Analysis of glucuronides by fast atom bombardment

High-performance tandem mass spectrometry in metabolism studies

1. High-performance tandem mass spectrometry provides unit resolution in both selection of precursor ions and analysis of fragment ions, and extensive and reproducible fragmentation through collisional activation at high energy. 2. Metabolites can be analysed that occur as minor components in h.p.l.c. peaks or other mixtures. Homogeneous isotopic species can be selected for unambiguous analysis of distributions of isotope labels. Fragmentation may be significantly enhanced to provide structural information. Overall, the signal to noise ratio is greatly improved and the spectrum is simplified. 3. These points are illustrated by isotope-labelling studies of the mechanisms of glutathione conjugation of the anti-tumour agent cyclophosphamide, the cytotoxic agent phosphoramide mustard and dimethylbilirubin, an analogue of bilirubin designed to be distinguishable from endogenous bilirubin. Analysis of isomeric mixed disulphides formed between glutathione and a peptide with an internal disulphide bond is discussed. 4. Reaction-induced decomposition is presented as an alternative to collisionally induced decomposition with more efficient energy transfer.

Preparative high-performance liquid chromatography and preparative thin-layer chromatography isolation of tocainide carbamoyl-O-beta-D-glucuronide: structural characterization by gas chromatography-mass spectrometry and fast atom bombardment-mass spectrometry

Tocainide carbamoyl-O-beta-D-glucuronide, a major urinary metabolite of the antiarrhythmic drug tocainide [2-amino-N-(2',6'-xylyl)propanoxylidide], was isolated by preparative-TLC and preparative-HPLC. The isolated glucuronide was hydrolyzed in sodium hydroxide (pH greater than 12) to 3-(2',6'-xylyl)-5-methylhydantoin. This hydantoin product was also identified when tocainide was reacted with urea in urine. Structural characterization of the isolated tocainide glucuronide was carried out using GC-MS of the permethylated derivative. The molecular ion of the permethylated glucuronide was not observed, but ion fragments at m/z 232(244), 277(288), and 334(349) were found to correspond to the postulated novel carbamoyl ester structure of the permethylated (perdeuteromethylated) glucuronide. Structural evidence for the underivatized tocainide glucuronide was obtained using fast atom bombardment-MS. The [M + H]+ ion at m/z 413 was observed. Characteristic sodium ion adducts [M + Na]+ and [M-H + 2Na]+ were also observed at m/z 435 and 457, respectively.

The metabolic fate of the dopamine agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin in rats after intravenous and oral administration. II. Isolation and identification of metabolites

1. The in vivo metabolic pathways of 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (I) in rats have been established, using in vitro metabolism as a complementary technique. 2. All identified metabolites were conjugates. Glucuronidation at the phenolic group yields the major metabolite, accounting for 50% (i.v.) or 65% (oral) of the dose. The corresponding sulphate conjugate of I is virtually absent (less than 0.2% dose). 3. Hydroxylation of I, at the ortho position to the phenolic hydroxy group, yields 6-hydroxy-I (II), accounting for about 13% (i.v.) or 9% (oral) dose. This catechol is excreted, as a glucuronide, almost exclusively into the bile. Both the 5- and the 6-glucuronide of II were detected in about equal amounts. 4. Metabolism of I in vitro showed that under oxidative conditions, depropylation of I occurred. Conjugation of 3H-I in the presence of UDPGA or PAPS, was successful in yielding the glucuronide and sulphate conjugates.

Characterization of acyl-linked glucuronides by electron impact and fast atom bombardment mass spectrometry

Thirty-one electron impact (EI) mass spectra and 22 fast atom bombardment (FAB) mass spectra were evaluated with regard to providing molecular weights and information about the structures of 1-O-acyl glucuronides. Molecular ion species were obtained by both techniques. Fragmentation of the glycosidic and carboxylate bonds produced ions characteristic of glucuronides as a class, and also ions unique to acyl glucuronides. In EI mass spectra of pertrimethylsilylated derivatives, pairs of [M - 481]+ and [M - 509]+ ions characterized the acyl linkage. Relative abundances within these pairs correlated with the benzylic, benzoic or aliphatic nature of the carboxylate group. Positive ion FAB spectra contained three sets of ions, with intervals of 28 and 46 mass units, which characterized the linkage. In negative ion FAB spectra, a characteristic pair of fragment ions 44 mass units apart were accompanied by anions of mass 193, which appeared to distinguish acyl from phenol and hydroxyl glucuronides.

Fast atom bombardment and tandem mass spectrometry for structure determination: remote site fragmentation of steroid conjugates and bile salts

A series of 35 steroid conjugates (sulfates and glucuronides) and bile salts were investigated by using fast atom bombardment and tandem mass spectrometry. Collisional activation of the [M - H]- anions of sulfate conjugates and bile salts predominantly yields fragment ions arising by reactions occurring remote from the charge site. These reactions are sometimes sensitive to differences in stereochemistry at positions remote from the charge site and are useful for positional isomer differentiation. On the other hand, collisional activation of the [M - H]- anions of the glucouronide conjugates leads primarily to charge-driven fragementations.

Direct analysis of rat bile for acetaminophen and two of its conjugated metabolites via thermospray liquid chromatography/mass spectrometry

Bile from rats treated with acetaminophen was analyzed by direct injection onto a thermospray liquid chromatography/mass spectrometry (LC/MS) system. Two conjugated metabolites of acetaminophen were separated by the high-pressure liquid chromatographic system and analyzed by mass spectrometry. The conjugates were identified as the glutathione-acetaminophen conjugate and the glucuronide-acetaminophen conjugate by comparison of the chromatographic retention times and the mass spectra to that of the synthetic standards. No evidence of acetaminophen metabolites was observed when bile samples were subjected to direct analysis by fast atom bombardment mass spectrometry.

A review of the methods of chemical synthesis of sulphate and glucuronide conjugates

1. Methods for the synthesis of drug conjugates with sulphuric acid have been reviewed. 2. Some analytical methods are presented for the analysis of sulphate conjugates. 3. The synthesis of several types of N, O and C beta-D-glucuronides is reviewed. Different beta-coupling reactions of protected glucuronides are presented. 4. Application of n.m.r. and mass spectrometry to the analysis of beta-D-glucuronides is discussed.

A mass spectrometric approach to the identification of conjugated drug metabolites

For the identification of intact underivatized drug conjugates, the mass spectrometric technique of choice is fast atom bombardment (FAB); the combined use of both positive and negative ion FAB usually provides information on the molecular mass and nature of conjugates under study, while the number of exchangeable hydrogen atoms can be determined using trideuterated glycerol as the FAB-matrix. Electron impact and desorption chemical ionization spectra can be used to study the aglycone part of the conjugated metabolites. With this approach metabolites conjugated with glucuronic acid, sulphuric acid and amino acids have been identified. The identification was supported by analysis of reference compounds, prepared by chemical synthesis. The examples given are selected from current metabolism studies on drug candidates in development within Organon's research.

Desorption chemical ionization and fast atom bombardment mass spectrometric studies of the glucuronide metabolites of doxylamine

Three glucuronide metabolites of doxylamine succinate were collected in a single fraction using high-performance liquid chromatography (HPLC) from the urine of dosed male Fischer 344 rats. The metabolites were then separated using an additional HPLC step into fractions containing predominantly a single glucuronide metabolite. Analysis of the metabolites by methane and ammonia desorption chemical ionization, with and without derivatization, revealed fragment ions suggestive of a hydroxylated doxylamine moiety. Identification of the metabolites as glucuronides of doxylamine, desmethyldoxylamine and didesmethyldoxylamine was accomplished, based on determination of the molecular weight and exact mass of each metabolite using fast atom bombardment (FAB) ionization. This assignment was confirmed by the fragmentation observed in FAB mass spectrometric and tandem mass spectrometric experiments. Para-substitution of the glucuronide on the phenyl moiety was observed by 500-MHz nuclear magnetic resonance (NMR) spectrometry. A fraction containing all three glucuronide metabolites, after a single stage of HPLC separation, was also analysed by FAB mass spectrometry, and the proton- and potassium-containing quasimolecular ions for all three metabolites were observed.

Positive and negative liquid secondary ion mass spectrometry of chloro- and nitrophenylglucuronides

Mass spectra of a series of chloro- and nitrophenylglucuronides by liquid secondary ion (LSI) mass spectrometry were obtained. In the positive ion mode class characteristic fragmentations and adduct ions are observed only in the presence of alkali salt additives. No additives were necessary in the negative ion mode to see abundant class characteristic [M-H]- and aglycone fragment ions. Cluster ion formation was found to be prominent but only in the negative ion mode.

Characterization of oxygen-linked glucuronides by laser desorption mass spectrometry

A laser desorption time-of-flight mass spectrometer is used for structural confirmation of several acyl- and ether-linked glucuronides. Abundant molecular ion species are produced, as well as fragmentation reflecting both the molecular structure and the stability of the conjugates. The major ions are produced by cationization, and detection limits are as low as 1.6 ng (5.0 pmol).