MS of the six isomers of (GlcN)2(GlcNAc)2 aminoglucan tetrasaccharides (diacetylchitotetraoses): Rules of fragmentation for the sodiated molecules and application to sequence analysis of hetero-chitooligosaccharides

Collision-Induced Dissociation of Fucose and Identification of Anomericity

Structural determination of carbohydrates using mass spectrometry remains challenging, particularly, the differentiation of anomeric configurations. In this work, we studied the collision-induced dissociation (CID) mechanisms of sodiated α- and β-l-fucose using an experimental method and quantum chemistry calculations. The calculations show that α-l-fucose is more likely to undergo dehydration due to the fact that O1 and O2 are on the same side of the sugar ring. In contrast, β-l-fucose is more prone to the ring-opening reaction because more OH groups are on the same side of the sugar ring as O1. These differences suggest a higher preference for the dehydration reaction in sodiated α-l-fucose but a lower preference for ring-opening compared to that of β-l-fucose. The calculation results, which are used to assign the CID mass spectra of α- and β-l-fucose separated by high-performance liquid chromatography, are supported by the fucose produced from the CID of disaccharides Fuc-β-(1 → 3)-GlcNAc and Fuc-α-(1 → 4)-GlcNAc. This study demonstrates that the correlation of cis- and trans-configurations of O1 and O2 to the relative branching ratios of dehydration and cross-ring dissociation in CID, observed in aldohexose and ketohexose in the pyranose form, can be extended to deoxyhexoses for anomericity determination.

Dissociation of Mannose-Rich Glycans Using Collision-Based and Electron-Based Ion Activation Methods

Three dissociation methods, including collision-induced dissociation (CID), electron capture dissociation (ECD), and electronic excitation dissociation (EED), were evaluated for the dissociation of doubly charged glycans using sodium or magnesium ions as charge carriers. CID produced mainly glycosidic cleavages, although more cross-ring fragment ions could be obtained at higher intensities when magnesium ions were used as charge carriers [M + Mg]²⁺. The ^0,2A₃, ^0,3A₃, and ^0,4A₃ ions provided structural information on the 3 → 1 and 6 → 1 linkages of the mannoses. Some internal fragment ions, such as ^2,4A₅_Y_3β, were also produced in high abundance, thus providing additional information on the glycan structure. ECD produced limited fragments compared to other dissociation methods when either of the metal ions were used as charge carriers. Cross-ring fragments were obtained in relatively high abundance, with the charge mainly retained on the nonreducing end. EED produced extensive glycosidic and cross-ring cleavages when either metal charge carrier was used. A higher fragmentation efficiency was achieved and more structural-specific fragments were produced when Na⁺ was used as the charge carrier. Of the 31 possible cross-ring cleavages, including 0,2-, 0,4-, 1,5-, 2,4-, and 3,5-cleavages, 25 were found, thus providing extensive linkage information. A wide range of fragment ions could be obtained in all dissociation methods when Mg²⁺ was used as the charge carrier. Two specific analytical approaches were found to produce extensively structural-specific information on the glycans studied, namely CID of magnesiated glycans and EED of sodiated glycans. These two methods were selected to further analyze the larger mannose-rich glycans Man₆GlcNAc₂ and Man₈GlcNAc₂ and generated extensive structural information.

Logically derived sequence tandem mass spectrometry for structural determination of Galactose oligosaccharides

Mass spectrometry has high sensitivity and is widely used in the identification of molecular structures, however, the structural determination of oligosaccharides through mass spectrometry is still challenging. A novel method, namely the logically derived sequence (LODES) tandem mass spectrometry (MSⁿ), for the structural determination of underivatized oligosaccharides was developed. This method, which is based on the dissociation mechanisms, involves sequential low-energy collision-induced dissociation (CID) of sodium ion adducts, a logical sequence for identifying the structurally decisive product ions for subsequent CID, and a specially prepared disaccharide CID spectrum database. In this work, we reported the assignment of the specially prepared galactose disaccharide CID spectra. We used galactose trisaccharides and tetrasaccharides as examples to demonstrate LODES/MSⁿ is a general method that can be used for the structural determination of hexose oligosaccharides. LODES/MSⁿ has the potential to be extended to oligosaccharides containing other monosaccharides provided the dissociation mechanisms are understood and the corresponding disaccharide database is available.

Simple Method for De Novo Structural Determination of Underivatised Glucose Oligosaccharides

Carbohydrates have various functions in biological systems. However, the structural analysis of carbohydrates remains challenging. Most of the commonly used methods involve derivatization of carbohydrates or can only identify part of the structure. Here, we report a de novo method for completely structural identification of underivatised oligosaccharides. This method, which can provide assignments of linkages, anomeric configurations, and branch locations, entails low-energy collision-induced dissociation (CID) of sodium ion adducts that enable the cleavage of selective chemical bonds, a logical procedure to identify structurally decisive fragment ions for subsequent CID, and the specially prepared disaccharide CID spectrum databases. This method was first applied to determine the structures of four underivatised glucose oligosaccharides. Then, high-performance liquid chromatography and a mass spectrometer with a built-in logical procedure were established to demonstrate the capability of the in situ CID spectrum measurement and structural determination of the oligosaccharides in chromatogram. This consolidation provides a simple, rapid, sensitive method for the structural determination of glucose oligosaccharides, and applications to oligosaccharides containing hexoses other than glucose can be made provided the corresponding disaccharide databases are available.

Simple Approach for De Novo Structural Identification of Mannose Trisaccharides

Oligosaccharides have diverse functions in biological systems. However, the structural determination of oligosaccharides remains difficult and has created a bottleneck in carbohydrate research. In this study, a new approach for the de novo structural determination of underivatized oligosaccharides is demonstrated. A low-energy collision-induced dissociation (CID) of sodium ion adducts was used to facilitate the cleavage of desired chemical bonds during the dissociation. The selection of fragments for the subsequent CID was guided using a procedure that we built from the understanding of the saccharide dissociation mechanism. The linkages, anomeric configurations, and branch locations of oligosaccharides were determined by comparing the CID spectra of oligosaccharide with the fragmentation patterns based on the dissociation mechanism and our specially prepared disaccharide CID spectrum database. The usefulness of this method was demonstrated to determine the structures of several mannose trisaccharides. This method can also be applied in the structural determination of oligosaccharides larger than trisaccharides and containing hexose other than mannose if authentic standards are available. Graphical Abstract.

Identification of structurally closely related monosaccharide and disaccharide isomers by PMP labeling in conjunction with IM-MS/MS

It remains particularly difficult for gaining unambiguous information on anomer, linkage, and position isomers of oligosaccharides using conventional mass spectrometry (MS) methods. In our laboratory, an ion mobility (IM) shift strategy was employed to improve confidence in the identification of structurally closely related disaccharide and monosaccharide isomers using IMMS. Higher separation between structural isomers was achieved using 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatization in comparison with phenylhydrazine (PHN) derivatization. Furthermore, the combination of pre-IM fragmentation of PMP derivatives provided sufficient resolution to separate the isomers not resolved in the IMMS. To chart the structural variation observed in IMMS, the collision cross sections (CCSs) for the corresponding ions were measured. We analyzed nine disaccharide and three monosaccharide isomers that differ in composition, linkages, or configuration. Our data show that coexisting carbohydrate isomers can be identified by the PMP labeling technique in conjunction with ion-mobility separation and tandem mass spectrometry. The practical application of this rapid and effective method that requires only small amounts of sample is demonstrated by the successful analysis of water-soluble ginseng extract. This demonstrated the potential of this method to measure a variety of heterogeneous sample mixtures, which may have an important impact on the field of glycomics.

Anomerization of Acrylated Glucose During Traveling Wave Ion Mobility Spectrometry

Anomerization of simple sugars in the liquid phase is known as an acid- and base-catalyzed process, which highly depends on solvent polarity. This reaction is reported here to occur in the gas phase, during traveling wave ion mobility spectrometry (TWIMS) experiments aimed at separating α- and β-anomers of penta-acrylated glucose generated as ammonium adducts in electrospray ionization. This compound was available in two samples prepared from glucose dissolved in solvents of different polarity, namely tetrahydrofuran (THF) and N,N-dimethylacetamide (DMAC), and analyzed by electrospray tandem mass spectrometry (ESI-MS/MS) as well as traveling wave ion mobility (ESI-TWIMS-MS). In MS/MS, an anchimerically-assisted process was found to be unique to the electrosprayed α-anomer, and was only observed for the THF sample. In ESI-TWIMS-MS, a signal was measured at the drift time expected for the α-anomer for both the THF and DMAC samples, in apparent contradiction to the MS/MS results, which indicated that the α-anomer was not present in the DMAC sample. However, MS/MS experiments performed after TWIMS separation revealed that ammonium adducts of the α-anomer produced from each sample, although exhibiting the same collision cross section, were clearly different. Indeed, while the α-anomer actually present in the THF sample was electrosprayed with the ammonium adducted at the C2 acrylate, its homologue only observed when the DMAC sample was subjected to TWIMS hold the adducted ammonium at the C1 acrylate. These findings were explained by a β/α inter-conversion upon injection in the TWIMS cell, as supported by theoretical calculation and dynamic molecular modeling.

Electron transfer dissociation of doubly charged ions with different cationizing agents

Electron transfer dissociation (ETD) studies have been performed on a peptide and a synthetic polysaccharide doubly charged by different cationization agents. The ETD of protonated-sodiated bombesin gave rise to contiguous series of abundant c- and z-type ions that identified the complete sequence. ETD of the doubly protonated peptide produced a different fragment distribution, which also allowed for complete sequence coverage, but the relative intensities of some sequence ions were very small. Collisionally activated dissociation (CAD) of either precursor rendered limited sequence information. ETD of the sodiated-ammoniated pentamer of a starch-derived linear polysaccharide caused extensive fragmentation through cross-ring cleavages that revealed the possible position of a hydroxyethyl substituent on the saccharide ring. In contrast, ETD of the di-sodiated pentasaccharide did not produce a structure-revealing fragmentation pattern. On the other hand, CAD resulted in efficient glycosidic bond cleavages, either directly (from the sodiated-ammoniated precursor) or via multi-stage fragmentation (from the di-sodiated precursor), which indicated that hydroxyethylation occurs randomly at any saccharide repeat unit along the chain. Overall, the use of different cationizing agents complements the information available by using identical charge sites and opens or enhances ETD pathways that unveil valuable sequence or positional information.

Applications of mass spectrometry to structural analysis of marine oligosaccharides

Marine oligosaccharides have attracted increasing attention recently in developing potential drugs and biomaterials for their particular physical and chemical properties. However, the composition and sequence analysis of marine oligosaccharides are very challenging for their structural complexity and heterogeneity. Mass spectrometry (MS) has become an important technique for carbohydrate analysis by providing more detailed structural information, including molecular mass, sugar constituent, sequence, inter-residue linkage position and substitution pattern. This paper provides an overview of the structural analysis based on MS approaches in marine oligosaccharides, which are derived from some biologically important marine polysaccharides, including agaran, carrageenan, alginate, sulfated fucan, chitosan, glycosaminoglycan (GAG) and GAG-like polysaccharides. Applications of electrospray ionization mass spectrometry (ESI-MS) are mainly presented and the general applications of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) are also outlined. Some technical challenges in the structural analysis of marine oligosaccharides by MS have also been pointed out.

Access to tetra-N-acetyl-chitopentaose by chemical N-acetylation of glucosamine pentamer

Nowadays, the easy access of tetra-N-acetyl-chitopentaose and its counterparts is highly interesting since such chemical compounds are precursors of biological signal molecules with a strong agro-economic impact. The chemical synthesis of tetra-N-acetyl-chitopentaose by controlled N-acetylation of the glucosamine pentamer hydrochloride under mild conditions is described herein. A systematic study on the influence of the different parameters involved in this reaction, such as the solvent, the acetylating agent, and the base used for the deprotonation of ammonium groups of the starting material was carried out. The characterization of final reaction products by HPLC and MALDI-TOF mass spectrometry showed that each of these parameters affects differently the acetylation reaction. Whereas the solvent plays an important role in the N- or O-acetylation selectivity, the acetylating agent and the base were found to influence both the degree of N-acetylation and the distribution of the partially N-acetylated derivatives in the product mixtures. Based on these results, optimized reaction conditions have been established allowing tetra-N-acetyl-chitopentaose to be synthesized in a one-pot deprotonation/N-acetylation of the glucosamine pentamer hydrochloride in a moderate yield (ca 30%).

Separation of isomeric disaccharides by traveling wave ion mobility mass spectrometry using CO2 as drift gas

The use of CO(2) as a massive and polarizable drift gas is shown to greatly improve peak-to-peak resolution (R(p-p) ), as compared with N(2) , for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline R(p-p) was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (R(p-p)  = 0.76), maltose and sucrose (R(p-p)  = 1.04), and maltose and lactose (R(p-p)  = 0.74). Ion mobility mass spectrometry using CO(2) as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides.