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Organic & Biomolecular Chemistry
propenꢀ1ꢀone) failed since the absorption maxima of this
S.A.) and the DAAD for a PhD scholarship for N.A.
compound lies beyond 300 nm and therefore our UVꢀVIS
detectionꢀbased method cannot be used.
Notes and references
5
1H NMR studies with different α,βꢀunsaturated natural products
have been used to successfully group these into reversible and
irreversible thiol sinks.11 Under the conditions used (DMSOꢀ
d6/dilution with CDCl3) there is no need for a chromophore and
important structural information is gained when more than one
straße 31, 93503 Regensburg, Germany. Fax: 49 941 943ꢀ4121; Tel: 49
941 943ꢀ4650; Eꢀmail: sabine.amslinger@chemie.uniꢀregensburg.de
† Electronic Supplementary Information (ESI) available: Experimental
details, 1H NMR, 13C NMR spectra of 14ꢀ18. CCDC 909409 (21). See
65 DOI: 10.1039/b000000x/
‡ These authors contributed equally to this work.
10 reactive site could be addressed in one molecule. On the other
hand, to quantitatively compare libraries of compounds like
chalcones where only small structural changes are introduced, our
method allows for a very precise assessment of the reactivity of
each single compound. Thus, our 96ꢀwellꢀmicrotiter plate assay
15 can facilitate the evaluation of many and very important classes
of molecules particularly aromatic α,βꢀunsaturated carbonyl
compounds like the polyphenols. Nevertheless, there are
limitations to use the reactivity in thiaꢀMichael additions for a
prediction of biological activity. When surface cysteins need to
20 be addressed as for example in the activation process of Nrf2 via
the Keap1ꢀNrf2 pathway or in the inhibition of NFꢀκB, reactivity
rather than accessibility determines whether an Sꢀalkylation of
their highly reactive sulfhydryl groups takes place. Very strong
electrophiles could certainly lead to unspecific reactions with less
25 reactive thiol groups, but they may be neutralized by the cellular
electrophile trap glutathione (GSH), whose cysteine residue
displays only moderate activity. This fact can be responsible for a
reduced activity of certain potent electrophiles which therefore
show less unspecific toxicity.12 Moreover, metabolic
30 transformations, such as the hydroxylation of the aromatic rings
of the α,βꢀunsaturated carbonyl compounds could change their
reactivity and therefore overall biological activity.13 Other α,βꢀ
unsaturated carbonyl compounds such as the flavonoles
kaempferol (34) and quercetin (35) show significant biological
35 activities such as cancer prevention,14 but have not proven to be
electrophiles. 34 and 35 are considered as antioxidants because of
their free phenolic hydroxyl groups that can act as reductants or
induce ROSꢀmediated processes. Moreover, their structure itself
could form nonꢀcovalent interactions and thus initiate biological
40 activity apart from alkylation and redox reactions.
1. For selected reviews see: a) M. L. Go, X. Wu and X. L. Liu, Curr.
Med. Chem., 2005, 12, 483ꢀ499; b) Z. Nowakowska, Eur. J. Med.
70
Chem., 2007, 42, 125ꢀ137; c) C. Kontogiorgis, M. Mantzanidou and
D. HadjipavlouꢀLitina, Mini Rev. Med. Chem., 2008, 8, 1224ꢀ1242;
d) A.ꢀM. Katsori and D. HadjipavlouꢀLitina, Expert Opin.Ther.
Patents, 2011, 21, 1575ꢀ1596.
2. S. Amslinger, ChemMedChem, 2010, 5, 351ꢀ356.
75 3. Kinetic data for a series of alphaꢀXꢀchalcones based on our thiol
assay will be published elsewhere.
4. a) D. G. Roux and D. Ferreira, Phytochemistry, 1974, 13, 2039ꢀ2048;
b) W. Greenaway and F. R. Whatley, Phytochemistry, 1990, 29,
2551ꢀ2554; c) R. Metuno, F. Ngandeu, A. T. Tchinda, B. Ngameni,
80
85
90
G. D. W. F. Kapche, P. C. Djemgou, B. T. Ngadjui, M. Bezabih and
B. M. Abegaz, Biochem. Syst. Ecol., 2008, 36, 148ꢀ152.
5. S. Sogawa, Y. Nihro, H. Ueda, A. Izumi, T. Miki, H. Matsumoto and
T. Satoh, J. Med. Chem., 1993, 36, 3904ꢀ3909.
6. A kinetic measurement performed of 19 in a 1:1 mixture of
MeCN/100 mM TRISꢀHCl pH 7.4 (A. T. DinkovaꢀKostova, M. A.
Massiah, R. E. Bozak, R. J. Hicks and P. Talalay, Proc. Natl. Acad.
Sci. U. S. A., 2001, 98, 3404ꢀ3409) gave a very fast reaction with
GSH.
7. G. A. Bagiyan, I. K. Koroleva, N. V. Soroka and A. V. Ufimtsev,
Russ. Chem. Bull., Int. Ed., 2003, 52, 1135ꢀ1141.
8. a) F. Jin, X. Y. Jin, Y. L. Jin, D. W. Sohn, S.ꢀA. Kim, D. H. Sohn, Y.
C. Kim and H. S. Kim, Arch. Pharm. Res., 2007, 30, 1359ꢀ1367; b)
A. T. DinkovaꢀKostova, C. Abeygunawardana and P. Talalay, J.
Med. Chem., 1998, 41, 5287ꢀ5296.
95 9. In some other aromatic α,βꢀunsaturated carbonyl compounds, orthoꢀ
hydroxyl groups in general proved to increase biological activity (A.
T. DinkovaꢀKostova and P. Talalay, Carcinogenesis, 1999, 20, 911ꢀ
914).
In summary, we have developed a new, simple kinetic assay
whose solvent system allows the inclusion of compounds with
quite different reactivities in Michael additions of thiols. We
45 could show a structureꢀactivity relationship within 16 chalcones
and could compare them with the well studied curcumin. This
assay can be used to better understand biological activities of
Michael acceptors and therefore to help to overcome their poor
standing in drug development.
10. J. H. v. Tonder, T. J. Muller and B. C. B. Bezuidenhoudt, Acta
100
Crystallogr., Sect. E: Struct. Rep. Online, 2010, 66, o1798ꢀo1799.
11. C. Avonto, O. TaglialatelaꢀScafati, F. Pollastro, A. Minassi, V. Di
Marzo, L. De Petrocellis and G. Appendino, Angew. Chem. Int. Ed.,
2011, 50, 467ꢀ471.
12. J. Heilmann, M. R. Wasescha and T. J. Schmidt, Biorg. Med. Chem.,
2001, 9, 2189ꢀ2194.
105
50
13. Y. Kohno, S. Kitamura, S. Sanoh, K. Sugihara, N. Fujimoto and S.
Ohta, Drug Metab. Dispos., 2005, 33, 1115ꢀ1123.
Acknowledgements
14. H. S. Aiyer, A. M. Warri, D. R. Woode, L. HilakiviꢀClarke and R.
Clarke, J. Agric. Food Chem., 2012, 60, 5693ꢀ5708.
We thank Karl Amslinger for developing an Excel sheet for easy
data processing, Sandra Schlee (Institut für Biophysik und
Physikalische Biochemie, Universität Regensburg) for expert
55 help with stoppedꢀflow experiments, the Mass Spectrometry Unit
(Universität Regensburg) for LCꢀMS measurements, the Fonds
der Chemischen Industrie for funding (Liebig scholarship for
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