Novel Cell Wall Antifungals Reveal a Special Synergistic Activity in pbr1 Mutants Resistant to the Glucan Synthesis Antifungals Papulacandins and Echinocandins

A series of 4 (arylmethylene)-3-isochromanones have been prepared with base-catalyzed Knoevenagel condensation starting from 3-isochromanone and aromatic aldehydes. The outcome of the reaction- the isomeric composition of the products depends on the aromatic aldehyde applied. These reactions afforded mostly the more stable -diastereoisomer, but some condensations resulted in the Z-diastereoisomer or mixture of the stereoisomers ( - ). The products showed antifungal effect against some pathogenic fungi. We wanted to extend this study and to synthesize a new generation of 4 (arylmethylene)-3-isochromanones. These condensations led mostly to -diastereoisomers ( - ). The structure verifications were performed by FT IR, H and C NMR methods. Both the - and the novel - compounds have been screened against the three yeast models, fission yeast (wild-type, and and mutants resistant to specific cell wall synthesis inhibitors), budding yeast (wild-type and ) and pathogenic yeast (wild-type, ATCC 26555, 90028 and SC5314). Osmotic protection with sorbitol attenuated the inhibition in living cells suggesting a cell wall-specific antifungal effect. Moreover, the wild-type and mutant strains were tested for their resistant or sensitive β(1,3)-glucan synthase (GS) activity. We found both in living cells and in the enzymatic GS assay a synergistic effect of higher sensitivity of the mutants resistant to the specific GS inhibitors papulacandins and echinocandins. These results may provide new insights into new strategies of combined antifungal therapy of GS inhibitors directed against spontaneous mutants resistant to echinocandins.