Synthesis, characterisation and cytotoxicity evaluation of rhenium(I) based ester functionalised dinuclear metallacyclophanes

Self-assembly of four components has resulted into the formation of M2L2 type dinuclear metallacyclophanes [Re(CO)3Br(μ-L)]2 (1–5), using flexible ester functionalised organic spacers and metal precursor containing fac-Re(CO)3 corners. The dinuclear metallacyclophanes were synthesized from ReBr(CO)5 and ditopic pyridyl ligands (L) (L = etdp, prdp, budp, pedp and hedp). The self-assembled compounds 1–5 were characterised by elemental analysis, IR, NMR, absorption and emission spectroscopic techniques. Molecular structure of 1 and 2 have been characterised by single crystal X-ray diffraction methods and the molecular masses of 3–5 were evaluated by ESI-MS. Cytotoxicity studies of metallacyclophanes 1, 3 and 5 on six different cancer and normal cells revealed that the metallacyclophanes selectively inhibit certain cancer cells. Especially, compound 5 showed broad-spectrum inhibitory activities in five cancer cells tested with low IC50 value comparable to a reference compound (cisplatin). The anticancer activity of compound 5 is attributed to the induction of early apoptosis. Hence, this class of compounds forms potential anticancer agents.