Kwok-Kong Tony Mong

Dimethylformamide: an unusual glycosylation modulator.

However, most of these methods require additional steps forthe installation of a specific functionality and are thereforeless convenient for routine synthesis. Herein, we report asimple and general a-glycosylation method in which N,N-dimethylformamide (DMF) is used as a modulating moleculeto direct the stereochemical course of glycosylation. Furtherelaboration of this approach led to a practical a-selectiveprocedure based on preactivation that is useful for theglycosylaton of both O-glycoside and thioglycoside acceptors.In a previous study of the chlorination of glycosylhemiacetals, we observed that residual DMF in the glyco-sylation mixture promoted the formation of 1,2-cis a-glyco-sidic bonds.

Low‐Concentration 1,2‐trans β‐Selective Glycosylation Strategy and Its Applications in Oligosaccharide Synthesis

This study develops an operationally easy, efficient, and general 1,2-trans beta-selective glycosylation reaction that proceeds in the absence of a C2 acyl function. This process employs chemically stable thioglycosyl donors and low substrate concentrations to achieve excellent beta-selectivities in glycosylation reactions. This method is widely applicable to a range of glycosyl substrates irrespective of their structures and hydroxyl-protecting functions. This low-concentration 1,2-trans beta-selective glycosylation in carbohydrate chemistry removes the restriction of using highly reactive thioglycosides to construct 1,2-trans beta-glycosidic bonds. This is beneficial to the design of new strategies for oligosaccharide synthesis, as illustrated in the preparation of the biologically relevant beta-(1-->6)-glucan trisaccharide, beta-linked Gb(3) and isoGb(3) derivatives.

Neighboring-Group Participation by C-2 Ether Functions in Glycosylations Directed by Nitrile Solvents

Ether-protecting functions at C-2 hydroxy groups have been found to play participating roles in glycosylations when the reactions are conducted in nitrile solvent mixtures. The participation mechanism is based on intramolecular interaction between the lone electron pair of the oxygen atom of the C-2 ether function and the nitrile molecule when they are positioned in a cis configuration. A 1,2-cis glycosyl oxazolinium intermediate is formed. This participation, in conjunction with the anomeric effect of the glycosyl donor, confers high 1,2-trans selectivities on glycosylations. Further application of this concept has led to efficient preparations of α-(1→5)-arabinan oligomers.

Synthesis of Neisseria meningitidis Serogroup W135 Capsular Oligosaccharides for Immunogenicity Comparison and Vaccine Development

Carbohydrate VaccineC.-H. Wang, S.-T. Li, T.-L. Lin, Y.-Y. Cheng,T.-H. Sun, J.-T. Wang, T.-J. R. Cheng,K. K. T. Mong, C.-H. Wong,C.-Y. Wu* &&&&—&&&&Synthesis of Neisseria meningitidisSerogroup W135 CapsularOligosaccharides for ImmunogenicityComparison and Vaccine DevelopmentSweetening the deal: N. meningitidisserogroup W135 capsular oligosacchar-ides were synthesized in lengths fromdisaccharides to decasaccharides. Serafrom mice immunized with these oligo-saccharide–protein conjugates wereexamined by a glycan microarray (seepicture) and bactericidal assay for anti-body specificity and the ability to killbacteria.

Modulating glycosylation with exogenous nucleophiles: an overview

The major challenge in carbohydrate synthesis is stereochemical control of glycosidic bond formation. Different glycosylation methods have been developed that are based on the modulation effect of external nucleophiles. This review highlights the development, synthetic application, challenges and outlook of the modulated glycosylation methods.

Ultrasonication-assisted spray ionization mass spectrometry for on-line monitoring of organic reactions

A straightforward on-line monitoring of organic reactions by ultrasonication-assisted spray ionization mass spectrometry (UASI MS) is demonstrated in this work.

Identification of Pseudomonas aeruginosa using functional magnetic nanoparticle-based affinity capture combined with MALDI MS analysis

PA-IL is a galactophilic lectin that is found on the outer membrane of Pseudomonas aeruginosa. Pigeon ovalbumin (POA), a phosphoprotein, contains high levels of terminal Gal alpha(1-->4)Gal units. Thus, magnetic nanoparticles with immobilized POA can be used as affinity probes for P. aeruginosa, functioning via the recognition of galactophilic PA-IL. We fabricated POA-bound nanoparticles (NPs) by immobilizing POA onto the surface of core/shell magnetic iron oxide/alumina NPs via metal-phosphate chelation. We then used the generated NPs to probe target bacteria from complex samples. The trapped bacterial cells were characterized based on their mass peak profiles obtained from MALDI MS analyses. In addition, we confirmed the determination of P. aeruginosa using a proteomic strategy: combining the resultant MALDI MS/MS spectra of its tryptic digest with protein database searching. The feasibility of using this approach to rapidly characterize P. aeruginosa from clinical samples without the need to perform culturing steps was also demonstrated.

Identification of Essential Residues of Human α-l-Fucosidase and Tests of Its Mechanism†

Fucosylated glycoconjugates have critical roles in biological processes, but a limited availability of alpha-l-fucosidase has hampered research on this human enzyme (h-Fuc) at a molecular level. After overexpressing h-Fuc in Escherichia coli as an active form, we investigated the catalytic function of this recombinant enzyme. Based on sequence alignment and structural analysis of close homologues of h-Fuc, nine residues of glutamate and aspartate in h-Fuc were selected for mutagenic tests to determine the essential residues. Among the mutants, D225N, E289Q, and E289G lost catalytic activity significantly; their k(cat) values are 1/5700, 1/430, and 1/340, respectively, of that of the wild-type enzyme. The Brønsted plot for k(cat)/K(m) for the E289G mutant is linear with beta(lg) = -0.93, but that for k(cat) is biphasic, with beta(lg) for poor substrates being -0.88 and for activated substrates being -0.11. The small magnitude of beta(lg) for the activated substrates may indicate that the rate-limiting step of the reaction is defucosylation, whereas the large magnitude of the latter beta(lg) value for the poor substrates indicates that the rate-limiting step of the reaction becomes fucosylation. The kinetic outcomes support an argument that Asp(225) functions as a nucleophile and Glu(289) as a general acid/base catalyst. As further evidence, azide significantly reactivated D225G and E289G, and (1)H NMR spectral analysis confirmed the formation of beta-fucosyl azide and alpha-fucosyl azide in the azide rescues of D225G and E289G catalyses, respectively. As direct evidence to prove the function of Glu(289), an accumulation of fucosyl-enzyme intermediate was detected directly through ESI/MS analysis.

Tuning Reactivity of Glycosyl Imidinium Intermediate for 2-Azido-2-deoxyglycosyl Donors in α-Glycosidic Bond Formation

The chemical properties of nucleophile additives were investigated in a modulated glycosylation context. N-Formylmorpholine (NFM) was found to be an effective modulator for glycosylation with less reactive 2-azido-2-deoxythioglucosyl and thiogalactosyl donors.

Online monitoring of chemical reactions by contactless atmospheric pressure ionization mass spectrometry

Online monitoring of the appearance of the intermediates and products during chemical reactions is helpful to understand reaction mechanisms. Various analytical tools including nuclear magnetic resonance spectroscopy, Raman spectroscopy and mass spectrometry (MS) have been employed for the study. MS is one of the most promising means among analytical tools that can provide information of mass-to-charge ratios for intermediates and products generated from chemical reactions. The main challenge for online monitoring of species generated from chemical reactions by MS is the interface design. The success of online monitoring of chemical reactions using MS relies on real-time recording of the generated species from reactions without sacrificing kinetic information during coupling. In addition, MS can only detect gas-phase ions. Nevertheless, most chemical reactions occur in liquid phase. Thus, generating gas-phase ions from liquid samples is vital for the success of this study. Electrospray ionization (ESI) is one of the most common atmospheric pressure ionization (API) methods that generate gas-phase ions from liquid-reacting species/products in the proximity of a mass spectrometer for online monitoring of chemical reactions. In addition, some recently developed ambient ionization methods such as desorption ESI, extractive ESI, electrospray desorption ionization, fused droplet ESI, low-temperature plasma probe for ambient desorption ionization and ultrasonication-assisted spray ionization [27] also have shown their usefulness in monitoring reactions in real time. High-voltage electric power supply, gas supply, or laser is generally required for these approaches. High-voltage free approaches such as Venturi easy ambient sonic-spray ionization with gas supply only have been used to online monitoring of organic reactions. A comprehensive description about the progress using MS to monitor chemical reactions can refer to the recently published book written by Santos. Some of these techniques may be suitable for monitoring fast reactions that take place during desorption/ionization process. However, our current study is focused on using a recently developed API technique for monitoring the changes of reacting species from an organic reaction requiring a long reaction time to reach the end of the reaction. A continuous-flow API method was recently explored, called contactless API (C-API), which uses a short tapered-capillary tip (~ 1 cm) as the spray emitter for the generation of gas-phase ions from a liquid solution. High-voltage electric power supply, gas supply and laser are not required for the C-API approach. The C-API approach only requires a tapered capillary for the generation of gas-phase ions in the proximity of MS (Fig. 1). The sample solution can flow continuously from the sample inlet