Synthesis and Antifungal Activities of Pyridine Bioisosteres of a Bismuth Heterocycle Derived from Diphenyl Sulfone

Heterocyclic iodobismuthanes 7-9 [IBi(C6H4-2-SO2C5H3N-1'-)] derived from phenyl pyridinyl sulfones were synthesized. Their antifungal activities against the yeast Saccharomyces cerevisiae were compared with those of halobismuthanes [XBi(RC6H3-2-SO2C6H4-1'-)] (1: X=Cl; 2: X=I, R=H) derived from diphenyl sulfone derivatives to determine how the bioisosteric replacement of the benzene ring in 2 with the pyridine ring in 7-9 affects their activities. The antifungal activities of 7-9 were higher or comparable to those of 1 and 2. The DFT calculations suggested that the generation of the antifungal activity of the bismuthanes was well understood by the nucleophilic addition of methanethiolate anion as a model biomolecule at the bismuth atom to give an intermediate ate complex.