| Summary: | <i>N</i>-Heterocyclic carbene gold(I) complexes derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*) represent a promising class of anticancer drugs. Complexes of the type NHC*-Au-L (L = Br<sup>−</sup>, I<sup>−</sup>, C≡C-R) and [NHC*-Au-L]<sup>+</sup> (L = NHC*, PPh<sub>3</sub>) have been synthesised. The X-ray crystal structures of all gold(I) complexes are presented; aurophilic interactions were observed in five of the complexes. The anticancer activity was assessed via MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based proliferation assays against the human colon carcinoma cell line HCT-116<sup>wt</sup> and the multidrug-resistant human breast carcinoma cell line MCF-7<sup>topo</sup>. Most complexes showed good cytotoxicity with IC<sub>50</sub> values in the low micromolar range, while excellent sub-micromolar activity was observed for <b>2c</b>, <b>3a</b> and <b>3b</b>. Generally, the activity of the ligands studied was as follows: carbene > phosphine > alkyne > halide, with an exception for the highly active iodido derivative <b>2c</b>.
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