chemical names and chemical structures of the said impurities are shown in Table 1.

[0032] Table 1 Chemical names and chemical structures of each impurity

[0033]

[0034]

[0035]

[0036]

[0037] Furthermore, a spiked test solution is prepared from the test solution to better prove that the analytical method of the present invention can effectively separate beclomethasone dipropionate and 18 impurities. The preparation process of the spiked test solution is as follows:

[0038] Take 8 - 12 mg each of the reference substances of impurity R, impurity U, impurity H, impurity A, impurity V, impurity B, impurity J, impurity D, impurity M, impurity I, impurity L, impurity Q, impurity C, impurity O, impurity S / E, impurity N, impurity F, weigh accurately, dissolve with acetonitrile and dilute to prepare an impurity stock solution containing 0.8 - 1.2 mg of each impurity per 1 mL. Take 8 - 12 mg of impurity V, weigh accurately, dissolve with N,N-dimethylformamide, and dilute with acetonitrile to prepare an impurity stock solution containing 0.8 - 1.2 mg of impurity V per 1 mL; take 20 - 30 mg of this product, weigh accurately, add appropriate amounts of each impurity stock solution to a 20 - 30 mL volumetric flask, dissolve with 10.5 mL of a tetrahydrofuran-acetonitrile-methanol solution, and dilute with potassium dihydrogen phosphate solution to prepare a mixed sample solution containing 0.8 - 1.2 mg of beclomethasone dipropionate and 0.8 - 1.2 μg of each impurity per 1 mL; among them, the volume ratio of this product to the tetrahydrofuran-acetonitrile-methanol solution is 1:(0.52 - 0.65).

[0039] As can be seen from the above technical solutions, the embodiments of the present invention have the following advantages:

[0040] The present invention uses high performance liquid chromatography to detect the related substances in beclomethasone dipropionate. Except for impurity S and impurity E, 16 other impurities can be effectively separated, and the 18 impurities are all baseline-separated, improving the detection accuracy and sensitivity, and the operation is simple; moreover, 18 impurities are detected simultaneously by using one analytical method. Description of the Drawings

[0041] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0042] Figure 1 It is the chromatogram detected in Example 1 of the present invention. Specific Embodiments

[0043] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0044] Embodiment

[0045] Embodiment 1

[0046] An analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography, comprising the following steps:

[0047] Take tetrahydrofuran, acetonitrile, and methanol in a volume ratio of 5:23:25 and mix them to prepare tetrahydrofuran-acetonitrile-methanol.

[0048] Take an appropriate amount of potassium dihydrogen phosphate and dissolve it in water, and add phosphoric acid to adjust the pH to 2.35 to prepare an aqueous potassium dihydrogen phosphate solution with a concentration of 2.72 g / L (adjust the pH value to 2.35 with phosphoric acid).

[0049] Blank solvent: Use an aqueous potassium dihydrogen phosphate solution with a concentration of 2.72 g / L (adjust the pH value to 2.35 with phosphoric acid)-(tetrahydrofuran-acetonitrile-methanol) as the blank solvent, wherein the volume ratio of the aqueous potassium dihydrogen phosphate solution to (tetrahydrofuran-acetonitrile-methanol) is 42:58;

[0050] Test spiked solution: Take 10 mg of each of the reference substances of impurity R, impurity U, impurity H, impurity A, impurity V, impurity B, impurity J, impurity D, impurity M, impurity I, impurity L, impurity Q, impurity C, impurity O, impurity S / E, impurity N, and impurity F, weigh accurately, dissolve with acetonitrile and dilute to prepare an impurity stock solution I containing 1 mg of each impurity per 1 mL.

[0051] Take 10 mg of impurity V, weigh accurately, dissolve with N,N-dimethylformamide, and dilute with acetonitrile to prepare an impurity stock solution containing 1 mg of impurity V per 1 mL.

[0052] Take 20 mg of beclomethasone dipropionate, accurately weigh it, transfer it to a 20 mL volumetric flask, add appropriate amounts of the stock solutions of each impurity I and impurity V, dissolve it with 10.5 mL of a tetrahydrofuran - acetonitrile - methanol solution, and dilute it with a 2.72 g / L potassium dihydrogen phosphate solution (adjust the pH value to 2.35 with phosphoric acid) to prepare a mixed sample solution containing 1 mg of beclomethasone dipropionate and 1 μg of each impurity per 1 mL.

[0053] Inject the blank solvent and the test spiked solution. Use a YMC - Triart C18 column (4.6 mm × 250 mm, 3 μm), and perform isocratic elution with an aqueous potassium dihydrogen phosphate solution (A) - tetrahydrofuran - acetonitrile - methanol solution (B) in a volume ratio of (40 - 45):(55 - 60). Carry out high - performance liquid chromatography analysis under the conditions of a flow rate of 1.0 mL / min, a column temperature of 50 °C, a detection wavelength of 254 nm, and an injection volume of 20 μL. Record the chromatogram, as Figure 1 shown;

[0054] It can be seen from Figure 1 that the blank solvent has no interference in the detection of related substances of this product; the resolution between the beclomethasone dipropionate peak and each known impurity peak in the test spiked solution meets the requirements.

[0055] In this example, the test spiked solution is used for high - performance liquid chromatography detection to better prove that the chromatographic conditions of the present invention can effectively separate beclomethasone dipropionate from 18 impurities. However, in the actual detection process, it is not necessary to prepare the test spiked solution. Just prepare the test sample solution for high - performance liquid chromatography detection to analyze whether beclomethasone dipropionate contains these 18 impurities and which specific impurities are contained.

[0056] The preparation process of the test sample solution is as follows: Take beclomethasone dipropionate, dissolve it with tetrahydrofuran - acetonitrile - methanol, and then dilute it with an aqueous potassium dihydrogen phosphate solution to prepare the test sample solution.

[0057] Example 2

[0058] Verify the stability of the test spiked solution in Example 1:

[0059] Prepare the test spiked solution using the preparation method in Example 1;

[0060] Under the chromatographic conditions of Example 1, inject the test spiked solution at 0, 3.5, 7, 10.5, 14, 17.5, 21, and 28 hours respectively for high - performance liquid chromatography analysis, record the chromatogram, and the experimental results are shown in Table 2 - Table 4.

[0061] Table 2 Experimental Result 1

[0062] Time (h) Impurity R Impurity U Impurity H Impurity A Impurity V Impurity B Impurity J 0 50860 37344 32060 32502 39121 53710 35900 3.5 50793 37258 32089 32511 39219 51978 36059 7 50745 37280 32214 32430 39110 51666 35824 10.5 50719 37497 32253 32351 39025 51932 35740 14 50755 37332 32025 32548 39188 51965 35996 17.5 50794 37512 32084 32623 39136 52037 34965 21 50710 37408 32001 32518 39238 51957 35912 28 50669 37428 32096 32557 39216 52021 35919 Average value 50892 37459 32002 32572 39509 51977 36092 RSD (%) 0.15 0.25 0.28 0.25 0.35 1.15 0.95

[0063] Table 3 Experimental Results II

[0064]

[0065]

[0066] Table 4 Experimental Results III

[0067]

[0068]

[0069] It can be seen from Tables 2 - 4 that the test spiked solution is stable within 28 hours.

[0070] Example 3

[0071] Prepare the test spiked solution using the preparation method in Example 1;

[0072] Precisely measure an appropriate amount of the test spiked solution, dilute it with the blank solution to prepare a solution containing 1 μg of beclomethasone dipropionate per 1 ml, shake well, and use it as the control solution;

[0073] Inject the test spiked solution and the control solution, and perform high - performance liquid chromatography analysis under the chromatographic conditions of Example 1, record the chromatogram, and the experimental results are shown in Table 5.

[0074] Table 5 Experimental Results

[0075]

[0076]

[0077] It can be seen from Table 5 that the repeatability of this method is good.

[0078] Comparative Example

[0079] Comparative Example 1

[0080] The detection method for related substances of beclomethasone dipropionate has been included in EP11.0. Octadecylsilyl silica gel is used as the filler; an aqueous solution of potassium dihydrogen phosphate at 2.72 g / L (adjusted to pH 2.35 with phosphoric acid) is used as mobile phase A, and tetrahydrofuran - acetonitrile - methanol (5:23:25) is used as mobile phase B. Gradient elution is carried out according to Table 6; the flow rate is 1.4 ml per minute; the column temperature is 50 °C; the detection wavelength is 254 nm. This analytical method can detect impurity A, impurity B, impurity C, impurity D, impurity F, impurity L, impurity M, and impurity N, but it cannot achieve the separation of 18 impurities simultaneously.

[0081] Table 6 Gradient Elution Program

[0082] Time / min Mobile phase A % Mobile phase B % 0-4 40 60 4-12 40-45 60-55 12-59 45 55

[0083] It can be seen from the comparison between Example 1 and Comparative Example 1 that the detection of related substances of beclomethasone dipropionate by high performance liquid chromatography in the present application improves the detection accuracy and sensitivity, and the operation is simple; moreover, 18 impurities can be detected simultaneously by using one analysis method.

[0084] As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography, characterized in that: It includes the following steps: Preparation of the test solution: Take beclomethasone dipropionate and dissolve it in tetrahydrofuran - acetonitrile - methanol, and then dilute it with an aqueous solution of potassium dihydrogen phosphate to obtain the test solution; Determination method: Take the test solution, use the aqueous solution of potassium dihydrogen phosphate as mobile phase A, and the tetrahydrofuran - acetonitrile - methanol solution as mobile phase B for high - performance liquid chromatography detection; The high - performance liquid chromatography is performed with isocratic elution; During the isocratic elution process, the volume ratio of mobile phase A to mobile phase B is (40 - 44):(56 - 60).

2. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1, wherein: During the high - performance liquid chromatography detection process, the chromatographic column is YMC - Triart C18, 4.6 mm×250 mm, 3 μm.

3. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: The concentration of the aqueous solution of potassium dihydrogen phosphate is 2.7 - 2.75 g / L, and the pH value is adjusted to 2 - 2.5 with phosphoric acid.

4. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: In the tetrahydrofuran - acetonitrile - methanol, the volume ratio of tetrahydrofuran, acetonitrile and methanol is (2 - 8):(20 - 25):(20 - 30).

5. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: During the high - performance liquid chromatography detection process, the flow rate is 0.8 - 1.2 mL / min.

6. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: During the high - performance liquid chromatography detection process, the column temperature is 45 - 55 °C.

7. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: During the high - performance liquid chromatography detection process, the detection wavelength is 250 - 260 nm, and the injection volume is 18 - 23 μL.

8. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: The analysis method also includes performing high - performance liquid chromatography detection on the blank solvent; The blank solvent is prepared by mixing the aqueous solution of potassium dihydrogen phosphate with tetrahydrofuran - acetonitrile - methanol.

9. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 1 or 2, characterized in that: Use the said analysis method to detect 18 impurities in beclomethasone dipropionate at one time.

10. The analytical method for detecting related substances of beclomethasone dipropionate by high performance liquid chromatography according to claim 9, characterized in that: The 18 impurities are respectively 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-21-propionate, denoted as impurity A; 21-(acetoxy)-9-chloro-11β-hydroxy-16β-methyl-3,20-dione pregn-1,4-diene-17-propionate, denoted as impurity B; 9-chloro-11β-hydroxy-16β-methyl-3,20-dione-17-(propionyloxy)-pregn-1,4-diene-21-butyrate, denoted as impurity C; 16β-methyl-11β,17α,21-trihydroxy-9α-bromopregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity D; 16β-methyl-11β,17α,21-trihydroxy-6α,9α-dichloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity E; 16β-methyl-11β,17α,21-trihydroxy-6α-bromo-9α-chloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity F; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-17-propionate, denoted as impurity H; 16β-methyl-17α,21-dihydroxypregn-1,4,9(11)-triene-3,20-dione-17,21-dipropionate, denoted as impurity I; 16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity J; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-4-ene-3,20-dione-17,21-dipropionate, denoted as impurity L; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-4,6-diene-3,20-dione-17,21-dipropionate, denoted as impurity M; 16β-methyl-11β,17α,21-trihydroxy-2-bromo-9α-chloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity N; 16β-methyl-17α,21-dihydroxy-11β,9α-dichloropregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity O; 16β-methyl-17α,21-dihydroxypregn-1,4-diene-3,20-dione-17,21-dipropionate, denoted as impurity Q; 9β,11β-epoxy-17α,21-diol-16β-methylpregn-1,4-diene-3,20-dione, denoted as impurity R; 16β-methyl-11β,17α,21-trihydroxy-9α-chloropregn-1,4-diene-3,20-dione-11,17,21-tripropionate, denoted as impurity S;16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-17-propionate, denoted as impurity U; 16β-methyl-17α,21-dihydroxy-9β,11β-epoxypregn-1,4-diene-3,20-dione-21-propionate, denoted as impurity V.;

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