Biosynthesis of citreothiolactone,citreopyrone and pyrenocine B

¹³C NMR spectroscopy using INADEQUATE pulse sequence method has been used to deduce the labelling patterns of the three metabolites of $\text{Penicillium citreo-viride}$ B. derived from [1,2-¹³C]acetate, indicating that their carbon skeletons consist of two different units [CH₃COCH₂COCH₂COS-Enzyme and CH₃COCH₂COS-Enzyme].     

Helical structures induced by laterally-connected chiral twin molecules

A novel chiral twin material, (R)-bis[5-octyloxy-2-(4-octyloxyphenoxycarbonyl)phenyl] 3-methyladipate, has been prepared, where two mesogenic parts are connected laterally by a spacer possessing a chiral centre. A weaker helical structure, in particular in the chiral smectic C (S*_c) phase, was found to be induced by the laterally-connected twin material than by the analogous terminally-connected twin material. If laterally-connected chiral twin molecules prefer to stay in the smectic layer structure so that the two mesogenic parts exist in the same smectic layer, the twist interaction between adjacent layers cannot be produced by direct correlation of motion and directions of two mesogenic parts. Thus, the helical structure in the S*_c phase induced by laterally-connected chiral twin molecules becomes weak. An analogous laterally-branched 'monomeric' compound, (S)-5-octyloxy-2-(4-octyloxyphenoxycarbonyl)phenyl 3-methyl-pentanoate, has also been prepared, and the induced helical structures compared.     

Computational exploration of the catalytic mechanism of dopamine beta-monooxygenase: modeling of its mononuclear copper active sites

Dopamine hydroxylation by the copper-superoxo, -hydroperoxo, and -oxo species of dopamine beta-monooxygenase (DBM) is investigated using theoretical calculations to identify the active species in its reaction and to reveal the key functions of the surrounding amino acid residues in substrate binding. A 3D model of rat DBM is constructed by homology modeling using the crystal structure of peptidylglycine alpha-hydroxylating monooxygenase (PHM) with a high sequence identity of 30% as a template. In the constructed 3D model, the CuA site in domain 1 is coordinated by three histidine residues, His265, His266, and His336, while the CuB site in domain 2 is coordinated by two histidine residues, His415 and His417, and by a methionine residue, Met490. The three Glu268, Glu369, and Tyr494 residues are suggested to play an important role in the substrate binding at the active site of DBM to enable the stereospecific hydrogen-atom abstraction. Quantum mechanical/molecular mechanical (QM/MM) calculations are performed to determine the structure of the copper-superoxo, -hydroperoxo, and -oxo species in the whole-enzyme model with about 4700 atoms. The reactivity of the three oxidants is evaluated in terms of density-functional-theory calculations with small models extracted from the QM region of the whole-enzyme model.     

Evidence for the importance of conformational equilibria in Rh-diphosphine complexes for the enantioselection in Rh-catalyzed asymmetric hydrogenation

The conformations of the chelate cycles in the X-ray structures of norbornadiene- and cyclooctadiene-rhodium complexes of (R,R)-1,2-bis[(o-methylphenyl)phenylphosphino]ethane are dramatically different. Nevertheless, they demonstrate the same sense of enantioselection in asymmetric hydrogenation of dehydroamino acids.     

Synthesis of 2-decenedioic acid (royal jelly acid) by sequential carbonylation of butadiene catalyzed by a palladium—phosphine complex and dicobalt octacarbonyl

Carbonylation of butadiene in t-butyl alcohol catalyzed by a palladium complex gave t-butyl-3,8-nonadienoate (I). Further carbonylation of I in methanol with Co₂(CO)₈ afforded t-butylmethyl-3-decenedioate (II) as the main product. Hydrolysis and base-catalyzed isomerization of II produced E-2-decenedioic acid.     

Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation

An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N₂⁺ 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed.     

The Pore Structure Determination of Carbon Aerogels

The detailed adsorption isotherms of nitrogen on carbon aerogels at 77 K were measured. The N2 adsorption isotherm had a marked hysteresis. The adsorption isotherms were analyzed by high resolution s-plots to evaluate their porosity. The s-plots showed an explicit upward deviation from the linearity below s = 0.5, suggesting the presence of micropores. The mesoporosity and microporosity were separately determined from the s-plot. The predominant pores in carbon aerogels were mesopores and the percentage of micropores was in the range of 5 to 10% of the total pore volume. The N2 adsorption hysteresis was analyzed with the Saam-Cole theory under the assumption of the cylindrical pore shape. The parameters determined from the Saam-Cole method were associated with the carbon aerogel structure.     

Studies on the construction of glycosidic linkage in guanofosfocins. Glycosylation of 8-oxoinosine and 8-oxoguanosine derivatives with mannopyranosyl bromide

In model studies directed to the total synthesis of guanofosfocins, a unique glycosydic bond formation between the 8-oxoinosine derivatives and mannopyranosyl donor is described. The reaction employing previously reported conditions resulted in the formation of two regioisomers, the 8-O- and N7-mannosylated inosine derivatives. However, the use of tetrabutylammonium iodide as a catalyst was found to improve the chemoselectivity towards O-glycosylation to afford the desired 8-O-mannosylated products in satisfactory yields. The established procedure was successfully applied for the synthesis of 8-(mannopyranosyloxy)guanosine derivative.