Characteristic Mass Spectral Fragmentation Research Articles

Development and Application of a Comprehensive Nontargeted Screening Strategy for Aristolochic Acid Analogues.

Aristolochic acid analogs (AAAs) are naturally occurring carcinogenic and toxic compounds that pose a safety threat to pharmaceuticals and the environment. It is challenging to screen AAAs due to their lack of characteristic mass spectral fragmentation and their presence of structural diversity. A comprehensive nontargeted screening strategy was proposed by taking into account diverse factors and incorporating various self-developed techniques, and a Python3-based toolkit called AAAs_finder was developed for its implementation. The main procedures consist of virtual structure and ultraviolet and visible (UV) spectra database creation, exact mass and UV spectra-based suspect data extraction, tandem mass spectra (MS/MS) anthropomorphic interpretation, and multicondition retention time (RT) prediction-based candidate structures ranking. To initially assess screening feasibility, eight hypothetical unknown samples were subjected to nontargeted screening using the AAAs_finder toolkit and two other advanced tools. The results showed that the former successfully identified all, while the latter two only managed to identify two and three, respectively, indicating that our strategy was more feasible. After that, the strategy was carefully evaluated for false positives and false negatives, instrument dependence, reproducibility, and sensitivity. After the evaluation, the strategy was successfully applied to the screening of AAAs in real samples, such as herbal medicine, spiked soil, and water. Overall, this study proposed a nontargeted screening strategy and toolkit independent of characteristic mass spectral fragmentation and able to overcome challenges posed by structural diversity for the AAAs screening, which is also valuable for other classes of compounds.

Identification of polybrominated diphenyl ether metabolites based on calculated boiling points from COSMO-RS, experimental retention times, and mass spectral fragmentation patterns.

The COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) was used to predict the boiling points of several polybrominated diphenyl ethers (PBDEs) and methylated derivatives (MeO-BDEs) of monohydroxylated BDE (OH-BDE) metabolites. The linear correlation obtained by plotting theoretical boiling points calculated by COSMO-RS against experimentally determined retention times from gas chromatography-mass spectrometry facilitated the identification of PBDEs and OH-BDEs. This paper demonstrates the applicability of COSMO-RS in identifying unknown PBDE metabolites of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',6-pentabromodiphenyl ether (BDE-100). Metabolites of BDE-47 and BDE-100 were formed through individual incubations of each PBDE with recombinant cytochrome P450 2B6. Using calculated boiling points and characteristic mass spectral fragmentation patterns of the MeO-BDE positional isomers, the identities of the unknown monohydroxylated metabolites were proposed to be 2'-hydroxy-2,3',4,4'-tetrabromodiphenyl ether (2'-OH-BDE-66) from BDE-47, and 2'-hydroxy-2,3',4,4',6-pentabromodiphenyl ether (2'-OH-BDE-119) and 4-hydroxy-2,2',3,4',6-pentabromodiphenyl ether (4-OH-BDE-91) from BDE-100. The collective use of boiling points predicted with COSMO-RS, and characteristic mass spectral fragmentation patterns provided a valuable tool toward the identification of isobaric compounds.

Characterization of bioactive plant ellagitannins by chromatographic, spectroscopic and mass spectrometric methods

Ellagitannins are widely distributed plant polyphenols showing potent anti-herbivore activities, but rather complex chemical structures. Here we show how ellagitannins with different structures can be efficiently characterized from plant extracts by utilizing the information obtained from four universal methods used for ellagitannin analysis: Sephadex LH-20 gel chromatography, high-performance liquid chromatography, ultraviolet spectroscopy, and mass spectrometry. We show that by combining the information obtained from the ellagitannins’ chromatographic elution order, specific shapes of the ultraviolet spectra, molecular masses and characteristic mass spectral fragmentations, it is possible to classify these polyphenols into different ellagitannin sub-groups, and even characterize the structures within the sub-groups. These findings aid in the fast screening of complex plant samples for their ellagitannin composition without having to isolate compounds for individual characterization.

Δ 11 desaturases of Trichoplusia ni and Spodoptera littoralis exhibit dual catalytic behaviour

The Δ 11 desaturases found in moths such as Spodoptera littoralis play a critical role in the biosynthesis of their sex pheromones. The ability to functionally express these enzymes in yeast has allowed one to study the transformation of long-chain fatty acyl substrates to their 11-ene products in greater mechanistic detail. In this article, we report on the detection and quantitation of a minor 11-hydroxylated byproduct (0.1% of total fatty acids), which is formed by the Δ 11 desaturases found in Trichoplusia ni and Spodoptera littoralis. The position of the hydroxyl group was determined by characteristic mass spectral fragmentation of the trimethylsilyl derivatives and is in accord with predictions based on previous mechanistic investigations of the Spodoptera Δ 11 desaturase. The level of 11-hydroxylation was insensitive to the mode of desaturase expression (constitutive vs. induced) and the presence or absence of a b5-fusion domain. Our findings suggest that in future, a search for hydroxylated products should be included in functional analyses of insect desaturase genes.

Structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in Cenomanian and Turonian black shales of Pasquia Hills (Saskatchewan, Canada)

Twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms (BAQCs; C 14–C 33 range) are present in the extractable organic matter of Cenomanian and Turonian black shales of Pasquia Hills (Saskatchewan, Canada). Five of these pseudohomologous series are also observed in a Holocene sample from the Russian Arctic. Three of the pseudohomologous series were identified by Kenig et al. [PNAS 100 (2003) 12554–12558] as 3,3- and 5,5-diethylalkanes (DEAs) and 2,2-dimethylalkanes (DMAs). The nine other pseudohomologous series of BAQCs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3,3-dimethylalkanes (DMAs), 3-ethyl-3-methyl- and 5-ethyl-5-methylalkanes, 9,9-, 7,7-, and 6,6-diethylalkanes (DEAs), 3,3,ω3,ω3- and 5,5,ω5,ω5-tetraethylalkanes, and 5-butyl-5-ethylalkanes. Pseudohomologous series of branched alkanes with tertiary carbon atoms, such as monomethyl- and monoethylalkanes are also present in the same carbon-number range. All these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers, clearly indicating a biosynthetic origin. BAQCs such as 5,5-DEAs, 3,3-DEAs and 3-ethyl-3-methylalkanes seem to be widespread in sediments and sedimentary rocks (ranging from modern to ∼2.1 billion years). A xenobiotic source for BAQCs can be excluded at this point. BAQCs seem to have a very low biodegradability, in part explaining their widespread occurrence in ancient sediments.

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.

A study of three reactions leading to isomeric 2-(N,N-disubstituted amino)thiazol-5-yl ketones

N-Imidoyl-N,N-disubstituted thioureas react with α-halogeno ketones in the presence of triethylamine to give the expected 2-(N,N-disubstituted amino) thiazol-5-yl ketones in high yield. The corresponding reactions of N-acyl-N,N-disubstituted thioureas lead to mixtures of these products and isomers which arise from rearrangement between cyclic intermediates. Mixtures of the isomeric thiazolyl ketones are also formed by treating N,N-disubstituted thioureas with 2-bromo 1,3-diketones. The mixtures from the second and third routes contain the same products but in significantly different proportions. A mechanistic scheme which accounts for the main findings was developed.During the work 40 new 2-(N,N-disubstituted amino)thiazol-5-yl ketones were prepared and their structures rigorously established; characteristic mass spectral fragmentation patterns were particularly useful in identifying the substituents at positions 4 and 5 of the thiazole ring.

Gas Chromatographic and Mass Spectrometric Determination of Ametryn and Its N-Dealkylated Products

Gas chromatographic and mass spectrometric properties of ametryn and its N-dealkylated products were studied to establish the potential use in a recently reported method describing the residue analyses of these compounds by gas chromatography with N-P detection. Electron impact mass spectra show base peaks at the molecular ion (M+), and methane chemical ionization mass spectra give base peaks at (M + 1) ion for all the compounds studied. Characteristic mass spectral fragmentations of ametryn, GS-11354, GS-11355, and GS-26831 are presented. Combined gas chromatography-mass spectrometry rather than gas chromatography alone provides unambiguous residue characterization. The technique also allows quantitation of ametryn and its N-dealkylated products that cochromatograph with interfering materials present in a complex substrate.

Microsomal hydroxylation of 3-methylcholanthrene: analysis by computerized gas chromatography—mass spectrometry

Microsomal metabolism of 3-methylcholanthrene (MC) was examined by computerized gas chromatography—mass spectrometry. Five mono-, four di- and thirteen trihydroxylated metabolites were found after incubation of MC in mouse liver microsomal fraction for 15 min, in the presence of NADPH. Among these metabolites, three mono- and three dihydroxylated metabolites were identified by means of authentic samples. The chemical structures of the other metabolites were deduced from their characteristic mass spectral fragmentations. This is the first description of trihydroxylated metabolites in MC metabolism in vitro and in vivo.

Studies directed toward synthesis of quassinoids VII. - Conversion of chenodeoxycholic acid to a δ-lactone quassinoid analog and generation of a-ring diosphenol acetate derivatives of deoxycholic acid

Chenodeoxycholic acid was converted to a new 5,14- epi -28,30-dinorquassinoid analog. Two isomeric A-ring diosphenol acetate derivatives of deoxycholic acid were synthesized. A 3-oxo-5β-steroid was transformed to a 4-acetoxy-3-oxo-Δ 4-steroid by treatment with base and oxygen or to a 2-acetoxy-3-oxo-Δ 2-steroid by reaction with cupric chloride in refluxing acetic acid followed by acetylation. Ketene extrusion is a characteristic mass spectral fragmentation of these diosphenol acetates.

Homoisopavinanes—a highly probable class of phenethylisoquinoline alkaloids

Homoisopavinanes have been prepared by acid-catalysed cyclisation of the appropriately substituted aminoacetaldehyde dimethylacetal derivatives. The characteristic mass spectral fragmentation patterns of these homoisopavinanes is described.

ChemInform Abstract: CHARACTERISTIC MASS SPECTRAL FRAGMENTATION OF SOME 6‐EXO‐5,6‐DIHYDRO PGI2 AND THEIR ANALOGUES

Chemischer InformationsdienstVolume 9, Issue 47 Physical Organic Chemistry ChemInform Abstract: CHARACTERISTIC MASS SPECTRAL FRAGMENTATION OF SOME 6-EXO-5,6-DIHYDRO PGI2 AND THEIR ANALOGUES E. PELLA, E. PELLASearch for more papers by this authorR. TONANI, R. TONANISearch for more papers by this authorF. FAUSTINI, F. FAUSTINISearch for more papers by this authorC. GANDOLFI, C. GANDOLFISearch for more papers by this authorA. SELVA, A. SELVASearch for more papers by this author E. PELLA, E. PELLASearch for more papers by this authorR. TONANI, R. TONANISearch for more papers by this authorF. FAUSTINI, F. FAUSTINISearch for more papers by this authorC. GANDOLFI, C. GANDOLFISearch for more papers by this authorA. SELVA, A. SELVASearch for more papers by this author First published: November 21, 1978 https://doi.org/10.1002/chin.197847050AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue47November 21, 1978 RelatedInformation

Mass spectrometry in structural and stereochemical problems–CXCIV: The mass spectrometric fragmentations of steroidal sapogenins

AbstractThe characteristic mass spectral fragmentation patterns of the basic structure of the steroidal sapogenin, (25R)‐5α‐spirostan, have been elucidated through the preparation of analogs with deuterium labels at positions 11, 12, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26 and 27. In addition, the effects of a change of stereochemistry at positions 14 and 20, of the introduction of oxygencontaining functionalities mostly in ring F, and of the incorporation of olefinic unsaturation have been determined through synthesis of many examples.

Studies on Pyrimidine Derivatives and Related Compounds. LXII. Cycloadditions of Alkyl Isothiocyanates with Thiamine and Related Thiazolium Ylids and Facile Conversions of the Adducts to Dihydroimidazo [4, 5-d] thiazole Derivatives

Thiamine and related thiazolium ylids react with alkyl isothiocyanates to give spiro-(perhydrofuro [2, 3-d] thiazole-2, 4'-imidazolidine) derivatives (IIa-i) involving two step cycloaddition. Confirmation of the structures is provided by chemical degradations and by infrared, ultraviolet, nuclear magnetic resonance spectroscopic evidences as well as by characteristic mass spectral fragmentations. On heating in acetic acid, some of these (1 : 2) adducts are readily converted to dihydroimidazo [4, 5-d] thiazole derivatives (XIa-d) involving a novel intramolecular cyclization.

Gas chromatographic—mass spectrometric studies of long chain hydroxy acids.—III.1 The mass spectra of the methyl esters trimethylsilyl ethers of aliphatic hydroxy acids. A facile method of double bond location

AbstractTrimethylsilylation has proved to be extremely useful in the gas chromatography and the mass spectrometry of hydroxy acid methyl esters. The characteristic mass spectral fragmentation patterns have shown these derivatives to be superior in some respects to others for structural elucidation; in particular, hydroxylation followed by trimethylsilylation provides a useful method of double bond location in unsaturated fatty acid esters.A preliminary presentation of this method has been given by G. Eglinton at the Lecture etting in Combined Gas Chromatography—Mass Spectrometry at the school of Pharmacy, London, August 9, 1967. It has come to the authors' attention that this method simultaneously developed by Dr. P. Capella, Institute di Industria Agrarie, University of Bologna, Italy1c (P. Capella and C. M. Zorzut, Anal. Chem. 41, 1458 (1968).)

Acetylenic esters. II. Further addition reactions with sulfur- and nitrogen-containing compounds

Substituted thiosemicarbazides react with dimethyl acetylenedicarboxylate to give 3-amino-2,3-dihydrothiazin-4-ones. Confirmation of the structures is provided by catalytic hydrogenation and by characteristic mass spectral fragmentations. 4-Substituted thiosemicarbazides react with methyl propiolate in the same way as monosubstituted hydrazines and hydrazides to give hydrazones, whereas 1-substituted thiosemicarbazides undergo smooth removal of the sulfur with the production of an equal mixture of cis–trans and cis–cis dimethyl-β-thiodiacrylic esters. Bicyclic heterocyclic structures are formed by reaction of dimethyl acetylenedicarboxylate with imidazolidone thione and with 5,5-dimethyl-2-thiohydantoin. Substituted guanidines react with dimethyl acetylenedicarboxylate in an analogous fashion, yielding substituted 2,3-dihydrodiazinones. The high-resolution mass spectra of the latter show many similarities to the spectra of the sulfur analogues. Thioamides, despite previous claims to the contrary, react with dimethyl acetylenedicarboxylate to give thioethers of fumarate ester or 1,3-thiazin-4-ones. In contrast, thioamides react with methyl propiolate to give an equal mixture of cis–trans and cis–cis dimethyl-β-thiodiacrylic esters.