Proof of principle for the synthesis of hydroxy-aryl esters of glycosidic polyols and non-reducing oligosaccharides with subsequent enzymatic coupling to a tyrosine-containing tripeptide

To enable enzymatic coupling of saccharides to proteins, several di- and trisaccharides were hydroxy-arylated using anhydrous transesterification with methyl 3-(4-hydroxyphenyl)propionate, catalyzed by potassium carbonate. This transesterification resulted in the attachment of up to 3 hydroxy-aryl units per oligosaccharide molecule, with the monosubstituted product being by far the most abundant. The alkaline reaction conditions, however, resulted in a partial breakdown of reducing sugars. This breakdown could easily be bypassed by a preceding sugar reduction step converting them to polyols. Hydroxy-arylated products were purified by using solid phase extraction, based on the number of hydroxy-aryl moieties attached. Monohydroxy-arylated saccharose was subsequently linked to a tyrosine-containing tripeptide using horseradish peroxidase, as monitored by LC-MSn. This proof of principle for peptide and protein glycation with a range of possible saccharides and glycosidic polyols can lead to products with unique new properties.