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requirement could be met by hydrolysis of
all
possibly formed
ellagitannins in the reaction mixtures to release free HHDP units (
5
)
from
any
reaction product. All these derivatives, in turn, would
spontaneously rearrange to only
one
product, the corresponding
dilactone, ellagic acid (
6
). This latter compound could thus serve as the
sole, general probe for numerous oxidative reactions. Moreover, working
with a pentagalloylglucopyranose (
3
) substrate labelled either uniformly
OG
O
GO
OG
GO
OG
3
In vitro
oxidation
GO
G
G
G
G
O
O
O
O
O
GO
O
O
OG
OG
OG
O
GO
O
G
OG
G
O
4
O
G
G
17
18
Hydrolysis
Hydrolysis
Anomerization
GO
G
G
G
G
O
O
O
O
O
O
O
GO
O
H
OH
α
GO
O
O
OG
G
G
O
O
OG
G
G
19
20
21
Total hydrolysis of ester bonds
OH
OH
HO
OH
O
O
OH
HOOC
Lactonization
COOH
HO
OH
HO
OO
OH
OH
6
5
Fig. 3.8 Strategies for elucidating the
in vitro
synthesis of ellagitannins. Oxidation of the
principal precursor, pentagalloyl-β-
D
-glucopyranose (
3
, shown in the
4
C
1
conformation)
and subsequent secondary reactions can afford numerous structurally related products.
Energetically less favored glucose conformations (
e.g.
,
1
C
4
) can provide additional
products. Also oligomerization reactions might occur. Total hydrolysis finally affords
ellagic acid (
6
) as a sole and general indicator of any preceding ellagitannin formation.
(
4
) Tellimagrandin II; (
17
) casuarictin; (
18
) pterocaryanin C; (
19
) tellimagrandin I; (
20
)
pedunculagin; (
21
) sanguiin H-4.
