Scheme 1.

Synthesis of LacNAc derivatives. Reagents and conditions: (a) galactose oxidase, HRP, catalase, O₂, 50 mmol/L PB, pH 7.0, 30 °C; (b) O-(2-azidoethyl)-hydroxylamine hydrochloride, O-(2-propynylethyl)-hydroxylamine hydrochloride, or biotin-ONH₂, pH 7.2, rt; (c) 3-azido-1-propanamine, 2-propynylamine, or coumarin-NH₂, NaCNBH₃, pH 6.0, 0 °C; (d) NH₂OH·HCl, Na₂CO₃, CH₃OH/H₂O, rt; NaBH₄, NiCl₂·6H₂O, 0 °C; (e) N-benzylthiourea, pH 8.0, rt; (f) DBCO-CONHS, pH 7.4, rt; (g) GDP-Fuc, α(1,3)-fucosyltransferase; (h) α(2,3)-sialyltransfererase, CMP-sialic acid, Tris-HCl buffer (100 mmol/L, pH 8.0); or α(2,6)-sialyltransferase (Pd2,6ST), CMP-sialic acid, Tris-HCl buffer (100 mmol/L, pH 8.0).