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radiolysis and metal-catalyzed oxidation of Trp [14, 345, 351, 352]. The oxida-
tion scheme in Figure 4.30 shows the addition of
•
OH to both the benzene ring
and the pyrrole moiety at the c-2 and c-3 double bond with a relative ratio
around 40 : 60 [353]. The oxidized products may further oxidize to yield dihy-
droxytryptophan and hydroxykynurenine. Such products were detected in the
radiolysis of Trp-NH
2
and tripeptide gWg [261, 354].
Figure 4.31 presents the +16 oxidation product of Tyr [261]. In the oxidation,
•
OH adds to the sites next to the original hydroxyl substituent at the side chain.
O
O
O
N
N
N
3
2
HO
•
O
2
HO-Trp
(Mixture of isomers)
+16 Da
NH
NH
NH
4
5
7
HO
•
6
HO
HO
O
O
O
O
N
N
N
N
OH
OH
O
2
+
O
+
O
•
NH
2
NH
NH
NHCHO
2-HO-Trp
+16 Da
N-Formylkynurenine
+32 Da
Kynurenine
+4 Da
Figure 4.30.
Oxidation of Trp by
•
OH radical (aapted from xu and chance [261] with
the permission of the American chemical Society).
O
O
O
N
HO
•
N
O
2
N
OO
•
•
OH
OH
OH
OH
H
H
OH
HOO
•
O
O
N
N
+16 Da
OH
O
OH
H
OH
Figure 4.31.
Oxidation of Tyr by
•
OH radical (adapted from xu and chance [261] with
the permission of the American chemical Society).
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