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predominant throughout summer until autumn. Three other related
compounds, tellimagrandin I ( 21 ), casuarictin ( 22 ) and the C -glycosidic
casuariin ( 24 ) (Okuda et al. , 1983), were also
isolated from the leaves collected in autumn (see
photo insert, Liquidambar formosana in
November, Japan). This seasonal variation of the
ellagitannin content in Liquidambar formosana
was proposed to reflect the following biogenetic
filiation (Fig. 9.6): from tellimagrandin II ( 20 ) to
pedunculagin ( 23 ) either via 1- O -degalloylation
into tellimagrandin I ( 21 ) followed by oxidative C-C coupling between
the O-2 and O-3 galloyl groups, or via a similar coupling to give first rise
to casuarictin ( 22 ) followed by 1- O -degalloylation, and hence, from
pedunculagin ( 23 ) to casuarinin ( 4 ) via casuariin ( 24 ) (Hatano et al. ,
1986). This filiation would imply that the formation of the C -glycosidic
bond precedes galloylation at the O-5 center, which is unveiled as a
consequence of the glucopyranose ring opening.
Another question still remained concerning the timing of this ring-
opening event from pedunculagin ( 23 ). Does this event precede or
concomitantly follow the formation of the C -glycosidic bond. Further
investigations on Liquidambar formosana enabled the Okuda's group to
find one important piece missing in this puzzle. They isolated (and
characterized) the open-chain aldehyde liquidambin ( 25 ), together with
its hydrated form (Okuda et al. , 1987). One can thus assumed that an
opening of the pedunculagin ( 23 ) glucopyranose ring, driven by a (fast)
5- O -galloylation, is the first key event that opens up the door to an access
to C -glycosidic ellagitannins (Fig. 9.6). Then follows the intramolecular
aldol-type nucleophilic addition of the 2,3-HHBP unit to the aldehyde
function of the resulting liquidambin ( 25 ), which gives rise to the
formation of the C -glycosidic bond such as in stachyurin ( 3 ) and its C-1
epimer casuarinin ( 4 ) (Okuda et al. , 1981, 1982, 1983, see also Nonaka
et al. , 1990). Their 5- O -degalloylation could then give rise to the
formation of 5-desgalloylstachyurin ( 26 ) (Lee et al. , 1990) and casuariin
( 24 ), respectively, and oxidative coupling between their 5-galloyl and
2,3-HHBP groups would in parallel furnish vescalagin ( 1 ) and castalagin
( 2 ) (Fig. 9.6) (Quideau et al. , 2004).
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