Synthesis and antifungal activities of novel polyheterocyclic spirooxindole derivatives

A series of spirooxindole tetrahydrofuran derivatives 3 were obtained in moderate to good yields via oxindole derivatives 1 and beta-arylacrylonitrile derivatives 2 via base-mediated cascade [3 + 2] double Michael reactions under mild conditions and the application of this method in the synthesis of bioactive analogues, such as functionalized spirooxindole octahydrofuro[3,4-c]pyridine derivatives 4 which contain two new heterocyclic rings and two quaternary carbon centers, has also been developed. Subsequently, antifungal activities of all of the synthesized compounds were evaluated against five phytopathogenic fungi (Rhizoctonia solani, Fusarium semitectum, Alternaria solani, Valsa mali and Fusarium graminearum) using the mycelium growth rate method. The preliminary results showed that the spirooxindole octahydrofuro[ 3,4-c]pyridine derivative 4 showed higher growth inhibition of Valsa mali and Fusarium graminearum, than spirooxindole tetrahydrofuran derivatives 3. For example, spirooxindole octahydrofuro [3,4-c]pyridine derivative 4ab, having a bromine atom at the meta position of the benzene ring, was the best compound in inhibiting F. g. with an IC50 value of 3.31, in particular with inhibition of 4ab on F. g. being similar to that of the control cycloheximide (IC50 = 3.3 mu g mL(-1)).