Antifungal activity of organobismuth compounds against the yeast Saccharomyces cerevisiae: structure-activity relationship

Antifungal activity of organobismuth(III) and (V) compounds 1-9 was examined against the yeast, Saccharomyces cerevisiae. A clear structure-activity relationship was observed in these compounds. Thus, triarylbismuth dichlorides 2 [(4-YC6H4)3BiCl2: Y=MeO, F, Cl, CF3, CN, NO2] and halobismuthanes 6 [2-(t)BuSO2C6H4(4-YC6H4)BiX: Y=MeO, Me, H, Cl; X=Cl, Br, I], 7 [Bi(X)(C6H4-2-SO2C6H4-1'-): X=Cl, Br, I], 8 [2-Me2NCH2C6H4(Ph)BiX: X=Cl, Br] and 9 [4-MeC6H4(8-Me2NC10H6-1-)BiCl] showed the growth inhibition effect, while triarylbismuth difluorides 3 [(4-YC6H4)3BiF2] and triarylbismuthanes 1 [(4-YC6H4)3Bi], 4 [2-(t)BuSO2C6H4(4-YC6H4)2Bi] and 5 [4-YC6H4Bi(C6H4-2-SO2C6H4-1'-)] were not active at all irrespective of the nature of the substituents. Generation of the inhibition effect is governed by the facility of nucleophilic reaction at the bismuth center and the Lewis acidic bismuth center is an active site. Of all the bismuth compounds attempted, halobismuthanes 7 derived from diphenyl sulfone exhibited the highest activities. An X-ray crystallographic study of 7a [Bi(Cl)(C6H4-2-SO2C6H4-1'-)] revealed that the bismuth center adopts a seven-coordinated geometry, which is unusual in organobismuth(III) compounds, through the intramolecular and intermolecular coordination between the bismuth and oxygen atoms. The marked inhibition effect of 7 may be attributed to such a highly coordinated geometry, which allows the bismuth center to bind tightly with some biomolecules playing important roles in the growth of S. cerevisiae.