Ald-Ph-PEG24-NHS ester

Ald-Ph-PEG24-NHS ester is a PEG-based heterobifunctional linker designed for constructing PROTACs that require orthogonal conjugation handles. It combines an aldehyde functionality with a phenyl-containing PEG scaffold and an NHS ester for efficient amide formation, enabling sequential attachment of ligands and subsequent assembly of targeted degradation constructs. Its flexible, hydrophilic PEG architecture can support favorable solubility and linker-mediated positioning in ternary complex formation. The detailed structural and reactivity features are described below.

Structure: The linker contains a reactive NHS ester for acyl transfer to primary amines, an aldehyde group suitable for chemoselective condensation, and a phenyl-substituted PEG chain that provides conformational flexibility. It features ester and aldehyde carbonyls, ether linkages in the PEG backbone, and aromatic character from the phenyl moiety, supporting water-compatible physicochemical behavior.

Reactivity: The NHS ester typically reacts under mildly basic aqueous buffer conditions with primary amines on protein-binding ligands to form stable amide bonds via nucleophilic acyl substitution. The aldehyde enables subsequent conjugation through reductive amination or reversible imine formation followed by stabilization, allowing stepwise assembly. Common approaches use controlled pH buffers, compatible co-solvents, and standard coupling reagents where needed to preserve aldehyde integrity during amide coupling.