H. Falk

Beiträge zur Chemie der Pyrrolpigmente, 18. Mitt.: Pyrromethenone—Partialstrukturen von Gallenpigmenten: Struktur und Eigenschaften in Lösung

Depending on solvent polarity and concentration a monomer—dimer equilibrium for pyrromethenones was deduced by means of absorption and fluorescence spectroscopy and measurement of a colligative property. The monomer could be characterized as asyn-(Z) form with a dihedral angle at the methine single bond of about fourty degrees using the lanthanide shift technique and nuclearOverhauser effect studies. Two types of dimer geometry with differing bond strengths were found by comparingPPP calculation results with the measured absorption spectra and the liquid crystal induced circular dichroism.The (Z) isomers can be transformed to the corresponding (E) isomers by means of a photoreaction. The latter is thermally stable but rather sensitive against oxygen, light and protons, an effect which varies strongly with the substitution pattern of the pyrrole fragment thus enabling isolation in certain cases only.

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.

Stereochemie von Metallocenen, 8. Mitt.: Die Absolute Konfiguration von Optisch Aktiven Benzol-chromtricarbonyl-derivaten; Asymmetrische Synthese und Kinetische Racematspaltung von Chiralen Metallocenen

Es wird uber die Synthese und Racematspaltung von drei Benzol-chromtricarbonyl-derivaten sowie der α-Methyl-ferrocen-carbonsaure berichtet. Die Absolutkonfiguration von (+)-(1-Tetralon)-Cr(CO)3 konnte als (1S) ermittelt werden. Bei den beiden isomeren Sauren (+)- bzw. (−)-(o- bzw. m-Tolylsaure)-Cr(CO)3 gelang erstmalig die konfigurative Korrelation eines α-mit einem β-disubstituierten Metallocen. Die Absolutkonfiguration des auch durch asymmetrische Synthese zuganglichen (+)-(o-Tolylsaure)-Cr(CO)3 lies sich auf Grund der Ergebnisse der kinetischen Racematspaltung der Anhydride der beiden racem. α-Methyl-metallocen-carbonsauren mit (−)-Menthol und (−)-α-Phenathylamin als (1 S) bestimmen, da die Konfiguration der Methyl-ferrocencarbonsaure (nach chemischer Korrelation) bekannt war.

Ferrocenasymmetrie, 2. Mitt.: Die relative Konfiguration von optisch aktiven, α-disubstituierten Ferrocenderivaten (21. Mitt. über Ferrocenderivate)

Ausgehend von den optisch aktiven, homoannular uberbruckten Verbindungen Ferroceno-cyclohexenon (I) und-tetrahydropyridin (II) konnte (u. a. durch Ringoffnungs- und-erweiterungsreaktionen) eine Reihe optisch aktiver Ferrocenderivate erhalten werden, die somit dieselbe Konfiguration besitzen wie I bzw. II. Da auch die Konfigurationen dieser beiden Verbindungen miteinander verknupft wurden, und es ferner moglich war, (+)-α-Aminomethyl-methylferrocen uber (+)-Methyl-athyl-ferrocen, den einfachsten optisch aktiven Ferrocen-“kohlenwasserstoff”, mit dem (+)-Ringamin (II) in Beziehung zu bringen sowie opt. akt. α-Athyl-acetylferrocen uber (+)-Athyl-vinyl-ferrocen in das Schema miteinzubeziehen, ist nun die relative Konfiguration von insgesamt 26 α-disubstituierten Ferrocenen bekannt und auf die des Ringketons I zuruckgefuhrt, das als Bezugssubstanz vorgeschlagen wird. —Schlieslich gelang auch die stereospezifische Synthese von 2 opt. akt. homoannular trisubstituierten Ferrocenderivaten, deren relative Konfiguration damit ebenfalls bekannt ist.

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, 24. Mitt. Über die Beziehung zwischen Lichtabsorption und Struktur von Bilatrienen-abc

Using the recently established solution structure of a bilatriene-abc derivative the parameter set of thePPP-SCF-LCAO-MO-Cl model was refined. The general trend, that molecular configuration itself does not so much determine the absorption spectra as was deduced by investigation of partial bile pigment structures, was confirmed for the bilatrienes-abc. Instead, the configuration at a particular double bond induces a certain torsional angle at the adjacent single bond which leads to dramatic spectral changes on isomerization of this double bond. Isomerization without this torsional effect brings about different relative intensities of the two main spectral bands. Comparing measured spectra of several bilatrienes-abc and calculated spectra a helicalsyn, syn, syn-conformation with three torsional angles at the methine fragments of appr. 20° was deduced for systems with (Z, Z, Z)-configuration. For a recently prepared (E, Z, Z)-derivative a nearly helicalsyn, syn, syn-conformation with torsional angles of 40°, 20° and 20° at the methine single bonds is the most probable.

Ferrocenasymmetrie, 3. Mitt.: Die Konfiguration von Mono- und Bis-(α-ketotetramethylen)-ferrocen 24. Mitt. über Ferrocenderivate

Die absolute Konfiguration von (+)-1,2-(α-Ketotetramethylen)-ferrocen (Ferroceno[1,2]cyclohexenon) wurde nach Uberfuhrung in dasexo-Carbinol (II) durch kinetische Racematspaltung von α-Phenyl-buttersaureanhydrid (Horeaus Methode) als (R) ermittelt. Eine Zuordnung der Konfigurationen fur die beiden isomeren (cis- bzw.trans-) Bis-(α-ketotetramethylen)-ferrocene war durch Spaltungsversuche moglich. Demnach handelt es sich beim tieferschmelzenden Bis-keton (Schmp. 160°) um das Racemat (trans-) und beim anderen Isomeren (Schmp. 170°) um dieMeso- (cis-) Form. Dem rechtsdrehenden Bis-keton, das in eine linksdrehende Bis-vinylverbindung (IX) uberfuhrbar ist, kommt sehr wahrscheinlich die(R),(R′)-Konfiguration zu.

Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen)

The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position.Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents.The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.

Beiträge zur Chemie der Pyrrolpigmente, 1. Mitt.: Der induzierte Circulardichroismus einiger Pyrromethenderivate in cholesterischer Mesophase

The electron absorption spectra of some symmetrically substituted alkyl-dipyrromethene derivatives were analyzed by means of a liquid-crystal-induced circular dichroism technique. The “main band” (440 nm) was found to be polarized parallel, whereas all short-wavelength bands (including one hidden by the main band) are polarized perpendicular to the “long” axis of the molecule.The electron absorption spectra of some symmetrically substituted alkyl-dipyrromethene derivatives were analyzed by means of a liquid-crystal-induced circular dichroism technique. The “main band” (440 nm) was found to be polarized parallel, whereas all short-wavelength bands (including one hidden by the main band) are polarized perpendicular to the “long” axis of the molecule.

Beiträge zur Chemie der Pyrrolpigmente, 16. Mitt.: 5-[5-Methyliden-(5H-pyrrolyl-2-methyliden)]-3-pyrrolin-2-on — eine Partialstruktur von Gallenpigmenten

By investigation of model systems related to 5-[5-methylidene-(5H-pyrrolyl-2-methylidene)]-3-pyrrolin-2-one by means of pK- and Lanthanide induced shift measurements (usingPDIGM-calculations),1H-NMR-, IR-, and UV-spectroscopy andPPP-calculations an intramolecular hydrogen bond has been shown to be characteristic of this bile pigment partial structure. As a consequence of this bond the system is coplanar (in solution) in contrast to the recently studied pyrromethenones and arylmethylidenepyrrolinones which have a twisted conformation at the methine single bond.