Synthesis and Cytotoxicity Studies of Novel NHC-Gold(I) Complexes Derived from Lepidiline A

Ten novel -heterocyclic carbene gold(I) complexes derived from lepidiline A (1,3-dibenzyl-4,5-dimethylimidazolium chloride) are reported here with full characterisation and biological testing. (1,3-Dibenzyl-4,5-diphenylimidazol-2-ylidene)gold(I) chloride (NHC*-AuCl) ( ) was modified by substituting the chloride for the following: cyanide ( ), dithiocarbamates ( ⁻ ), -mercaptobenzoate derivatives ( ⁻ ) and -acetyl-l-cysteine derivatives ( ⁻ ). All complexes were synthesised in good yields of 57⁻78%. Complexes , , , and were further characterised by X-ray crystallography. Initial evaluation of the biological activity was conducted on all ten complexes against the multidrug resistant MCF-7 breast cancer, HCT-116 , and p53 knockout mutant HCT-116 colon carcinoma cell lines. Across the three cell lines tested, mainly single-digit micromolar IC values were observed. Nanomolar activity was exhibited on the MCF-7 cell line with displaying an IC of 0.28 μM ± 0.03 μM. Complexes incorporating a Au⁻S bond resulted in higher cytotoxic activity when compared to complexes and . Theoretical calculations, carried out at the MN15/6⁻311++G(2df,p) computational level, show that NHC* is the more favourable ligand for Au(I)-Cl when compared to PPh₃.