Mass spectrometric identification of amino acid thiohydantoins

Amino acid thiohydantoins were identified using electron impact and chemical ionization mass spectrometry. Some fragmentations of thiohydantoin ring were also identified. These results suggest that the thiohydantoin method should be useful for the stepwise peptide sequence analysis starting from the carboxyl terminus. The sequence of a model tripeptide was determined by the combination of the thiohydantoin method and mass spectrometry. In the case of peptide which contained a proline residue as their C-terminal peptide, cleavage of the peptide bond cannot be achieved.     

Mass spectrometric identification of toxins of biological origin

The chemical/biological (CB) threat spectrum encompasses a wide range of potential agents including chemical warfare agents, biological warfare agents and toxins of biological origin that fall between these two main agent categories. These proteinaceous and non-proteinaceous toxins, commonly referred to as mid-spectrum agents, range in molecular mass from a few hundred to more than a hundred thousand daltons. The large number of potential candidates as well as the structural diversity of possible mid-spectrum agents makes identification of these compounds a challenge. The NATO defense community has recognized these challenges and has a working group that is developing identification protocols and evaluating methods through a series of international analytical exercises. Identification strategies rely heavily on recent advances that have been made in both mass spectrometry (MS) and liquid chromatography (LC), with LC-MS typically being employed as the primary method for separation/identification. While this paper focuses on the application of these and related instrumental analytical techniques for the identification of mid-spectrum agents, the approach described could be applied in the fields of toxicology, forensic science and environmental analysis. Areas for future research have been identified and application of developed mid-spectrum identification methods to the ongoing biological and toxin weapons convention (BTWC) are anticipated.     

Mass spectrometric identification of oleanolic and ursolic acids

p-Toluidides of 3-acetoxy ursolic and 3-acetoxy oleanolic acids were prepared. On the basis of different intensities of the m/e 452 and 453 peaks the identification of oleanolic and ursolic acids is possible.     

Mass spectrometric identification of peptide hormones in doping-control analysis

The identification power of mass spectrometry has enabled the determination of hundreds of prohibited drugs in doping-control analysis. A few years ago, its utility was extended to peptide hormones such as erythropoietins, synthetic insulins and corticotrophins detectable in blood or urine. New assays have been established to improve the fight against doping, employing highly selective and sensitive detection methods based on chromatographic and tandem mass spectrometric techniques. In particular, in light of recent scandals related to assumed peptide hormone misuse and attempts at the alteration of urine, sophisticated analytical tools are essential for obtaining unequivocal results in sports drug testing.     

Gas chromatographic — Mass spectrometric identification of alkylcyclohexanes and cyclohexenes

Summary A series of 34 alkylcyclohexane hydrocarbons structurally related top-menthane, including all saturated, monoolefinic and aromatic structural precursors from cyclohexane, have been characterized by GC and MS. Kováts retention indices have been determined on five stationary phases (squalane, SE-30, Apiezon L, OV-225, PEG 20M) and the corresponding polarity, temperature and structural increments have been calculated. From the information acquired 10 alicyclic hydrocarbons have been identified for the first time in a pyrolysis naphtha.     

Mass spectrometric detection and identification of ortho, para-benzyltoluenes and oligotoluenes

Mass spectrometric detection and identification of ortho- and para-benzyltoluenes and oligotoluenes, C(21)-C(49), in several reaction mixtures was performed. Thus, the corresponding electron impact spectra were acquired and analyzed, this in addition to constant B/E linked scans and high-resolution data. Copyright 2000 John Wiley & Sons, Ltd.     

Mass spectrometric approaches for the identification of anthracycline analogs produced by actinobacteria

Anthracyclines are a well‐known chemical class produced by actinobacteria used effectively in cancer treatment; however, these compounds are usually produced in few amounts because of being toxic against their producers. In this work, we successfully explored the mass spectrometry versatility to detect 18 anthracyclines in microbial crude extract. From collision‐induced dissociation and nuclear magnetic resonance spectra, we proposed structures for five new and identified three more anthracyclines already described in the literature, nocardicyclins A and B and nothramicin. One new compound 8 (4‐[4‐(dimethylamino)‐5‐hydroxy‐4,6‐dimethyloxan‐2‐yl]oxy‐2,5,7,12‐tetrahydroxy‐3,10‐dimethoxy‐2‐methyl‐3,4‐dihydrotetracene‐1,6,11‐trione) was isolated and had its structure confirmed by ¹H nuclear magnetic resonance. The anthracyclines identified in this work show an interesting aminoglycoside, poorly found in natural products, 3‐methyl‐rhodosamine and derivatives. This fact encouraged to develop a focused method to identify compounds with aminoglycosides (rhodosamine, m/z 158; 3‐methyl‐rhodosamine, m/z 172; 4′‐O‐acethyl‐3‐C‐methyl‐rhodosamine, m/z 214). This method allowed the detection of four more anthracyclines. This focused method can also be applied in the search of these aminoglycosides in other microbial crude extracts. Additionally, it was observed that nocardicyclin A, nothramicin and compound 8 were able to interact to DNA through a DNA‐binding study by mass spectrometry, showing its potential as anticancer drugs. Copyright © 2016 John Wiley & Sons, Ltd.     

Mass spectrometric identification of monoglycosylglycerins in the form of esters of phenylboric acid

Conclusions The mass spectra of phenylboric esters of 3-O--D-glucopyranosyl-, 3-O--D-glucopyranosyl-, 3-O--D-galactopyranosyl-, 3-O--D-galactopyranosyl-, and 3-O--D-mannopyranosyl-L-glycerins were studied. The mass spectra permit a distinguishment of the enumerated compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 821–828, April, 1975.     

Mass spectrometric identification of formaldehyde-induced peptide modifications under in vivo protein cross-linking conditions

Formaldehyde cross-linking of proteins is emerging as a novel approach to study protein-protein interactions in living cells. It has been shown to be compatible with standard techniques used in functional proteomics such as affinity-based protein enrichment, enzymatic digestion, and mass spectrometric protein identification. So far, the lack of knowledge on formaldehyde-induced protein modifications and suitable mass spectrometric methods for their targeted detection has impeded the identification of the different types of cross-linked peptides in these samples. In particular, it has remained unclear whether in vitro studies that identified a multitude of amino acid residues reacting with formaldehyde over the course of several days are suitable substitutes for the much shorter reaction times of 10-20 min used in cross-linking experiments in living cells. The current study on model peptides identifies amino-termini as well as lysine, tryptophan, and cysteine side chains, i.e. a small subset of those modified after several days, as the major reactive sites under such conditions, and suggests relative position in the peptide sequence as well as sequence microenvironment to be important factors that govern reactivity. Using MALDI-MS, mass increases of 12 Da on amino groups and 30 Da on cysteines were detected as the major reaction products, while peptide fragment ion analysis by tandem mass spectrometry was used to localize the actual modification sites on a peptide. Non-specific cross-linking was absent, and could only be detected with low yield at elevated peptide concentrations. The detailed knowledge on the constraints and products of the formaldehyde reaction with peptides after short incubation times presented in this study is expected to facilitate the targeted mass spectrometric analysis of proteins after in vivo formaldehyde cross-linking.     

Mass spectrometric detection,identification, and fragmentation of arseno‐phytochelatins

Phytochelatins (PC) are cystein‐rich oligopeptides in plants for coordination with toxic metals and metalloids via their thiol groups. The composition, structure, and mass spectrometric fragmentation of arseno‐PC (As‐PC) with PC of different degree of oligomerization (PC2–PC5) in solution were studied using liquid chromatography coupled in parallel to inductively coupled plasma mass spectrometry and electrospray ionization quadrupole time‐of‐flight mass spectrometry. As‐PC were detected from As(PC2) to As(PC5) with an increasing number of isomers that differ in the position of thiol groups bound to As. Thermodynamic modeling supported the identification process in case of these isomers. Mass spectrometric fragmentation of the As‐PC does not follow the established pattern of peptides but is governed by the formation of series of As‐containing annular cations, which coordinate to As via S, N, or O. Structure proposals for 30 As‐PC fragment ions in the range m/z 147.92 to m/z 1290.18 are elaborated. Many of these fragment ions are characteristic to several As‐PC and may be suited for a screening for As‐PC in plant extracts. The mass spectrometric data offer the perspective for a future more sensitive determination of As‐PC by means of liquid chromatography tandem mass spectrometry with multiple reaction monitoring. Copyright © 2014 John Wiley & Sons, Ltd.     

Mass spectrometric identification of double bond positional isomers of hexadecenyl acetate without chemical derivatization

A method for the identification of the double bond positional isomers of hexadecenyl acetate has been established by analysing similarity of the mass spectra patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were selected as standard parameters for the characterization of the double bond position. The procedure was tested with △2 to △15-isomers of chemically unmodified hexadecenyl acetate, and the original double bond position in the acetates was located unambiguously.     

Mass spectrometric investigation of benzyliderieaniline

The mass spectral fragmentation of benzylideneaniline has been studied by deuterium labelling. Under electron impact, molecular ions undergo simple fission at the phenyl–N, phenyl–C and C?N bonds, hydrogen migration reactions, and skeletal rearrangement fragmentations. Except in the skeletal rearrangement reactions, hydrogen scrambling does not feature in benzylideneaniline upon electron impact.     

Mass spectrometric investigation of carbohydrates

Conclusions The pathways of the fragmentation of completely methylated- methyl-L-arabopyranoside were studied in detail. The data obtained will serve as a basis for establishing the structure of the partially methylated pentopyranosides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 277–283, February, 1967.The authors would like to express their deep gratitude to R. A. Khmel'nitskii and A. A. Polyakova for kindly permitting the use of a mass spectrometer, equipped with a multiloop oscillograph.     

Mass spectrometric study of organocyclosiloxanes

Organocyclosiloxanes of various chemical structures were studied by mass spectrometry using different ionization methods. The electron ionization mass spectra contain no peaks of molecular ions, and the main fragment ions are formed due to complicated rearrangements in a molecular ion, which provides no comprehensive view about the molecular structure. The desorption spectra exhibit peaks of quasimolecular and fragment ions, which characterize both molecular weights and chemical structures of the compounds under study. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1746–1749, September, 2007.     

Mass spectrometric analysis of enzymatic digestion of denatured collagen for identification of collagen type

Collagen type II and I from bovine were thermally denatured and digested with trypsin. The digest mixture was analyzed with liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS). Peptides in the digest mixture were identified by mass spectrometry/mass spectrometry (MS/MS) sequencing. The results indicated that the digest mixtures of collagen type II and I contained lots of specific peptides and common peptides. Specific peptides could be used as index for identifying collagen type. Articular cartilage from bovine was pretreated and analyzed with the same method to determine the collagen types. The result indicated that the method developed was effective for identification of collagen types. The research provided a possible approach for collagen identification in particular tissues.     

Mass spectrometric identification of proteins and characterization of their post-translational modifications in proteome analysis

High-throughput DNA sequencing has resulted in increasing input in protein sequence databases. Today more than 20 genomes have been sequenced and many more will be completed in the near future, including the largest of them all, the human genome. Presently, sequence databases contain entries for more than 425.000 protein sequences. However, the cellular functions are determined by the set of proteins expressed in the cell--the proteome. Two-dimensional gel electrophoresis, mass spectrometry and bioinformatics have become important tools in correlating the proteome with the genome. The current dominant strategies for identification of proteins from gels based on peptide mass spectrometric fingerprinting and partial sequencing by mass spectrometry are described. After identification of the proteins the next challenge in proteome analysis is characterization of their post-translational modifications. The general problems associated with characterization of these directly from gel separated proteins are described and the current state of art for the determination of phosphorylation, glycosylation and proteolytic processing is illustrated.