Thomas Schlederer

Beiträge zur Chemie der Pyrrolpigmente, 35. Mitt.: Eine regioselektive, reversible Addition an Bilatriene-abc

Using spectroscopic methods (UV-VIS,1H-NMR) the reversible addition of donors (alcohols, amines, thiols, HCN, bisulfit and C-H acidic compounds) to bilatrienes-abc was investigated. This equilibrium is in close analogy to the addition of donors to a carbonyl group (as was deduced from thermodynamic and kinetic measurements) and is also the basis for understanding the photochemical isomerization of bilatrienes-abc in the adsorbed state. Based thereon a recipe for the isomerization of bilatrienes-abc in homogeneous phase giving high yields of the (E, Z, Z)-diastereomer is presented; in addition the (E, Z, E)-diastereomer of aetiobiliverdin-IV-γ was isolated and characterized for the first time. A model compound representing the intramolecular addition of a donor attached to a side chain (mimicking a peptide unit) was synthesized and studied with respect to its photochemical behaviour.

Beiträge zur Chemie der Pyrrolpigmente, 25. Mitt. Die diastereomeren (geometrisch isomeren) Biliverdindimethylester—Struktur, Konfiguration und Konformation

Photoisomerization of the symmetrically substituted bilatrienes-abc1 and2 adsorbed on aluminum oxide yields the photoisomers1′ and2′, whereas the biliverdindimethylester (3) gives rise to two isomers3′ and3″. By X-ray photoelectron spectrometry of the N1s-level all these diastereomers were shown to have a bislactam structure. From1H-NMR experiments (chemical shifts, Lanthanide induced shifts, double resonance experiments) the configurations (Z,Z,Z) at the methin positions were assigned to the educts—the photoisomers1′ and2′ having the configurations (Z,Z,E). The configurations (Z,Z,E) and (E,Z,Z) could be assigned to the diastereomers3′ and3″. The conformational aspects within these series are discussed and on the basis of several studies asyn-syn-syn-helical arrangement is deduced for the systems of configuration (Z,Z,Z). For the (Z,Z,E) isomers in the region of (Z)-configuration a conformation resembling the (Z,Z,Z)-systems is reasonable, but in the region of configuration (E) a stronger twisting at the methin single bond due to steric crowding should be favoured.

Beiträge zur Chemie der Pyrrolpigmente, 38. Mitt.: Zur Assoziation von Gallenpigmenten

The long standing problem of solvent dependent absorption spectra of certain bile pigments such as bilirubindimethylester has been solved by measurement of molecular masses by means of vapour pressure osmometry. Using this method and the investigation of the concentration and temperature dependence of the absorption spectra on several model compounds an association equilibrium for pigments of the rubinoid structural type could be confirmed. Moreover the optical properties of the coexisting species and the corresponding equilibrium constants could be deduced by spectroscopic techniques. Verdinoid pigments lacking free carboxylic functions on the other hand tend to be monomeric in solution. A heteroassociated species involving equimolar amounts of a verdinoid and a rubinoid pigment could be verified existing on adsorbents like silicagel.

Beiträge zur Chemie der Pyrrolpigmente, 40. Mitt.: Azafulvene, Schlüsselstellen beim Aufbau von Pyrrolpigmenten? —Eine neue Synthese von verdinoiden und rubinoiden Gallenfarbstoffen

Substituted azafulvenes were generated by dehydrogenation of 5′-methyl-substituted pyrromethenones withDDQ and characterized by UV- and1H-NMR-spectroscopy. Their electrophilic properties were demonstrated using several quenchers and furthermore they were used for a synthesis of verdinoid bile pigments (which easily can be converted to rubinoid systems by the action of NaBH4) with nearly any desired unsymmetrical alkyl substitution patter: The azafulvene spezies was generated by the action ofDDQ on a 5′-methylpyrromethenone and was quenched by an 5′-unsubstituted pyrromethenone. The resulting rubinoid adduct was dehydrogenated immediatly byDDQ — yields were good to high.

Eine formal nucleophile Substitution an Bilatrienen-abc

Reaction of Aetiobiliverdine-IV-γ with cyanide ion in dimethylsulfoxide yieldsvia nucleophilic addition and oxidation the 10-cyano derivative exclusively. Its structure was established from its spectroscopic properties.

Beiträge zur Chemie der Pyrrolpigmente, 22. Mitt.: Die Selektivität photochemischer Isomerisierungen bifunktioneller und bichromophorer Verbindungen mit geometrischer Isomerie — Studien an Gallenpigmentstrukturmodellsystemen

Bifunctional molecules of structural type5 and6 (resembling bilatrienes-abc) containing double bonds show a strong selectivity toward photochemical isomerization: Starting from the (Z,Z)-isomer the (Z,E)-isomer, is obtained but none of the (E,E)-isomer. The reason for this selectivity could be established by conformational analysis,PPP-calculations and the photochemical behaviour of N-methylated derivatives (8 and9). The configuration, (Z) at a particular double bond induces a certain amount of twisting at the attached, single bond on steric reasons. This twisting is smaller than the twisting observed for the double-single-bond system of configuration (E). It is this differrential twist which causes the observed selectivity.On the other hand bichromophoric systems like2 or4 give no selectivity on photochemical isomerization.Based on the experimental data an energy scheme for the singlet isomerization paths for bichromophoric and bifunctional systems was deduced.

Beiträge zur Chemie der Pyrrolpigmente, 31. Mitt.: Die Spin-Gitter-Relaxation in den1H-NMR-Spektren von Bilatrienen-abc

The1H-NMR spin lattice relaxation times of aetiobiliverdin-IV-γ and biliverdindimethylester were determined using the inversion recovery technique. The relaxation times of protons attached to the terminal rings A and D are longer than those situated at the rings B and C which points to a higher mobility of rings A and D. Moreover these measurements allowed an independent assignment of the1H-NMR-signals of the methyl groups of biliverdindimethylester.The1H-NMR spin lattice relaxation times of aetiobiliverdin-IV-γ and biliverdindimethylester were determined using the inversion recovery technique. The relaxation times of protons attached to the terminal rings A and D are longer than those situated at the rings B and C which points to a higher mobility of rings A and D. Moreover these measurements allowed an independent assignment of the1H-NMR-signals of the methyl groups of biliverdindimethylester.