TCO-PEG3-NHS ester

TCO-PEG3-NHS ester is a bifunctional PROTAC linker building block designed to connect a targeting ligand to an E3 ligase recruiter through a PEG-based spacer and a reactive NHS ester handle. Its flexible ethylene glycol segment can improve solubility and spatial presentation of conjugated partners, while the trans-cyclooctene (TCO) motif supports fast, bioorthogonal tetrazine-mediated ligation in targeted degradation workflows. The following sections provide detailed structure and reactivity guidance for PROTAC assembly.

Structure: The linker combines a trans-cyclooctene moiety with a PEG3 ethylene glycol spacer and an activated N-hydroxysuccinimide ester. It contains an NHS ester functional group for acyl transfer, ether linkages within the PEG chain, and a strained alkene suitable for tetrazine ligation, enabling stable yet modular conjugation chemistry.

Reactivity: The NHS ester reacts with primary amines to form stable amide bonds under mild aqueous buffer conditions, typically requiring controlled pH to favor nucleophilic acyl substitution. The TCO group undergoes strain-promoted inverse electron-demand Diels–Alder reactions with tetrazines, proceeding rapidly without added catalysts. For PROTAC construction, prepare amine-functionalized ligands for coupling, then perform tetrazine ligation using compatible solvents that maintain ligand integrity and minimize side reactions.