Final ligation of the glycopeptide fragments. (a) 20, 21, PhSH, Gnd·HCl, Na2HPO4, TCEP·HCl, H2O (pH = 7.4) (b) NH2OMe·HCl, Gnd·HCl, TCEP·HCl (pH = 4.8) (c) 4, PhSH, Gnd·HCl, Na2HPO4, TCEP·HCl, H2O (pH = 7.4) (d) NH2OMe·HCl, Gnd·HCl, TCEP·HCl (pH = 4.8). (e) 5, PhSH, Gnd·HCl, Na2HPO4, TCEP·HCl, H2O (pH = 7.3). Mass spectrum of compound 2 (inset).