TCO-PEG4-biotin

TCO-PEG4-biotin is a bifunctional PROTAC-oriented linker that combines a strained trans-cyclooctene (TCO) moiety with a PEG-based spacer and a biotin handle for affinity-compatible conjugation workflows. Its design supports efficient, bioorthogonal pairing with tetrazine partners and provides conformational flexibility through the polyethylene glycol segment, which can improve effective reach between binding elements in targeted degradation constructs. The points below describe the structure and practical reactivity considerations in detail.

Structure: The linker incorporates a strained TCO alkene embedded in a conjugatable scaffold, connected to a polyethylene glycol spacer that increases hydrophilicity and chain flexibility, and terminating in a biotin-derived affinity motif. It contains ether linkages in the PEG segment and amide or ester-type connectivity depending on the final conjugation scheme.

Reactivity: TCO groups undergo rapid inverse-electron-demand Diels–Alder reactions with tetrazines under mild aqueous-compatible conditions, typically without the need for metal catalysts. For PROTAC assembly, the linker is commonly pre-functionalized to match the electrophile/nucleophile requirements of the targeting ligand and then reacted with tetrazine-bearing partners to form a stable covalent adduct. Solvent systems that maintain solubility of PEGylated constructs and preserve tetrazine reactivity are generally used, with reaction monitoring by chromatographic or spectroscopic methods.