TCO NHS, also known as trans-cyclooctene-N-hydroxysuccinimidyl carbonate, is a highly reactive amine-targeting reagent used in bioorthogonal chemistry. It features a strained trans-cyclooctene (TCO) moiety linked to an NHS carbonate group, enabling efficient conjugation to primary amines on biomolecules such as proteins, peptides, or small molecules.

This reagent plays a pivotal role in constructing advanced bioconjugates for imaging or drug delivery. By introducing the TCO moiety onto amine-containing substrates, researchers can prepare molecules that undergo rapid and selective click reactions with tetrazines. TCO NHS is especially valuable for synthesizing cleavable linkers and multifunctional cross-linkers.