The determination of ring junction stereochemistry in steroids using mass-analysed ion kinetic energy spectrometry

The unimolecular mass-analysed ion kinetic energy (MIKE) spectra of 9 pairs of hydrocarbon and ketone steroid isomers, differing only in the stereochemistry at the A/B and C/D ring junctions, have been measured and are discussed with a view to unambiguous structural identification. Reproducible differences in the MIKE spectra are observed, which are large enough in certain instances to suggest that MIKE spectrometry may be used for determining the stereochemistry of the A/B and C/D ring junctions in steroidal isomers, even if the second isomer is not available. This fortunate situation is rarely observed in conventional mass spectrometry of stereoisomeric steroids. Furthermore, these differences in the MIKE spectra may be correlated with differences in strain energy between configurational isomers. The sensitivity of MIKE spectrometry to differences in strain energies makes it a potentially powerful stereochemical probe.     

Characterization and differentiation of heterocyclic isomers. tandem mass spectrometry and molecular orbital calculations on 3-methylisoxazolo- and 2-methyloxazolopyridines

Metastable mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation MIKE spectrometries have been applied to the study of all members of two classes of heteroaromatic isomers: 3-methylisoxazolo-and 2-methyloxazolopyridines. The study revealed that tandem mass spectrometry can characterize and differentiate the isomeric ion structures produced by these heterocycles. In particular, the MIKE spectra of both the molecular ions and abundant fragments formed by CO and CH₃CN losses show characteristic differences that allow distinction among the isomers dependent on the position of the nitrogen atom in the pyridine ring, and distinction of isoxazole derivatives from oxazoles. The results indicate that the isomerization of the isoxazole moiety to oxazole-proposed for other analogous compounds—does not occur in these heterocyclic systems. The experimental work is supported by molecular orbital calculations both on neutral molecules and on molecular and fragment ions.     

Ferrocene compounds: XVI. Mass-analyzed ion kinetic energy (MIKE) spectra of some monosubstituted ferrocene derivatives

The mass-analyzed ion kinetic energy (MIKE) spectra of some monosubstituted ferrocenes having an unsaturated moiety in the α- or β-position to the cyclopentadienyl ring and β-phenyl-γ-ferrocenoylbutyric acid are presented and discussed.     

Nachweis von Fragment-Genesen im Massenspektrometer. 5. Mitteilung Aminosäure-Sequenzanalyse: Vergleich der DADI/MIKE-, ‘linked scan’- und Kollisionsaktivierungs-Spektrometrie an aliphatischen Aminosäuren

Detection of Fragment Genesis in the Mass Spectrometer. V. Amino Acid Sequence Analysis by DADI/MIKE, Linked Scan and Collisional Activation Mass Spectrometry. Aliphatic Amino Acids The amino acid sequence in tripeptides and tetrapeptides has been analyzed by DADI/MIKE and B/E-‘linked scan’ spectrometry, as well as by collisional activation in the first and second field free region of a mass spectrometer embodying the inverse Nier-Johnson geometry. Collisional activation enhances the intensity of fragment ions.     

Influence of instrumental parameters and sample preparation on mass-analysed ion kinetic energy spectra with fast atom bombardment exemplified with the oxonium ion of peracetylated ribopyranose

When mass-analysed ion kinetic energy (MIKE) spectra are required to discriminate between isomeric ions formed under conditons of fast atom bombardment (FAB) in the ion source, severe interference may be observed. The interfering peaks in MIKE spectra obtained with a reversed-geometry instrument can arise from different sources. Moreover, the intensity distribution of the true ions from the selected precursor ion may depend strongly on the instrument being used. This means that the FAB–MIKE or collisionally induced dissociation (CID) spectrum is not an absolute characteristic of a particular ion. The [M + H ? HOAc]⁺ ion in the spectrum of peracetylated ribopyranose is used as an example to illustrate this and to trace and discuss the origin of the phenomena observed.     

Negative-ion mass spectrometry of substituted adenine bases and adenosine nucleosides

The negative-ion chemical ionization (ammonia, 5 Pa source pressure) mass spectra of a series of substituted adenine bases, adenosine nucleosides, and the trimethylsilyl derivatives of the nucleosides are described. Selected ions from these spectra were subject to collisionally activated dissociation with mass-analysed ion kinetic energy (CAD/MIKE) analysis of the products and the spectra assessed for information content. In addition to observing strong peaks due to quasimolecular ions and heterocyclic-base ions, it proved possible to differentiate between 2'-, 3'- and 5'-deoxy and between 2'- and 3'-O-methyl isomers. The negative-ion chemical ionization spectra of four methyladenines are essentially identical, but could be clearly distinguished from each other by CAD/MIKE analysis.     

Unimolecular metastable decompositions of gem-dimethoxyalkanes (RR'C(OCH(3))(2)) upon electron impact. I. Dimethoxymethane and 1, 1-dimethoxyethane

The unimolecular metastable decompositions of dimethoxymethane (CH(2)(OCH(3))(2), 1) and 1,1-dimethoxyethane (CH(3)CH(OCH(3))(2), 2) upon electron impact have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry, collision-induced dissociation (CID) spectrometry and D-labeling techniques. Both molecular ions are formed at extremely low abundance. Sequential transfers of a methyl group and a hydrogen atom to an ether oxygen are observed during the decomposition of [M - H](+) ions from 1 and 2. The [M - H](+) ion from 2 also decomposes into the m/z 43 ion by the loss of dimethyl ether. Almost complete hydrogen exchange is observed prior to the loss of CH(4) from the m/z 45 ion ([M - OCH(3)](+)) of 1. The m/z 59 ions ([M - OCH(3)](+)) of 2 decompose competitively into the m/z 31 and 29 ions by the losses of C(2)H(4) and CH(2)O, respectively. The former loss occurs via two different fragmentation pathways. The relative abundances of the ions in the MIKE spectra increase with decreases in the total heat of formation (Sigma DeltaH(f)) of the ion plus the neutral fragment. Copyright 2000 John Wiley & Sons, Ltd.     

Analysis of tetrabenzyl N-giucosidic,N-mannosidic and N-galactosidic Isomers using fast atom bombardment/mass-analysed ion kinetic energy spectrometry

A series of new synthetic tetrabenzyl N-glucosidic, N-mannosidic and N-galactosidic isomers were investigated by fast atom bombardment (FAB)/mass-analysed ion kinetic energy (MIKE) spectrometry. The [M + H]⁺ ions were obtained with high abundance in the FAB spectra when using 3-nitrobenzyl alcohol as the matrix. The FAB/MIKE spectra provide characteristic daughter ions fragmented from selected molecular parent ions, allowing these isomers to be differentiated. In addition, an interesting rearrangement was found from the MIKE spectra, indicating that the benzyl (Bzl) group on the sugar ring is rearranged on to the N atom of the base (R) group to form [R + Bzl + H]⁺ and [R+ 2Bzl]⁺ ions.     

Translational energy release and stereochemistry of steroids. XI—Determination of the configuration of α,β-unsaturated 3-keto steroid alcohols with the hydroxyl group in rings C and D

The elimination of water from metastable molecular ions of epimeric hydroxy steroids of the Δ⁴-3-keto series containing a hydroxyl group in the conformationally rigid rings C and D has been studied. The measurement of translational energy released during the loss of water and collision-induced decomposition (CID) mass-analysed ion kinetic energy (MIKE) spectrometry were the techniques used. It was found that it is possible to determine the configuration of the hydroxy steroids of this series on the basis of the CID MIKE spectra of [M ? H₂O]^+˙ ions formed by dehydration of metastable molecular ions in the first field-free region of a reversed geometry double-focusing mass spectrometer.     

Benzyl ions from 1,1-(2,2'-dimethoxyphenyl)-substituted 2-methylpropanes under electron ionization

The electron ionization (EI)-induced fragmentations of a series of 1,1-(2,2'-dimethoxyphenyl)-substituted 2-methylpropanes (1-20) in both 70 eV and mass-analyzed ion kinetic energy (MIKE) spectra have been investigated. The EI-MS spectra of these compounds are characterized by the presence of abundant benzyl ions. These ions result from competitive hydrogen migration from the 2- and 2'-methoxy groups on the carbenium center of the diphenylmethyl cations formed by benzylic cleavage of the molecular ions. The relative abundances of the benzyl ions arising from such competitive processes are discussed and rationalized. The steric effect of the 3- or 3'-substituents is the main discriminating factor between the two competitive processes. The structural information, arising either from the 70 eV or the MIKE spectra, is discussed.     

Differentiation of anomeric C-glycosides by mass spectrometry using fast atom bombardment,mass-analysed ion kinetic energy and collision-activated dissociation

Positive-ion fast atom bombardment mass spectrometry appears to be a useful method for the differentiation of anomeric C-glycosides. The mass-analysed ion kinetic energy (MIKE) and collision-activated dissociation (CAD) MIKE spectra of selected positive ions can be used as fingerprints of the α- or β-anomers. The main fragmentation routes and particularly the formation of the [M ? H]⁺ ion and the [M + H ? PhCH₂OH]⁺ ion were traced for each anomer.     

Quantitation by fast-atom bombardment/mass-analysed ion kinetic energy spectrometry: kinetic analysis of cyclic nucleotide phosphodiesterase activity

Quantitation of cyclic nucleotide phosphodiesterase activity by means of fast-atom bombardment (FAB) mass spectrometry with mass-analysed ion kinetic energy (MIKE) spectrum scanning is described. Characteristic peaks of the substrate, cyclic AMP, and product, AMP, were identified in positive-ion FAB mass spectra and MIKE scans of the protonated molecules. By spiking enzyme incubates with known quantities of cyclic AMP and AMP and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the concentrations of cyclic AMP and AMP in solution at the end of a series of enzyme incubations have been estimated. From the data obtained the Km and Vmax of the enzymes were calculated as 181 microM and 28.6 nmol/min respectively, showing excellent agreement with values of the Michaelis constant, Km = 205 microM and the maximum velocity Vmax = 33.2 nmol/min obtained by radioactive assay.     

Application of Mass Spectrometry/Mass Spectrometry (MS/MS) to the Identification of Natural Products in Psilocybe Cyanescens

Abstract

Temperature profiling of MIKE spectra allows identification of protonated psilocin in the presence of other compounds with the same mass. The use of multiple ionizing methods to give ions (M+H)⁺, (M+ML₄)⁺, and M is shown to assist in determining the molecular weights of new natural products. Structural information is obtained from the MIKE spectra. All these determinations can be made on the intact mushroom or its simple alcoholic extracts.     

Fragmentation pathways of isomeric dodecenols studied by electron impact mass spectrometry

Electron impact-induced fragmentations of isomeric dodecen-1-ols were investigated using mass-analysed ion kinetic energy (MIKE) spectrometry and high-resolution data. The principal fragmentation pathways of the positional isomers studied are dominated by the C?C double bond and involve migration and radical-site rearrangements along the carbon chain with the aid of consecutive rearrangements of hydrogen atoms.     

N,O-heterocyclics. 13. Isoxazolidinium salts as synthons to N,N, O-trisubstituted hydroxylamines

Substituted isoxazolidinium salts react with lithium aluminium hydride to yield open-ring products which have hydroxylamine structures. The bimolecular reaction-mechanism has been investigated by substituent effect and the structure of the products ascertained by spectroscopic methods with the aid of the MIKE technique. The overall process of the ring-opening substitution is controlled by the polarisation of the C? N bond with steric and conformational factors acting mainly at the C-5 position of the nucleus. The mechanism of isoxazolidinium ion reaction defines the use of these synthons towards the synthesis of N,N,O-trisubstituted hydroxylamines and substituted 1,3-amino-alcohols.     

Fragmentation and rearrangement patterns of phospho-ureas. Possible consequences for biotin activation

Analysis by electron impact and metastable ions (MIKE technique) of the fragmentation patterns for one acyclic and two cyclic N-phosphorylated ureas reveals for the first case an isomerization from nitrogen to the ureido oxygen atom of the phosphoryl group and subsequent fragmentation. For the other two cases, fragments result from P? N bond breaking and ring-opening. Possible involvement in the biotin-ATP activation process is discussed.     

Mass-analysed ion kinetic energy and collisionally induced dissociation mass spectra of clusters of acetylated xylo-oligosaecharides with protonated ammonia and methylannine

Per-O-acetylated methyl glycosides of D -xylan-type di- and trisaccharides were studied by mass-analysed ion kinetic energy (MIKE) and collisionally induced dissociation (CID) mass Spectrometry using protonated ammonia and methylamine, respectively, as reaction gases in chemical ionization (CI). The oligosaccharides form abundant cluster ions, [M + NH₄]⁺ or [M + CH₃NH₃]⁺, and the main fragmentation of these ions in the MIKE and CID spectra is the cleavage of interglycosidic linkages. Thus, CI (NH₃) or CI (CH₃NH₂) spectra in combination with the MIKE or CID spectra allow the molecular masses, the masses of monosaccharide units and the branching point in oligosaccharides to be established. In the case of disaccharides, it is possible to distinguish the (1 → 2) linkage from the other types of linkages.     

Collision-Induced decomposition of peptides. An investigation into the effect of collision gas pressure on translational energy losses

The dependence on the gas pressure of translational energy losses, ΔE, suffered by incident ions in collision with helium target gas atoms was investigated for the [M + Na]⁺ ion of valinomycin. ΔE was measured from the fragment ion peak positions in the mass-analysed ion kinetic energy (MIKE) spectra. The variation of ΔE with target gas pressure was found to be different for different fragment ions. The implications of the results for the number of collisions which may occur under normal collision-induced decomposition conditions (30–40% transmission) are discussed.     

Mass spectrometric study of the formaldehyde and hydroxymethylene dications

The hydroxymethylene dication HCOH²⁺ is shown to the stable in the gas phase, while the isomeric formaldehyde dication is not. The energetics of formation and decomposition of the former is determined from MIKE (mass-analyzed ion kinetic energy) experiments. The experimental findings are shown to be in pleasing agreement with results from ab initio molecular orbital calculations.     

Direct analysis of mixtures by double quadrupole mass spectrometry

The double quadrupole mass spectrometer is shown to be applicable to differentiation of isomeric C₅ ketones and for the detection of camphor in a drug and a cosmetic. Detection limits in the picogram range are demonstrated. The similarity between the low-energy QQ collision-induced dissociations and those of high-energy MIKE spectrometry facilitates use of both techniques for mass spectrometry/mass spectrometry.