Sugar-boronate ester scaffold tethered pyridyl-imine palladium(II) complexes: synthesis and their in vitro anticancer...

A series of five palladium(ii) pyridyl-imine Schiff base complexes 5a-e containing boronate esters with protected sugar diols derived from d-xylose, l-sorbose and d-mannitol were designed and synthesized starting from pyridyl-imines generated in situ from 3-aminophenyl boronate ester of sugars 3a-e and 2-pyridinecarboxaldehyde, followed by the addition of Pd(cod)Cl2 in dichloromethane solvent. All the complexes are remarkably stable orange/yellow crystalline solids and were obtained in good yields. The complexes were fully characterized by FT-IR, multinuclear NMR ((1)H, (13)C and (11)B), UV-visible spectroscopy, and elemental analysis. The solid state structures of 3a and 5a were established by single crystal X-ray diffraction analysis. The complexes have been tested for their in vitro anticancer activities against human colon cancer (HT-29) and breast cancer (MDA-MB-231) cell lines. All the complexes have shown moderate to good cytotoxicity in both the cancer cell lines with IC50 values ranging from 4.27 to 34.76 μM. Strikingly, 5a displayed selective anticancer activity against both HT-29 and MDA-MB-231 cells with low IC50 values 6.71 and 8.58 μM respectively. Results also demonstrate that some of these complexes are highly potent against HT-29 cells as compared to the other cancer cell lines. In particular, 1,2:5,6-di-O-isopropylidene-d-mannitol complex 5d showed a two-fold higher toxicity against HT-29 cells in comparison with that of cisplatin. In addition, these complexes are less toxic to model non-tumorigenic human embryonic kidney cells (HEK-293T). Furthermore, the interaction of the complexes with calf thymus DNA (CT-DNA) was investigated using spectroscopy and viscosity measurements. It was found that they intercalate with DNA.