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In fact, the other four pyrogallol units are probably also to some
extent, but reversibly, converted into
ortho
-quinones. As alluded to
above, all of the pyrogallol rings of a
C
-glycosidic ellagitannin such as
vescalagin (
1
) would follow the same behavior under wine oxygenation
conditions in oak barrels. However, in the case of a flavano-ellagitannin
such as acutissimin A (
14
, also present in wine, see Section 9.3.1), the
ortho
-quinone derived from the pyrogallol I-ring is the only one that can
be irreversibly trapped by the proximal flavanol unit with its 7-OH group
well-positioned to engage in such an intramolecular reaction.
9.4 Conclusion and Perspectives
The ellagitannin chemistry discussed in this chapter is yet another
example of the remarkable impact of natural products on human
activities. Isn't it fascinating to realize that natural products derived from
the metabolism of plants for their protection against pathogens and
herbivores (Hart and Willis, 1972, Scalbert and Haslam, 1987, Scalbert,
1991), then identified as active principles of plant extracts used in folk
medicines and later as promising drug leads, end up being investigated
for their role in the elaboration of the biophysico-chemical and
organoleptic profile of a beverage such as wine. Herein, the most
illustrating and fascinating example of such a natural product connection
with human practices is the formation of the potent human DNA
topoisomerase II inhibitor, acutissimin A (
14
), in wine as a consequence
of the mixing in solution of grape catechin and oak vescalagin during
aging in barrels.
The chemistry that our laboratory has unveiled at the molecular level
on the physico-chemical behavior of oak
C
-glycosidic ellagitannins
should help wine scientists and enologists in their long-standing and
continuous endeavor toward a better understanding of wine chemistry.
The various complex and hybrid ellagitannins described herein are only a
few examples of a large panel of compounds that can be derived from
vescalagin (
1
) and its analogous oak congeners in combination with a
multitude of nucleophilic species available in wine. Other yet
unpublished examples involving
inter alia
a phenolic stilbene such as
