Stereospecific Synthesis of 2,3-Dimethoxynaphtho[1,2-b] indolizidine

(11aS)- and (11aR)-2,3-dimethoxy-naphtho[1,2-b]indolizidine (9a and 9b) were synthesized from optically pure L- and D-glutamic acid through several steps (scheme 1). All the intermediates of the route to the optical antipodes of 9 exhibit identical physical and spectral properties except the sign of the optical rotation values. The optical purity of the enantiomers of 6 was checked by 1H-NMR spectra using Eu(tfc)3, that of the enantiomers of 9 by HPLC-separation on a chiral column; the amount of racemization was less than 3% in 9a and 9b, respectively. Die (11aS)- und (11aR)-2,3-Dimethoxy-naphtho[1,2-b]indolizidine (9a) und (9b) wurden, ausgehend von optisch reiner L- bzw. D-Glutaminsäure, synthetisiert (Schema 1). Alle Zwischenprodukte auf dem Weg zu 9 zeigen identische physikalische und spektrale Eigenschaften mit Ausnahme des Drehsinns. Die optische Reinheit der 6-Enantiomere wurde durch 1H-NMRSpektroskopie mit Eu(tfc)3 bestimmt, die der 9-Enantiomere durch HPLCTrennung auf einer chiralen Säule: die Razemisierungsrate war in 9a und 9b <3%

Die Abhangigkeit der Massenspektren organischer Verbindungen von instrumentellen Parametern

Das Aussehen des Massenspektrums einer organischen Verbindung kann, abgesehen von den spezifischen Fragmentierungsprozessen, von mehreren Faktoren abhangen, namlich 1) Umwandlungen vor der Ionisierung, 2) Ionen-Molekill-Reaktionen in der Ionenquelle, 3) der Art der Ionisierung und der Ionisierungsenergie, 4) der thermischen Energie des Molekills und 5) der Zeitspanne zwischen Ionisierung und Registrierung. Dies wird an Hand von Beispielen erliiutert

Impaired maturation of the siderophore pyoverdine chromophore in Pseudomonas fluorescens ATCC 17400 deficient for the cytochrome c biogenesis protein CcmC

AbstractPyoverdines are the main siderophores of fluorescent pseudomonads. They comprise a quinoline chromophore, a peptide chain, and a dicarboxylic acid or a dicarboxylic acid amide side chain. Each Pseudomonas species produces a pyoverdine with a different peptide chain. A cytochrome c biogenesis ΔccmC mutant of Pseudomonas fluorescens ATCC 17400 produces multiple pyoverdine forms, showing differences at the level of the chromophore or the side chain. When grown in the presence of L-cysteine, ΔccmC produces only ferribactin, a non-fluorescent precursor of pyoverdine, while addition of oxidized glutathione improves pyoverdine production. We suggest that the conversion of ferribactin to pyoverdine does not take place in the ΔccmC mutant because of lack of oxidizing power in the periplasm

The peptide alkaloid Anachelin: NMR spectroscopic evidence for β-Turn formation in aqueous solution

Anachelin, a complex secondary metabolite isolated from Anabaena cylindrica, possesses an unusual structure combining polyketide, peptide and alkaloid building blocks. This natural product was postulated to act as siderophore with catecholate and salicylate groups for putative iron binding with the three-dimensional solution structure of anachelin remaining unknown. In this preliminary communication, the conformation of anachelin in aqueous solution is investigated. ROESY experiments revealed several interresidual NOEs characteristic of a compact,folded structure. A β-turn type structure of the central tripeptide sequence L-Thr-D-Ser-L-Ser structure involving D-Ser at position (i+1) and L-Ser at position (i+2) would be in agreement with the observed experimental data. In particular, this conformation of the free ligand would align the putative metal binding groups (structural preorganization)and thus lower the free energy for Fe binding. As it is highly unusual to see such a small tripeptide fragment folding into a compact structure, it appears reasonable to assume that both the cationic tetrahydroquinolinium ring as well as the trihydroxylated ε-amino acid contribute to the stabilization of the folded structure

Gas phase kinetics of metal ion ligation by pyrene

Investigation of simple ligation reactions of metal M+ ions with pyrene (Py) within the ICR FT mass spectrometer indicates relatively fast consecutive formation of MPy+ and MPy2+ ions, and if E-i(M+) > E-i(Py) accompanied also by formation of Py+ due to charge exchange. The much slower reaction and equilibrium Py+ + Py reversible arrow Py-2(+), for which the thermodynamic parameters are known, makes it possible to determine the concentration of Py during the ligation reactions and to calculate the second order rate constants from the set of pseudo first order constants obtained by iterative nonlinear least square fitting of experimental snapshot mass spectral data with the proposed kinetic scheme

Genomic, genetic and structural analysis of pyoverdine-mediated iron acquisition in the plant growth-promoting bacterium Pseudomonas fluorescens SBW25

<p>Abstract</p> <p>Background</p> <p>Pyoverdines (PVDs) are high affinity siderophores, for which the molecular mechanisms of biosynthesis, uptake and regulation have been extensively studied in <it>Pseudomonas aeruginosa </it>PAO1. However, the extent to which this regulatory model applies to other pseudomonads is unknown. Here, we describe the results of a genomic, genetic and structural analysis of pyoverdine-mediated iron uptake by the plant growth-promoting bacterium <it>P. fluorescens </it>SBW25.</p> <p>Results</p> <p><it>In silico </it>analysis of the complete, but un-annotated, SBW25 genome sequence identified 31 genes putatively involved in PVD biosynthesis, transport or regulation, which are distributed across seven different regions of the genome. PVD gene iron-responsiveness was tested using '<it>lacZ </it>fusions to five PVD loci, representative of structural and regulatory genes. Transcription of all fusions increased in response to iron starvation. <it>In silico </it>analyses suggested that regulation of <it>fpvR </it>(which is predicted to encode a cytoplasmic membrane-spanning anti-sigma factor) may be unique. Transcriptional assays using gene expression constructs showed that <it>fpvR </it>is positively regulated by FpvI (an extracytoplasmic family (ECF) sigma factor), and not directly by the ferric uptake regulator (Fur) as for PAO1. Deletion of <it>pvdL</it>, encoding a predicted non-ribosomal peptide synthetase (NRPS) involved in PVD chromophore biosynthesis confirmed the necessity of PvdL for PVD production and for normal growth in iron-limited media. Structural analysis of the SBW25 PVD shows a partly cyclic seven residue peptide backbone, identical to that of <it>P. fluorescens </it>ATCC13525. At least 24 putative siderophore receptor genes are present in the SBW25 genome enabling the bacterium to utilize 19 structurally distinct PVDs from 25 different <it>Pseudomonas </it>isolates.</p> <p>Conclusion</p> <p>The genome of <it>P. fluorescens </it>SBW25 contains an extensively dispersed set of PVD genes in comparison to other sequenced <it>Pseudomonas </it>strains. The PAO1 PVD regulatory model, which involves a branched Fpv signaling pathway, is generally conserved in SBW25, however there is a significant difference in <it>fpvR </it>regulation. SBW25 produces PVD with a partly cyclic seven amino acid residue backbone, and is able to utilize a wide variety of exogenous PVDs.</p

STRUCTURE OF METHYLPHEOPHORBIDE-RCI

he methanolic extract of the cyanobacterium (blue-green alga) Spirulina geitleri has been treated with methanolic acid to convert all chlorophyllous pigments to their methylpheophorbides. Fractionation of the latter from methylpheophorbide a by thin layer chromatography and high pressure liquid chromatography yielded methylpheophorbide-RCI. Its structure has been determined as 132S-hydroxy-20-chloro-methylpheophorbide a by 1H-nuclear magnetic resonance, absorption and circular dichroism spectroscopy, mass spectrometry and by partial synthesis from chlorophyll a. The pigment is isolated from Spirulina geitleri irrespective of the use or omission of chlorinated substances during the isolation procedure