Estimation of impurity profiles of drugs and related materials: part 19: theme with variations. Identification of impurities in 3-oxosteroids.

Due to the varied reactions leading to the 3-oxo group in steroids and the reactivity of its environment, a large number of impurities related to this group are formed during the reaction steps and the degradation studies. In this paper the experiences from the authors laboratory with the 3-oxo-related impurities in 19-nor-4-ene-3-oxosteroids (norgestrel, norethisterone, nandrolone, its esters and Nestorone) as well as corticosteroids (prednisolone, mazipredone, etc) are presented. The impurities include saturated 3-ones, 1-ene-3-ones, 5(10)-ene-3-ones, 3-deoxo and 3-ethinyl-3,5-diene derivatives, 6-ene, 8(14)-ene, 6,8(14)-diene, 6-hydroxy (alpha and beta), 10beta-hydroxy and 6-one derivatives in 4-ene-3-oxosteroids and 8(9)-ene, 9(11)-ene, 11alpha-hydroxy, 11-oxo and 4-ene-3-one derivatives in 11beta-hydroxy-1,4-diene-3-oxosteroids. The chromatographic, spectroscopic and hyphenated techniques used in this study include TLC, GC, HPLC with diode array UV detector, GC-MS, LC-MS and NMR methods.

Estimation of impurity profiles of drugs and related materials. Part 16: Identification of the side-products of the ethinylation step in the synthesis of contraceptive gestogens.

A new apolar impurity (3,17 alpha-diethinyl-13-ethyl-3,5-gonadiene-17-ol, IIb) was detected and identified in norgestrel with the aid of thin-layer and high-performance chromatography and spectroscopic techniques. IIb is the product of the acid-catalysed dehydration of an overethinylated side product (Ib) of the ethinylation step in the synthesis of norgestrel. IIb can be determined by thin-layer densitometry and high-performance liquid chromatography. Another impurity (17 alpha-ethinyl-13-ethyl-4-gonene-17-ol, IV), originating from a side product of the Birch reduction step in the synthesis of norgestrel was also detected and identified. The spot of IV overlaps with that of IIb in the TLC system of USP XXIII but can be separated and quantification by more selective TLC systems and by gas chromatography.

Drug impurity profiling strategies.

A general scheme is set up for the estimation of the impurity profile of bulk drug substances by the complex use of chromatographic, spectroscopic and hyphenated techniques. Several examples are presented as illustrations to the scheme from the authors' laboratory involving the use of chromatographic methods such as thin-layer-(TLC), gas-(GC), analytical and preparative high-performance liquid chromatography (HPLC), spectroscopic methods such as mass spectrometry (MS) and NMR spectroscopy as well as hyphenated techniques (HPLC/diode-array UV, GC/MS and HPLC/MS). In addition to summarizing earlier work, new examples are also presented: identification of an impurity (propyl 4-[diethylcarbamoyl(methoxy)]-3-methoxy phenylglyoxylate, II) in propanidid (I) and two unsaturated impurities in allylstrenol (VII) by GC/MS and HPLC/diode-array UV as well as estimation of the impurity profile of mazipredone (III) by HPLC/MS and HPLC/diode-array UV.

Estimation of impurity profiles of drugs and related materials. 12. Isolation and identification of an isomeric impurity in danazol.

We report on a new isomeric impurity of danazol. This impurity designated as isodanazol was detected by reversed-phase high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). Its structure was determined after separation by preparative HPLC. Mass spectrometry revealed the isomeric nature of the impurity while the UV spectrum indicated profound difference in the isoxazole moieties. The structure of the isomeric isoxazole ring in isodanazol was determined by NMR spectroscopy using COSY, HETCOR and NOE measurements. The difference between the UV spectra of danazol and isodanazol is explained on the basis of the difference between the aromaticities of their isoxazole rings supported by quantum chemical calculations. The quantitative determination of the impurity down to the 0.05% level can be performed by HPLC, gas chromatography and TLC densitometry.

Estimation of impurity profiles in drugs and related materials. Part 11--The role of chromatographic and spectroscopic methods in the estimation of side-reactions in drug syntheses.

Impurities in drugs are classified on the basis of the types of side-reactions in drug syntheses resulting in their formation. This is shown by summarizing the authors' earlier results in the field of impurity profiling of 19-nor-steroids, ethynodiol diacetate, mazipredone, pipecuronium bromide, flumecinol, enalapril, pyridinol carbamate, phenylbutazone, thymotrinan and some new results related to danazol and famotidine.

[Analysis of steroids. Part 44: Analytical investigation of the intermediates of the synthesis of pipecuronium bromide (Arduan)]. / Adatok a szteránvázas vegyületek analitikájához 44. Pipecuronium bromid (Arduan) szintézis intermedierjeinek analitikája.

The following methods are described for the analytical investigation of the intermediates of the synthesis of pipecuronium bromide (Arduan) (for the numbering of the intermediates and their impurities see Figure 1.). 1. Gas chromatographic methods (capillary GC using fused silica capillaries Ultra-2 and Silar 10C WCOT) for the impurity profiling of intermediates I, II, IV and V including the identification and spectroscopic characterization of their impurities; 2. TLC methods for the similar characterisation of the further intermediates (III, VI, VII and VIII); 3. Gas chromatographic assay methods for IV and V using fused silica capillary technique and internal standards; 4. Potentiometric titration methods for the determination of VII and VIII using 0.1 M hydrochloric acid as the titrant.

[Analysis of steroids. Part 42. By-products of the ethynylation of 17-ketosteroids (isolation, identification and determination)]. / Adatok a szteránvázas vegyületek analitikájához 42. 17-Ketoszteroidok etinilezésének melléktermékei (elválasztás, azonosítás, meghatározás).

The therapeutically very important 17 alpha-ethynyl steroids are prepared from 17-keto steroids by means of addition of acetylene. Two important side reactions of this procedure are known: the formation of the isomeric beta-ethynyl derivative and the formation of a dimeric product with acetylene bridge. The aim of this paper is to approach this problem from the point of view of impurity profiling of 17 alpha-ethynyl steroids (norethisterone, ethisterone, norgestrel and delta 9(11)-ethisterone) i.e. isolation, identification and quantification of the above mentioned by-products as impurities in the bulk drugs. Capillary gas chromatography is an ideal tool for the separation and quantitative determination of the beta-ethynyl derivatives (20 m long fused silica capillary, I.D 0.2 mm; stationary phase Ultra-2: 5% phenylmethyl silicon gum phase with a film thickness of 0.33 mu; column temperature 240-250 degrees C). The dimeric impurity cannot be determined directly by gas chromatography as it decomposes in the flash heater to the 17 alpha-ethynyl and the 17-keto derivatives. For this reason reversed-phase HPLC was preferred for their separation and quantitation; (column: 250 x 4 mm LiChrosorb RP-18, 10 microns; eluent methanol-water 7:3; UV detector 240 nm). The HPLC method is suitable for the separation and determination of the beta-ethynyl impurities, too. The chemical shifts of the protons and carbon atoms in the vicinity of C-17 in the 1H and 13C NMR spectra of the epimeric 17-ethynyl steroids greatly depend on the configuration of the ethynyl group and for this reason they (especially that of the C-18 are eminently suitable for the characterization of the isomers.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of impurity profiles in drugs and related materials.

The estimation of impurity profiles in drugs and related materials has been demonstrated using combinations of chromatographic and spectroscopic techniques. Examples chosen to illustrate this approach are: (1) an examination of flumecinol and its impurities using packed column GC-mass spectrometry; (2) the estimation of 17beta-ethinyl-17alpha-hydroxy impurities in 17alpha-ethinyl-17beta-hydroxy steroids using capillary GC; (3) the identification of impurities in hexoestrol using HPLC-linear photodiode array detection (LDA) and off-line mass spectrometry; (4) the estimation of 9(11)-dehydromestranol in mestranol using HPLC-LDA; and (5) the estimation of an l-threo impurity in a d-threo hydroxy acid intermediate using a chiral column containing covalently bonded bovine serum albumin.

New derivatization reactions in pharmaceutical analysis.

The application of chemical reactions in conjunction with spectrometric and chromatographic methods is exemplified by the formation of 2-nitrophenylhydrazide derivatives for the spectrometric assay of carboxylic acids; silylation and trifluoroacetylation of drugs for gas chromatography; selective reduction of steroid ketones for their IR spectrometric identification; the use of epoxidation in discriminating between saturated and unsaturated steroids in gas chromatography; increasing the selectivity and sensitivity of the spectrometric and gas chromatographic determination of isomeric Delta4- and Delta5-3-ethylenedioxy steroids by treatment with hydrochloric acid; and the use of the same reagent in the difference spectrometric determination of 2,5-dimethyl-alpha-ethyl benzhydrol.

Analytical methods based on transformations with hydrochloric acid.

Ultraviolet spectrophotometric methods are described for alpha-ethyl benzhydrol derivatives, 3-trifluoromethyl-alpha-ethyl benzhydrol (flumecinol), 2,5-dimethyl-alpha-ethyl benzhydrol (RGH-3395) an impurity of the latter, (1,4-di-(2,5-dimethyl-phenyl)-1,4-diphenyl-butan-1,4-diol). The methods are based on dehydrations catalysed by hydrochloric acid yielding unsaturated aromatic chromophores. The determination of 2-acetyl-3-phenyl-tetrahydro-1,2,4-oxadiazin-5-one (RGH-4615) is also based on treatment with hydrochloric acid; the chromophoric compound is a benzaldoxime derivative. The hydrochloric acid-catalysed transformation of ethynodiol diacetate to its 3,5-diene derivative enables the parent compound to be determined by gas chromatography.