Synthesis and mass spectra of rearrangement bio-signature metabolites of anaerobic alkane degradation via fumarate addition

Metabolite profiling in anaerobic alkane biodegradation plays an important role in revealing activation mechanisms. Apart from alkylsuccinates, which are considered to be the usual biomarkers via fumarate addition, the downstream metabolites of C-skeleton rearrangement can also be regarded as biomarkers. However, it is difficult to detect intermediate metabolites in both environmental samples and enrichment cultures, resulting in lacking direct evidence to prove the occurrence of fumarate addition pathway. In this work, a synthetic method of rearrangement metabolites was established. Four compounds, namely, propylmalonic acid, 2-(2-methylbutyl)malonic acid, 2-(2-methylpentyl)malonic acid and 2-(2-methyloctyl)malonic acid, were synthesized and determined by four derivatization approaches. Besides, their mass spectra were obtained. Four characteristic ions were observed at m/z 133 + 14n, 160 + 28n, 173 + 28n and [M - (45 + 14n)]⁺ (n = 0 and 2 for ethyl and n-butyl esters, respectively). For methyl esterification, mass spectral features were m/z 132, 145 and [M - 31]⁺, while for silylation, fragments were m/z 73, 147, 217, 248, 261 and [M - 15]⁺. These data provide basis on identification of potential rearrangement metabolites in anaerobic alkane biodegradation via fumarate addition.

MASS SPECTROMETRIC FRAGMENTATION OF TRIMETHYLSILYL AND RELATED ALKYLSILYL DERIVATIVES

This review describes the mass spectral fragmentation of trimethylsilyl (TMS) and related alkylsilyl derivatives used for preparing samples for analysis, mainly by combined gas chromatography and mass spectrometry (GC/MS). The review is divided into three sections. The first section is concerned with the TMS derivatives themselves and describes fragmentation of derivatized alcohols, thiols, amines, ketones, carboxylic acids and bifunctional compounds such as hydroxy- and amino-acids, halo acids and hydroxy ethers. More complex compounds such as glycerides, sphingolipids, carbohydrates, organic phosphates, phosphonates, steroids, vitamin D, cannabinoids, and prostaglandins are discussed next. The second section describes intermolecular reactions of siliconium ions such as the TMS cation and the third section discusses other alkylsilyl derivatives. Among these latter compounds are di- and trialkyl-silyl derivatives, various substituted-alkyldimethylsilyl derivatives such as the tert-butyldimethylsilyl ethers, cyclic silyl derivatives, alkoxysilyl derivatives, and 3-pyridylmethyldimethylsilyl esters used for double bond location in fatty acid spectra. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 0000:1-107, 2019.

Revisiting the metabolism of 19-nortestosterone using isotope ratio and high resolution/high accuracy mass spectrometry

The synthetic anabolic androgenic steroid 19-nortestosterone is prohibited in sports according to the regulations of the World Anti-Doping Agency (WADA) due to its performance-enhancing effects. Today, doping controls focus predominantly on one main urinary metabolite, 19-norandrosterone glucuronide, which offers the required detection windows for an appropriate retrospectivity of sports drug testing programs. As 19-norandrosterone can also be found in urine at low concentrations originating from in situ demethylation of other abundant steroids or from endogenous production, the exogenous source of 19-norandrosterone needs to be verified, which is commonly accomplished by carbon isotope ratio analyses. The aim of this study was to re-investigate the metabolism of 19-nortestosterone in order to probe for additional diagnostic long-term metabolites, which might support the unambiguous attribution of an endo- or exogenous source of detected 19-nortestosterone metabolites. Employing a recently introduced strategy for metabolite identification, threefold deuterated 19-nortestosterone (16,16,17-(2)H3-NT) was administered to one healthy male volunteer and urine samples were collected for 20 days. Samples were prepared with established methods separating unconjugated, glucuronidated and sulfated steroids, and analytes were further purified by means of high-performance liquid chromatography before trimethylsilylation. Deuterated metabolites were identified using gas chromatograph/thermal conversion/isotope ratio mass spectrometer comprising an additional single quadrupole mass spectrometer. Additional structural information was obtained by gas chromatography/time-of-flight mass spectrometry and liquid chromatography/high resolution mass spectrometry. In general, sulfo-conjugated metabolites were excreted for a longer time period than the corresponding glucuronides. Several unexpected losses of the arguably stable isotope labels were observed and characterized, attributed to metabolic reactions and sample preparation procedures. The detection window of one of the newly detected metabolites was higher than currently used metabolites. The suitability of this metabolite to differentiate between endo- or exogenous sources could however not be verified conclusively.

Synthesis and characterization of anaerobic degradation biomarkers of n-alkanes via hydroxylation/carboxylation pathways

Metabolite profiling is a powerful method in research on anaerobic biodegradation of hydrocarbons. Hydroxylation and carboxylation are proposed pathways in anaerobic degradation but very little direct evidence is available about metabolites and signature biomarkers. 2-Acetylalkanoic acid is a potential signature metabolite because of its unique and specific structure among possible intermediates. A procedure for the synthesis of four homologues with various carbon chain lengths was proposed and the characteristics of 2-acetyl- alkanoic acid esters were investigated using four derivatization processes, namely methyl, ethyl, n-butyl and trimethylsilyl esterification. Four intermediate fragments observed were at m/z 73 + 14n, 87 + 14n, 102 + 14n (n = 1, 2 and 4 for methyl, ethyl and n-butyl ester, respectively) and [M - 42]+ for three of the derivatization methods. For silylation, characteristic ions were observed at m/z 73, 117, [M - 42](+) and [M - 55](+). These are basic and significant data for the future identification of potential intermediates of the hydroxylation and carboxylation pathways in hydrocarbon degradation.

Synthesis of anaerobic degradation biomarkers alkyl-, aryl- and cycloalkylsuccinic acids and their mass spectral characteristics

Anaerobic biodegradation of petroleum hydrocarbons has been reported to proceed predominantly via fumarate addition to yield substituted succinate metabolites. These metabolites, commonly regarded as signature biomarkers, are specific indicators of anaero- bic hydrocarbon degradation by microbial activity. To the best of our knowledge, mass spectrometry information for 2-(1-methylalkylj succinic acids, 2-arylsuccinic acids, 2-cycloalkylsuccinic acids and/or their derivatives is still incomplete, especially for the analysis of environmental samples. Here, a novel approach is proposed for the successful synthesis of five hydrocarbon-derived succinic acids. The characteristic fragments of 2-[1-methylalkyllsuccinic acid diesters were investigated by four derivatization processes (methyl, ethyl, n-butyl and trimethylsilyl esterification], some of which are not available in official Libraries. Under electron ionization mass spec- trometry conditions, informative fragments of various molecular masses have been obtained. Results confirmed characteristic differ- ences among the derivatization processes of the chemically synthesized compounds. In the case of 2-[cyclo)alkylsuccinate esters, four intermediate fragments were observed at m/z 114 + 14n, 118 + 28n, [M - [17 + 14n1]]+ and [M - (59 + 14n)]+ (n = 1, 2 and 4 for methyl, ethyl and n-butyl ester]. However, for silylation the abundant fragment ions are at m/z 262, 217, 172, 147, 73 and [M - 15]+. These data provide information for the identification of hydrocarbon-derived succinic acids as anaerobic biodegradation intermediates in hydrocarbons- rich environments.

A new insight into the role of rat cytochrome P450 24A1 in metabolism of selective analogs of 1α,25-dihydroxyvitamin D₃

We examined the metabolism of two synthetic analogs of 1α,25-dihydroxyvitamin D₃ (1), namely 1α,25-dihydroxy-16-ene-23-yne-vitamin D₃ (2) and 1α,25-dihydroxy-16-ene-23-yne-26,27-dimethyl-vitamin D₃ (4) using rat cytochrome P450 24A1 (CYP24A1) in a reconstituted system. We noted that 2 is metabolized into a single metabolite identified as C26-hydroxy-2 while 4 is metabolized into two metabolites, identified as C26-hydroxy-4 and C26a-hydroxy-4. The structural modification of adding methyl groups to the side chain of 1 as in 4 is also featured in another analog, 1α,25-dihydroxy-22,24-diene-24,26,27-trihomo-vitamin D₃ (6). In a previous study, 6 was shown to be metabolized exactly like 4, however, the enzyme responsible for its metabolism was found to be not CYP24A1. To gain a better insight into the structural determinants for substrate recognition of different analogs, we performed an in silico docking analysis using the crystal structure of rat CYP24A1 that had been solved for the substrate-free open form. Whereas analogs 2 and 4 docked similar to 1, 6 showed altered interactions for both the A-ring and side chain, despite prototypical recognition of the CD-ring. These findings hint that CYP24A1 metabolizes selectively different analogs of 1, based on their ability to generate discrete recognition cues required to close the enzyme and trigger the catalytic mechanism.

Mass spectrometric characterization of urinary metabolites of the selective androgen receptor modulator andarine (S-4) for routine doping control purposes

Selective androgen receptor modulators (SARMs) are potent anabolic agents with tissue-selective properties. Due to their potential misuse in elite sport, the World Anti-Doping Agency (WADA) has prohibited SARMs since 2008, and although no representative drug candidate has yet received full clinical approval, recent findings of SARMs illegally sold via the internet have further supported the need to efficiently test for these compounds in doping controls. In the present communication, the mass spectrometric characterization of urinary metabolites of the SARM Andarine (also referred to as S-4) compared with earlier in vitro and animal studies is reported. Liquid chromatography interfaced to high-resolution/high-accuracy (tandem) mass spectrometry was used to identify phase I and II metabolites, confirming the predicted target analytes for sports drug testing purposes including the glucuronic acid conjugates of the active drug, its monohydroxylated and/or deacetylated product, the hydrolysis product resulting from the removal of the compound's B-ring, as well as the sulfate of the monohydroxylated and the deacetylated phase I metabolite. The obtained data will support future efforts to effectively screen for and confirm the misuse of the non-approved drug candidate Andarine.

Mass spectrometric analysis of androstan-17beta-ol-3-one and androstadiene-17beta-ol-3-one isomers

Mass spectrometric identification and characterization of steroids using electrospray ionization and tandem mass spectrometry has advantages in drug testing and doping control analysis attributable to limitations of gas chromatography followed by electron ionization mass spectrometry. Steroids with an androstadiene-17beta-ol-3-one nucleus and double bonds located either at C-1 and C-4, C-4 and C-9, or C-4 and C-6 were used to determine characteristic fragmentation pathways. Diagnostic dissociation routes are proposed using deuterium labeling, MS3 experiments, and analyses of structurally closely related compounds. Steroids such as boldenone (androst-1,4-diene-17beta-ol-3-one) produced characteristic product ions at m/z 121, 135, and 147. Compounds with double bonds at C-4 and C-9 generated abundant product ions at m/z 145 and 147. Conjugated double bonds at C-4 and C-6 gave rise to an intense and characteristic signal at m/z 133. Stereochemical differentiation between 5alpha- and 5beta-isomers of androstan-17beta-ol-3-ones was possible because of significant differences in relative abundance of product ions generated by elimination of acetone from alpha,beta-saturated 3-keto steroids.

Fragmentation of negative ions from carbohydrates: part 2. Fragmentation of high-mannose N-linked glycans

[M + NO3]- And [M + (NO3)2]2- ions were produced by electrospray from neutral high-mannose ([Man](5-9)[GlcNAc]2, [Glc](1-3)[Man](4-9)[GlcNAc]2) N-linked glycans and their 2-aminobenzamide derivatives sprayed from methanol:water containing ammonium nitrate. Low energy collision-induced decomposition (CID) spectra of both types of ions were almost identical and dominated by cross-ring and C-type fragments, unlike the corresponding spectra of the positive ions that contained mainly B- and Y-type glycosidic fragments. This behavior could be rationalized by an initial proton abstraction from various hydroxy groups by the initially-formed anionic adduct. These negative ion spectra were more informative than the corresponding positive ion spectra and contained prominent ions that were diagnostic of structural features such as the composition of individual antennas that were not easily obtainable by other means. C-ions defined the sequence of the constituent monosaccharide residues. Detailed fragmentation mechanisms are proposed to account for many of the diagnostic ions.

Electron ionization mass spectral fragmentation of cholestane-3beta,4alpha,5alpha-triol and cholestane-3beta,5alpha,6alpha/beta-triol bis- and tris-trimethylsilyl derivatives

The electron ionization (EI) mass spectral fragmentation of the bis- and tris-trimethylsilyl derivatives of cholestane-3beta,4alpha,5alpha-triol, cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol was investigated. The EI mass spectrum of the 3beta,4alpha-bis-trimethylsilyl derivative of cholestane-3beta,4alpha,5alpha-triol exhibits interesting fragment ions at m/z 142 and 332 resulting from the initial loss of TMSOH between the carbons 2 and 3 and subsequent retro-Diels-Alder (RDA) cleavage of the ring A. Trimethylsilyl transfer between the 4alpha- and the 5alpha-hydroxy groups acts significantly before RDA cleavage affording an ion at m/z 404. Complete silylation of cholestane-3beta,4alpha,5alpha-triol strongly stabilizes the molecule, affording an abundant molecular ion at m/z 636 and decreasing the abundance of the RDA cleavage. Loss of water (from the non-silylated 5alpha-hydroxy group) plays a very important role during the decomposition of the molecular ion of 3beta,6alpha/beta-bis-trimethylsilyl derivatives of cholestane-3beta,5alpha,6alpha/beta-triols. These derivatives appear to be very useful in assigning the configuration of the carbon 6. This assignment is based on the abundance of the fragment ions at m/z 321, 367 and 403, which are more prominent in the EI mass spectrum of the beta-isomer. In contrast, EI mass spectra of the tris-trimethylsilyl derivatives of cholestane-3beta,5alpha,6beta-triol and cholestane-3beta,5alpha,6alpha-triol differ only slightly and appear to be poorly informative.

In vivo biotransformation of 17 alpha-methyltestosterone in the horse revisited: identification of 17-hydroxymethyl metabolites in equine urine by capillary gas chromatography/mass spectrometry

The in vivo phase I biotransformation of 17 alpha-methyltestosterone in the horse leads to the formation of a complex mixture of regio- and stereoisomeric C(20)O(2), C(20)O(3) and C(20)O(4) metabolites, excreted in urine as glucuronide and sulphate phase II conjugates. The major pathways of in vivo metabolism are the reduction of the A-ring (di- and tetrahydro), epimerisation at C-17 and oxidations mainly at C-6 and C-16. Some phase I metabolites have been identified previously by positive ion electron ionisation capillary gas chromatography/mass spectrometry (GC/EI + MS) mainly from the characteristic fragmentation patterns of their methyloxime-trimethylsilyl ether (MO-TMS), enol-TMS or TMS ether derivatives. Following oral administration of 17 alpha-methyltestosterone to two castrated thoroughbred male horses, the glucuronic acid conjugates excreted in post-administration urine samples were selectively hydrolysed by E. coli beta-glucuronidase enzymes. Unconjugated metabolites and the steroid aglycones obtained after enzymatic deconjugation were isolated from urine by solid-phase extraction, derivatised as MO-TMS ethers and analysed by GC/EI + MS. In addition to some of the known metabolites previously identified from the characteristic mass spectral fragmentation patterns of 17 alpha-methyl steroids, some isobaric compounds exhibiting a diagnostic loss of 103 mass units from the molecular ions with subsequent losses of trimethylsilanol or methoxy groups and an absence of the classical D-ring fragment ion were detected. From an interpretation of their mass spectra, these compounds were identified as 17-hydroxymethyl metabolites, formed in vivo in the horse by oxidation of the 17-methyl moiety of 17 alpha-methyltestosterone. This study reports on the GC/EI + MS identification of these novel 17-hydroxymethyl C(20)O(3) and C(20)O(4) metabolites of 17 alpha-methyltestosterone excreted in thoroughbred horse urine.

Evaluation of human hepatocyte incubation as a new tool for metabolism study of androstenedione and norandrostenedione in a doping control perspective

Human hepatocyte incubations were used to study the metabolism of precursors of testosterone and nortestosterone and to evaluate qualitatively the correlation between in vitro and published in vivo urinary metabolic profiles. Both phase I and phase II biotransformations were observed in vitro: oxidoreduction at C-3 and C-17, reduction at C-4,5, hydroxylation at C-6 beta and C-16, glucuronidation and sulfation. All major metabolites detected in urine following oral administration of androstenedione and norandrostenedione were present in human hepatocyte incubations. The good correlation between in vitro and in vivo metabolic profiles indicates that hepatocyte incubations can be a useful tool to identify and characterize metabolites that could be potential urinary markers for detection of steroid abuse by athletes.

"Internal residue loss": rearrangements occurring during the fragmentation of carbohydrates derivatized at the reducing terminus

Rearrangement reactions involving migration of fucose and, occasionally, other residues have been found in the CID spectra of [M + H]+ and [M + 2H]2+ ions, but not [M + Na]+ ions, generated from several O-linked carbohydrates and milk sugars derivatized at their reducing termini with aromatic amines such as 2-aminobenzamide. Such rearrangements, which are similar to those reported by other investigators from several underivatized carbohydrates and glycosides, cause an apparent loss of sugar residues from within a carbohydrate chain and can produce ambiguous results during spectral interpretation. A mechanism, involving initial protonation of the amine nitrogen atom of the derivative, is proposed to account for the formation of the observed ions.

Metabolism of methandrostenolone in the horse: a gas chromatographic-mass spectrometric investigation of phase I and phase II metabolism

The phase I and phase II metabolism of the anabolic steroid methandrostenolone was investigated following oral administration to a standardbred gelding. In the phase I study, metabolites were isolated from the urine by solid-phase extraction, deconjugated by acid catalysed methanolysis and converted to their O-methyloxime trimethylsilyl derivatives. GC-MS analysis indicated the major metabolic processes to be sequential reduction of the A-ring and hydroxylation at C6 and C16. In the phase II study, unconjugated, beta-glucuronidated and sulfated metabolites were fractionated and deconjugated using a combination of liquid-liquid extraction, enzyme hydrolysis, solid-phase extraction and acid catalysed methanolysis. Derivatization followed by GC-MS analysis revealed extensive conjugation to both glucuronic and sulfuric acids, with only a small proportion of metabolites occurring in unconjugated form.

Degradation of fluoranthene by Pasteurella sp. IFA and Mycobacterium sp. PYR-1:isolation and identification of metabolites

The findings from a biodegradability study of fluoranthene using two pure bacterial strains, Pasteurella sp. IFA (B-2) and Mycobacterium sp. PYR-1 (AM) are reported. Of total fluoranthene, 24% (B-2) and 46% (AM) was biodegraded in an aqueous medium during 14 d of incubation at room temperature. During this period the bacteria were capable of mineralizing approximately two-thirds (B-2) and four-fifths (AM) of biodegraded fluoranthene to CO2, while one-third (B-2) and one-fifth (AM) of the original fluoranthene remained as stable metabolic products. These metabolites were isolated using liquid-liquid extraction and identified using gas chromatography-mass spectrometry (GC-MS) and derivatization techniques. Two metabolites (9-fluorenone-1-carboxylic acid and 9-fluorenone) were identified by GC-MS directly, while the metabolites 9-fluorenone-1-carboxylic acid, 9-hydroxyfluorene, 9-hydroxy-1-fluorene-carboxylic acid, 2-carboxybenzaldehyde, benzoic acid and phenylacetic acid were determined in their derivatized forms. From the identified metabolites, a fluoranthene biodegradation pathway was proposed for Pasteurella sp. IFA.

Reinvestigation of lipid peroxidation of linolenic acid

Recently, we deduced a mechanism for lipid peroxidation of linoleic acid [1]. This mechanism was now applied to predict the occurrence of previously unknown lipid peroxidation products of linolenic acid. The proposed structures of peroxidation products allowed to search for these predicted compounds in reaction mixtures with the aid of 'ion trace' by mass spectrometry. Thus, a great number of previously unknown lipid peroxidation products was detected. It is assumed that these compounds also occur--at least as intermediates--in lipid peroxidation processes in mammalian tissue.

alpha-Hydroxyaldehydes, products of lipid peroxidation

Besides the well known products of lipid peroxidation, 4-hydroxy-2-nonenal, saturated and unsaturated aldehydes, 2-hydroxy-heptanal was found to be a major aldehydic product of lipid peroxidation (LPO) of n-6 fatty acids (linoleic acid 18:2, arachidonic acid 20:4). 2-Hydroxyhexanal is produced also, but only in much lower yield. 2-Hydroxyalkanales with 8,9,10 and 11 C-atoms are derived from hydroperoxides of oleic acid. An oxidation product of all unsaturated fatty acids is glyoxal. Analyses were performed after aldehyde specific derivatization reactions by GC-MS.

Detection of methandienone (methandrostenolone) and metabolites in horse urine by gas chromatography-mass spectrometry

The metabolic transformation of methandienone (I) in the horse was investigated. After administration of a commercial drug preparation to a female horse (0.5 mg/kg), urine samples were collected up to 96 h and processed without enzymic hydrolysis. Extraction was performed by a series of solid-liquid and liquid-liquid extractions, thus avoiding laborious purification techniques. For analysis by gas chromatography-mass spectrometry, the extracts were trimethylsilylated. Besides the parent compound I and its C-17 epimer II, three monohydroxylated metabolites were identified: 6 beta-hydroxymethandienone (III), its C-17 epimer (IV) and 16 beta-hydroxymethandienone (V). In addition, three isomers of 6 beta,16-dihydroxymethandienone (VIa-c) were discovered. Apparently, reduction of the delta 4 double bond of 16 beta-hydroxymethandienone (V) in the horse yields 16 beta,17 beta-dihydroxy-17 alpha-methyl-5 beta-androst-1-en-3-one (VII). Reduction of the isomers VIa-c results in the corresponding 6 beta,16,17-trihydroxy-17-methyl-5 beta-androst-1-en-3-ones (VIIIa-c). The data presented here suggest that screening for the isomers of VI and VIII, applying the selected-ion monitoring technique, will be the most successful way of proving methandienone administration to a horse.

Identification of 2 alpha-hydroxy-4-pregnene-3,20-dione in human pregnancy urine

2 alpha-Hydroxyprogesterone (2 alpha-hydroxy-4-pregnene-3,20-dione) was identified in human late pregnancy urine by liquid-gel chromatography, GLC and GC-MS. In addition, the following 2-hydroxylated C21 steroids were found and identified as 2 zeta-hydroxy-5 zeta-pregnane-3,20-dione, 2 zeta,20 zeta-dihydroxy-4-pregnen-3-one, 2 alpha,3 alpha-dihydroxy-5 alpha- (and 5 beta)-pregnan-20-one, two isomers of pregnane-2,3,20-triol and 2 zeta,3 zeta,16 zeta-trihydroxy-5 zeta-pregnan-20-one.

Studies on anabolic steroids--6. Identification of urinary metabolites of stenbolone acetate (17 beta-acetoxy-2-methyl-5 alpha-androst-1-en-3-one) in human by gas chromatography/mass spectrometry

The metabolism of stenbolone acetate (17 beta-acetoxy-2-methyl-5 alpha-androst-1-en-3-one), a synthetic anabolic steroid, has been investigated in man. Nine metabolites were detected in urine either as glucuronic or sulfuric acid aglycones after oral administration of a single 50 mg dose to a male volunteer. Stenbolone, the parent compound, was detected for more than 120 h after administration and its cumulative excretion accounted for 6.6% of the ingested dose. Most of the stenbolone acetate metabolites were isolated from the glucuronic acid fraction, namely: stenbolone, 3 alpha-hydroxy-2-methyl-5 alpha-androst-1-en- 17-one, 3 alpha-hydroxy-2 xi-methyl-5 alpha-androst-17-one; 3 isomers of 3 xi, 16 xi-dihydroxy-2-methyl-5 alpha-androst-1-en-17-one; 16 alpha and 16 beta-hydroxy-2-methyl-5 alpha-androst-1-ene-3, 17-dione; and 16 xi, 17 beta-dihydroxy-2-methyl-5 alpha-androst-1-en-3-one. Only isomeric metabolites bearing a 16 alpha or a 16 beta-hydroxyl group were detected in the sulfate fraction. Interestingly, no metabolite was detected in the unconjugated steroid fraction. The steroids identities were assigned on the basis of their TMS ether, TMS enol-TMS ether, MO-TMS and d9-TMS ether derivatives and by comparison with reference and structurally related steroids. Data indicated that stenbolone acetate was metabolized into several compounds resulting from oxidation of the 17 beta-hydroxyl group and/or reduction of A-ring delta-1 and/or 3-keto functions with or without hydroxylation at the C16 position. Finally, comparison of stenbolone acetate urinary metabolites with that of methenolone acetate shows similar biotransformation pathways for both delta-1-3-keto anabolic steroids. This indicates that the position of the methyl group at the C1 or C2 position in these steroids has little effect on their major biotransformation routes in human, to the exception that stenbolone cannot give rise to metabolites bearing a 2-methylene group since its 2-methyl group cannot isomerize into a 2-methylene function through enolization of the 3-keto group as previously observed for methenolone.

Biotransformation of 1-dehydrotestosterone in the equine male castrate: identification of the neutral unconjugated and glucuronic acid conjugated metabolites in horse urine

The in vivo biotransformation of (1,2(n)-3H)1-dehydrotestosterone was studied in three equine male castrates and a number of neutral metabolites were identified in the urinary unconjugated and glucuronic acid conjugate fractions by gas chromatography/mass spectrometry. The metabolites were extracted from aliquots of the 0-24 h urine samples by Amberlite XAD-2 and separated into combined unconjugated plus glucuronic acid conjugated and sulphoconjugated fractions by Sephadex LH-20 column chromatography. After enzymatic hydrolysis of the glucuronides, the crude neutral unconjugated steroids plus the aglycones were partially purified by Kieselgel H chromatography and identified as their methyloxime trimethylsilyl derivatives. In the unconjugated fraction, the major metabolites were isomers of androsta-1,4-diene-6,16,17-triol-3-one. In the aglycone fraction a small amount of the parent steroid was present but the major metabolite was the 17 alpha isomer androsta-1,4-dien-17 alpha-ol-3-one. Other metabolites containing the 1,4-dien-3-one group were isomers of androsta-1,4-diene-16,17-diol-3-one and androsta-1,4-diene-6,16-diol-3-one. Reduction of the 4-ene functionality leading to the formation of 5-androst-1-en-16-ol-3,17-dione, 5-androst-1-ene-16,17-diol-3-one and of the 1-ene functionality leading to the formation of testosterone and its further reduction leading to the formation of C19O2 and C19O3 androstane metabolites was observed. Some interesting features on the electron impact fragmentations of the methyloxime trimethylsilyl derivatives of steroids containing a 1,4-dien-3-one group were also observed.

15- and 16-hydroxylations of androgens and estrogens in the human fetal liver: a critical step in estetrol biosynthesis

To elucidate the main metabolic pathways which lead to the foeto-placental biosynthesis of estetrol (I), we investigated the 15 alpha- and 16 alpha-hydroxylations of potential precursors of this estrogen in the human fetal liver. We determined the 15 alpha- and 16 alpha-hydroxylation capacity of the fetal liver for each precursor by GC-MS. The results suggest that estetrol is derived only from estradiol sulfate (II) and DHEA sulfate (III). 15 alpha-Hydroxy-androstenedione (IV) can no longer be regarded as a good precursor of estetrol. The phenolic pathway appears to be a more likely route than the neutral pathway, even when derived from DHEA sulfate.

Aromatization of 15 alpha and 16 alpha hydroxylated androgens in the human placental using [1,2-3H]-substrates

This in vitro study reports data on the aromatization of [1,2-3H]-C19 steroids in the human term placenta [androstenedione (III), testosterone (IV), 15 alpha-hydroxy-androstenedione (V), 15 alpha-hydroxy-testosterone (VI), 16 alpha-hydroxy-androstenedione (VII)]. The hydroxylated androgens were microbiologically synthesized from commercially radiolabelled [1,2-3H]-androstenedione and testosterone. Androstenedione and testosterone were good substrates for the human placental aromatase (low Km values, high Vmax); they strongly inhibited the 15 and 16 hydroxylated androgens aromatizations. On the other hand, these hydroxylated compounds acted as poor substrates and were only non-competitive inhibitors of the androstenedione and testosterone aromatizations. However, 15 alpha-hydroxy-androstenedione could not be disregarded as a potential precursor of 15 alpha-hydroxylated estrogens in the human placenta.

Occurrence of highly oxygen-substituted androgens in hemofiltrates of uremic patients

The steroid fraction of hemofiltrate contains a large number of unknown steroids, which were separated by a combination of different chromatographic procedures and finally characterized by gas chromatography mass spectrometry. Besides different isomeric 3,16,17-trihydroxyandrostanes in a rather polar fraction a 3,16,17-trihydroxy-11-ketoandrostane was detected, obviously the first naturally occurring representative of 3,11,16,17-oxygen-tetrasubstituted androstanes.

The electron impact induced cleavage of the C-17--C-20 bond and D-ring in trimethylsilyl derivatives of C21 steroids. Reciprocal exchange of trimethylsilyl groups

The cleavage of the C-17--C-20 bond in the trimethylsilyl derivatives of C21 steroids has been investigated with the aid of isotopic labelling. A significant amount of reciprocal exchange was observed between trimethylsilyl groups or hydrogen atoms on the 20-O- and 17-O-positions. The loss of positional identity of these groups was found to influence the specificity of fragmentation reactions associated with the 17 beta-sidechain and the D-ring. It is supposed that the interchange of these silyl groups is facilitated by donation of the non-bonding electrons on oxygen to the empty d orbitals of silicon.

Influence of the 6-trimethylsilyl group on the fragmentation of the trimethylsilyl derivatives of some 6-hydroxy- and 3,6-dihydroxy-steroids and related compounds

The 25 eV mass spectra of the trimethylsilyl derivatives of a number of 6-hydroxy and 3,6-dihydroxy steroids together with deuterium and 18O-labeled analogs have been examined to determine the influence of the 6-OTMS group on fragmentation patterns. Ions in the cholestane series at m/z 321 and 403 were the most characteristic ions derived from the 6-OTMS function; their relative abundances, although low in the spectra of 6-OTMS steroids themselves, were considerably elevated when a 3-OTMS or 3-oxo group was present. Similar ions were present in the spectra of androstane and pregnane derivatives. No correlation was found between the abundance of these ions and the stereochemistry at C3, C5, or C6. Fragmentation mechanisms and gas chromatographic data are discussed.

Analysis of C19O3 steroids by thin-layer and gas-liquid chromatography and mass spectrometry

The separation of twenty-six saturated and two unsaturated C19O3 steroids has been studied by thin-layer chromatography on silica gel F254, with seven mobile phases, and by gas-liquid chromatography on packed columns with four stationary phases; combination of both techniques permitted separation of all the test compounds. The mass spectra of the steroids were obtained by gas chromatography-mass spectrometry and are presented. Fragmentation processes have been studied, and characteristic ions that may be used for multiple ion detection or lead to identification of biologically produced C19O3 steroids are discussed.

Location of functional groups with the aid of mass spectrometry. XVI.--Mass spectra of trimethylsilylated androstan-3,16,17 beta-triols

The mass spectra of androstan-3,16,17beta-triols are very similar, so that a distinction between isomers is rather difficult. Main degradation reactions correspond to expulsion of substituents and loss of parts of the D-ring system.

Mass spectra of sterically crowded trialkylsilyl ether derivatives of steroids

The electron-impact mass spectra of the title compounds have some important features which give these derivatives certain advantages over the widely studied trimethylsilyl analogues. There is significantly less extensive fragmentation, and abundant ions at (M - t.Bu)+ or (M - i.Pr)+ serve as indicators of molecular weight and should be useful for selected ion monitoring. From various precursors, the ease of elimination of HX2SiOH, via a proposed multi-centre transition state, appears to depend upon conformational and stereochemical factors, as well as the position of the parent silyloxy group, RX2SiO, on the steroid skeleton. This particular fragmentation appears to be a powerful diagnostic method for distinguishing between stereoisomers, being especially useful for differentiation between epimers. In addition, the presence of a 17-silyloxy function promotes a characteristic cleavage of ring B in a skeletally saturated steroid. Elimination of silanol, RX2SiOH, at various stages in the fragmentations of bis-silylated steroids is also an important process, but other familiar features of the spectra of steroid trimethylsilyl ethers, though usually present, are very much suppressed.

Trimethylsilyl group migration during electron impact and chemical ionization mass spectrometry of the trimethylsilyl ethers of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones

The electron impact and chemical ionization (isobutane) mass spectra of the TMS derivatives of 20-hydroxy-5alpha-pregnan-3-ones and 20-hydroxy-4-pregnen-3-ones include ions [M--44]+-attributable to loss of a CH3CHO fragment from C-17 with migration of the TMS group to the charge-retaining fragment. Mass spectra of isotopically labelled ([3-18O], [20-18O] and [2H9-TMS]) analogues are consistent with this mechanism; [2H9-TMS] labelling further indicates that subsequent loss of a methyl group from [M--44]+-ions does not involve the TMS group. Corresponding ions are not observed at significant abundance in the spectra of 20beta-trimethylsilyloxy-5alpha-pregnane and 20beta-trimethylsilyloxy-4-pregnen-3-one 3-O-methyloxime. In the electron impact mass spectrum of the t-butyldimethylsilyl ether of 20beta-hydroxy-4-pregnen-3-one, an ion is observed corresponding to loss of 44 atomic mass units from the intense [M--C4H9]+ ion.