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  E -diastereoisomer, but some condensations resulted in the Z-diastereoisomer or mixture of the stereoisomers ( 1 - 16 ). 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  E -diastereoisomers ( 17 - 30 ). The structure verifications were performed by FT IR,  1 H and 13 C NMR methods. Both the  1 - 16  and the novel  17 - 30  compounds have been screened against the three yeast models, fission yeast  Schizosaccharomyces pombe  (wild-type, and  pbr1-6  and  pbr1-8  mutants resistant to specific cell wall synthesis inhibitors), budding yeast  Saccharomyces cerevisiae  (wild-type and  pbr1-1 ) and pathogenic yeast  Candida albicans  (wild-type, ATCC 26555, 90028 and SC5314). Osmotic protection with sorbitol attenuated the  in vivo  inhibition in living cells suggesting a cell wall-specific antifungal effect. Moreover, the  S. pombe  wild-type and mutant strains were tested for their resistant or sensitive  in vitro  β(1,3)-glucan synthase (GS) activity. We found both  in vivo  in living cells and  in vitro  in the enzymatic GS assay a synergistic effect of higher sensitivity of the  pbr1  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.