Total synthesis of myceliothermophins A-E

Total synthesis of an antitumor compound myceliothermophin A and related compounds based on a convergent synthetic strategy was investigated. A common decalin skeleton of myceliothermophins was stereoselectively constructed by an IMDA reaction. The fully elaborated precursor of myceliothermophins was obtained via aldol reaction of N-protected γ-methoxylactam with decalin aldehyde. By using Teoc group for the protection of nitrogen atom of lactam ring, selective deprotection prior to the hydrolysis of methoxyaminal moiety was successfully achieved to obtain γ-methoxylactams (myceliothermophins C and D). Subsequent hydrolysis of these compounds afforded the corresponding γ-hydroxylactam, and myceliothermophins A and B in high yield. Myceliothermophin E was also synthesized by dehydration of the obtained γ-hydroxylactams. The absolute configurations of myceliothermophins A-E were also successfully determined.     

Synthesis of lipophilic bisanthracene fluorophores: versatile building blocks toward the synthesis of new light-harvesting dendrimers

Lipophilic bisanthracene-based fluorophore and its derivatives were synthesized by the Suzuki-Miyaura cross-coupling reaction of 9-anthrylboronic acid with a substituted dibromobenzene. In addition to desirable fluorescent properties, these molecular systems were demonstrated to serve as versatile building blocks toward the synthesis of two types of new light-harvesting dendrimers due to their chemical stability.     

Meeting announcement

Diffusion and solution behavior of methanol vapor in two diblock copolymers, poly(2-vinylpyridine)—block—polyisoprene [P(2VPbI)] and poly(2-vinylpyridine)—block—polystyrene [P(2VPbS)], was studied by the weighing method at 25°C. The domain structure of films of both copolymers showed an alternating lamellar arrangement. Methanol is a good solvent for P2VP, but a nonsolvent for PI and PS. Methanol dissolved exclusively in the P2VP phase of the copolymers. For both copolymer systems, absorption and desorption processes of non-Fickian type were observed as characterized by a thickness anomaly. However, the magnitude of the deviations from purely Fickian behavior was small, and the integral diffusion coefficient, D?, was obtainable with reasonable accuracy. At low and medium concentrations, D? for P(2VPbI) was greater, by about one order of magnitude, than that for P2VP, while D? for P(2VPbS) was lower than that for P2VP. A similar trend was observed in plots of the permeability coefficient against the vapor pressure of methanol. The results indicate that the rubbery PI phase may facilitate the transport of penetrant molecules in the P(2VPbI) film. On the other hand, the glassy PS phase in the P(2VPbS) film merely interferes with the transport of methanol molecules.     

A novel synthesis of α-methylene-γ-butyrolactones from 1-(N,N-dimethylaminomethyl)cyclopropanecarboxylate esters

A new method is reported for constructing α-methylene-γ-butyrolactone moiety under neutral, anhydrous conditions. Olefin-dibromocarbene adducts are transformed to methyl 1-(N,N-dimethylaminomethyl)cyclopropanecarboxylates which in turn are treated with trimethylsilyl iodide and the crude products distilled to give the title compounds with high regio- and stereoselectivity.     

Estimation of monomer reactivity ratios by nonlinear least-squares procedure with consideration of the weight of experimental data

To obtain the optimum values of the monomer reactivity ratios for the copolymerization systems with largely different reactivities between both monomers, a nonlinear least-squares procedure which took into account the weights of experimental data, was proposed and discussed. The weights of the data were treated for the errors arisen from the amounts of monomers charged, the densities of monomers, the weights of copolymer formed, and the composition of copolymer. The least-squares procedure with the consideration of the weights was applicable to both differentiated equation and integrated equation derived by Lewis and Mayo. This procedure was applied to radical copolymerizations of α-substituted crotonic esters with styrene, and reasonable monomer reactivity ratios were obtained. It was noted that errors from the copolymer composition were more important than those from the other factors and that the use of the integrated equation was recommended even when the copolymers were isolated at low conversions.     

Oxygen vacancy promoting catalytic dehydration of formic acid on TiO2(110) by in situ scanning tunneling microscopic observation

The catalytic dehydration reaction processes of formic acid on a TiO2(110) surface at 350 K have been studied to visualize reaction intermediates and their dynamic behaviors by scanning tunneling microscopy. Three types of configurations of adsorbed formates on the surface were identified by their shapes and positions in STM images. Successive STM observations revealed transformations among the three configurations, i.e., bridge formate on a 5-fold coordinated Ti4+ row, bridge formate on an oxygen vacancy site with an oxygen atom of formate and on a 5-fold coordinated Ti4+ ion and with the other formate oxygen atom, and a monodentate formate on an oxygen vacancy site with an oxygen atom of formate. The decomposition of the monodentate formate to carbon monoxide and hydroxyl was also imaged, which is a rate-determining step in the catalytic dehydration of formic acid. Combined with first-principle DFT calculations, the overall reaction processes of the catalytic dehydration of formic acid on the surface have been elucidated. Oxygen vacancies on the surface that can be produced by dehydration of two hydroxyls in situ under the catalytic reaction conditions are essential for the reaction.