Synthesis of Schiff bases modified inulin derivatives for potential antifungal and antioxidant applications

In this study, the structure of inulin was chemically modified by Schiff bases in order to improve its biological activity. A total of 6 kinds of inulin derivatives were synthesized according to aza-Wittig reaction. Their structures were confirmed by FTIR, ¹H NMR, and ¹³C NMR spectroscopy. The antioxidant activity of the inulin derivatives was evaluated in vitro. Their antifungal activities against three kinds of plant pathogenic fungi, including Botrytis cinerea, Fusarium oxysporum f. sp. cucumerium Owen, and Phomopsis asparagi, were also studied. The results showed that the biological activities of the derivatives were significantly improved compared to pure inulin. 3HBSAIL could completely scavenge hydroxyl radical and DPPH radical at 1.6mgmL^-1. 3,4DHBSAIL and 2,3,4THBSAIL exhibited strong antioxidant activity as far as the four tested antioxidant systems. Moreover, the scavenging rates of 3,4DHBSAIL and 2,3,4THBSAIL against DPPH radicals were both 100% even at the lowest test concentration (0.1mgmL^-1). The synthetic inulin derivatives showed a broad antifungal spectrum against the tested fungi. At 1.6mgmL^-1, the inhibitory rates of 3HBSAIL against Botrytis cinerea, Fusarium oxysporum f. sp. cucumerium Owen, and Phomopsis asparagi were 93%, 83%, and 82%, respectively. The biological activities of the inulin derivatives were closely related to the DS, the number of phenolic hydroxyl groups and their substitutive positions. The products described in this paper have great potential as biomaterials with good bioactivity and biocompatibility.