Abstract
Ustiloxins were cyclopeptide mycotoxins from rice false smut balls (FSBs) that formed in rice spikelets infected by the fungal pathogen Ustilaginoidea virens. To investigate the chemical diversity of these metabolites and their bioactivities, one new cyclopeptide, ustiloxin G (1), together with four known congeners—ustiloxins A (2), B (3), D (4), and F (5)—were isolated from water extract of rice FSBs. Their structures were elucidated by analyses of their physical and spectroscopic data, including ultraviolet spectrometry (UV), infrared spectroscopy (IR), 1D and 2D nuclear magnetic resonance (NMR), and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS). All the compounds were evaluated for their cytotoxic as well as radicle and germ elongation inhibitory activities. Ustiloxin B (3) showed the best activity against the cell line BGC-823 with an IC50 value of 1.03 µM, while ustiloxin G (1) showed moderate activity against the cell lines A549 and A375 with IC50 values of 36.5 µM and 22.5 µM, respectively. Ustiloxins A (2), B (3), and G (1) showed strong inhibition of radicle and germ elongation of rice seeds. When their concentrations were at 200 µg/mL, the inhibitory ratios of radicle and germ elongation were more than 90% and 50%, respectively, the same effect as that of positive control (glyphosate). They also induced abnormal swelling of the roots and germs of rice seedlings.
Highlights
Rice false smut is one of the most destructive rice fungal disease caused by ascomycete fungusVillosiclava virens Tanaka and Tanaka [1]
The water extract of rice false smut balls (FSBs) was successively subjected to the repeated column chromatography overof macroporous adsorption subjected resin SP207, Sephadex
2–5 (Figure known cyclopeptides were1,identified as high-performance liquidcyclopeptides chromatography (HPLC)1)
Summary
Rice false smut is one of the most destructive rice fungal disease caused by ascomycete fungus. Ustiloxins to arisks group water-soluble cyclopeptides which leads to both considerable financial damagebelong and safety [5].ofChemical investigations of the containing a 13-membered cyclic core with of antwo ether linkage [6,7] They exhibit variety of rice FSBs have led to the isolation andstructure identification kinds of mycotoxins, namelya ustiloxins biological activities, [6,7,8,9,10,11,12,13]. When domestic animals were fed with the rice grains and feedstuff biological activities, including antimitotic activity by inhibiting microtubule assembly and skeleton contaminated by eukaryotic the rice false smut pathogen, they showedasa potential variety ofantitumor symptomsagents such asfor diarrhea, formation of the cells, and have been regarded clinical hemorrhage, poor growth, ovarian atrophy, abortion, and damage of liver, heart, and kidney [10]. We described the isolation and structural elucidation of the ustiloxins from rice FSBs, as well as their biological activities
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