DBCO-NHCO-PEG4-NHBoc

 DBCO (Dibenzocyclooctyne) is used in the azide-alkyne cycloaddition (SPAAC) reaction without the need for copper ion catalysis, which has a secondary reaction kinetic constant of up to 1. The DBCO family of products includes DBCO-acid, DBCO-amine, and DBCO-PEG-COOH for further linkage, DBCO-PEG-amine, as well as DBCO-labeled biotin, fluorescent dyes, and biochemical small molecules.