What are the backbones of mucins?
The backbone structures of many mucin-type oligosaccharide alditols are built up from alternating βGal and βGlcNAc residues. In principle, both backbone types, Gal (β1-3)GlcNAc (type 1) and Gal (β1-4)GlcNAc (type 2), do occur. For βGal the H1 signal is found in the range δ 4.40–4.50, and for βGlcNAc in the range δ 4.50–4.80. It will be evident that in complex systems with different peripheral elements, some overlap can occur between both regions. Full data can be obtained through Table 9 and in a previous review. 2
What is the alditol acetate procedure?
The alditol acetate procedure was the first developed in which the anomeric centre is eliminated. The anomeric centre is converted by borohydride reduction (although later borodeuteride was introduced) to an alcohol prior to acetylation (to produce a volatile derivative).
What is PBA used for?
PBA has also been applied to the separation of oligosaccharides from their alditols and interfering amino acids and glycopeptides. The purification of an oligosaccharide–lipid conjugate (neoglycolipid) formed by the reductive amination of the sugar lactose with phosphatidylethanolamine dipalmitoyl (PPEADP) has also been demonstrated.
Does borate inhibit acylation?
Unfortunately, borate derived from the added borohydride, or borodeuteride, inhibits the subsequent acylation step. The classical procedure employs a multi-step evaporation with methanol–acetic acid to remove borate as tetramethyl borate gas in between the reduction and acetylation steps (Figure 1 ). Figure 1.
Can sodium acetate be used as a catalyst?
Furthermore, in the presence of moisture and/or borate, acetylation can be somewhat unpredictable. When using sodium acetate as a catalyst following removal of borate and moisture , these problems do no occur but unfortunately, the process to remove borate and moisture is te dious to perform .
Is pyridine more efficient than sodium acetate?
In the 1960s, sodium acetate and pyridine were introduced as catalysts for acetylation, pyridine being more efficient than sodium acetate. However, in both cases borate must be removed prior to acetylation.
Is pyridine a side reaction?
Unfortunately, many catalysts (including both pyridine and methylimidizole) often generate side-reaction products (from reaction with acetic anhydride) that produce chr omatograms contaminated with extraneous peaks. Furthermore, in the presence of moisture and/or borate, acetylation can be somewhat unpredictable.
