Rotamere 2-Phenyl-1,3-dioxane

By means of dipole moment measurements, NMR-spectroscopical methods and force field calculations of o-, m- and p-substituted 2-phenyl-1,3-dioxanes a systematic study concerning the rotameric behaviour of the phenyl group was performed.In o-substituted 2-phenyl-1,3-dioxanes the preferred conformation of the phenyl ligand was found to be displaced about 60 degs. from thecisoid-bisectional conformer. Introduction of an additional substituent in the second o-position gives rise to a change in the rotameric state, the preferred conformation now being bisectional. In contrast, the barriers resisting rotation about the C_ar–C-2-bond in 2-phenyl-1,3-dioxane and its m- and p-substituted derivates turn out to be much lower. Thus at room temperature an ensemble of approximately bisectional rotamers exists.The conformations and rotational barriers determined are discussed in terms of non bonded and dipole-dipole interactions.

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6. Mitt.:H. Lehner, Mh. Chem.107, 565 (1976).     

Synthesen 2-substituierter 3-Indol-alkansäuren

A synthetic approach to 2-alkoxycarbonyl-3-indolealkanoic acidsvia partial saponification of the corresponding diesters is presented. 2-Ethoxycarbonyl-3-indoleacetic acid as well as the homologous propionic and butyric acids may conveniently be prepared by this method. A different synthesis of 3-indoleacetic acids functionalized at position 2 can be accomplished by decomposition of ethyl diazoacetate in the presence of the indole derivative at elevated temperature. Cyclization of 2-hydroxymethyl-3-indoleacetic acid, thus prepared, yields the corresponding -valerolactone. With 1-acyl-indoles and ethyl diazoacetate addition of the carbene to the C-2=C-3 double bond prevails, resulting in the formation of cyclopropanecarboxylic esters.     

Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of chiral semicorrin ligands and general concepts

An efficient synthesis of chiral semicorrin ligands is described (see 6 – 9 , Schemes 2 and 3). Both enantiomers are readily obtained in enantiomerically pure form starting either from D -or L -pyroglutamic acid ( 1 ). Semicorrins of this type possess several features that make them attractive ligands for enantioselective control of metal-catalyzed reactions. Their structure is characterized by C₂ symmetry, a conformationally rigid ligand system, and two stereogenic centers adjacent to the coordination sphere. In a metal complex, the two substituents at the stereogenic centers shield the metal atom from two opposite directions and, therefore, are expected to have a pronounced effect on the stereochemical course of a reaction occurring in the coordination sphere. The structure of these two substituents can be easily modified in a variety of ways. A series of (semicorrinato)copper(II) complexes (see 10 – 14 , Scheme 4) has been prepared, and in one case ( 14 ), the three-dimensional structure has been determined by X-ray analysis (Fig. 1).     

Methodological factors influencing measurement and processing of plasma reelin in humans

Background

Reelin, intensively studied as an extracellular protein that regulates brain development, is also expressed in a variety of tissues and a circulating pool of reelin exists in adult mammals. Here we describe the methodological and biological foundation for carrying out and interpreting clinical studies of plasma reelin.

Results

Reelin in human plasma was sensitive to proteolysis, freeze-thawing and heating during long-term storage, sample preparation and electrophoresis. Reelin in plasma was a dimer under denaturing conditions. Boiling of samples resulted in laddering, suggesting that each of the 8 repeats expressed in reelin contains a heat-labile covalent bond susceptible to breakage. Urinary-type and tissue-type plasminogen activator converted reelin to a discrete 310 kDa fragment co-migrating with the major immunoreactive reelin fragment seen in plasma and also detected in brain. (In contrast, plasmin produced a spectrum of smaller unstable reelin fragments.) We examined archival plasma of 10 pairs of age-matched male individuals differing in repeat length of a CGG repeat polymorphism of the 5'-untranslated region of the reelin gene (both alleles < 11 repeats vs. one allele having >11 repeats). Reelin 310 kDa band content was lower in subjects having the long repeats in all 10 pairs, by 25% on average (p < 0.001). In contrast, no difference was noted for amyloid precursor protein.

Conclusions

Our studies indicate the need for caution in measuring reelin in archival blood samples, and suggest that assays of plasma reelin should take into account three dimensions that might vary independently: a) the total amount of reelin protein; b) the relative amounts of reelin vs. its proteolytic processing products; and c) the aggregation state of the native protein. Reelin-plasminogen activator interactions may affect their roles in synaptic plasticity. Our results also suggest that the human CGG repeat polymorphism affects reelin gene expression, and may affect susceptibility to human disease.

     

Structural reassignment of the mono- and bis-addition products from the addition reactions of N-(Diphenylmethylene)glycinate esters to [60]fullerene under Bingel conditions

The addition of N-(diphenylmethylene)glycinate esters (Ph2C=NCH2CO2R) to [60]fullerene under Bingel conditions gives [60]fullerenyldihydropyrroles and not methano[60]fullerenyl iminoesters [C60C(CO2R)(N=CPh2)] as previously reported. Unequivocal evidence for the structure of C60C(CO2Et)(N=CPh2) was provided by INADEQUATE NMR studies on 13C enriched material. New mechanistic details are proposed to account for the formation of [60]fullerenyldihydropyrroles and their reductive ring-opening reactions.     

A novel approach for one-step forming ε-caprolactam from cyclohexane nitrozation catalyzed by transition metal salt

The nitrozation reaction of cyclohexane in one-step reaction to form ε-caprolactam has been studied using transition metal salt as catalysts in this work. The results indicated that the catalysts play an especially important role. This method is expected to be a novel way to synthesize other lactam by similar reaction. The possible mechanism was suggested.     

The hydrophobicity of nanostructured alkane and perfluoro alkane surfaces: a comparison by molecular dynamics simulation

In this contribution we investigate the differences in the hydrophobicity of a perfluoro-n-eicosane crystal and the n-eicosane crystal by molecular dynamics simulation. The results were analysed in terms of density of water at the interface, the chemical potential of water at the interface and the orientational ordering of water at the interface. The perfluoro-n-eicosane crystal-water interface is found to have a less density, higher chemical potential and a weaker orientational ordering at the interface than the corresponding n-eicosane crystal.