Synthetic approach to natural products by Claisen rearrangement of glyceraldehyde derivatives

For the purpose of organic syntheses of some corynanthe-type indole alkaloids, sesquiterpenes, and steroids, optically active intermediates cyclopentanone 3-allylalcohol, α-methylene-γ-butylo lactones andtrans-hydrindanone-propionic acid, were synthesized from (R)- and (S)-isopropylideneglyceraldehyde derived fromD-mannitol andLascorbic acid, respectively, utilizing Claisen rearrangement as a key reaction. Actually total syntheses of natural alkaloids, (-)-antirhine, (+)-dihydroantirhine and (-) dihydrocorynantheol were accomplished.     

Crystal structure of a methyl(methoxy)carbene complex of nickel(II), trans-[Ni(C6Cl5)(PMe2Ph)2{C(OMe)Me}]BF4

The structure of a nickel(II) complex, trans-[Ni(C₆Cl₅)(PMe₂Ph)₂{C(OMe)Me}]BF₄, containing the simplest alkyl(alkoxy)carbene ligand has been determined by X-ray crystallography (R = 0.091). The geometry around the nickel atom is square-planar. The comparatively short NiC(1) bond length of 1.843(10) Å showed the presence of π-bonding in the nickel-carbene bond.     

Catalytic specificity exhibited by p-sulfonatocalix[n]arenes in the methanolysis of N-acetyl-l-amino acids

Specific acid catalysis of p-sulfonatocalix[n]arenes (n = 4, Calix-S4; n = 6, Calix-S6; n = 8, Calix-S8) was observed in the alcoholysis of N-acetyl-l-amino acids in methanol. The methanolysis rates of basic amino acid substrates (His, Lys, and Arg) were markedly enhanced in the presence of Calix-Sn, as compared with rates observed with p-hydroxybenzenesulfonic acid (pHBS), which is a noncyclic analogue of Calix-Sn. This catalytic effect of Calix-Sn was not observed for the methanolysis of Phe, Tyr, and Trp substrates. On the other hand, (1)H NMR experiments following the effect of Calix-Sn on N-acetyl-l-amino acid substrates in CD(3)OD showed that the spectrum of a mixture of the His substrate with Calix-Sn was significantly different from the combined spectra of the respective compounds. These changes in spectra support the formation of an inclusion complex of Calix-Sn with basic amino acids. Furthermore, it was obvious that methanolysis of the His substrate catalyzed by Calix-S4 and Calix-S6 obeyed Michaelis-Menten kinetics. These results indicate that the catalytic activity of Calix-Sn originates from its forming a complex with specific substrates (basic amino acids), similar to enzymatic reactions.     

First principles investigations of hydrazine adsorption conformations on Ni(111) surface

Theoretical investigation on hydrazine (N₂H₄) adsorption on Ni(111) was done by using density functional theory. Stability and mechanism of hydrazine adsorption in anti, gauche and cis conformation on nickel surface were studied. Charge transfer between lone-pair orbital and d-band was found to stabilize the anti-conformation as the most stable conformation, in contrast with hydrazine in the gas-phase where gauche conformation is more favored. However, the derived anti-bonding state between adsorbate and substrate is partially occupied due to the spin-polarization in the local states near the Fermi level and thus contributes in weakening the bonding. The stable adsorption structure was further verified by comparing the calculated vibrational frequencies with HREELS measurement results. The results were found to be in agreement with experimental results. It was also found that the adsorption in cis-conformation is a transition state as evident from the existence of imaginary frequency on its lowest vibrational mode which belongs to NH₂ torsional movement around N–N axis.     

Hydrazine (N2H4) adsorption on Ni(1 0 0) – Density functional theory investigation

A theoretical study on the structure and adsorption mechanism of hydrazine (N₂H₄) on Ni(1 0 0) are presented. The hydrazine molecule was found to adsorb on the surface through one of its nitrogen atom in its anti-conformation. The charge transfer from hydrazine lone pair orbitals played a key role in the formation of the bonding. The mechanism involved in the bonding was found to reduce the necessity of hyper-conjugation interaction, that reduces the gauche effect found in hydrazine at the gas-phase. Upon adsorption to the surface, the reduced interaction resulted in the promotion of a more favored conformation through its anti-conformation.     

A new ent-kaurane diterpenoid glycoside from the leaves of Cussonia bojeri,a Malagasy endemic plant

A new ent-kaurane diterpene glycoside, beta-D-glucopyranosyl 17-hydroxy-ent-kauran-19-oate-16-O-beta-D-glucopyranoside (4) was isolated from the dried leaves of Cussonia bojeri SEEM., together with four known compounds identified as 16beta,17-dihydroxy-kauran-19-oic acid (1), beta-D-glucopyranosyl 16beta,17-dihydroxy-(-)-kauran-19-oate (2), paniculoside IV (3), and rutin (5). The structure of 4 was deduced on the basis of chemical and spectroscopic evidence.     

Continuous variables quantum switch teleportation using two-mode squeezed light

We propose a novel quantum switch teleportation with a continuous variable, which can teleport a quantum state to two different receivers alternatively, using a pair of two-mode squeezed lights as the quantum switching to manipulate the transmission route. In this scheme, the EPR entangled beams shared by sender and receivers are produced by mixing a pair of two-mode squeezed lights on one beamsplitter and separating them by using a polarizing beam splitter. The teleportation capability of this system is examined by the criteria proposed by Ralph and Lam [#!ralph!#] from a small signal quantum optical point of view. Received 20 May 2002 / Received in final form 29 July 2002 Published online 24 September 2002 RID="a" ID="a"e-mail: zhangyun@crl.go.jp     

III–V quantum devices and circuits based on nanoscale Schottky gate control of hexagonal quantum wire networks

The concept, the present status, key issues and future prospects of a novel hexagonal binary decision diagram (BDD) quantum circuit approach for III–V quantum large-scale integrated circuits (QLSIs) are presented and discussed. In this approach, the BDD logic circuits are implemented on III–V semiconductor-based hexagonal nanowire networks controlled by nanoscale Schottky gates. The hexagonal BDD QLSIs can operate at delay-power products near the quantum limit in the quantum regime as well as in the many-electron classical regime. To demonstrate the feasibility of the present approach, GaAs Schottky wrap gate (WPG)-based single-electron BDD node devices and their integrated circuits were fabricated and their proper operations were confirmed. Selectively grown InGaAs sub-10 nm quantum wires and their hexagonal networks have been investigated to form high-density hexagonal BDD QLSIs operating in the quantum regime at room temperature.