Biology Reference
In-Depth Information
2.2.3 Oligomers linked with an isomeric valoneoyl group
Sanguisorboyl, tergalloyl, and macaranoyl groups are isomeric valoneoyl
groups. In addition to the oligomers possessing these groups described in
Chapter 1, euphorbins B (
88
) and I (
89
) (Amakura
et al.
, 1996) from
Euphorbia
species possess (
R
)-tergalloyl and (
R
)-macaranoyl groups as
their linking unit, respectively. Euphorbins C (
90
) and D (
91
) are unique
dimers possessing a D(OG)
2
-type (euphorbinoyl) linking unit in which
a tergalloyl or a valoneoyl group is linked to a galloyl group.
2.2.4
C
-Glycosidic ellagitannin oligomers
Oligomeric
C
-glycosidic ellagitannins are regarded as the products of
intermolecular C-C coupling between the anomeric carbon of one
monomer and the HHDP or galloyl group of the other monomer. Since
1991, approximately 30
C
-glycosidic ellagitannin oligomers have been
isolated from various plant species in the
Fagaceae
,
Casuarinaceae
,
Melastomataceae
(Yoshida
et al
., 1992b),
Elaeagnaceae
, and
Combretaceae
. Vescalagin (
44
)-based oligomers include roburins A-D
(
92
-
95
) (Hervé du Penhoat
et al.
, 1991), and anogeissusins A (
96
) and B
(
97
) (Lin
et al
., 1991) isolated from an European oak species (
Quercus
robur
) and
Anogeissus acuminata
, respectively.
Stachyurin (
46
)-based oligomers include alienanin B (
98
) (Nonaka
et al
., 1991; Yoshida
et al
., 1992b) and casuglaunin A (
99
) (Shimokawa
et al
., 1991). The leaves of
Elaeagnus umbellata
produce the analogs
elaeagnatins D (
100
)-G (Ito
et al
., 1999b). In the dimers anogeissinin
(
101
) (Lin
et al
., 1991) and casuglaunin B (
102
) (Ito
et al
., 1999b,
Shimokawa
et al
., 1991), two molecules of a vescalagin (or stachyurin)
type monomer are connected through the A-ring of catechin. Cowaniin
(
103
), a putative precursor of
102
, was found in
Cowania mexicana
(Ito
et al
., 2007) and
Melaleuca squarrosa
(Yoshida
et al
., 2008). As for
C
-
glycosidic tannin oligomers that are larger than dimers, castaneanins
[dimer to pentamer (
104
-
107
)] (Tanaka
et al
., 1996) from the heartwood
of the Japanese chestnut tree and melasquanins B, C, and D (
108
) from
M
.
squarrosa
(Yoshida
et al
., 2008) have been identified. In all of these
C
-glycosidic ellagitannin oligomers, the intermolecular linkage at the
