Thermorubin Biosynthesis Initiated by a Salicylate Synthase Suggests an Unusual Conversion of Phenols to Pyrones

Thermorubin is a tetracyclic naphthoisocoumarin natural product that demands investigation due to its novel mechanism of bacterial protein synthesis inhibition and its unusual structural features. In this work, we describe the identification of the biosynthetic cluster responsible for thermorubin from the sequenced Laceyella sacchari producer species and its confirmation via heterologous production in Escherichia coli. Based on an in-depth annotation of the cluster, we propose a biosynthetic pathway that accounts for the formation of the unique, nonterminal pyrone. Additionally, the expression and use of salicylate synthase TheO enabled testing of the stability properties of this extremophile-derived enzyme. TheO displayed rapid kinetics and a remarkably robust secondary structure, converting chorismate to salicylate with a K_M of 109 ± 12 μM, k_cat of 9.17 ± 0.36 min^-1, and catalytic efficiency (k_cat/K_M) of 84 ± 9 nM^-1 min^-1, and retained significant activity up to 50 °C. These studies serve as the basis for continued biosynthetic investigations and bioinspired synthetic approaches.

3-Amino-4-(diphenylamino)-1H-2-benzopyran-1-one

Various synthetic methodologies to obtain 3,4-diaminoisocumarin nucleus have been reported and described. However, mechanistic analysis based on experimental evidence is lacking. Herein, we report the synthesis of the novel 3-amino-4-(diphenylamino)-1H-2-benzopyran-1-one using a two-step methodology with a new mechanistic proposal to explain the formation of the latter based on previously reported precursors and the established conditions. This compound was afforded in 80% yield.

Furanone Derivatives from Terrestrial Streptomyces spp

Chemical investigation of the terrestrial Streptomyces sp. isolates GT2005/020 and ANK148 led to the isolation of two microbial furanone derivatives, 5-hydroxy-4-methylnaphtho[1,2-b]furan-3-one (1) and 4-hydroxy-5-methyl-furan-3-one (2), respectively, which have some similarity to quorum sensing molecules of the AI-2 type. In addition, the known compounds chalcomycin, ferulic acid, indole-3-acetic acid, uracil, thymine, 2′-deoxy-thymidin, monensin B (3), phencomycin, and 1-acetyl-β-carboline were isolated. The structures of 1 and 2 were deduced from extensive studies of NMR (1D and 2D) and mass spectra. Additionally, the complete NMR shift assignments for monensin B (3) using H-H COSY, HMQC and HMBC experiments are reported here for the first time. We are describing the taxonomy and fermentation of the producing strains, the structure elucidation of the new metabolites and their bioactivity.