Scheme 1: Reagents and conditions: (a) Ac2O, pyridine, cat. DMAP, N2, r.t., overnight; (b) HBr/AcOH (30%), CH2Cl2, N2, r.t., 2 h; (c) NaN3, DMF, sonication, r.t., 15 min; (d) Pd/C (10%), H2, MeOH, 30 min; (e) EDC, CH2Cl2, cat. DMAP, N2, r.t., 18 h.