Regio- and stereoselectivity of polar [2+3] cycloaddition reactions between (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone and selected (E)-2-substituted nitroethenes

[2+3] Cycloaddition reactions of the highly reactive (Z)-C-(3,4,5-trimethoxyphenyl)-N-methylnitrone with (E)-2-R-nitroethenes proceed under mild conditions and yield mixtures of stereoisomeric 2-methyl-3-(3,4,5-trimethoxyphenyl)-4-nitro-5-R-isoxazolidines. The effect of regiospecificity of the cycloadditions may be accounted for by the theory of electrophilicity indexes. Stereoselectivity, however, is determined by a compilation of steric and secondary orbital effects.      

Improved Procedure for the Preparation of cis‐2,4‐Dimethylglutaranhydride

Addition of 2.5 mol% DBU to a mixture of isomeric 2,4‐dimethylglutaric anhydrides in ethyl acetate promotes crystallization‐induced transformation, affording the pure cis‐2,4‐dimethylglutaric anhydride in 87% yield.     

Enantioselective Synthesis of D-erythro-Sphingosine and of Ceramide

The enynol 2 was transformed into D -erythro-sphingosine 11 (7 steps, 46%) and into ceramide 1 (8 steps, 41% overall yield). The key steps were the mono-epoxidation of the enynol 5 (Ti(t-BuO)₄, (?)-D -diethyl tartrate, t-BuOOH) to 6 (86%, ≥ 98% ee), the regioselective intramolecular opening of the oxirane 6 via the benzylurethane 7 , and the reductive tranformation of the acetylene 9 into the oxazolidinone 10 (Li, EtNH₂, 88%).     

Functional cellular assays with multiparametric silicon sensor chips

Multiparametric silicon sensor chips mounted into biocompatible cell culture units have been used for investigations on cellular microphysiological patterns. Potentiometric, amperometric and impedimetric microsensors are combined on a common cell culture surface on the chip with an area of approximately 29 mm2. Extracellular acidification rates (with pH-sensitive field effect transistors, ISFETs), cellular oxygen consumption rates (with amperometric electrode structures) and cell morphological alterations (with impedimetric electrode structures, IDES) are monitored on single chips simultaneously for up to several days. The corresponding test device accommodates six of such sensor chips in parallel, provides electronic circuitry and maintains the required cell culture conditions (temperature, fluid perfusion system). Sensor data are transformed into quantitative information about microphysiologic conditions. The outcome of this transformation as well as reliability and sensitivity in detection of drug effects is discussed. This is the first report on multiparametric cell based assays with data obtained solely with integrated sensors on silicon chips. Those assays are required in different fields of application such as pharmaceutical drug screening, tumor chemosensitivity tests and environmental monitoring.     

Does a fluorinated Lewis acid catalyst change the molecular mechanism of the decomposition process of nitroethyl carboxylates?

The molecular mechanism of the decomposition reaction of nitroethyl benzoates catalyzed by Lewis acids based on boron element—BH₃ and BF₃—was studied using density functional theory methods. These reactions take place much faster than the uncatalyzed process. However, the presence of fluorinated Lewis acids has a unique influence on the molecular mechanism. In the case of BF₃, a change from a one-step mechanism to a two-step one involving a zwitterionic intermediate is observed.