aReagents and conditions: (a) PmST1, CMP-Neu5Ac, 100 mM Tris-HCl (pH 8.0), 37 °C, 81% for 2, 75% for 5, 74% for 10, 76% for 12; (b) CgtA, UDP-GalNAc, 10 mM MgCl2, 50 mM Tris-HCl (pH 7.5), 37 °C, 92% for 3, 88% for 8; (c) CgtB, UDP-Gal, 10 mM MgCl2, 50 mM Tris-HCl (pH 7.5), 37 °C, 83% for 4, 80% for 9; (d) CstII, CMP-Neu5Ac, 100 mM Tris-HCl (pH 8.0), 37 °C, 76% for 6, 77% for 7, 74% for 13; (e) α2–3,6,8,9 neuraminidase A from Arthrobacter ureafaciens, 5 mM CaCl2, 50 mM sodium acetate (pH 5.5), 37 °C, 94%.