A New Pentaoxygenated Xanthone from the Fern Cystopteris fragilis

Pharmacological activity (e.g. antipsychotic ac­ tion [1]) and chemotaxonomic interest of xanthones may explain the increasing interest in these substances in recent years. It has been suggested [2] that Cystopteris fragilis complex is the most inter­ esting biosystematic problem in ferns. Xanthone analysis may be of interest in the study of relation­ ships of the taxa of this complex since previous work on the xanthones and flavonoids of Appala­ chian Asplenium complex [3] and Asplenium adiantum-nigrum complex [4] has shown that these two groups of ferns provide a classic example of addi­ tive inheritance of chemical characters. Earlier work on the chemical constituents of Cystopteris fragilis has led to the identification of two C-glycosylxanthones (mangiferin and isomangiferin) [5] and four flavonoids based on kaempferol (the 3-O-glucoside, the 3,4'-bis-glucoside, the 3-0-(3"-sulphate)glucoside and the 3-0(6"-sulphate)glucoside [6], In the present work a pentaoxygenated xanthone has been found for the first time in ferns and it has been shown that this compound (isolated from Cystopteris fragilis Bernh) is l,6-dihydroxy-3,5,7-trimethoxyxanthone (1) which is a new natural product o f biosynthetic interest in ferns.