Comparative stability, cytotoxicity and anti-leishmanial activity of analogous organometallic Sb(V) and Bi(V) acetato complexes: Sb confirms potential while Bi fails the test.

A series of sixteen triphenyl Bi(V) and Sb(V) acetato complexes of general formula [MPh(OCCR)] and one oxido-bridge antimony complex [(SbPh(OCOC(O)Me))O], have been synthesised and characterised, thirteen of which are novel. The solid-state structures of fifteen of the complexes have been successfully authenticated by single crystal X-ray diffraction. All structures, excluding the oxido-bridge antimony complex, adopt a typical trigonal bipyramidal confirmation with the phenyl rings in a propeller-like orientation in the equatorial plane. Fourteen of the complexes were screened for their anti-leishmanial activity and cytotoxicity towards mammalian cells. The Bi(V) complexes were found to be unstable in DMEM culture media and to be severely toxic towards mammalian cells, with IC values in the range 11.4 μM-19.8 μM. In contrast, the Sb(V) complexes demonstrated a high degree of stability and selectivity, with IC values 6.18-19.1 μM for the promastigote assay, and of 73.8-≤100 μM for the human fibroblasts. Assessment of the Sb(V) complexes against the clinically relevant amastigote form of these parasites at 10 μM showed all but the oxido-bridged complex to be effective, with % infection values ranging from 7.0 ± 1.7-40.5 ± 2.0.