Preparation of 1-ferrocenyl-2-methyl-1-propylamine,a highly effective chiral template in asymmetrically induced synthesis

The 1-ferrocenyl-2-methyl-1-propylamine (2a)is the most effective chiral template in asymmetrically induced peptide synthesis by stereoselective four component condensation (4CC). Two routes for the synthesis of this amine via its N,N-dimethyl derivative (12a) an described. One route involves the conversion of 12a into the corresponding azide 14a by treatment with methyl iodide/sodium azide in diglyme/water and subsequent reduction of the azide. The preferred other route consists of treating 12a with thioglycolic acid/formic acid to yield the carboxymethylmercapto derivative 9a and transformation of the latter into 2a with aqueous ammonia/ammonium chloride/mercuric chloride. Some related reactions are also discussed.     

Different approaches toward an automatic structural alignment of drug molecules: Applications to sterol mimics,thrombin and thermolysin inhibitors

Summary A relative comparison of the binding properties of different drug molecules requires their mutual superposition with respect to various alignment criteria. In order to validate the results of different alignment methods, the crystallographically observed binding geometries of ligands in the pocket of a common protein receptor have been used. The alignment function in the program SEAL that calculates the mutual superposition of molecules has been optimized with respect to these references. Across the reference data set, alignments could be produced that show mean rms deviations of approximately 1 Å compared to the experimental situation. For structures with obvious skeletal similarities a multiple-flexible fit, linking common pharmacophoric groups by virtual springs, has been incorporated into the molecular mechanics program MOMO. In order to combine conformational searching with comparative alignments, the optimized SEAL approach has been applied to sets of conformers generated by MIMUMBA, a program for conformational analysis. Multiple-flexible fits have been calculated for inhibitors of ergosterol biosynthesis. Sets of different thrombin and thermolysin inhibitors have been conformationally analyzed and subsequently aligned by a combined MIMUMBA/SEAL approach. Since for these examples crystallographic data on their mutual alignment are available, an objective assessment of the computed results could be performed. Among the generated conformers, one geometry could be selected for the thrombin and thermolysin inhibitors that approached reasonably well the experimentally observed alignment.     

Die Bestimmung geringer Mengen Quecksilber

Zusammenfassung Durch colorimetrische Bestimmung mit p-Dimethylaminobenzylidenrhodanin ist es möglich, 20–150 g Quecksilber in 100 ml Lösung gut reproduzierbar neben den meisten anderen Metallen direkt zu erfassen. Ist der Quecksilbergehalt der zu analysierenden Proben gering, kann Quecksilber durch Zementation mit Kupferpulver angereichert werden. Die Zementation gelingt aus schwach sauren, auch salpetersäurehaltigen Lösungen praktisch vollständig, wenn 3 Std gerührt wird und etwa in der Lösung vorhandene oxydierende Substanzen zuvor mit SO₂ reduziert werden. Zur Zementation gut geeignetes Kupferpulver ist durch Ausfällen mit Zinkpulver aus schwach saurer Kupfersulfatlösung zu gewinnen. Das Zementat, Kupferpulver mit anhaftendem Quecksilber, wird nach Filtration in Salpetersäure gelöst und die Lösung dann direkt colorimetriert. Bei Einwaagen von etwa 10 g Probesubstanz können nach der beschriebenen Methode noch Gehalte von 2–5 ppm Hg mit einem Fehler von ±10% bestimmt werden.     

CZE separations of basic proteins at low pH in fused silica capillaries with surfaces modified by silane derivatization and/or adsorption of polar polymers

Mixtures of several basic proteins have been used to test CZE capillaries with surfaces modified by new pretreatment procedures; the performance obtained has been compared with that achieved using capillaries treated by procedures described in the literature. It has been shown that addition of non-ionic polyvinylalcohols (PVA) to CZE buffer solutions deactivates even bare, i.e. untreated, fused silica surfaces and renders them suitable for separations of basic proteins. The performance obtained from such surfaces was comparable with that of capillaries modified by the more elaborate procedures of etching, silanol derivatization, and/or adsorptive coating (again with polymers). A home-made device is described which enables derivatization and coating reactions to be performed on fused silica capillaries under an inert atmosphere, i.e. one free from oxygen and water.     

Optical sensor materials for the detection of amines in organic solvents

A new optical polymer-based sensor was developed, which is able to recognize amines in organic solvents with high sensitivity. Thin polymer membranes were prepared and investigated, which contain a chromogenic functional dye (reactand) that shows a significant colour change during a reversible chemical reaction with the analyte. For that purpose the azo dye 4-trifluoroacetyl-4′-[N-(methacryloxyethyl)-N-(ethyl)amino]-azobenzene (CR-465) was synthesized, which contains a trifluoroacetyl moiety (receptor for interaction with amines) and in addition, a polymerizable methacrylate group. The methacrylate group links the dye covalently to the polymer matrix and the receptor recognizes the analyte via covalent binding. For immobilisation of the dye cross-linked methacrylate polymers with different composition were used. The highly cross-linked polymer network was stable against most organic solvents and exhibited enhanced stability against mechanical strain compared to plasticized PVC. The sensitivity of the reaction between the analyte and the dye was tailored by the choice of the solvent in which the analysis of the sensor layer was performed, with equilibrium constants for 1-butylamine ranging from 80 to 2000 M⁻¹ in chloroform and DMSO, respectively. In toluene as the solvent, sensor layers typically exhibited equilibrium constants of 100 M⁻¹ for 1-butylamine, 1300 M⁻¹ for 1,4-diaminobutane and 20,000 M⁻¹ for tris-(2-aminoethyl)amine. We have also investigated the cross-linked sensor layers with respect to molecular imprinting and did not find any enhancement in selectivity through imprinting in the presence of different analyte molecules.     

DETERMINATION OF THE KINETICS OF THE BACK REACTION OF PHOTOSYSTEM II IN THE PRESENCE OF 3–(3,4-DICHLORPHENYL)-1,1-DIMETHYLUREA FROM LUMINESCENCE MEASUREMENTS

Abstract— An alternative method to that used by Mar and Roy (1974) for the determination of the kinetics of the back reaction of photosystem II from the luminescence decay curve in the presence of 3–(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) has been suggested. The new theory relies upon two hypotheses: the well-known recombination hypothesis of luminescence and the assumption that the luminescence yield in the seconds region is given by the variable part of the live fluorescence yield. The second hypothesis was introduced since assuming a constant luminescence yield results in kinetic data that are not consistent with measurements of the kinetics of the back reaction by the restoration of the area over the fluorescence rise curve. The dependence of the live fluorescence yield from the concentration of closed PS II traps was assumed to be represented by Delosme's expression originally derived for the rise curve of the fluorescence yield in the presence of DCMU.
The theory is based on the fact that then the partial and total light sums of luminescence are simple functions of the concentration of the primary electron acceptor Q^- of PS II. Thus, after integrating the luminescence decay curve the theory permits a convenient evaluation of the kinetics of the back reaction [Q^-]( t ) in terms of the partial and total light sum.
This method was applied in order to determine the kinetics of the back reaction in Chlorella fusca in the presence of DCMU. It is shown that the kinetics of deactivation of the S, state can be described using the expression for the kinetics of the back reaction derived by Mar and Roy. As an alternative explanation, a biphasic first order decay of S₂ is proposed.     

Elektrophile Substitution und nucleophile Addition an 3,4-Dihydro-5(1H)-pyrromethenonen

3,4-Dihydro-5(1H)-pyrromethenones are easier attacked at themeso-position by electrophiles than 5(1H)-pyrromethenones. This is demonstrated both by aMannich-type-substitution or deuterium-exchange-experiments and by the addition of O-, S-, and N-Nucleophiles to the exocyclic double bond of the model-dihydropyrromethenone (Z)-1 under very mild reaction conditions. Applying these results to the chemistry of 2,3-dihydro-bilatrienes-abc, their chemical characteristics—especially their tautomeric behavior and their dominant C-5-selectivity towards electrophiles—become better understandable.

     

Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh₃)(CH₃CN)₂]⁺ (E=P, As, Sb, Bi) and [RuCp(EPh₃)(η³-C₃H₅)Br]⁺ have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh₃ either via a RuE or a η⁶-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH₃CN)₃]⁺ does not react with BiPh₃ to give [RuCp(BiPh₃)(CH₃CN)₂]⁺ but instead gives only the η⁶-arene species [RuCp(η⁶-PhBiPh₂)]⁺ and [(RuCp)₂(μ-η⁶,η⁶-Ph₂BiPh)]²⁺. Similarly, the EPh₃ ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh₃)(CH₃CN)₂]⁺ for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E=P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh₃)(CH₃CN)₂]⁺ is stable in a non-aromatic solvent, whereas both [RuCp(AsPh₃)(CH₃CN)₂]⁺ and [RuCp(SbPh₃)(CH₃CN)₂]⁺ rearrange upon warming to [RuCp(η⁶-PhEPh₂)]⁺ and related compounds. In addition, the potential of [RuCp(EPh₃)(CH₃CN)₂]⁺ as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile η⁶-arene coordination leading to catalyst's deactivation.     

Grenzfälle des Zintl-Konzepts Zur Kenntnis von Ba7Ga4Sb9

On the Limits of the Zintl Concept. The New Compound Ba₇Ga₄Sb₉ The new compound Ba₇Ga₄Sb₉ crystallizes in the orthorhombic system, space group Pmmn (No. 59) with the lattice constants GaSb₄ tetrahedra are connected by common corners and edges to strings, which are connected by long Sb? Sb bonds to sheets, separated by the Ba ions. The compound is not in accordance to the Zintl concept.     

Über die Strukturaufklärung von (Hydroxy-oxo-cyclopentenyl)alkansäuren,den Aldolkondensationsprodukten von Dioxoencarbonsäuren aus Rinderleber

Structure Elucidation of (Hydroxy-oxo-cyclopentenyl)alkanoic Acids, the Aldol-Condensation Products of Dioxoene Acids from Cattle Liver During homogenization of cattle liver the highly instable dioxoene acids 13a , 13b , and 13c are formed. These acids cyclize in alkaline solution to yield pairs of stable (hydroxy-oxo-cyclopentenyl)alkanoic acids, which were isolated as methyl esters 4a / 5a , 4b / 5b , and 4c / 5c . The structures of these compounds were deduced from an enriched 3-mg mixture sample by microchemical reactions combined with a GC/MS analysis of the reaction products. Compound 13a was obtained as methyl ester by oxidation of the methyl ester of the corresponding F-acid with NaOCl. It was not possible to isolate 13a in pure form due to its high sensitivity. Instead of the methyl ester of 13a , 4a and 5a were isolated, of which the structures were established.