Negative-ion electrospray ionization tandem mass spectrometry of N-phosphoryl amino acids and dipeptides

The negative-ions of N-phosphoryl amino acids were studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The negative-ion ESI-MS/MS of N-phosphoryl amino acids showed characteristic fragmentation patterns different from those observed in the corresponding positive-ion ESI-MS/MS and negative-ion fast-atom bombardment mass spectra. For negative-ion ESI-MS/MS, a unique fragmentation from the N-terminal of N-phosphoryl amino acids or peptides containing a free beta-OH or CO(2)H group was observed to yield the characteristic fragment ion (RO)(2)P(O)O(-). The ease of the rearrangement depended on the position of the hydroxyl group in amino acids or peptides, and the N --> O rearrangement mechanism was proposed to involve the participation of the hydroxyl group. From previous solution-phase experiments and theoretical calculations, it was found that the beta-OH group was more active than gamma-OH, and the corresponding difference in negative-ion ESI-MS/MS was consistent with those previous findings.     

Skeletal Wagner-Meerwein rearrangement of perhydro-3a,6;4,5-diepoxyisoindoles

An investigation of a skeletal Wagner-Meerwein rearrangement of variously substituted or quinoline-annulated 3a,6;4,5-diepoxyisoindol-1-ones is reported. Optimum reaction conditions (Ac₂O, BF₃·OEt₂, rt) were discovered for the formation of the target 4,6-epoxycyclopenta[c]pyridines in 40-80% yields. It was shown that the direction of the sigmatropic rearrangement of 3a,6;4,5-diepoxyisoindol-1-ones depended dramatically on the carboxyl group position (exo-/endo-) in the oxabicyclo[2.2.1]heptane moiety. The spatial structure of previously unknown 7,9-epoxycyclopenta[4,5]pyrido[1,2-a]quinolines derived from Wagner-Meerwein rearrangement of 2,11b-epoxyoxireno[6,7]isoindolo[2,1-a]quinolines was established based on the X-ray analysis data. The skeletal rearrangement proceeded regio- and stereospecifically in all the cases examined due to the absence of the epimerization of the carbon atoms adjacent to the carbocation centres.     

Applications of LC/ESI-MS/MS and UHPLC QqTOF MS for the determination of 148 pesticides in fruits and vegetables

This paper presented the applications of liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) and ultra-high-pressure liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC QqTOF MS) for the determination of 148 pesticides in fruits and vegetables. Pesticides were extracted from fruits and vegetables using a buffered QuEChERS method. Quantification was achieved using matrix-matched standard calibration curves with isotopically labeled standards or a chemical analog as internal standards in an analytical range from 5 to 500 μg/kg. The method performance parameters including overall recovery, intermediate precision, and measurement uncertainty were evaluated according to a statistically designed experiment, i.e., a nested design. For LC/ESI-MS/MS, 95% of the pesticides had recoveries between 81% and 110%; 97% had an intermediate precision ≤20%; and 95% (in fruits) or 93% (in vegetables) showed measurement uncertainty ≤40%. Compared to LC/ESI-MS/MS, UHPLC QqTOF MS showed a relatively poor repeatability and large measurement uncertainty. About 93% (in fruits) or 94% (in vegetables) of the pesticides had recoveries between 81% and 110%; 86% (in fruits) or 90% (in vegetables) had an intermediate precision ≤20%; and 79% (in fruits) or 88% (in vegetables) showed measurement uncertainty ≤40%. LC/ESI-MS/MS proved to be the first choice for quantification or pre-target analysis due to its superior sensitivity and good repeatability. UHPLC QqTOF MS provided accurate mass measurement and isotopic patterns, and was an ideal tool for post-target screening and confirmation.     

Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides

The fragmentation characteristics of peptides derivatized at the side-chain ε-amino group of lysyl residues via reductive amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic cleavage of the C_ζ-N_ε bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative as a benzylic or tropylium carbocation and a (n − l)⁺-charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway increases with increasing charge of the precursor ion. For the benzylmodified tryptic peptides analyzed in this study, peaks representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed reaction contingent upon protonation of the secondary ε-amino group of the benzyl-derivatized lysyl side chain. If the secondary ε-amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary ε-amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective control over the relative abundance of product ions generated from the two pathways.     

A Novel Stereoselective Reaction Cascade Leading from α-Silylated Allylic Alcohols to Aldol-Type Products

The treatment of α-silylated allylic alcohols with epoxidizing reagents afforded in a highly stereocontrolled fashion α-silylated aldols. The transformation is proposed to proceed either by a reaction cascade involving stereospecific epoxidation of the allylic-alcohol moiety followed by an acid-supported pinacol-type rearrangement, or by a sequence consisting of a π-face-selective electrophilic attack at the allylic silane moiety with hyperconjugative stabilization of the evolving carbocation, followed by rearrangement of the thus obtained pentacoordinated silanium ion (see Scheme 3). Depending on the reaction conditions, the π-face selectivity of the oxidation step is controlled by the stereogenic C-atom or the more remote Si-center of chirality.     

Studies on CH3CN-assisted decomposition of 1st Grubbs catalyst by electrospray ionization tandem mass spectrometry

The CH(3)CN-assisted decomposition reaction of the 1(st) Grubbs catalyst (1) was studied using electrospray ionization tandem mass spectrometry (ESI-MS/MS). We detected a series of Ru-intermediates and decomposition products by off-line and on-line ESI-MS(/MS) monitoring of the decomposition process. In particular, an on-line microreactor method was applied with ESI-MS/MS to profile the change and relationship of various Ru-intermediates by controlling the reaction within the first 30 s of its time scale. The main fast decomposition mechanism of Ru-catalyst 1 in the presence of CH(3)CN was similar to that proposed by Grubbs, and this was confirmed by detecting the (PhCH(2)PCy(3))(+) ion at m/z 371 as the major decomposition products with ESI-MS. We also studied the time evolution of the transient reactive Ru-intermediate ions step by step with ESI-MS/MS and detected the C-H bond activation products of toluene--dehydrogenated PCy(3), such as P(Cy)(2)(C(6)H(9)), P(Cy)(2)Ph--by analyzing the decomposition reaction solution by gas chromatography (GC)/MS. The mechanism of another minor decomposition pathway involving the phosphine activation of catalyst 1 was proposed on the basis of the ESI-MS(/MS) interception and characterization of the transient reactive Ru-species in the decomposition reaction solution. Finally the coordination effect of the CH(3)CN in assisting the decomposition and stabilizing the transient Ru-complexes is discussed.     

Characterization of electrospray ionization mass spectrometry for N-diisopropyloxyphosphoryl dipeptide methyl esters

A systematic study of the fragmentation pattern of N-diisopropyloxyphosphoryl (DIPP) dipeptide methyl esters in an electrospray ionization (ESI) tandem mass spectrometry (MS/MS) was presented. A combination of accurate mass measurement and tandem mass spectrometry had been used to characterize the major fragment ions observed in the ESI mass spectrum. It was found that the alkali metal ions acted as a fixed charge site and expelled the DIPP group after transferring a proton to the amide nitrogen. For all the N-phosphoryl dipeptide methyl esters, under the activation of a metal ion, the rearrangement product ion at m/z 163 was observed and confirmed to be the sodium adduct of phosphoric acid mono-isopropyl esters (PAIE), via a specific five-membered penta-co-ordinated phosphorus intermediate. However, no rearrangement ion was observed when a beta-amino acid was at the N-terminal. This could be used to develop a novel method for differentiating isomeric compounds when either alpha- or beta-amino acid are at the N-terminus of peptides. From the [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters (DIPP Xaa1 Xaa2 OMe), the peaks corresponding to the [M+Na Xaa1 C3H6]+ were observed and explained. The [M+Na]+ ESI-MS/MS spectra of N-phosphoryl dipeptide methyl esters with Phe located in the C-terminal, such as DIPPValPheOMe, DIPPLeuPheOMe, DIPPIlePheOMe, DIPPAlaPheOMe and DIPPPhePheOMe, had characteristic fragmentation. Two unusual gas-phase intramolecular rearrangement mechanisms were first proposed for this fragmentation. These rearrangements were not observed in dipeptide methyl ester analogs which did not contain the DIPP at the N-terminal, suggesting that this moiety was critical for the rearrangement.     

Coumarin Photocaging Groups Modified with an Electron‐Rich Styryl Moiety at the 3‐Position: Long‐Wavelength Excitation,Rapid Photolysis,and Photobleaching

A new class of coumarin photocaging groups modified with an electron‐rich styryl moiety at the 3‐position was constructed. The large π‐conjugated structure and stabilization of the carbocation intermediates by electron donors endowed the new photocaging groups with excellent long‐wavelength absorption, large two‐photon absorption cross‐sections, and high uncaging quantum yields. Moreover, the new photocaging groups displayed unique photobleaching properties after photocleavage as a result of the intramolecular cyclization rearrangement of a carbocation intermediate to form five‐membered ring byproducts and block the styryl conjugation at the 3‐position. These superior properties of the new photocaging groups are extremely beneficial for high‐concentration samples and thick specimens, thus extending the application of photocaging groups in many fields.     

Coumarin Photocaging Groups Modified with an Electron‐Rich Styryl Moiety at the 3‐Position: Long‐Wavelength Excitation,Rapid Photolysis,and Photobleaching

A new class of coumarin photocaging groups modified with an electron‐rich styryl moiety at the 3‐position was constructed. The large π‐conjugated structure and stabilization of the carbocation intermediates by electron donors endowed the new photocaging groups with excellent long‐wavelength absorption, large two‐photon absorption cross‐sections, and high uncaging quantum yields. Moreover, the new photocaging groups displayed unique photobleaching properties after photocleavage as a result of the intramolecular cyclization rearrangement of a carbocation intermediate to form five‐membered ring byproducts and block the styryl conjugation at the 3‐position. These superior properties of the new photocaging groups are extremely beneficial for high‐concentration samples and thick specimens, thus extending the application of photocaging groups in many fields.     

Gas Phase Decarbonylation and Cyclization Reactions of Protonated N-Methyl-N-Phenylmethacrylamide and Its Derivatives Via an Amide Claisen Rearrangement

Gas phase decarbonylation and cyclization reactions of protonated N-methyl-N-phenylmethacrylamide and its derivatives (M·H⁺) were studied by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). MS/MS experiments of M·H⁺ showed product ions were formed by loss of CO, which could only occur with an amide Claisen rearrangement. Mechanisms for the gas phase decarbonylation and cyclization reactions were proposed based on the accurate m/z measurements and MS/MS experiments with deuterated compounds. Theoretical computations showed the gas phase Claisen rearrangement was a major driving force for initiating gas phase decarbonylation and cyclization reactions of M·H⁺. Finally, the influence of different phenyl substituents on the gas phase Claisen rearrangement was evaluated. Electron-donating groups at the para-position of the phenyl moiety promoted the gas phase Claisen rearrangement to give a high abundance of fragment ions [M ? CO + H]⁺. By contrast, electron-withdrawing groups on the phenyl moiety retarded the Claisen rearrangement, but gave a fragment ion at m/z 175 by loss of neutral radicals of substituents on the phenyl, and a fragment ion at m/z 160 by further loss of a methyl radical.     

Differentiating alpha- and beta-aspartic acids by electrospray ionization and low-energy tandem mass spectrometry

Spectra obtained by low-energy electrospray ionization tandem mass spectrometry (ESI-MS/MS) of 34 peptides containing aspartic acids at position n were studied and unambiguously differentiated. beta-Aspartic acid yields an internal rearrangement similar to that of the C-terminal rearrangements of protonated and cationized peptides. As a result of this rearrangement, two different ions containing the N- and the C-terminal ends of the original peptide are formed, namely, the bn-1 + H2O and y"l - n + 1 - 46 ions, respectively, where e is the number of amino acid residues in the peptide. The structure suggested for the y"l - n + 1 - 46 ion is identical to that proposed for the vn ions observed upon high-energy collision-induced dissociation (CID) experiments. The intensity of these ions in the low-energy MS/MS spectra is greatly influenced by the presence and position of basic amino acids within the sequences. Peptides with a basic amino acid residue at position n - 1 with respect to the beta-aspartic acid yield very intense bn-1 + H2O ions, while the y"l - n + 1 - 46 ion was observed mostly in tryptic peptides. Comparison between the high- and low-energy MS/MS spectra of several isopeptides suggests that a metastable fragmentation process is the main contributor to this rearrangement, whereas for long peptides (40 AA) CID plays a more important role. We also found that alpha-aspartic acid containing peptides yield the normal immonium ion at 88 Da, while peptides containing beta-aspartic acid yield an ion at m/z 70, and a mechanism to explain this phenomenon is proposed. Derivatizing isopeptides to form quaternary amines, and performing MS/MS on the sodium adducts of isopeptides, both improve the relative intensity of the bn + 1 + H2O ions. Based on the above findings, it was possible to determine the isomerization sites of two aged recombinant growth proteins.     

Profiling and relative quantification of phosphatidylethanolamine based on acetone stable isotope derivatization

Phosphatidylethanolamine (PE) is considered to be one of the pivotal lipids for normal cellular function as well as disease initiation and progression. In this study, a simple, efficient, reliable, and inexpensive method for the qualitative analysis and relative quantification of PE, based on acetone stable isotope derivatization combined with double neutral loss scan-shotgun electrospray ionization tandem-quadrupole mass spectrometry analysis (ASID-DNLS-Shotgun ESI-MS/MS), was developed. The ASID method led to alkylation of the primary amino groups of PE with an isopropyl moiety. The use of acetone (d₀-acetone) and deuterium-labeled acetone (d₆-acetone) introduced a 6 Da mass shift that was ideally suited for relative quantitative analysis, and enhanced sensitivity for mass analysis. The DNLS model was introduced to simultaneously analyze the differential derivatized PEs by shotgun ESI-MS/MS with high selectivity and accuracy. The reaction specificity, labeling efficiency, and linearity of the ASID method were thoroughly evaluated in this study. Its excellent applicability was validated by qualitative and relative quantitative analysis of PE species presented in liver samples from rats fed different diets. Using the ASID-DNLS-Shotgun ESI-MS/MS method, 45 PE species from rat livers have been identified and quantified in an efficient manner. The level of total PEs tended to decrease in the livers of rats on high fat diets compared with controls. The levels of PE 32:1, 34:3, 34:2, 36:3, 36:2, 42:10, plasmalogen PE 36:1 and lyso PE 22:6 were significantly reduced, while levels of PE 36:1 and lyso PE 16:0 increased.     

Mass spectrometric identification and characterization of antimony complexes with ribose-containing biomolecules and an RNA oligomer

Mass spectrometric techniques have been used to study the interaction of inorganic Sb(V) with biomolecules containing a ribose or deoxyribose moiety. Electrospray (ES) mass spectra of reaction mixtures containing inorganic Sb(V) and one of several biomolecules (adenosine, cytidine, guanosine, uridine, adenosine-5′-monophosphate, adenosine-3′,5′-cyclic monophosphate, ribose, or 2′-deoxyadenosine) afforded high-mass antimony-containing ions corresponding to Sb(V)–biomolecule complexes of stoichiometry 1:1, 1:2, or 1:3. The complexes were characterized by collision-induced dissociation (CID) tandem mass spectrometry (MS) using ion-trap multistage MS. The CID results revealed that Sb(V) binds to the ribose or deoxyribose moiety. Structures are proposed for the Sb–biomolecule complexes. Analysis of the reaction mixtures by reversed-phase chromatography coupled on-line to either inductively coupled plasma (ICP) MS or ES–MS showed that in solution Sb(V) forms complexes with all the analyzed biomolecules with vicinal cis hydroxyl groups. Evidence (from size-exclusion chromatography ICP–MS and direct infusion ES–MS) of complexation of Sb(V) with an RNA oligomer, but not with a DNA oligomer, supports the suggestion that the presence of vicinal cis hydroxyl groups is critical for complexation to occur. This is the first direct evidence of complexation of Sb(V) with RNA. Results obtained by studying the effect of changing reaction conditions, i.e. pH, reaction time, and Sb/biomolecule molar ratio, on the extent of Sb–biomolecule formation suggest the reaction may be of physiological importance. Selected reaction monitoring (SRM) and precursor-ion-scanning tandem MS were investigated to determine their potential to detect trace levels of the Sb–biomolecule complexes in biological samples. Application of SRM MS–MS in combination with high-performance liquid chromatography enabled successful detection of an Sb–adenosine complex that had been spiked into a complex biological matrix (liver homogenate).Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Confirmation of the structure of lipid A from Enterobacter agglomerans by electrospray ionization tandem mass spectrometry

Electrospray ionization (ESI) combined with tandem mass spectrometry (MS/MS) was utilized for the structural confirmation of lipid A derived from Enterobacter agglomerans, a Gram-negative bacterium commonly found in field cotton. Previous ESI-MS studies conducted in our laboratory found that similarities exist between the fatty acid side-chains in the lipid A of E. agglomerans and that of Salmonella minnesota. It was noted that heterogeneity at the fatty acyl chain at position 3' of the diglucosamine backbone of E. agglomerans can take the form of either a myristyloxymyristyl group or, less commonly, a hydroxymyristyloxymyristyl moiety. In this work, tandem mass spectra obtained from heptaacyl and hexaacyl lipid A precursors derived from E. agglomerans and a known standard S. minnesota were compared to assist in structural elucidation. These ESI-MS/MS experiments confirmed the previously reported structure for lipid A derived from E. agglomerans. Moreover, MS/MS data indicated that the additional hydroxyl group of the 3'-position hydroxymyristyloxymyristyl moiety is present as the alpha-isomer.     

The early glycation products of the Maillard reaction: mass spectrometric characterization of novel imidazolidinones derived from an opioid pentapeptide and glucose

Glucose-substituted imidazolidinones related to the endogenous opioid peptide leucine-enkephalin have been investigated using fast atom bombardment tandem mass spectrometry (FAB-MS/MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). In addition to Amadori compounds, the studied imidazolidinones represent a novel type of the early glycation products formed in the Maillard reaction. To obtain insight into the fragmentation behavior of these carbohydrate-peptide adducts, we also studied synthetic precursors of the glucose-substituted imidazolidinones as well as the corresponding isopropylidene derivatives. The collision-induced dissociation (CID) spectra of [M + H](+) ions of all these imidazolidinones have been compared. Detailed analysis showed that fragmentation of each compound generates two ions at m/z 566 and m/z 598 which are characteristic and undoubtedly confirm the imidazolidinone-type structure. These two significant ions were identified as the M + 10 and M + 42 modifications of the N-terminus of the parent opioid pentapeptide effected by the carbohydrate moiety. Furthermore, the ion at m/z 178 is identified as the M + 42 modification of the immonium ion of the N-terminal amino acid (tyrosine) also effected by the carbohydrate moiety. They can be used as diagnostic ions for imidazolidinone-type compounds in studying the Maillard reaction. Thus, we have demonstrated the utility of FAB-MS/MS and ESI-MS/MS in the structural determination and identification of such novel peptide-carbohydrate adducts, useful in understanding the details of the mechanism of non-enzymatic glycation in vivo.     

Functionalization of polyisobutylene and polyisobutylene oligomers via the ritter reaction

The Ritter reaction, that is, reaction of a carbocation with a nitrile, was carried out on polyisobutylene (PIB) using a variety of reaction conditions. End quenching of PIB carbocations with acrylonitrile under living polymerization conditions (methyl chloride (MeCl)/hexane 60/40 (v/v) solvent mixtures at −70 °C) resulted in either tert‐chloride end groups or loss of chain‐end fidelity via carbocation rearrangement, as evidenced by NMR spectroscopy. Exo‐olefin functionalized PIB substrates were also reacted with nitriles under a variety of reaction conditions including various acid and solvent medium combinations. In all cases, the result was either no reaction or PIB that had undergone severe backbone degradation, as determined via NMR spectroscopy and gel permeation chromatography. Finally, the Ritter reaction was performed on a series of exo‐olefin functionalized oligoisobutylenes using acrylonitrile as the nitrile and either 60/40 dichloromethane/hexane or excess acrylonitrile as the solvent. In 60/40 dichloromethane/hexane, significant carbocation rearrangement and/or degradation resulted in a variety of isomeric, acrylamide‐functionalized oligomers. In excess acrylonitrile, the desired Ritter reaction was the only reaction observed, resulting in the smooth formation of the terminal acrylamide. The various N‐oligoisobutylacrylamides thus obtained represent new hydrophobic monomers useful for the introduction of hydrophobic moieties into acrylamide‐based water‐soluble polymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 840–852     

DFT (density functional theory) studies on cycloisomerization of 15–membered triazatriacetylenic macrocycle

The mechanism as well the stereochemistry of cascade cycloisomerization of 15–membered triazatriacetylenic macrocycle was investigated theoretically by using M062X/6–31+G(d,p) and M062X/LANL2DZ calculations. The results showed that the mechanism and outcome of the reaction depended on the absence and presence of a transition metal catalyst. So that, in thermal-induced condition, the reaction had to experience several suprafacial concerted reactions including Ene-reaction (DG^#=35.38 kcal/mol), Diels–Alder cycloaddition (DG^# = 17.16 kcal/mol), and sigmatropic H-shift rearrangement (DG^# = 56.21 kcal/mol) to produce diastereoselective fused cis–tetracyclic aromatic bearing a pyrrole moiety by following kinetic considerations. Also, the [2+2+2] cycloaddition mechanism was neglected in thermal–induced conditions because of high activation free Gibbs energy (DG^# = 63.90 kcal/mol). In the presence of palladium catalyst, Pd(0) formed an adduct by coordinating to C = C bonds and decreased the DG^# of the process to 29.58 kcal/mol, and consequently provided a facilitated media for the reaction to follow the [2+2+2] to produce more stable fused tetracyclic benzenoid aromatic by passing through the lower energy barrier.     

Mechanism for selective <Emphasis Type="Italic">para</Emphasis>-disproportionation of toluene on pentasil-based catalysts

We propose a bimolecular mechanism for disproportionation of toluene to form benzene and para-xylene via protonation of the toluene molecule at the methyl group, reaction of the carbocation formed with the para position of the next toluene molecule, and α-scission of the complex obtained. The mechanism presumes formation of methyl diphenyl methane as a byproduct of disproportionation.     

Electrospray tandem mass spectrometric analysis of novel synthetic quinoxalinone derivatives

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) using a hybrid QqToF-MS/MS instrument has aided the structural characterization and differentiation of a novel series of medicinal synthetic 1-N-glycoside-quinoxalinone derivatives. These derivatives 7 and 8 are formed by an amino bond between the cyclic N-1 of the quinoxaline moiety and the C-6 position of a fully protected methyl or allyl alpha-D-mannofuranoside 3 and 4, and subsequent deprotection of the mannopyranoside moiety. In general the novel synthetic quinoxaline derivatives afforded the protonated molecules in ESI. The breakdown routes of the protonated molecules were rationalized by conducting low-energy CID-MS/MS analyses. In addition, re-confirmation of the various established fragmentation routes was achieved by conducting a series of ESI-CID-QqTof-MS/MS product ion scans on various selected precursor ions, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. ESI-QqToF-MS/MS analysis has proven to be a specific and very sensitive method for the structural identification in the gas phase of these novel glycoquinoxalinamine derivatives.