Réactivité de β-énaminones cycliques. II. Cyclocondensation directe d'amidines,d'hydrazines et de l'hydroxylamine sur la pyrrolidinométhylène-3 chromanone-4

The reaction of pyrrolidinomethylenechromanone 1 with guanidine and amidines gave benzopyrannopyrimidines 5 in good yields. Treatment of enaminone 1 with hydroxylamine in the presence of hydrochloric acid afforded the isoxazole 9 . When hydrazine and phenylhydrazine were used as the condensing agents under acidic conditions, benzopyranno-pyrazoles 11a and 11b formed similarly; with methylhydrazine, a mixture of methyl isomers 11c and 11′c formed in a ratio of 7525.     

Light-Induced Synthesis of Tricyclic Thiolane Derivatives from 2(5H)-thiophenones via consecutive radical ring closure

Two α,β-unsaturated thiolactones, 5-(2-propynyl)-2(5H)-thiophenone (5) and 3,5-di(2-propenyl)?2(5H)-thiophenone (6) , were newly synthesized. Irradiation (λ = 300 nm) of 5 in MeOH containing cyclopentene afforded a 3:1 mixture of diasteroisomeric methyl 7-thiatricyclo[6.4.0.0^2,6]dodec-10-ene-12-carboxylates (8a/8b) , while irradiation of 6 in MeOH saturated with 2-methylpropene gives a 3:2 mixture of diastereoisomeric methyl 3,3,9-trimethyl-5-thiatricyclo[6.2.1.0^2,6]undecane-1-carboxylates ( 10a / 10b ).     

La reaction de wittig-horner en milieu heterogene VI1. Selectivite de la reaction sur des composes bifonctionnels

Heterogenous media of low basicity (K₂CO₃ or KHCO ₃), liquid-liquid or solid-liquid allow the Wittig-Horner reaction of fragile and unprotected aldehydes (hydroxyaldehydes, nitroaldehyde and ketoaldehydes) with excellent yields. The reaction is applied to the synthesis of Royal Jelly acid and Queen Substance of Honey bee.     

Application of hyphenated techniques to the chromatographic authentication of flavors in food products and perfumes

This work presents two techniques for testing for the adulteration of flavors. One uses multidimensional gas chromatography on cyclodextrin derivatives to separate chiral compounds, the other uses isotope ratio mass spectrometry coupled with gas chromatography to determine stable isotope ratios. Applications to fruits and plants for the food and perfume industry are introduced.     

N,N'-linked oligoureas as foldamers: chain length requirements for helix formation in protic solvent investigated by circular dichroism, NMR spectroscopy, and molecular dynamics

N,N'-linked oligoureas with proteinogenic side chains are peptide backbone mimetics belonging to the gamma-peptide lineage. In pyridine, heptamer 4 adopts a stable helical fold reminiscent of the 2.6(14) helical structure proposed for gamma-peptide foldamers. In the present study, we have used a combination of CD and NMR spectroscopies to correlate far-UV chiroptical properties and conformational preferences of oligoureas as a function of chain length from tetramer to nonamer. Both the intensity of the CD spectra and NMR chemical shift differences between alphaCH2 diastereotopic protons experienced a marked increase for oligomers between four and seven residues. No major change in CD spectra occurred between seven and nine residues, thus suggesting that seven residues could be the minimum length required for stabilizing a dominant conformation. Unexpectedly, in-depth NMR conformational investigation of heptamer 4 in CD3OH revealed that the 2.5 helix probably coexists with partially (un)folded conformations and that Z-E urea isomerization occurs, to some degree, along the backbone. Removing unfavorable electrostatic interactions at the amino terminal end of 4 and adding one H-bond acceptor by acylation with alkyl isocyanate (4 --> 7) was found to reinforce the 2.5 helical population. The stability of the 2.5 helical fold in MeOH is further discussed in light of unrestrained molecular dynamics (MD) simulation. Taken together, these new data provide additional insight into the folding propensity of oligoureas in protic solvent and should be of practical value for the design of helical bioactive oligoureas.     

Nitrite catalyzes ferriheme protein reductive nitrosylation

Nitrite ion is found to catalyze the NO reduction of met-hemoglobin and met-myoglobin in pH 7.0 buffered aqueous solution. The catalysis rate constants for these ferriheme proteins and for two water-soluble ferriheme model systems follow the same order as do the FeIII/II reduction potentials of the ferric nitrosyl complexes. This is consistent with a proposed mechanism occurring via outer sphere reduction of the FeIII(NO) center by NO2- to give the FeII(NO) product plus NO2. Although the first step is thermodynamically uphill, the NO2 generated would be rapidly trapped by excess NO to form N2O3, which would hydrolyze. We speculate that, if formed in the proximity of the protein, the strong nitrosating agent N2O3 could also result in protein modifications.     

Peracid oxidation of benzothiopyranthiones and benzopyranthiones

Benzothiopyran-2 and 4-thiones and benzopyran-2-thiones undergo oxidation to sulphines which on further oxidation give the carbonyl derivatives or polymeric products.

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Persäure-Oxidation von Benzothiopyranthionen und Benzopyranthionen (Kurze Mitteilung)

Zusammenfassung Benzothiopyran-2 und 4-thione und Benzopyran-2-thione werden mit Persäuren zu Sulfinen oxidiert, die ihrerseits bei weiterer Oxidation die Carbonylderivate oder polymere Produkte ergeben.

     

Asymmetric ABC-triblock copolymer membranes induce a directed insertion of membrane proteins

Asymmetric molecules and materials provide an important basis for the organization and function of biological systems. It is well known that, for example, the inner and outer leaflets of biological membranes are strictly asymmetric with respect to lipid composition and distribution. This plays a crucial role for many membrane-related processes like carrier-mediated transport or insertion and orientation of integral membrane proteins. Most artificial membrane systems are, however, symmetric with respect to their midplane and membrane proteins are incorporated with random orientation. Here we describe a new approach to induce a directed insertion of membrane proteins into asymmetric membranes formed by amphiphilic ABC triblock copolymers with two chemically different water-soluble blocks A and C. In a comparative study we have reconstituted His-tag labeled Aquaporin 0 in lipid, ABA block copolymer, and ABC block copolymer vesicles. Immunolabeling, colorimetric, and fluorescence studies clearly show that a preferential orientation of the protein is only observed in the asymmetric ABC triblock copolymer membranes.     

Luminescent transition metal complexes as sensors: structural effects on pH response

A series of luminescent transition metal complexes using the pH-sensitive ligand 5-carboxy-1,10-phenanthroline has been synthesized and characterized. The complexes, based on Ru(II) and Re(I), show monotonic changes in both luminescent intensity and lifetime with pH values over the range 2 < pH < 9. The impact of various structural features on both the range of pH sensitivity and dynamic response was studied using both intensity and lifetime measurements. It was possible to predictably tune the pH sensitivity range over about 1.5 pKa units. While significant variation in the dynamic response range was observed, the correlation with structural features needs further study.