Enantioselective catalysis in fine chemicals production

The application of enantioselective catalysis to the fine chemicals industry has great potential both from economic and ecological points of view, but to date has not been widely implemented on a technical scale. The author hopes that the award of the 2001 Chemistry Nobel Prize in this field will give the necessary impetus to future applications.     

Application of atmospheric pressure ionization HPLC-MS-MS for the analysis of natural products

Summary The development of techniques utilizing atmospheric pressure ionization, namely atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), has pioneered the coupling of liquid chromatography (HPLC) with mass spectrometry in recent years. Both ESI and APCI generate ions from polar and labile biomaterials with remarkable ease and efficiency. In particular, the use of HPLC with tandem mass spectrometry (MS-MS) opens further dimensions in the field of bioorganic analysis. Thus, HPLC-MS-MS provides the tools for direct elucidation of the structure and variety of polar natural compounds in complex matrices. In order to develop efficient and straightforward strategies for the analysis of polar natural products, the potential and the limitations of these hyphenated analytical techniques are discussed using heterocyclic aromatic amines, fumonisins, acylated glycoconjugates and regioisomeric fatty acid hydroperoxides as examples. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Dialkylmetallhydroxamate-monomere metallorganische fünfringmoleküle des galliums,indiums und thalliums

The reaction of HON(CH₃)C(O)CH₃ with the trialkyl derivatives of gallium, indium and thallium yields dialkylmetal hydroxamates. The IR-, Raman and ¹H NMR-spectra of these monomeric products with five-membered ringskeletons are discussed. ab]Die Trialkyle des Galliums, Indiums und Thalliums reagieren mit HON(CH₃)C(O)CH₃ unter Bildung von Dialkylmetallhydroxamaten. Die IR-, Raman- und ¹H- NMR-Spektren dieser monomeren Fünfringmoleküle werden diskutiert.     

Enantioselective epoxidation with chiral MN(III)(salen) catalysts: kinetic resolution of aryl-substituted allylic alcohols

A set of aryl-substituted allylic alcohols rac-2 has been epoxidized by chiral Mn(salen*) complexes 1 as the catalyst and iodosyl benzene (PhIO) as the oxygen source. Whereas one enantiomer of the allylic alcohol 2 is preferentially epoxidized to give the threo- or cis-epoxy alcohol 3 (up to 80% ee) as the main product (dr up to >95:5), the other enantiomer of 2 is enriched (up to 53% ee). In the case of 1,1-dimethyl-1,2-dihydronaphthalen-2-ol (2c), the CH oxidation to the enone 4c proceeds enantioselectively and competes with the epoxidation. The absolute configurations of the allylic alcohols 2 and their epoxides 3 have been determined by chemical correlation or CD spectroscopy. The observed diastereo- and enantioselectivities in the epoxidation reactions are rationalized in terms of a beneficial interplay between the hydroxy-directing effect and the attack along the Katsuki trajectory.     

Highly efficient proteinase assay with chromogenic substrates and its application in a study of enzyme inhibitors

A simple and rapid method for the determination of enzyme activities with chromogenic substrates is described. Trypsin and papain were used as model proteinases and N-benzoyl-dl-arginine p-nitroanilide (BAPNA) was applied as substrate. The enzyme assay was performed on a multi-scale using 96-well microtitration plates and product release was detected with the aid of an automatic plate reader, widely used in ELISA tests. The procedure was used for electrophoretic studies of trypsin and a crude papain preparation. It was also applied for the investigation of N-peptidyl-O-acylhydroxylamine proteinase inhibitors. In comparison with commonly used procedures with chromogenic substrates, the proposed approach consumes markedly reduced amounts of all reagents. It allows an almost unlimited number of samples to be assayed in a short time and should be applicable to the detection and determination of any enzyme activitiy where chromogenic substrates are applicable.     

(Cycloheptatrienyl)hydridotungsten Complexes

Carbonyl(cycloheptatrienyl)iodo(phosphorus donor)tungstens ([WI(C₇H₇)(CO)L]; L = P(OMe)₃, 1a ; L = P[O(i-Pr)]₃, 1b ; L = PPh₃, 1c ) were prepared from dicarbonyl(cycloheptatrienyl)iodotungsten ([WI(C₇H₇)(CO)₂)] via a carbonyl-substitution process. Similarly, bromocarbonyl(phosphorus donor)(1,2,4,6-tetramethylcycloheptatrienyl)tungstens ([WBr(Me₄C₇H₃)(CO)L]; L = P(OMe)₃, 6a ; L = P[O(i-Pr)]₃, 6b ; L = PPh₃, 6c ) were obtained from the reaction of bromodicarbonyl(1,2,4,6)-tetramethylcycloheptatrienyl)tungsten ([WBr(Me₄C₇H₃)(CO)₂]; 4 ) with L. The reduction of 1a - c , 4 , and 6a , b with sodiumdihydridobis(2-methoxyethoxy)aluminium in toluene led to stable hydrido complexes [WH(R₄C₇H₃)(CO)L] (R = H, L = P(OMe)₃, 2a ; R = H, L = P[O(i-Pr)]₃, 2b ; R = H, L = PPh₃, 2c ; R = Me, L = P(OMe)₃, 7a ; R = Me, L = P[O(i-Pr)]₃, 7b ; R = Me, L = CO, 7d ). Complexes 2a and 7b were characterized by X-ray structure analyses.     

Bicyclic diironcryptates with mobile guest cations: A new class of solid ionic conductors

Polycrystalline bicyclic diironcryptates with different mobile guest cations were synthesized and characterized by XRD analysis, IR spectroscopy, FAB-mass spectroscopy, elemental analysis, electrical conductivity spectroscopy and ion exchange experiments. We find strong indication that the guest cations exhibit a long-range mobility and that their mobility is governed by their size relative to the size of the cryptand molecules. On the other hand, the valence of the guest cations seems to play a minor role for the mobility. These results are discussed in comparison to the properties of conventional solid cationic conductors.