ChemInform Abstract: MASS SPECTROMETRY IN STRUCTURAL AND STEREOCHEMICAL PROBLEMS. PART 256. THE MASS SPECTROMETRIC BEHAVIOR OF 3α,5-CYCLO-5α-CHOLESTAN-6β-YL ALKYL ETHERS

The 3α,5-cyclo-6β-methoxy (i-methyl ether) moiety is a common protective grouping in steroid partial synthesis. Therefore, the mass spectrometric behavior of 6β-hydroxy-3α,5-cyclo-5α-cholestane, the corresponding methyl, ethyl, and tert-butyl ethers, the analogous ketone, and the parent hydrocarbon has been investigated in order to determine the mechanisms of the characteristic fragmentations of these compounds. Such knowledge is essential for unequivocal structure elucidation by mass spectrometry and also bears on the current interest in the stereospecificity of electron impact induced eliminations. Deuterium labeling of carbon atoms 1,2,3,4,7,8,9, and 19 of 6β-methoxy-3α,5-cyclo-5α-cholestane established the course of methanol extrusion and the identity of the highly diagnostic A ring cleavage ion [Formula: see text] Mechanisms are proposed for these key fragmentations. The mass spectra of the methyl, ethyl, and tert-butyl ethers of cholesterol are analyzed, and the features distinguishing these compounds from the isomeric 3,5-cyclosteroids are noted.

Download Full-text

ChemInform Abstract: MASS SPECTROMETRIC BEHAVIOR OF NITROGEN COMPOUNDS. 25. SYNTHESIS OF ISOMERIC AND HOMOLOGOUS SPERMIDINE AND SPERMINE DERIVATIVES AND THEIR IDENTIFICATION BY MASS SPECTROMETRY

Chemischer Informationsdienst ◽

10.1002/chin.197716046 ◽

1977 ◽

Vol 8 (16) ◽

pp. no-no

Author(s):

A. GUGGISBERG ◽

R. W. GRAY ◽

M. HESSE

Keyword(s):

Mass Spectrometry ◽

Mass Spectrometric ◽

Nitrogen Compounds ◽

Mass Spectrometric Behavior

Download Full-text

Synthesis and Mass Spectral Fragmentation Patterns of Brassinolide Early Biosynthetic Precursors Labeled at C-26

Natural Product Communications ◽

10.1177/1934578x1300800622 ◽

2013 ◽

Vol 8 (6) ◽

pp. 1934578X1300800

Author(s):

Vladimir A. Khripach ◽

Danuše Tarkowská ◽

Vladimir N. Zhabinskii ◽

Olga V. Gulyakevich ◽

Yurii V. Ermolovich ◽

...

Keyword(s):

Mass Spectrometry ◽

Liquid Chromatography ◽

Mass Spectrometric ◽

Keto Group ◽

Liquid Chromatography Mass Spectrometry ◽

Mass Spectral Fragmentation ◽

Mass Spectral ◽

Fragmentation Patterns ◽

Natural Brassinosteroids ◽

Mass Spectrometric Behavior

New analogues of brassinolide biosynthetic precursors with three deuterium atoms at non-exchangeable positions have been synthesized to be used as standards for quantification of natural brassinosteroids by liquid chromatography-mass spectrometry. [26-2H3](22 R,23 R,24 S)-22,23-Dihydroxy-6β-methoxy-24-methyl-3α,5-cyclo-5α-cholestane was used as a starting material for the preparation of campestane derivatives having a 22 R,23 R-diol functionality and either a hydroxy or keto group at C-3 and labeled at C-26. The mass spectrometric behavior of the newly synthesized compounds has been studied.

Download Full-text

Confounding contaminants in mass spectrometric reaction monitoring

10.26434/chemrxiv.7488737.v1 ◽

2018 ◽

Author(s):

Gilian T. Thomas ◽

Landon MacGillivray ◽

Natalie L. Dean ◽

Rhonda L. Stoddard ◽

Lars Yunker ◽

...

Keyword(s):

Mass Spectrometry ◽

Mass Spectrometric ◽

Negative Ion ◽

Reaction Monitoring ◽

Schlenk Flask ◽

Dynamic Analyses ◽

Rubber Septa ◽

Negative Ion Mode ◽

Mode A

<p>Reactions carried out in the presence of rubber septa run the risk of additives being leached out by the solvent. Normally, such species are present at low enough levels that they do not interfere with the reaction significantly. However, when studying reactions using sensitive methods such as mass spectrometry, the appearance of even trace amounts of material can confuse dynamic analyses of reactions. A wide variety of additives are present in rubber along with the polymer: antioxidants, dyes, detergent, and vulcanization agents, and these are all especially problematic in negative ion mode. A redesigned Schlenk flask for pressurized sample infusion (PSI) is presented as a means of practically eliminating the presence of contaminants during reaction analyses.</p>

Download Full-text

Resolution of a protein sequence ambiguity by X-ray crystallographic and mass spectrometric methods

Journal of Applied Crystallography ◽

10.1107/s0021889891011986 ◽

1992 ◽

Vol 25 (2) ◽

pp. 205-210 ◽

Cited By ~ 8

Author(s):

L. J. Keefe ◽

E. E. Lattman ◽

C. Wolkow ◽

A. Woods ◽

M. Chevrier ◽

...

Keyword(s):

Mass Spectrometry ◽

Amino Acid ◽

Electron Density ◽

Mass Spectrometric ◽

Amino Acid Sequences ◽

Data Matrix ◽

Protein Crystal ◽

Insertion Mutant ◽

Laser Desorption Mass Spectrometry ◽

X Ray

Ambiguities in amino acid sequences are a potential problem in X-ray crystallographic studies of proteins. Amino acid side chains often cannot be reliably identified from the electron density. Many protein crystal structures that are now being solved are simple variants of a known wild-type structure. Thus, cloning artifacts or other untoward events can readily lead to cases in which the proposed sequence is not correct. An example is presented showing that mass spectrometry provides an excellent tool for analyzing suspected errors. The X-ray crystal structure of an insertion mutant of Staphylococcal nuclease has been solved to 1.67 Å resolution and refined to a crystallographic R value of 0.170 [Keefe & Lattman (1992). In preparation]. A single residue has been inserted in the C-terminal α helix. The inserted amino acid was believed to be an alanine residue, but the final electron density maps strongly indicated that a glycine had been inserted instead. To confirm the observations from the X-ray data, matrix-assisted laser desorption mass spectrometry was employed to verify the glycine insertion. This mass spectrometric technique has sufficient mass accuracy to detect the methyl group that distinguishes glycine from alanine and can be extended to the more common situation in which crystallographic measurements suggest a problem with the sequence, but cannot pinpoint its location or nature.

Download Full-text

Vitamin D analyses in veterinary feeds by gas chromatography-tandem mass spectrometry

European Journal of Mass Spectrometry ◽

10.1177/14690667211000244 ◽

2021 ◽

pp. 146906672110002

Author(s):

Andreas Lehner ◽

Margaret Johnson ◽

Alan Zimmerman ◽

Justin Zyskowski ◽

John Buchweitz

Keyword(s):

Mass Spectrometry ◽

Vitamin D ◽

Gas Chromatography ◽

Liquid Chromatography ◽

Tandem Mass Spectrometry ◽

Vitamin D3 ◽

Mass Spectrometric ◽

Chromatographic Behavior ◽

Tandem Mass ◽

Chromatography Tandem Mass Spectrometry

This report examines the feasibility of determination of Vitamin D3, D2 and their 25-hydroxy metabolites utilizing Gas Chromatography Tandem Mass Spectrometry (GC/MS/MS) as a potential alternative to popular Liquid Chromatography Tandem Mass Spectrometric (LC/MS/MS) methodologies. The GC/MS/MS approach was found to operate reasonably well despite long-standing concerns that gas-liquid chromatography of vitamin D compounds invoke thermal rearrangements owing to the relatively high inlet and capillary column temperatures used. The workup procedure involved incubation of feed samples with concentrated potassium hydroxide for overnight fat saponification, extraction of D Vitamins in n-hexane and reaction with N,O-bis(trimethylsilyl)trifluoroacetamide at 70 °C for 30 mins. In addition to parent compounds, small amounts of pyro-, isopyro-, and iso-vitamin D and isotachysterol3 variants were obtained from each Vitamin D-related compound upon extraction and GC/MS/MS analysis. Mass spectral and chromatographic behavior of these compounds are herein described and interpreted. Multiple Reaction Monitoring settings on GC/MS/MS included m/z 456→351 for Vitamin D3 and m/z 486→363 for Vitamin D2. Trimethylsilylation enabled single predominant peaks for Vitamins D3 and D2, and sample workup in the presence of deuterated Vitamin D analogs enabled accurate and precise sensitivity to 1 ppb (ng/g) in feeds. The method could be extended with reasonable accuracy to 25-hydroxy (25OH) compounds, but accuracies would be significantly improved by inclusion of respective 25OH-specific deuterated internal standards. The method was applied to 27 submissions of suspect dog foods of which 22% were discovered elevated and 44% were discovered to contain toxic levels of Vitamin D3. The described method was thus discovered to provide a suitable mass spectrometric approach for Vitamin D, proving itself here specifically of value in detection of ergocalciferol and cholecalciferol in animal feeds. The specificity and sensitivity of the tandem quadrupole approach can enable suitable applicability to serum determination if desired.

Download Full-text