Scheme 1.

Synthesis of sialo derivative 2 with atom labelling. Reagents and conditions: (a) BnBr, DBU, DMF, room temperature, 18 h; (b) TsCl, Py, room temperature, 18 h; (c) Ac₂O, DMAP, Py, room temperature, 5 h; (d) NaN₃, dry DMF, 70 °C, 5 h; (e) PhSH, BF₃⋅Et₂O, dry DCM, room temperature, 18 h; (f) PPh₃, CH₂Cl₂, room temperature, 48 h; (g) NIS, TfOH, dry CH₃CN/CH₂Cl₂ (10 : 1), −40 °C, 4 h; (h) AcOH 80 %, 40 °C, 18 h; (i) Pd/C, H₂, MeOH, room temperature, 72 h; (l) NH₃ 4 M in MeOH, room temperature, 120 h.