Scheme 1: Reagents and conditions: (i) NaOH 1 N, reflux, 2 h; (ii) acetic anhydride, rt, 24 h; (iii) DIEA, HOBt.H2O, EDC.HCl, acetic acid, dry THF, rt, 18 h; (iv) benzoyl chloride, K2CO3, acetone, reflux, 3 h; (v) p-anisoyl chloride, NEt3, dry CH2Cl2, reflux, 2 h; (vi) benzyl bromide, K2CO3, acetone, reflux ,4 h; (vii) DIEA, (Boc)2O, 1,4-dioxane, water, rt, 24 h; (viii) (a) MeOH, NH4OH, reflux, 15 min; (b) NH4OH, rt, 24 h.