SPDP-PEG4-NHS ester

SPDP-PEG4-NHS ester is a PEG-based heterobifunctional linker designed for efficient conjugation in targeted protein degradation workflows. It combines an NHS-activated ester for rapid amide-bond formation with a thiol-reactive disulfide-containing handle, enabling modular assembly of PROTACs from ligands bearing appropriate functional groups. Its PEG spacer supports favorable solubility and spacing effects, improving coupling efficiency and ease of downstream handling.

Structure: The molecule contains a polyethylene glycol spacer terminating in an NHS-activated ester, providing a stable acylating group for nucleophilic attack. A disulfide-bearing functional motif confers thiol-reactivity upon reduction. The linker features ester and ether linkages that contribute to water compatibility and conformational flexibility.

Reactivity: NHS ester conjugation is typically performed under mild, aqueous or mixed-solvent conditions using primary amines as nucleophiles, with pH controlled to favor acyl substitution while minimizing hydrolysis. The disulfide functionality enables thiol-mediated exchange, often after reduction to generate a reactive thiol or via thiol capture depending on the PROTAC assembly strategy. Common coupling solvents include buffered aqueous systems or polar organic mixtures; catalysts are generally not required for NHS acylation, but careful exclusion of competing nucleophiles is recommended.