High pressure FTIR study of intramolecular hydrogen bonding and conformation of a small peptide in solution

Effect of pressure on conformational equilibria of a small peptide N-acetyl-l-Pro-l-Leu-Gly-NH₂ in a chloroform solution has been studied by FTIR spectroscopy. Absorption in the NH stretching region was measured at pressures in the 1–1080 bar range and at 296 K, and decomposed into component bands by least-squares fitting. Intensity ratios of bands which were assigned to a hydrogen-bond-free conformer and intramolecularly hydrogen-bonded conformers with 10- and 13-membered hydrogen bonded rings, respectively, were examined as a function of pressure. It was found that the conformer with the 13-membered ring has definitely smaller partial molar volume than the other two conformers which have nearly the same volume with each other. On the basis of a simple dielectric model, we have shown that the conformer with the 13-membered hydrogen-bonded ring has a considerably large dipole moment which is consistent with the α-helical structure suggested by the previous variable-temperature FTIR study.     

Short and flexible route to 3,4-diarylpyrrole marine alkaloids: syntheses of permethyl storniamide A, ningalin B, and lamellarin G trimethyl ether

A highly efficient route to 3,4-diarylpyrrole marine alkaloids has been developed using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki cross-coupling of the 3,4-dihydroxypyrrole bis-triflate derivatives as key reactions. Based on this approach, formal syntheses of permethyl storniamide A and ningalin B, and a total synthesis of lamellarin G trimethyl ether have been achieved.     

AMPHIPHILIC COPOLYMERS AS MEDIA FOR LIGHT-INDUCED ELECTRON TRANSFER-II. ELECTROSTATIC EFFECT ON THE BACK ELECTRON TRANSFER

Abstract— Photosensitized reduction of zwitterionic viologen (SPV) and methyl viologen (MV²⁺) was investigated using an amphiliphilic copolymer having phenanthryl and sulfonate groups (APh) as photosensitizer in aqueous solutions. In the presence of triethanolamine the accumulation of SPV * (photoproduct) was found to be faster than that of MV⁺. This attributed to the electrostatic repulsion between SPV. and anionic segments of APh. Such difference between SPV and MV²⁺ was minimized in the case of the related monomer model. Retardation of the back reaction for the APh-SPV system was also demonstrated by laser photolysis, k _b= 8.7 × 10⁷ M ^-1 s^-1 for the polymer system as compared to k _b= 2.8 × 10⁹ M ^-1 s^-1 for the monomer model system. Strong salt-effects on the yield of the photoreduction and the rate of back reaction confirm the strong electrostatic interaction between the photoproducts and polyanions. This remarkable electrostatic effect of the polyanions was simulated by electrochemical redox reactions by using a graphite electrode coated with APh.     

The Biological Effects of Forsythia Leaves Containing the Cyclic AMP Phosphodiesterase 4 Inhibitor Phillyrin

Forsythia fruit (Forsythia suspensa Vahl (Oleaceae)) is a common component of Kampo medicines for treating the common cold, influenza, and allergies. The main polyphenolic compounds in the leaves of F. suspensa are pinoresinol β-d-glucoside, phillyrin and forsythiaside, and their levels are higher in the leaves of the plant than in the fruit. It is known that polyphenolic compounds stimulate lipid catabolism in the liver and suppress dyslipidemia, thereby attenuating diet-induced obesity and polyphenolic anti-oxidants might attenuate obesity in animals consuming high-fat diets. Recently, phillyrin was reported as a novel cyclic AMP phosphodiesterase 4 (PDE4) inhibitor derived from forsythia fruit. It was expected that the leaves of F. suspensa might display anti-obesity effects and serve as a health food material. In this review, we summarized our studies on the biological effects of forsythia leaves containing phillyrin and other polyphenolic compounds, particularly against obesity, atopic dermatitis, and influenza A virus infection, and its potential as a phytoestrogen.     

Convergent synthesis of the ABCDE ring fragment of ciguatoxins

Synthesis of the ABCDE ring fragment of ciguatoxins has been achieved in a highly stereocontrolled and convergent manner via the B-alkyl Suzuki-Miyaura coupling-based approach.     

Electron Spin Resonance Study on Grafting of Tetrafluoroethylene onto Polyethylene

An ESR study has been made on the course of grafting of tetrafluoroethylene onto polyethylene. Alkyl and allyl radicals trapped in the polymers were measured under various grafting conditions. It was observed that alkyl radicals decay very rapidly when monomers are in contact with the irradiated polymer, while allyl radicals decay very slowly even in the presence of monomers as in the decay of radicals in irradiated polymers without monomers. The effect of pre-irradiation temperature on grafting was also studied, and the rate of grafting was found to be much faster for lower pre-irradiation temperatures. From these experimental results it was concluded that alkyl radicals play an important Tole in the initiation reaction of grafting.