Biology Reference
In-Depth Information
A final cleavage of the methyl ether bonds would have led to the
corresponding natural product corilagin, but in spite of several trials run
under various reaction conditions, this ultimate transformation could not
be cleanly done, notably because of an unavoidable competing cleavage
of the anomeric galloyl ester function in nonamethylcorilagin (
108
).
5.3 Conclusion
Up to now, a large number of structurally characterized ellagitannins has
been identified. Although these ellagitannins possess complex structures,
all of them have at least one axially chiral hexahydroxydiphenoyl
(HHDP) unit. Some ellagitannins possess interesting biological
activities. However, it is not easy to isolate them in sufficient amount
from natural sources for further studies. Although this class of natural
products has been well established, not a single method had been
developed for their total synthesis until 1994. Through the pioneer work
of Feldman on the development of a method for the total synthesis of
ellagitannins, some of them became accessible by total synthesis for the
first time and the research activities on their synthesis consequently
received a considerable boost. The characteristic step of this method is
the diastereoselective oxidative galloyl coupling to the corresponding
biaryl unit. Thereafter, a new method has been developed, in which a
pre-synthesized biaryl compound is used either as its racemic mixture or
in atropoisomerically pure form. This method allows the total synthesis
of numerous ellagitannins in a few steps. The last developed method in
this area concerned the construction of an ellagitannin precursor with a
1
C
4
-glucose unit. This method could constitute a successful route to the
total synthesis of ellagitannins with a
1
C
4
-glucose unit in the future.
5.4 Bibliography
Abe, I., Kashiwagi, Y., Noguchi, H., Tanaka, T., Ikeshiro, Y. and Kashiwada, Y. (2001).
Ellagitannins and hexahydroxydiphenoyl esters as inhibitors of vertebrate squalene
epoxidase,
J. Nat. Prod.
, 64, pp. 1010-1014.
Albright, J. D. and Goldman, L. (1965a). Dimethyl sulfoxide-acid anhydride mixtures.
New reagents for oxidation of alcohols,
J. Am. Chem. Soc.
, 87, pp. 4214-4216.
