Synthesis and analytics of rigidified peptide architectures [Elektronische Ressource] : neuropeptide Y dipeptide scan, ring-chain-equilibria of iminopeptides, thiazole amino acids for thiopeptide antibiotics = Synthese und Analytik fixierter Peptidarchitekturen / vorgelegt von Sebastian Enck

Enck

Informations

• Publié par: philipps-universitat_marburg
• Publié le: 01 janvier 2010
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 21 Mo

Extrait

Synthesis and Analytics of Rigidified Peptide Architectures

Neuropeptide Y Dipeptide Scan
Ring-Chain-Equilibria of Iminopeptides
Thiazole Amino Acids for Thiopeptide Antibiotics
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Synthese und Analytik fixierter Peptidarchitekturen

Dipeptid-Scan am Neuropeptid Y
Ring-Kette-Gleichgewichte von Iminopeptiden
Thiazol-Aminosäuren für Thiopeptid-Antibiotika


Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften
(Dr. rer. nat.)



dem
Fachbereich Chemie
der Philipps-Universität Marburg



vorgelegt von
Sebastian Enck
aus München

Marburg / Lahn 2010

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Vom Fachbereich Chemie
der Philipps-Universität Marburg als Dissertation angenommen am 16.07.2010.

Erstgutachter: Herr Prof. Dr. Armin Geyer
Zweitgutachter: Herr Prof. Dr. Mohamed A. Marahiel

Tag der mündlichen Prüfung am 13.08.2010.
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Dedicated to my mother († 12/04/2000)



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The experimental work described in this thesis was performed from August 2006
to June 2010 at the Department of Chemistry, Philipps-Universität Marburg.






















I owe special thanks to

Prof. Dr. Armin Geyer

for his generous support of my Ph.D. thesis and the excellent scientific guidance,
allowing me to work on several exciting projects with great flexibility.


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“Wine?“
thFeeb E. in Guest House Paradiso, 6 scene






“There are three stages of scientific discovery:
first people deny it is true;
then they deny it is important;
finally they credit the wrong person.”

Alexander von Humboldt


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Abstract

The functional spectrum of naturally occurring peptides encompasses the role as hormones,
neurotransmitters and as chemical warfare agents utilized by microorganisms for the purpose of
defending their respective ecological niche. The action of peptide ligands relies on the
interaction with binding partners by which a certain biological signal is triggered or inhibited. In
order to be able to perform its dedicated task a peptide must exhibit a high affinity to a certain
binding partner. This must occur with a minimum extent of selectivity, which means that binding
to other partners (and, thereby, further biological effects) has to be excluded. These properties
depend on the structure of the peptide, which in other words is the specific alignment of certain
functional units. It is the rigidification of a structure in its biologically active conformation which
is a key to the generation and enhancement of biological activity and selectivity.
In principle, there are three possibilities for the fixation of a molecular structure. By the
formation of small rings local rigid structural motifs are generated, whereas macrocyclizations
restrict the global flexibility. Finally, various examples are found in nature in which these both
strategies are combined. Each of the three chapters of this thesis deals with one of these three
options, thereby addressing questions that concern the analysis of rigid peptide structures and
their preparation by chemical synthesis.

In the first chapter a novel scanning technique is described which by the incorporation of a rigid
bicyclic dehydroalanine-thiaproline dipeptide (Dha=Tap) effects a local fixation of the peptide
backbone and thus enables its structural analysis. The denotation “=” indicates the fixation of
the backbone by a second covalent bond. The method was tested with Neuropeptide Y (NPY), a
linear peptide whose various functions in the human organism result from its multiple receptor
affinity. To understanding and control these binding processes is prerequisite for the
development and application of therapeutic NPY analogs. In cooperation with the Beck-Sickinger
group (University of Leipzig) a series of NPY analogs with systematically varied Dha=Tap single-,
double-, and triple substitutions was examined with respect to the receptor binding properties.
This enabled for the first time to identify trends in the receptor affinities and selectivities which
depend on the number and the exact positions of the substitutions. For a series of NPY analogs,
detailed structural studies were undertaken using NMR spectroscopy in the presence of a
membrane mimetic. These investigations demonstrated the excellent applicability of the
Dha=Tap unit as NMR label for structure elucidation and to determine details of the membrane
coordination of a peptide.
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The second part of this work deals with the thermodynamic characterization of
macrocyclizations. The inclination of a linear precursor to form the corresponding macrocycle is
dependent on its preferred conformations, but no details of the structural prerequisites are
known, which is why one has to rely on empirical or computational data for the planning of this
challenging synthetic step. Furthermore, no methodical approach exists which deals with this
process and which quantifies the loss of flexibility of a peptide chain upon macrocyclization. A
solution to this problem is given by peptides which macrocyclize by forming a reversible carbonyl
bond and which thereby enable a thermodynamic analysis. In cooperation with the Marahiel
group it was possible to quantify the pH- and temperature dependence of the ring-chain
equilibria of various naturally occurring and synthetically modified iminopeptides. This allowed
to identify structural determinants for the formation of a macrocycle as well as the first
quantification of the entropy balance of such processes.

The third research project of this thesis encompassed the development of a novel synthetic
strategy towards highly functionalized thiazole dipeptides. Thiazoles are generated by the
cyclization of a Cysteine side chain with the N-terminally adjoining backbone amide and for
example occur in the thiopeptide antibiotics. These natural products constitute complex three-
dimensional peptide networks, and their high toxicity against microorganisms bases on the
combination of macrocyclic structures and several thiazoles in the backbone. An efficient
synthetic access towards the thiopeptide thiazole dipeptides which are linked up to four-fold to
the backbone and which in addition carry a glycosylation site is the prerequisite for the total
synthesis of these last-resort antibiotics and for the generation of analogs thereof. In the present
work, a synthetic approach was developed which bases on condensation products of uronic
acids and Cysteine and which enables a few-step stereoselective synthesis of polyhydroxylated
thiazole depsidipeptides. Finally, by N/O-exchange a first synthetic pathway was established to
the (2S,3S,4S)-dihydroxyglutamate dipeptide which constitutes the central linking motif in the
nocathiacin and thiazomycin antibiotics. In addition, directed side chain functionalizations also
allowed to obtain epimers and homologs of this compound.
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Zusammenfassung
Die funktionelle Bandbreite natürlich vorkommender Peptide umfasst den Einsatz als Hormone,
als Neurotransmitter sowie als Mittel zur biologischen Verteidigung, mit welcher sich Mikro-
organismen ihre Existenz in der jeweiligen ökologischen Nische sichern. Die Wirkung von
Peptidliganden beruht auf der Wechselwirkung mit Bindungspartnern, wodurch ein bestimmtes
biologisches Signal ausgelöst oder inhibiert wird. Um seine spezifische Aufgabe erfüllen zu
können, mus