First synthesis of (±)-pseudohygrophorone A12, an anti-fungal cyclohexenone derivative isolated from Hygrophorus abieticola

Pseudohygrophorones A¹² and B¹² are cyclohexenone derivatives isolated from Hygrophorus abieticola (Basidiomycete) as anti-phytopathogenic compounds. In this study, the first synthesis of (±)-pseudohygrophorones A¹² is reported, utilizing Michael–aldol cascade reaction for constructing the 3,3-dimethyl-2,4-dioxabicyclo[3.1.1]nonan-9-one skeleton and the diastereoselective addition of alkyllithium to the one-side blocked ketone as the key steps.     

A novel synthesis of (−)-callicarpenal

Callicarpenal, isolated from the leaves of American beautyberry (Callicarpa americana) and Japanese beautyberry (Callicarpa japonica), exhibits significant mosquito bite-deterring activity and repellent activity against ticks and fire ants. The mosquito bite-deterring activity level of callicarpenal was reported to be similar to that of N,N-diethyl-m-toluamide. The novel synthesis of (?)-callicarpenal reported herein was accomplished by starting from (+)-pulegone. In our original approach, a novel Prins-type cyclization based on Meyer–Schuster rearrangement was featured as a key step.     

Growth of carbon-doped base GaAs/AlGaAs HBT by gas-source MBE using TEG, TEA, TMG, AsH3, and Si2H6

High-performance carbon-doped-base GaAs/AlGaAs heterobipolar transistors (HBTs) were grown by gas-source MBE using only gaseous sources including dopant sources. The AlGaAs emitter layer was doped with Si from uncracked SI₂H₆ (n = 9 × 10¹⁷ cm^-3), and the base layer (92.5 nm) was doped with carbon from TMG (p = 4 × 10¹⁹ cm^-3). From SIMS analysis it was confirmed that a well-defined emitter-base junction with sharp carbon profile was obtained. The base-current ideality factor from the Gummel plot was 1.47, and the emitter-base junction ideality factor was 1.12. A high DC current gain of 53 was obtained at a current density of 4 × 10⁴ A/cm². The device characteristics of our carbon-doped HBTs were found to be stable under current stress.     

Three novel cantharidin-related compounds from the Chinese blister beetle, Mylabris phalerata Pall

Three novel cantharidin analogues were isolated from the Chinese blister beetle, Mylabris phalerata PALL. (Meloidae), which has been used in traditional Chinese medicine for the treatment of cancer. Their structures were determined on the basis of heteronuclear multiple-bond connectivity and nuclear Overhauser effect spectroscopy experiments, and chemical data confirmed them to be so-called cantharimides, in which the anhydride oxygen atoms are replaced by the basic amino acid L-lysine, L-ornithine, and L-arginine moieties.     

Competition of magnetic order and superconductivity investigated by positive muon spin rotation in La2−x M x CuO4 (M = Ba,Sr) aroundx=0.12

Muon spin rotation (SR) is applied to La_2–x Ba _x CuO₄ aroundx=0.12 where the superconductivity (SC) is suppressed remarkably. The magnetic ordering of Cu-moments appears below 35 K in the narrow range ofx where a lattice instability from the low temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) structure exists. The present study suggests strongly that the magnetic ordering of Cu-moments is an important factor in the suppression of high-T _c superconductivity aroundx=0.12 in La_2–x Ba _x CuO₄. Similar results are obtained for the La_2–x Sr _x CuO₄ and La_2–x–y Sr _x Nd _y CuO₄ systems.     

Synthesis and antibacterial activity of lactivicin derivatives

The chemical modification of the 4-acetylamino group on the cycloserine moiety of lactivicin (1a) was carried out. The lactivicin derivatives (1d, k--p and w) having heterocyclic acylamino groups which have been often utilized in beta-lactam antibiotics showed potent antibacterial activities. Ester prodrugs (7a--d) of lactivicin derivatives were also prepared in order to improve the bioavailability on oral administration. The pivaloyloxymethyl (POM) esters (7a and 7b) and 1-ethoxycarbonyloxyethyl (EOE) ester (7c) were found to have slightly improved protective effect in vivo compared with their parent compounds 1c and 1k.     

Mechanisms of the Photochemical Rearrangement of Diphenyl Ethers

The mechanism of the photochemical rearrangement of diphenyl ether (1a) was studied. Irradiation of 1a in ethanol gave 2-phenylphenol (2, 42%) and 4-phenylphenol (3, 11%) as rearrangement products, in addition to phenol (4, 30%) and benzene (5, 25%) as diffusion products. Cross-coupling experiments employing [(2)H(10)]1a demonstrated that the formation of 2- and 4-phenylphenol was an intramolecular process. Irradiation of 1a in benzene or in toluene gave biphenyls in good yields. The combined yields of rearrangement products (2and 3) increased with increase of solvent viscosity, with a concomitant decrease in the formation of 4. All the results can be rationalized in terms of excitation of 1a to the singlet state and dissociation to a radical pair intermediate involving phenoxy and phenyl radicals. Intramolecular recombination of these radicals gives rearrangement products, and escape followed by hydrogen abstraction from the solvent gives diffusion products. When position 4 of 1a was occupied by an electron-donating substituent (1b-e), aryloxy-phenyl bond cleavage to give the corresponding rearrangement products prevailed over phenoxy-aryl bond cleavage. The opposite was the case for substrates with an electron-withdrawing substituent at position 4 (1h,i).