Stereoselective synthesis of (±)-senepoxyde and (±)-crotepoxide1

Stereoselective synthesis of (±)-senepoxyde and (±) crotepoxide is described starting from 2-hydroxymethyl-1, 4-benzoquinone through the retro-Diels-Alder reaction.     

Synthesis of pyrenocine A and B

From 5-acetyl-4-hydroxy-6-methyl-α-pyrone, two phytotoxins, pyrenocine A and B, were synthesized and erroneous β-pyrone structure of the starting compound was corrected on the basis of spectroscopic data.     

Electronic nature of the aza substituent of pyridyl and quinolyl groups for reactivities in an insulated system

A new set of σ^o values was determined for all positions of pyridyl and quinolyl groups, reliably excluding steric effect by perihydrogen, on the basis of the rates of the alkaline hydrolysis of substituted 2-methylbenzoates and pyridylmethyl and quinolylmethyl 2-methylbenzoates in 70% aq acetone.     

Regioselective Dichlorination of a Non‐Activated Aliphatic Carbon Atom and Phenolic Bismethylation by a Multifunctional Fungal Flavoenzyme

The regioselective functionalization of non‐activated carbon atoms such as aliphatic halogenation is a major synthetic challenge. A novel multifunctional enzyme catalyzing the geminal dichlorination of a methyl group was discovered in Aspergillus oryzae (Koji mold), an important fungus that is widely used for Asian food fermentation. A biosynthetic pathway encoded on two different chromosomes yields mono‐ and dichlorinated polyketides (diaporthin derivatives), including the cytotoxic dichlorodiaporthin as the main product. Bioinformatic analyses and functional genetics revealed an unprecedented hybrid enzyme (AoiQ) with two functional domains, one for halogenation and one for O‐methylation. AoiQ was successfully reconstituted in vivo and in vitro, unequivocally showing that this FADH₂‐dependent enzyme is uniquely capable of the stepwise gem‐dichlorination of a non‐activated carbon atom on a freestanding substrate. Genome mining indicated that related hybrid enzymes are encoded in cryptic gene clusters in numerous ecologically relevant fungi.     

Synthesis of procyanidins by stepwise- and self-condensation using 3,4-cis-4-acetoxy-3-O-acetyl-4-dehydro-5,7,3′,4′-tetra-O-benzyl-(+)-catechin and (−)-epicatechin as a key building monomer

3,4-cis-4-Acetoxy-3-O-acetyl-4-dehydro-5,7,3′,4′-tetra-O-benzyl-(+)-catechin (1a) or (−)-epicatechin (1b) reacted high regio- and stereo-selectively with 1.5 equiv of the 5,7,3′,4′-tetra-O-benzyloxyflavan-3-ol (4a or 4b) in the presence of 1 equiv of TMSOTf to give the corresponding procyanidins. On the other hand, the self-condensation of 1a in the presence of a catalytic amount of B(C₆F₅)₃ afforded wide-range procyanidins from dimer to 15-mer like a biomass.     

Reduction of 2-chloro-N-phenylpropanamide and 2-methyl-N-phenylaziridine with lithium aluminium hydride

The reduction of 2-chloro-N-phenylpropanamide with LiAlH(4) has been re-examined. In contrast to previous findings, we obtain in almost equal quantities two amines from this reaction, namely N-propylaniline and the rearranged product N-isopropylaniline. 2-Methyl-N-phenylaziridine is an intermediate in the reduction and can be isolated from reactions with less LiAlH(4). Reduction of 2-methyl-N-phenylaziridine itself proceeds non-regioselectively to provide a mixture of propyl- and isopropylanilines. Formation of the amines by reduction of the aziridine is much slower than formation by reduction of the 2-chloropropanamide, which indicates that Lewis acid catalysis (by aluminium chlorohydrides) facilitates the reduction of the aziridine. In addition, Lewis acid catalysis increases the relative yield of the propylamine product. The reduction of 2-chloro-N-phenylpropanamide furnishes 2-phenylamino-1-propanol as a by-product, rather than the previously proposed 1-phenylamino-2-propanol.     

Qualitative properties of generalized principal eigenvalues for superquadratic viscous Hamilton–Jacobi equations

This paper is concerned with the ergodic problem for superquadratic viscous Hamilton–Jacobi equations with exponent \(m>2\). We prove that the generalized principal eigenvalue of the equation converges to a constant as \(m\rightarrow \infty \), and that the limit coincides with the generalized principal eigenvalue of an ergodic problem with gradient constraint. We also investigate some qualitative properties of the generalized principal eigenvalue with respect to a perturbation of the potential function. It turns out that different situations take place according to \(m=2\), \(2<m<\infty \), and the limiting case \(m=\infty \).     

Characterization of chitosan nanofiber fabric by electrospray deposition: electrokinetic and adsorption behavior

Cationic biopolymer nanofiber fabrics were prepared from a chitosan/poly(ethylene oxide) blend solution by electrospray deposition. Their electrokinetic properties and DNA adsorption behavior were analyzed as a function of pH. The zeta potential was determined from streaming potential/streaming current measurements. The adsorption of DNA onto the fabrics was investigated by spectrophotoscopy. The adsorption behavior of DNA correlated well with the electrokinetic properties of the fabrics. This revealed that the electrokinetic approach was a useful option for characterization of novel nanofiber assemblies made by the electrostatic spray process. In addition, these results provided fundamental information about chitosan nanofiber fabrics for both biomedical and analytical applications.     

Hyperbolic sections in surface bundles

We give conditions assuring that the given section in a surface bundle over the circle is hyperbolic in terms of the ‘‘projection" in the fiber surface according to the Nielsen-Thurston types of the monodromies.     

Four new eremophilane-type alcohols from Cremanthodium helianthus collected in China

Four new eremophilane-type sesquiterpenoid alcohols were isolated from Cremanthodium helianthus collected in China and their structures established on the basis of spectroscopic analyses. All of them had 9-en-8-one partial structures with one more double bond either delta11, delta11(13), or delta7(11). Two of them had a hydroxy group at C-1 position.