Abstract
Ustilaginoidins are bis-naphtho-γ-pyrone mycotoxins isolated from the rice false smut balls (FSBs) infected by the pathogen Villosiclava virens in rice spikelets on panicles. In order to obtain large amounts of pure ustilaginoidins to further evaluate their biological activities and functions, phytotoxicity on rice, security to human and animals as well as to accelerate their applications as pharmaceuticals, preparative high-speed counter-current chromatography (HSCCC) was successfully applied to the isolation and purification of seven bis-naphtho-γ-pyrone mycotoxins, namely ustilaginoidins A (1), G (2), B (3), H (4), I (5), C (6), and J (7) from the ethyl acetate crude extract of rice FSBs. Both 1 and 2 were prepared by HSCCC from the low-polarity fraction of the crude extract using the two-phase solvent system composed of n-hexane-ethyl acetate-methanol-water at the volume ratio of 6.5:3.5:5.0:5.0. Similarly, 3, 4 and 5 were prepared from the medium-polarity fraction using the system at the volume ratio of 4.0:5.0:5.0:6.0, and 6 and 7 were prepared from the higher-polarity fraction using the system at volume ratio of 3.0:5.0:4.0:6.7. A total of 6.2 mg of 1, 5.1 mg of 2, 3.9 mg of 3, 1.2 mg of 4, 5.7 mg of 5, 3.5 mg of 6, and 6.1 mg of 7 with purities of 88%, 82%, 91%, 80%, 92%, 81% and 83%, respectively, were yielded from total 62 mg fraction samples in three independent HSCCC runs. The structures of the purified ustilaginoidins were characterized by means of physicochemical and spectrometric analysis.
Highlights
The rice false smut caused by the ascomycetous pathogen Villosiclava virens (Nakata) Tanaka and Tanaka is an emerging, increasingly significant and worldwide fungal disease in many rice (Oryza sativa L.) cultivation areas over the past few years [1,2].This disease was once considered a minor disease with low frequency of occurrence in rice-growing areas
The preliminary studies were carried out to determine the K values of the target compounds in the most widely used two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water at various volume ratios of 3.0:5.0:3.0:5.0, 3.0:5.0:4.0:6.7, 4.0:5.0:4.0:5.0, 4.0:5.0:5.0:6.0, 6.5:3.5:5.0:5.0, and 7.0:3.0:5.0:5.0, coded as S1–S6, respectively, by high performance liquid chromatography (HPLC) analysis
The ustilaginoidins with hydroxymethyl groups at C-2 or C-21 have not been isolated from the fermentation cultures of the pathogen. It seems that ustilaginoidins B (3), H (4), I (5), C (6), and J (7) with hydroxymethyl groups at C-2 or C-21 were only found in the rice false smut balls (FSBs) formed in the natural rice field. These ustilaginoidins with a high degree of oxidation in the rice FSBs may have their physiological and ecological functions which need to be studied in detail
Summary
The rice false smut caused by the ascomycetous pathogen Villosiclava virens (Nakata) Tanaka and Tanaka (anamorph: Ustilaginoidea virens Takahashi) is an emerging, increasingly significant and worldwide fungal disease in many rice (Oryza sativa L.) cultivation areas over the past few years [1,2]. 9-9 single bond, and false smut balls (FSBs), in spikelets during the late phase of pathogen infection [7] With regard to their absolute configurations have been determined be R according (i.e., to the Cotton effects shown from the chemical constituents of the FSBs, there are twoto types of mycotoxins ustiloxins and ustilaginoidins) circular (CD) [13]. The biological of ustilaginoidins ustilaginoidins as antitumor agents and antimicrobials as well as their promising bioactivities have during the occurrence and spread of rice false smut along with their potential risks to grain production led tosafety considerable in theThus, pharmaceutical community [12].large. It is necessary to obtain amounts of pure ustilaginoidins of ustilaginoidins during the occurrence and spread of rice false smut along with their potential risks to further evaluate their biological activities and functions, phytotoxicity on rice, security to human to grain production and food safety remain unclarified.
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