Inhibitory activity of the novel Zn[(OPPh2)(SePPh2)N]2 complex towards the Platelet Activating Factor (PAF) and thrombin: Comparison with its isomorphous Co(II) and Ni(II) analogues

The Zn[(OPPh2)(SePPh2)N]2 complex was prepared by a metathetical reaction between a Zn(II) salt and the deprotonated form of the dichalcogenoimidodiphosphinato ligand [(OPPh2)(SePPh2)N]−. X-ray crystallography revealed a pseudo-tetrahedral MO2Se2 coordination sphere, owed to the asymmetric (O,Se) nature of the chelating ligand. A comparison between the structural features of the M[(OPPh2)(SePPh2)N]2 complexes, M = Co, Ni, Zn, shows that the three complexes are isomorphous. The IR and 31P NMR properties of Zn[(OPPh2)(SePPh2)N]2 are analyzed in the framework of its crystallographic structure, and are compared with data on similar systems. The above three complexes, along with the (OPPh2)(SePPh2)NH ligand and SeO2, are investigated as inhibitors of the Platelet Activating Factor (PAF) and thrombin activities. The paramagnetic M[(OPPh2)(SePPh2)N]2 complexes, M = Co, Ni, exhibit an approximately 65-fold increased activity, compared to diamagnetic Zn[(OPPh2)(SePPh2)N]2, in both the PAF- and the thrombin-induced aggregation of washed rabbit platelets (WRP). The above three complexes show a comparable significant inhibitory activity in the PAF-induced aggregation of rabbit platelet rich plasma (RPR). Remarkably, SeO2, a form of Se present in blood, exhibits a very strong and selective inhibitory activity towards the PAF-induced aggregation of WPR. Our studies extend the dataset of metal complexes investigated as inhibitors of PAF and thrombin.