Methyl 3 5 dihydroxybenzoate

Ligand 1 (LacNAc; Galβ4GlcNAc) was obtained from Carbosynth (Compton, UK). The preparation of β-galactosidase from Bacillus circulans Biolacta^® was from Daiwa Kasei (Aichi, Japan). β-Alanine, 2,2′-azobisisobutyronitrile (AIBN), 2-cyanopropan-2-yl dithiobenzoate, 2-thiazoline-2-thiol (CTA), CuBr, methyl 3,5-dihydroxybenzoate, methyl-3,4,5-trihydroxybenzoate, N-Boc-ethylenediamine, and N,N-diisopropylethylamine (DIPEA) were obtained from Sigma-Aldrich (Prague, Czech Republic). Propargyl bromide was purchased from Acros Organics (Pardubice, Czech Republic), and trifluoroacetic acid (TFA) was acquired from Iris Biotech (Marktredwitz, Germany).

All reagents and solvents were used without additional purification unless specified otherwise. Poly(ethylene glycol) with molecular mass 5000 Da (PEG5k, M_w/M_n = 1.02) and 11,000 Da (PEG11k, M_w/M_n = 1.04) were purchased from Polysciences, Inc. (Warrington, PA, USA). 2,2-Bis(hydroxymethyl)propionic acid, bis-MPA, (99+%) sodium azide, and NaN₃ (98%, powder) were acquired from Acros. Sodium hydride, NaH, (95%, dry powder), 4-di(methylamino)pyridine, DMAP, (≥99%), copper(I) bromide, CuBr, (98%), propargyl bromide (80 wt.% in toluene), N,N′-dicyclohexylcarbodiimide, DCC, (99%), methyl 3,5-dihydroxybenzoate, 3,5-MDHB, (97%), 3,5-dihydroxybenzyl alcohol, 3,5-DHBA (98%), benzyl bromide (98%), sodium ascorbate, Na-Asc (≥99%), potassium carbonate, K₂CO₃ (≥98%, powder), 18-crown-6 (99%), 2,5-dihydroxybenzoic acid, 2,5-DHBA, (98%), phenylboronic acid, PBA, (95%), 4′-bromoacetophenone, 4′-BAcP, (99%), triethylamine, TEA (99.5%), and tetrahydrofuran, THF (HPLC grade) were all purchased from Sigma-Aldrich (Miwaukee, WI, USA). Dichloro-bis(benzonitrile) palladium, Pd(PhCN)₂Cl₂, (99%) was obtained from Strem Chemicals (Newburyport, MA, USA); diethyl ether, ethyl acetate, EtOAc, hexanes, and methanol (all reagent grade) were received from Pharmco, Inc. (Brookfield, CT, USA), and dichloromethane, DCM, (spectrophotometric grade) was purchased from Spectrum/Gleason Chemicals (Syracuse, NY, USA).