Structural and solution studies of phenylbismuth(III) sulfonate complexes and their activity against Helicobacter pylori

Abstract

Three bis-phenylbismuth sulfonates [Ph₂Bi(O₃SR)]_∞ (R = p-tolyl 1, mesityl 2 or S-(+)-10-camphoryl 3) have been synthesised and characterised. Their tendency for ligand redistribution in solution, and activity against the bacterium Helicobacter pylori have been investigated. The structures of 2 and 3 have been authenticated by X-ray diffraction crystallography. They are structurally very similar with polymeric helical chain structures composed of four coordinate Bi atoms which bridge between two sulfonate O atoms with near linear O–Bi–O bond angles. The two phenyl rings are cis to one another and trans to the stereochemically active lone pair. Upon dissolution of the pure compounds 1, 2 and 3, a ligand redistribution reaction occurs in which the mono-phenylbismuth bis-sulfonates, the bismuth tris-sulfonates and triphenylbismuth are formed. Two further complexes of general formula [PhBi(O₃SR)₂]_∞ (where R = p-tolyl 4, and mesityl 5) were thus obtained and their crystal structures determined. The presence of the single sulfonato ligand in compounds 1, 2 and 3 resulted in a dramatic increase in bacteriocidial activity towards H. pylori (MIC values of ≥6.25 μg mL⁻¹) relative to BiPh₃ (>64 μg mL⁻¹) and the sulfonic acids, which were essentially inactive.