Formation of lactones from sialylated MUC1 glycopeptides

Abstract

The tumor-associated carbohydrate antigens TN, T, sialyl TN and sialyl T are expressed on mucins in several epithelial cancers. This has stimulated studies directed towards development of glycopeptide-based anticancer vaccines. Formation of intramolecular lactones involving sialic acid residues and suitably positioned hydroxyl groups in neighboring saccharide moieties is known to occur for glycolipids such as gangliosides. It has been suggested that these lactones are more immunogenic and tumor-specific than their native counterparts and that they might find use as cancer vaccines. We have now investigated if lactonization also occurs for the sialyl TN and T antigens of mucins. It was found that the model compound sialyl T benzyl glycoside , and the glycopeptide Ala-Pro-Asp-Thr-Arg-Pro-Ala from the tandem repeat of the mucin MUC1, in which Thr stands for the 2,3-sialyl-T antigen, lactonized during treatment with glacial acetic acid. Compound gave the 1''--> 2' lactone as the major product and the corresponding 1''--> 4' lactone as the minor product. For glycopeptide the 1''--> 4' lactone constitued the major product, whereas the 1''--> 2' lactone was the minor one. When lactonized was dissolved in water the 1''--> 4' lactone underwent slow hydrolysis, whereas the 1''--> 2' remained stable even after a 30 days incubation. In contrast the corresponding 2,6-sialyl-TN glycopeptide did not lactonize in glacial acetic acid.

Capillary electrophoresis–mass spectrometry for direct structural identification of serum N-glycans

“…Many of these larger structures (e.g., the isomer at m/z 1087) exhibit an extremely low fraction of α2,3 linked sialic acids which does not agree with earlier reported abundances 51 or our own glycosidase digestions. Lactones may not be sufficiently stable and could hydrolyze prior to analysis to regenerate the carboxyl group of sialic acid, 66 consequently forming amides by reacting with surrounding ammonium chloride. Thus, a small portion of α2,3 linked sialic acid lactones could appear as amides, which would give a slightly higher apparent abundance of α2,6 linked sialic acid isomers.…”

Derivatization of sialic acids for stabilization in matrix‐assisted laser desorption/ionization mass spectrometry and concomitant differentiation of α(2 → 3)‐ and α(2 → 6)‐isomers

“…The relative proportions of the α (2 → 3)‐ and α (2 → 6)linked sialic acids was roughly the same as that reported by Green et al 9. The lactone is probably a mixture of products with cyclization to the 2‐ or 4‐hydroxyl groups of the adjacent galactose residue, as determined by NMR 22. Although it was not investigated in this study because sialic acid linked to galactose is by far the most common in N ‐glycans, we expect that linkage of sialic acids attached to other positions, such as α 2 → 8 (common in glycosphingolipids), would show similar properties in cases where a hydroxyl group was positioned such that it could only interact with the sialic acid in α 2 → 3 linkage.…”

Toward Homogeneous Erythropoietin: Non-NCL-Based Chemical Synthesis of the Gln78−Arg166 Glycopeptide Domain

“…ESI mass spectrometry analysis confirmed the identity of the glycopeptide 1 (Supporting Information, Figure 29). 46 The mass data of 1 also indicated the presence of lactones involving the sialic acid and the neighboring galactose units,47 which will be hydrolyzed under mild conditions after the completion of the full-length EPO synthesis 48…”