Synthesis, characterization and antifungal activity of coumarin-functionalized chitosan derivatives

Four novel coumarin-functionalized chitosan derivatives 4a-4d were synthesized via condensation reactions of thiosemicarbazide chitosan with coumarin derivatives. Their structures were confirmed by FT-IR, ¹³C NMR, XRD and elemental analysis. Their antifungal activities against three kinds of phytopathogens, Alternaria solani sorauer (A. solani), Fusarium oxysporum f.sp. vasinfectum (F. oxysporum) and Fusarium moniliforme (F. moniliforme), were tested using the mycelial growth rate in vitro at 0.1, 0.5, and 1.0mg/mL. The degree of substitution for 4a-4d ranged from 40 to 60%. At 1mg/mL, 4a inhibited F. moniliforme growth by 58.1%, and had an inhibitory index against F. Moniliforme of 77.2%. Derivative 4a was more effective than unmodified chitosan whose antifungal index was 9.7%. The fungicidal tests showed that the synthesized chitosan derivatives have higher activity against the tested fungi compared to unmodified chitosan. Moreover, the introduction of halogen atoms into the chitosan derivatives causes an increase in antifungal activity.