Biosynthetic studies on chlorinated anthraquinones in the lichen Nephroma laevigatum

• Published in: Phytochemistry (Oxford) 1996-07, Vol.42 (5), p.1325-1329
• Main Authors: Cohen, Peter A., Neil Towers, G.H.
• Format: Article
• Language: English
• Subjects: 5-chloro-l-o-methyl-omega-hydroxyemodin; 5-chloro-l-o-methylemodin; 5-chloro-omega-hydroxyemodin; 5-choroemodin; 7-chloro-l-o-methyl-omega-hydroxyemodin; 7-chloro-l-o-methylemodin; 7-chloromodin; acetates; anthraquinones; biochemical pathways; Biological and medical sciences; biosynthesis; chemical structure; chlorine; derivatives; emodin; Fundamental and applied biological sciences. Psychology; lichens; Metabolism; Metabolism. Physicochemical requirements; molecular conformation; Nephroma laevigatum; Plant physiology and development; precursors; spectral analysis
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/0031-9422(96)00148-3

Eight anthraquinones were produced by the lichen Nephroma laevigatum Ach. during laboratory incubation. They were characterized by 1H NMR, 13C NMR and mass spectrometry as emodin, 7-chloromodin, 7-chloro-1- O-methylemodin, 7-chloro-1- O-methyl- ω-hydroxyemodin, 5-chloroemodin, 5-chloro-1- O-methylemodin, 5-chloro-1- O-methyl- ω-hydoxyemodin and 5-chloro- ω-hydroxyemodin. The 5-chloroemodins are new lichen substances, although 5-chloro-1- O-methylemodin was isolated previously from a fungus. Radiolabelled 7-chloroemodin derivatives were obtained upon incubation of the lichen with Na [2- 14C]acetate, demonstrating the utilization of acetate in their formation. 7-Chloro-1- O-methylemodin, enriched with 13C, was isolated following incubation with Na [1- 13C]acetate. Analysis of its 13C NMR spectrum showed that the lichen anthraquinones are biosynthesized through the polyketide pathway. Efficient incorporation of label from Na 36Cl into 7-chloroemodin and 7-chloro-1- O-methylemodin showed that the lichen is capable of chlorinating preformed anthraquinones.