Reaction of tetraazathiapentalene and thiadiazolopyrimidine derivatives with heterocumulenes: Cycloaddition and elimination reactions via hypervalent sulfur intermediates

Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2‐pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a‐b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described.     

Asymmetric cyclization of 2-alkenylphenols. A comparative study on the use of palladium(II) and titanium(IV) complexes

The oxidative cyclization of 2-(3-pentenyl)phenol catalyzed by [(η³-pinene)PdOAc]₂ gives optically active (+)-2-vinylchroman (25% e.e.), while (−)-2-(1-hydroxyethyl)chroman (56% e.e.) is formed as a single diastereomer upon treatment with t-BuOOH in the presence of Ti(OⁱPr)₄ and -(+)-diethyl tartrate. 2-(2-Butenyl)phenol also undergoes the Ti-promoted asymmetric cyclization to give (2S,1′R)-(−)-2-(1-hydroxyethyl)-2,3-dihydrobenzofuran (29% e.e.).     

Complete replacement of H2 by D2 via Pd/C-catalyzed H/D exchange reaction

[reaction: see text] A general and in situ D2 gas generation method using 10% Pd/C-catalyzed H2-D2 exchange reaction in a H2-D2O system has been developed. H2 gas sealed in a reaction flask was efficiently converted into nearly pure D2 gas, which can be used for the reductive deuteration of substrates possessing reducible functionalities within the molecule.     

Two-carbon ring expansion of cyclobutanone skeletons by nickel-catalyzed intermolecular alkyne insertion

The reaction of cyclobutanone with an alkyne in the presence of a nickel(0) catalyst formally achieves intermolecular alkyne insertion between the carbonyl carbon and the α-carbon of a cyclobutanone, providing a six-membered carbocyclic skeleton.     

The characteristic fragment ions and visualization of cationic starches on pulp fiber using ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium‐labeled cationic starches were prepared and analyzed using ToF‐SIMS. The starch 2‐hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H₂C?N(CH₃)₂]⁺ and [N(CH₃)₃]^+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Direct observation of the multistep helix formation of poly-L-glutamic acids

The helix formation dynamics of poly-L-glutamic acids (PGAs) were observed by the microsecond-resolved Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopies. The helix formation of 34-residue PGA from random coil at pH (or pD for FTIR) 8.0 was initiated by a pH jump to 4.9 using the rapid solution mixer whose mixing dead time is 50 micros. The amide I' line in the time-resolved FTIR spectra exhibited the fast (<100 micros) increase of the total helical content. The time-resolved CD spectra of the same process also showed the fast (<150 micros) formation of short helical segments (5 +/- 1 residues), which was followed by the slower (<1 ms) elongation of the short helices to longer helices (>10 residues). Similar dynamics were observed for the same pH jump of approximately 190-residue PGA, although there were additional steps that made the helix formation of approximately 190-residue PGA more complex. The observed multistep helix formation is likely caused by the strong hydrogen-bonding interactions between the protonated side chains of PGAs.     

Rapid fermentation of beer using an immobilized yeast multistage bioreactor

The characteristics of yeast sulfite metabolism in a multistage bioreactor system for beer fermentation were investigated. No sulfite was produced in the continuous stirred-tank reactor (CSTR). However, large amounts were produced in the packed-bed reactor (PBR). Production of sulfite in the PBR seems to be inevitable when it is operated continuously. In order to control the sulfite level in the young beer, the yeast needs to be reactivated into the growth phase. One possible strategy to achieve this is to aerate and periodically remove yeast clogged in the reactor once every 6–7 months before the sulfite level exceeds a given concentration (e.g., 20 mg/L). It was confirmed that sulfite production is closely related to the growth condition of the yeast and is therefore important to consider in the control strategy for sulfite when using the immobilized yeast reactor for beer production.     

Synthesis and anti-HIV-1 activity of novel 10-thiaisoalloxazines,a structural analog of C-5 and/or C-6 substituted pyrimidine acyclonucleoside

A series of novel 10-thiaisoalloxazine derivatives bearing an alkoxymethyl or benzyloxymethyl moiety at the N-1 position has been synthesized through the bromination of 1-substituted-5-hydroxyuracils and subsequent condensation with aminobenzenethiol in a one-pot reaction. Contrary to the previous report, the formation of intermediary 5,6-diethoxy-5-hydroxy-5,6-dihydrouracil seems to be not the necessary factor for the formation of the thiaisoalloxazines, since the reaction proceeds in tetrahydrofuran (THF) or acetonitrile far more smoothly than in ethanol. The anti-human immunodeficiency virus (HIV)-1 activity of the resulted thiaisoalloxazine derivatives was evaluated in lymphocyte cells based on the inhibitory activity against the viral-induced cytopathic activity. Among the derivatives, compounds 6, 7, and 8 bearing an alkoxymethyl moiety at the N-1 position exhibited modest inhibitory activity towards the cytotopathic effect of HIV-1.     

Oxime-based salen-type tetradentate ligands with high stability against imine metathesis reaction

Although salen and its analogues are versatile chelate ligands in inorganic and organometallic chemistry, synthesis of unsymmetrical salen derivatives consisting of two different salicylideneimine moieties is difficult because of the C=N bond recombination. To develop stable analogues of salen-type ligands, we synthesized a series of new ligands salamo (=1,2-bis(salicylideneaminooxy)ethane) on the basis of O-alkyl oxime instead of the imine moiety. Eight salamo ligands 1a-h were prepared in 64-88% yields as colorless crystals from the corresponding salicylaldehydes 2a-h. The crystal structure of 1a-c suggests that the oxime-OH form is more predominant than the keto-NH form. The reaction of 2a-e with excess 1,2-bis(aminooxy)ethane gave monooximes 3a-e in 59-86%, which further reacted with a different salicylaldehyde to afford unsymmetrical salamo ligands 4-8 as stable crystals in 51-70%. No reaction took place when a mixture of salamo derivatives 1a and 1b was treated at 40 degrees C in H2O/MeCN (5:95). However, the metathesis reaction of salen derivatives 9a and 9b completed in 2 h to give a statistical mixture. Monooxime 3b was much more stable than monoimine 11 which is difficult to be isolated. These results indicate the extremely high stability of the salamo derivatives 1 and precursors 3.     

Determination of phosphorus in biological material using electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser

Phosphorus has been determined by electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser. The effects of interferents on the phosphorus signal have been investigated. Chemical interferences were eliminated by high-temperature pyrolysis. The detection limit for the molybdenum tube system was 2.3 ng (corresponding to 2.3 micrograms ml-1 when 1 microliter was injected into the atomiser) and the characteristic mass was 1.9 ng of phosphorus. A calibration graph method combined with high-temperature pyrolysis has been evaluated through the determination of phosphorus in biological materials. The sensitivity, accuracy and precision of the method were superior to or nearly equal to those of graphite furnace atomic absorption spectrometry. The advantages of the high-temperature pyrolysis method are its simplicity and low cost.