两类三组份反应产物：1,3-恶嗪及嘧啶-2-酮类化合物的质谱学行为研究

电喷雾质谱被应用于分辨2-氨基-1,3-恶嗪及六氢化-4-苯基-吡喃[2,3-d]嘧啶-2-酮的杂环结构。两类化合物均为三组份反应的产物,且其杂环的结构很难用NMR判断。实验首次系统研究了两类化合物的质谱学行为（包括氘代实验和高分辨质谱研究）,发现前者在CID实验中丢失CH2N2和HCNO,而后者为直接丢失尿素。这些特征丢失为该类衍生物的结构判断,尤其是高通量的合成产物分析提供了重要的依据。     

Pharmaceutical metabolite profiling using quadrupole/ion mobility spectrometry/time‐of‐flight mass spectrometry

The use of hybrid quadrupole ion mobility spectrometry time‐of‐flight mass spectrometry (Q/IMS/TOFMS) in the metabolite profiling of leflunomide (LEF) and acetaminophen (APAP) is presented. The IMS drift times (T_d) of the drugs and their metabolites were determined in the IMS/TOFMS experiments and correlated with their exact monoisotopic masses and other in silico generated structural properties, such as connolly molecular area (CMA), connolly solvent‐excluded volume (CSEV), principal moments of inertia along the X, Y and Z Cartesian coordinates (MI‐X, MI‐Y and MI‐Z), inverse mobility and collision cross‐section (CCS). The correlation of T_d with these parameters is presented and discussed. IMS/TOF tandem mass spectrometry experiments (MS² and MS³) were successfully performed on the N‐acetyl‐p‐benzoquinoneimine glutathione (NAPQI‐GSH) adduct derived from the in vitro microsomal metabolism of APAP. As comparison, similar experiments were also performed using hybrid triple quadrupole linear ion trap mass spectrometry (QTRAPMS) and quadrupole time‐of‐flight mass spectrometry (QTOFMS). The abilities to resolve the product ions of the metabolite within the drift tube and fragment the ion mobility resolved product ions in the transfer travelling wave‐enabled stacked ring ion guide (TWIG) demonstrated the potential applicability of the Q/IMS/TOFMS technique in pharmaceutical metabolite profiling. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of active naphtodianthrone St John's Wort compounds by electrospray ionization Fourier transform ion cyclotron resonance and multi‐stage mass spectrometry in sustained off‐resonance irradiation collision‐induced dissociation and infrared multiphoton dissociation modes

Five well‐known active naphtodianthrone constituents of Hypericum perforatum (St John's Wort) extracts have been investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICRMS) and ESI‐FTICRMSⁿ. The studied compounds were hypericin, pseudohypericin, protohypericin, protopseudohypericin (biosynthetic precursors of the two former compounds, respectively) and isopseudohypericin (alkaline degradation product of pseudohypericin). Dissociation mass spectrometry measurements performed on the [M–H]^? ion presented a variable efficiency as a function of the used activation mode. Sustained off‐resonance irradiation collision‐induced dissociation (SORI–CID) only led to a restricted number of fragment ions. In contrast, IRMPD ensured the detection of numerous product ions. Ions detected in ESI‐FTICRMS and ESI‐FTICRMSⁿ experiments were measured with a very high mass accuracy (typically mass error is lower than 0.5 mDa at m/z close to 500) that allowed unambiguous formulae to be assigned to each signal observed in a mass spectrum. In spite of similar structures, specific fragmentation patterns were observed for the different compounds investigated. This study may be useful in the future to characterize in natural extracts these compounds (or derivatives of these compounds) by liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments by considering the MS/MS transitions highlighted in this paper. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of Some New 2‐Oxo‐N‐[(10H‐phenothiazin‐10‐yl)alkyl] Derivatives of Azetidine‐1‐carboxamides

The synthesis of a new series of 4‐aryl‐3‐chloro‐2‐oxo‐N‐[3‐(10H‐phenothiazin‐10‐yl)propyl]azetidine‐1‐carboxamides, 4a – 4m , is described. Phenothiazine on reaction with Cl(CH₂)₃Br at room temperature gave 10‐(3‐chloropropyl)‐10H‐phenothiazine ( 1 ), and the latter reacted with urea to yield 1‐[3‐(10H‐phenothiazin‐10‐yl)propyl]urea ( 2 ). Further reaction of 2 with several substituted aromatic aldehydes led to N‐(arylmethylidene)‐N′‐[3‐(phenothiazin‐10‐yl)propyl]ureas 3a – 3m , which, on treatment with ClCH₂COCl in the presence of Et₃N, furnished the desired racemic trans‐2‐oxoazetidin‐1‐carboxamide derivatives 4a – 4m . The structures of all new compounds were confirmed by IR, and ¹H‐ and ¹³C‐NMR spectroscopy, FAB mass spectrometry, and chemical methods.     

Identification of autoxidation oligomers of flavan‐3‐ols in model solutions by HPLC‐MS/MS

Autoxidation of flavan‐3‐ols was carried out in aqueous/methanol model solutions under mildly acidic conditions (pH 6.0), and these autoxidation products were analyzed by using high performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS). The results showed that (+)‐catechins and (?)‐epicatechins generated autoxidation reaction with each other to form a series of oligomers that had the same [M ? H]^? molecular ions (MS¹) as those of natural procyanidins, but had completely different fragment ions (MS²). According to MS/MS analysis, the major fragments of these oligomers were derived not only from the retro‐Diels–Alder (RDA) dissociations on the C‐rings of the flavan‐3‐ol units, but also from the quinone‐methide (QM) cleavage of the interflavan linkages (IFL), and thus they were identified as B‐type dehydrodicatechins, B‐type dehydrotricatechins and A‐type dehydrotricatechins, respectively. The potential structures of their [M ? H]^? molecular ions and partial fragment ions were deduced on the basis of the MS/MS characterization and the oxidation of flavan‐3‐ols in previous reports. Some specific fragment ions were found to be very useful for identifying the autoxidation oligomers (the B‐type dehydrodicatechins at m/z 393, the B‐type dehydrotricatechins at m/z 681 and the A‐type dehydrotricatechins at m/z 725). Copyright © 2008 John Wiley & Sons, Ltd.     

Unexpected detection of 3‐aroylbenzofuran side products in the preparation of 2‐arylbenzofurans: Identification,characterization, and comparison with chalcone's fragmentation patterns using EI/MSn

A gas chromatography‐mass spectrometry study of the intramolecular Wittig reaction revealed, together with the expected 2‐phenylbenzofuran, the formation of an unexpected side product that has not been reported until now. This study reports the identification of the by‐product, ie, the 3‐benzoyl‐2‐phenylbenzofuran, on the base of its mass spectrometric behaviour using a combination of electron ionization, exact mass measurement, multiple stage mass spectrometry, and labelled compounds. This study reports the common fragmentation pathways and discusses possible fragment structures of characteristic ions from a series of 3‐aroyl‐2‐arylbenzofuran derivatives obtained as by‐product under Wittig conditions. Emphasis is laid on the formation and structure investigation of the [M‐H]⁺ and [M‐OH]⁺ ions. Our results showed interesting analogies with the mass spectrometric behaviour of chalcones.     

UPLC‐QTOF‐MSE‐based diagnostic product ion filtering to unveil unstable C6‐C2 glucoside conjugates in Forsythia suspensa

Forsythia suspensa contains C₆‐C₂ glucoside conjugates (CCGCs) that are chemically unstable, thereby hindering their isolation and purification. In the present study, ultra‐performance liquid chromatography‐quadrupole time‐of‐flight mass spectrometry (UPLC‐QTOF) was utilized to screen and identify unstable CCGCs in the fruits and leaves of F. suspensa without any tedious isolation and purified process based on independent information acquisition (also called MS^E) and individual MS/MS experiments. Diagnostic product ion filtering (DPIF) was further applied to mine unknown analogs in MS^E high energy levels based on characteristic m/z of key substructures. A modified nomenclature for CCGCs is hereby proposed to facilitate discussions. Possible fragmentation pathways of major types of known CCGCs were proposed and used for deducing their structures. A total of 8 potentially new CCGCs were discovered and initially identified. The accuracy of their identification was further verified by structural elucidation of 3 unstable CCGCs isolated from the fruits of F. suspensa using 1D and 2D‐NMR spectroscopy. The established UPLC‐QTOF‐MS^E‐based DPIF technique facilitates the rapid discovery and direct identification of unstable CCGCs in fruits and leaves of F. suspensa .     

Mass spectrometry of rhenium complexes: a comparative study by using LDI‐MS,MALDI‐MS,PESI‐MS and ESI‐MS

A group of rhenium (I) complexes including in their structure ligands such as CF₃SO₃‐, CH₃CO₂‐, CO, 2,2′‐bipyridine, dipyridil[3,2‐a:2′3′‐c]phenazine, naphthalene‐2‐carboxylate, anthracene‐9‐carboxylate, pyrene‐1‐carboxylate and 1,10‐phenanthroline have been studied for the first time by mass spectrometry. The probe electrospray ionization (PESI) is a technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid metal needle. In this work, mass spectra for organometallic complexes obtained by PESI were compared with those obtained by classical ESI and high flow rate electrospray ionization assisted by corona discharge (HF‐ESI‐CD), an ideal method to avoid decomposition of the complexes and to induce their oxidation to yield intact molecular cation radicals in gas state [M]^+. and to produce their reduction yielding the gas species [M]^–.. It was found that both techniques showed in general the intact molecular ions of the organometallics studied and provided additional structure characteristic diagnostic fragments. As the rhenium complexes studied in the present work showed strong absorption in the UV–visible region, particularly at 355 nm, laser desorption ionization (LDI) mass spectrometry experiments could be conducted. Although intact molecular ions could be detected in a few cases, LDI mass spectra showed diagnostic fragments for characterization of the complexes structure. Furthermore, matrix‐assisted laser desorption ionization (MALDI) mass spectra were obtained. Nor‐harmane, a compound with basic character, was used as matrix, and the intact molecular ions were detected in two examples, in negative ion mode as the [M]^–. species. Results obtained with 2‐[(2E)‐3‐(4‐tert‐buthylphenyl)‐2‐methylprop‐2‐enylidene] malononitrile (DCTB) as matrix are also described. LDI experiments provided more information about the rhenium complex structures than did the MALDI ones. Copyright © 2012 John Wiley & Sons, Ltd.     

In vivo metabolite identification of acotiamide in rats using ultra‐performance liquid chromatography–quadrupole/time‐of‐flight mass spectrometry

Acotiamide hydrochloride (ACT) is a drug used for the treatment of functional dyspepsia. Understanding which metabolites are likely to be formed in vivo is essential for interpreting pharmacology, pharmacokinetic and toxicology data. The metabolism of ACT has been investigated using a specific and sensitive liquid chromatography positive ion electrospray ionization high‐resolution tandem mass spectrometry method. In vivo samples including rat plasma, urine and feces were collected separately after dosing healthy Sprague–Dawley rats at a dose of 20 mg kg ⁻¹ ACT at different time points up to 24 h. The metabolites were enriched by optimized sample preparation involving protein precipitation using acetonitrile followed by solid‐phase extraction. The mass defect filter technique was used for better detection of both predicted and unexpected drug metabolites with the majority of interference ions removed. The structural elucidation of the metabolites was performed by comparing their [M + H]⁺ ions and their product ions with those of the parent drug. As a result, a total of seven hitherto unknown metabolites were characterized from the biosamples. The only phase I metabolite detected was N‐ despropyl acotiamide, whereas six phase II glucuronide conjugate metabolites were identified.     

Study of the end‐group contribution to ToF‐SIMS and G‐SIMS spectra of poly (lactic acid) using deuterium labelling

In this study, polymeric (MW 50 000) and oligomeric (MW 2000) poly (lactic acid) (PLA), both with and without end‐group deuterium exchange, were analysed using static secondary ion mass spectrometry (SSIMS) to investigate the contribution of end‐group‐derived secondary ions to the SSIMS spectra. By monitoring the SSIMS intensities between the non‐deuterated and deuterated PLA, it is evident that the only significant end‐group‐derived secondary ions are [nM + H]⁺ (n > 1) and C₄H₉O₂⁺. The gentle‐SIMS (G‐SIMS) methodology was employed to establish that deuterated fragments were produced through low energy processes and were not the result of substantial rearrangements. It was noted that end‐group‐derived secondary ions had higher G‐SIMS intensities for oligomeric PLA than polymeric PLA, showing that these secondary ions are simple fragment products that are not the result of rearrangement or degraded product ions. Copyright © 2007 John Wiley & Sons, Ltd.     

New potential biomarkers for mesterolone misuse in human urine by liquid chromatography quadrupole time‐of‐flight mass spectrometry

In this paper, mesterolone metabolic profiles were investigated carefully. Mesterolone was administered to one healthy male volunteer. Urinary extracts were analyzed by liquid chromatography quadruple time‐of‐flight mass spectrometry (LC‐QTOFMS) for the first time. Liquid–liquid extraction was applied to processing urine samples, and dilute‐shoot analyses of intact metabolites were also presented. In LC‐QTOFMS analysis, chromatographic peaks for potential metabolites were hunt down by using the theoretical [M–H]^? as target ions in full scan experiment, and their actual deprotonated ions were analyzed in targeted MS/MS mode. Ten metabolites including seven new sulfate and three glucuronide conjugates were found for mesterolone. Because of no useful fragment ion for structural elucidation, gas chromatography–mass spectrometry instrumentation was employed to obtain structural details of the trimethylsilylated phase I metabolite released after solvolysis. Thus, their potential structures were proposed particularly by a combined MS approach. All the metabolites were also evaluated in terms of how long they could be detected, and S1 (1α‐methyl‐5α‐androst‐3‐one‐17β‐sulfate) together with S2 (1α‐methyl‐5α‐androst‐17‐one‐3β‐sulfate) was detected up to 9 days after oral administration, which could be the new potential biomarkers for mesterolone misuse. Copyright © 2015 John Wiley & Sons, Ltd.     

Collision‐induced dissociation study of poly(2‐ethyl‐2‐oxazoline) using survival yields and breakdown curves

Poly(2‐ethyl‐2‐oxazoline), a synthetic polymer was analysed by mass spectrometry using different ion sources. Two distributions could be identified in the mass spectra which related to two different polymer series (one with hydrogen and hydroxyl end‐groups and the other with methyl and hydroxyl end‐groups). The fragmentation behaviour of the protonated oligomers was studied in a quadrupole time‐of‐flight mass spectrometer (MS) with electrospray, atmospheric pressure chemical ionization and direct analysis in real time soft ionization techniques. Three product ion series were identified in the MS/MS spectra independently of the ion source used. Based on the results, a mechanism was proposed for the dissociation by means of the accurate mass of the product ions, pseudo MS³ experiments and the energy dependence of the product ion intensity, i.e. breakdown curves. The survival yield method was used to highlight the correlation between the size of the oligomers and the laboratory frame collision energy. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural determination of glucosylceramides isolated from marine sponge by fast atom bombardment collision‐induced dissociation linked scan at constant B/E

Five glucosylceramides (GlcCers) were isolated by reversed phase high‐performance liquid chromatography from the MeOH extracts of a marine sponge, Haliclona (Reniera) sp., collected from the coast of Ulleung Island, Korea, and analyzed by fast atom bombardment mass spectrometry (FAB–MS) in positive‐ion mode. FAB‐mass spectra of these compounds included protonated molecules [M + H]⁺ and abundant sodiated molecules [M + Na]⁺ from a mixture of m‐NBA and NaI. The structures of these GlcCers, which were similar, were elucidated by FAB‐linked scan at constant B/E. To find diagnostic ions for their characterization, the GlcCers were analyzed by collision‐induced dissociation (CID) linked scan at constant B/E. The CID‐linked scan at constant B/E of [M + H]⁺ and [M + Na]⁺ precursor ions resulted in the formation of numerous characteristic product ions via a series of dissociative processes. The product ions formed by charge‐remote fragmentation provided important information for the characterization of the fatty N‐acyl chain moiety and the sphingoid base, commonly referred to as the long‐chain base. The product ions at m/z 203 and 502 were diagnostic for the presence of a sodiated sugar ring and β‐D ‐glucosylsphinganine, respectively. For further confirmation of the structure of the fatty N‐acyl chain moiety in each GlcCer, fatty acid methyl esters were obtained from the five GlcCers by methanolysis and analyzed by FAB–MS in positive‐ion mode. On the basis of these dissociation patterns, the structures of the five GlcCers from marine sponge were elucidated. In addition, the accurate mass measurement was performed to obtain the elemental composition of the GlcCers isolated from marine sponge. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of temperature on the stability of compounds used as UV‐MALDI‐MS matrix: 2,5‐dihydroxybenzoic acid, 2,4,6‐trihydroxyacetophenone, α‐cyano‐4‐hydroxycinnamic acid, 3,5‐dimethoxy‐4‐hydroxycinnamic acid,nor‐harmane and harmane

The thermal stability of several commonly used crystalline matrix‐assisted ultraviolet laser desorption/ionization mass spectrometry (UV‐MALDI‐MS) matrices, 2,5‐dihydroxybenzoic acid (gentisic acid; GA), 2,4,6‐trihydroxyacetophenone (THA), α‐cyano‐4‐hydroxycinnamic acid (CHC), 3,5‐dimethoxy‐4‐hydroxycinnamic acid (sinapinic acid; SA), 9H‐pirido[3,4‐b]indole (nor‐harmane; nor‐Ho), 1‐methyl‐9H‐pirido[3,4‐b]indole (harmane; Ho), perchlorate of nor‐harmanonium ([nor‐Ho + H]⁺) and perchlorate of harmanonium ([Ho + H]⁺) was studied by heating them at their melting point and characterizing the remaining material by using different MS techniques [electron ionization mass spectrometry (EI‐MS), ultraviolet laserdesorption/ionization‐time‐of‐flight‐mass spectrometry (UV‐LDI‐TOF‐MS) and electrospray ionization‐time‐of‐flight‐mass spectrometry (ESI‐TOF‐MS)] as well as by thin layer chromatography analysis (TLC), electronic spectroscopy (UV‐absorption, fluorescence emission and excitation spectroscopy) and ¹H nuclear magnetic resonance spectroscopy (¹H‐NMR). In general, all compounds, except for CHC and SA, remained unchanged after fusion. CHC showed loss of CO₂, yielding the trans‐/cis‐4‐hydroxyphenylacrilonitrile mixture. This mixture was unambiguously characterized by MS and ¹H‐NMR spectroscopy, and its sublimation capability was demonstrated. These results explain the well‐known cluster formation, fading (vanishing) and further recovering of CHC when used as a matrix in UV‐MALDI‐MS. Commercial SA (SA 98%; trans‐SA/cis‐SA 5 : 1) showed mainly cis‐ to‐trans thermal isomerization and, with very poor yield, loss of CO₂, yielding (3′,5′‐dimethoxy‐4′‐hydroxyphenyl)‐1‐ethene as the decarboxilated product. These thermal conversions would not drastically affect its behavior as a UV‐MALDI matrix as happens in the case of CHC. Complementary studies of the photochemical stability of these matrices in solid state were also conducted. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural determination of glycopeptidolipids of Mycobacterium smegmatis by high‐resolution multiple‐stage linear ion‐trap mass spectrometry with electrospray ionization

Glycopeptidolipids (GPLs) are abundant in the cell walls of different species of mycobacteria and consist of tripeptide‐amino‐alcohol core of D‐Phe‐D‐allo‐Thr‐D‐Ala‐L‐alaninol linked to 3‐hydroxy or 3‐methoxy C_26–34 fatty acyl chain at the N‐terminal of D‐Phe via amide linkage, and a 6‐deoxytalose (6‐dTal) and an O‐methyl rhamnose residues, respectively, attach to D‐allo‐Thr and the terminal L‐alaninol. They are important cell‐surface antigens that are implicated in the pathogenesis of opportunistic mycobacteria belonging to the Mycobacterium avium complex. In this contribution, we described multiple‐stage linear ion trap in conjunction with high‐resolution mass spectrometry towards structural characterization of complex GPLs as [M + Na]⁺ ions isolated from Mycobacterium smegmatis, a fast‐growing and non‐pathogenic mycobacterial species. Following resonance excitation in an ion trap, MSⁿ spectra of the [M + Na]⁺ ions of GPLs contained mainly b and y series ions that readily determine the peptide sequence. Fragment ions from MSⁿ also afford locating the 6‐dTal and O‐methyl rhamnose residues linked to the D‐allo‐Thr and terminal L‐alaninol of the peptide core, respectively, as well as recognizing the modifications of the glycosides, including their acetylation and methylation states and the presence of succinyl group. The GPL families consisting of 3‐hydroxy fatty acyl and of 3‐methoxy fatty acyl substituents are readily distinguishable. The MS profiles of the GPLs from cells are dependant on the conditions they were grown, and several isobaric isomers were identified for many of the molecular species. These multiple‐stage mass spectrometric approaches give detailed structures of GPL in complex mixtures of which the isomeric structures are difficult to define using other analytical methods. Copyright © 2012 John Wiley & Sons, Ltd.     

Identification of the absorptive constituents and their metabolites in vivo of Puerariae Lobatae Radix decoction orally administered in WZS‐miniature pigs by HPLC‐ESI‐Q‐TOFMS

In this study, the technique of high‐performance liquid chromatography coupled with electrospray ionization quadrupole time‐of‐flight mass spectrometry (HPLC‐ESI‐Q‐TOFMS) was used to analyze and identify the absorptive constituents and their metabolites in drug‐containing urine of Wuzhishan (WZS)‐miniature pigs administered with Puerariae Lobatae Radix (PLR) decoction. With the accurate mass measurements (<5 ppm) and effective MS² fragment ions, 96 compounds, including eight original constituents and 88 metabolites, were identified from the drug‐containing urine. Among these, 64 metabolites were new ones and their structures can be categorized into five types: isoflavones, puerols, O‐desmethylangolensins, equols and isoflavanones. In particular, puerol‐type constituents in PLR were first proved to be absorptive in vivo. Meanwhile, the metabolic pathways of PLR in vivo were investigated. On the basis of relative content of the identified compounds, 13 major metabolites accounting for approximately 50% of the contents, as well as their corresponding 12 prototype compounds, were determined as the major original absorptive constituents and metabolites of PLR in vivo. The HPLC‐ESI‐Q‐TOFMS technique proved to be powerful for characterizing the chemical constituents from the complicated traditional Chinese medicine matrices in this research. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural elucidation of new urinary tamoxifen metabolites by liquid chromatography quadrupole time‐of‐flight mass spectrometry

In this study, tamoxifen metabolic profiles were investigated carefully. Tamoxifen was administered to two healthy male volunteers and one female patient suffering from breast cancer. Urinary extracts were analyzed by liquid chromatography quadruple time‐of‐flight mass spectrometry using full scan and targeted MS/MS techniques with accurate mass measurement. Chromatographic peaks for potential metabolites were selected by using the theoretical [M + H]⁺ as precursor ion in full‐scan experiment and m/z 72, 58 or 44 as characteristic product ions for N,N‐dimethyl, N‐desmethyl and N,N‐didesmethyl metabolites in targeted MS/MS experiment, respectively. Tamoxifen and 37 metabolites were detected in extraction study samples. Chemical structures of seven unreported metabolites were elucidated particularly on the basis of fragmentation patterns observed for these metabolites. Several metabolic pathways containing mono‐ and di‐hydroxylation, methoxylation, N‐desmethylation, N,N‐didesmethylation, oxidation and combinations were suggested. All the metabolites were detected in the urine samples up to 1 week. Copyright © 2014 John Wiley & Sons, Ltd.     

ESI‐MS/MS analysis of protonated N‐methyl amino acids and their immonium ions

Methylation is one of the important posttranslational modifications of biological systems. At the metabolite level, the methylation process is expected to convert bioactive compounds such as amino acids, fatty acids, lipids, sugars, and other organic acids into their methylated forms. A few of the methylated amino acids are identified and have been proved as potential biomarkers for several metabolic disorders by using mass spectrometry–based metabolomics workstation. As it is possible to encounter all the N‐methyl forms of the proteinogenic amino acids in plant/biological systems, it is essential to have analytical data of all N‐methyl amino acids for their detection and identification. In earlier studies, we have reported the ESI‐MS/MS data of all methylated proteinogenic amino acids, except that of mono‐N‐methyl amino acids. In this study, the N‐methyl amino acids of all the amino acids ( 1 ‐ 21 ; including one isomeric pair) were synthesized and characterized by ESI‐MS/MS, LC/MS/MS, and HRMS. These data could be useful for detection and identification of N‐methyl amino acids in biological systems for future metabolomics studies. The MS/MS spectra of [M + H]⁺ ions of most N‐methyl amino acids showed respective immonium ions by the loss of (H₂O, CO). The other most common product ions detected were [MH‐(NH₂CH₃]⁺, [MH‐(RH)]⁺ (where R = side chain group) ions, and the selective structure indicative product ions due to side chain and N‐methyl group. The isomeric/isobaric N‐methyl amino acids could easily be differentiated by their distinct MS/MS spectra. Further, the MS/MS of immonium ions inferred side chain structure and methyl group on α‐nitrogen of the N‐methyl amino acids.     

Screening of drugs of abuse and toxic compounds in human whole blood using online solid‐phase extraction and high‐performance liquid chromatography with time‐of‐flight mass spectrometry

A novel method for the screening of 151 drugs of abuse and toxic compounds in human whole blood has been developed and validated by online solid‐phase extraction with liquid chromatography coupled to time‐of‐flight mass spectrometry. Analytes were extracted and separated by using a fully automated online solid‐phase extraction liquid chromatography system with total chromatographic run time of 26 min. Time‐of‐flight mass spectrometry screening of 151 drugs of abuse and toxic compounds was performed in a full‐scan (m/z 50–800) mode using an MS^E acquisition of molecular ions and fragment ions data at two collision energies (one was 6 eV and another one was in the range of 5–45 eV). The compounds were identified based on retention times and exact mass of molecular ions and fragment ions. The limit of detection ranged from 1 to 100 ng/mL and the recovery of the method ranged from 6.3 to 163.5%. This method is proved to be a valuable screening method allowing fast and specific identification of drugs in human whole blood.     

Characterization of complex,heterogeneous lipid A samples using HPLC‐MS/MS technique III. Positive‐ion mode tandem mass spectrometry to reveal phosphorylation and acylation patterns of lipid A

In this study, we report the detailed analysis of the fragmentation patterns of positively charged lipid A species based on their tandem mass spectra obtained under low‐energy collision‐induced dissociation conditions of an electrospray quadrupole time‐of‐flight mass spectrometer. The tandem mass spectrometry experiments were performed after the separation of the compounds with a reversed‐phase high performance liquid chromatography method. We found that both, phosphorylated and nonphosphorylated lipid A molecules can be readily ionized in the positive‐ion mode by adduct formation with triethylamine added to the eluent. The tandem mass spectra of the lipid A triethylammonium adduct ions showed several product ions corresponding to inter‐ring glycosidic cleavages of the sugar residues, as well as consecutive and competitive eliminations of fatty acids, phosphoric acid, and water following the neutral loss of triethylamine. Characteristic product ions provided direct information on the phosphorylation site(s), also when phosphorylation isomers (ie, containing either a C1 or a C4′ phosphate group) were simultaneously present in the sample. Continuous series of high‐abundance B‐type and low‐abundance Y‐type inter‐ring fragment ions were indicative of the fatty acyl distribution between the nonreducing and reducing ends of the lipid A backbone. The previously reported lipid A structures of Proteus morganii O34 and Escherichia coli O111 bacteria were used as standards. Although, the fragmentation pathways of the differently phosphorylated lipid A species significantly differed in the negative‐ion mode, they were very similar in the positive‐ion mode. The complementary use of positive‐ion and negative‐ion mode tandem mass spectrometry was found to be essential for the full structural characterization of the C1‐monophosphorylated lipid A species.