| Summary: | Field samples of the foliose lichens Nephroma Iaevigatum Ach. and Hetero
dermia obscurata (NyL) Trevis. were analyzed for anthraquinone and anthraquinone
like pigments. Both lichens were found to contain emodin, 7-chioroemodin and 7,7’-
dichiorohypericin. In addition, the N. Iaevigatum specimen contained 7-chloro-1 -
O-
methylemodin, 7-chloro- 1- O-methyl-ψ-hydroxyemodin (7-ch lorocarviolin) and 2,2’,
7,7’-tetrachlorohypericin, while the H. obscurata sample contained 5 ,7-dichloroemodin,
flavoobscurin A and flavoobscurin B. Laboratory incubation studies with N. Iaevi
gatum (
in the presence of sodium [
1-¹³C]acetate) also revealed the formation of 5-
chloroemodin, 5-chloro- 1- O-methylemodin, 5-chloro-ψ-hydroxyemodin and 5-chloro-
1- O-methyl-ψ-hydroxyemodin (5-chiorocarviolin). These compounds had not
been identified in any previous examination of field-collected lichen, and 5-chloro-1
-O-methylemodin, although known from a
fungus, has not been reported to occur in
any lichen. The structures of the compounds were determined by a combination of
UV, MS, ¹H NMR and
¹³C NMR spectral methods.
Feeding experiments with sodium [2-¹⁴C]acetate and sodium [1-¹³C]acetate
demonstrated that anthraquinones are biosynthesized in Nephroma Iaevigatum
through the polyketide pathway, analogous to the pathways operating in fungi and
higher plants. The lichen was also capable of chlorinating endogenous anthraquinones during incubation with sodium ³⁶chloride
Biohalogenation experiments with a partially purified lichen chioroperoxidase and a commercially available fungal chloroperoxidase demonstrated enzymesubstrate
specificity with respect to the production of different chlorinated anthraquinones. 5,7-Dichloroemodin was produced, in excellent yield, from 7-chioroemodin
by the commercial enzyme; the lichen chloroperoxidase, however, yielded only 7-
chloroemodin from emodin and did not further chlorinate 7-chloroemodin. 5-Chloroemodin
was a product from both the control and commercial enzyme reactions.
Twelve lichen anthraquinones, bianthrones, hypericin derivatives, and syn
thetic hypericin were tested for their virucidal activity in end-point CPE (viral cyto
pathic effects) and plaque assays with herpes simplex virus type 1 (HSV-1). Emodin, 7-chloroemodin, 7-chloro- 1- O-methylemodin, 5,7-dichloroemodin, hypericin
and 7,7’-dichlorohypericin exhibited fair to good antiviral activity in the presence
of light. In the plaque assay, 5,7-dichioroemodin, hypericin and 7,7’-dichlorohypericin
completely inhibited the virus at a concentration of 1.0 μg/mI. Only hypericin was active at 0.01 μg/mI. The other anthraquinones and bianthrones
were inactive at a concentration of 5.0 μg/mI. === Science, Faculty of === Botany, Department of === Graduate
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