N-Mal-N-bis(PEG2-NHS ester)

This PEG-based bifunctional linker is designed for building PROTACs by providing two NHS-ester reactive handles for efficient conjugation to primary amines on targeting ligands and/or E3 ligase binders. Its flexible ethylene glycol segments enhance aqueous compatibility and can improve the effective reach and conformational freedom of the assembled degrader. The linker’s dual reactivity supports streamlined, modular synthesis, and the detailed structural and reactivity considerations are provided below.

Structure: N-Mal-N-bis(PEG2-NHS ester) contains a central tertiary amide (N-malonyl motif) linked to two short PEG chains terminating in N-hydroxysuccinimide ester groups. It features ester electrophiles, amide connectivity, and ether-rich PEG segments that impart hydrophilicity and conformational flexibility in solution.

Reactivity: The NHS ester groups react with primary amines via nucleophilic acyl substitution, forming stable amide bonds while releasing N-hydroxysuccinimide. Suitable conditions typically use mildly basic aqueous buffers to maintain NHS ester reactivity while minimizing hydrolysis; low-to-moderate temperatures and controlled stoichiometry help preserve coupling efficiency. No special catalysts are required, but careful exclusion of excess water and sequential addition can improve selectivity when assembling PROTAC constructs.