Studies directed toward the synthesis of protein-bound GPI anchor

Mannobioside-linked phosphoethanolamine , a prototype model of the GPI anchor, was synthesized via glycosidation of the monosaccharide donor and acceptor, and subsequent phosphorylation. In order to test the reactivity of the amino group involved in against the activated amino acid esters, was reacted with N-protected amino acid pentafluorophenyl esters in the presence of HOBt. The reactions gave the aminoacylated products in moderate yields. When Fmoc-Ser-OPfp and Fmoc-Cys(SBut)-OPfp were reacted with , byproducts , and derived from N- and O-acylation were produced. In contrast, reactions of and N-protected amino acid thioesters were promoted with AgNO3, HOSu, and DIEA to afford the coupling products without the undesired O-acylation. Peptidylation of with the synthesized oligopeptide thioesters and was also successful under the segment coupling conditions of the peptide thioester method as well as those of the native chemical ligation.