TCO-PEG12-NHS ester

TCO-PEG12-NHS ester, is designed to enable efficient conjugation between a targeting ligand and a reactive partner in targeted protein degradation workflows. Its PEG-based spacer improves solubility and provides conformational flexibility, while the NHS ester supports robust amide-bond formation under standard bioconjugation conditions. The resulting constructs are well suited for subsequent bioorthogonal coupling strategies commonly used in PROTAC assembly. Detailed structural and reactivity considerations are provided below.

Structure: The linker contains a PEG-derived hydrophilic chain that spaces functional groups and promotes aqueous compatibility. It features an NHS ester electrophile for acyl transfer and a trans-cyclooctene (TCO) motif suitable for strain-promoted bioorthogonal reactions. The molecule includes ester and amide-reactive carbonyl functionality and ether linkages within the PEG segment.

Reactivity: The NHS ester reacts with primary amines to form stable amide bonds via nucleophilic acyl substitution. Typical coupling is performed in aqueous or mixed aqueous buffers at controlled pH, using amine-containing ligands and allowing formation of the activated ester–amine intermediate followed by expulsion of NHS. The TCO group is preserved for strain-promoted cycloaddition with complementary tetrazine partners, generally without metal catalysts, in conditions compatible with sensitive biomolecules.