Tridensenal,A Sesquiterpene of Novel Skeleton from the Taiwanese Liverwort Bazzania Tridens

The sesquiterpene aldehyde, tridensenal, of previously unknown skeleton was isolated from the Taiwanese liverwort Bazzania tridens. The structure of tridensenal was elucidated on the basis of spectral data and proved by synthesis of the diastereomeric mixture.     

Palladium catalyzed thiono-thiolo allylic rearrangement of o-allyl phosphoro- and phosphonothionates

A new thiono-thiolo allylic rearrangement of phosphoro- and phosphono-thionates with Pd(PPh₃)₄ catalyst is described, where a variety of thionates are converted to the corresponding thiolates in excellent yields.     

1,2,4-triazines. 1. A convenient synthesis of 4,5-dihydro-1,2,4-triazin-3-(2H)one and its 6-substituted derivatives

A facile synthesis of 4,5-dihydro-1,2,4-triazin-3-(2H)one (2a) from 5-methylthio-1,2,4-triazin-3-(2H)one (1a) with sodium borohydride is described. The reaction provides a convenient method for its 6-substituted derivatives (2b-h).     

O-selective condensation using P-N bond cleavage in RNA synthesis without base protection

In RNA synthesis without base protection, a new method for O-selective condensation with more than 99% selectivity was developed by 6-nitro-HOBt-mediated cleavage of undesired P(III)-N bonds on nucleobase moieties. Moreover, we for the first time succeeded in synthesizing oligoRNAs without base protection.     

Synthesis and properties of DNA oligomers containing 2'-deoxynucleoside N-oxide derivatives

Cytosine and adenine N-oxide derivatives have long been known as products resulting from the oxidative damage of DNA by peroxides such as hydrogen peroxide. Although the synthesis and properties of 2'-deoxynucleoside N-oxide derivatives have been well described, little has been reported about the chemical and biochemical behavior of initially formed DNA oligomers containing these N-oxide bases. In this study, we established a convenient method for the solid-phase synthesis of oligodeoxynucleotides incorporating 2'-deoxycytidine N-oxide (dC O) or 2'-deoxyadenosine N-oxide (dA O) by using the postsynthetic oxidation of N-protected DNA oligomers except for the target dC or dA site with m-CPBA in MeOH in a highly selective manner. In this strategy, the benzoyl, phthaloyl, and (4-isopropylphenoxy)acetyl groups proved to serve as base protecting groups to avoid oxidation of adenine, cytosine, and guanine, respectively, at the unmodified sites.     

Cytosolic Cysteine Synthase Switch Cysteine and Mimosine Production in <Emphasis Type="Italic">Leucaena leucocephala</Emphasis>

In higher plants, multiple copies of the cysteine synthase gene are present for cysteine biosynthesis. Some of these genes also have the potential to produce various kinds of β-substitute alanine. In the present study, we cloned a 1275-bp cDNA for cytosolic O-acetylserine(thiol)lyase (cysteine synthase) (Cy-OASTL) from Leucaena leucocephala. The purified protein product showed a dual function of cysteine and mimosine synthesis. Kinetics studies showed pH optima of 7.5 and 8.0, while temperature optima of 40 and 35 °C, respectively, for cysteine and mimosine synthesis. The kinetic parameters such as apparent K_m, k_cat were determined for both cysteine and mimosine synthesis with substrates O-acetylserine (OAS) and Na₂S or 3-hydroxy-4-pyridone (3H4P). From the in vitro results with the common substrate OAS, the apparent k_cat for Cys production is over sixfold higher than mimosine synthesis and the apparent K_m is 3.7 times lower, suggesting Cys synthesis is the favored pathway.     

Electrochemical study of the assisted transfer of silver ion by 1,5-cyclooctadiene at the 1,6-dichlorohexane/water interface.

The transfer of Ag+ ion across a polarized 1,6-dichlorohexane/water interface assisted by an alkene or olefin ligand, 1,5-cyclooctadiene (COD), was studied by cyclic voltammetry. Even if COD was absent from the organic phase, Ag+ ion gave a reversible voltammetric wave, and the formal potential of the non-assisted ion-transfer at the 1,6-dichlorohexane/water interface was determined from the reversible half-wave potential. By the addition of COD to the organic phase, the reversible half-wave potential shifted to more negative potentials with increasing concentration of COD. The concentration dependence of the half-wave potential revealed that the transfer of Ag+ ion is assisted by the formation of 1:1 and 1:2 Ag+-COD pi-complexes in 1,6-dichlorohexane with overall formation constants of (2.1 +/- 0.2) x 10(3) M(-1) and (7.8 +/- 1.0) x 10(3) M(-2), respectively. The formal potential and the formation constants coincide well with those obtained by the potentiometry of Ag+ ion in aqueous and organic media with a Ag electrode.     

Chemoselective fluorination for primary alcohols

Primary alcohols and their silylated derivatives are selectively fluorinated by tetraalkylammonium fluoride and aryl (or alkyl )sulfonyl fluoride.     

A bioelectrocatalysis method for the kinetic measurement of thermal inactivation of a redox enzyme, bilirubin oxidase.

The thermal stability of a redox enzyme, bilirubin oxidase (BOD), has been quantitatively evaluated by measuring the inactivation kinetics of BOD at several temperatures. The enzyme activity is directly related to the mediated bioelectrocatalytic current for the BOD-catalyzed reduction of O(2). Thus, the inactivation process is measured by the time-dependent decrease in the bioelectrocatalytic current. The results reveal that the inactivation obeys first-order kinetics, whose rate constants (k) are determined at pH 7.0 and at 50 - 70 degrees C. The half life of BOD activity, calculated from the k value at 50 degrees C is 114 min, which is in harmony with the thermal-stability data given in a catalog by Amano Enzyme Inc. The bioelectrocatalysis method allows in situ measurements of the inactivation kinetics in the period of a few minutes at relatively high temperatures. The rate constants show a large temperature dependence, leading to a large Arrhenius activation energy (E(A)) of 221 kJ mol(-1). The activation Gibbs energy (DeltaG(not equal)), activation enthalpy (DeltaH(not equal)), and activation entropy (DeltaS(not equal)) are also determined.