Azido-PEG4-hydrazide

Azido-PEG4-hydrazide, provides a modular polyethylene glycol spacer terminating in an azide handle and a hydrazide functional group. Its flexible, hydrophilic architecture supports efficient conjugation of targeting ligands and improves linker solubility and accessibility in ternary-complex formation. The azide enables bioorthogonal coupling strategies, while the hydrazide supports stable amide/semicarbazone-type linkage design. Detailed structural and reactivity considerations are provided below.

Structure: Azido-PEG4-hydrazide contains a PEG-based flexible ether backbone, an azide substituent, and a hydrazide moiety. The molecule features ether linkages, carbonyl and N–N bonding within the hydrazide, and a terminal azide group suitable for click-type transformations. Overall polarity and conformational flexibility are characteristic of PEG linkers.

Reactivity: The azide group is well suited for copper-catalyzed azide–alkyne cycloaddition or strain-promoted cycloaddition, enabling attachment to alkyne-bearing PROTAC fragments under mild, orthogonal conditions. The hydrazide can participate in acyl-transfer/condensation chemistry with appropriately activated carbonyl partners to form robust linkages common in linker–ligand assembly. Typical coupling workflows use standard peptide/amide-compatible reagents and polar aprotic or aqueous-organic solvents, with reaction control to preserve sensitive functional groups.