2.5 CuAAC and Metal-Free 1,3-Dipolar Huisgen Cycloadditions in Drug Discovery

Proclaimed by Sharpless in 2001, the manifesto of click chemistry philosophy shifted the focus from target-oriented to drug-like-oriented synthesis, and has enormously accelerated the drug-discovery process over the last two decades. Copper(I)-catalyzed and metal-free versions of the Huisgen 1,3-dipolar cycloaddition of azides and alkynes have become the reference click chemistry synthetic tools. These processes are adaptable to various drug-design modes such as kinetic target guided synthesis (in situ click chemistry assembling; KTGS), combinatorial chemistry/high-throughput-screening approaches, or structure-based rational projecting. Moreover, the facile click chemistry derivatization of natural or synthetic products, linking molecules or improving the stability of leads by installation of 1,2,3-triazoles, is another important stream of bioactivities. This review is intended to provide a general overview of click-chemistry-powered drug design, with dozens of successful examples resulting in the discovery of nanomolar-active 1,2,3-triazoles in every stage of drug development.