Functional group targets carbohydrates

Easily available advanced synthons, such as the carbohydrates, amino acids, hydroxyacids, and terpenoids, make the synthetic task easier than the complexity metrics of the target suggests this is especially true for the glycosides, if the carbohydrate portion can be introduced intactly. It must also be borne in mind that the S metric is counted in a linearly additive hion, neglecting interactions between the functional groups (Whitlock 1998) such interactions are not treated adequately by any method so far proposed to calculate the molecular complexity. Moreover, no attention was paid here to the graphic analysis of the synthesis plan based on the molecular complexity of the intermediates these aspects have recently been reviewed (Bertz 1993 Whitlock 1998 Chanon 1998). 

On the other end of the cross-linker, the hydrazide functional group can react with periodate-oxidized carbohydrate molecules to form hydrazone linkages (Chapter 1, Sections 2 and 4.5). Thus, glycoproteins can be targeted specifically at their polysaccharide chains, avoiding cross-linking at active sites which can lead to activity losses (Fig. 167). 

The hydrazide derivative can be used to modify aldehyde- or ketone-containing molecules, including cytosine residues using the bisulfite activation procedure described in Chapter 17, Section 2.1. The sulfonyl hydrazine group of Texas Red hydrazide reacts with aldehydes or ketones in target functional groups to form hy-drazone bonds (Fig. 218). Carbohydrates and glycoconjugates can be specifically labeled at the polysaccharide portion if the required aldehydes are first formed by periodate oxidation or another such method (Chapter 1, Section 4.4). 

Enzymes that contain carbohydrate, such as HRP or GO, may be oxidized with periodate to create active derivatives that subsequently can be used to label antibodies or other targeting molecules at their amine functional groups. The aldehyde—HRP intermediate may be stored for extended periods in a frozen or lyophilized state without loss of activity (either enzymatic or coupling potential). Avoid, however, storage in a liquid state, since polymerization may occur—resulting in precipitation and loss of activity. 

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