CHO-Ph-CONH-PEG4-COOtBu

CHO-Ph-CONH-PEG4-COOtBu, is designed to connect a warhead to an E3 ligase ligand through a flexible polyethylene glycol spacer while maintaining a stable amide linkage for efficient conjugation. Its ether-rich PEG segment supports conformational adaptability that can improve productive ternary complex formation. The protected carboxyl functionality enables controlled coupling chemistry, and the linker is well suited for modular PROTAC assembly; the structural and reactivity considerations are described in detail below.

Structure: The linker contains an aromatic phenyl core connected to a carbonyl-bearing amide, followed by a PEG-based polyether chain that provides flexibility and polarity. A terminal protected carboxyl group is present as a tert-butyl ester, which is chemically stable under many coupling conditions yet removable when needed.

Reactivity: PROTAC construction using this linker typically relies on orthogonal functional-group strategies: the tert-butyl ester can be retained during amide-forming steps and later deprotected to reveal a carboxylic acid for subsequent coupling. Suitable transformations include amide bond formation via activated carboxyl derivatives, commonly using coupling reagents under standard organic solvent conditions. Mechanistically, nucleophilic acyl substitution governs amide formation, while PEG-linked linkers generally tolerate mild base and common coupling media.