posted on 2022-12-14, 20:39authored byAnnemiek van Zadelhoff, Lieke Meijvogel, Anna-Marie Seelen, Wouter J.C. de Bruijn, Jean-Paul Vincken
Oxidative coupling of hydroxycinnamoylagmatines in barley
(Hordeum vulgare) and related Hordeum species is part of the plant defense mechanism.
Three linkage types
have been reported for hydroxycinnamoylagmatine dimers, but knowledge
on oxidative coupling reactions underlying their formation is limited.
In this study, the monomers coumaroylagmatine, feruloylagmatine, and
sinapoylagmatine were each incubated with horseradish peroxidase.
Their coupling reactivity was in line with the order of peak potentials
measured: sinapoylagmatine (245 mV) > feruloylagmatine (341 mV)
>
coumaroylagmatine (506 mV). Structure elucidation of fourteen in vitro coupling products by NMR and MS revealed that the
three main linkage types were identical to those naturally present
in Hordeum species, namely, 4-O-7′/3-8′,
2-7′/8-8′, and 8-8′/9-N-7′.
Furthermore, we identified two linkage types that were not previously
reported for hydroxycinnamoylagmatine dimers, namely, 8-8′
and 4-O-8′. We conclude that oxidative coupling
by horseradish peroxidase can be used for biomimetic formation of
natural antifungal hydroxycinnamoylagmatine dimers from barley.