Synthesis and Cytotoxicity in Vitro of N‐Aryl‐4‐(tert‐butyl)‐5‐(1H‐1,2,4‐triazol‐1‐yl)thiazol‐2‐amine

A series of novel N‐aryl‐4‐(tert‐butyl)‐5‐(1H‐1,2,4‐triazol‐1‐yl)thiazol‐2‐amines synthesized in a green way. H₂O₂‐NaBr Brominating circulatory system was used in the synthesis of the key intermediate in a mild condition. All of the target compounds were confirmed by ¹H NMR and elemental analysis and tested for their cytotoxicity against two different human cancer cell lines. The cytotoxicity assay revealed that some of the title compounds showed moderate to strong cytotoxic activities. Compound 2i was the most potent compound with the IC₅₀ values of 9 μM against Hela cells and 15 μM against Bel–7402 cells, respectively.     

Analysis of hydroxyl radical‐induced oxidation process of glucagon by reversed‐phase HPLC and ESI‐MS/MS

Structural modification of a polypeptide hormone, glucagon, by a hydroxyl radical in vitro was investigated by reversed‐phase high‐performance liquid chromatography (RP‐HPLC), and the oxidized site of glucagon was detected by electrospray ionization tandem mass spectrometry (ESI‐MS/MS). It was shown that ²⁷methionine (Met) was oxidized to ²⁷Met sulfoxide by hydroxyl radical, and the production rate of ²⁷Met sulfoxide was faster than that by hydrogen peroxide. In addition, production of ²⁷Met sulfoxide enantiomer was confirmed by RP‐HPLC analysis. cAMP production in a HepG2 cell induced by ²⁷Met sulfoxide glucagon was reduced to approximately 75% as compared with that induced by the native form of glucagon. Copyright © 2009 John Wiley & Sons, Ltd.     

The human mast cell line‐1 cell membrane chromatography coupled with HPLC‐ESI‐MS/MS method for screening potentical anaphylactic components from chuanxinlian injection

Chuanxinlian injection is a traditional Chinese medicine injection widely used in China to treat sore throat, cough and dysentery, although a high occurrence of severe adverse reactions has been reported in clinical practice in recent years. In the present study, a human mast cell line‐1 cell membrane chromatography coupled with HPLC‐ESI‐MS/MS method was established to screen and identify potentical anaphylactic components in chuanxinlian injection, and the dehydroandrographolide was identified as a potential anaphylactic component. In vitro anaphylactic assay showed that intracellular Ca²⁺ concentration clearly increased under dehydroandrographolide (100 μm ) treatment. β ‐Hexosaminidase and histamine release in human mast cell line‐1 cells were both markedly enhanced with increased concentrations of dehydroandrographolide, confirming the anaphylactic activity of dehydroandrographolide. The application for chuanxinlian injection in this study suggested that the developed human mast cell line‐1 cell membrane chromatography coupled with HPLC‐ESI‐MS/MS system may be effective and rapid for screening the potentical anaphylactic components from complex samples.     

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.     

Synthesis,structure and biological activity of new 6,6‐dimethyl‐2‐oxo‐4‐{2‐[5‐organylsilyl(germyl)]furan(thiophen)‐2‐yl}vinyl‐5,6‐dihydro‐2H‐pyran‐3‐carbonitriles

New 6,6‐dimethyl‐2‐oxo‐4‐{2‐[5‐alkylsilyl(germyl)]furan(thiophen)‐2‐yl}vinyl‐5,6‐dihydro‐2H‐pyran‐3‐carbonitriles (IC₅₀: 1–6 µg ml^?1) have been prepared by the condensation of corresponding silicon‐ and germanium‐containing furyl(thienyl)‐2‐carbaldehydes with 3‐cyano‐4,6,6‐trimethyl‐5,6‐dihydropyran‐2‐one using piperidine acetate as a catalyst. The obtained carbonitriles were identified using NMR (¹H, ¹³C and ²⁹Si) spectroscopy and GC‐MS. The structure of 6,6‐dimethyl‐2‐oxo‐4‐[2‐(5‐trimethylsilyl)thiophen‐2‐yl]‐5,6‐dihydro‐2H‐pyran‐3‐carbonitrile was studied using X‐ray diffractometry. The influences of the heterocycle and the structure of the organoelement substituent on cytotoxicity and on matrix metalloproteinase inhibition have been studied. Copyright © 2015 John Wiley & Sons, Ltd.     

Anticancer Potency and Multidrug‐Resistant Studies of Self‐Assembled Arene–Ruthenium Metallarectangles

A suite of three tetraruthenium metallacycles have been obtained from [2+2] self‐assemblies between N,N′‐Di‐(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarbo–xydiimide ( 4 ) and one of the three dinuclear arene ruthenium clips, (η⁶‐p‐iPrC₆H₄Me)₂Ru₂(OO∩OO)][OTf]₂ (OO∩OO=oxalate 1 , 2,5‐dioxydo‐1,4‐benzoquinonato (dobq) 2 , 5,8‐dihydroxy‐1,4‐naphthaquinonato (donq) 3 ; OTf=triflate). All complexes were isolated in good yield (>85 %) as triflate salts and were fully characterized by using ¹H NMR and UV/Vis spectroscopies, and high‐resolution electrospray mass spectrometry. A single crystal of the metallarectangle 5 was suitable for X‐ray diffraction structural characterization. The biological activities of the metallacycles were determined by using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assays, establishing their in vitro anticancer properties. Our results show that for the AGC (gastric cancer) cell lines, the cytotoxicity of (donq)‐containing SCC 7 exceeds that of cisplatin, which was used as a control. For HCT15 (colon cancer) cell lines, the cytotoxicity is comparable to both cisplatin and doxorubicin. An in vivo hollow fiber model was used to show growth‐inhibitory activity against HCT15 and image‐based cytometry experiments indicated that 7 induced apoptosis as the mode of cell death. Complex 7 also showed significant antitumor activity for multidrug‐resistant HCT15/CLO2 cell lines, for which doxorubicin was ineffective.     

Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry

Dopamine [DA]⁺ (m/z 154), DA dimer [2DA‐H]⁺ (m/z 307) and DA quinone [DAQ]⁺ (m/z 152) are detected in positive ion mode electrospray ionization mass spectrometry (ESI MS) of dopamine in 50/1/49 (vol%) water/acetic acid/methanol. H/D exchange experiments support a covalent structure of DA dimer. Thus, ESI of DA may involve 1e^?, 1H⁺ oxidation processes followed by rapid radical dimerization. The DA quinone signal is low in ESI MS, which indicates a low efficiency of the 2e^?, 2H⁺ oxidation reaction. On‐line electrochemistry ESI MS (EC/ESI MS) with low electrochemical cell voltage floated on high ES voltage increases electrospray current and improves sensitivity for DA. The DA quinone signal increases and DA dimer signal decreases. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity of ESI and EC/ESI MS measurements. A DA quinone‐cysteine adduct [DAQ+Cys]⁺ was detected in solutions of DA with cysteine (Cys). ESI MS and EC/ESI MS indicate formation of the DA quinone‐cysteine adduct by 1e^? pathway. Oxidation pathways in ESI MS are relevant to biological reactivity of DA and Cys.     

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.     

Cell‐based studies of the first‐in‐class half‐sandwich Ir(III) complex containing histone deacetylase inhibitor 4‐phenylbutyrate

We report on a cytotoxic half‐sandwich iridium(III) complex [Ir(η⁵‐Cp^ph)(phen)(PB)]PF₆ ( 1‐PB ), containing a monodentate coordinated O‐donor 4‐phenylbutyrato ligand (PB) belonging to the family of histone deacetylase inhibitors (HDACi); HCp^ph = (2,3,4,5‐tetramethylcyclopenta‐2,4‐dien‐1‐yl)benzene, phen = 1,?10‐phenanthroline. The solution behaviour studies indicated that complex 1‐PB partially hydrolysed in the mixture of methanol and water (1:4, v/v), resulting in the release of the PB ligand. The extent of the PB ligand release increased in the presence of 2 molar equiv. of the reduced glutathione (GSH). Complex 1‐PB exhibited comparable in vitro cytotoxicity against the cisplatin‐sensitive (IC₅₀ = 15.8 μM) and ‐resistant (IC₅₀ = 13.0 μM) variants of the A2780 human ovarian carcinoma cells, while its potency against the MRC‐5 human normal fibroblast cells was markedly lower (IC₅₀ = 124.1 μM). The cytotoxicity studies revealed an ability of complex 1‐PB to overcome the acquired resistance against cisplatin, with the resistance factor (RF = 0.8) being markedly lower than for complex 1‐Cl (RF = 1.8) and cisplatin (RF = 2.9). The A2780 cell‐based flow cytometry experiments showed different cell cycle modification induced by complex 1‐PB and cisplatin, induction of production of reactive oxygen species, and higher mitochondria membrane potential depleted cell populations after the treatment by complex 1‐PB as compared with cisplatin. In the cell‐free assay, complex 1‐PB inhibited the HDAC activity to ca 66% as compared to ca 74% valid for NaPB. The [Ir(η⁵‐Cp^ph)(phen)(H₂O)]²⁺ species ( 1‐OH ₂ ), representing the hydrolysis product of both complexes 1‐PB and 1‐Cl , induced hydroxyl radical from the hydrogen peroxide, as proved by the EPR spin trapping studies with the 5‐(diethoxyphosphoryl)‐5‐methyl‐1‐pyrroline‐N‐oxide (DEPMPO) spin trap.     

首次合成来源于鼠李属植物中的两个新颖的蒽环鼠李糖苷，2’, 3’-Di-O-acetylfrangulin A 和 Prinoidin

首次全合成来源于鼠李属植物中的两个天然产物2’, 3’-di-O-acetylfrangulin A (1) 和 prinoidin (2),它们对KB细胞表现出较好的细胞毒活性。通过1H NMR, 13C NMR, 1H-1H COSY, HMQC 和 HMBC确证了两个化合物的结构。     

Novel 5‐Methyl‐2‐[(un)substituted phenyl]‐4‐{4,5‐dihydro‐ 3‐[(un)substituted phenyl]‐5‐(1,2,3,4‐tetrahydroisoquinoline‐2‐yl)pyrazol‐1‐yl}‐oxazole Derivatives: Synthesis and Anticancer Activity

Eleven novel 5‐methyl‐2‐[(un)substituted phenyl]‐4‐{4,5‐dihydro‐3‐[(un)substituted phenyl]‐5‐(1,2,3,4‐tetrahydroisoquinoline‐2‐yl)pyrazol‐1‐yl}‐oxazole derivatives were synthesized and characterized by elemental analysis, ESI‐MS, ¹H NMR and ¹³C NMR. All of the compounds have been screened for their antiproliferative activities against PC‐3 cell (human prostate cancer) and A431 cell (human epidermoid carcinoma cancer) lines in vitro. The results revealed that compounds 4g , 4j and 4k exhibited the strong inhibitory activities against the PC‐3 cell lines (with IC₅₀ values of 2.8±0.11, 3.1±0.10 and 3.0±0.06 μg/mL, respectively).     

Multiple mechanisms for cytotoxicity induced by copper(II) complexes of 2‐acetylpyrazine‐N‐substituted thiosemicarbazones

The purpose of this study was to evaluate the mechanism by which 2‐acetylpyrazine‐⁴N‐substituted thiosemicarbazone copper II complexes mediate their cytotoxicity. These compounds were shown to be cytotoxic to a variety of human and rodent tumors in cell culture and are potent cytocidal agents as determined by dilute agar colony assays. They demonstrated the ability to inhibit several enzymes in vitro including DNA topoisomerase II activity. The data presented suggest that cytotoxicity may be mediated by the cumulative effect of several enzymes being inhibited by the agents. Copyright © 1999 John Wiley & Sons, Ltd.     

HPLC‐DAD and HPLC‐ESI‐MS separation,determination and identification of the spin‐labeled diastereoisomers of podophyllotoxin

Spin‐labeled nitroxide derivatives of podophyllotoxin had better antitumor activity and less toxicity than that of the parent compounds. However, the 2‐H configurations of these spin‐labeled derivatives cannot be determined by nuclear magnetic resonance (NMR) methods. In the present paper, a high‐performance liquid chromatography‐diode array detection (HPLC‐DAD) and a high‐performance liquid chromatography‐electrospray ionization tandem mass spectrometry (HPLC‐ESI/MS/MS) method were developed and validated for the separation, identification of four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 position. In the HPLC‐ESI/MS spectra, each pair of diastereoisomers of the spin‐labeled derivatives in the mixture was directly confirmed and identified by [M+H]⁺ ions and ion ratios of relative abundance of [M‐ROH+H]⁺ (ion 397) to [M+H]⁺. When the [M‐ROH+H]⁺ ions (at m/z 397) were selected as the precursor ions to perform the MS/MS product ion scan. The product ions at m/z 313, 282, and 229 were the common diagnostic ions. The ion ratios of relative abundance of the [M‐ROH+H]⁺ (ion 397) to [M+H]⁺, [A+H]⁺ (ion 313) to [M‐ROH+H]⁺, [A+H‐OCH₃]⁺ (ion 282) to [M‐ROH+H]⁺ and [M‐ROH‐ArH+H]⁺ (ion 229) to [M‐ROH+H]⁺ of each pair of diastereoisomers of the derivatives specifically exhibited a stereochemical effect. Thus, by using identical chromatographic conditions, the combination of DAD and MS/MS data permitted the separation and identification of the four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 in the mixture.     

Biotransformation and metabolic profile of caudatin‐2,6‐dideoxy‐3‐O‐methy‐β‐d‐cymaropyranoside with human intestinal microflora by liquid chromatography quadrupole time‐of‐flight mass spectrometry

In our previous studies, caudatin‐2,6‐dideoxy‐3‐O‐methy‐β‐d‐ cymaropyranoside (CDMC) was for the first time isolated from Cynanchum auriculatum Royle ex Wightand and was reported to possess a wide range of biological activities. However, the routes and metabolites of CDMC produced by intestinal bacteria are not well understood. In this study, ultra‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry (UPLC‐Q‐TOF‐MS) technique combined with Metabolynx^TMsoftware was applied to analyze metabolites of CDMC by human intestinal bacteria. The incubated samples collected for 48 h in an anaerobic incubator and extracted with ethyl acetate were analyzed by UPLC‐Q‐TOF‐MS within 12 min. Eight metabolites were identified based on MS and MS/MS data. The results indicated that hydrolysis, hydrogenation, demethylation and hydroxylation were the major metabolic pathways of CDMC in vitro. Seven strains of bacteria including Bacillus sp. 46, Enterococcus sp. 30 and sp. 45, Escherichia sp. 49A, sp. 64, sp. 68 and sp. 75 were further identified using 16S rRNA gene sequencing owing to their relatively strong metabolic capacity toward CDMC. The present study provides important information about metabolic routes of CDMC and the roles of different intestinal bacteria in the metabolism of CDMC. Moreover, those metabolites might influence the biological effect of CDMC in vivo, which affects the clinical effects of this medicinal plant. Copyright © 2015 John Wiley & Sons, Ltd.     

立体选择性合成2-(a-噻吩甲酰基)-3-取代苯基-4-乙氧羰基-5-甲基-反式-2,3-二氢呋喃

溴化(a-噻吩甲酰基)甲基三苯鉮1与3-取代苯甲叉基-2,4-戊二酮 2以碳酸钾为碱,在苯中55℃条件下反应,可以较好的收率、高立体选择性地生成反-2-(a-噻吩甲酰基)-3-取代苯基-4-乙氧羰基-5-甲基-2,3-二氢呋喃3。产物结构均经波谱予以确定。本文还提出了生成产物的可能机理。     

Synthesis of (3,5‐Aryl/methyl‐1H‐Pyrazol‐1‐yl)‐(5‐Arylamino‐2H‐1,2,3‐Triazol‐4‐yl)Methanone

Some new (3,5‐aryl/methyl‐1H‐pyrazol‐1‐yl)‐(5‐arylamino‐2H‐1,2,3‐triazol‐4‐yl)methanones were synthesized and characterized by ¹HNMR, ¹³C NMR, MS, IR spectra data and elemental analyses or high resolution mass spectra (HRMS). During the procedure, Dimroth rearrangement was used in this synthesis.     

Efficient Synthesis of 2,3‐Disubstituted‐1,3‐benzoxazines by Chlorotrimethylsilane‐Mediated Aza‐Acetalizations of Aromatic Aldehydes

A series of novel substituted 3,4‐dihydro‐2H‐1,3‐benzoxazines were prepared in moderate to good yields by aza‐acetalizations of aromatic aldehydes with 2‐(N‐substituted aminomethyl)phenols in the presence of chlorotrimethylsilane or SnCl₄. It was found that chlorotrimethylsilane was more effective for the reaction, especially for the reaction of fluorobenzaldehyde, and thereby, an efficient method for the preparation of 3,4‐dihydro‐2H‐1,3‐benzoxazines was developed. The structures of the compounds were determined by FT‐IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis.     

Induction and inversion of chirality in poly‐L‐lysine and methyl orange complex

The mechanism of complexation of poly‐L‐lysine (PLL) with methyl orange (MO) and the appearance of induced circular dichroism (ICD) were investigated as a function of dye concentration and temperature and compared with that of the PLL‐ethyl orange complex. The formation of stoichiometric complexes with uniform size and intensities of ICDs depended on the length of alkyl groups (methyl and ethyl) as determined from quartz crystal microbalance measurement, absorption spectra, and CD spectra data. Furthermore, at constant PLL concentration, a dependence of the inversion of the ICD on the MO concentration (CMO) was observed in the PLL‐MO complexes, which to our knowledge has not been reported for a constant dye concentration system. The positive ICD in the PLL‐MO complexes observed at CMO lower than 2.0 × 10^?5 M showed reversible changes in response to heating and cooling, whereas the negative ICD in PLL‐MO complexes observed at higher CMO inverted to positive ICD values in response to a decrease in temperature. These results demonstrate the alkyl group substituent in the dye, dye concentration, and temperature play important roles in the formation of PLL‐azo dye complex and ICD appearance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Iotroridoside‐A,a Novel Cytotoxic Glycosphingolipid from the Marine Sponge Iotrochota ridley

A new cytotoxic glycosphingolipid, Iotroridoside‐A, was isolated from the marine sponge Iotrochota ridley collected from the South China Sea near Hainan Island, China. On the basis of chemical degradation method and IR, MS, ¹H NMR, ¹³C NMR and 2D NMR spectrometry, its structure was assigned as 1‐O‐β‐D‐glucopyranosyl‐2‐[(4′ Z)‐2′‐hydroxytetracosene amido]‐4‐tetradecyl‐1, 3, 4‐butantriol. The new compound exhibits strong cytotoxicity against L1210 murine leukemia cells in vitro (ED₅₀ = 0.08 μg/mL).     

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.