Distinguishing Linkage Position and Anomeric Configuration of Glucose–Glucose Disaccharides by Water Adduction to Lithiated Molecules

Study of Mono and Di-O-caffeoylquinic Acid Isomers in Acmella oleracea Extracts by HPLC-MS/MS and Application of Linear Equation of Deconvolution Analysis Algorithm for Their Characterization

Chlorogenic acids, the esters of caffeic and quinic acids, are the main phenolic acids detected in Acmella oleracea extracts and have gained increasing interest in recent years due to their important biological activities. Given their structural similarity and instability, the correct analysis and identification of these compounds in plants is challenging. This study aimed to propose a simple and rapid determination of the A. oleracea caffeoylquinic isomers, applying an HPLC-MS/MS method supported by a mathematical algorithm (Linear Equation of Deconvolution Analysis (LEDA)). The three mono- and the three di-caffeoylquinic acids in roots of Acmella plants were studied by an ion trap MS analyzer. A separation by a conventional chromatographic method was firstly performed and an MS/MS characterization by energetic dimension of collision-induced dissociation mechanism was carried out. The analyses were then replicated using a short HPLC column and a fast elution gradient (ten minutes). Each acquired MS/MS data were processed by LEDA algorithm which allowed to assign a relative abundance in the reference ion signal to each isomer present. Quantitative results showed no significant differences between the two chromatographic systems proposed, proving that the use of LEDA algorithm allowed the distinction of the six isomers in a quarter of the time.

Isomers Recognition in HPLC-MS/MS Analysis of Human Plasma Samples by Using an Ion Trap Supported by a Linear Equations-Based Algorithm

The tandem mass spectrometry (MS/MS) approach employing an ion trap mass analyzer (IT) was evaluated in isomers recognition. The proposed approach consists of sole, simple, and rapid liquid chromatographic separation (HPLC) without requiring resolution between the analytes. Then, the MS/MS properties were optimized to solve the signal assignment using post-processing data elaboration (LEDA). The IT-MS/MS experiment uses the same site, helium as collision gas, and different time steps to modify the applied conditions on the studied ions. Nevertheless, helium cannot ensure the quick energization of the precursor ion due to its small cross-section. Then, different combinations between excitation amplitude (ExA) and excitation time (ExT) were tested to achieve the activation of the fragmentation channels and the formation of the MS/MS spectrum. Usually, the IT-MS/MS acquisition cycle is longer for other multistage instruments, decreasing the frequency of sample data collection and influencing the chromatographic profile. To solve these problems, two time segments were set up, and the elution conditions were optimized with a compromise between peaks distinction and run time reduction. The developed HPLC-MS/MS method was checked and applied to analyze a series of human plasma samples spiked with an equimolar mixture of pair of isomers.

Tandem mass spectrometry approaches for recognition of isomeric compounds mixtures

The present review aims to collect the published literature pertaining the recognition of isobaric compounds (isomers or stereoisomers) using the features of tandem mass spectrometry (MS) experiments without any chromatographic separation or chemical modification (derivatization or isotopic enrichment) of the analytes. MS/MS methods possess high selectivity, wide dynamic range and high throughput capabilities. Generally, tandem MS has limited capability for distinguishing isomers that fragment similarly. However, some MS/MS methods have been developed and positively applied to isomers discrimination. Among the literature on this topic, the applications that fit on the review subject can be summarized as follow: (1) chiral discrimination by the kinetic method, (2) the use energy-resolved tandem mass spectra and the survival yield (SY) representation, (3) the kinetics evaluation of the ion-molecule interaction and (4) the postprocessing mathematical algorithm to resolve the isomers in MS/MS signal.

Gas-Phase Behavior of Galactofuranosides upon Collisional Fragmentation: A Multistage High-Resolution Ion Mobility Study

Carbohydrates are ubiquitous in nature but are among the least conserved biomolecules in life. These biopolymers pose a particular challenge to analytical chemists because of their high diversity and structural heterogeneity. In addition, they contain many isomerisms that complicate their structural characterization, notably by mass spectrometry. The tautomerism of the constitutive subunits is of particular interest. A given cyclized monosaccharide unit can take two forms: a most common 6-membered ring (pyranose, p) and a more flexible 5-membered ring (furanose, f). The tautomers impact the biological properties of polysaccharides, resulting in interesting properties of the derived oligosaccharides. From an analytical point of view, the impact of tautomerism on the gas-phase behavior of ions has scarcely been described in the literature. In this work, we study the behavior of Galf-containing oligosaccharides, ionized as [M+Li]⁺ species, under collisional dissociation (CID) conditions using high-resolution and multistage ion mobility (IMS) on a Cyclic IMS platform. In the first part of this work, we studied whether disaccharidic fragments released from Galf-containing (Gal)₁(Man)₂ trisaccharides (and their Galp counterpart) would match the corresponding disaccharide standards, and─despite the fragments generally being a good match─we showed the possibility of Galf migrations and other unidentified alterations in the IMS profile. Next, we expanded on these unknown features using multistage IMS and molecular dynamics, unveiling the contributions of additional gas-phase conformers in the profile of fragments from a Galf-containing trisaccharide compared with the corresponding disaccharides.

Direct Identification of Disaccharide Structural Isomers Using Ambient Ionization Tandem Mass Spectrometry with In Situ Methylation

Carbohydrates play critically important roles in energy supply and biological functions in living systems. However, it has been a great challenge to identify saccharides and distinguish their isomers because they have highly similar structures and many possible positions for glycosidic linkages. In this work, an ambient ionization tandem mass spectrometry method was developed to characterize disaccharide structural isomers with in situ methylation. The direct analysis in real time ion source can be used to facilitate the methylation reaction of disaccharides with tetramethylammonium hydroxide. The hydroxyl groups of disaccharides can be methylated instantaneously, and the products can be ionized at the same time. The methylated product ions from full scan mass spectrometry (MS) and tandem MS can be used to distinguish a variety of disaccharide structural isomers with different glycosidic linkages, compositions, and configurations. Characteristic marker ions were discovered, and they can be used for the assignment of linkage type and identification of specific isomeric forms. The method was used for the direct identification of disaccharide isomers from real commercial products such as honey, wine, and milk without complex sample pretreatment or chromatographic separation.

Quantification of disaccharides in solution using isomer-selective ultraviolet photodissociation of hydrogen-bonded clusters in the gas phase

Chemical properties of gas-phase hydrogen-bonded clusters were investigated as a model for interstellar molecular clouds. Cold gas-phase hydrogen-bonded clusters of tryptophan (Trp) enantiomers and disaccharide isomers, including d-maltose and d-cellobiose, were generated by electrospray ionization and collisional cooling in an ion trap at 8 K. Product ion spectra in the 265-290 nm wavelength range were obtained using tandem mass spectrometry. NH₂CHCOOH loss via the C_α-C_β bond cleavage of Trp occurred frequently in homochiral H⁺(d-Trp)(d-maltose) compared with heterochiral H⁺(l-Trp)(d-maltose) at 278 nm, indicating that an enantiomeric excess of l-Trp was formed via the enantiomer-selective photodissociation. The photoreactivity differed between the enantiomers and isomers contained in the clusters at the photoexcitation of 278 nm. A calibration curve for the quantification of disaccharide isomers in solution was constructed by photoexcitation of the hydrogen-bonded clusters of disaccharide isomers with H⁺(l-Trp) at 278 nm. A linear relationship between the natural logarithm of the relative product ion abundance and the mole fraction of d-maltose to d-cellobiose ratio in the solution was obtained, indicating that the mole fraction could be determined from a single product ion spectrum. A calibration curve, for quantification of Trp enantiomers, was also obtained using d-maltose as a chiral auxiliary.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Carboxyl-Based CPMP Tag for Ultrasensitive Analysis of Disaccharides by Negative Tandem Mass Spectrometry

Here, we develop a sensitive method for glucose-containing disaccharide analysis by 1-(4-carboxyphenyl)-3-methyl-5-pyrazolone (CPMP) derivatization using mass spectrometry. The intense anion of [M - H]^- (m/z 759) was observed for CPMP-labeled disaccharides in a negative mode. After derivatization, its sensitivity was significantly increased with the limits of detection (LODs) and limits of quantification (LOQ) ranging from 3.90 to 8.67 ng L^-1 and 12.99 to 28.92 ng L^-1, respectively. During CID-MS/MS analysis, the fragment patterns of CPMP derivatized disaccharides in the negative mode were simpler and clearer than their counterparts in a positive mode, which further could be applied to distinct and relatively quantitative isomeric disaccharides with ultrahigh sensitivity and good reproducibility. The great linear relationships could be achieved under wider concentration ratios from 0.01 to 20 compared to the previous report. Eventually, the developed methodology was applicable to identify isomeric disaccharides in beers. No sucrose was discovered. All beers contain 1,4- and 1,6-linked disaccharides. Some of them also have a mixture of 1,2- and 1,3-linked disaccharides. Through the integration of statistical analysis, beers with different production processes were finally discriminated, and the relative quantification of isomaltose and maltose was realized. In general, this method is sensitive, fast, and reliable for the discrimination and relative quantification of isomeric disaccharides in complex matrices. This study provides a new idea for the structural analysis of oligosaccharides in food, plants, and animals and an important theoretical basis for the exploration of new functions of oligosaccharides.

Multidimensional identification of disaccharide isomers based on non-covalent complexes and tandem mass spectrometry

Glycans are the most abundant organic polymers in nature. They are essential to living organisms and regulate a wide range of biological functions. However, mass spectrometry-based identification of glycan isomers remains challenging due to the complexity of their structures including their complex compositions, linkages, and anomeric configurations. In this study, two novel complex ions, the mononuclear copper-bound dimeric ions [(Cu²⁺)(A)(L-His)-H]⁺ and the mononuclear copper-bound quaternary ions [(Cu²⁺)(A)(L-Ser)₃-H]⁺ (where A denotes a disaccharide, and L-Ser/His denotes l-serine/histidine), were designed for the collision-induced dissociation-based identification and relative quantification of 14 disaccharide isomers. When the unique fragmentation patterns of the above two types of complex ions were mapped into a three-dimensional vector, all the isomers were completely distinguished. Of note, the established method is able to identify mixtures of linkage isomers only using tandem mass spectrometry based on linkage-specific fragment ions of histidine-based complex ions. Finally, the method was successfully applied to the identification and relative quantification of two disaccharide isomers (lactose and sucrose) in dairy beverages. In conclusion, the established method is sensitive to subtle structural differences in disaccharide isomers and has the potential to be used for the differentiation of various glycans.

Application of LEDA algorithm for the recognition of P-glycoprotein and Carbonic Anhydrase hybrid inhibitors and evaluation of their plasma stability by HPLC-MS/MS analysis

Design and synthesis of new candidate drugs produces a large number of compounds that must be qualified and tested to evaluate their characteristics and potential applications. Therefore, many studies will be scheduled and, consequently, it will be necessary to arrange specific, reliable, fast and relatively cheap analytic methods to support this research. The manuscript proposes a new approach in the HPLC-MS/MS analysis by using a sole chromatographic set up, tuned to minimize the run time, without requiring high efficiency or resolution between the analytes. The chromatographic column was used only to avoid or limit the interference of sample matrix towards the analyte ionization process (matrix-effects). Then, the MS/MS properties were explored to solve the signal assignment, by performing a series of energy resolved experiments to optimize the parameters and applying an interesting post-processing data elaboration tool (LEDA). The reliability of the new approach was evaluated in a chemical stability study in PBS and human plasma samples of a series of isomeric compounds P-glycoprotein/Carbonic Anhydrase (P-gp/CA) hybrid inhibitors. The obtained results demonstrated the effectiveness (reliability 97%-100%) of the LEDA algorithm to recognize and to separate the possible isomers present in the samples. The obtained matrix-effects values (ME 96%-106%) established that the chromatographic set up (short column and fast elution gradient) was proper to avoid the matrix interferences, while recovery values (RE 88%-108%) indicate a suitable sample preparation, despite only a protein precipitation was carried out. The quantitative performances of proposed HPLC-MS/MS methods showed an accuracy ranging between 92% and 108% and a precision lower than 13% that allows to be confident on the determination of new P-gp/CA hybrid inhibitors in the degradation study. Therefore, the general procedure proposed was found adequate to study a series of isomeric compounds without their chromatographic separation but only by applying and developing the MS/MS features.

Distinguishment of Glycan Isomers by Trapped Ion Mobility Spectrometry

The in-depth study of glycan has drawn large research interests since it is one of the main biopolymers on the earth with a variety of biological functions. However, the distinguishment of glycans is still difficult due to the similarity of the monosaccharide building block, the anomer, and the linkage of glycosidic bonds. In this study, four novel and representative copper-bound diastereoisomeric complex ions were simultaneously detected in a single measurement by trapped ion mobility mass spectrometry, including mononuclear copper-bound dimeric ions [(Cu²⁺)(A)(l-Ser)-H]⁺ and [(Cu²⁺)(A)(l-His)-H]⁺, the mononuclear copper-bound trimeric ion [(Cu²⁺)(A)(l-Ser)(l-His)-H]⁺, and the binuclear copper-bound tetrameric ion [(Cu²⁺)₂(A)(l-Ser)₂(l-His)-3H]⁺ (where A denotes an oligosaccharide, and l-Ser and l-His denote l-serine and l-histidine, respectively). By combining the collision cross sections of complex ions, 23 oligosaccharide isomers were successfully distinguished including two pairs of sialylated glycan linkage isomers. In addition, due to the unique dissociation pathways of the trimeric ion, both the relative and absolute quantification of the individual isomer in the mixture could be determined using a mass spectrometry-based kinetic method. Finally, the method established above was successfully applied to the identification and quantification of glycan isomers in dairy beverages and juice. The method in the present study was sensitive to the fine difference of glycan isomers and might have wide applicability in glycoscience.

A TIMS-TOF mass spectrometry study of disaccharides from in situ ESI derivatization with 3-pyridinylboronate

Mobilograms of in situ ESI 3-pyridinylboronic acid tagging of isomaltose in the positive or negative mode.

A Comparative Analysis of Methods for Quantitation of Sugars during the Corn-to-Ethanol Fermentation Process

The quantitation of sugars, including glucose, the primary fermentable sugar; maltose (DP2); and maltotriose (DP3), is a standard procedure during the corn-to-ethanol fermentation process. The quantitation of glucose by the Megazyme Assay utilizing glucose oxidase and peroxidase enzymes (GOPOD) and UV-Vis detection, high-performance liquid chromatography with refractive index detection (HPLC-RID), and liquid chromatography mass spectrometry (LC-MS) with electrospray ionization (ESI) and selected ion monitoring (SIM) was studied. Three biological flask fermentation replicates were analyzed every 12 h beginning at 14 h of fermentation (T14) until near completion of fermentation (T62).The method comparison results for glucose quantitation showed that the LC-MS SIM analysis had the lowest limit of quantitation (LOQ) at 2 ppm and the widest dynamic range of 2.7 orders of magnitude. The HPLC-RID analysis had a linear dynamic range (LDR) of 1.5 orders of magnitude with an LOQ of 1500 ppm. The Megazyme GOPOD analysis had an LDR of 0.9 orders of magnitude with an LOQ of 120 ppm.The HPLC-RID method was ideal for glucose quantitation when it was present in high concentrations. In contrast, maltose and maltotriose components were found to be present in lower concentrations, such that simultaneous quantitation of the three analytes is difficult during fermentation. The LC-MS method was the only method able to quantify the concentration of glucose successfully and simultaneously with DP2 and DP3 in all the fermentation broth samples collected from T14 through T62 during the corn-to-ethanol fermentation process.

Advancing Solutions to the Carbohydrate Sequencing Challenge

Carbohydrates possess a variety of distinct features with stereochemistry playing a particularly important role in distinguishing their structure and function. Monosaccharide building blocks are defined by a high density of chiral centers. Additionally, the anomericity and regiochemistry of the glycosidic linkages carry important biological information. Any carbohydrate-sequencing method needs to be precise in determining all aspects of this stereodiversity. Recently, several advances have been made in developing fast and precise analytical techniques that have the potential to address the stereochemical complexity of carbohydrates. This perspective seeks to provide an overview of some of these emerging techniques, focusing on those that are based on NMR and MS-hybridized technologies including ion mobility spectrometry and IR spectroscopy.

Sequence Ion Structures and Dissociation Chemistry of Deprotonated Sucrose Anions

We investigate the tandem mass spectrometry of regiospecifically labeled, deprotonated sucrose analytes. We utilize density functional theory calculations to model the pertinent gas-phase fragmentation chemistry of the prevalent glycosidic bond cleavages (B₁-Y₁ and C₁-Z₁ reactions) and compare these predictions to infrared spectroscopy experiments on the resulting B₁ and C₁ product anions. For the C₁ anions, barriers to interconversion of the pyranose [α-glucose-H]^-, C₁ anions to entropically favorable ring-open aldehyde-terminated forms were modest (41 kJ mol^-1) consistent with the observation of a band assigned to a carbonyl stretch at ~ 1680-1720 cm^-1. For the B₁ anions, our transition structure calculations predict the presence of both deprotonated 1,6-anhydroglucose and carbon 2-ketone ((4S,5S,6R)-4,5-dihydroxy-6-(hydroxymethyl)dihydro-2H-pyran-3(4H)-one) anion structures, with the latter predominating. This hypothesis is supported by our spectroscopic data which show diagnostic bands at 1600, 1674, and 1699 cm^-1 (deprotonated carbon 2-ketone structures), and at ~ 1541 cm^-1 (both types of structure) and RRKM rate calculations. The deprotonated carbon 2-ketone structures are also the lowest energy product B₁ anions. Graphical Abstract ᅟ.

Fragmentation Pathways of Lithiated Hexose Monosaccharides

We characterize the primary fragmentation reactions of three isomeric lithiated D-hexose sugars (glucose, galactose, and mannose) utilizing tandem mass spectrometry, regiospecific labeling, and theory. We provide evidence that these three isomers populate similar fragmentation pathways to produce the abundant cross-ring cleavage peaks (^0,2A₁ and ^0,3A₁). These pathways are highly consistent with the prior literature (Hofmeister et al. J. Am. Chem. Soc. 113, 5964-5970, 1991, Bythell et al. J. Am. Soc. Mass Spectrom. 28, 688-703, 2017, Rabus et al. Phys. Chem. Chem. Phys. 19, 25643-25652, 2017) and the present labeling data. However, the structure-specific energetics and rate-determining steps of these reactions differ as a function of precursor sugar and anomeric configuration. The lowest energy water loss pathways involve loss of the anomeric oxygen to furnish B₁ ions. For glucose and galactose, the lithiated α-anomers generate ketone structures at C2 in a concerted reaction involving a 1,2-migration of the C2-H to the anomeric carbon (C1). In contrast, the β-anomers are predicted to form 1,3-anhydroglucose/galactose B₁ ion structures. Initiation of the water loss reactions from each anomeric configuration requires distinct reactive conformers, resulting in different product ion structures. Inversion of the stereochemistry at C2 has marked consequences. Both lithiated mannose forms expel water to form 1,2-anhydromannose B₁ ions with the newly formed epoxide group above the ring. Additionally, provided water loss is not instantaneous, the α-anomer can also isomerize to generate a ketone structure at C2 in a concerted reaction involving a 1,2-migration of the C2-H to C1. This product is indistinguishable to that from α-glucose. The energetics and interplay of these pathways are discussed. Graphical Abstract ᅟ.

Deprotonated carbohydrate anion fragmentation chemistry: structural evidence from tandem mass spectrometry, infra-red spectroscopy, and theory

We investigate the gas-phase structures and fragmentation chemistry of deprotonated carbohydrate anions using combined tandem mass spectrometry, infrared spectroscopy, regioselective labelling, and theory.