Biology Reference
In-Depth Information
9.1.1.1
Oak and chestnut C-glycosidic ellagitannins
Vescalagin (
1
) and its C-1 epimer castalagin (
2
) are the first
C
-glycosidic
ellagitannins that have been investigated after their isolation thirty years
ago from
Castanea
(chestnut) and
Quercus
(oak) woody species of the
Fagaceae
family by Mayer and co-workers (Mayer
et al.
, 1967, 1969,
1971a). Their structures, as well as those of their 2,3-HHBP-bearing
analogues, stachyurin (
3
) and casuarinin (
4
) (Okuda
et al.
, 1981, 1982,
1983), were fully determined much later after revision of their respective
configuration at C-1 by the Nishioka's group (Nonaka
et al.
, 1990). The
combined amount of these two epimers in the heartwood of oak species
such as
Quercus petraea
and
Quercus robur
has been evaluated to vary
from
ca
. 3 to 57 mg/g of dry wood, depending on the species, age and
sampling position in the tree (Mosedale
et al.
, 2001, Fernández de Simón
et al.
, 1999, Vivas
et al.
, 1996, Masson
et al.
, 1995, 1996, Viriot
et al.
,
1994). The heartwood of chestnut species such as
Castanea
sativa
can
even contain up to 63 mg of vescalagin (
1
) and castalagin (
2
) per gram of
dry wood,
i.e.
, more than 6% (!) by weight of dry material (Viriot
et al.
,
1994). Six other NHTP-containing
C
-glycosidic ellagitannins were later
isolated from fagaceous
Quercus
and
Castanea
hardwood species,
i.e.
,
the dimers roburins A (
5
) and D (
6
), and the lyxose/xylose-bearing
monomers grandinin (
7
) and roburin E (
8
) and dimers roburins B (
9
) and
C (
10
) (Fig. 9.2) (Nonaka
et al.
, 1989, Hervé du Penhoat
et al.
, 1991a/b).
Among these eight typical NHTP-containing
C
-glycosidic ellagitannins,
vescalagin (
1
) and castalagin (
2
) largely predominate in the fagaceous
woody species containing them, representing for example between 40%
and about 60% by weight of this group of ellagitannins in
Quercus
petraea
and
robur
heartwoods (Fernández de Simón
et al.
, 1999, Masson
et al.
, 1994, 1995, 1996).
Many additional
C
-glycosidic ellagitannins, including monomers,
oligomers and complex tannins (
vide infra
), have been identified over the
years from species belonging to the selection of plant families mentioned
above (for a compendium of identified structures, see Section 1.3.3 in
Chapter 1 and Sections 2.1.4, 2.1.5 and 2.2.4 in Chapter 2, see also
Haslam and Cai, 1994). A large majority of these structurally complex
natural products (including all types of ellagitannins) has been identified