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  • 1
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 52. Mitt. (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 101-111 
    Details
    ISSN: 1434-4475
    Keywords: Bilatriene-violin conversion ; Dark reaction sequence ; 2,3-Dihydrobilatrienes-abc ; Phytochrome models ; Ring-chain tautomerism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The Δ-4 bond of 2,3-dihydrobilatrienes is susceptible to nucleophilic attack. This is verified by using an intramolecular reaction which provides as a model an entropic situation comparable to the natural protein environment of the phytochrome-chromophore. A carboxylic group can be added to Δ-4 yielding a lactone which vice versa may be opened by a base catalysed elimination reaction. The chromophoric group is thereby transformed forth and back from the bilatriene to the violin type. The mechanistic implications are discussed using deuteriation experiments as well as derivatives methylated in strategic positions. Reactions of this type may be involved in the dark reaction sequences of phytochrome transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798426
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  • 2
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 61. Mitt. (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 939-959 
    Details
    ISSN: 1434-4475
    Keywords: Absorption spectra ; Conformation ; PPP-Calculation ; 2,3-Dihydrobilatrienes-abc ; Phytochrome models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The parameters of aPPP-SCF-LCAO-MO-CI treatment adjusted earlier for studies in the bilatriene-abc series are checked by means of a 3,4-dihydropyrromethenone of known conformation. This method is then applied to the calculation of π-electron densities, bond orders, reactivities and absorption spectra of the various tautomeric forms, diastereomers and conformations of the 2,3-dihydrobilatrieneabc chromophor, which is of interest as the prosthetic group of the plant photoreceptor phytochrome and of antenna pigments of algae. The results are compared to13C-,15N-NMR and X-ray data as well as absorption spectra of available tautomeric model compounds and diastereomers with conformations known from experiment. The monomeric nature of the absorbing species is checked in some cases by vapour pressure osmometry. In case of the 2,3-dihydrobilatrienes-abc in their N23-H tautomeric form (which was consolidated experimentally earlier) isomerization of the (Z,Z,Z) configured parent compound doesnot yield significant changes of the type of absorption spectra. The “stretched chromophore criterion” deduced byMoscowitz et al. for bilatrienes-abc (i.e., the intensity of the long wavelength band exceeds that of the short wavelength band) is refined for the 2,3-dihydro-derivatives, as only conformational changes fromsyn toanti at the single bonds 10–11 and 14–15 yield this effect. This change at 10–11 may be discriminated from the one at 14–15 by a strong secondary band in the long wavelength region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809188
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Chemie der Pyrrolpigmente, 62. Mitt. (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 1065-1085 
    Details
    ISSN: 1434-4475
    Keywords: Phytochrome models ; 2,3-Dihydrobilatrienes-abc ; Conformation ; Circular dichroism ; Dipolar effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sixteen diastereomeric 2,3-dihydrobilatrienes-abc substituted in position 3 with various chiral ligands, seven chiral derivatives of a 2,3-dihydrobilatriene-abc-12-propionic acid and a chiral derivative of a 8,12-bilatriene-abc-dipropionic acid were prepared. The chiroptical properties (CD) of these compounds were used as a monitor for the conformational influence of the various ligands. Therefrom it could be deduced that steric effects play a minor role in determining the topology of the chromophore. On the contrary, dipole-dipole interactions of the various partial moments of bile pigments and of the attached ligands crucially influence the conformational situation of the chromophore. This fact may be significant for the stabilization of certain chromophore conformations in biliproteids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809198
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  • 4
    Electronic Resource
    Electronic Resource
    Zur Chemie von Pyrrolpigmenten, 55. Mitt. (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 1071-1080 
    Details
    ISSN: 1434-4475
    Keywords: 2,3-Dihydrobilatrienes-abc ; Non-conjugated charges ; Phytochrome models ; UV-VIS spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 2,3-Dihydrobilatrienes-abc substituted with carboxy and amino residue bearing groups in 3- and 12-positions have been prepared. Spectrophotometric titrations of these derivatives revealed that the influence of a non-conjugated positive or negative charge in the vicinity of the chromophore has only marginal influence on the absorption spectra. Rather small hypsochromic and bathochromic shifts of the long wavelength absorption band were observed and are discussed with respect to their origin. The results indicate that the influence of non-conjugated charges is not a main reason for spectral shifts accompanying photochemical and thermal transformations of the phytochrome chromophore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798774
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  • 5
    Electronic Resource
    Electronic Resource
    Zur Chemie der Pyrrolpigmente, 54. Mitt.: Phytochrommodellstudien: Ein 2,3-Dihydrobilatrien-abc-3-Cholesterylderivat (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 837-852 
    Details
    ISSN: 1434-4475
    Keywords: 2 D-1H-NMR ; 2,3-Dihydrobilatrienes-abc ; Enantiospecific synthesis ; Hydrophobic interactions ; NOESY ; Phytochrome models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using1H- and13C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a “compact” conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01120979
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  • 6
    Electronic Resource
    Electronic Resource
    Zur Chemie der Pyrrolpigmente, 63. Mitt. (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 1087-1097 
    Details
    ISSN: 1434-4475
    Keywords: Phytochrome models ; 2,3-Dihydrobilatrienes-abc ; Hexamethylphosphoric acid triamide ; Stretched chromophore-conformation ; NMR-techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using hexamethylphosphoric acid triamide (HMPT) as solvent for bilatrienesabc and mainly for 2,3-dihydrobilatrienes-abc (which serve as the most suitable models for the biliproteid chromophores) a small hypsochromic shift and a dramatic change of the relative intensities of short and long wavelength absorption bands, as compared to solutions in CCl4, is observed. Applying NMR-spectroscopic techniques (15N-,13C-,1H-) a predominance of the (4Z,9E,15Z) diastereomer forming a 5syn-, 10anti-, 14syn-periplanar orclinal conformation is deduced. The stabilisation of this configuration and conformation arises from strong hydrogen bonds between the acidic protons of the bilins andHMPT. Interactions of this kind seem to be the main source of energy to stretch the otherwise coiled bilin chromophore of (4Z,9Z,15Z)-5sp,10sp,14sp geometry. Stretched systems of the type bilin-HMPT may serve as a valuable model for the natural biliproteides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809199
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  • 7
    Electronic Resource
    Electronic Resource
    Zur Chemie der Pyrrolpigmente, 56. Mitt. (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 1081-1099 
    Details
    ISSN: 1434-4475
    Keywords: Bilatrienes-abc ; CD ; ICD ; Optical activity ; Phytochrome models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract From an investigation of the ICD of bilatrienes-abc and 2,3-dihydrobilatrienes-abc induced by mixtures of CCl4 with (+)-cis-Pinane, (−)-lactic and (+)-tartaric acid esters it is concluded that specific interactions between chromophore and the chiral reagents afford a partial resolution of the labile racemate of helices. Attaching chiral residues covalently to the chromophore induces very low resolution of the same kind in case of apolar ligands like a cholesteryl-residue. However, with polar ligands as in the case ofBoc-lysyl derivatives enantiomeric excesses up to 90% are achieved depending on the solvent used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798775
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  • 8
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 59. Mitt. (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 53-63 
    Details
    ISSN: 1434-4475
    Keywords: Bilatrienes-abc ; 2,3-Dihydrobilatrienes-abc ; 13C-NMR ; Phytochrome models ; Tautomerism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract By investigation of bilatrienes-abc possessing a rigid tautomeric structure within their pyrromethene fragment, using13C-NMR spectroscopy, a criterion for the fixation of tautomerism was deduced: if there is a signal in the otherwise unoccupied shift region between 157 and 170 ppm corresponding to an azomethine fragment, tautomerism is fixed. If there is no signal in this region there is a rapidly equilibrating system of the two possible tautomers. This criterion may be used as well for natural substitution patterns. Moreover, assignment of the13C-signals by correlation with the easily assigned1H-NMR signals establishes the position of the fixed tautomeric system. The criterion is applied as well to the 2,3-dihydrobilatrienes-abc where it is in accord with the results gained from a coupling criterion reported earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798279
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  • 9
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 45. Mitt. (1982)
    Springer
    Monatshefte für Chemie 113 (1982), S. 1329-1348 
    Details
    ISSN: 1434-4475
    Keywords: Diastereomers ; 3,4-Dihydro-5(1H)pyrromethenones ; 5(4H) Dipyrrylmethanones ; Phytochrome models ; Tautomerism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Model compounds for the (Z)- and (E)-3,4-Dihydro-5(1H)-pyrromethenon—5(4H)-Dipyrrylmethanon—system differently substituted in positions “3”, “4” and the N-atoms were synthesised. The solvent dependent equilibria between the derivatives with endo- and exocyclic double bond as well as those between the two diastereomers were studied. An investigation of the mechanistic aspects of the reactions leading to equilibration is included.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808748
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  • 10
    Electronic Resource
    Electronic Resource
    Beiträge zur Chemie der Pyrrolpigmente, 51. Mitt.: Phytochrommodellstudien: Zur Deprotonierung von 3,4-Dihydropyrromethenonen und 2,3-Dihydrobilatrienen-abc (1983)
    Springer
    Monatshefte für Chemie 114 (1983), S. 1107-1123 
    Details
    ISSN: 1434-4475
    Keywords: Bilatrienes-abc ; Methin-1H-NMR-shifts ; Phytochrome models ; pKa Measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 3,4-Dihydropyrromethenones and 2,3-dihydrobilatrienes-abc are deprotonated with a characteristicpK a value of about 11–12 at the NH of the saturated lactam ring. This deprotonation step depends on the availability of stabilisation by hydrogen bonding and charge delocalisation. This was deduced bypK a measurements of 20 derivates bearing methyl groups at certain N-positions to block deprotonation selectively. Moreover, a1H-NMR shift criterion was established to detect the deprotonation site. Fluorescence data are given for several 2,3-dihydrobilatrienes-abc; a crossover of relative acidity and basicity in the excited state was observed in the case of a “normal” 2,3-dihydrobilatriene-abc by applying aFörster cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00799035
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