Purification and characterization of two grandiuvarones from Desmos chinensis leaves and their antimicrobial activities

Abstract

A novel aromatic compound, grandiuvarone B (5-acetoxy-3-benzoyloxymethyl-5H-oxepin-4-one), along with a known compound grandiuvarone A (5-acetoxy-6-benzoyloxymethyl-5H-oxepin-4-one) were isolated from methanol extracts of Desmos chinensis leaves. Their structures were determined by various spectroscopic techniques including nuclear magnetic resonance (NMR), high-resolution electrospray ionisation mass spectrometry (HR-ESI-MS) and circular dichroism (CD). Grandiuvarone A and grandiuvarone B are isomers and the S configuration of grandiuvarone B was reported for the first time. We then determined their antifungal activity against Aspergillus flavus. Results revealed that grandiuvarone B exhibited better antifungal activity against A. flavus, with MIC values of 0.01 mg/mL compared to grandiuvarone A (MIC values of 0.02 mg/mL). In the presence of each active compound at 160 μg/g of aquafeed, A. flavus growth was completely inhibited. Grandiuvarone B also showed antibacterial activity against the plant pathogen Ralstonia solanacearum.

Graphical Abstract

Keywords:

• Desmos chinensis
• antifungal activity
• grandiuvarone
• Aspergillus flavus

Acknowledgements

This work was supported by the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2016B020204001), and the National Natural Science Foundation of China (Grant No. 31470198) to Z.M.H.

Disclosure statement

No potential conflict of interest was reported by the authors.