Absolute configuration of azaphilones from Monascus kaoliang KB9 and solvent effects on their keto and enol forms.

Monascus fermented rice, also known as red yeast rice, exhibits a broad spectrum of biological activities due to its chemical constituents, such as monacolins and azaphilone pigments. Here, we cultured Monascus kaoliang KB9 in a liquid malt medium instead of on rice as a carbon source. Eleven known compounds (1-11) containing azaphilones and their early intermediate were isolated and identified. However, this was the first time that angular tricyclic azaphilones, monasfluols A (4) and B (7), acetyl-monasfluol A (5) and monasfluore A (6), were isolated from this species. Interestingly, all isolated tricyclic azaphilones existed exclusively in enol form in CD3OD, as evidenced by NMR spectroscopy. The absolute configuration of compounds 4-7 was also first experimentally identified based on ECD spectroscopy combined with conformational analyses using computational techniques. The assigned stereochemistry of Monascus azaphilones in this work provides essential structural information that will benefit future biological and pharmaceutical investigations.

Anthranilic Acid Accumulation in Saccharomyces cerevisiae Induced by Expression of a Nonribosomal Peptide Synthetase Gene from Paecilomyces cinnamomeus BCC 9616.

Heterologous expression of nrps33, a nonribosomal peptide synthetase gene, from Paecilomyces cinnamomeus BCC 9616 in Saccharomyces cerevisiae unexpectedly resulted in the accumulation of anthranilic acid, an intermediate in tryptophan biosynthesis. Based on transcriptomic and real-time quantitative polymerase chain reaction (RT-qPCR) results, expression of nrps33 affected the transcription of tryptophan biosynthesis genes especially TRP1 which is also the selectable auxotrophic marker for the expression vector used in this work. The product of nrps33 could inhibit the activity of Trp4 involved in the conversion of anthranilate to N-(5'-phosphoribosyl)anthranilate and therefore caused the accumulation of anthranilic acid. This accumulation could in turn result in down-regulation of downstream tryptophan biosynthesis genes. Anthranilic acid is typically produced by chemical synthesis and has been used as a substrate for synthesising bioactive compounds including commercial drugs; our results could provide a new biological platform for production of this compound.

Determination of arsenic species in rice from Thailand and other Asian countries using simple extraction and HPLC-ICP-MS analysis.

Human exposure to arsenic (As) via rice consumption is of increasing concern. In the present study, the extraction and HPLC-ICP-MS analysis for As speciation in rice were investigated. A simple extraction with water and digestion with α-amylase followed by the analysis using ion-paring mode HPLC separation was developed. The method showed good extraction efficiencies (generally >80%) and column efficiencies (>90%) for rice samples. The optimization of mobile phase showed well separated peaks of As species. The limits of quantification (LOQ) of As(III), As(V), MMA, and DMA that were calculated based on sample mass were 1.6, 2.0, 2.0, and 1.6 µg kg(-1), respectively. A total of 185 rice samples (various types of rice) collected from different four regions in Thailand and some other Asian countries were analyzed. The total As and inorganic As in rice samples were in the ranges of 22.51-375.39 and 13.89-232.62 µg kg(-1), respectively. The estimated weekly intake of inorganic As from rice by Thai people accounted for 13.91-29.22% of the provisional tolerable weekly intake (PTWI).