4-Hydroxy pyridones are a class of fungi-derived polyketide–nonribosomal
peptide products featuring a core of 4-hydroxy-2-pyridone which have
a wide range of biological activities. Genome mining of in-house strains
using polyketide synthase–nonribosomal peptide synthase as
a query identified an endophyte Tolypocladium sp.
49Y, which possesses a potential 4-hydroxy pyridone biosynthetic gene
cluster. Heterologous expression in Aspergillus oryzae NSAR1 revealed that this gene cluster is functional and able to
produce a rare type of 4-hydroxy pyridones called tolypyridones (compounds 3 and 4). Tolypocladium sp.
49Y was grown in a variety of media which led to the isolation of
six 4-hydroxy pyridones (5–10) and
one pyrrolidone (11) from a rice culture, and compounds 3 and 9 showed antifungal activity. These latter
compounds are different from those obtained by heterologous expression.
This study shows that both heterologous expression and cultivation
of the native host are complementary approaches to discover new natural
products.
Twenty new malabaricane triterpenoids, astramalabaricosides A−T (1−20), were isolated from the roots of Astragalus membranaceus var. mongholicus (Astragali Radix). Their structures were determined by spectroscopic analysis, and the use of the circular dichroism exciton chirality method, quantum chemical calculations, and chemical methods. Malabaricane triterpenoids, an unusual group with the 6-6-5-tricyclic core, are distributed in plants (e.g., Simaroubaceae, Polypodiaceae, and Fabaceae), a marine sponge, and fungi, and their number obtained to date is limited. Compounds 1−20 were characterized as glycosides with a highly oxygenated side chain, and 13−20 were the first cyclic carbonate derivatives among the malabaricane triterpenoids. The stereocluster formed from the continuous hydroxylated chiral carbons in each highly oxygenated side chain and the 6-6-5-tricyclic core system were entirely segregated, and the independent identification of their stereoconfigurations required considerable effort. The migratory inhibitory and antiproliferative activities of 1−20 were evaluated by wound-healing and cell-viability assays, respectively. Most compounds showed significant migratory inhibitory activity, and a preliminary structure−activity relationship was developed. Malabaricane triterpenoids are being reported in the genus Astragalus for the first time.
Fixed exposure will lead to underexposure or overexposure of collected flame radiation images using CCD, which has a great influence on the temperature measuring accuracy. A temperature measurement method was proposed by image fusion with multi-exposure, which can eliminate the influence of insufficient underexposure and overexposure. The approach was first to acquire a group of flame radiation images during different exposures. Then a partial region with good exposure effect in each radiation image was obtained by segmentation, with which the complete flame image can be spliced together. An experimental system was built to calibrate the temperature measurement parameters by two-color pyrometry through a blackbody furnace. The relation between exposure time and monochromatic gray level, as well as the relation between the temperature and temperature measurement coefficient were obtained. A candle flame was selected as the measuring object and the complete and accurate flame temperature distribution was acquired following our proposed method. The experimental results show that, compared with the temperature measurement using a single exposure time, our method can effectively avoid the measurement error caused by underexposure and overexposure, and improve the measurement accuracy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.