Synthesis, crystal and solution structures of platinacyclic complexes containing eugenol, the main bioactive constituent of Ocimum sanctum L. oil

Abstract

The dinuclear platinacyclic complex [Pt2Cl2(Eug-1H)2] (1) (Eug-1H = deprotonated eugenol) has been synthesized. Reaction of 1 with amines afforded [PtCl(Eug-1H)(pyridine)] (2), [PtCl(Eug-1H)(4-Me-pyridine)] (3), [PtCl(Eug-1H)(piperidine)] (4), [PtCl(Eug-1H)(quinoline)] (5), [PtCl(Eug-1H)(NH3)] (6), [PtCl(Eug-1H)(4-Me-aniline)] (7), [PtCl(Eug-1H)(4-Cl-aniline)] (8), [Pt(Eug-1H)(8-O-quinoline)] (9) and [Pt(Eug-1H)(8-O-2-Me-quinoline)] (10). X-ray diffraction and NMR analysis show that in complexes 1–10 the chelating eugenol ligand is bound with the Pt(II) ion both through the ethylenic double bond of the allyl group and at a benzene carbon atom; in 2–10 the donor N atom of the amine is in the cis-position with respect to the ethylenic double bond. For complexes 2 and 3, two types of relatively strong highly directional intermolecular interactions are observed in the crystal packing: O–H…ClPt(II) hydrogen bonds and C–H…π interactions, in 3 further complemented by C–H…Cl interactions. The crystal packing of 7 is dominated by dimer formation through O–H…O, N–H…Cl, C–H…Cl and C–H…π interactions. In a d-chloroform solution of 2–5 two types of strong intermolecular interactions were detected: a Cl3C-D…ClPt(II) hydrogen bond and Cl2DC-Cl…Pt(II) halogen bond. Complex 9 exhibits significant activities on the human cancer cells KB, Hep-G2, MCF-7 and Lu, with IC50 values of 8.7, 10.8, 9.9 and 10.4 µM respectively.