AZD-PEG13-PFP is a PEG linker featuring an AZD group and a PFP ester group, where the PFP ester acts as an active ester capable of reacting with primary amines to form amide bonds. The PFP ester shows greater stability compared to other amine-reactive groups due to its reduced likelihood of hydrolysis. Its hydrophilic PEG spacer enhances solubility in aqueous environments.