Synthesis and antifungal activity of novel amide derivatives from quinic acid against the sweet potato pathogen Ceratocystis fimbriata.

Background: Ceratocystis fimbriata is a fungal pathogen that infects sweet potato roots, producing enormous economic losses. Cyclic polyhydroxy compound quinic acid is a common metabolite synthesized in plant tissues, including sweet potato tubers, showing weak antifungal properties. Although several O-acylated quinic acid derivatives have been synthesized and found in nature and their antifungal properties have been explored, derivatives based on modification of the carboxylic acid have never been evaluated.

Results: In this study, amide derivatives were synthesized via linkage of amines with the carboxylic acid moiety of quinic acid. Derivatives with high dipolar moments and a low number of rotatable bonds showed greater antifungal activities toward C. fimbriata in vitro than quinic and chlorogenic acids. Derivative 5b, which was synthesized by coupling p-aminobenzoic acid (pABA) with quinic acid, had the greatest antifungal activity. 5b showed iron(II)-chelating properties and reduced ergosterol content in C. fimbriata cells, causing irregularities in the fungal cell wall and inhibiting conidia agglutination. Application of 3 mm 5b reduced black rot symptoms in sweet potatoes by 70.1%.

Conclusions: Collectively, derivatization of the carboxylic acid from quinic acid was demonstrated to be a suitable strategy to improve the antifungal properties of this compound. This study reveals a new efficient strategy for management of the sweet potato pathogen C. fimbriata. © 2024 Society of Chemical Industry.