2024-03-28T10:11:59Z
https://meral.edu.mm/oai
oai:meral.edu.mm:recid/2177
2021-12-13T03:22:54Z
1582963390870:1582967633684
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Reactions of the melatonin metabolite N1-acetyl-5- methoxykynuramine (AMK) with the ABTS cation radical: identification of new oxidation products
Ni Ni Than
Heer, Christina
Laatsch, Hartmut
Hardeland, Rüdiger
The melatonin metabolite N1
-acetyl-5-methoxykynuramine (AMK; 1), which was previously shown
to be a potent radical scavenger, was oxidized using the ABTS cation radical [ABTS = 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic
acid)]. Several new oxidation products were obtained, which
were separated by repeated chromatography and characterized by spectroscopic methods such as
mass spectrometry (ESI-MS and ESI-HRMS), 1
H-NMR and 13C-NMR, HMBC, HSQC, H,H COSY
correlations and IR spectroscopy. The main products were oligomers of 1 (3 dimers, 1 trimer and 2
tetramers). In all cases, the amino group N2 was involved in the reactions. Two of the dimers turned
out to be cis (2a) and trans (2b) isomers containing an azo bond. In the other dimer (3a), the
nitrogen atom N2 was attached to atom C5 of the second aromatic amine, with loss of the methoxy
group. In the trimer (5), one N2 formed a bridge to C5 of unit B, as in the respective dimer, while this
one of C had bridged to C6 of B. One of the tetramers (6) was composed of a trimer 5 attached to N2
of a fourth 1 molecule via an azo bond as in 2a/b. In the other tetramer (7), an additional C–C bond
between rings B and C in 6 is assumed. Although oligomers of AMK may only attain low in vivo
concentrations, the types of reactions observed shed light on the physiologically possible
metabolism of AMK once reacted with a free radical. The displacement of a methoxy group, rarely
seen in the oxidation of methoxylated biomolecules, underlines the reactivity of AMK (1).
Preliminary data show that, in the presence of ABTS cation radicals, AMK (1) can interact with side
chains of aromatic amino acids, a finding which may be crucial for understanding to date
unidentified protein modification by a melatonin metabolite detected earlier in experiments with
radioactively labeled melatonin.
2005
http://hdl.handle.net/20.500.12678/0000002177
https://meral.edu.mm/records/2177