Synthesis and Photochromic Behaviour of Naphthopyrans,Pyranoquinolines, Pyranoquinazolines and Pyranoquinoxalines

New chromenes annulated with different six-membered azaheterocycles were prepared, i.e., the 3H-pyra-no[3,2-f]quinolines 9/10 and 14 , the 8H-pyrano[2,3-h]isoquinoline 11 , the 8H-pyrano[3,2-f]quinazolme 12 , the 8-H-pyrano[3,2-f]quinoxaline 13 , and the 2H-pyrano[2,3-f]isoquinoline 15. The synthesis was achieved using conveniently substituted α,β-unsaturated aldehydes and organotitanium intermediates arising from azaheterocyclic phenols. Their photochromic behaviour (photocolouration yield, UV/VIS spectrum of photomerocyanines, rate constant of thermal bleaching) were studied besides those of corresponding naphthopyrans. The heterocycle effect and the role of substituents in the pyran moiety were investigated quantitatively through the study of the photochromic properties and the solvent effects. Diaryl-substituted azino-fused chromenes, especially isoquinoline derivatives, exhibit increased colourabilities and bathochromically shifted spectra for photomerocyanines which open up new prospects for photochromic applications.     

Synthesis of Allosamidin

The previously prepared disaccharide 2 was deprotected (→ 3 ) and transformed into the trichloroacetimidate 4 . In the presence of Me₃SiOTf, 4 reacted regioselectively with the racemic allosamizoline benzyl ether 5 , to yield (61%) the pseudotrisaccharides 7–10 (44:40:9:7) and the elimination product 6 (Scheme 1). Selective dephthaloylation (MeNH₂, MeOH) of 7 and 8 , followed by acetylation, gave 12 (73%) and 13 (74%), respectively (Scheme 2); harsher conditions (NH₂NH₂.H₂O, EtOH, reflux), followed by acetylation, transformed 7 into 11 . Deacetylation of 11–13 yielded 14–16 , respectively. Allosamidin ( 1 ) was obtained in high yield by hydrogenation of 15 under acidic conditions (Scheme 3). Similarly, 16 and 14 were transformed into 17 and 18 , respectively. Preliminary data on the inhibition of endochitinases by 1 and 17 are reported.     

Direct and indirect effects of UV radiation on DNA and its components.

In this survey, emphasis was placed on the main photoreactions of nucleic acid components, involving both direct and indirect effects. The main UVB- and UVA-induced DNA photoproducts, together with the mechanisms of their formation, are described. Information on the photoproduct distribution within cellular DNA is also provided, taking into account the limitations of the different analytical methods applied to monitor the formation of the DNA damage. Thus, the formation of the main DNA dimeric pyrimidine lesions produced by direct absorption of UVB photons was assessed using a powerful HPLC-tandem mass spectrometry assay. In addition, it was found that UVA photooxidation damage mostly involves the guanine residues of cellular DNA as the result of singlet oxygen generation by still unknown endogenous photosensitizers.     

The Enantioselective Synthesis of the ‘Southern Part’ of Soraphen A

Using a series of enantioselective aldol condensations followed by an ester enolate addition, the cyclic hemiacetal 2 was prepared stereospecifically. Hemiacetal 2 represents the synthetically most challenging ‘southern part’ of the antifungal macrolide soraphen A ( 1 ). Spontaneous enolisation of 26 , the C(2) epimer of 2 , revealed that 2 is the most stable diastereoisomer at room temperature.     

Liquid chromatographic-thermospray mass spectrometric analysis of sesquiterpenes of Armillaria (Eumycota: Basidiomycotina) species

Conventional HPLC analysis of the sesquiterpene aryl esters present in the crude extracts of the pathogenic basidiomycete Armillaria is complicated by difficulties in identification solely on the basis of retention time. On-line coupling of liquid chromatography with thermospray mass spectrometry (LC-TSP-MS) provides a means for their direct detection. Crude extracts of seven Armillaria species were analysed providing a semi-quantitative survey of sesquiterpene aryl ester production within the genus. The distribution of these metabolites and its significance with regard to species differentiation and pathogenicity are discussed. Unknown components were also detected by on-line LC-TSP-MS screening of extracts, facilitating a targeted isolation route.     

Sine-Gordon Theory for the Equation of State of Classical Hard-Core Coulomb Systems. II. High-Temperature Expansion

We perform a high-temperature expansion of the grand potential of the restrictive primitive model of electrolytes in the frame of the extended sine-Gordon theory exposed in the companion paper. We recover a result already obtained by Stell an Lebowitz (J. Chem. Phys. 49, 3706 (1968)) by means of diagrammatic expansions.     

Photo-thermal oxidation of thermoplastic polyurethane elastomers: Part 3—Influence of the excitation wavelengths on the oxidative evolution of polyurethanes in the solid state

The detrimental oxidative reactions which occur in thermoplastic polyurethane elastomers based on aromatic isocyanate monomers during irradiation with polychromatic light (λ > 300 nm) may be accounted for by the interference of two mechanisms. The first mechanism, observed at λ < 330–340 nm, involves a photo-Fries rearrangement. The second mechanism is a photo-induced hydroperoxidation. The photo-Fries products exhibit an anti-ultraviolet effect and partially inhibit the photo-induced oxidation. In contrast to aromatic polyurethane elastomers, aliphatic models exposed to ultraviolet light undergo a photo-induced oxidation which is independent of the excitation wavelength.     

NiCl2-catalyzed hydrophosphinylation

[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating.     

Synthesis, characterization of dihydrolipoic acid capped gold nanoparticles, and functionalization by the electroluminescent luminol

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH > or = 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.