Information about the biomolecules involved in cellular processes is essential for understanding them. This information includes their location and interactions. The molecules must be labeled in a way that does not affect physiological processes (bioorthogonality). The markers can be selectively and quickly coupled with small molecules using "click chemistry" and small molecules. A team of researchers have now published a new type of click reaction in the journal Angewandte Chemie. It is suitable for living cells as well as organisms.Injecting an antibody that binds specifically to the tumor cells' molecules allows for labeling biomolecules, which can be used to identify and characterize tumors. The dye is also injected. Both the antibodies and dye have small molecular group that have little to no effect on cellular processes. They bind to their counterparts immediately, with no side effects. It's as easy as two pieces clicking together. Click chemistry is a result of this. It is only possible to detect tumor cells if the dye remains attached to them.The azide-alkyne reaction is the most famous click chemistry reaction. A five-membered ring is formed when an azide group reacts to an alkyne molecule. This reaction is not suitable for living systems because it requires a toxic copper catalyst. Alternative options include cyclic alkynes. In these cases, the triple bond is so stressed that it works without the need for a catalyst. However, some applications may not be suitable for the cycle.Justin Kim, from the Dana-Farber Cancer Institute (Boston, USA), has developed an alternative click reaction using linear, terminal alkynes. It works quickly and is free of catalysts under complicated physiological conditions. The team was able to determine which alkynes have enough reactive potential by analyzing the electronic interactions and testing them with various substituents. It was important to balance the different influences from the substituents to ensure that the alkynes could be activated sufficiently (push-pull activation), without the need for a catalyst, while still being protected against attack by cellular components. The team used N,N-dialkylhydroxylamines (organic compound containing both oxygen and nitrogen) to make the click unit. The resulting reaction products, enamine-Noxides, are biocompatible.These click reactions (also known as retro-Cope eliminations), are extremely fast. These products are created regioselectively and are stable enough to be easily introduced to biomolecules. This expands the range of bioorthogonal coupling reaction for cellular labeling within living systems.###About the AuthorJustin Kim is Assistant Professor of Biological Chemistry & Molecular Pharmacology at Dana-Farber Cancer Institute. He also teaches at Harvard Medical School. His expertise is in the development and use of chemical reactions that are biologically compatible. These chemical reactions allow for the manipulation of protein-protein interactions.