m-PEG4-phosphonic acid ethyl ester

This m-PEG4-phosphonic acid ethyl ester linker is designed for constructing PROTACs that require a stable, hydrophilic spacer to tune solubility, conformational flexibility, and effective proximity between the target-binding ligand and the E3-recruiting moiety. Its phosphonate functionality supports robust conjugation strategies commonly used in targeted protein degradation workflows. The following sections describe the linker’s structure and practical reactivity considerations in PROTAC synthesis in detail below.

Structure: The linker comprises a meta-substituted ethylene glycol (PEG) segment providing a flexible, water-compatible chain, connected to a phosphonate ester. It contains P–O and P–C linkages with an ethyl phosphonate group, alongside ether linkages characteristic of PEG frameworks.

Reactivity: Phosphonate ester chemistry enables controlled functionalization under conditions compatible with PEG ethers and typical PROTAC ligands. Conjugation is commonly achieved via nucleophilic substitution or ester activation followed by coupling to complementary nucleophiles, often using mild base or activating reagents and polar aprotic solvents. Reaction design should prioritize maintaining linker integrity and avoiding conditions that promote PEG cleavage or phosphonate hydrolysis.