Synthesis and antifungal property of N-(aryl) and quaternary N-(aryl) chitosan derivatives against Botrytis cinerea

A series of N-(aryl) and their quaternary N-(aryl) chitosan derivatives were synthesized and evaluated for their antifungal activity against crop-threatening fungus Botrytis cinerea. Schiff bases were firstly synthesized by the reaction of chitosan with cinnamaldehyde, cuminaldehyde and 4-dimethylaminobenzaldehyde followed by reduction with sodium borohydride to form N-(aryl) chitosans. Quaternary N-(aryl) chitosans were then obtained by reaction of N-(aryl) chitosan compounds with ethyl iodide. The chemical structures were characterized by ¹H-NMR, FT-IR and UV spectroscopic techniques. The antifungal activity was evaluated in vitro against B. cinerea by mycelial growth inhibition method and in vivo by application of compounds to tomato plants prior to inoculation with fungal spores. In an in vitro experiment, all quaternized chitosans were more active than N-(aryl) chitosan derivatives and N,N,N-(diethylcinnamyl) chitosan (QC1) was the most potent (EC₅₀ = 1,147 mg/L) against mecelia however, N,N,N-(diethyl-p-dimethylaminobenzyl) chitosan (QC3) was the most potent (EC₅₀ = 334 mg/L) against spores. In an in vivo study, no disease incidence (0.0 %) was observed with QC1 and QC3 at 1,000 mg/L. Spray liquid chitosan enhanced total phenolics and guaiacol peroxidase in inoculated leaves.