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Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity.

ABSTRACT: The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels-Alder trapping of the BCB by either pendant or external electron-deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three-component process joining the benzyne first with an electron-rich and then with an electron-poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4??diene component in Diels-Alder reactions are reported. The results also shed new light on aspects of the hexadehydro-Diels-Alder reaction used to generate the benzynes.

SUBMITTER: Xiao X

PROVIDER: S-EPMC6296485 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity.

Xiao Xiao X Woods Brian P BP Xiu Wen W Hoye Thomas R TR

Angewandte Chemie (International ed. in English) 20180704 31

The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels-Alder trapping of the BCB by either pendant or external electron-deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three-component process joining the benzyne first with an electron-rich and then with an electron-poor alkyne was uncovered. Reactions in which the BCB functions in a rare ...[more]

PMID: 29874408

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Project description:Cervimycins A-D are bis-glycosylated polyketide antibiotics produced by Streptomyces tendae HKI 0179 with bactericidal activity against Gram-positive bacteria. In this study, cervimycin C (CmC) treatment caused a spaghetti-like phenotype in Bacillus subtilis 168, with elongated curved cells, which stayed joined after cell division, and exhibited a chromosome segregation defect, resulting in ghost cells without DNA. Electron microscopy of cervimycin treated S. aureus (3 x MIC) revealed swollen cells, misshapen septa, cell wall thickening, and a rough cell wall surface. Incorporation tests in B. subtilis indicated an effect on DNA biosynthesis at high cervimycin concentrations. Indeed, artificial down-regulation of the DNA gyrase subunit B gene (gyrB) increased the activity of cervimycin in agar diffusion tests, and, in high concentrations (starting at 62.5 x MIC), the antibiotic inhibited S. aureus DNA gyrase supercoiling activity in vitro. To obtain a more global view on the mode of action of CmC, transcriptomics and proteomics of cervimycin treated versus untreated S. aureus cells were performed. Interestingly, 3 x MIC of cervimycin did not induce the SOS response, which would indicate disturbance of the DNA gyrase activity in vivo. Instead, cervimycin induced the expression of the CtsR/HrcA heat shock operon and the expression of autolysins, exhibiting similarity to the ribosome-targeting gentamicin. In summary, we identified the DNA gyrase as a target, but at low concentrations electron microscopy and omics data revealed a more complex mode of action of cervimycin, that comprised induction of the heat shock response, indicating protein stress in the cell. A synergistic effect was seen when sodium chloride (NaCl) was added during cervimycin MIC testing of S. aureus SG511. Thus, transcriptomics of S. aureus cells under osmotic stress (1 M NaCl) were performed. The stress response was compared to the cervimycin stress response to identify factors which might contribute to the synergistic antibacterial effect of the two molecules.

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Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity.

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Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity.

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