Fine Tuning of physico-chemical parameters to optimise a new series of novobiocin analogues

Synthesis and Melanogenesis Effect of 7,8-Dimethoxy-4-Methylcoumarin via MAPK Signaling-Mediated Microphthalmia-Associated Transcription Factor Upregulation

Tyrosinase ultimately controls the melanogenesis rate of the skin, and tanning and haircare products generally induce the activation of tyrosinase. Moreover, various enzymes, including tyrosinase, tyrosinase-related protein 1 (TRP1), and tyrosinase-related protein 2 (TRP2), mediate melanogenesis in which microphthalmia-associated transcription factor (MITF) is a master regulator. One coumarin family member 7,8-dihydroxy-4-methylcoumarin (DHMC) shows extensive biological activities with beneficial health effects; however, it also induces cytotoxicity and its melanogenic effect has not been reported yet. Therefore, we first synthesized DHMC derivatives via methylation to obtain 7,8-dimethoxy-4-methylcoumairn (DMMC), and investigated the pro- or anti-melanogenic effects of DHMC and DMMC in B16-F10 melanoma cells as well as the underlying mechanism. DHMC showed cytotoxicity at all tested concentrations, whereas DMMC did not reduce cell viability, even at the high concentration. DMMC also drives the significant increase in intracellular melanin and tyrosinase activity. Moreover, DMMC induced MITF expression by significantly increasing tyrosinase activity, which activates the gene expression of TRP1 and TRP2. Western blotting confirmed that DMMC induced the activation of mitogen-activated protein kinase (MAPK) signaling by the phosphorylation of C-Jun N-terminal kinase (JNK), resulting in the increased melanin production and the decreased phosphorylation of protein kinase B. Collectively, this study showed the pro-melanogenic effect of DMMC and its potential as a safe tanning and dyeing agent.

Coumarin-piperazine derivatives as biologically active compounds

A number of psychiatric disorders, including anxiety, schizophrenia, Parkinson's disease, depression and others CNS diseases are known to induce defects in the function of neural pathways sustained by the neurotransmitters, like dopamine and serotonin. N-arylpiperazine moiety is important for CNS-activity, particularly for serotonergic and dopaminergic activity. In the scientific literature there are many examples of coumarin-piperazine derivatives, particularly with arylpiperazines linked to a coumarin system via an alkyl liner, which can modulate serotonin, dopamine and adrenergic receptors. Numerous studies have revealed that the inclusion of a piperazine moiety could occasionally provide unexpected improvements in the bioactivity of various biologically active compounds. The piperazine analogs have been shown to have a potent antimicrobial activity and they can also act as BACE-1 inhibitors. On the other hand, arylpiperazines linked to coumarin derivatives have been shown to have antiproliferative activity against leukemia, lung, colon, breast, and prostate tumors. Recently, it has been reported that coumarin-piperazine derivatives exhibit a Fneuroprotective effect by their antioxidant and anti-inflammatory activities and they also show activity as acetylcholinesterase inhibitors and antifilarial activity. In this work we provide a summary of the latest advances in coumarin-related chemistry relevant for biological activity.

A New-Class Antibacterial-Almost. Lessons in Drug Discovery and Development: A Critical Analysis of More than 50 Years of Effort toward ATPase Inhibitors of DNA Gyrase and Topoisomerase IV

The introduction into clinical practice of an ATPase inhibitor of bacterial DNA gyrase and topoisomerase IV (topo IV) would represent a new-class agent for the treatment of resistant bacterial infections. Novobiocin, the only historical member of this class, established the clinical proof of concept for this novel mechanism during the late 1950s, but its use declined rapidly and it was eventually withdrawn from the market. Despite significant and prolonged effort across the biopharmaceutical industry to develop other agents of this class, novobiocin remains the only ATPase inhibitor of gyrase and topo IV ever to progress beyond Phase I. In this review, we analyze the historical attempts to discover and develop agents within this class and highlight factors that might have hindered those efforts. Within the last 15 years, however, our technical understanding of the molecular details of the inhibition of the gyrase and topo IV ATPases, the factors governing resistance development to such inhibitors, and our knowledge of the physical properties required for robust clinical drug candidates have all matured to the point wherein the industry may now address this mechanism of action with greater confidence. The antibacterial spectrum within this class has recently been extended to begin to include serious Gram negative pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. In spite of this recent technical progress, adverse economics associated with antibacterial R&D over the last 20 years has diminished industry's ability to commit the resources and perseverance needed to bring new-class agents to launch. Consequently, a number of recent efforts in the ATPase class have been derailed by organizational rather than scientific factors. Nevertheless, within this context we discuss the unique opportunity for the development of ATPase inhibitors of gyrase and topo IV as new-class antibacterial agents with broad spectrum potential.

Thermodynamic computational approach to capture molecular recognition in the binding of different inhibitors to the DNA gyrase B subunit from Escherichia coli

DNA gyrase subunit B, that catalyzes the hydrolysis of ATP, is an attractive target for the development of antibacterial drugs. This work is intended to rationalize molecular recognition at DNA gyrase B enzyme - inhibitor binding interface through the evaluation of different scoring functions in finding the correct pose and scoring properly 50 Escherichia coli DNA Gyrase B inhibitors belonging to five different classes. Improving the binding free energy calculation accuracy is further attempted by using rescoring schemes after short molecular dynamic simulations of the obtained docked complexes. These data are then compared with the corresponding experimental enzyme activity data. The results are analyzed from a structural point of view emphasizing the strengths and limitations of the techniques applied in the study.

Structure-based discovery of substituted 4,5'-bithiazoles as novel DNA gyrase inhibitors

Bacterial DNA gyrase is a well-established and validated target for the development of novel antibacterials. Starting from the available structural information about the binding of the natural product inhibitor, clorobiocin, we identified a novel series of 4'-methyl-N(2)-phenyl-[4,5'-bithiazole]-2,2'-diamine inhibitors of gyrase B with a low micromolar inhibitory activity by implementing a two-step structure-based design procedure. This novel class of DNA gyrase inhibitors was extensively investigated by various techniques (differential scanning fluorimetry, surface plasmon resonance, and microscale thermophoresis). The binding mode of the potent inhibitor 18 was revealed by X-ray crystallography, confirming our initial in silico binding model. Furthermore, the high resolution of the complex structure allowed for the placement of the Gly97-Ser108 flexible loop, thus revealing its role in binding of this class of compounds. The crystal structure of the complex protein G24 and inhibitor 18 provides valuable information for further optimization of this novel class of DNA gyrase B inhibitors.

Mannich reaction derivatives of novobiocin with modulated physiochemical properties and their antibacterial activities

Synthetic derivatives of the natural product antibiotic novobiocin were synthesized in order to improve their physiochemical properties. A Mannich reaction was used to introduce new side chains at a solvent-exposed position of the molecule, and a diverse panel of functional groups was evaluated at this position. Novobiocin and the new derivatives were tested for their binding to gyrase B and their antibacterial activities against Staphylococcus aureus, Mycobacterium tuberculosis, Francisella tularensis and Escherichia coli. While the new derivatives still bound the gyrase B protein potently (0.07-1.8 μM, IC(50)), they had significantly less antibacterial activity. Two compounds were identified with increased antibacterial activity against M. tuberculosis, with a minimum inhibitory concentration of 2.5 μg/ml.

Synthesis and antibacterial activity of quinolone-based compounds containing a coumarin moiety

A new series of quinolone-based compounds containing a coumarin moiety have been synthesized and studied for their antibacterial activity against a panel of gram-positive and gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). The results of the antibacterial evaluation of N-[2-(coumarin-3-yl)ethyl]piperazinyl quinolone derivatives in comparison with parent quinolones (norfloxacin, ciprofloxacin, and enoxacin) indicated that N-[2-(coumarin-3-yl)-2-oxoethyl]ciprofloxacin derivative (compound 8b) showed comparable or more potent antibacterial activity with respect to the reference drugs against the test strains. Generally, in both gram-positive and gram-negative bacteria, better results are obtained with cyclopropyl at the N-1 position of the quinolone ring and 2-oxo- on the ethyl spacer of coumarin and piperazine rings.

In vitro characterization of the antibacterial spectrum of novel bacterial type II topoisomerase inhibitors of the aminobenzimidazole class

Antibiotics with novel mechanisms of action are becoming increasingly important in the battle against bacterial resistance to all currently used classes of antibiotics. Bacterial DNA gyrase and topoisomerase IV (topoIV) are the familiar targets of fluoroquinolone and coumarin antibiotics. Here we present the characterization of two members of a new class of synthetic bacterial topoII ATPase inhibitors: VRT-125853 and VRT-752586. These aminobenzimidazole compounds were potent inhibitors of both DNA gyrase and topoIV and had excellent antibacterial activities against a wide spectrum of problematic pathogens responsible for both nosocomial and community-acquired infections, including staphylococci, streptococci, enterococci, and mycobacteria. Consistent with the novelty of their structures and mechanisms of action, antibacterial potency was unaffected by commonly encountered resistance phenotypes, including fluoroquinolone resistance. In time-kill assays, VRT-125853 and VRT-752586 were bactericidal against Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, and Haemophilus influenzae, causing 3-log reductions in viable cells within 24 h. Finally, similar to the fluoroquinolones, relatively low frequencies of spontaneous resistance to VRT-125853 and VRT-752586 were found, a property consistent with their in vitro dual-targeting activities.

Structure-based design of 7-carbamate analogs of geldanamycin

The 7-carbamate groups of geldanamycin and its 17-(2-dimethylaminoethyl)amino-17-demethoxy derivative (17-DMAG) bind the N-terminal domain of Hsp90 by establishing a network of hydrogen bonds which involve four buried water molecules. In this study, a structure-based approach was used to investigate the effects of displacing some of these waters by modification of the 7-carbamate. A general loss of binding to human Hsp90 was observed, except for replacement of the carbamate with a hydroxamate group which gave an analog with weak activity. Modeling of Hsp90-ligand interactions suggested that the hydroxamate was not able to displace the buried water molecules, while bulkier substituents able to do so proved inactive.

Metabolic Engineering of Aminocoumarins: Inactivation of the Methyltransferase Gene cloP and Generation of New Clorobiocin Derivatives in a Heterologous Host

Aminocoumarin antibiotics are highly potent inhibitors of bacterial gyrase and represent a class of antibiotics that are very suitable for the generation of new compounds by metabolic engineering. In this study, the putative methyltransferase gene cloP in the biosynthetic gene cluster of clorobiocin was inactivated. Expression of the modified gene cluster in the heterologous host Streptomyces coelicolor M512 gave three new aminocoumarin antibiotics. The structures of the new compounds were elucidated by MS and 1H NMR, and their antibacterial activities were determined. All three compounds lacked clorobiocin's methyl group at 4-OH of the deoxysugar moiety, noviose. They differed from each other in the position of the 5-methylpyrrole-2-carbonyl group, which was found to be attached to either 2-OH, 3-OH or 4-OH of noviose. Attachment at 4-OH resulted in the highest antibacterial activity. This is the first time that an aminocoumarin antibiotic acylated at 4-OH in noviose has been detected.

Cationic Chalcone Antibiotics. Design, Synthesis, and Mechanism of Action

This paper describes how the introduction of "cationic" aliphatic amino groups in the chalcone scaffold results in potent antibacterial compounds. It is shown that the most favorable position for the aliphatic amino group is the 2-position of the B-ring, in particular in combination with a lipophilic substituent in the 5-position of the B-ring. We demonstrate that the compounds act by unselective disruption of cell membranes. Introduction of an additional aliphatic amino group in the A-ring results in compounds that are selective for bacterial membranes combined with a high antibacterial activity against both Gram-positive and -negative pathogens. The most potent compound in this study (78) has an MIC value of 2 muM against methicillin resistant Staphylococus aureus.

D-Gulonolactone as a synthon for L-noviose: first preparation of 4-O-demethyl-L-noviofuranose and related derivatives

[reaction: see text] A new synthesis of L-noviose (11), a sugar moiety of novobiocin, is presented. D-Gulonolactone was initially converted in a few steps to the key ester derivative 7 [1-O-benzyl methyl 2,3-O-(1-methylethylidene)-alpha-L-lyxofuranosiduronate]. An appropriate selection of protecting groups enabled transformation of 7 under mild reaction conditions to 4-O-demethyl-L-noviofuranose 9a and related 9b-c. Derivatives 9 were further converted either to L-lyxopyranoses (10a and 10b) or to methyl L-lyxofuranoside 12.

Signal transduction mediated by the Ras/Raf/MEK/ERK pathway from cytokine receptors to transcription factors: potential targeting for therapeutic intervention

The Ras/Raf/Mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) cascade couples signals from cell surface receptors to transcription factors, which regulate gene expression. Depending upon the stimulus and cell type, this pathway can transmit signals, which result in the prevention or induction of apoptosis or cell cycle progression. Thus, it is an appropriate pathway to target for therapeutic intervention. This pathway becomes more complex daily, as there are multiple members of the kinase and transcription factor families, which can be activated or inactivated by protein phosphorylation. The diversity of signals transduced by this pathway is increased, as different family members heterodimerize to transmit different signals. Furthermore, additional signal transduction pathways interact with the Raf/MEK/ERK pathway to regulate positively or negatively its activity, or to alter the phosphorylation status of downstream targets. Abnormal activation of this pathway occurs in leukemia because of mutations at Ras as well as genes in other pathways (eg PI3K, PTEN, Akt), which serve to regulate its activity. Dysregulation of this pathway can result in autocrine transformation of hematopoietic cells since cytokine genes such as interleukin-3 and granulocyte/macrophage colony-stimulating factor contain the transacting binding sites for the transcription factors regulated by this pathway. Inhibitors of Ras, Raf, MEK and some downstream targets have been developed and many are currently in clinical trials. This review will summarize our current understanding of the Ras/Raf/MEK/ERK signal transduction pathway and the downstream transcription factors. The prospects of targeting this pathway for therapeutic intervention in leukemia and other cancers will be evaluated.