bioorthogonality

Bioorthogonality refers to chemical reactions that can proceed inside living systems without interfering with native biochemical processes. The concept, introduced and developed in the early 2000s by Carolyn R. Bertozzi and collaborators, aims to enable selective coupling of biomolecules in aqueous, physiological environments without perturbing cells or organisms. Reactions chosen as bioorthogonal typically use functional groups not present in natural biochemistry and proceed rapidly under mild, biocompatible conditions.

Key criteria for bioorthogonal reactions include compatibility with water and physiological pH and temperature, absence of interference with cellular processes or toxicity, chemoselectivity for the chosen partners, and reaction rates sufficient for practical use in cells or organisms. The reagents should remain stable until the moment of reaction and should not react with common cellular functionalities such as amines, thiols, or sugars.

Prominent bioorthogonal reactions span several families. CuAAC, or copper-catalyzed azide–alkyne cycloaddition, is highly efficient but copper can be toxic in vivo, prompting copper-free variants such as the strain-promoted azide–alkyne cycloaddition (SPAAC). Other methods include the Staudinger ligation, oxime and hydrazone ligations, and the inverse-electron-demand Diels–Alder reaction between tetrazines and strained alkenes or alkynes. These reactions enable labeling, tracking, and modification of biomolecules such as proteins, nucleic acids, and glycans in living cells and animals.

Applications of bioorthogonal chemistry include imaging, targeted drug delivery, and the construction of functional biomaterials, contributing to advances in chemical biology, diagnostics, and therapeutic development.