Chemische und chemoenzymatische Synthesezugänge zu neuen Ansamitocinderivaten

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Construction of a new class of tetracycline lead structures with potent antibacterial activity through biosynthetic engineering

Antimicrobial resistance and the shortage of novel antibiotics have led to an urgent need for new antibacterial drug leads. Several existing natural product scaffolds (including chelocardins) have not been developed because their suboptimal pharmacological properties could not be addressed at the time. It is demonstrated here that reviving such compounds through the application of biosynthetic engineering can deliver novel drug candidates. Through a rational approach, the carboxamido moiety of tetracyclines (an important structural feature for their bioactivity) was introduced into the chelocardins, which are atypical tetracyclines with an unknown mode of action. A broad-spectrum antibiotic lead was generated with significantly improved activity, including against all Gram-negative pathogens of the ESKAPE panel. Since the lead structure is also amenable to further chemical modification, it is a platform for further development through medicinal chemistry and genetic engineering

A semipinacol rearrangement directed by an enzymatic system featuring dual-function FAD-dependent monooxygenase

Nature has invented ingenious ways to biosynthesize biologically active small molecules that have been applied ever since to benefit human life in various ways. During the underlying biosynthetic processes, highly elaborate chemical reactions are often catalyzed by enzymatic systems, thereby enabling transformations under physiological conditions that would require harsh conditions or are hardly possible without enzymatic catalysis. Consequently, understanding novel biochemical transformations is of importance to eventually apply the knowledge gained to generate molecules of interest

Preparation of new alkyne-modified ansamitocins by mutasynthesis

The preparation of alkyne-modified ansamitocins by mutasynthetic supplementation of Actinosynnema pretiosum mutants with alkyne-substituted aminobenzoic acids is described. This modification paved the way to introduce a thiol linker by Huisgen-type cycloaddition which can principally be utilized to create tumor targeting conjugates. In bioactivity tests, only those new ansamitocin derivatives showed strong antiproliferative activity that bear an ester side chain at C-3

Preparation of new alkyne-modified ansamitocins by mutasynthesis Full Research Paper Open Access

Abstract The preparation of alkyne-modified ansamitocins by mutasynthetic supplementation of Actinosynnema pretiosum mutants with alkyne-substituted aminobenzoic acids is described. This modification paved the way to introduce a thiol linker by Huisgen-type cycloaddition which can principally be utilized to create tumor targeting conjugates. In bioactivity tests, only those new ansamitocin derivatives showed strong antiproliferative activity that bear an ester side chain at C-3. 53

Siderophore conjugation with cleavable linkers boosts the potency of RNA polymerase inhibitors against multidrug-resistant E. coli

The growing antibiotic resistance, foremost in Gram-negative bacteria, requires novel therapeutic approaches. We aimed to enhance the potency of well-established antibiotics targeting the RNA polymerase (RNAP) by utilizing the microbial iron transport machinery to improve drug translocation across their cell membrane. As covalent modifications resulted in moderate-low antibiotic activity, cleavable linkers were designed that permit a release of the antibiotic payload inside the bacteria and unperturbed target binding. A panel of ten cleavable siderophore-ciprofloxacin conjugates with systematic variation at the chelator and the linker moiety was used to identify the quinone trimethyl lock in conjugates 8 and 12 as the superior linker system, displaying minimal inhibitory concentrations (MICs) of ≤1 μM. Then, rifamycins, sorangicin A and corallopyronin A, representatives of three structurally and mechanistically different natural product RNAP inhibitor classes, were conjugated via the quinone linker to hexadentate hydroxamate and catecholate siderophores in 15-19 synthetic steps. MIC assays revealed an up to 32-fold increase in antibiotic activity against multidrug-resistant E. coli for conjugates such as 24 or 29 compared to free rifamycin. Experiments with knockout mutants in the transport system showed that translocation and antibiotic effects were conferred by several outer membrane receptors, whose coupling to the TonB protein was essential for activity. A functional release mechanism was demonstrated analytically by enzyme assays in vitro, and a combination of subcellular fractionation and quantitative mass spectrometry proved cellular uptake of the conjugate, release of the antibiotic, and its increased accumulation in the cytosol of bacteria. The study demonstrates how the potency of existing antibiotics against resistant Gram-negative pathogens can be boosted by adding functions for active transport and intracellular release

Cystobactamids : myxobacterial topoisomerase inhibitors exhibiting potent antibacterial activity

The development of new antibiotics faces a severe crisis inter alia owing to a lack of innovative chemical scaffolds with activities against Gram-negative and multiresistant pathogens. Herein, we report highly potent novel antibacterial compounds, the myxobacteria-derived cystobactamids 1–3, which were isolated from Cystobacter sp. and show minimum inhibitory concentrations in the low μmL⁻¹ range. We describe the isolation and structure elucidation of three congeners as well as the identification and annotation of their biosynthetic gene cluster. By studying the self-resistance mechanism in the natural producer organism, the molecular targets were identified as bacterial type IIa topoisomerases. As quinolones are largely exhausted as a template for new type II topoisomerase inhibitors, the cystobactamids offer exciting alternatives to generate novel antibiotics using medicinal chemistry and biosynthetic engineering

Selective Bacterial Targeting and Infection-Triggered Release of Antibiotic Colistin Conjugates.

In order to render potent, but toxic antibiotics more selective, we have explored a novel conjugation strategy that includes drug accumulation followed by infection-triggered release of the drug. Bacterial targeting was achieved using a modified fragment of the human antimicrobial peptide ubiquicidin, as demonstrated by fluorophore-tagged variants. To limit the release of the effector colistin only to infection-related situations, we introduced a linker that was cleaved by neutrophil elastase (NE), an enzyme secreted by neutrophil granulocytes at infection sites. The linker carried an optimized sequence of amino acids that was required to assure sufficient cleavage efficiency. The antibacterial activity of five regioisomeric conjugates prepared by total synthesis was masked, but was released upon exposure to recombinant NE when the linker was attached to amino acids at the 1- or the 3-position of colistin. A proof-of-concept was achieved in co-cultures of primary human neutrophils and Escherichia coli that induced the secretion of NE, the release of free colistin, and an antibacterial efficacy that was equal to that of free colistin

Thiamyxins: Structure and Biosynthesis of Myxobacterial RNA-Virus-Inhibitors

During our search for novel myxobacterial natural products, we discovered the Thiamyxins: thiazole- and thiazoline-rich non-ribosomal peptide-polyketide hybrids with potent antiviral activity. We isolated two cyclized and two open-chain congeners of this unprecedented natural product family, whereof the non-cyclized Thiamyxin D was found to be fused to a glycerol unit attached to the C-terminal carboxyl function. Alongside their structure elucidation and absolute stereochemistry, we present the biosynthetic origin of the Thiamyxins supported by a concise biosynthesis model based on biosynthetic gene cluster analysis and feeding experiments with isotope labelled precursors. We report an unprecedented incorporation of a 2-(hydroxymethyl)-4-methylpent-3-enoic acid moiety originating from the involved polyketide synthase featuring a rare GCN5-related N-acetyltransferase-like decarboxylase domain. The Thiamyxins showed potent inhibition of different RNA-viruses as analysed in cell culture models of corona, zika and dengue virus infection. Their potency up to a half maximal inhibitory concentration of 560 nM combined with milder cytotoxic effects on human cell lines indicate a potential for further development of the Thiamyxins as broad-spectrum antivirals targeting RNA-viruses