m-PEG9-Hydrazide

m-PEG9-Hydrazide is a PEG-based linker designed to support PROTAC assembly by providing a hydrazide handle for reliable conjugation chemistry and a flexible, water-compatible spacer to modulate effective ternary complex formation. Its polyethylene glycol segment can improve solubility and reduce nonspecific interactions, which are commonly beneficial in targeted protein degradation workflows. The details below describe the linker’s structure and the practical reactivity considerations for constructing PROTACs using this building block.

Structure: The linker contains a polyethylene glycol chain terminating in a hydrazide functional group. It features ether linkages along the PEG backbone and a carbonyl-containing hydrazide moiety capable of forming stable covalent linkages under appropriate activation. The overall structure is flexible and typically exhibits strong hydration and favorable aqueous compatibility.

Reactivity: The hydrazide group is suited for coupling strategies that form amide or related hydrazone/amide linkages, depending on the electrophile and activation method used during PROTAC synthesis. Typical approaches involve activation of a complementary carboxylic acid (or equivalent derivative) to enable nucleophilic acyl substitution, or formation of hydrazone intermediates under controlled conditions followed by stabilization as required. Mild bases and aqueous-organic solvent systems are commonly used to balance reactivity and minimize side reactions, while reaction progress is monitored by standard analytical methods.