Model studies related to the synthesis of fredericamycin A

Clive, Derrick L. J.; Khodabocus, Ahmad; Vernon, Peter G.; Angoh, A. G.; Bordeleau, Luc; Middleton, Donald S.; Lowe, Christopher; Kellner, Dorit

doi:10.1039/p19910001433

Cited by 29 publications

(16 citation statements)

References 46 publications

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“…Although the bromination of bulky and unreactive aromatic compounds is well documented in the literature, the bromination of compound 16 proved to be a challenge. Bromination of 16 with a series of bromination reagents (such as Br 2 /AcOH,24 pyridinium bromide perbromide,25 NBS26 and NBS/HBF 4 ·Et 2 O27) did not yield the desired product. Only Br 2 in the presence of iron powder28 yielded a brominated product in 43% yield (Scheme 2).…”

Section: Resultsmentioning

confidence: 98%

Chlorination Increases the Persistence of Semiquinone Free Radicals Derived from Polychlorinated Biphenyl Hydroquinones and Quinones

et al. 2008

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Polychlorinated biphenyls (PCBs) comprise a group of persistent organic pollutants that differ significantly in their physicochemical properties, their persistence, and their biological activities. They can be metabolized via hydroxylated and dihydroxylated metabolites to PCB quinone intermediates. We have recently demonstrated that both dihydroxy PCBs and PCB quinones can form semiquinone radicals (SQ •− ) in vitro. These semiquinone radicals are reactive intermediates that have been implicated in the toxicity of lower chlorinated PCB congeners. Here we describe the synthesis of selected PCB metabolites with differing degrees of chlorination on the oxygenated phenyl ring, e.g. 4,4′-dichloro-biphenyl-2,5-diol, 3,6,4′-trichloro-biphenyl-2,5-diol, 3,4,6,-trichlorobiphenyl-2,5-diol and their corresponding quinones. In addition two chlorinated orthohydroquinones were prepared, 6-chloro-biphenyl-3,4-diol and 6,4′-dichloro-biphenyl-3,4-diol. These PCB (hydro-)quinones readily react with oxygen or via comproportionation to yield the corresponding semiquinone free radicals, as detected by electron paramagnetic resonance spectroscopy (EPR alias ESR). The greater the number of chlorines on the (hydro-)quinone (oxygenated) ring, the higher the steady-state level of the resulting semiquinone radical at near neutral pH.

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Section: Resultsmentioning

confidence: 98%

Chlorination Increases the Persistence of Semiquinone Free Radicals Derived from Polychlorinated Biphenyl Hydroquinones and Quinones

et al. 2008

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“…[19] Similar methods have been applied to aromatic compounds, but to our knowledge this is the first report on its application to heteroaromatic compounds. Acidic cleavage of the oxygen bridge mediated by paratoluenesulfonic acid [20] provided free phenol 16. When dichloromethane was used as the solvent, as described in the literature, the reaction time exceeded several months; it was therefore replaced by THF.…”

Section: Steffen Lang and Ulrich Groth*mentioning

confidence: 99%

Total Syntheses of Cytotoxic, Naturally Occurring Kalasinamide, Geovanine, and Marcanine A

Lang

Groth

2009

Angew Chem Int Ed

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“…2). We hoped that subjecting 23 to acid conditions would pro- Our synthesis of the acetylene fragment commenced from known bromoquinone 27 (Scheme 6) [24]. Interestingly, allyloxylation of 27 resulted in a mixture of regioisomers, where substitution had occurred at both C-2 and C-3.…”

Section: Rubromycinmentioning

confidence: 99%

Synthetic approaches to [5,6]-benzannulated spiroketal natural products

McLeod

Brimble

Rathwell

et al. 2011

Pure and Applied Chemistry

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Studies toward the synthesis of three biologically active [5,6]-benzannulated spiroketal natural products are described. The first total synthesis of paecilospirone is reported, employing a late-stage, pH-neutral spiroketalization. A formal synthesis of γ-rubromycin is described, where the spiroketal moiety is formed by delicate manipulation of the electronic properties of the spirocyclization precursor. Finally, model work toward the total synthesis of berkelic acid is summarized, introducing a novel Horner-Wadsworth-Emmons/oxa-Michael (HWE/oxa-M) cascade to access the spiroketal precursor.Sonogashira reaction of 25 and 26 afforded propargylic alchohol 24 (Scheme 8). We found that the use of a non-amine base (cesium carbonate) and degassed solvents were required to minimize the formation of homocoupled product. Reduction of the triple bond by hydrogenation over 10 % Pd/C buffered with sodium bicarbonate, followed by oxidation of the secondary alcohol with o-iodosoxybenzoic acid (IBX) provided ketone 23. The key spiroketalization step was then attempted using the mild procedure previously developed by our group [23]. Pleasingly, treatment of 23 with silica-supported sodium hydrogen sulfate in dichloromethane afforded spiroketal 35 in 80 % yield. Finally, selective saponification of the aliphatic ester and adjustment of the naphthalene moiety oxidation state M. C. MCLEOD et al. Scheme 7 Synthesis of iodide 26. Scheme 8 Completion of formal synthesis. Brought to you by | Scheme 11 Synthesis of bromide 38 and completion of total synthesis. Brought to you by |

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Model studies related to the synthesis of fredericamycin A

Cited by 29 publications

References 46 publications

Chlorination Increases the Persistence of Semiquinone Free Radicals Derived from Polychlorinated Biphenyl Hydroquinones and Quinones

Chlorination Increases the Persistence of Semiquinone Free Radicals Derived from Polychlorinated Biphenyl Hydroquinones and Quinones

Total Syntheses of Cytotoxic, Naturally Occurring Kalasinamide, Geovanine, and Marcanine A

Synthetic approaches to [5,6]-benzannulated spiroketal natural products

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