New aplysiatoxin derivatives from the Okinawan cyanobacterium Moorea producens

The marine cyanobacterium Moorea producens is a rich source of diverse compounds that possess a variety of biological activities. In the present study, eight new aplysiatoxin derivatives, namely 6, 8–13, and 15, along with aplysiatoxin (1), debromoaplysiatoxin (2), 3-methoxyaplysiatoxin (3), anhydroaplysiatoxin (4), anhydrodebromoaplysiatoxin (5), oscillatoxin B2 (7), and 30-methyloscillatoxin D (14) were isolated and identified from the Okinawan M. producens. In cytotoxicity and diatom growth inhibition tests, the fifteen compounds tested (1–15) showed moderate or no activity at a concentration of 10?μg/mL.     

Effects of magnesium salts and amines on the stereoselectivity in the imine aldol reaction

In the imine aldol reactions of 1 with aromatic aldehydes using magnesium salts in the presence of amines, the threo/erythro ratios of products increased in the order Mg(ClO4)2>MgI2>MgBr2>MgCl2>Mg(OTf)2 and N,N,N',N'-tetramethylethylenediamine (TMEDA)>Et3N. This increase in the threo/erythro ratios of products was estimated to be caused by a retro-imine aldol reaction under thermodynamic control.     

Me‐BIPAM for the Synthesis of Optically Active 3‐Aryl‐3‐hydroxy‐2‐oxindoles by Ruthenium‐catalyzed Addition of Arylboronic Acids to Isatins

A chiral O‐linked C₂‐symmetric bidentate phosphoramidite (Me‐BIPAM) was found to be efficient for the ruthenium‐catalyzed addition of arylboronic acids to isatins. Asymmetric synthesis of 3‐aryl‐3‐hydroxy‐2‐oxindoles by 1,2‐addition of arylboronic acids to isatins was carried out in the presence of [RuCl₂(PPh₃)₃]/(R,R)‐Me‐BIPAM and KF, resulting in an enantioselectivity as high as 90 % ee. It was found that the reaction with N‐protected isatins proceeds with high yields and good enantioselectivities. The best protective groups on the nitrogen atom were different depending on the substituents on the aromatic ring. The use of a N‐benzyl group resulted in excellent enantioselectivities in many substrates compared with other groups.     

A novel synthesis of α-methylene-γ-butyrolactones from 1-(N,N-dimethylaminomethyl)cyclopropanecarboxylate esters

A new method is reported for constructing α-methylene-γ-butyrolactone moiety under neutral, anhydrous conditions. Olefin-dibromocarbene adducts are transformed to methyl 1-(N,N-dimethylaminomethyl)cyclopropanecarboxylates which in turn are treated with trimethylsilyl iodide and the crude products distilled to give the title compounds with high regio- and stereoselectivity.     

A novel synthesis of the carbapen-2-em derivatives

A new synthesis of the carbapen-2-em ring system, the basic nucleus of thienamycin and its relatives, is described.     

Investigation on the arrangement of lithium ions in LixLa(1/3)NbO3 with perovskite structure

The relationship between the Li arrangement and the electrochemical behavior has been examined as a function of composition x in electrochemically lithiated A-site deficient perovskite, Li(x)()La(1/3)NbO(3). The cell potential diagram and powder X-ray diffraction (XRD) study indicated that the Li ions are inserted into the vacant Perovskite A-site with an electrochemical reaction. In addition, the derivatives of the cell potential diagram showed three cathodic peaks, indicating a stepwise Li insertion mechanism takes place. Such a stepwise behavior would be ascribed to the changes in arrangement of inserted Li ions in the Perovskite lattice, since the XRD patterns of pristine La(1/3)NbO(3) showed that the La arrangement in La(1/3)NbO(3) was ordered along the c-axis, causing two kinds of A-site vacancies. To reveal the changes in the arrangement of Li ions, the entropy measurement of the reaction was performed by both the electrochemical and the calorimetric techniques. Moreover, the formation energy of the Perovskite structure with various Li arrangements was compared by using an ab initio calculation. The results of experiment and computation suggested that the electrochemical reaction proceeded via two kinds of superstructures of Li(1/6)La(1/3)NbO(3) and Li(1/2)La(1/3)NbO(3) due to the ordered arrangement of Li ions.     

Oxygen triggering reversible modulation of Vibrio fischeri strain Y1 bioluminescence in vivo

Yellow-emitting Vibrio fischeri Y1 modulates its bioluminescence (BL) depending on the dissolved O2 concentration. On supplying O2 to the cells under anaerobiosis, the cells begin to emit striking yellow BL peaking around 535 nm. The enhanced yellow emission reverts reversibly to the original level after O2 is consumed. Moreover, the reversible rise and fall of the yellow emission occurs repeatedly in accord with the repeating cycles of aeration on and off. This indicates that an increase in the cellular amount of yellow fluorescent protein (YFP) is not an immediate cause of the yellow emission enhancement. One suggested explanation is that the activity of YFP originating from its highly fluorescent property is altered by redox interaction with the respiratory components, including the soluble cytochrome c. Under the O2-limited conditions, the cellular YFP molecules, in part, seem to lose the fluorescent property possibly because of being reduced via redox interaction with some respiratory components in reduced form. On stimulating aerobic respiration with O2 supply, the reduced YFP seems to retrieve its fluorescent property via oxidation possibly with both O2, diffused across the cell membrane, and ferricytochrome c, generated during the respiratory turnover. The suggested redox interactions seem primarily to cause the reversible BL modulation.