Recent Advances in Medicinal Applications of Coinage-Metal (Cu and Ag) N-Heterocyclic Carbene Complexes

The enhanced application of N-heterocyclic carbene (NHC) complexes has over the last few years also triggered a steadily increasing number of studies in the fields of medicinal chemistry, which take advantage of the fascinating chemical properties of these complexes. In fact it has been demonstrated that metal-NHC complexes can be used to develop highly efficient metal based drugs with possible applications in the treatment of cancer or infectious diseases. In particular they represent new anticancer agents, normally with low toxicity profiles, and provide a range of versatile structures for targeted biological applications. Most of these complexes have shown higher cytotoxicity than cisplatin. In the present review the medicinal applications of copper(I) and silver(I) metal NHC complexes are summarized. Specifically, azolium precursors and related Cu(I)- and Ag(I)-NHC complexes of functionalized and non-functionalized imidazole-, triazole- thiazole and benzimidazole-based NHC systems employed in anticancer applications are reviewed. The possibility of using novel azolium precursors and copper(I) and silver(I) acceptors should offer interesting perspectives for the rapid and selective construction of libraries of high molecular diversity and complexity, thus providing a basis for the design and development of metal-based drugs associated with unprecedented biological targets. An overview of the most relevant chemical features is presented and copper(I) and silver(I) NHCs complexes used as anticancer drugs are given together with the description of structure-activity relationships as far as possible.