Sequential glycoproteins: Practical method for the synthesis of antifreeze glycoprotein models containing base labile groups

Practical and versatile methods for the preparation of glycopeptide polymers containing base labile moieties were established by use of 1-isobuthoxycarbonyl-2-isobuthoxy-1,2-dihydroquinoline (IIDQ) or 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) as polycondensation agents of glycopeptide units without any protection on the carbohydrate residues. These methods were applied for the synthesis of mucin-like glycoprotein mimics related to antifreeze glycoproteins (AFGPs), giving the target O-acetylated glycopolypeptides efficiently, while the conventional DPPA (diphenylphosphoryl azide) method gave complex mixtures of acyl migrated compounds.