Solution Phase Synthesis of Amide-Linked N-Acetyl Neuraminic Acid, α-Amino Acid, and Sugar Amino Acid Conjugates

Peracetylated N-acetylneuraminic acid (NeuAc) was efficiently coupled to esters of glycine, alanine, and serine using BOP and HOBT in the presence of DIEA. Deprotection of the esters readied the NeuAc-α-amino acid conjugates for further elaboration. Coupling of the NeuAc-gly adduct with β-O-methoxy neuraminic acid methyl ester afforded a selectively protected glycine linked sialic acid dimer. 2-Amino-3,4-di-O-benzyl-(1→6)-anhydroglucose and alanine benzyl ester were also efficiently coupled to the bis adduct giving novel trimeric analogs. Elimination of the anomeric acetate from the NeuAc-gly dimer followed by global deprotection provided a novel saccharopeptide with modest clostridial sialidase inhibitory activity.