| A new method for the synthesis of O-linked glycopeptides is described. The method uses the carbohydrate C1-O nucleophilic ring-opening of aziridine-2-carboxamides to access the target O-linked glycopeptides. The synthesis of the alpha-GalNAc-Ser class of glycopeptides is emphasized and either the alpha- or beta-glycoside can be accessed by judicious selection of solvent and metal counter-ion, even in the presence of the native carbohydrate C2-NHAc group. Other classes of 0-glycosyl serine constructs, such as the beta-GlcNAc-Ser and alpha-Man-Ser linkages, are also prepared by this approach. In the course of these studies, the ortho-allylbenzyl (ABn) moiety was developed as a new C-terminus secondary amide protective group for carboxylic acids, which allows for oxidative C-terminus extension of amino acids following the carbohydrate-aziridine coupling reaction. A new protocol for deprotection of p-nitrobenzenesulfonamides with in situ peptide coupling is also reported. This reaction allows for direct N-terminus extension of p-nitrobenzenesulfonyl protected amino acids, or glycosyl amino acids, in one synthetic step. |
