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Fluorinated glycosides are known to resist the glycosidase-catalyzed glycosidic bond cleavage; however, the synthesis of such glycans, especially 3-fluoro-sialic acid (3F-Neu5Ac) containing sialosides, has been a major challenge. Though the enzymatic synthesis of α-2,3-linked 3F-sialosides was reported, until recently there has not been any effective method available for the synthesis of 3F-sialosides in the α-2,6-linkage. In order to understand the biological effect of such modification, we report here a chemical synthesis of 3Fax-Neu5Ac-α2,6-Gal as a building block for the assembly of 3Fax-Neu5Ac-containing sialosides and a representative homogeneous antibody glycoform. Our results showed that the sialosides are stable under sialidase catalysis and the rituximab glycoform with a sialylated complex-type biantennary glycan terminated with 3Fax-Neu5Ac in the α-2,6-linkage (α2,6-F-SCT) has a similar binding avidity as its parent glycoform. These findings open up new opportunities for the development of ther...

Inhibitors of transglycosylases may serve as potent antibiotics that are less prone to resistance development in bacterial pathogens. To facilitate the search of such compounds, a transglycosylase (TGase) domain of the membrane integral multidomain Streptococcus pneumoniae PBP1b was cloned and expressed. This TGase domain was characterized by a substrate-dependent fluorescence coupled enzyme assay and an inhibitor-tethered surface plasmon resonance binding assay. Both assays show that the catalytic efficiency of the domain is comparable to that of the monofunctional transglycosylases, and it is fully active in the absence of other domains. The isolation of the active TGase domain makes it possible to screen for potential antibiotics targeting transglycosylases.

Tackling the problem of carbohydrate recognition is a subject of current interest. Our strategies in this regard include development of new methods for the synthesis of saccharides and sugar arrays for screening, design of d-peptides to target bacterial cell-surface sugars, preparation of mechanism-based inhibitors of the enzymes involved in the biosynthesis of saccharides and the synthesis of aminoglycoside mimetics to target RNA.

C1 Nitrogen iminocyclitols are potent inhibitors of N-acetyl-beta-hexosaminidases. Given hexosaminidases' important roles in osteoarthritis, we developed two straightforward and efficient syntheses of C1 nitrogen iminocyclitols from two readily available starting materials, D-mannosamine hydrochloride and the microbial oxidation product of fructose. A diversity-oriented synthetic strategy was then performed by coupling these core structures with various aldehydes, carboxylic acids, and alkynes to generate three separate libraries. High-throughput screening of the generated libraries with human N-acetyl-beta-hexosaminidases produced only moderate inhibitory activities. However, the synthetic approach and screening strategy for these compounds will be applied to develop new potent inhibitors of human N-acetyl-beta-hexosaminidases, particularly when combined with the structural information of these enzymes.

A general method for preparing glycoprotein mimetics with defined glycan structure using the Z domain protein as an example is reported. An unnatural amino acid containing the keto group was site-specifically incorporated into a target protein, Z domain, in response to the amber nonsense codon with high translational fidelity and efficiency. An aminooxy saccharide derivative was then selectively coupled to this genetically encoded keto group. The resulting saccharide core was elaborated to a glycan complex with glycosyltransferases. Alternatively, aminooxy analogues of more complicated glycans were prepared and directly attached to the keto group. Homogeneous glycoprotein mimetics thus prepared should prove useful for the study of carbohydrate effects on glycoprotein structure and function. This method may also lead to the production of glycoprotein therapeutics from Escherichia coli.