Reaktionen an komplexgebundenen liganden: XXIX. Ein einfacher weg zu azomethin-komplexen: Kondensation von chrom—, molybdän—, wolfram—, mangan— und eisen—ammoniak-komplexen und ketonen zu ketimin-komplexen

Treatment of transition-metal—ammonia complexes with ketones yields complexes with RR′CNH ligands. Of particular interest is the stabilization of dialkylketimines such as e.g. (CH₃)₂CNH and C₆H₁₀NH in [M(CO)₅{NHC(CH₃)₂}] or [M(CO)₅ {NHC₆H₁₀}] (M = Cr, Mo, W). The principle of synthesis may be applied to a wide range of different metals and types of complexes, as can be shown by the synthesis of [C₅H₅Mn(CO)₂ {NHC(CH₃)₂}], [C₅H₅Fe(CO)₂{NHC(CH₃)₂}]PF₆, [M(CO)₄L₂] (M = Cr, Mo, W; L = (CH₃)₂CNH, C₆H₁₀NH) and [W(CO)₃(diphos){NHC(CH₃)}₂]. Treatment of [Cr(CO)₅NH₃] with urotropine gives [Cr(CO)₅ {N₄(CH₂)₆}] which is also obtained from [Cr(CO)₅THF] and urotropine. The methods of preparation, reactions and spectroscopic properties of the complexes are reported.     

13C-NMR und konformation eines membran-modifizierenden synthetischen nonadekapeptid-analogons von alamethicin und seiner zwischenstufen

The ¹³C-NMR spectra of the synthetic membrane modifying nonadecapeptide Boc-(Aib-l-Ala)₅-Gly-Ala-Aib-Pro-Ala- Aib-Aib-Glu(OBz)-Gln-OMe (Aib = α-aminoisobutyric acid), and of synthetic intermediates were used for conformational analysis in solution. The assignments of the ¹³C-NMR signals of Aib are based on the magnetic nonequivalence (MNE) of the geminal C_β-signals in asymmetric environment resulting in a shift difference of 0.2–0.5 ppm due to neighbouring chiral residues. More than 4 ppm MNE are observed due to α-helical conformation and about 2.5 ppm for Aib situated in the corners of a rigid β-turn. The Ala-C_α signal is also sensitive to different secondary structures. The C_α signal for C-terminal alanine is found at 49–50 ppm, and for alanine within unordered oligopeptides it absorbs at 50–51 ppm. α-Helical environment shifts the Ala-C_α signal to lower field down to 54 ppm. In methanolic solution the nonadecapeptide shows a α-helical N-terminal region. For the C-terminus beginning with proline-14 no periodically ordered conformation is observed, and we suggest a sequence of β-turns. Furthermore the typical E/Z isomerism of the prolyl-peptide bond can be observed on proline itself and on its neighbour alanine.     

Aminierende reduktive Kupplung aromatischer Aldehyde mit niervalenten Titan-Reagenzien zu 1,2-Diarylethylendiaminen

Preparation of 1,2-Diarylethylenediamines by Aminative Reductive Coupling of Aromatic Aldehydes with Low-Valent Titanium Reagents In a novel McMurry- Type one-pot reaction, aromatic aldehydes and secondary amines are poupled of give the N, N, N′, N′-tetraalkyl-1,2-diarylethylendiamines 1–22 (Table 3). To this end, a lithium dialkylamide is added to an aromatic aldehyde to give the adduct B which is then treated with 1 equiv. of TiC1₄ to yield a coloured suspension of a reagent synthetically equivalent to a iminium salt ( C/D in Scheme 4). After treatment with a low-valent Ti reagent which is prepared by reduction of TiC1₄ with either K or, preferably, Mg, the coupling products are isolated in 23 to 81% yield as a 1:1 mixture of the diastereoisomers (meso- and rac-form). These are separated either by chromatography or by crystallization and characterized.     

Präparative chromatographische Enantiomerentrennung von synthetisch nützlichen cyclischen Acetalen

Preparative Chromatographic Resolution of Synthetically Useful Cyclic Acetals Racemic cyclic acetals derived from aldehydes and glycine, glycolic acid, thioglycolic acid, formylacetic acid, and acetoacetic acid (oxazolidinones 4 – 13 , dioxolanones 14 , 15 , oxathiolanone 16 , dioxinones 17 – 23 ) are resolved by preparative high-pressure liquid chromatography on silica gel coated with the polymer from N-acryloylphenylalanine ethyl ester (Chiraspher®). The separation factors α range from1,1 to 2,4. Use of a Prepbar®-chromatography system allows injection of several grams at a time. The enantiomeric acetals thus obtained are fully characterized. First application to amino-acid synthesis are mentioned.     

Synthesis of Hexadentate Hexahydro-1,3,5-triazine-Based Ligands and their Copper(I) Complexes

Summary.  Hexadentate ligands were formed by the reaction of primary dimethylaminoethyl- or methoxyethylamines with formaldehyde. The resulting N, N′, N″-functionalized hexahydro-1,3,5-triazines contain pending amino or ether functionalities which are able to coordinate to metals in addition to the ring nitrogen atoms. Both ligands were reacted with CuBr, and novel tricopper clusters were isolated and characterized by X-ray structure analysis. In these compounds a ring nitrogen atom, the pending amino or ether functionality, and two bridging bromine atoms coordinate each of the copper atoms. Received January 22, 2002; accepted (revised) March 22, 2002     

Perfluoralkyljod-verbindungen: Darstellungen und eigenschaften von CF3JO,CF3JOF2 und CF3JO2

Perfluoroalkyl iodine compounds: preparations and properties of CF₃IO, CF₃IOF₂, and CF₃IO₂. The trifluoromethyl iodine compounds CF₃IO, CF₃IOF₂, and CF₃IO₂ are formed from the reactions of CF₃I, CF₃IF₂ or CF₃IF₄ with ozone or silicon dioxide respectively. Their preparartions, properties, ¹⁹F-nmr spectra, and ir spectra are described.     

Enantioselective Preparation of 2‐Aminomethyl Carboxylic Acid Derivatives: Solving the β2‐Amino Acid Problem with the Chiral Auxiliary 4‐Isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ). Preliminary Communication

Multigram amounts of suitably protected β²‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β²‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield.     

Synthese monodisperser linearer und cyclischer Oligomere der (R)-3-Hydroxybuttersäure mit bis zu 128 Einheiten

Monodisperse Linear and Cyclic Oligo[(R)-3-hydroxybutanoates] Containing up to 128 Monomeric Units Using benzyl ester/(tert-butyl)diphenylsilyl ether protection, (COCl)₂/pyridine esterification conditions, and a fragment-coupling strategy (with H₂/Pd-C debenzylation and HF · pyridine desilylation), linear oligomers of (R)-3-hydroxybutanoic acid (3-HB) containing up to 128 3-HB building blocks (mol. weight > 11 000 Da) are assembled (Schemes 1,2,5, and 6). In contrast to the previously employed protecting-group combination, and due to the low-temperature esterifying conditions, this procedure leads to monodisperse oligomers: all steps occur without loss of single 3-HB units. The product oligomers with two, one, and no terminal protecting groups (mostly prepared in multi-gram amounts) are characterized by all standard spectroscopic methods, especially by mass spectroscopy (Figs. 2 and 3), by their optical activity, and by elemental analyses. Cyclization of the oligo[(R)-3-hydroxybutanoic acids] with up to 32 3-HB units, using thiopyridine activation and CuBr₂ for the ring closure, produces oligolides consisting of up to 128 ring atoms (Scheme 7). Mixed oligolides containing 3-HB and (R)-3-hydroxypentanoic units are prepared from the corresponding linear trimers, using Yamaguchi's method for the ring closure (Scheme 8 and Fig.4 (X-ray crystal structures of two folded conformers)). Comparisons of melting points (Table 1), of [α] values (Tables 2 and 3), of ¹H-NMR coupling constants (Table 3), and of molecular volume/hydroxyalkanoate unit (Table 4) of linear and cyclic oligomer derivatives and of the high-molecular-weigh polymer show that the monodisperse oligomers appear to be surprisingly good models for the polymer. Besides this insight, our synthesis is supplying the samples to further test the role of P(3-HB) (ca. 140 units) as a component of complexes forming channels through cell-wall phospholipid bilayers.     

Stir bar sorptive extraction based on restricted access material for the direct extraction of caffeine and metabolites in biological fluids

A biocompatible stir bar sorptive extraction (SBSE) device was prepared using an alkyl-diol-silica (ADS) restricted access material (RAM) as the SBSE coating. The RAM-SBSE bar was able to simultaneously fractionate the protein component from a biological sample, while directly extracting caffeine and its metabolites, overcoming the present disadvantages of direct sampling in biological matrices by SBSE, such as fouling of the extraction coating by proteins. Desorption of the analytes was performed by stirring the bar in a water/ACN mixture (3/1, v/v) and subsequently reconcentrating the sample solution in water to enable HPLC-UV analysis to be performed. The limit of detection, based on a signal to noise ratio of 3, for caffeine was 25 ng/mL in plasma. The method was confirmed to be linear over the range of 0.5-100 microg/mL of caffeine with an average linear coefficient (R2) value of 0.9981. The injection repeatability and intra-assay precision of the method were evaluated over ten injections, resulting in a %RSD of approximately 8%. The RAM-SBSE device was robust (>50 extraction in plasma without significant signal loss) and simple to use, providing many direct extractions and subsequent determination of caffeine and its metabolites in biological fluids. In contrast to existing sample preparation methods for the analysis of caffeine and selected metabolites in biological fluids, this feasibility study using a biocompatible SBSE approach was advantageous in terms of simplifying the sample preparation procedures.     

Perfluoralkyljod-verbindungen: das trifluormethyljod-bis-trifluoracetat CF3J(OCOCF3)2

CF₃I(OCOCF₃)₂ is formed from the reactions of CF₃IF₂ or CF₃IO with trifluoroacetic anhydride at low temperature. During the reaction of CF₃IF₂ with (CF₃CO)₂O CF₃IF(OCOCF₃) is formed as an intermediate product. The preparation, the ¹⁹F-nmr spectra and the thermal decomposition are described.