(Benzylthio)- und (Arylthio)-substituierte Nitril-ylide: Thermische Erzeugung und Reaktionen

Thermal Generation and Reactions of (Benzylthio)-and (Arylthio)-Substituted Nitrile Ylides Thermolysis of 4-(benzylthio)- and 4-(arylthio)-1,3-oxazol-5(2H)-ones 6 , at 110–155° in the presence of dipolarophiles with activated C≡C, C?C, C?O, C?S, and N?N bonds, led to 5-membered cyclo-adducts and CO² (cf. Schemes 3, 5-7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline-3-carboxylate ( 19 ) and ethyl pyridine-3-carboxylate( 22 ), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio-substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3-dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]-H shift to give 2-aza-1,3-butadienes of type 20 . The latter are trapped in a Diels-Alder reaction with ethyl propiolate (cf. Scheme 8).     

Mise au point d'un calorimetre de reaction en milieu fluorhydrique - enthalpies de dissolution de kf dans les solutions aqueuses de HF

A calorimeter designed for studies of reactions in hydrofluoric acid has been constructed. Enthalpies of dissolution of KF in aqueous solutions of HF (from 1,05 N to 28,3 N) have been measured.     

Etude des enthalpies de dissolution A 298 K des fluorures alcalins dans les solutions aqueuses de HF

Enthalpies of solution of alkali fluorides in aqueous HF have been measured over a wide range of HF concentrations.     

Field desorption mass spectrometry of oligosaccharides in the presence of metallic salts

In the field desorption mass spectrometry of oligosaccharides, traces of contaminating salts in polar solvents decrease the detection sensitivity, and in some cases no ion could be detected in the molecular range. The present work shows that the addition of alkaline salts (NaI or KI) greatly increases the sensitivity, and cationized molecular ions are obtained. The influence of the molar ratio sugar/salt on the nature and relative intensity of the desorbed species has been studied on mixtures of α-D -trehalose and NaI. At the low salt ratio (100:1), high molecular weight clusters [X M + Na]⁺ are preferentially formed. At the high salt ratio (1:10), mixed clusters [M + NaI + Na]⁺, doubly charged ions [M + 2Na]²⁺ and monomeric cationized ions [M + Na]⁺ are observed along with salt clusters [NaI + Na]⁺ and [2NaI + Na]⁺. In the range of molar ratios sugar/salt of 10:1 to 1:1, the field desorption mass spectra exhibit a cationized ion [M + Na]⁺, which contributes more than 80% of Σ₁₀₀. This cationization technique has been applied to the field desorption mass spectrometry of several oligosaccharides. In all cases, the salt effect causes the replacement of the [M + H]⁺ ion by a [M + C]⁺ ion. (Note: the term [M + C]⁺ and similar ones mean an association between the whole molecule studied (M) and an alkaline cation [C]⁺ ([K)]⁺, [Na]⁺, [Li]⁺).) Thus, di, tri- and tetrasaccharides exhibit intense [M + Na]⁺ ions in the presence of NaI and only a few fragment peaks are observed in their field desorption mass spectra. This technique has been applied successfully to the detection of the hexasaccharide ajugose in a natural sample of pentasaccharide, and has also allowed the unambiguous determination of the composition of a mixture of partially methylated trehaloses. The salt effects are dicussed in terms of selective adsorption on the emitter, pre-existing soluble complexes sugar-salt, interactions between these species in the electric field and dissociative desorption of ionic complexes.     

Reactions of triacetic acid lactone with carbonyl compounds. X-Ray structure determination of 3-acetoacetyl-2-chromenone and 3,6,9,12-tetramethyl-1H,6H,7H,12H-6,12-methanodipyrano[4,3-b:4,3-f]-dioxocin-1,7-dione

The structure of 3-acetoacetyl-2-chromenone has been definitely assigned to the product resulting from the reaction of 4-hydroxy-6-methyl-2-pyrone, 1 , with 2-hydroxybenzaldehyde. Also, the reaction of the pyrone 1 with pentane-2,4-dione in a 2:1 molar ratio gives 3,6,9,12-tetramethyl-1H,6H,7H,12H-6,12-methanodypirano[4,3-b:4,3-f]dioxocin-1,7-dione. X-Ray analyses of both products are presented.     

Thermal stability of perfluoroalkanesulfonic acids and their anhydrides. New and easy approach to RFSO2ORF esters.

Perfluoroalkanesulfonic anhydrides (R_FSO₂)₂O when mixed with acids decompose into perfluoroalkanesulfonic esters R_FSO₂OR_F, thereby providing a new facile synthesis of these esters from perfluoroalkanesulfonic acids and phosphorus pentoxide.     

Observation of reversible,rapid changes in drug susceptibility of hypoxic tumor cells in a microfluidic device

Hypoxia is a major stimulus for increased drug resistance and for survival of tumor cells. Work from our group and others has shown that hypoxia increases resistance to anti-cancer compounds, radiation, and other damage-pathway cytotoxic agents. In this work we utilize a microfluidic culture system capable of rapid switching of local oxygen concentrations to determine changes in drug resistance in prostate cancer cells. We observed rapid adaptation to hypoxia, with drug resistance to 2 μM staurosporine established within 30 min of hypoxia. Annexin-V/Sytox Green apoptosis assays over 9 h showed 78.0% viability, compared to 84.5% viability in control cells (normoxic cells with no staurosporine). Normoxic cells exposed to the same staurosporine concentration had a viability of 48.6% after 9 h. Hypoxia adaptation was rapid and reversible, with Hypoxic cells treated with 20% oxygen for 30 min responding to staurosporine with 51.6% viability after drug treatment for 9 h. Induction of apoptosis through the receptor-mediated pathway, which bypasses anti-apoptosis mechanisms induced by hypoxia, resulted in 39.4 ± 7% cell viability. The rapid reversibility indicates co-treatment of oxygen with anti-cancer compounds may be a potential therapeutic target.