Synthesis, Characterization, and Biological Studies of a Piperidinyl Appended Dipicolylamine Ligand and Its Rhenium Tricarbonyl Complex as Potential Therapeutic Agents for Human Breast Cancer

A novel ligand bearing a central piperidinyl sulfonamide group, N(SO(2)pip)dpa, and its corresponding Re tricarbonyl complex, [Re(CO)(3)(N(SO(2)pip)dpa)](+), have been synthesized in good yield. The methylene CH(2) signal seen as a singlet (4.54 ppm) in a (1)H NMR spectrum of the ligand in DMSO-d (6) appears as two doublets (5.39, 5.01 ppm) in a spectrum of the [Re(CO)(3)(N(SO(2)pip)dpa)](+) complex and confirms the presence of magnetically nonequivalent protons upon coordination to Re. Structural results revealed that the Re–N bond lengths fall within the normal range establishing coordination of ligand to metal. The presence of intraligand π → π (⁎) and n → π (⁎) transitions is indicated by the absorption peaks around 200–250 nm in UV-visible spectra. Absorption peaks in UV-visible spectra around 300 nm for metal complexes were identified as MLCT transitions. The S–N stretch observed as a strong peak at 923 cm(−1) for N(SO(2)pip)dpa appeared at a shorter frequency, at 830 cm(−1) in an FTIR spectrum of the [Re(CO)(3)(N(SO(2)pip)dpa)](+). The intense fluorescence displayed by the N(SO(2)pip)dpa ligand has quenched upon coordination to Re. Relatively low IC(50) values given by human breast cancer cells, MCF-7, (N(SO(2)pip)dpa = 139 μM, [Re(CO)(3)(N(SO(2)pip)dpa)](+) = 360 μM) indicate that N(SO(2)pip)dpa and [Re(CO)(3)(N(SO(2)pip)dpa)](+) are promising novel compounds that can be further investigated on their usage as potential anticancer agents.