m-PEG7-CH2CH2CHO

This PEG-based linker is designed to connect a ligand for an E3 ligase to a target-binding moiety in PROTAC constructs, providing a flexible, hydrophilic spacer that can improve effective ternary complex formation. Its ether-rich backbone supports solubility and reduces nonspecific hydrophobic interactions, while the terminal aldehyde functionality enables straightforward conjugation strategies. Detailed structural and reactivity considerations are provided below to support experimental PROTAC linker incorporation.

Structure: The linker comprises an oligo(ethylene glycol) chain terminated with a propanal aldehyde, featuring multiple ether linkages and an aliphatic aldehyde at the terminus. It presents a polar, flexible scaffold with a primary aldehyde reactive center suitable for chemoselective bond formation under mild conditions.

Reactivity: The terminal aldehyde can undergo nucleophilic addition/condensation with aminooxy or hydrazide/semicarbazide partners to form oxime or hydrazone linkages commonly used in bioconjugation workflows. Suitable conditions typically employ aqueous or mixed aqueous organic solvents with controlled pH to favor condensation while minimizing side reactions. Catalysis may be achieved using mild acid or aniline-type catalysts for oxime formation, and reactions are generally performed at temperatures that preserve ligand integrity.