Biology Reference
In-Depth Information
and antidiarrheic in China. The herb of
Geum japonicum
(
Rosaceae
),
which contains
inter alia
dimeric gemins A, B and C, was used in Japan
as a diuretic. The herb of
Rubus triphyllus
(
Rosaceae
), which contains
sanguiins H-6 and H-11, was used as an antidiarrheic and a tonic
medicine in Japan (Tanaka
et al.
, 1985).
1.6 Properties and Primary Activities of Ellagitannins
The remarkable chemical stability of most ellagitannins allows accurate
evaluation of their biological and pharmacological activities, in contrast
to other types of tannins for which such evaluations are often difficult to
perform.
1.6.1 Reduction, stabilization and precipitation of other substances
by tannins, and solubilization of precipitates by excess tannin
At room temperature, ellagitannins, like other tannins, reduce metallic
ions such as Cu
2+
, Fe
3+
and Cr
6+
into Cu
+
, Fe
2+
and Cr
3+
, respectively
(Okuda
et al.
, 1982i). Such reductions are presumably accompanied by
oxidation of the tannin molecules into quinonoid species. The
discoloration of natural pigments,
e.g.
, shikonin and β-carotene, that
occurrs during storage of their respective solution in ethanol in the
presence of oxygen under light exposure was remarkably suppressed by
addition of geraniin. This suppressing effect was further enhanced in the
presence of metallic ions such as Ca
2+
and Mg
2+
. The precipitates
produced by mixing punicalin with Fe
3+
or Cu
2+
at a concentration of
punicalin of 5.0 × 10
-3
M were solubilized at higher concentrations of
punicalin, and the precipitates produced by mixing chebulinic acid with
quinine, cinchonine, berberine or papaverine were also solubilized by
increasing the concentration of chebulinic acid over 1.0 mg/10ml (Okuda
et al
., 1982j). Such solubilizations of precipitates are attributable to the
higher solubility of the complexes formed when using higher
concentrations of these tannins.
