Palladacyclopentadienyl complexes bearing purine-based N-heterocyclic carbenes: A new class of promising antiproliferative agents against human ovarian cancer

A complete protocol for the synthesis of new palladacyclopentadienyl complexes with purine-based carbenes as supporting ligands is described. The new organometallic compounds were exhaustively characterized using NMR and infrared spectroscopies and elemental analysis. The single-crystal X-ray structure of complex 2b coordinating also a triphenylphosphine was resolved. Some of these complexes showed an antiproliferative activity comparable to or better than that of cisplatin on two human ovarian cancer lines: A2780 (cisplatin-sensitive) and A2780cis (cisplatin-resistant). Moreover, for complexes 2 and 3 (coordinating one purine-based N-heterocyclic carbene ligand and one phosphine) the cytotoxicity is associated with an evident induction of apoptosis. Finally, complexes 3, bearing one purine-based N-heterocyclic carbene ligand and one 1,3,5-triaza-7-phosphaadamantane, proved practically inactive on non-tumour fibroblast cells (MRC-5).