Biotin-PEG8-NHS ester

Biotin-PEG8-NHS ester is a polyethylene glycol (PEG)-based, NHS-activated linker designed to enable efficient conjugation of biomolecular targeting ligands within PROTAC workflows. Its biotin handle supports affinity-based capture and assay compatibility, while the flexible PEG spacer helps mitigate steric hindrance and improves effective contact between recruited components. The NHS ester functionality provides a robust route for forming stable amide linkages under standard bioconjugation conditions. The following points describe its structure and practical reactivity for linker installation in PROTAC constructs.

Structure: The linker combines a biotin moiety with a PEG chain terminating in an N-hydroxysuccinimide ester. It contains an NHS-activated carboxyl group for acyl transfer, ether linkages along the PEG backbone, and amide-forming electrophilic carbonyl chemistry. The PEG segment imparts hydrophilicity and conformational flexibility.

Reactivity: Reactivity centers on the NHS ester, which undergoes nucleophilic acyl substitution with primary amines to form amide bonds. Suitable conditions typically use mildly basic aqueous buffers that preserve NHS ester stability while promoting amine nucleophilicity. The reaction is commonly performed at controlled temperature with careful exclusion of competing nucleophiles such as excess primary amines or thiols. No special catalysts are required; purification is often used to remove unreacted activated ester and succinimide byproducts.