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[figure: see text] A tandem anionic 5-exo-dig cyclization/Claisen rearrangement sequence was used to effect a facile, "one-pot" conversion of an appropriately substituted 4-alkyn-1-ol to the tetracyclic carbon core structure of phorbol. The synthesis was conducted using readily available nonracemic starting materials to provide the target structure as a single enantiomer in high chemical yield.
[reaction: see text] A facile Lewis acid induced interrupted Nazarov reaction of gem-divinyl dihydrofurans to bicyclic lactones is described.
[reaction: see text] Enantiomerically enriched beta-substituted diphenylsilyl enol ethers, which can be prepared from Cu-catalyzed asymmetric conjugate reduction, are utilized in the Pd-catalyzed arylation of various aryl bromides. This new method provides a simple route to alpha-arylated cycloalkanones with excellent levels of enantiomeric and diastereomeric purity. The isolation of the intermediate, diphenylsilyl enol ethers is not necessary; the procedure can be carried out in one-pot.
Lesions indistinguishable from those of the generalized Shwartzman reaction occured in rabbits when a single intravenous injection of Gram-negative bacterial endotoxin was accompanied, or followed, by an injection of one of the following synthetic, heparin-like, acidic polymers-sodium polyanethol sulfonate, dextran sulfate, or sodium polyvinyl alcohol sulfonate. These reactions were produced by doses of polymer or of endotoxin which were without demonstrable effect when given singly. Heparin, in those similar to those previously shown to protect rabbits against the lesions of the generalized Shwartzman reaction, prevented the reaction to the combined injection of endotoxin and acidic polymers. Nitrogen mustard, which was previously shown to prevent the lesions of the generalized Shwartzman reaction from occurring after two intravenous injections of endotoxin, had no protective action against the lesions produced by the combined injection of endotoxin and polymer. Cortisone did not affect the reaction to endotoxin and polymer. The role of fibrinogen in the reaction under study is discussed in the paper which follows.
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The amount of insecticide that reaches a critical site of action within an insect is affected by a number of physical and chemical processes both within and outside the insect. This paper reviews some of these processes, with particular attention to those external to the insect, whose action commences at the moment an insecticide is released into the environment. On the basis of research that has been conducted on such processes, conclusions are drawn as to the properties that are desirable, from the point of view of insecticidal efficiency, in new compounds.
Properties of six chloroethylenes which could serve as indicators of their relative metabolic behavior and carcinogenic activity have been calculated using Modified Neglect of Diatomic Overlap (MNDO), a semiempirical, all valence electron, molecular orbital method. Possible pathways of transformation of parent compounds to acylchlorides, chloroaldehydes and epoxides--their putative ultimate carcinogens--were considered, and heats of formation and relative stabilities of intermediates were calculated. Our results indicate that carbonyl compounds could be formed with and without the intermediacy of epoxides, suggesting the possibility of more than one pathway in activation of parent compounds. Electronic properties of carbonyl products and epoxide carbocations, putative ultimate carcinogens which could serve as indicators of their relative electrophilicities, were also calculated. The results obtained indicated that the relative extent of metabolism to carbonyl products, rather than their electrophilicity, is a determinant of the relative carcinogenic activity of the parent compound. Of the various thermodynamic criteria investigated, four were found to be indicators of both relative metabolic behavior and carcinogenic activity.
An analysis of the electronic molecular structure of 2-furylethylene derivatives is carried out using a molecular orbital method. The differences in the electronic features of the nitro groups at two different positions of the furylethylene framework are well-accounted for in the present study. It is shown that nitro groups at position 5 of the furan ring of these compounds are more sensible to reduction in biological media that those at position beta of the exocyclic double bond. This greater sensitivity to reduction of 5-nitro compounds is given by the atomic and group charges on nitro group as well as for the low values of the energy of the lowest unoccupied molecular orbital. Discriminant functions able to classify 2-furylethylenes as mutagenic or not mutagenic are also obtained. These functions permitted the classification of 2-furylethylenes having or not nitro group in their structures. Finally, some quantitative models that describe the mutagenic potency of active compounds in terms of electronic molecular parameters were obtained. In all cases the models developed are in complete agreement with the experimental findings reported for this kind of compounds.
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Suzuki-Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl- and vinylboronic acids proceed in very good to excellent yield with the use of 2-(2',6'-dimethoxybiphenyl)dicyclohexylphosphine, SPhos (1). This ligand confers unprecedented activity for these processes, allowing reactions to be performed at low catalyst levels, to prepare extremely hindered biaryls and to be carried out, in general, for reactions of aryl chlorides at room temperature. Additionally, structural studies of various 1.Pd complexes are presented along with computational data that help elucidate the efficacy that 1 imparts on Suzuki-Miyaura coupling processes. Moreover, a comparison of the reactions with 1 and with 2-(2',4',6'-triisopropylbiphenyl)diphenylphosphine (2) is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an interesting C-H bond functionalization-cross-coupling sequence intervenes to provide product in high yield.
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We propose a new strategy for constructing a mediator-type biosensor as a Bio-MicroElectroMechanical Systems (BioMEMS) application. A vinylferrocene plasma-polymerized film (PPF) was deposited directly onto the surface of an electrode under dry conditions. The resulting redox film was extremely thin, adhered well onto a substrate (electrode), and had a highly crosslinked network structure. This technique, capable of polymeric deposition of any kind of monomer, can also serve the purpose of anti-fouling coating, or layer-to-layer interface creation. With a subsequent plasma process, additional polymeric layer of hydrophilic acetonitrile was superimposed onto the existing vinylferrocene-PPF surface to offer crucial features such that the wettability could be adjusted for a better electron transfer, and amino functional groups could be attached to immobilize a large amount of enzyme. Based upon this scheme, the device fabrication could be designed in a manner that the whole procedure was made up of dry wafer-handling processes, which is compatible with mass production. A prototype device was fabricated to have an array of needle-shaped amperometric micro-biosensors. The resultant thin polymer layer carried a large number of the mediator molecules, accomplishing a lower overpotential (+410 mV) and a rapid response time (<5s). Stressing the advantages of the plasma polymerization process together with some additional features accomplished in our device fabrication, we would discuss new possibilities in the field of BioMEMS.