Abstract
Hydroxycinnamoylamides are specialised
metabolites widely distributed in the plant kingdom.
These are phenolic moieties covalently linked to
mono- or polyamines through amide bonds. Their
oxidative coupling (dimerisation) leads to neolignanamides,
a group of compounds showing high
chemical, structural and functional diversity. Typical
to barley, dehydro dimers of hydroxycinnamoylagmatines,
hordatines are primarily found in germinated
seeds and at the seedling stage. The first step in the
biosynthesis of hordatines is catalysed by acyl-coenzyme
A-dependent N-hydroxycinnamoyltransferases,
and lead to the formation of hydroxycinnamoylagmatines
(HCAgms). The oxidative homo- or heterodimerisation
of the latter results in different hordatines
(A, B, C or D). Hordatines can also undergo various
types of conjugation and form hydroxylated, methylated
or glycosylated derivatives. Although the
research on the bioactivities of the hordatines is still
nascent, the in planta antifungal properties have long
been recognised. While hordatines are naturally and
uniquely synthesised in barley plants, these molecules
or lead compounds derived therefrom, also exhibit
medicinal and pharmaceutical uses important for
human health, stimulating research into the utilisation
of biotechnology in alternative production hosts and to
enhance agricultural yields and value-added production.
This review summarises the older and recent
knowledge about hordatines and derivatives and may
serve as a springboard for future research on this
intriguing class of secondary plant metabolites.