Effect of Brønsted acid co-catalyst in asymmetric conjugate addition of 3-aryloxindoles to maleimide under base-free phase-transfer conditions

Highly diastereo- and enantioselective conjugate addition of 3-aryloxindoles to maleimide was accomplished under base-free phase-transfer conditions. The effect of Brønsted acid co-catalyst was examined, and we found that the use of a phenol derivative as co-catalyst was effective for obtaining the target conjugate adduct in good yield with high stereoselectivity.     

Regioselective Cage Opening of La2@D2(10611)‐C72 with 5,6‐Diphenyl‐3‐(2‐pyridyl)‐1,2,4‐triazine

The thermal reaction of the endohedral metallofullerene La₂@D₂(10611)‐C₇₂, which contains two pentalene units at opposite ends of the cage, with 5,6‐diphenyl‐3‐(2‐pyridyl)‐1,2,4‐triazine proceeded selectively to afford only two bisfulleroid isomers. The molecular structure of one isomer was determined using single‐crystal X‐ray crystallography. The results suggest that the [4+2] cycloaddition was initiated in a highly regioselective manner at the C? C bond connecting two pentagon rings of C₇₂. Subsequent intramolecular electrocyclization followed by cycloreversion resulted in the formation of an open‐cage derivative having three seven‐membered ring orifices on the cage and a significantly elongated cage geometry. The reduction potentials of the open‐cage derivatives were similar to those of La₂@D₂‐C₇₂ whereas the oxidation potentials were shifted more negative than those of La₂@D₂‐C₇₂. These results point out that further oxidation could occur easily in the derivatives.     

PyBidine–Cu(OTf)2‐Catalyzed Asymmetric [3+2] Cycloaddition with Imino Esters: Harmony of Cu–Lewis Acid and Imidazolidine‐NH Hydrogen Bonding in Concerto Catalysis

A bis(imidazolidine)pyridine (PyBidine)–Cu(OTf)₂ complex catalyzing the endo‐selective [3+2] cycloaddition of nitroalkenes with imino esters was applied to the reaction of methyleneindolinones with imino esters to afford spiro[pyrrolidin‐3,3′‐oxindole]s in up to 98 % ee. X‐ray crystallographic analysis of the PyBidine–Cu(OTf)₂ complex and DFT calculations suggested that an intermediate Cu enolate of the imino ester reacts with nitroalkenes or methyleneindolinones, which are activated by NH‐hydrogen bonding with the PyBidine–Cu(OTf)₂ catalyst.     

Regio‐ and Stereoselective Conjugate Addition of Aldehydes to β‐Tosyl Enones under the Catalysis of a Binaphthyl‐Modified Chiral Amine

A simple axially chiral amine catalyst promoted the regio‐, diastereo‐, and enantioselective conjugate addition of aldehydes to β‐tosyl enones, which serve as ynone surrogates. The adducts were readily converted by treatment with L‐selectride into less accessible enones with a γ stereogenic center. Such compounds cannot be prepared through the amine‐catalyzed conjugate addition of aldehydes to ynones. The obtained enones underwent further conjugate addition of diorganozinc compounds in the presence of a copper catalyst.     

Biomineralization of a Cadmium Chloride Nanocrystal by a Designed Symmetrical Protein

We have engineered a metal‐binding site into the novel artificial β‐propeller protein Pizza. This new Pizza variant carries two nearly identical domains per polypeptide chain, and forms a trimer with three‐fold symmetry. The designed single metal ion binding site lies on the symmetry axis, bonding the trimer together. Two copies of the trimer associate in the presence of cadmium chloride in solution, and very high‐resolution X‐ray crystallographic analysis reveals a nanocrystal of cadmium chloride, sandwiched between two trimers of the protein. This nanocrystal, containing seven cadmium ions lying in a plane and twelve interspersed chloride ions, is the smallest reported to date. Our results indicate the feasibility of using rationally designed symmetrical proteins to biomineralize nanocrystals with useful properties.     

Parallel computing of radiative transfer in relativistic jets using Monte Carlo method

We present numerical attempts of radiative transfer in a relativistic scattering flow that can produce gamma rays using a three-dimensional Monte Carlo code. We prepared an initial background flowfield obtained from hydrodynamical simulation of a relativistic jet in which Thomson scattering dominates compared to absorption, and solved the radiative transfer equation for the background evolved by a simple expansion model. Since a large number of sample particles is required for an accurate computation, we have parallelized the Monte Carlo code in order to obtain solutions in a practical computational time even for a long-term simulation coupled with a time-dependent flowfield. Using this code, higher parallel efficiency is achieved with larger number of particles. The obtained light curve from the simple model shows a signal of the transition from the opaque post-shock flow to the transparent regime as the flow expands, and the high-energy photons are generated by not only the Doppler boosting but also the inverse Compton scattering.     

Synthetic construction of a fucosyl chitobiose as an allergen-associated carbohydrate epitope and the glycopolymer involving highly clustered trisaccharidic sequences

Synthetic construction of fucosyl chitobiose [GlcNAcβ1→4(Fucα1→3)GlcNAc] as an allergy-associated carbohydrate epitope was accomplished from three building blocks. The trisaccharidic unit was further transformed into a carbohydrate monomer and polymerization of the glycomonomer proceeded smoothly to provide a series of glycopolymers having various carbohydrate densities. In addition to the organic syntheses, biological evaluations of the glycomonomer and the polymers were carried out and sugar-clustering effects were observed.