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Esculetin is an important plant-derived natural product that has multiple bioactivities and applications. Phytophthora capsici is a notorious plant pathogen capable of infecting a broad range of hosts. In this study, we evaluated the antifungal activity of esculetin against P. capsici. The baseline sensitivity of P. capsici to esculetin was established using 108 isolates collected from various geographical regions in the Jiangsu and Shandong Provinces of China. The median effective concentration (EC50) values for esculetin ranged from 2.08 to 16.46 μg/ml (mean, 6.87 ± 2.70 μg/ml) and were normally distributed. Furthermore, both zoospore production and germination were strongly inhibited by esculetin. Importantly, esculetin exhibited protective as well as curative activities against P. capsici on tomato and was capable of restricting the early infection of P. capsici on Nicotiana benthamiana. We found that the esculetin treatment led to cell membrane damage of P. capsici, as revealed by morphological observations and measurements of relative conductivity and malondialdehyde (MDA). Finally, our results also suggested that esculetin may adversely affect P. capsici by inhibiting its DNA and protein synthesis. These findings will contribute to the broader evaluation of the use of esculetin to control diseases caused by P. capsici and toward a better understanding of its mode of action as a potential fungicide.

Two novel lathyrane-type diterpenoids, the Euphorbia factors L2a (1) and L2b (2), and their stereoisomer Euphorbia factor L2 (3) were obtained from seeds of Euphorbia lathyris. Both Euphorbia factors L2a and L2b possess an unprecedented trans-gem-dimethylcyclopropane as structural feature. Also, the Euphorbia factor L2a is the first example of a lathyrane diterpenoid with an endocyclic 12(Z)-double bond. The structures of the molecules and their absolute configurations were elucidated by comprehensive spectroscopic analyses, Cu-Kα radiation X-ray diffraction, and comparison with calculated electronic circular dichroism (ECD) data. The Euphorbia factor L2b exhibited an inhibitory effect against U937 cell line with an IC50 value of 0.87 μM.

Phytophthora capsici is a notorious pathogen capable of infecting various host plants and causing serious threats to agriculture worldwide. Tetradium glabrifolium fruit essential oil (TFO) is widely utilized in traditional Chinese medicine treatment, but its antimicrobial activity is unknown. In this study, we first investigated the inhibitory efficacy of TFO against P. capsici and found TFO strongly inhibited the development of phytophthora blight on pepper by in vivo inoculation assay. Second, we found TFO could significantly suppress vegetative and reproductive growth of P. capsici in vitro. Microscope observations indicated that TFO destroyed the mycelial morphology and cellular ultrastructure of P. capsici. Additionally, TFO could damage the cell membrane integrity of the pathogen, leading to cellular leakages of intercellular contents of P. capsici. Third, TFO could enhance the activities of defence-related enzymes in pepper fruits during pathogen infection. Finally, we identified the chemical composition of TFO by GC-MS analysis and demonstrated three abundant components ( D -limonene, β-elemene, and 2-tridecanone) contributed to the antifungal activity of TFO. Together, out results revealed that TFO had outstanding inhibitory efficacy against P. capsici, and uncovered its potential antifungal mechanism. This study would propose the application of TFO as an efficient alternative approach for controlling phytophthora blight.

Euphorbia factor L1 (EFL1), a lathyrane-type diterpenoid, is one of the important components of traditional Chinese medicine caper spurge. The aim of this work is to have a deep understanding of molecular structure, properties and potential biological activities of EFL1. Firstly, the molecular structure of EFL1 was studies by a combination of Cu-Kα radiation X-ray diffraction and quantum chemistry calculation. The absolute configuration of EFL1 was elucidated and the geometrical structure optimized by DFT was consistent with the crystal structure determined by X-ray diffraction. Meanwhile, crystal packing, IR and Hirshfeld methods were performed to analyze the crystal packing system, which demonstrated intermolecular hydrogen bonding was the mainly force to stabilize this system. Molecular electrostatic potentials further confirmed the possibilities of such interactions. Furthermore, the electronic transition and energy gap of frontier molecular orbitals revealed the chemical stability and well kinetic stableness of EFL1. Finally, the potential biological activities, targets, diseases and mechanism were also predicted by network pharmacology in silico. This work provides a comprehensive structural analysis and a detailed biological activity analysis of Euphorbia factor L1 which are beneficial to the quality control, structural modification and biological activity studies.