Solvent-free synthesis and antifungal activity of 3-alkenyl oxindole derivatives

A simple, efficient, and environmentally benign green approach was developed for the synthesis of 3-alkenyl oxindole derivatives with effective antifungal properties. The targeted compounds (3a-3g) were synthesized by using Knoevenagel condensation with oxindole and substituted aromatic aldehydes in the solvent-free, microwave-assisted reaction conditions. Silica extracted from rice husk waste was functionalized with (3-aminopropyl) triethoxysilane (APTES) to use as an eco-friendly, reusable, and solvent-free reaction medium. The structures of the final products were confirmed by their melting points, IR, 1H-NMR, 13C-NMR, and elemental analysis. The desired products were isolated with 72-88% yields in 12 minutes. The in vitro antimicrobial activity against ATCC standard cultures of human pathogenic Candida species, clinical isolates of Candida albicans, and several Gram-positive and Gram-negative bacteria were investigated and reported. All the synthesized 3-alkenyl oxindole derivatives exhibited the selective antifungal properties with the minimum inhibitory concentration (MIC) values ranging from 2 µg/mL to 125 µg/mL against tested Candida species. The findings of this study emphasized that green synthesized 3-alkenyl oxindole derivatives can be considered as the potential lead compounds to develop the effective antifungals against human pathogenic Candida species.