Rapid access to the tricyclic spirotetronic core of abyssomicins

[reaction: see text] Abyssomicins, a novel class of polyketide antibiotics, are characterized by an unprecedented spirotetronic tricyclic subunit in their structure. In this letter, a short synthesis of a suitably functionalized tricyclic precursor of abyssomicins is reported. Key steps of the synthesis are (i) the highly stereoselective Al(III)-tethered Diels-Alder reaction and (ii) the tandem Dieckmann cyclization/TBS trapping of the C9 hydroxyl group followed by a regioselective intramolecular epoxide opening for the assembly of the target tricyclic structure.     

Some natural aqueous extracts of plants as green inhibitor for carbon steel corrosion in 0.5 M sulfuric acid

The inhibiting impact of natural aqueous extracts of some plants such as curcumin, parsley and cassia bark extracts for the corrosion of carbon steel (C-steel) in 0.5 M H₂SO₄ solution was inspected utilizing some techniques such as galvanostatic and potentiodynamic anodic polarization and weight loss measurements. Outcomes indicated that the percentage inhibition efficiency increases with increasing the concentration of the extract due to its horizontal adsorption on the C-steel surface. The process of adsorption is followed by the Temkin isotherm. These natural extracts acted as pitting corrosion inhibitors by shifting the pitting potential to more noble values. The sequence of inhibition efficiency of the natural extracts decreases in the following order: cassia bark extract > parsley extract > curcumin extract. This arrangement is related to the molecular size of the major components of the three natural extracts used.     

Information in Quantal Response Data and Random Censoring

In this paper we study interesting properties of Fisher and divergence type measures of information for quantal, complete and incomplete random censoring, and not censoring at all. It is shown that, while quantal random censoring is less expensive, it is less informative than complete random censoring. It is also shown that in experiments which are mixtures of quantal and complete random censoring, the information received from these experiments is a convex combination of quantal information and the information in complete random censoring. Finally, the "total information" property is studied, in which the information received by the uncensored experiment can be expressed as the sum of the information provided by random censoring and the loss of information due to censoring. The results for Fisher's measure of information are an extension of already known results to the multiparameter case. The investigation of the previous information properties for divergence type measures is a new element, as well as the comparison of byproducts of Fisher information matrices.     

Short total synthesis of (+/-)-sceptrin

Gifted with novel chemical features and extraordinary biological activity, sceptrin has remained a prominent unanswered synthetic challenge since its characterization in 1981 by Faulkner and Clardy. A concise and practical solution to the myriad of chemical challenges posed by sceptrin is reported in this Communication. Thus, through a sequence involving rearrangement of an oxaquadricyclane, a new method for chemo- and regioselective halogenation, a mild sequence for 2-aminoimidazole formation, and careful synthetic choreography, (+/-)-sceptrin is obtained in a minimum of steps and in 24% overall yield from dimethyl acetylenedicarboxylate without a single use of chromatography.     

Reactions of N-hydroxysuccinimide esters of anthranilic acids with anions of beta-keto esters. A new route to 4-oxo-3-quinolinecarboxylic acid derivatives

A new approach for the synthesis of 4-oxo-3-quinolinecarboxylic acid derivatives is described. This methodology involves the C-acylation of the anions of appropriate beta-keto esters with novel N-hydroxysuccinimide esters of anthranilic acids. The intermediate C-acylation products 3 are spontaneously cyclized to afford 3-ethoxycarbonyl-4-oxoquinoline derivatives 4. The introduction of a variety of substituents at positions 1 and 2 of the quinoline ring is feasible with the selection of suitable anthranilic acids and beta-keto esters. The structure of the obtained 2-substituted 3-ethoxycarbonyl-4-oxoquinolines was confirmed by IR and NMR spectral data.     

Detecting electronic states at stacking faults in magnetic thin films by tunneling spectroscopy

Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated with the stacking fault are visualized by tunneling spectroscopy, and its origin is identified by band structure calculations.