Biology Reference
In-Depth Information
2.2.2 Oligomers linked with valoneoyl and dehydrovaloneoyl groups
The
m
-DOG-type oligomers that bear a valoneoyl group or its oxidized
variant as linking unit(s) constitute the largest class of oligomeric
ellagitannins, and are distributed in a wide range of plant families. The
structural diversity in these oligomers arises from the variation in the
positions of the HHDP and galloyl groups that participate in the
formation of a valoneoyl group through the intermolecular oxidative
coupling of monomers.
Typical oligomers with 4,6-, 2,3-, or 3,6-valoneoyl groups on their
glucose core include the dimers heterophylliins A, B and C (
68
, Yoshida
et al.
, 1991d) and the trimer heterophylliin G (Jin
et al.
, 1998),
davuriciins D
1
(
69
) and T
1
(Yoshida
et al.
, 1991e), the dimers coriariins
D and E (Hatano
et al.
, 1986), nobotanins A (
70
), B (
78
), F (
71
), G, H, I
(Yoshida
et al.
, 1991f, 1991g), malabathrins B (
72
), C and D (Yoshida
et
al.
, 1992), cornusiins A (
73
), D and E, and the trimers cornusiin C (
74
)
(Hatano
et al.
, 1989) and trapanin A (
75
, Hatano
et al.
, 1990b), the
dimers camptothins A and B (Hatano
et al.
, 1988a), calamanins B and C
(Tanaka
et al.
, 1991), isorugosins D (
76
) and E (Hatano
et al.
, 1988b),
camelliatannins D (
80
) and H (Han
et al.
, 1994, Hatano
et al.
, 1995),
eumaculins A-C (Agata
et al.
, 1991, Amakura
et al.
, 1997), bishofianin
(Tanaka
et al.
, 1995) and mallotannins A (
85
) and B (Saijo
et al.
, 1989).
Plant sources of these oligomers and others discussed below are listed in
Table 2.3.
Worthy of particular mention are the dimers resinins A, B, C (
77
)
and D (
79
, Xu
et al.
, 1991) isolated from
Lagerstroemia flos-reginae
, as
well as heterophylliins B and C (
68
) from
Corylus heterophylla
, for they
contain a
C
-glycosidic ellagitannin as one of their constituting
monomers. The
C
-glycosidic tannin monomer in resinin C (
77
) has a
pentose residue in which the anomeric center is C-C-linked to the C-1
center of the
C
-glycosidic tannin unit. It is also worth noting that the
dimers euphorbins A (
81
, Yoshida
et al.
, 1988) and F (
82
, Yoshida
et al.
,
1991h), euphorhellin (
83
, Lee
et al.
, 1991) and excoecarianin (
84
, Lin
et
al.
, 1990) from plant species of the
Euphorbiaceae
family have geraniin-
based structures. Since they have not been encountered in any other plant
family, this type of dimer is chemotaxonomically significant.
