S1 Synthesis of an End-to-End Protein-Glycopolymer Conjugate via Bio-Orthogonal Chemistry Hailong Zhang, Jacob Weingart, Valentinas Gruzdys, and Xue-Long Sun* SUPPORTING INFORMATION 1. Synthesis of p-Amido[tetra(ethylene glycol)]-N-dibenzylcyclooctynephenyl-β-ᴅ- galactopyranoside (DBCO-PEG 4 -CONH-Ph-β-ᴅ-Gal) Scheme 1s. Synthesis of DBCO-PEG 4 -CONH-Ph-β-ᴅ-Gal To a vial containing 3.2 mg of p-aminophenyl-β-ᴅ-galactopyranoside and a stir bar, 0.1 mL Et 3 N was added and the reaction mixture was then allowed to stir for 15 min at room temperature. After 15 min, then a 1 mL solution of dry DMF containing 9 mg (1.1 eqv) DBCO- PEG4-NHS ester was added via syringe. The vial was then flushed with N 2 (g) and capped to stir at room temperature for 24 h. The reaction prior to work up was checked by TLC 1:4 MeOH/CHCl 3 against the starting materials to confirm reaction completion. Then the solvent in the vial was reduced to near dryness under vacuum. The residue was then chromatographed on silica gel using 1:4 MeOH/CHCl 3 solution as eluent. The isolated compound, exhibiting long- wave UV-Vis fluorescence (R f ~ 0.45, 1:4 MeOH/CHCl 3 ), was collected and reduced to dryness achieving DBCO-PEG4-CONH-phenylgalactose (4.7 mg, 47%). 1 H NMR (CDCl 3 , 300 MHz) δ: 7.64 (d, 1H, H-Ar of DBCO), 7.46 – 7.34 (m, 12H, H-Ar of DBCO and Ph), 7.24 (d, 1H, H-Ar of DBCO), 7.06 (d, 2H, H-Ph), 5.11 (d, 1H, H 1 -Gal), 4.84 (d, 2H, CH 2 of DBCO), 3.92 (s, 1H, H-