Photoexcitation of pheomelanin produces high-energy singlet
oxygen
and the superoxide anion, which are reactive species in damage of
cellular targets. In principle, these species can be involved in processes
of synthetic utility when adequate experimental conditions are defined.
Here, we describe that pheomelanin performs as a selective UVA antenna
for the horseradish peroxidase oxidative coupling of substituted phenols
to biologically active Pummerer’s ketones under 2-methyltetrahydrofuran/buffer
biphasic conditions. In this system, singlet oxygen is scavenged by
conversion of 2-methyltetrahydrofuran into the corresponding organic
hydroperoxide, while the superoxide anion is dismutated into hydrogen
peroxide. Both these intermediates are able to oxidize the active
site of horseradish peroxidase triggering the oxidative coupling reaction.
Trimer derivatives, produced by addition of phenoxy radicals on preformed
Pummerer’s ketones were also isolated, suggesting the possibility
to further improve the structural complexity of the reaction products.
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