Biology Reference
In-Depth Information
1 center of
1
via either its nucleophilic C-8 center, leading to acutissimin
A (
14
), or its C-6 center, leading to acutissimin B (
15
).
Fagaceous woody species are generally very resistant to pathogens
and herbivores. In particular,
Quercus acutissima
, from which the
acutissimins A and B were first isolated, is usually pest-free and disease-
free. Of particular curiosity is the fact that this robust oak species, native
to Japan, has been selected as an ornamental tree in North America urban
areas where air pollution, poor drainage and/or drought are common.
Plant extracts containing acutissimins are used worldwide in folk
medicines to treat diseases including gastritis and gastric ulcer
(Khennouf
et al.
, 2003), diarrhea, various inflammations (
e.g.
, oral,
genital and anal mucosa, skin) (König
et al.
, 1994), and are used as tonic
and antitussive medicines (see Section 1.5 in Chapter 1). Kashiwada and
co-workers were first to report the extremely potent
in vitro
activity of
acutissimin A against human DNA topoisomerase II (Kashiwada
et al.
,
1993). We later confirmed their results in the course of our investigations
on bioactive wine-related polyphenols (Quideau
et al.
, 2005).
Indeed, our first incentive to study these complex tannins raised from
the fact that they are present in the bark of oak species commonly used in
France to make barrels, such as
Quercus robur
and
Quercus petraea
(König
et al.
, 1994), and in which fine wines are aged. However, the
bark is removed from oak tree logs, and the heartwood part from which
the staves are cut to manufacture barrels (Mosedale and Puech, 1998)
does not contain any acutissimin. Nevertheless, the heartwood of the
aforementioned oak species used for cooperage is a rich source of
C
-
glycosidic ellagitannins (
i.e.
, up to 10% by weight of dry wood, Peng
et
al.
, 1991), and notably of vescalagin (
1
, see Section 9.1.1). Even though
the long-term seasoning, or drying, of wood and the various pyrolytic
heating stages involved in the construction of the cask (Chatonnet
et al.
,
1989, Mosedale and Puech, 1998) considerably diminish the quantity of
1
and its congeners, a non-negligible portion resists these drastic
conditions (Doussot
et al.
, 2002, Cadahía
et al.
, 2001, Moutounet
et al.
,
1992). During aging in oak barrels, the hydroalcoholic and slightly acidic
(
i.e.
, pH ~ 3-4) wine solution enables the solid-liquid extraction of
1
and
its congeners. Once in the wine solution, these ellagitannins are slowly
but continuously transformed through possible physical complexations
