A novel approach for the parallel synthesis of glycopeptides by combining solid-phase peptide synthesis and dendrimer-supported enzymatic modifications

Functionalized, high-generation (G7) polyamidoamine (PAMAM) dendrimers are a convenient scaffold for the fully automated enzymatic synthesis of oligosaccharides such as biologically important sialyl Lewis X tetrasaccharide derivatives. In this study, we expanded this strategy to the synthesis of more complicated glycopeptides by assessing the feasibility of G7 PAMAM dendrimer-based polymer supports for attaching glycopeptide intermediates during the subsequent enzymatic modification steps. A monosaccharide-attached glycopeptide containing an N-terminal heterobifunctional linker was prepared by microwave-assisted solid-phase synthesis and was coupled with an aminooxy-functionalized G7 PAMAM dendrimer through oxime bond formation. This reaction proceeded smoothly at pH 4 and afforded the conjugates in 98% yield when 0.2 equivalents of the glycopeptide were combined with 1 equivalent of the aminooxy group of dendrimer. Although modifications using recombinant human β1,4-galactosyltransferase/uridine-5′-diphospho-α-D-galactose disodium salt and recombinant rat α2,3-sialyltransferase/cytidine-5′-monophospho-β-D-N-acetylneuraminic acid disodium salt gave the trisaccharide Neu5Acα2,3Galβ1,4GlcNAc in quantitative yields, treatment with recombinant human α1,3-fucosyltransferase in the presence of excess guanosine 5′-diphospho-β-L-fucose disodium salt did not convert this trisaccharide into the tetrasaccharide sialyl Lewis X tetrasaccharide on the dendrimer. Further optimization studies are required to improve the efficiency of branched-type sugar elongations and product release from polymers by selective peptidases for constructing a high-throughput glycopeptide synthetic system.