The hazimicins, a new class of antibiotics. Taxonomy, fermentation, isolation, characterization and biological properties

Actinobacterial chalkophores: the biosynthesis of hazimycins

Copper is a transition metal element with significant effects on the morphological development and secondary metabolism of actinobacteria. In some microorganisms, copper-binding natural products are employed to modulate copper homeostasis, although their significance in actinobacteria remains largely unknown. Here, we identified the biosynthetic genes of the diisocyanide natural product hazimycin in Kitasatospora purpeofusca HV058, through gene knock-out and heterologous expression. Biochemical analyses revealed that hazimycin A specifically binds to copper, which diminishes its antimicrobial activity. The presence of a set of putative importer/exporter genes surrounding the biosynthetic genes suggested that hazimycin is a chalkophore that modulates the intracellular copper level. A bioinformatic survey of homologous gene cassettes, as well as the identification of two previously unknown hazimycin-producing Streptomyces strains, indicated that the isocyanide-based mechanism of copper homeostasis is prevalent in actinobacteria.

Micromonospora: A Prolific Source of Bioactive Secondary Metabolites with Therapeutic Potential

Micromonospora, one of the most important actinomycetes genera, is well-known as the treasure trove of bioactive secondary metabolites (SMs). Herein, together with an in-depth genomic analysis of the reported Micromonospora strains, all SMs from this genus are comprehensively summarized, containing structural features, bioactive properties, and mode of actions as well as their biosynthetic and chemical synthesis pathways. The perspective enables a detailed view of Micromonospora-derived SMs, which will enrich the chemical diversity of natural products and inspire new drug discovery in the pharmaceutical industry.

Medicinal Chemistry of Isocyanides

In eons of evolution, isocyanides carved out a niche in the ecological systems probably thanks to their metal coordinating properties. In 1859 the first isocyanide was synthesized by humans and in 1950 the first natural isocyanide was discovered. Now, at the beginning of XXI century, hundreds of isocyanides have been isolated both in prokaryotes and eukaryotes and thousands have been synthesized in the laboratory. For some of them their ecological role is known, and their potent biological activity as antibacterial, antifungal, antimalarial, antifouling, and antitumoral compounds has been described. Notwithstanding, the isocyanides have not gained a good reputation among medicinal chemists who have erroneously considered them either too reactive or metabolically unstable, and this has restricted their main use to technical applications as ligands in coordination chemistry. The aim of this review is therefore to show the richness in biological activity of the isocyanide-containing molecules, to support the idea of using the isocyanide functional group as an unconventional pharmacophore especially useful as a metal coordinating warhead. The unhidden hope is to convince the skeptical medicinal chemists of the isocyanide potential in many areas of drug discovery and considering them in the design of future drugs.

Discovery of new hazimycin congeners from Kitasatospora sp. P07101

In an analytical study of microbial broths, the actinomycete strain Kitasatospora sp. P07101 was found to produce three new congeners, which were designated hazimycins B (1), C (2), and D (3), together with the previously reported hazimycin (renamed hazimycin A (4)). The structures of these hazimycins were examined using various spectroscopic methods including nuclear magnetic resonance (NMR), and the results revealed that 1-3 were analogues of hazimycin with the replacement of one of the two isonitrile groups in 4 by an NH-formyl group in 1, the two isonitrile groups and an amide group by two NH-formyl groups and a nitrile group in 2, and the two isonitrile groups and two amide groups by two NH-formyl groups and two nitrile groups in 3. Only hazimycin A exhibited moderate antimicrobial activities against Gram-positive bacteria and Candida albicans. These results indicated that the presence of two isonitrile groups in the hazimycin structure is essential for antimicrobial activity.

Discovery and characterization of aryl isonitriles as a new class of compounds versus methicillin- and vancomycin-resistant Staphylococcus aureus

Methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA and VRSA) have emerged as a global health concern. A new class of compounds featuring an aryl isonitrile moiety has been discovered that exhibits potent inhibitory activity against several clinically-relevant MRSA and VRSA isolates. Structure-activity relationship studies have been conducted to identify the aryl isonitrile group as the key functional group responsible for the observed antibacterial activity. The most potent antibacterial aryl isonitrile analogs (MIC 2 μM) did not show any toxicity against mammalian cells up to a concentration of 64 μM.