ISBN: 978-83-60043-10-3 - eurobic9

Eurobic9, 2-6 September, 2008, Wrocław, Poland
P97. Peptides Conjugated with Quinoxalines and Their Affinity to Metal
Ions Analysed by High Resolution Mass Spectrometry
A. Kluczyk, B. Predko, A. Staszewska, P. Stefanowicz, M. Jeżowska-Bojczuk, Z. Szewczuk
Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland
e-mail: kluczyk@wchuwr.pl
The search for new bioactive peptides directed our attention to new methods for introducing heterocyclic motifs
into peptide side chains [1]. Considering the biological activity and complexing abilities of quinoxalines we
developed a direct solid-phase synthesis of quinoxaline-peptide conjugates, expecting these new compounds to
express novel biological properties [2].
We investigated two solid phase protocols of synthesis of quinoxaline-containing peptides. The first method uses
the commercially available 4-amino-3-nitrobenzoic acid, which could be attached to the ε-amino group of lysine
or the N-terminal α-amino group of peptide. For the second procedure we developed a special phenylalanine
derivative, Fmoc-Phe(4’-NH2-3’-NO2)-OH, which can be used as a building block for standard Fmoc protocol
for peptide synthesis [2]. In both these methods the quinoxaline formation involves reduction of the aromatic
nitro group and the subsequent condensation of the o-phenylenediamine intermediate with
α-dicarbonyl reagents.
N
N
N
N
N
N
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216
A
N
N
O
Aaa
O
NH
NH
Peptides containing quinoxaline motifs: A - as a modification of amino groups, B - in the form of a novel amino
acid residue. Aaa represents amino acid residue or peptide fragment.
Using these procedures we obtained a series of peptides conjugated with quinoxalines containing various
substituents. We concentrated our attention on compounds with two 2-pyridil moieties attached to the
quinoxaline skeletons. Such heterocyclic systems are known for their affinity to metal ions [3], whereas
bipyridine-peptide conjugates complexed with ruthenium ion and additional quinoxaline derivative were
investigated as metallointercalators [4].
We investigated the binding of copper (II) ions to both types of quinoxaline-peptide conjugates using high
resolution electrospray mass spectrometry. The method is ideal for initial screening of potential high affinity
ligands because of minimal sample consumption and the insight into the structure of the complex through the
fragmentation analysis and the experiments involving proton-deuter exchange.
Acknowledgements: Supported in part by Grant No. N N204 1616 33 from the MSHE (Poland).
References:
[1] A. Kluczyk, A. Staszewska, P. Stefanowicz et al., J. Peptide Sci., 12, 111 (2006).
[2] A. Staszewska, P. Stefanowicz, Z. Szewczuk, Tetrahedron Lett., 46, 5525 (2005).
[3] A.A. Abdel-Shafi, M.M.H. Khalil, H.H. Abdalla, R.M. Ramadan, Transition Metal Chemistry, 27, 69 (2002).
[4] K.D. Copeland, A.M.K. Lueras, E.D.A. Stemp, J.K. Barton, Biochemistry, 41, 12785 (2002).
O
Aaa
N
Aaa
B
N
N
NH
O
N
Aaa