A unique reversal of elution order during direct enantiomeric resolution of amide derivatives of 1-phenyl-2-aminopropane by high performance liquid chromatography on chiral stationary phases

Enantiomeric amide derivatives of (S)- and (R)-1-phenyl-2-aminopropane (dextro- and levoamphetamine, respectively) were resolved by high performance liquid chromatography on commercially available ionically and covalently bonded chiral stationary phases ((R)-N-(3,5-dinitrobenzoyl)phenylglycine). Ten enantiomeric amide pairs were synthesized and chromatographed on the columns by using a mobile phase of hexane-isopropanol (97 : 3), a flow rate of 2 ml/min, and a column temperature of 20°C. The (R)-isomer of all 10 amides eluted first on the covalent column as did the (R)-isomer of nine derivatives on the ionic column. however, the 3,5-dinitrobenzoyl amide of (S)- amphetamine eluted before the (R)-isomer on the ionic column. This reversal in enantiomeric elution order reveals the complexity of the interactions occurring on these columns and emphasizes the hazards of relying on observed elution order as an a priori indication of absolute configuration.     

Evidence of steric factors in the fungitoxic mechanisms of 8-quinolinol and its 2-, 3-, 4-, 5-, 6-and 7-chloro and bromo analogues

Summary A study was made of the fungitoxicity of 2-, 3-, 4-, 5-, 6- and 7-chloro and bromo-8-quinolinols againstAspergillus niger,A. oryzae,Myrothecium verrucaria,Trichoderma viride andTrichophyton mentagrophytes in Sabouraud dextrose broth and in Yeast Nitrogen Base supplemented with 1%D-glucose and 0.088%L-asparagine. Based on the presence or absence of synergism between pairs of substituted 8-quinolinols and reversal or nonreversal of toxicity byL-cysteine or N-acetyl-L-cysteine, the following conclusions were reached: (1) substituents on the quinoline ring change the site(s) of action of the toxicant; (2) the sites of action of the 5-, 6-, and 7-chloro-8-quinolinols are different from each other and from 8-quinolinol and its 2-, 3-, and 4-chloro analogues, and the same is true for the corresponding bromo compounds; (3) 8-quinolinol and its 3- and 4-chloro and bromo analogues appear to share common sites of action; (4) for good antifungal activity the 2 position of the ring must not be substituted by sterically bulky groups; (5) the geometry of the binding sites of action are not so constrained that they cannot accommodate the analogously substituted chloro- and bromo-8-quinolinols.

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Nachweis sterischer Faktoren bei der Fungitoxizität von 8-Chinolinol und seinen 2-, 3-, 4-, 5-, 6- und 7-Chlor- und -Brom-Analogen

Zusammenfassung Es wurde eine Studie der Fungitoxizität von 2-, 3-, 4-, 5-, 6- und 7-Chlor- und-Brom-8-chinolinol gegenüberAspergillus niger,A. oryzae,Myrothecium verrucaria,Trichoderma viride undTrichphyton mentagrophytes in Sabouraud Dextrose Nährmedium und in Hefe-N-Base mit 1%D-Glucose und 0.088%L-Asparagin unternommen. Auf der Basis des Zutreffens oder der Abwesenheit eines Synergismus zwischen Paaren von substituierten 8-Chinolinolen und der Umkehrung oder Nichtumkehrung der Toxizität durchL-Cystein oder N-Acetyl-L-cystein wurden folgende Schlußfolgerungen abgeleitet: (1) Substituenten am Chinolin-Ring ändern die Aktionsstelle(n) des Toxikans; (2) Die Angriffsstellen der 5-, 6- und 7-Chlor-8-chinolinole sind untereinander und von 8-Chinolinol und seinen 2-, 3- und 4-Chlor-Analogen verschieden, wobei das auch für die entsprechenden Brom-Verbindungen gilt; (3) 8-Chinolinol und seine 3- und 4-Chlor- und -Brom-Analogen scheinen gemeinsame Aktionsstellen zu teilen; (4) für eine gute antifungale Aktivität darf die 2-Position des Rings nicht mit sterisch anspruchsvollen Gruppen besetzt sein; (5) Die Geometrie des Bindungsstellen der Wirkung ist nicht so gespannt, daß nicht sowohl analoge Chlor- oder Brom-8-chinolinole Platz finden.

     

Reversal of elution order of N‐(2,4‐dinitrophenyl)‐proline and N‐(2,4‐dinitrophenyl)‐serine in HPLC by BSA chiral stationary phase

N‐(2,4‐dinitrophenyl)‐proline and N‐(2,4‐dinitrophenyl)‐serine were enantiomerically resolved on the BSA chiral stationary phase by HPLC in reversed‐phase mode. Effects of chromatographic conditions on enantioseparation and elution order have been investigated in detail. For these two samples, reversal of enantiomer elution order was observed by changing buffer pH, the content of acetonitrile, or alcohol modifiers in mobile phase, which is firstly reported in the BSA chiral stationary phase studies. More interestingly, combined effect between buffer pH and the content of acetonitrile was also observed. In addition, coelution range of enantiomers varied along with the content of acetonitrile in mobile phase.     

Organocatalytic asymmetric fulvene formation

The first catalytic asymmetric formation of a fulvene from a racemic α,α-disubstituted aldehyde has been developed. Dynamic kinetic resolution of rac-2-phenylpropanal by a simple, modularly designed supramolecular organocatalyst consisting of inexpensive components has been established, producing the desired fulvene in good yields and moderate enantioselectivities. Herein we propose a mechanistic interpretation of the observed solvent- and additive-induced stereoselectivity reversal.     

Enantiomer elution order reversal of fluorenylmethoxycarbonyl-isoleucine in high-performance liquid chromatography by changing the mobile phase temperature and composition

In this paper the elution order reversal of enantiomers of fluorenylmethoxycarbonyl- or FMOC-isoleucine is described depending on the separation temperature and composition of the mobile phase when using the polysaccharide-based chiral column Lux Cellulose-1 in HPLC with normal-phase eluent. Reversal of the enantiomer elution order (EEO) in HPLC depending on the column temperature and content of the polar modifier in the mobile phase has been reported before in the literature. However, EEO reversal by changing the content of acidic modifier in the mobile phase seems to be described for the first time in the present work.     

On use of ghost-less beam splitter in reversal shear interferometer for measurement of spatial coherence of large cross-section laser beam

A configuration of reversal shear interferometer suitable for measurement of spatial coherence of high average power, large cross-section laser beam has been discussed. Ghost-less beam splitters in which unwanted multiple reflections from the surfaces have been suppressed by total internal reflection are used for beam splitting and re-combination. Advantages and drawbacks of this configuration have been discussed.     

New strategy for reversal tolerant anode for automotive polymer electrolyte fuel cell

New approach for the reversal tolerant anode for polymer electrolyte membrane fuel cell is suggested by using the multifunctional IrRu alloy catalyst having concurrent superior activities towards hydrogen oxidation reaction and oxygen evolution reaction to mitigate the degradation of anode under the fuel starvation condition.     

On finding multiple Pareto-optimal solutions using classical and evolutionary generating methods

In solving multi-objective optimization problems, evolutionary algorithms have been adequately applied to demonstrate that multiple and well-spread Pareto-optimal solutions can be found in a single simulation run. In this paper, we discuss and put together various different classical generating methods which are either quite well-known or are in oblivion due to publication in less accessible journals and some of which were even suggested before the inception of evolutionary methodologies. These generating methods specialize either in finding multiple Pareto-optimal solutions in a single simulation run or specialize in maintaining a good diversity by systematically solving a number of scalarizing problems. Most classical generating methodologies are classified into four groups mainly based on their working principles and one representative method from each group is chosen in the present study for a detailed discussion and for its performance comparison with a state-of-the-art evolutionary method. On visual comparisons of the efficient frontiers obtained for a number of two and three-objective test problems, the results bring out interesting insights about the strengths and weaknesses of these approaches. The results should motivate researchers to design hybrid multi-objective optimization algorithms which may be better than each of the individual methods.     

基因组重组问题的一个更快算法

寻找一个基因组(源基因组)转化成另一个基因组(目标基因组)所需最少数目移位和翻转的问题,称为基因组重组问题.此问题的“瓶颈”在于寻找源基因组的一个最优“联接”;若源基因组和目标基因组是“共尾”的,Hannenhalli和Pevzner给出一个O(n2)算法得到源基因组的一个最优“联接”,本文将此算法复杂性将低到O(n),其中n为基因组中所含基因的个数.从而由Eric.T和MarieFrance的结果得到求“共尾”标号基因组间重组序列的一个O(nnlogn)算法.     

Arrangement effects of triangular defects on magnetization reversal process in a permalloy dot

The arrangement effects of triangular defects on the magnetization configurations and switching process of a permalloy disk are investigated by micromagnetic simulations. For the case of one defect, the vortex is nucleated via the S state (W state) as the direction of the triangular defect is parallel (perpendicular) to the orientation of the external field. For the case of two defects, two types of switching processes are found dependent on their arrangement. For the two triangular defects with the same direction, the reversal occurs via formation, pinning, depinning and annihilation of the vortex state, however, for the two triangular defects with the opposite directions, the reversal is realized by formation and annihilation of the double-vortex state. The nucleation field for the disk with a triangular defect is more sensitive to the defect position than the case of a circular (square) defect, and it shows different variation trends for different triangular directions. The chirality of the vortex state nucleated in the reversal process can be controlled by the triangular defect.