1-(Aminomethyl)-Trans-Cyclooct-4-Ene, a New TCO Derivative for Target Visualization and Target Engagement Measurement in Cells

Click probes have enabled a thorough study of drug interactions in relevant disease models. Proper design of the probes, including the choice of the click moiety coupled to the drug, is crucial to ensure good performance and broad application. A new trans -cyclooctene derivative, amTCO, was synthesised using a phthalimide protecting group as a built-in photosensitiser for the cyclooctene isomerization. The 1-(aminomethyl)- trans -cyclooct-4-ene (amTCO) displays a primary amine group that facilitates conjugation with carboxylic acid or hydroxyl-containing compounds. It can help tuning the physical chemical properties of the resulting probes. An amTCO probe targeting indoleamine 2,3-dioxygenase (IDO1) was superior to a TCO variant. The new probe is an effective tool for visualizing IDO1 and measuring the binding affinities of small molecule inhibitors to IDO1 in cells.