Enantiopure fluorous bis(oxazolines): synthesis and applications in catalytic asymmetric reactions

Various enantiopure fluorous bis(oxazolines) with fluorine content between 52.7 and 58.7% have been synthesized by a simple reaction sequence that involved the introduction of two fluorinated ponytails by alkylation of the corresponding nonfluorous bis(oxazolines). These new ligands have been used in palladium-catalyzed alkylation of rac-(E)-1,3-diphenylpropenyl acetate with carbon nucleophiles and in copper-catalyzed oxidation of cycloalkenes; these ligands exhibited enantioselectivities up to 98 and 77%, respectively, quite close to the values obtained using the analogous nonfluorous bis(oxazolines). These ligands could be easily recovered by liquid-liquid extraction or solid-liquid separation and reused with the same enantioselectivities.     

LCAO-MO-SCF-CI semi-empirical π-electron calculations on heteroaromatic systems

The electronic spectra and structure for phenol, the three dihydroxybenzene isomers, and - and -naphthol have been calculated using a modification of the Pariser-Parr-Pople method. Core integrals are defined to be essentially independent of geometry and orthogonalized atomic orbitals are used. The electronic transitions considered involve singlet-singlet and triplet-triplet ^* excitations. A limited configuration interaction has been included, involving either single electron excitations or both single and double electron excitations between the two highest occupied and the two lowest unoccupied molecular orbitals. Agreement between calculated and experimental values is good, and calculated values for oscillator strengths are considerably improved when double electron excitations are admitted.

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Zusammenfassung Die Elektronenspektren und Struktur von Phenol, den drei Isomeren des Dihydroxybenzols und - und -Naphthol wurden mit einer Modifikation der PPP-Methode berechnet. Die Rumpfintegrale werden so definiert, daß sie im wesentlichen unabhängig von der Geometrie sind; es werden orthogonalisierte Atomorbitale benutzt. Die betrachteten Elektronenübergänge enthalten Singulett-Singulett- und Triplett-Triplett- ^*-Übergänge. Es wurde eine begrenzte Konfigurationswechselwirkung eingeschlossen, die nur Einelektronen- oder Ein- und Zweielektronenanregung zwischen den beiden höchsten besetzten und den beiden niedrigsten unbesetzten MO's enthält. Es besteht gute Übereinstimmung von berechneten und experimentellen Daten. Die berechneten Werte für Oszillatorenstärken werden erheblich verbessert, wenn man Zweielektronenanregung einbezieht.

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Résumé Les spectres électroniques et les structures du phénol, des trois dihydroxybenzènes isomères, de l' et du naphtol ont été calculé pour une variante de la méthode de Pariser-Parr-Pople. Les intégrales de coeur sont définies de manière à être indépendantes de la géométrie et des orbitales atomiques orthogonalisées sont employées. On considère les transitions électroniques ^* singulet-singulet et triplet-triplet. Une interaction de configuration limitée a été effectuée en considérant soit des minoexcitations soit des mono et des diexcitations de la plus haute orbitale occupée aux deux orbitales libres les plus basses. L'accord entre les valeurs calculées et les valeurs expérimentales est bon, et les valeurs calculées des forces oscillatrices sont considérablement améliorées lorsque l'on tient compte des états diexcités.

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This investigation was supported by a National Science Foundation grant, No. GB-4065. Abstracted in part from the Ph. D. thesis of G. W. Pukanic, Duquesne University, 1967.     

Solid State NMR and TG/MS Study on the Transformation of Methyl Groups During Pyrolysis of Preceramic Precursors to SiOC Glasses

The sol-gel method was used to prepare two different starting gels containing SiCH₃-groups for the preparation of SiOC ceramics. To understand the role of Si—H bonds in the incorporation of carbon into the SiOC network, gels prepared from a 1:2 mixture of triethoxysilane and methyldiethoxysilane (T^HD^H2) and solely methyltriethoxysilane (T^Me) were investigated. Thermogravimetric analysis coupled with mass spectroscopy (TG-MS) in inert atmosphere was performed to attain an insight into the decomposition reactions involved during gel-glass transformation. Samples calcined at different temperatures up to 1000°C were characterized by ²⁹Si and ¹³C magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The presence of SiH groups in the starting gel allows an efficient conversion of Si—CH₃ groups into CSi₄ sites at lower temperatures. As a result, despite a much lower amount of carbon in the starting T^HD^H2 gel (C/Si = 0.33) compared to the T^Me gel (C/Si = 1), the amount of carbon inserted into the SiOC network of both glasses is equivalent, but the T^Me sample contains the 10 fold amount of free carbon.     

EVENTS SURROUNDING THE EARLY DEVELOPMENT OF EUGLENA CHLOROPLASTS. 12. SPECTROSCOPIC EXAMINATION OF THE PROTOCHLOROPHYLL(IDE) PHOTOTRANSFORMATION IN INTACT CELLS*

Abstract— Absorption measurements in the 600–720 nm region of dark-grown cells of Euglena gracilis Klebs var. bacillaris Cori were made in vivo at room temperature using computer-assisted spectrophotometry. Dark-grown wild-type cells have a prominent absorption maximum at 634 nm due to protochlorophyll(ide) absorption. Upon illumination, the absorption at 634nm decreases and a peak appears at 674nm, representing the phototransformation of protochlorophyll(ide) to chlorophyll(ide). Using difference spectroscopy, the resynthesis in the dark of protochlorophyll(ide) by previously-illuminated wild-type dark-grown cells was found to begin at about 10min after illumination and reached completion by about 25 min, the amount of protochlorophyll(ide) resynthesized being equivalent to that of dark-grown cells. Resynthesis of protochlorophyll(ide) following a second illumination follows the same kinetics, indicating that protochlorophyll(ide) resynthesis is under tight regulation, possibly via feedback control. Cells of dark-grown wild-type and W₃BUL, a mutant lacking protochlorophyll(ide) contain a component absorbing at 658 nm which does not undergo phototransformation when examined by difference spectroscopy at room and liquid N₂ temperatures. Following the phototransformation of protochlorophyll(ide) 634 to chlorophyll(ide) 674, the chlorophyll(ide) 674 shifts to shorter wavelengths, ultimately to 671 nm. Possible relationships among the various spectroscopic forms of protochlorophyll(ide) and chlorophyll(ide) at room temperature and liquid N₂ temperature in Euglena and higher plants are presented. It is concluded that Euglena, unlike older, etiolated higher plants, contains only protochlorophyll(ide) 634, making it an excellent system in which to examine the phototransformation of this pigment species in the absence of other forms.     

Spectral,Optical and Mechanical studies on pure and thiourea doped ammonium di-hydrogen phosphate NLO single crystals

Pure and thiourea substituted single crystals of ammonium di-hydrogen phosphate have been grown from aqueous solution by isothermal solvent evaporation technique. Doped crystal exhibits prominent changes in physical and chemical properties. Single crystal XRD analyses of the samples are carried out and the results are compared. FTIR and UV–vis–NIR spectral analyses have been employed to identify the presence of various functional groups and the UV cut-off range in the grown crystals. Density measurements have been made and Photoconductivity studies revealed the negative photo conducting nature. Hardness measurement shows that the mechanical strength of the doped crystal is high when compared to pure ammonium di-hydrogen phosphate. The dielectric response of the samples has been studied in the frequency range 100 Hz–5 MHz at room temperature and the results are discussed.     

An Efficient Process for the Synthesis of Renin Inhibitor,ABT-517

An efficient process for the preparation of renin inhibitor, ABT-517 is described. The process avoids solvent extractions or chromatographic purifications and is used on multi-kilogram scale.     

VinaMPI: Facilitating multiple receptor high‐throughput virtual docking on high‐performance computers

The program VinaMPI has been developed to enable massively large virtual drug screens on leadership‐class computing resources, using a large number of cores to decrease the time‐to‐completion of the screen. VinaMPI is a massively parallel Message Passing Interface (MPI) program based on the multithreaded virtual docking program AutodockVina, and is used to distribute tasks while multithreading is used to speed‐up individual docking tasks. VinaMPI uses a distribution scheme in which tasks are evenly distributed to the workers based on the complexity of each task, as defined by the number of rotatable bonds in each chemical compound investigated. VinaMPI efficiently handles multiple proteins in a ligand screen, allowing for high‐throughput inverse docking that presents new opportunities for improving the efficiency of the drug discovery pipeline. VinaMPI successfully ran on 84,672 cores with a continual decrease in job completion time with increasing core count. The ratio of the number of tasks in a screening to the number of workers should be at least around 100 in order to have a good load balance and an optimal job completion time. The code is freely available and downloadable. Instructions for downloading and using the code are provided in the Supporting Information. © 2013 Wiley Periodicals, Inc.