"N-acyliminium ion pool" as a heterodiene in [4 + 2] cycloaddition reaction

[reaction: see text] An N-acyliminium ion pool was found to undergo cycloaddition reaction with a variety of dienophiles such as alkenes and alkynes. A concerted mechanism seems to be most likely for alkyl-substituted alkenes as suggested by the DFT calculations, whereas a stepwise mechanism plays the major role for aryl-substituted alkenes. It is also noteworthy that the present study demonstrates the potential of the combination of the cation pool method and the micromixing in both mechanistic and synthetic aspects.     

Synthesis of a useful lauryl thioglycoside of sialic acid and its application

An efficient synthesis of a useful thioglycosyl donor 2 was accomplished directly from known peracetylated sialic acid methyl ester and 1-dodecanethiol (lauryl mercaptan) in the presence of BF₃-OEt₂. The reactivities of the lauryl glycosides for glycosidation by means of TMSOTf as a convenient promoter were investigated, and the lauryl thioglycoside showed satisfactory activities. Further transformation of the lauryl glycoside was also attempted to give a 5-azide analogue 14 of the sialic acid, which was also reacted with a secondary alcohol in the presence of TMSOTf to give known glycoside 15 in high yield.     

Vibrational spectra of saccharin nitranion and its orientation on the surface of silver metal particles

Infrared-reflectance spectra of the saccharin nitranion adsorbed on silver powder was observed. Surface-Enhanced Raman Scattering (SERS) spectra of the saccharin nitranion were also recorded using cellulose acetate films doped with fine silver particles. The spectra suggested that the saccharin nitranion is bonded to the silver metal surface through the oxygen atom of carbonyl and the nitrogen atom of the imide ring groups and that the nitranion tilts at the surface.     

Synthesis of 2,3,5-trisubstituted furans by the acid-catalyzed decomposition of 1,2-dioxan-3-ols

Thirteen new 2,3,5-trisubstituted furans were prepared by the acid-catalyzed decomposition of 6,6-di-substituted 1,2-dioxan-3-ols in 57-93% yields. The reaction could be accounted for as the consequence of an oxygen-oxygen bond cleavage by acid and the migration of a phenyl group at the C-6 position followed by cyclization and elimination of a phenol. The migratory aptitude was in the order of 4-MeOC₆H₄- > 4-MeC₆H₄- > Ph- = 4-FC₆H₄- > 4-ClC₆H₄- = 4-BrC₆H₄- that was found from the competitive phenyl migration in the reaction of 1,2-dioxan-3-ols bearing two different substituents at the C-6 position.     

Thermotropic liquid crystalline poly(L-glutamate) esters with long alkyl chain containing aromatic segment at terminal position

Poly(L -glutamate) esters ( 3a – 3d ) with long alkyl side chains containing a mesogenic aromatic segment at the terminal position were synthesized. The superstructure of these polypeptides in solution and film were found to hold a α-helical conformation which was confirmed by CD, IR, and dichroic IR spectroscopy. The thermotropic liquid crystalline behavior was investigated by DSC, x-ray diffraction, and polarizing microscopy with hot stage. Polymers 3a and 3b , having transesterification over 60%, were assumed at least to have two liquid crystalline states. Polymer 3c-H-95 exhibited one crystalline state and two liquid crystalline states; however, 3d-H-97 did not show distinct liquid crystalline states.     

Photoinduced membrane potential changes. Bi-ionic potential across poly(vinyl chloride) membranes entrapping a photoresponsive bis(15-crown-5) derivative and the effects of photoirradiation

Bi-ionic potential (BIP) across poly(vinyl chloride) membranes containing azobenzene-modified bis(15-crown-5) was measured in the presence of alkali-metal chlorides. The BIP measurements revealed the cation selectivity sequence of the membranes (K⁺ > Rb⁺ > Cs⁺ ? Na⁺ > Li⁺), which agreed well with the potentiometric selectivity order of 15-crown-5–based ion-selective electrodes developed so far. UV-light irradiation induced the positive or negative shift of BIP. The magnitude and sign of the photoinduced potential shift depended considerably upon the kind and concentration of electrolytes and, as well, the direction from which the membrane was irradiated. The results were explained in terms of the surface-potential changes induced by light irradiation.     

Two-metal ion, Ni(II) and Cu(II), binding alpha-helical coiled coil peptide

Metalloproteins are an attractive target for de novo design. Usually, natural proteins incorporate two or more (hetero- or homo-) metal ions into their frameworks to perform their functions, but the design of multiple metal-binding sites is usually difficult to achieve. Here, we undertook the de novo engineering of heterometal-binding sites, Ni(II) and Cu(II), into a designed coiled coil structure based on an isoleucine zipper (IZ) peptide. Previously, we described two peptides, IZ-3adH and IZ-3aH. The former has two His residues and forms a triple-stranded coiled coil after binding Ni(II), Zn(II), or Cu(II). The latter has one His residue, which allowed binding with Cu(II) and Zn(II), but not with Ni(II). On the basis of these properties, we newly designed IZ(5)-2a3adH as a heterometal-binding peptide. This peptide can bind Cu(II) and Ni(II) simultaneously in the hydrophobic core of the triple-stranded coiled coil. The first metal ion binding induced the folding of the peptide into the triple-stranded coiled coil, thereby promoting the second metal ion binding. This is the first example of a peptide that can bind two different metal ions. This construction should provide valuable insights for the de novo design of metalloproteins.     

Synthesis of amphiphilic polysiloxanes and their properties for formation of nano-aggregates

In this study, we prepared amphiphilic polysiloxanes by introduction of hydrophobic and hydrophilic parts into a water-soluble poly(3-aminopropyl)siloxane. Fatty acid (lauroyl, myristoyl, palmitoyl, and stearoyl) chlorides and gluconolactone were employed as the reactants for the hydrophobic and hydrophilic parts, respectively. The reaction of the poly(3-aminopropyl)siloxane with fatty acid chlorides was performed in water/DMF, followed by the reaction with gluconolactone in DMSO, giving the corresponding amphiphilic polysiloxanes. The results of the NMR spectra, SEM observations, and DLS measurements indicated the formation of nano-aggregates from the amphiphilic polysiloxanes in water. These analytical data also suggested that the structures and functionalities of the hydrophobic parts affected the formation properties of the nano-aggregates.     

Catalytic four-component assembly based on allenylboronate platform: new access to privileged allylic amine structures

We developed a novel palladium-catalyzed four-component assembly based on allenylboronate platform, by which privileged allylic amine structures can be constructed in a regioselective, stereoselective, and diversity-oriented manner. The boryl group acts not only as a useful group that can be transformed to various functional groups afterward but also as a stereochemical controller in the generation of key (pi-allyl)palladium intermediates. A short synthesis of rolipram (selective phosphodiesterase-4 inhibitor) is also demonstrated.     

Pressure effect on bulk weak ferromagnets: (BDH-TTP)[M(isoq)2(NCS)4] (M = Cr(III), Fe(III); isoq = Isoquinoline)

The pressure dependence of the magnetic properties of weak ferromagnets (BDH-TTP)[M(isoq)2(NCS)4] [BDH-TTP = 2,5-bis(1',3'-dithiolan-2'-ylidene)-1,3,4,6-tetrathiapentalene; M = Cr, Fe; isoq = isoquinoline] is discussed. These salts form two-dimensional magnetic sheets, where ferrimagnetic chains of donor cation radical (S = 1/2) and anion [S = 3/2 (Cr), 5/2 (Fe)] are antiferromagnetically connected by weak donor-donor and anion-anion interchain S...S contacts. Under ambient pressure, both the Cr and Fe salts undergo a weak ferromagnetic transition at Tc = 7.6 K, below which a spontaneous magnetization emerges along the direction perpendicular to the sheets. The application of the pressure elevates the transition temperatures up to 16.6 and 11.6 K at 9 kbar for M = Cr and Fe, respectively. As the pressure increases, the remanent magnetization M(r) decreases, whose pressure dependence for the Cr salt is larger than that for the Fe salt. This difference indicates that the spin-canting angle of the Cr salt is reduced because of the increase of antiferromagnetic interaction by applied pressure, in contrast to the Fe salt, where single-ion anisotropy contributes less. The quantitative analysis of the magnetization curves of the Cr salt using the mean-field approximation reveals that the intermolecular exchange interaction increases as the pressure increases, among which the interchain anion-anion interaction has the highest pressure sensitivity. This result is consistent with the temperature dependence of the crystal structure showing that the thermal contraction in the distances of interchain anion-anion S...S contacts is the most remarkable in intrachain S...S contacts. The large pressure dependence of the transition temperature of these salts is therefore explained as a result of the fact that the interchain interactions, the anion-anion interaction in particular, are strengthened by applied pressure.