Mannose-Inspired Mesoionic Carbenes: Building Antitumor Palladium(II) Allyl Complexes

The synthesis and anticancer evaluation of palladium(II) complexes bearing mannose-conjugated mesoionic carbenes and their triazolium precursors (triazolium palladates) is reported. Ligand precursors are easily obtained via copper-catalyzed azide–alkyne cycloaddition. Palladium allyl carbene complexes are prepared extending the weak base route protocol to triazolium salts by reacting the metal precursor and azolium salts with potassium carbonate as the base in acetonitrile and under mild conditions. Additionally, triazolium allyl palladates are isolated, which represent the first examples of triazolium palladate complexes described in the literature. In vitro tests on a panel of cancer cell lines (A2780, A2780cis, DLD-1) reveal better or comparable cytotoxicity to cisplatin. The majority of complexes exhibit low cytotoxicity (>100 μM) toward MRC-5 and FT-190 nontumoral cell lines demonstrating remarkable in vitro selectivity.