Synthesis of acylated derivatives of chitosan oligosaccharide and evaluation of their potential antifungal agents on Fusarium oxysporum.

Chitosan oligosaccharide (COS) is an important carbohydrate-based biomaterial for synthesizing candidate drugs and biological agents. This study synthesized COS derivatives by grafting acyl chlorides of different alkyl chain lengths (C8, C10, and C12) onto COS molecules and further investigated their physicochemical properties and antimicrobial activity. The COS acylated derivatives were characterized using Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance spectroscopy, X-ray diffraction, and thermogravimetric analysis. COS acylated derivatives were successfully synthesized and possessed high solubility and thermal stability. As for the evaluation of antibacterial activity, COS acylated derivatives did not significantly inhibit Escherichia coli and Staphylococcus aureus, but they significantly inhibited Fusarium oxysporum, which was superior to that of COS. Transcriptomic analysis revealed that COS acylated derivatives exerted antifungal activity mainly by downregulating the expression of efflux pumps, disrupting cell wall integrity, and impeding normal cell metabolism. Our findings provided a fundamental theory for the development of environmentally friendly antifungal agents.