THE JOINT OCCURRENCE OF CHLOROXANTHONES IN LICHENS, AND A FURTHER 13 NEW LICHEN XANTHONES

The following new xanthones are shown to co-occur in various combinations with other known naturally occurring xanthones: 2-chloronorlichexane (in Lecanora populicola Lecanora sp.), 7-chloronorlichexanthone (in Lecanora populicola, Lecanora sp.), 5-chloro-6-O-methylnorlichexanthone (in Lecanora contractula), 5-chlorolichexanthone (in Lecanora contractula), 7-chloro-6-O-methylnorlichexanthone (in Lecanora populicola, L. salina, L. sp.), 2,4-dichloronorlichexanthone (in Lecidella vorax), 2,7-dichloro-3-O-methylnorlichexanthone (in Lecanora behringii, L. salina, L. sp.), 2,7-dichloro-6-O-methylnorlichexanthone (in Lecanora behringii, L. populicola, L. salina, L. sp.), 2,5,7-trichlorolichexanthone (in Lecanora broccha), 4,5,7-trichloro-6-O-methylnorlichexanthone (in Pertusaria pycnothelia var. A), 3-O-methylthiophanic acid (in Lecidella meiococca), and 6-O-methylthiophanic acid (in Micarea isabellina). Griseoxanthone C (3-O-methylnorlichexanthone) is reported for the first time from a lichen (Lecanora vinetorum). The joint occurrence of these chloroxanthones has been rationalized in biosynthetic terms and represented in a series of pathway diagrams. All were found to constitute coherent arrays of major xanthones and biosequentially related satellite derivatives. In so doing we have established the methodology for predicting expected co-occurrences and completing similar data sets for other xanthone-containing species.