Kunzeanones A, B, and C: novel alkylated phloroglucinol metabolites from Kunzea ambigua

Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract.     

Biogenetically inspired approach to the Strychnos alkaloids. Concise syntheses of (+/-)-akuammicine and (+/-)-strychnine

A linear synthesis of the indole alkaloid (+/-)-akuammicine (2) was completed by a novel sequence of reactions requiring only 10 steps from commercially available starting materials. The approach features a tandem vinylogous Mannich addition and an intramolecular hetero Diels-Alder reaction to rapidly assemble the pentacyclic heteroyohimboid derivative 8 from the readily available hydrocarboline 6. Oxidation of the E ring of 8 gave the lactone 9 that was converted into deformylgeissoschizine (11). The subsequent elaboration of 11 into 2 was effected by a biomimetically patterned transformation that involved sequential oxidation and base-induced skeletal reorganization. A variation of these tactics was then applied to the synthesis of the C(18) hydroxylated akuammicine derivative 36. Because 36 had previously been converted into strychnine (1) in four steps, its preparation constitutes a concise, formal synthesis of this complex alkaloid.     

Engineering Plant Alternative Oxidase Function in Mammalian Cells: Substitution of the Motif-like Sequence ENV for QDT Diminishes Catalytic Activity of Arum concinnatum AOX1a Expressed in HeLa Cells

Alternative oxidase (AOX) is a nonproton motive quinol–oxygen oxidoreductase which is a component of the mitochondrial respiratory chain in higher plants. In this study, we have characterized the catalytic activity and regulatory behaviors of Arum concinnatum AOX isoforms, namely AcoAOX1a and AcoAOX1b, and their artificial mutants in HeLa cells. We demonstrated that substitution of the motif-like sequence ENV on the C-terminal half of AcoAOX1a for QDT diminishes its activity and proposed that the innate inactivity of AcoAOX1b in HeLa cells is, at least in part, attributable to its QDT motif. Furthermore, we show that introduction of F130L in the hydrophilic N-terminal extension of AcoAOX1a resulted in greater activity in the presence of pyruvate. This result indicates that functional significance of the N-terminal extension is not particular to the conventional regulatory cysteine. On the basis of these findings, we discuss new insights into the structural integrity of AOX in HeLa cells and the applicability of mammalian cells for functional analysis of this enzyme.     

Vortex Counter-Current Chromatography: Performance of a New Preparative Column

A new preparative column for the vortex counter-current chromatograph was fabricated by making many (966) cylindrical separation units to a high-density polyethylene disk and then threading them with 6–40 taps. The resulting column had a total capacity of 364 mL. The performance of this vortex column was examined with three different two-phase solvent systems each using a set of suitable test samples: hexane–ethyl acetate–methanol–0.1 M hydrochloric acid (1:1:1:1, v/v) for the separation of DNP-amino acids; 1-butanol–acetic acid–water (4:1:5, v/v) for the separation of dipeptides; and hexane–acetonitrile–water (20:15:2, v/v) for the separation of Sudan dyes. Most of the separations show high partition efficiency of over a thousand theoretical plates, as expected based on the results previously obtained in preliminary separations with a small column. Overall, the results of the present study suggest that further improvement of the partition efficiency can be obtained by the modifying column configuration.

     

Radical reaction of chlorophyll derivatives triggered by AIBN

Radical reactions of a C3-vinylated chlorophyll derivative, methyl pyropheophorbide-a, which were induced by thiols and the conventional initiator azobisisobutyronitrile (AIBN) were examined in vitro for the first time. Thiyl radicals attacked regioselectively at the sole C3-vinyl group, and the anti-Markovnikov sulfanyl adducts were obtained as major products. The other peripheral substituents, as well as the chlorin macrocycle, remained intact. The AIBN-induced radical reaction competed with co-oxidation that afforded the C3-formyl chlorin. This method can open new routes to derivatization of vinyl chlorins.     

Involvement of Proton Transfer for Carbon Dioxide Reduction Coupled with Extracellular Electron Uptake in Shewanella oneidensis MR‐1

Microbial biosynthesis of hydrocarbon from CO₂ reduction driven by electron uptake process from the cathodic electrode has gained intensive attention in terms of potential industrial application. However, a lack of a model system for detailed studies on the mechanism of the CO₂ reduction hinders the improvement in efficiency for microbial electrosynthesis. Here, we examined the mechanism of microbial CO₂ reduction at the cathode by a well‐described microbe for extracellular electron uptake, Shewanella oneidensis MR‐1, capable of reducing gaseous CO₂ to produce formic acid. Using whole‐cell electrochemical assay, we observed stable cathodic current production at ?0.65 V vs Ag/AgCl KCl sat. associated with the introduction of CO₂. The observed cathodic current was enhanced by the addition of 4 μM riboflavin, which specifically accelerates the electron uptake process of MR‐1 by the interaction to its outer‐membrane c‐type cytochromes. The significant impact of an uncoupler agent and a mutant strain of MR‐1 lacking sole F‐type ATPase suggested the importance of proton import to the cytoplasm for the cathodic CO₂ reduction. The present data suggest that MR‐1 potentially serves as a model system for microbial electrosynthesis from CO₂.     

Two-dimensional hydrophilic interaction chromatography coupling anion-exchange and hydrophilic interaction columns for separation of 2-pyridylamino derivatives of neutral and sialylated N-glycans

A novel chromatographic approach coupling anion-exchange (diethylaminoethylene) and hydrophilic-interaction (amide or zwitterionic type) columns was developed for the separating of 2-pyridylamino derivatives of N-glycans (PA-N-glycans). This is a kind of on-line, two-dimensional (2D) separation approach in hydrophilic-interaction chromatography (called the 2D-HILIC method), analogous to that of coupling cation- (or anion-, or mixed ion-) exchange and reversed-phase columns in hydrophobic interaction (reversed-phase) chromatography. The efficiency of the 2D-HILIC method was tested with biantennary neutral and sialylated PA-N-glycan standards by properly combining linear gradient elutions of water-acetonitrile and spiked-salt (ammonium acetate) elutions. The retention time RSDs of all the peaks in three sequential runs of a 100 min cycle are less than 0.52%, which indicates a reasonably good repeatability of the 2D-HILIC method. Then, the method was applied to a complex mixture of PA-N-glycans from human serum proteins. It was demonstrated that the neutral PA-N-glycans and mono-, di-, tri-, and tetrasialylated PA-N-glycans are able to be eluted in turn according to the number of sialic acids in an automated (programmed) single run.     

Separation and purification of isoflavones from Pueraria lobata by high-speed counter-current chromatography.

High-speed counter-current chromatography (HSCCC) was applied to the semipreparative separation and purification of puerarin and related isoflavones from a crude extract of Pueraria lobata. Analytical HSCCC was used for the preliminary selection of a suitable solvent system composed of ethyl acetate-n-butanol-water (2:1:3, v/v/v). Using the above solvent system the preparative HSCCC was successfully performed yielding six relatively pure isoflavones including puerarin from 80 mg of the crude extract in one-step separation.     

Rapid breakdown mechanisms of open air nanosecond dielectric barrier discharges

The discharge initiation mechanism of nanosecond dielectric barrier discharges in open air has been clarified with time-dependent measurement of the discharge electric field by electric-field-induced coherent Raman scattering and optical emission. Our experimental observations have revealed that, in the prebreakdown phase of a nanosecond dielectric barrier discharge, the externally applied fast-rising electric field is strongly enhanced near the cathode due to large accumulation of space charge, which then strongly enhances ionization near the cathode. Once a sufficiently large number of ionizations take place, the location of peak ionization forms a front and propagates toward the cathode with strong optical emission, which establishes the discharge. This process is essentially different from the well-known Townsend mechanism for slower discharges.