Scheme 2.

Synthesis of ^TCCSia‐LacNAc‐DBCO (2). Reagents and conditions: a) 3 (1.0 equiv), UDP‐Gal (1.3 equiv), MgCl₂ (20 × 10⁻³ m), Tris‐HCl buffer (100 × 10⁻³ m, pH 7.5), LgtB, 37 °C, overnight; b) 4 (1.0 equiv), 5 (1.5 equiv), cytidine‐5′‐triphosphate (CTP; 1.5 equiv), MgCl₂ (20 × 10⁻³ m), Tris‐HCl buffer (100 × 10⁻³ m, pH 8.5), Neisseria meningitidis CMP‐sialic acid synthetase (NmCSS), PmST1, 37 °C, overnight; c) 6 (1.0 equiv), 7 (1.5 equiv), THF/H₂O, TEA; d) Pd/C, H₂, CH₃OH/H₂O; e) 9 (1.0 equiv), 10 (1.5 equiv), THF/H₂O, TEA.