m-PEG4-phosphonic acid

m-PEG4-phosphonic acid is a polyethylene glycol (PEG)-based phosphonic acid linker designed to support the construction of PROTACs by enabling reliable conjugation chemistry and providing a hydrated, flexible spacer between targeting and recruiting modules. Its phosphonic acid functionality supports stable attachment strategies that can improve effective proximity and solubility in aqueous workflows. The structural and reactivity characteristics relevant to PROTAC synthesis are described in detail below.

Structure: The linker comprises an m-PEG4 ethylene glycol segment terminated by a phosphonic acid group. It contains ether linkages typical of PEG chains and a phosphonate moiety capable of strong hydrogen bonding and metal/oxide interactions. Overall, it is highly polar and water-compatible, with conformational flexibility from the PEG backbone.

Reactivity: The phosphonic acid group can be used as a reactive handle for linker installation via established phosphonate chemistry, including coupling to activated electrophiles under standard amide- or ester-forming conditions where applicable. Typical PROTAC synthesis workflows employ dry polar aprotic solvents, mild bases, and coupling reagents compatible with phosphonate stability. Reaction design generally follows principles of chemoselective functional group activation to preserve the PEG chain and maintain aqueous compatibility.