Biology Reference
In-Depth Information
5.1 Introduction
With more than 500 structurally characterised members so far,
ellagitannins constitute one of the most important classes of tannins,
exhibiting a variety of interesting biological activities such as anti-
oxidative, anticancer and antiviral activities. This and the fact that
ellagitannins are usually not toxic for humans make them important and
interesting compounds for pharmaceutical purposes. However, their
broad application in pharmacy is hindered by the fact that they are hardly
accessible in pure forms and in sufficient quantities from their natural
sources. The first total synthesis of an ellagitannin was performed by
Feldman in 1994.
The search for biologically active compounds is one of the most
important aims in pharmaceutical research. The isolation of secondary
metabolites from natural sources, especially from bacteria, fungi, and
higher plants, has become increasingly important in the search for new
lead compounds. In the search for biologically active compounds from
plant extracts, a large number of tannins with various activities has been
identified and characterised since the early 1980s (Haslam, 1996).
Extensive biological evaluations have shown that numerous tannins
possess antibacterial (Hada
et al.
, 1989, see also Chapter 2), antiviral
(Fukuchi
et al.
, 1989, Nakashima
et al.
, 1992, Xie
et al.
, 1995) and
anticancer properties (Miyamoto
et al.
, 1987, Yoshida
et al.
, 1989,
1990a/b, 1991a/b, Kashiwada
et al.
, 1992b, 1993). The observed high
selectivity of the tannins is frequently caused by the inhibition of specific
enzymes (Jankun, 1997). The natural products that inhibit specific
enzymes have a great potential for the development of new
pharmaceuticals, especially in AIDS and cancer therapy.
Many papers have appeared on the biosynthesis, isolation, and
biological activity of tannins, especially ellagitannins, over the last
twenty years (
e.g.
, Xie
et al.
, 1995, Yoshida
et al.
, 1982, 1984, 1985,
1986, 1989, 1990a/b, 1991a-d, 1992a/b, 1995, Nonaka
et al.
, 1980, 1984,
1989a-c, 1990, Tanaka
et al.
, 1986a/b, 1990, 1992a/b, 2001, Hatano
et
al.
, 1988, 1989, 1990a-c, 1991, 1995, Lin
et al.
, 1990, Nishizawa
et al.
,
1982, 1983, Haddock
et al.
, 1982a/b, Kashiwada
et al.
, 1992a/b, 1993,
Kadota
et al.
, 1990, Okuda
et al.
, 1982a-e, 1983a/b, El-Mekkawy
et al.
,
