Structures of jietacines: unique alpha,beta-unsaturated azoxy antibiotics

Natural products as anthelmintics: safeguarding animal health

Covering literature to December 2022This review provides a comprehensive account of all natural products (500 compounds, including 17 semi-synthetic derivatives) described in the primary literature up to December 2022, reported to be capable of inhibiting the egg hatching, motility, larval development and/or the survival of helminths (i.e., nematodes, flukes and tapeworms). These parasitic worms infect and compromise the health and welfare, productivity and lives of commercial livestock (i.e., sheep, cattle, horses, pigs, poultry and fish), companion animals (i.e., dogs and cats) and other high value, endangered and/or exotic animals. Attention is given to chemical structures, as well as source organisms and anthelmintic properties, including the nature of bioassay target species, in vivo animal hosts, and measures of potency.

Jietacin Derivative Inhibits TNF-α-Mediated Inflammatory Cytokines Production via Suppression of the NF-κB Pathway in Synovial Cells

Synovial inflammation plays a central role in joint destruction and pain in osteoarthritis (OA). The NF-κB pathway plays an important role in the inflammatory process and is activated in OA. A previous study reported that a jietacin derivative (JD), (Z)-2-(8-oxodec-9-yn-1-yl)-1-vinyldiazene 1-oxide, suppressed the nuclear translocation of NF-κB in a range of cancer cell lines. However, the effect of JD in synovial cells and the exact mechanism of JD as an NF-κB inhibitor remain to be determined. We investigated the effect of JD on TNF-α-induced inflammatory reaction in a synovial cell line, SW982 and human primary synovial fibroblasts (hPSFs). Additionally, we examined phosphorylated levels of p65 and p38 and expression of importin α3 and β1 using Western blotting. RNA-Seq analysis revealed that JD suppressed TNF-α-induced differential expression: among 204 genes significantly differentially expressed between vehicle and TNF-α-stimulated SW982 (183 upregulated and 21 downregulated) (FC ≥ 2, Q < 0.05), expression of 130 upregulated genes, including inflammatory cytokines (IL1A, IL1B, IL6, IL8) and chemokines (CCL2, CCL3, CCL5, CCL20, CXCL9, 10, 11), was decreased by JD treatment and that of 14 downregulated genes was increased. KEGG pathway analysis showed that DEGs were increased in the cytokine−cytokine receptor interaction, TNF signaling pathway, NF-κB signaling pathway, and rheumatoid arthritis. JD inhibited IL1B, IL6 and IL8 mRNA expression and IL-6 and IL-8 protein production in both SW982 and hPSFs. JD also suppressed p65 phosphorylation in both SW982 and hPSFs. In contrast, JD did not alter p38 phosphorylation. JD may inhibit TNF-α-mediated inflammatory cytokine production via suppression of p65 phosphorylation in both SW982 and hPSFs. Our results suggest that JD may have therapeutic potential for OA due to its anti-inflammatory action through selective suppression of the NF-κB pathway on synovial cells.

Exploration of inhibitory action of Azo imidazole derivatives against COVID-19 main protease (Mpro): A computational study

Four novel ionic liquid tagged azo-azomethine derivatives (L1-L4) have been prepared by the condensation reaction of azo-coupled ortho-vaniline precursor with amino functionalised imidazole derivative and the synthesized derivatives (L1-L4) have been characterized by different analytical and spectroscopic techniques. Molecular docking studies were carried out to ascertain the inhibitory action of studied ligands (L1-L4) against the Main Protease (6LU7) of novel coronavisrus (COVID-19). The result of the docking of L1-L4 showed a significant inhibitory action against the Main protease (Mpro) of SARS-CoV-2 and the binding energy (ΔG) values of the ligands (L1-L4) against the protein 6LU7 have found to be -7.7 Kcal/mole (L1), -7.0 Kcal/mole (L2), -7.9 Kcal/mole (L3), and -7.9 Kcal/mole (L4).The efficiency of the ligands has been compared with the FDA approved and clinically trial drugs such as remdesivir, Chloroquin and Hydroxychloroquin and native ligand N3 of main protease 6LU7 to ascertain the inhibitory potential of the studied ligands (L1-L4) against the protein 6LU7. Pharmacokinetic properties (ADME) of the ligands (L1-L4) have also been studied.

Chemistry and Biology of Natural Azoxy Compounds

Azoxy compounds belong to a small yet intriguing group of natural products sharing a common functional group with the general structure RN═N⁺(O^-)R. Their intriguing chemical structures, diverse biological activities, and important industrial applications have received attention from researchers in natural product chemistry, total synthesis, and biosynthesis. This review presents current updates about the structural diversity of natural azoxy compounds isolated from different organisms and highlights the enzymes and biological logic involved in their construction. We assume that the identification of key enzymes will provide efficient tools in biocatalysis to generate new azoxy compounds, while genome mining may result in novel natural azoxy compounds of medical and industrial interest.

Jietacins, azoxy natural products, as novel NF-κB inhibitors: Discovery, synthesis, biological activity, and mode of action

Deregulation of NF-κB plays an important role in various diseases by controlling cell growth, inflammation, the immune response, and cytokine production. Although many NF-κB inhibitors have been developed, to the best of our knowledge, none of them have been successfully translated into clinical practice as medicines. To overcome this issue, we aimed to develop a new class of NF-κB inhibitors. Previous reports indicated that the N-terminal cysteine is a promising target for NF-κB. Based on this, we first selected 10 natural products or their derivatives from the natural product library that we developed and examined the effect on NF-κB and the viability of cancer cells with constitutively strong NF-κB activity. Among them, we found that an azoxy natural product, jietacin A, with a vinylazoxy group and an aliphatic side chain, reduced cell viability and inhibited nuclear translocation of free NF-κB. In addition, we performed design, synthesis, and biological evaluation of jietacin derivatives for development of a novel NF-κB inhibitor. Of these derivatives, a fully synthesized derivative 25 with vinylazoxy and ynone groups had a potent effect. We clarified the structure-activity relationship of this compound. Jietacin A and 25 also inhibited tumor necrosis factor-α-mediated induction of NF-κB. The NF-κB inhibitory effect depended on the N-terminal cysteine and the neighboring Arg-Ser-Ala-Gly-Ser-Ile (RSAGSI) domain of NF-κB. We also found that 25 inhibited the association between NF-κB and importin α, suggesting inhibition of NF-κB at an early step of nuclear translocation. Overall, this study indicated that the vinylazoxy motif may compose a new class of NF-κB inhibitors, providing further insight for rational drug design and rendering a unique mode of action.

Jietacins, azoxy antibiotics with potent nematocidal activity: Design, synthesis, and biological evaluation against parasitic nematodes

Jietacins, an azoxy antibiotic class of chemicals, were isolated from the culture broth of Streptomyces sp. KP-197. They have a unique structural motif, including a vinyl azoxy group and a long acyclic aliphatic chain, which is usually branched but non-branched in the case of jietacin C. During a drug discovery program, we found that jietacins display potent anthelmintic activity against parasitic nematodes and that jietacin A has a moderate or low acute toxicity (LD₅₀ > 300 mg/kg) and no mutagenic potential in a mini Ames screen. This suggests that jietacins have potential for drug discovery research. In order to create a novel anthelmintic agent, we performed design, synthesis, and biological evaluation of jietacin derivatives against parasitic nematodes. Of these derivatives, we found that a fully synthesized simplified derivative exhibited better anthelmintic activity against three parasitic nematodes than natural jietacins. In addition, it had a better efficacy in vivo through oral administration against a mouse nematode. This indicated that the azoxy motif could prove useful as a template for anthelmintic discovery, possibly creating a class of anthelmintic with novel skeletons, a potential new mode of action, and providing further insight for rational drug design.

Pharmacological and Predicted Activities of Natural Azo Compounds

This paper describes research on natural azo compounds isolated from fungi, plant, bacteria, and invertebrates. More than 120 biologically active diazene containing alkaloids demonstrate confirmed pharmacological activity, including antitumor, antimicrobial, and antibacterial effects. The structures, origin, and biological activities of azo compounds are reviewed. Utilizing the computer program PASS, some structure-activity relationship new activities are also predicted, pointing toward possible new applications of these compounds. This article emphasizes the role of natural azo compounds as an important source of drug prototypes and leads for drug discovery.

Investigations of valanimycin biosynthesis: elucidation of the role of seryl-tRNA

The antibiotic valanimycin is a naturally occurring azoxy compound produced by Streptomyces viridifaciens MG456-hF10. Precursor incorporation experiments showed that valanimycin is derived from l-valine and l-serine via the intermediacy of isobutylamine and isobutylhydroxylamine. Enzymatic and genetic investigations led to the cloning and sequencing of the valanimycin biosynthetic gene cluster, which was found to contain 14 genes. A novel feature of the valanimycin biosynthetic gene cluster is the presence of a gene (vlmL) that encodes a class II seryl-tRNA synthetase. Previous studies suggested that the role of this enzyme is to provide seryl-tRNA for the valanimycin biosynthetic pathway. Here, we report the results of investigations to elucidate the role of seryl-tRNA in valanimycin biosynthesis. A combination of enzymatic and chemical studies has revealed that the VlmA protein encoded by the valanimycin biosynthetic gene cluster catalyzes the transfer of the seryl residue from seryl-tRNA to the hydroxyl group of isobutylhydroxylamine to produce the ester O-seryl-isobutylhydroxylamine. These findings provide an example of the involvement of an aminoacyl-tRNA in an antibiotic biosynthetic pathway.

Biochemical characterization of VlmL, a Seryl-tRNA synthetase encoded by the valanimycin biosynthetic gene cluster

Previous studies have shown that the valanimycin producer Streptomyces viridifaciens contains two genes encoding proteins that are similar to seryl-tRNA synthetases (SerRSs). One of these proteins (SvsR) is presumed to function in protein biosynthesis, because it exhibits a high degree of similarity to the single SerRS of Streptomyces coelicolor. The second protein (VlmL), which exhibits a low similarity to the S. coelicolor SerRS, is hypothesized to play a role in valanimycin biosynthesis, because the vlmL gene resides within the valanimycin biosynthetic gene cluster. To investigate the role of VlmL in valanimycin biosynthesis, VlmL and SvsR have been overproduced in soluble form in Escherichia coli, and the biochemical properties of both proteins have been analyzed and compared. Both proteins were found to catalyze a serine-dependent exchange of 32P-labeled pyrophosphate into ATP and to aminoacylate total E. coli tRNA with L-serine. Kinetic parameters for the two enzymes show that SvsR is catalytically more efficient than VlmL. The results of these experiments suggest that the role of VlmL in valanimycin biosynthesis is to produce seryl-tRNA, which is then utilized for a subsequent step in the biosynthetic pathway. Orthologs of VlmL were identified in two other actinomycetes species that also contain orthologs of the S. coelicolor SerRS. The significance of these findings is herein discussed.

Valanimycin biosynthesis: investigations of the mechanism of isobutylhydroxylamine incorporation

[reaction: see text] The incorporation of [(15)N, (18)O]-isobutylhydroxylamine into the antibiotic valanimycin by Streptomyces viridifaciens has been shown to proceed with loss of the (18)O label, thereby demonstrating that the azoxy oxygen atom of valanimycin is not derived from the oxygen atom of isobutylhydroxylamine.

Molecular characterization and analysis of the biosynthetic gene cluster for the azoxy antibiotic valanimycin

Streptomyces viridifaciens MG456-hF10 produces the antibiotic valanimycin, a naturally occurring azoxy compound. Valanimycin is known to be derived from valine and serine with the intermediacy of isobutylamine and isobutylhydroxylamine, but little is known about the stages in the pathway leading to the formation of the azoxy group. In previous studies, a cosmid containing S. viridifaciens DNA was isolated that conferred valanimycin production upon Strepto-myces lividans TK24. Subcloning of DNA from the valanimycin-producing cosmid has led to the identi-fication of a 22 kb segment of DNA sufficient to allow valanimycin production in S. lividans TK24. Sequencing of this DNA segment and the surrounding DNA revealed the presence of 20 genes. Gene disruption experiments defined the boundaries of the valanimycin gene cluster, which appears to contain 14 genes. The cluster includes an amino acid decar-boxylase gene (vlmD), a valanimycin resistance gene (vlmF ), at least two regulatory genes (vlmE, vlmI ), two genes encoding a flavin monooxygenase (vlmH, vlmR), a seryl tRNA synthetase gene (vlmL ) and seven genes of unknown function. Overproduction and characterization of VlmD demonstrated that it catalyses the decarboxylation of l-valine. An unusual feature of the valanimycin gene cluster is that four genes involved in branched amino acid biosynthesis are located near its 5' end.

Determination of the stereochemistry of hydride transfer from NADPH to FAD catalyzed by VlmR, a flavin reductase from the valanimycin biosynthetic pathway

[structure: see text]. The stereospecificity of hydride transfer from NADPH to FAD catalyzed by VlmR, a flavin reductase from the valanimycin biosynthetic pathway has been determined. By using stereospecifically deuterated NADPH, it has been shown that the 4-pro R hydrogen of NADPH is transferred.

A novel valanimycin-resistance determinant (vlmF) from Streptomyces viridifaciens MG456-hF10

A novel valanimycin-resistance determinant (vImF) was isolated from a cosmid containing Streptomyces viridifaciens DNA that leads to valanimycin production in Streptomyces lividans. Expression of the vImF gene in both Escherichia coli and S. lividans provided valanimycin resistance. The nucleotide sequence of vImF consists of 1206 bp and the deduced amino acid sequence encodes a polypeptide with 12 putative transmembrane-spanning segments and a calculated pI of 10.1. VImF shows significant similarities to other known or putative transmembrane efflux proteins that confer antibiotic resistance, but it appears to be specific for valanimycin. The sequence similarities suggest that VImF is a member of the DHA12 family within the major facilitator superfamily of transport proteins and that it is probably involved in active valanimycin efflux energized by a proton-dependent electrochemical gradient.

An NADPH:FAD oxidoreductase from the valanimycin producer, Streptomyces viridifaciens. Cloning, analysis, and overexpression

The valanimycin producer Streptomyces viridifaciens contains a two-component enzyme system that catalyzes the oxidation of isobutylamine to isobutylhydroxylamine. One component of this enzyme system is isobutylamine hydroxylase, and the other component is a flavin reductase. The gene (vlmR) encoding the flavin reductase required by isobutylamine hydroxylase has been cloned from S. viridifaciens by chromosome walking. The gene codes for a protein of 194 amino acids with a calculated mass of 21,265 Da and a calculated pI of 10.2. Overexpression of the vlmR gene in Escherichia coli as an N-terminal His-tag derivative yielded a soluble protein that was purified to homogeneity. Removal of the N-terminal His-tag from the overexpressed protein by thrombin cleavage also produced a soluble protein. Both forms of the protein exhibited a high degree of flavin reductase activity, and the thrombin-cleaved form functioned in combination with isobutylamine hydroxylase to catalyze the conversion of isobutylamine to isobutylhydroxylamine. Kinetic data indicate that the overexpressed protein utilizes FAD and NADPH in preference to FMN, riboflavin, and NADH. The deduced amino acid sequence of the VlmR protein exhibited similarity to several other flavin reductases that may constitute a new family of flavin reductases.

Purification and characterization of isobutylamine N-hydroxylase from the valanimycin producer Streptomyces viridifaciens MG456-hF10

Streptomyces viridifaciens MG456-hF10 produces the antitumor agent valanimycin, which is a member of a family of antibiotics containing the azoxy group. An enzyme involved in the biosynthesis of valanimycin has been purified 360-fold from S. viridifaciens. This enzyme, isobutylamine N-hydroxylase, catalyzes the oxidation of isobutylamine to isobutylhydroxylamine in the presence of oxygen and a reduced flavin cofactor. Unlike other known N-hydroxylases, isobutylamine N-hydroxylase cannot carry out the reduction of the flavin cofactor. Rather, the reduced flavin is supplied by a separate flavin reductase that is present in extracts of S. viridifaciens. The reduced flavin cofactor could also be supplied by the flavin mononucleotide reductase of Vibrio fischeri. The requirement for molecular oxygen and a reduced flavin indicates that the N-hydroxylase is a flavin monooxygenase and that the mechanism for the hydroxylation is likely to proceed via the formation of a flavin 4a-hydroperoxide. Isobutylamine N-hydroxylase exhibited a subunit molecular mass of 40 kDa and existed in dimeric or trimeric form depending upon buffer conditions. The pI of the protein was found to be ca. 5.1 and the enzyme exhibited a sensitivity to thiol-directed reagents.

Cloning, analysis, and overexpression of the gene encoding isobutylamine N-hydroxylase from the valanimycin producer, Streptomyces viridifaciens

The flavoprotein isobutylamine N-hydroxylase (IBAH) catalyzes the oxidation of isobutylamine to isobutylhydroxylamine, a key step in the biosynthesis of the azoxy antibiotic valanimycin. By using oligonucleotide primers designed from peptide sequence information derived from native IBAH, a fragment of the gene (vlmH) encoding IBAH was amplified by PCR from a genomic library of the valanimycin-producing organism, Streptomyces viridifaciens MG456-hF10. The gene fragment was then employed as a probe to clone the entire vlmH gene from an S. viridifaciens genomic library. Overexpression of the vlmH gene in Escherichia coli gave a soluble protein that was purified to homogeneity. The purified protein exhibited the catalytic activity expected for IBAH. The deduced amino acid sequence of IBAH exhibited the greatest similarity to the Sox/DszC protein from Rhodococcus sp. strain IGT38, a flavoprotein involved in the oxidation of dibenzothiophene to the corresponding sulfone. Significant similarities were also found between the amino acid sequence of IBAH and those of the acyl coenzyme A dehydrogenases.

Trends in the search for bioactive microbial metabolites

Bioactive microbial metabolites are attracting increasing attention as useful agents for medicine, veterinary medicine, agriculture, and as unique biochemical tools. A review of the current trends in the discovery of new metabolites shows that the number of active compounds with non-antibiotic type of activity has increased, resulting in an expansion of the variety of bioactivity of microbial metabolites. Factors that contribute to the increased rate of discovery include: development of new methods for activity measurement, exploitation of novel groups of microorganisms as sources of active compounds, new directions for chemical modification, and incorporation of newer knowledge of biotechnology into screening systems. To exemplify this, typical screening methods, and chemical and biological properties of several bioactive compounds obtained by these methods are discussed.