Studies on the chemical biology of natural and chemical ribonucleotide modifications [Elektronische Ressource] / vorgelegt von Salifu Seidu-Larry

Todenn

Sujets

• Biologie

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2009
• Nombre de lectures: 45
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

INAUGURAL–DISSERTATION


Zur Erlangung der Doktorwürde

der

Naturwissenschaftlich–Mathematischen Gesamtfakultät

der

Ruprecht-Karls-Universität

Heidelberg





Vorgelegt von

M. Sc. Chem. Salifu Seidu-Larry

Aus Ghana



Tag der mündlichen Prüfung: 09.07.2009






















Studies on the Chemical Biology of Natural and
Chemical Ribonucleotide Modifications








Gutachter: Prof. Dr. Andres Jäschke
PD. Dr. Mark Helm


























Die vorliegende Arbeit wurde in der Arbeitsgruppe von PD. Dr. Mark Helm in der Zeit von Nov.
2004 bis August 2008 am Institut für Pharmazie und Molekulare Biotechnologie (IPMB),
Abteilung Chemie der Fakultät für Biowissenschaften der Ruprecht-Karls-Universität Heidelberg
angerfertigt.

Hiermit erkläre ich eidesstattlich, dass ich die vorliegende Arbeit selbständig und unter
Verwendung Quellen und Hilfsmittel angefertigt habe, sowie wörtliche oder inhältliche Zitale als
solche gekennzeichnet habe



Salifu Seidu-Larry













Acknowledgement

I first give thanks to the Almighty God whose grace has been part of this long journey away from
the bigger family and relations.
I would like to thank PD Dr. Mark Helm who gave me the opportunity to undertake my PhD
thesis in his group and for being a dedicated and patient supervisor whom I could consult for any
questions. I really appreciated the interesting discussions in his office during the later-months of
the PhD. I am also very thankful to PD Dr. Mark Helm for his patient and also the interesting
project that I was in charge of and especially the freedom of creating my own ideas during the
work. I should say that I did not only learn science but human relations as well.
I want to say profoundly from the bottom of my heart a very big thank you to the following
persons: Prof. Dr. A Jäschke, first for being a co-supervisor, and creating a scientifically
conducive atmosphere for work and lastly for the knowledge impacted during my stay in
Heidelberg. I also say a big thank you to Prof. Dr. Jürgen Reichling and Prof. Dr. Gert Fricker
who both opted to be part of the final defence examining board. To Frau Viola Funk and and
Frau Karin Weiss whose help in all spheres (work and social) are unquantifiable I say (Nye yi
wala do on) thank you.
Thanks also go to Herrn Heiko Rudy, Tobias Timmerman and Frau Sandra Suhm for the
technical and friendly support during my work here. I would very much express my feeling of
warmth to Markus Petermeier and Ayan Samanta who do manage out of the precious time of a
Phd student to spend some time with my family. Also of whose special visit to my two little girls
I consider invaluable is Florentine Wahl. The ‘Seidu-Larrys’ do appreciate it and we thank you
immensely. Many thanks to all the former lab members who helped me acclimatize to
Heidelberg: Julius M., Felix V-H., Roberto F., etc to mention a few. Thanks also go to Felix V.-
H., Niklas F. and Barbara S. W. for the night life in Heidelberg before I got married. The
Wednesday morning soccer section which got me hospitalized also send memories of the nice
time we shared among Pierre Fournier, Richard Wombacher, Markus L Petermeier and the
members of the AK Metzler-Nolte. Many thanks to Mihaela who got me oriented into the use of
most of the gadgets in the lab not forgetting Steffi Pfander too. Those of us who share a common
reading desk or area: Martin Hengesbach who helped for the correction of the diffult ‘stress-
induced grammar’, Armine Hayrapetyan who coached me on UV melting curves and a lot more,
thank you soo soo much. Markus Hirsch welcome back to AK Helm. Thanks go also to the
following: Alexander Nierth, Anna Wiesmayr, Juliane Schoch, Marco Singer, Marie-Luiz Winz,
Michaela Kotaskova, Olwen Domingo, Steffi Draeger, Stefanie Gehrig, Steffi Kraut and Valeska
Dernedde for creating a friendly working environment. To Mr. ‘Sandy’Ameta Sandeep, I am
more than grateful for you keeping vigil with me in order to get this thesis into a printable
manuscript. Enver Cagri, Lars Ludicke, Stefanie Kellner, Dominic Riedel, Anne Neef and
Chandrabali Bhattacharya who contributed in every small way during the time we spent together
in the Lab, to you I say (Ayekoo) thank you in abundance. To those who by virtue of me being
stress-hung I forgot that we spend some valuable time during this work, thank you too.
To the very ‘old padies’ Kristof Lindner and Karifala Dumbuya your friendship have I always
cherished. To my Ghanaian links in Heidelberg, Maame Manful Theresa, Ernest Osei and David
Ankrah thanks for the nice times spent together here in Heidelberg. My final and my hearthy
gratitude go to my wife Frau Belinda S.-Larry for the patience, love and warmth we shared. I do
not forget the two ‘lovely girls’ Moindan and Todenn who tried helping Papa type during the
night. Before I finally say Tschuss, I say a big thank you to my family back home in Ghana
especially my mum whose constant encouragement makes life worth a journey.

I

Summary Seidu-Larry, Salifu; M. Sc. Chem.

Title: Studies on the chemical biology of natural and chemical ribonucleotide
modifications

1. Examiner: Prof. Dr. Andres Jäschke
2. Examiner: PD. Dr. Mark Helm

This work is centered on the synthesis and chemical recognition of modified RNA.
5 1 2 2Phosphoramidites of m U, Ψ, m G, m G and m G were synthesized and were incorporated into 2
RNA oligomers by standard SPS. The synthesized oligomers were used for two purposes: (i) the
total construction of tRNA via enzyme catalyzed ligation, and (ii) investigations of modifications
in siRNAs.
IleThe construction of human mitochondrial tRNA (i) with and without modification was
achieved in a one-pot 3 fragments ligation using T4-DNA-ligase with a DNA-splint. The yield
for the ligation was 20-30 % and the products were further investigated for the stability of the
tertiary structure via UV-melting curve analysis. The unmodified tRNA was found to be
significantly less stable than the fully modified tRNA.
In the second case (ii) RNAi efficiency and the immunostimulation in cells were investigated
with 22 nucleotide long double-stranded siRNAs that were synthesized containing the
1 2 2modifications m G, m G, m G, rT and Ψ in varying stochiometry. The investigations showed 2
differential effects in knock-down as well as immunostimulation.
In a related perspective, compounds for the chemical recognition of modifications in RNA were
synthesized. Since the recognition of pseudouridine by 4-bromomethyl-coumarin derivates is of
particular interest, 7-azido-4-bromomethyl-coumarin was obtained with an overall yield of 44 %
in a 5-step synthesis. Another derivative, the biotinylated 4-bromomethyl-coumarin spaced with
jeffamine-148 was obtained in a 6-step synthesis with an overall yield of 17 %, to allow the use
of strepavidin for affinity separation.
In the course of further investigations of coumarine conjugates, mild and bio-compatible
conditions for the syntheses of rhodols and rhodamines were discovered. The conversion of
fluorescein into the 3’-mesylated or 3’-6’-dimesylated derivate and the subsequent displacement
of the mesylate with a nitrogenous nucleophile gave rise to rhodols or rhodamines, respectively.
As these reaction conditions are compatible with biomolecular labeling, the tagging of
polypeptides was investigated. Tri-and pentapeptides were synthesized, and dye-labeled via
3’/6’-xanthene substitution, and the product identity confirmed by MALDI-TOF-MS. Further
syntheses via 3’/6’-xanthene substitution lead to moderate yields of 3',6'-bis(dimethylamino)-3H-
spiro[isobenzofuran-1,9'-xanthen]-3-one, 3',6'-di(piperidin-1-yl)-3H-spiro[isobenzofuran-1,9'-
xanthen]-3-one and the 3',6'-bis(2-(2-(2-aminoethoxy)ethoxy)ethyl amino)-3H--xanthen]-3-one.





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