Abstract
Isolation and structure determination, accompanied by measurement of various biological
activities of each isolated tannin, particularly of ellagitannins, have brought about
a marked change in the concept of tannins as active constituents of medicinal plants.
Their biological activities should now be discussed on the basis of the structural
differences among each tannin, in a way similar to that of the other types of natural
organic compounds. The anti-tumor activity exclusively exhibited by several oligomeric
ellagitannins, and their anti-HIV activities are examples of such biological activities.
The inhibitory activity against lipid peroxidation, which is different in the strength
among tannins of various structures, is exhibited in general more strongly by ellagitannins
than by the other types of tannins of similar structures. The radical-scavenging activities
of tannins as the mechanism of their inhibition, which is regarded to participate
in several biological activities of tannins, have been supported by the ESR spectral
measurements. Other biological activities, i.e., inhibition of mutagenicity of carcinogens,
inhibition of tumor promotion, etc., have been found for tannins including ellagitannins.
