Dbco dibenzylcyclooctyne acid

8 arm PEG-hydroxyl (M_n = 20 kg mol⁻¹, tripentaerythritol core), 8 arm PEG-amine (M_n = 20 kg mol⁻¹, tripentaerythritol core), and 8 arm PEG-thiol (M_n = 20 kg mol⁻¹, tripentaerythritol core) were purchased from JenKem Technology USA. DBCO (dibenzylcyclooctyne) acid was purchased from Click Chemistry Tools (Scottsdale, AZ). All other chemicals were purchased from Sigma Aldrich (St. Louis, MO) or Thermo Fisher Scientific (Waltham, MA), and used as received unless otherwise noted.

Octa-arm PEG-hydroxyl (M_n = 20 kg mol⁻¹, tripentaerythritol core) and octa-arm PEG-amine (M_n = 20 kg mol⁻¹, hexaglycerol core or tripentaerythritol core) were purchased from JenKem Technology USA. DBCO (dibenzylcyclooctyne) acid, 3-azidopropinoic acid, and azido propylamine were purchased from Click Chemistry Tools. All chemicals for peptide synthesis were purchased from Chem-Impex International Inc. All other chemicals were purchased from Sigma Aldrich or Fisher and used as received unless otherwise noted.
¹H NMR and ¹³C NMR were recorded on a 400 MHz Bruker AVANCE spectrometer. The residual undeuterated solvent peaks were used for references (7.26 ppm for CDCl₃,). Octa-arm PEG-azide, azido-GRGDS, octa-arm PEG DBCO, octa-arm PEG-azide/ Fluorophenylboronic acid (FPBA), octa-arm PEG-azide/ Nitrodopamine (ND), and their intermediate products were synthesized as previously described in detail.^{[31 ]} Importantly, for both octa-arm PEG-azide/FPBA and octa-arm PEG azide/ND, 2 arms were first functionalized with azide group and confirmed through a TNBS (2,4,6-trinitrobenzene sulfonic acid) assay before the remaining 6 arms were functionalized with either FPBA or ND respectively.