Bioactive compounds from lichens and mycobionts in Trypetheliaceae family

Abstract

Chemical constituents of two lichens Marcelaria cumingii and Trypethelium subeluteriae, and four cultured mycobionts from M. cumingii, T. platystomum, T. eluteriae and Trypethelium sp. (Trypetheliaceae) were explored. Their secondary metabolites were structurally elucidated by spectroscopic methods as xanthones, anthraquinones, naphthoquinones and phenalenones. Lichexanthone, parietin, xanthorin and emodin were disclosed as constituents of lichens M. cumingii. Whereas, two anthraquinones: parietin and emodin could be isolated from T. subeluteriae together with another anthraquinone, haematommone. The chemical compositions of four cultured mycobionts were found to totally differ from those from lichen. The phenalenone bipolaride C was derived from T. platystomum while two 1,2-naphthoquinones, 8-hydroxytrypethelone methyl ether and 4'-hydroxytrypethelone, were isolated from Trypethelium sp. The other five 1,2-naphthoquinones, namely (–)-(2'S,3'S)-4'-hydroxytrypethelone (a new compound), three compounds with new absolute configuration (–)-(2'S)-trypethelone methyl ether, (–)-(2'S)-8-methoxytrypethelone methyl ether, and (–)-(2'S,3'R)-4'-hydroxy-8-methoxytrypethelone methyl ether, along with the known compound, (–)-(2'S)-trypethelone were isolated from M. cumingii. Cytotoxicity test revealed that (–)-(2'S)-trypethelone methyl ether exhibited selective inhibition against HCT116 and A549 cell lines with IC₅₀ of 0.32 ± 0.03 and 1.05 ± 0.12 µM, respectively. A compound with new absolute configuration: (+)-(2'R)-bipolaride D, and three known compounds: (+)-(2'R)-sclerodin, trypethelone, and 8-hydroxy-7-methoxytrypethelone were isolated from T. eluteriae. The latter revealed potential inhibition of amyloid-ß aggregation with IC₅₀ 9.9 µM.