Synthesis and Antifungal Evaluation of Cinnamic Acid-Geraniol Hybrids as Potential Fungicides

Cinnamic acid and geraniol are two well-known antifungal natural products and widely applied in food and cosmetics industries. To discover novel natural product-based fungicide candidates with more potent activity and good ecological compatibility for the management of plant diseases, a series of cinnamic acid-geraniol hybrids were prepared by means of molecular hybridization and their chemical structures were well confirmed by spectral analysis. The antifungal activities of the target compounds against three phytopathogenic fungi Fusarium graminearum, Gaeumannomyces graminis (Sacc.) Arx et Oliver var. tritici (Sacc.) Walker, and Valsa mali were evaluated. Among them, compounds 5 e and 5 f showed the remarkable antifungal activity against G. graminis with the EC₅₀ values of 82.719 and 91.828 μg/mL, respectively; while compounds 5 f and 6 b exhibited the obvious antifungal activity against V. mali. It suggested that compound 5 f can be further optimized for the design of novel broad-spectrum fungicide molecules as the secondary lead compound. In addition, some interesting structure-antifungal activity relationships were obtained. This work will provide some reference and guidance for the further discovery of novel fungicide candidates based on cinnamic acid and geraniol.