Comparative stability, toxicity and anti-leishmanial activity of triphenyl antimony(v) and bismuth(v) α-hydroxy carboxylato complexes

Abstract

A series of triphenyl Sb(V) and Bi(V) α-hydroxy carboxylato complexes of the general formula [MPh₃(O₂CROH)₂] and [MPh₃(O₂CRO)] have been successfully synthesised and characterised, and subsequently assayed for their comparative activity towards Leishmania parasites and human fibroblast cells. Four complexes are novel; [SbPh₃Gly], [BiPh₃(GlyH)₂], [SbPh₃(R-ManH)₂] and [SbPh₃(S-ManH)₂], and have been structurally characterised through X-ray diffraction. These were combined in the study with the known complexes; ([SbPh₃(R-Man)], [SbPh₃(S-Man)], [BiPh₃(R-ManH)₂], [BiPh₃(R-ManH)₂], [SbPh₃(BenzH)₂], [BiPh₃(BenzH)₂], for which the crystal structures of [BiPh₃(S-ManH)₂] and [BiPh₃(R-Man)₂] have now been authenticated (GlyH₂ = glycolic acid, R/S-ManH₂ = mandelic acid, BenzH₂ = benzilic acid). The complexes adopt a typical bipyramidal 7-coordinate geometry with the phenyl rings occupying the equatorial plane, and the ligands on the axial. In contrast to previous studies the Bi(V) compounds show a relatively high degree of stability in DMEM culture media. Promastigote and human fibroblast cell assays showed the Bi(V) analogues to be non-selectively toxic with a respective IC₅₀ range of 3.58–6.33 μM and 5.83–7.01 μM. In contrast, the Sb(V) analogues provided much greater selectivity (promastigotes 12.5–20.7; fibroblasts 72.8–≥100 μM). Assessment of the Sb(V) complexes against amastigotes at 10 μM showed them to be effective with % infection values ranging from 9.5 ± 0.5–30 ± 1.3.