Gabriele Wagner

MOLECULES WITH POTENTIAL APPLICATIONS FOR NON-LINEAR OPTICS: THE COMBINATION OF FERROCENE AND AZULENE

Abstract The synthesis of ferrocene derivatives connected by an imino bridge to the azulene moiety is described, and the properties of the compounds were studied (NMR, UV–vis, redox potentials). The first hyperpolarizability of one of the compounds was determined by hyper-Rayleigh scattering (HRS).

PlexinA1 interacts with PTK7 and is required for neural crest migration.

Members of the plexin protein family are known regulators of axon guidance, but recent data indicate that they have broader functions in the regulation of embryonic morphogenesis. Here we provide further evidence of this by showing that PlexinA1 is expressed in Xenopus neural crest cells and is required for their migration. PlexinA1 expression is detected in migrating cranial neural crest cells and knockdown of PlexinA1 expression using Morpholino oligonucleotides inhibits neural crest migration. PlexinA1 likely affects neural crest migration by interaction with PTK7, a regulator of planar cell polarity that is required for neural crest migration. PlexinA1 and PTK7 interact in immunoprecipitation assays and show phenotypic interaction in co-injection experiments. Considering that plexins and PTK7 have been shown to genetically interact in Drosophila axon guidance and chick cardiac morphogenesis, our data suggest that this interaction is evolutionary conserved and may be relevant for a broad range of morphogenetic events including the migration of neural crest cells in Xenopus laevis.

Inhibition of chloroplast photo-oxidation by flavonoids and mechanisms of the antioxidative action

Abstract The influence of the flavonoid compounds quercetin and rutin on the photo-oxidation of chloroplast membranes was investigated. Both substances retarded pigment loss and inhibited lipid peroxidation, measured as ethane release. The inhibition of photo-oxidation was independent of the mechanism of initiation. Quercetin and rutin were also found to be able to scavenge singlet oxygen and were degraded in the process. It is proposed that flavonoid inhibition of pigment photobleaching and lipid peroxidation is due to general antioxidative properties of the compounds.

Iminoacylation: Part 6: Coupling of chloro- and amidoximes Ar(R)CNOH (R=Cl, NH2) with acetonitrile ligands coordinated to platinum(IV)

Abstract Addition of chloro- and amidoximes RR1CNOH (R/R1=Cl/Ph, Cl/C6H4-p-Me, Cl/C6H4-p-NO2, NH2/Ph) to the acetonitrile ligands in trans-[PtCl4(MeCN)2] proceeds much slower as compared to ketoximes with donor substituents R/R1 [V.Yu. Kukushkin, T.B. Pakhomova, Yu.N. Kukushkin, R. Herrmann, G. Wagner, A.J.L. Pombeiro, Inorg. Chem. 37 (1998) 6511] and leads to the complexes with iminoacylated species [ligating (alkylideneaminooxy)imines] trans-[PtCl4{NHC(Me)ONCRR1}2]. X-ray crystal structure determination of two iminoacylated compounds (R/R1=Cl/C6H4-p-Me, Cl/C6H4-p-NO2) disclosed their overall trans geometry with monodentate organic ligands in E-conformation and indicated NH ⋯ N hydrogen bonding between the imino H atom and the oxime nitrogen.

Iminoacylation: 2. Addition of alkylated hydroxylamines via oxygen to platinum(IV)-bound nitriles

Addition of R 2 NOH (R=Me, Et, CH 2 Ph) to the acetonitrile ligands in the platinum(IV) complex trans -[PtCl 4 (MeCN) 2 ] leads to unprecedented O-iminoacylation of the dialkylhydroxylamines to produce trans -[PtCl 4 (NH(Me)CONR 2 ) 2 ].

Ferrocene derivatives containing anthracene linked by spacers

Abstract Several ferrocene derivatives linked by a non-conjugated spacer to a 9,10-diphenylanthracene unit have been prepared, among them an amphiphilic isoquinolinium salt. By X-ray structure analysis of the intermediate 9,10-bis(4-hydroxyphenyl)anthracene, an almost perpendicular arrangement of the phenyl groups with respect to the anthracene was found. The properties of the compounds were studied by NMR and cyclovoltammetry, which suggest that the isoquinolinium salt forms inverse micelles in organic solvents. No indication for intramolecular aggregation of ferrocene and isoquinolinium moieties by folding of the flexible alkyl spacers could be detected. The compound forms a monolayer when spread on water which can be transferred to a quartz surface. Repeated transfer leads to a non-centrosymmetric Z-type array of layers in the Langmuir-Blodgett film.

Microwave‐Assisted Selenium Dioxide Oxidation of Camphor Derivatives to α‐Dicarbonyl Compounds and Oxoimines

Abstract Camphor‐derived α‐dicarbonyl compounds and 3‐oxo‐camphorsulfonylimine have been synthesized from the corresponding ketones or sulfonylimine by microwave‐assisted oxidation with selenium dioxide. Compared to the classical reaction conditions, good yields were obtained in much shorter reaction times. Additionally, the selenium precipitation is more quantitative, and its removal from the reaction mixture is easier.

Ferrocenylethenylsilatranes and a cymantrenylsilatrane

Abstract The syntheses, properties and crystal structures of two isomeric ferrocenylethenylsilatranes and 1-(3-methylcymantrenyl)silatrane are reported. The organometallic moieties and the silatrane show little structural influence on each other. The SiN distances remain in the expected range of 2.13–2.22 A, asserting the hypervalency of silicon. The electron-donating effect of the silatrane group is transmitted through the CC double bond to ferrocene, as shown by the redox potentials. The first hyperpolarizability of the ferrocene derivatives was determined by hyper-Rayleigh scattering.

Reactivity of ferrocenylalkyl isocyanides. Formation of potential antibiotics and of gold(I) complexes

Abstract Reactions of the ferrocenylalkyl isocyanides CNCH(R)Fc (Fc=Fe( η 5 -C 5 H 5 )( η 5 -C 5 H 4 ), R= c Hex, t Bu) with imines and carboxylic acids lead to derivatives of valine or of antibiotics ( β -lactams and penicillins) containing the ferrocenyl group which could not be cleaved from the molecules under acidic conditions. The formation of the penicillin derivatives is stereoselective. The isocyanides CNCH(R)Fc (R=H, i Pr, c Hex) and CN(EtO 2 C)CCHFc react with [AuCl(PPh 3 )] to give the corresponding gold(I) complexes [AuL(PPh 3 )]A (L=ferrocenyl alkyl isocyanide, A=Cl or BPh 4 when the reaction is carried out in the presence of Na[BPh 4 ]). Cyclic voltammetry in aprotic medium shows that these complexes undergo a reversible single electron oxidation at the iron(II) site at a platinum electrode at a potential which is similar to that observed for the corresponding uncoordinated isocyanides.

Cycloaddition of nitrones to free and coordinated (E)-cinnamonitrile: effect of metal coordination and microwave irradiation on the selectivity of the reaction

[2 + 3] Cycloaddition of N-methyl-C-phenylnitrone to transition metal coordinated (E)-cinnamonitrile occurs exclusively at the nitrile CN bond, leading to Δ4-1,2,4-oxadiazoline complexes, from which the heterocyclic ligand can be released and isolated in high yield. In contrast, the reaction of the nitrone with free cinnamonitrile involves the CC bond only, yielding a diastereomeric mixture of isoxazolidine-4-carbonitriles. Microwave irradiation enhances the reaction rates of both transformations considerably, without changing their regioselectivity with respect to the thermal reactions. The two nitrile ligands in complexes of the type [MCl2(cinnamonitrile)2] (M = Pt or Pd) are significantly different in reactivity. Thus, short-time microwave irradiation allows for the selective synthesis of the mono-cycloaddition product [PtCl2(cinnamonitrile)(oxadiazoline)], even in the presence of an excess of nitrone. Using longer irratiation times, this complex can be further transformed into the bis-cycloaddition product [PtCl2(oxadiazoline)2]. The latter compound is also produced when thermal heating is applied, however, the formation of the mono-cycloaddition product fails to be selective under thermal conditions.