The quinonoid pigments of the lichens nephroma laevigatum and heterodermia obscurata

• Main Author: Cohen, Peter Altman
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7223

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