A new isochromanequinone antibiotic, SCH 38519, with a novel sugar linkage

Discovery of C-Glycosylpyranonaphthoquinones in Streptomyces sp. MBT76 by a Combined NMR-Based Metabolomics and Bioinformatics Workflow

Mining of microbial genomes has revealed that actinomycetes harbor far more biosynthetic potential for bioactive natural products than anticipated. Activation of (cryptic) biosynthetic gene clusters and identification of the corresponding metabolites has become a focal point for drug discovery. Here, we applied NMR-based metabolomics combined with bioinformatics to identify novel C-glycosylpyranonaphthoquinones in Streptomyces sp. MBT76 and to elucidate the biosynthetic pathway. Following activation of the cryptic qin gene cluster for a type II polyketide synthase (PKS) by constitutive expression of its pathway-specific activator, bioinformatics coupled to NMR profiling facilitated the chromatographic isolation and structural elucidation of qinimycins A-C (1-3). The intriguing structural features of the qinimycins, including 8-C-glycosylation, 5,14-epoxidation, and 13-hydroxylation, distinguished these molecules from the model pyranonaphthoquinones actinorhodin, medermycin, and granaticin. Another novelty lies in the unusual fusion of a deoxyaminosugar to the pyranonaphthoquinone backbone during biosynthesis of the antibiotics BE-54238 A and B (4, 5). Qinimycins showed weak antimicrobial activity against Gram-positive bacteria. Our work shows the utility of combining bioinformatics, targeted activation of cryptic gene clusters, and NMR-based metabolic profiling as an effective pipeline for the discovery of microbial natural products with distinctive skeletons.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Synthesis and antibiotic activity of the tricyclic furo[3,2-c] isochromen-2-trione unit of the pyranonaphthoquinones

The elaboration and biological activity of 15, containing the proposed pharmacophore for the antibiotic activity of the pyranonaphthoquinones, are reported. The synthetic strategy involved acid-catalyzed lactonization of mandelate 17 for isochroman ring formation, in combination with a Wittig-oxa-Michael functionalization of isochroman-3-ol derivative 20, a lactonization involving configurational inversion of a benzylic alcohol and a final AgO oxidation. Compound 15 showed activity against Staphylococcus aureus and Bacillus subtilis with MIC of 64 and 32 microg/mL, respectively.

Novel screen methodologies for identification of new microbial metabolites with pharmacological activity

Micro-organisms continue to provide an important source of chemical diversity for the discovery of compounds with new biological activities. Microbial metabolites discovered recently using assays to detect compounds with potential pharmacological utility are surveyed and found to represent an extensive range of structural types produced by a wide variety of organisms. Assays used for screening samples produced by microbial processes must be robust, sensitive and specific and able to operate above a background of potential interferences from a number of sources. Discovery assays currently in use fall into three main categories cell-based, receptor-ligand interaction and enzyme inhibition assays. Trends in the use of these assays and new developments in assay technology applicable to the screening of microbial samples are examined with particular reference to the high throughput screening environment. For microbial screening to be a competitive route to new drug leads, the disciplines involved must be engineered into a seamlessly integrated process to deliver novel compounds with the required biological properties rapidly.