Glycan Conjugation Methods

The use of other functionalities (either indigenous or created) on polysaccharide molecules to effect a crosslinking reaction can be done in similar 2- or 3-step strategies. 

Retention of native carbohydrate structure also is important in applications that utilize the conjugated polysaccharide in binding studies with receptors or lectins. In these cases, the carbohydrate should be modified at limited sites, preferentially only at its reducing end. Section 4.6 of this chapter discusses glycan conjugation techniques in greater detail. 

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The following method for carbohydrate conjugation to dendrimers may be used to couple a variety of reducing sugars to amine-dendrimers, including saccharides, longer-chain carbohydrates, and even complex glycans after release from a protein (see Chapter 1, Section 4.6). 

The generation of such tools, based on the conjugation of saccharide entities to different and heterogeneous materials, requires not only the availability of a wide variety of glycans of biological relevance (obtained by isolation from natural sources or by synthesis), but more importantly and specifically, the availability of efficient methods for linking them to supports of different types and size. 

Covalently immobilized arrays are formatted by glycans with functionalized spacers that react with a complementary activated surface to form a covalent bond. Several different covalent interactions were reported to construct a specified glycan array. Amine chemistry and thiol chemistry are the two major methods to conjugate glycans to the reactive substrate in the array surface (Fig. 15.2). Thiol chemistry was first adapted by Injae Shin in 2002 to react with the maleimide functional group (Fig. 15.2a, b) [7,41 ]. Disulfide bond formation was then reported for the fabrication... 

The extracted GSLs were briefly treated by ozone and heated in neutral buffer to release free-reducing glycans that can be permethylated for MS analysis or conjugated to a bifunctional linker for HPLC separation and microarray study. Like other methods based on (1-elimination, this method is also not suitable for sphinganine and phytosphingosine GSLs that lack the C=C bond. 

These workers have also applied the strain-induced [3-1-2] cycloaddition method for in vivo conjugation in Caenorhabditis elegans (this is a model organism for studies of glycan dynamics). They... 

Although cyclooctynes enable copper-free Click reactions, they are not compatible with bioconjugations in aqueous media, because of their hydrophobic character. Thus, Bertozzi and coworkers uncovered a new method for the synthesis of a biocompatible cyclooctyne (6,7-dimethoxyazacyclooct-4-yne = DIMAC) to detect azide-labeled biomolecules via copper-free Click chemistry. The first conjugations to biotin as well as ceU-surface glycans were arranged. 

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