Boc-PEG4-phosphonic acid ethyl ester

Boc-PEG4-phosphonic acid ethyl ester is a PEG-based phosphonate linker designed for assembling PROTACs that require a hydrophilic, flexible spacer between a ligand and a reactive handle. Its protected phosphonate functionality supports controlled coupling strategies, while the Boc group enables orthogonal deprotection to expose reactive sites when needed. This product is particularly useful for constructing targeted protein degradation conjugates where solubility, linker length, and stepwise synthesis are critical; the following points describe its structure and reactivity in more detail.

Structure: The linker comprises a Boc-protected functional group connected to a polyethylene glycol chain and a phosphonate ethyl ester. It contains carbamate and ester linkages, along with phosphonate P–O bonds, providing a polar, hydrogen-bonding-rich scaffold. The PEG segment enhances aqueous compatibility and conformational flexibility.

Reactivity: The phosphonic acid ethyl ester can be converted to a free phosphonic acid under standard deprotection conditions, enabling subsequent formation of phosphonate-based coupling motifs commonly used in PROTAC linker chemistry. The Boc group is typically removed under mild acid-mediated conditions to reveal the corresponding reactive functionality for orthogonal conjugation. Coupling steps generally employ dry polar solvents and activating reagents appropriate for phosphonate or carbamate chemistry, with reaction monitoring by standard analytical methods.