Novel Anticancer NHC*-Gold(I) Complexes Inspired by Lepidiline A

N-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-, I-, C equivalent to C-R) and [NHC*-Au-L](+)(L = NHC*, PPh3) 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(wt)and the multidrug-resistant human breast carcinoma cell line MCF-7(topo). Most complexes showed good cytotoxicity with IC(50)values in the low micromolar range, while excellent sub-micromolar activity was observed for2c,3aand3b. Generally, the activity of the ligands studied was as follows: carbene > phosphine > alkyne > halide, with an exception for the highly active iodido derivative2c.