Stereoselective reduction of the steroidal 23-en-22-one: a route to the side chain of the plant growth promoter brassinolide.

The side chain of brassinolide (1) was stereoselectively synthesized, in which the 20(S)- and the 22(R)-configurations were introduced by the alkylation (S_N2) of the 20(R)-tosyloxy steroid 7 with the protected cyanohydrin 8 followed by the stereoselective reduction of the 23-en-22-one 10 with Dibal-H.     

Radiation-induced copolymerization of hexafluoroacetone with 2-methyl-1-pentene

Copolymerization of hexafluoroacetone (HFA) with 2-methyl-1-pentene (2MP) in trichlorotrifluoroethane (R-113) was carried out by γ-ray irradiation in a low-temperature region of ?100 to 0°C. Though HFA does not homopolymerize and 2MP scarcely does, the copolymerization took place at various monomer compositions. The copolymerization rate and the molecular weight in the low-temperature region were much higher than those at 0°C. Above room temperature the copolymerization did not take place and only the adduct of monomers was formed. The copolymerization was inhibited to some extent by cation scavengers, but not by radical or electron scavengers. Elemental analysis and nuclear magnetic resonance (NMR) spectra show that the copolymer consists of almost equimolar monomer units and has two types of structure, head to tail and head to head or tail to tail. It has been concluded that copolymerization probably proceeds via a cationic mechanism to form an alternating copolymer.     

Chemiluminescence in autoxidation of phosphonate carbanions. Phospha-1,2-dioxetanes as the most likely high-energy intermediates

Autoxidation of the phosphonate carbanions derived from 9-phosphono-10-hydroacridanes provided chemiluminescence ascribed to the excited acridone anion. The intramolecular CIEEL (chemically initiated electron exchange luminescence) mechanism can be applied to this chemiluminescence because of the much higher emission efficiency compared to that of 9-phosphono-10-methylacridanes. The effect of the phosphonate substituents on the emission efficiency and especially on the rates of the chemiluminescence decay can be interpreted to originate from the valence deviation of the phosphorus atoms, which is connected with the substituent effect on the geometrical selectivity in the olefination reaction of the phosphonate carbanions. The enhanced chemiluminescence in the presence of the fluorophores was also detected in autoxidation of the carbanions of diethyl diphenylmethylphosphonate and fluorenylphosphonate. Although the evidence is circumstantial, these results strongly support the belief that phospha-1,2-dioxetane is the most likely high-energy intermediate generating the excited molecules.     

Pharmacokinetic study of allixin, a phytoalexin produced by garlic

The pharmacokinetic behavior of allixin (3-hydroxy-5-methoxy-6-methyl-2-penthyl-4H-pyran-4-one) was investigated in an experimental animal, mice. Allixin was administered using an inclusion compound because the solubility of allixin in aqueous solution is very low. The allixin content in serum and in the organs of administered animals was analyzed by liquid chromatography (LC)-MS. Most of the administered allixin disappeared within 2 h, and the bioavailability of allixin was estimated to be 31% by obtained area under the blood concentration-time curve (AUC). The metabolites of allixin were studied using the metabolic enzyme fraction of liver and liver homogenate. Several new peaks corresponding to allixin metabolites were observed in the HPLC chromatoprofile. The chemical structure of the metabolites was investigated using LC-MS and NMR. Three of them were identified as allixin metabolites having a hydroxylated pentyl group.     

Peroxyoxalate chemiluminescence of N,N'-bistosyl-1H,4H-quinoxaline-2,3-dione and related compounds. Dependence on electronic nature of fluorophores

The title compound N,N'-bistosyl-1H,4H-quinoxaline-2,3-dione (TsQD) provides peroxyoxalate chemiluminescence (PO-CL) when reacted with hydrogen peroxide in the presence of fluorophores. The chemiluminescence (CL) efficiency of TsQD was superior to that of other related compounds such as bis(2,4,6-trichlorophenyl) oxalate (TCPO), a typical oxalate for the peroxyoxalate PO-CL, under an aqueous condition. Factors affecting the PO-CL efficiency are discussed from the viewpoint of the structures of the substrates and the electronic nature of the fluorophores. A linear correlation of the logarithmic values evaluated from the CL quantum yields with the oxidation potentials of the aromatic fluorophores supports the involvement of the chemically initiated electron exchange luminescence (CIEEL) mechanism in both TsQD- and TCPO-CL systems. Also, an excellent Hammett relationship was derived from the correlation between the sigma(+) values and the relative singlet excitation yields in TsQD-CL enhanced by a series of fluorescent para,para'-disubstituted distyrylbenzenes.     

Structure and Raman scattering study on Ba8GaxSi46−x (x=10 and 16) type I clathrates

Structure and vibrational properties of Ba₈Ga_xSi_46−x (x=10 and 16) clathrates were studied by X-ray diffraction and Raman scattering measurements. The temperature dependent electrical resistivity measurement on Ba₈Ga₁₀Si₃₆ has shown semiconducting nature of that clathrate with an energy band gap value of 0.31 eV. On the other hand the measurement on Ba₈Ga₁₆Si₃₀ has shown metallic like electrical conductivity of that clathrate. The origin of semiconductivity in Ba₈Ga₁₀Si₃₆ was found to be due to the vacancy disorder in the framework sites. Room temperature Raman scattering measurements resolved several Raman vibrational modes, including low frequencies ones corresponding to the rattling motion of Ba atoms. The low frequency positions of Ba in the respective clathrates at 49.4, 73.7 and 97.3 cm⁻¹ for Ba₈Ga₁₀Si₃₆ and at 43.7, 74.5 and 92.4 cm⁻¹ for Ba₈Ga₁₆Si₃₀ were found to be in agreement with the reported density functional (DF) calculated low frequency modes of Ba₈Ga₁₆Si₃₀. The framework gallium difference and vacancy disorders were found to influence the position and widths of frequency modes. Room temperature lattice thermal conductivity of Ba₈Ga₁₀Si₃₆ and Ba₈Ga₁₆Si₃₀ were 1.128 and 1.071 Wm⁻¹ K⁻¹, respectively, and this low value was attributed to the resonant scattering between the framework acoustic and Ba rattling modes.     

A new apparatus and procedure for gas permeability measurements on water-swollen gel membranes

An improved apparatus for the measurement of gas permeability through water-swollen gel membranes is described. The apparatus is fitted with a water bubble chamber and a water reservoir to prevent evaporation of water from the swollen membranes. Permeabilities to O₂ and N₂ of two kinds of poly (vinyl alcohol) (PVA) membranes and cationically modified PVA membranes with a swelling ratio of 0.3–0.8 were measured. It was found that the introduction of charged groups at 3.5 mol/100 mol monomer units into the PVA membranes with the above swelling ratio range does not significantly alter the permeability of the membranes to the gases. The permeability values are independent of the upstream pressure up to 4.6 atm.     

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene. III. Polymerization mechanism

In the radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene, the dose rate dependence, the effect of emulsifier concentration, and the effect of monomer composition were studied. The rate of polymerization was proportional to the 0.90 power of the dose rate and the 0.26 power of the emulsifier concentration. The degree of polymerization was independent of the dose rate and the emulsifier concentration. Both the rate of polymerization and the degree of polymerization increased with tetrafluoroethylene content in the monomer mixture. The resulting copolymer was an alternating polymer over a wide range of monomer composition. It was concluded from the dose rate dependence of the rate of polymerization that the emulsion copolymerization is mainly terminated by degradative chain transfer of the propagating radical to propylene.     

SOME OBSERVATIONS ON THE MORPHOGENESIS OF LATTICE STRUCTURE IN THE PURPLE MEMBRANE

Abstract— The formation process of purple membrane was studied morphologically by freeze-fracture and etching methods. The bacteria, H. halobium R₁, cultured in the medium containing 2m M nicotine, did not show the hexagonal structure of purple membrane, but a particle free area was frequently observed in the plasma membrane. However, within 24h after returning to the normal medium, hexagonal and triclinic lattices with spacings of 6 to 8nm occurred as small patches on the P face of the plasma membrane. Furthermore, it was revealed that the retinal was not required for the formation of the two-dimensional hexagonal lattice structure of purple membrane, since the mutant bacteria, H. halobium R₁mW, lacking the ability of retinal synthesis, displayed a similar lattice. The other mutant, H. halobium R₁mR, lacking the ability of bacterio-opsin synthesis, never showed any highly ordered arrangement. This evidence suggests that membrane proteins other than bacterio-opsin or bacteriorhodopsin do not form highly ordered lattices in the membrane.     

Palladium-catalyzed chirality transfer of 1,3-diene monoepoxides and its application to the synthesis of steroid side chains

The palladium-catalyzed 1,4-addition of nucleophiles to 15β,16β-epoxy-E-Δ¹⁷⁽²⁰⁾-isoheptylidene steroid 8 and 15β,16β-epoxy-E-Δ¹⁷⁽²⁰⁾-ethylidene steroid 13 has been studied as a good method for regio- and stereoselective introduction of steroid side chains.