87 research outputs found
Synthetic and computational studies on the tricarboxylate core of 6,7-dideoxysqualestatin H5 involving a carbonyl ylide cycloadditionârearrangement
Reaction of diazodiketoesters 17 and 28 with methyl glyoxylate in the presence of catalytic rhodium(II) acetate generates predominantly the 6,8-dioxabicyclo[3.2.1]octanes 29 and 30, respectively. Acid-catalysed rearrangement of the corresponding alcohol 31 favours, at equilibrium, the 2,8-dioxabicyclo[3.2.1]octane skeleton 33 of the squalestatinsâzaragozic acids. Force field calculations on the position of the equilibrium gave misleading results. DFT calculations were correct in suggesting that the energy difference between 31 and 33 should be small, but did not always suggest the right major product. Calculation of the NMR spectra of the similar structures could be used to assign the isomers with a high level of confidence
Asenjonamides AâC, antibacterial metabolites isolated from Streptomyces asenjonii strain KNN 42.f from an extreme-hyper arid Atacama Desert soil
Bio-guided fractionation of the culture broth extract of Streptomyces asenjonii strain KNN 42.f recovered from an extreme hyper-arid Atacama Desert soil in northern Chile led to the isolation of three new bioactive ?-diketones; asenjonamides AâC (1â3) in addition to the known N-(2-(1H-indol-3-yl)-2-oxoethyl)acetamide (4), a series of bioactive acylated 4-aminoheptosyl-?-N-glycosides; spicamycins AâE (5â9), and seven known diketopiperazines (10â16). All isolated compounds were characterized by HRESIMS and NMR analyses and tested for their antibacterial effect against a panel of bacteria
Catalytic, Asymmetric, Interrupted FeistâBĂ©nary Reactions of α-Tosyloxyacetophenones
Practical, Catalytic, Asymmetric Synthesis of b-Lactones via a Sequential Ketene Dimerization/Hydrogenation Process: Inhibitors of the Thioesterase Domain of Fatty Acid Synthase
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