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linking unit repeatedly participates in the construction of an oligomeric
ellagitannin system.
a
OH
HO
OH
HO
p
m
OH
OH
b
O
O
a
b
HO
OH
OH
HO
HO
OH
HO
O
OH
O
OH
OH
O
O
O
O
m
-GOG
(dehydrodigalloyl)
group
p
-GOG
(isodehydrodigalloyl)
group
HO
OH
OH
O
OH
OH
OH
HO
HO
HO
m
-GO-
m
-GOG
(hellinoyl)
group
O
O
OH
O
O
O
Fig. 1.5 Formation of the GOG and GOGOG oligomeric linking units.
1.3.4.2.1 The GOG- and GOGOG-type units
The GOG-type linking units are produced by C-O coupling between two
galloyl groups (Fig. 1.5), as found in the
p
-GOG isodehydrodigalloyl
group (
p-O
of a galloyl group C-linked to another galloyl group, mode
a
)
and the
m
-
GOG dehydrodigalloyl group (
m
-
O
of a galloyl group C-
linked to another galloyl group, mode
b
). The GOGOG-type units are
formed via an additional oxidative C-O coupling of a galloyl group with
a GOG group. Agrimoniin and laevigatins B, C, D (Yoshida
et al
.,
1989a) and E, as well as gemin A, are examples of dimers featuring the
GOG-type linkage, and tamarixinin A and hirtellin B (Yoshida
et al
.,
