Recent applications of ionic liquid-based tags in glycoscience

The functionalization of glycosides with ionic compounds such as ionic liquids provides enhanced polarity for the labelled glycans thanks to the presence of a permanent positive charge. The chemical derivatisation of glycans with ionic liquids constitutes an emerging strategy to boost the detection sensitivity in MS applications. This allows the straightforward monitoring and detection of the presence of labelled glycans in complex matrices and in those cases where very limited amounts of material were available such as in biological samples and chemoenzymatic reactions. The use of ionic liquid based derivatisation agents can be further exploited for the labelling of live cells via metabolic oligosaccharide engineering for the detection of cancer biomarkers and for the tuning of live cells-surface properties with implications in cancer prognosis and progression. In this mini-review we summarise the latest development of the ionic liquid based derivatisation agents in glycoscience focussing on their use for sensitive MS applications.

A promiscuous glycosyltransferase generates poly-β-1,4-glucan derivatives that facilitate mass spectrometry-based detection of cellulolytic enzymes

Promiscuous activity of a glycosyltransferase was exploited to polymerise glucose from UDP-glucose via the generation of β-1,4-glycosidic linkages. The biocatalyst was incorporated into biocatalytic cascades and chemo-enzymatic strategies to synthesise cello-oligosaccharides with tailored functionalities on a scale suitable for employment in mass spectrometry-based assays. The resulting glycan structures enabled reporting of the activity and selectivity of celluloltic enzymes.

Sugar-Based Ionic Liquids: Multifaceted Challenges and Intriguing Potential

Carbohydrates represent a promising option in transitioning from oil-based chemical resources to renewable ones, with the goal of developing chemistries for a sustainable future. Cellulose, hemicellulose, and largely available monosaccharides already provide useful chemical building blocks, so-called platform chemicals, such as levulinic acid and hydroxymethyl furfural, as well as solvents like cyrene or gamma-valerolactone. Therefore, there is great anticipation for novel applications involving materials and chemicals derived from sugars. In the field of ionic liquids (ILs), sugar-based ILs have been overlooked for a long time, mainly on account of their multistep demanding preparation. However, exploring new strategies for accessing sugar-based ILs, their study, and their exploitation, are attracting increasing interest. This is due to the growing concerns about the negative (eco)toxicity profile of most ILs in conjunction with their non-sustainable nature. In the present review, a literature survey concerning the development of sugar-based ILs since 2011 is presented. Their preparation strategies and thermal behavior analyses, sorted by sugar type, make up the first two sections with the intention to provide the reader with a useful guide. A final overview of the potential applications of sugar-based ILs and their future perspectives complement the present analysis.

Rapid assembly of phosphate-bridged tetra-mannose by ionic liquid-supported oligosaccharide synthesis

An efficient ionic liquid-supported oligosaccharide synthesis (ILSOS) strategy was described for the synthesis of linear oligo-phosphomannan. A new cleavable benzyl carbamate-type IL supporter containing 5-aminopentanyl linker was designed as an acceptor IL tag to facilitate this synthesis. The chain elongation on IL tag was achieved by H-phosphonate chemistry, including condensation with α-mannosyl H-phosphonate, in situ oxidation reaction and subsequent deprotection. After four cycles, linear α-(1 → 6)-tetra-mannan phosphate was obtained with a total yield of 52.7% within 45 h. The IL tagged product exhibited a tunable solubility in polar and non-polar solvent systems that facilitate a chromatography-free purification in the assembly process. The IL tag could be easily removed after hydrogenolysis treatment after the final step, to afford an amine terminated linker at the reducing end of phosphoglycan for further conjugation with a carrier protein. This methodology offered an efficient and chromatography-free approach for the synthesis of phosphoglycan.

1-(2-Aminoethyl)-3-methyl-1H-imidazol-3-ium tetrafluoroborate: synthesis and application in carbohydrate analysis

Reductive alkylation of the carbonyl group of carbohydrates with fluorescence or ionizing labels is a prerequisite for the sensitive analysis of carbohydrates by chromatographic and mass spectrometric techniques. Herein, 1-(2-aminoethyl)-3-methyl-1H-imidazol-3-ium tetrafluoroborate ([MIEA][BF4]) was successfully synthesized using tert-butyl N-(2-bromoethyl)carbamate and N-methylimidazole as starting materials. MIEA+ was then investigated as a multifunctional oligosaccharide label for glycan profiling and identification using LC-ESI-ToF and by MALDI-ToF mass spectrometry. The reductive amination of this diazole with carbohydrates was exemplified by labeling N-glycans from the model glycoproteins horseradish peroxidase, RNase B, and bovine lactoferrin. The produced MIEA+ glycan profiles were comparable to the corresponding 2AB labeled glycan derivatives and showed improved ESI-MS ionization efficiency over the respective 2AB derivatives, with detection sensitivity in the low picomol to the high femtomol range.

Ionic liquid-assisted catalysis for glycosidation of two triterpenoid sapogenins

In order to study the universality of ionic liquids-assisted glycosidation and explore their catalytic behaviors together with potential, oleanolic acid and ursolic acid were selected to establish catalytic system as typical triterpene sapogenins.

"One-Pot" Protection, Glycosylation, and Protection-Glycosylation Strategies of Carbohydrates

Carbohydrates, which are ubiquitously distributed throughout the three domains of life, play significant roles in a variety of vital biological processes. Access to unique and homogeneous carbohydrate materials is important to understand their physical properties, biological functions, and disease-related features. It is difficult to isolate carbohydrates in acceptable purity and amounts from natural sources. Therefore, complex saccharides with well-defined structures are often most conviently accessed through chemical syntheses. Two major hurdles, regioselective protection and stereoselective glycosylation, are faced by carbohydrate chemists in synthesizing these highly complicated molecules. Over the past few years, there has been a radical change in tackling these problems and speeding up the synthesis of oligosaccharides. This is largely due to the development of one-pot protection, one-pot glycosylation, and one-pot protection-glycosylation protocols and streamlined approaches to orthogonally protected building blocks, including those from rare sugars, that can be used in glycan coupling. In addition, new automated strategies for oligosaccharide syntheses have been reported not only for program-controlled assembly on solid support but also by the stepwise glycosylation in solution phase. As a result, various sugar molecules with highly complex, large structures could be successfully synthesized. To summarize these recent advances, this review describes the methodologies for one-pot protection and their one-pot glycosylation into the complex glycans and the chronological developments associated with automated syntheses of oligosaccharides.

Ionic-liquid supported rapid synthesis of an N-glycan core pentasaccharide on a 10 g scale

A hetero-branched N-glycan core pentasaccharide was rapidly assembled on a new ionic liquid support on a 10 g scale.

Imidazolium-labeled glycosides as probes to harness glycosyltransferase activity in human breast milk

Imidazolium-labeled (ITag-) glycosides are used to harness the glycosyltransferase activity directly from human breast milk. The covalently attached ionic labels provide a bifunctional chemical handle that is used to monitor reaction progress by MS, as well as aid in product purification from complex mixtures. The technology is exemplified in the synthesis of biologically relevant oligosaccharide analogs, LacNAc-ITag, ITag-Lewisx and ITag-Lewisa, in a matter of days from human breast milk without having to isolate specific enzymes.

Imidazolium-tagged glycan probes for non-covalent labeling of live cells

The use imidazolium tagged-mannosamine derivative for the non-covalent, rapid and site-specific labeling of sialic acid containing glycoproteins using commercial N-nitrilotriacetate fluorescent reagents in a range of live cells is reported.

Convergent synthesis of oligosaccharides on the gram-scale using cetyl thioglycoside based on a hydrophobically assisted switching phase method

A hydrophobically assisted switching phase (HASP) method is an efficient strategy for the synthesis of carrier-loaded oligosaccharides.

Efficient assembly of oligomannosides using the hydrophobically assisted switching phase method

The hydrophobically assisted switching phase (HASP) method was applied in the assembly of oligomannosides. A new mannosyl donor with high reactivity was selected after a series of optimization studies, which was suitable for the synthesis of oligomannosides via the HASP method. The practicability of the HASP method towards the synthesis of branched oligosaccharides was explored and two branched penta-mannosides were assembled efficiently.

Rapid and mild silylation of β-amino alcohols at room temperature mediated by N-methylimidazole for enhanced detectability by gas chromatography/electron ionization mass spectrometry

RATIONALE

In this work, we expand the use of in situ activation of chloro(dimethyl)phenylsilane using N-methylimidazole (NMI) for the effective derivatization of β-aminoethyl alcohols. Due to its enhanced nucleophilic character, NMI is expected to act as an efficient activator in these reactions.

METHODS

The derivatization of a panel of β-aminoethyl alcohols was accomplished by reacting the analyte with chloro(dimethyl)phenylsilane in the presence of either NMI or pyridine. After the addition of chloro(dimethyl)phenylsilane, the vials were gently tumbled for 1 h at ambient temperature. The phenyldimethylsilyl derivatives were identified using gas chromatography/electron ionization mass spectrometry (GC/EI-MS).

RESULTS

A total of ten β-aminoethyl alcohols were successfully derivatized via in situ activation of chloro(dimethyl)-phenylsilane with NMI. Derivatization with NMI was significantly more efficient than with pyridine by a factor of 3-6 for the studied alcohols. The derivatizations in the presence of NMI were found to occur in just 1 h and were conveniently executed at ambient temperature.

CONCLUSIONS

The use of the nitrogenous base NMI in order to activate chloro(dimethyl)phenylsilane for the efficient silylation of a panel of β-aminoethyl alcohols has been demonstrated. The present work shows that NMI is an efficient base for the smooth derivatization of these types of alcohols. Furthermore, the installation of the bulky PDMS group onto these alcohols adds to the certainty that this is a viable approach for the installation of the more commonly employed, trimethylsilyl group. Published in 2014. This article is a U.S. Government work and is in the public domain in the USA.

Glycopeptide synthesis on an ionic liquid support

An ionic liquid-supported synthetic method for the construction of glycopeptides in high yields is reported. This method avoids the use of large excesses of reagents and chromatographic purification and, therefore, represents a useful addition to existing approaches for the ionic liquid-supported synthesis of oligosaccharides and peptides.

Carbohydrate-based N-heterocyclic carbenes for enantioselective catalysis

Versatile syntheses of C2-linked and C₂-symmetric carbohydrate-based NHC·HCls from functionalised amino-carbohydrate derivatives are reported. The corresponding Rh complexes were evaluated in asymmetric hydrosilylation of ketones.

Superarming of glycosyl donors by combined neighboring and conformational effects

A novel glycosyl donor that combines the concepts of both conformational and electronic superarming has been synthesized. The reactivity and selectivity of the donor have been tested in competition experiments.

HPLC-assisted automated oligosaccharide synthesis

A standard HPLC was adapted to polymer supported oligosaccharide synthesis. Solution-based reagents are delivered using a software-controlled solvent delivery system. The reaction progress and completion can be monitored in real time using a standard UV detector. All steps of oligosaccharide assembly including loading, glycosylation, deprotection, and cleavage can be performed using this setup.

Reverse orthogonal strategy for oligosaccharide synthesis

Herein, we report the invention of a novel expeditious concept for oligosaccharide synthesis. Unlike the classic orthogonal strategy based on leaving groups, the reverse approach is based on orthogonal protecting groups, herein p-methoxybenzyl and 4-pentenoyl, which allows for efficient oligosaccharide assembly in the reverse direction.