Chemical synthesis of 6'-O-sulfo-LexβProNH2 (9) and 6,6'-di-O-sulfo-LexβProNH2 (10). Reagents and conditions: a) N-iodosuccinimide (NIS), TMSOTf, MS 4 Å, CH2Cl2, −40 °C, 30 min; b) N-iodosuccinimide (NIS), TMSOTf, MS 4 Å, CH2Cl2-Et2O (1:1), −18 °C, 45 min; c) H2N(CH2)2NH2, n-BuOH, 90 °C, 8 h; d) pyridine, Ac2O, r.t., 10 h; e) HF·pyridine, 0 °C to r.t., overnight; f) SO3·pyridine, pyridine, 0 °C to r.t.; g) 0.1 M NaOMe, MeOH, r.t., 3 h; h) Pd(OH)2/C, H2, CH3OH, 48 h.