Tetrabutylammonium bromide

6× His-TRAIL was obtained from UBPBio. Mouse Anti-Human TRAIL-UNLB and mouse Anti-Human TRAIL-BIOT (Dallas, TX, USA) were purchased from SouthernBiotech (Birmingham, AL, USA) for ELISA. Dulbecco’s Modified Eagle Medium (DMEM), penicillin–streptomycin, fetal bovine serum (FBS), trypsin, and phosphate-buffered saline (PBS) were purchased from Corning (Corning, NY, USA). Heparin and Bacteroides Heparinase II were received from Selleckchem (Radnor, PA, USA) and New England Biolabs (Beverly, MA, USA), respectively. EZ-Cytox was purchased from DoGenBio (Seoul, Korea). Fmoc-Asp and Fmoc-Arg were obtained from BOC Science (Shirley, NY, US). Monomethoxy polyethylene glycol 750, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), N-hydroxy succinimide (NHS), tetrabutylammonium bromide (TBAB), 4-dimethyl amino pyridine (DMAP), dimethyl formamide (DMF) (anhydrous), 1,4-dioxane, piperidine, 3,3′,5,5′-Tetramethylbenzidine (TMB), and streptavidin-HRP conjugate were obtained from Sigma-Aldrich (St. Louis, MO, USA). Ethylene glycol diglycidyl ether (EGDE) was obtained from TCI (Tokyo, Japan). Protease inhibitor and Live and dead staining kit were obtained from ThermoScientific (Waltham, MA, USA).

Unless otherwise indicated, all solvents
were purchased from commercial sources and were used without further
purification. 3,4-Diethoxycyclobut-3-ene-1,2-dione (95%, ABCR), zinc
trifluoromethanesulfonate (98%, Sigma-Aldrich), 4-vinylaniline (97%,
Sigma-Aldrich), 2-aminoethyl methacrylate hydrochloride (90%, Sigma-Aldrich), N,N-diisopropylethylamine (DIPEA, >99%,
Sigma-Aldrich), N,N-dimethylacrylamide
(DMAAm, 99%, Sigma-Aldrich), ethylene glycol dimethacrylate (EGDMA,
98%, Sigma-Aldrich), 2,2′-azobis(2-methylpropionitrile) (AIBN,
98%, Sigma-Aldrich), tetrabutylammonium fluoride hydrate ([Bu₄N]⁺[F]⁻, 98%, ABCR), tetrabutylammonium
chloride ([Bu₄N]⁺[Cl]⁻, >97%,
Sigma-Aldrich), tetrabutylammonium bromide ([Bu₄N]⁺[Br]⁻, >98%, Sigma-Aldrich), tetrabutylammonium
iodide ([Bu₄N]⁺[I]⁻, 98%,
Sigma-Aldrich), and tetrabutylammonium acetate ([Bu₄N]⁺[AcO]⁻, 95%, ABCR) were used as received.
AIBN was recrystallized from methanol prior to use and stored below
5 °C. To remove the residual inhibitor, the main monomer DMAAm
was destabilized via a short column of basic alumina prior use.

ε-Caprolactone (ε-CL) (Aldrich) and Cyclohexene oxide (CHO) (Aldrich) were distilled over calcium hyride (CaH₂) and stored in a refrigerator under nitrogen before use. Acetylene-functionalized benzoin (PI-alkyne) was synthesized by slightly modifying the procedure described in the literature.[15 (link)] Stannous-2-ethylhexanoate (Sn(Oct)₂) (Aldrich), 3-cyclohexene-1-methanol (Aldrich), Sodium azide (Aldrich), Propargyl bromide (80 wt. % in toluene, Aldrich), Diphenyliodonium hexafluorophosphate (Fluka), CuBr (Aldrich), Iodic acid (HIO₃) (Sigma-Aldrich), Potassium bromide (KBr) (Sigma-Aldrich), Sodium thiosulfate (Na₂S₂O₃) (Sigma-Aldrich), Sodium azide (NaN₃) (Merck), Tetrabutylammonium bromide (Sigma-Aldrich), and 2,2ꞌ-bipyridine (Merck) were used as received. 1-Ethoxy-2-methylpyridinium hexafluorophosphate (EMP⁺PF₆⁻) was prepared according to the published procedure.[33 (link)] Solvents, dichloromethane (CH₂Cl₂), toluene, and tetrahydrofuran (THF), were distilled over drying agents under nitrogen prior to use.