Structure determination of two new sesquiterpenoids from Streptomyces sanglieri
Sesquiterpenoids are a group of abundant and structurally diverse secondary metabolites mainly derived from plant and fungi. By contrast, they are rarely isolated from bacteria, and the terpene synthase genes had been considered to be silent in prokaryotes. Recently, more and more terpenes were identified from bacteria, and the biosynthesis of some terpenes has been discussed in heterologous bacteria. Actually, it demonstrated that the terpene synthases are widely distributed in bacteria, including streptomycete, and some new sesquiterpenoids and diterpenoids had been obtained through heterologous expression of terpene synthase genes derived from Streptomyces microorganism. In our ongoing investigation of new bioactive natural products from streptomycete, two new sesquiterpenes, 15-hydroxy-(+)-epicubenol (1) and 7β-hydroxy-7-epi-α-eudesmol (2), were identified from a fermentation broth of Streptomyces sanglieri (YIM 121209-2), which was isolated from the forest soil sample collected from Wuyi Mountain, Fujian Province, China. The structures of compounds 1 and 2 (Fig. 1) were elucidated based on detailed spectroscopic data analyses, including 1D and 2D NMR techniques. The cytotoxicity against two human cancer cell lines and antimicrobial activity against a panel of bacteria and fungi of 1 and 2 were evaluated. None of them showed cytotoxic or antimicrobial activities at 100μg/ml.
Identification of (8S,9S,10S)-8,10-dimethyl-1-octalin, a key intermediate in the biosynthesis of geosmin in bacteria.
(-)-Geosmin (1, blue) is an important odor component produced by many bacteria, including actinomycetes, myxobacteria, and cyanobacteria, but has also been reported for eukaryotic organisms such as fungi, liverworts, insects, and plants. Recent research has shown that the biosynthesis of 1 starts with the cyclization of farnesyl pyrophosphate to (1(10)E,5E)-germacradien-11-ol (2, yellow), the first key intermediate en route. In a retro-Prins-reaction acetone is lost, and the second key intermediate, (8S,9S,10S)-8,10-dimethyl-1-octalin (3, red), is formed. After reprotonation, a 1,2-H-shift, and attack of water, geosmin is finally released. Octalin 3 occurs in the bouquets of volatiles released by myxobacteria as well as in enzyme extracts of incubation experiments of the purified geosmin synthase from Streptomyces coelicolor. Here the identification of 3, a new natural compound, the elucidation of its stereochemistry, and its synthesis are reported.
Net Spaces in Categorical Topology a
In the paper we introduce the notion of S‐nets, S a nonempty construct, as a generalization of the usual nets. S‐net spaces and continuous maps between them are then defined in a natural way. For S‐net spaces we introduce a number of axioms and study the categories obtained. We find some topological and Cartesian closed categories of S‐net spaces and describe their relations to certain known topological categories.