Anthraquinones from the saline-alkali plant endophytic fungus Eurotium rubrum.

Abstract

Saline-alkali plant endophytes similar as marine mangrove plant-derived ones are a big member of microbes inhabiting in tissues of plants without causing obvious disease to their hosts, and they must adapt to the extreme environment of high osmolarity and nutrient deprivation in plant, which are different from terrestrial plant endophytes. Owing to the unique bio-environments, endophytes originated from mangrove plants are being considered as a new resource of natural product research and diverse secondary metabolites with a wide range of bioactivities have been isolated.1, 2, 3 Compared with those of marine mangrove plant-derived endophytes, chemical investigation of saline-alkali plant-derived endophytic fungi have just begun, and only several natural products were isolated from these unique environmental fungi.4,5,6,7Suaeda salsa L., an important model halophytic plant, is distributed at different saline-alkali soil especially at seaside. This plant possesses the ability to absorb salt from saline soils and accumulate them in the plant tissues. Some results revealed that the total salt contents in shoot and root were 23–27% and 10–12%, respectively.8 During our ongoing chemical investigation from unique fungal species as sources of new bioactive natural products, a halo-tolerant endophytic fungus Eurotium rubrum isolated from salt-tolerance wild plant S. salsa L. collected from ‘BoHai’ seaside was chosen to chemical investigation. Previous reports revealed that E. rubrumwas frequently isolated from mangrove plants, and different secondary metabolites with a wide range of bioactivities have been isolated from this endophytic fungus.9, 10, 11, 12, 13 Purification of the solid culture extract of this fungus led to isolate a new anthraquinone named rubrumol (1) with poly-hydroxyl groups together with four known analogs catenarin (2),14 rubrocristin (3),15 emodin (4)16 and 2-methyleurotinone (5).15 In this paper, the structural elucidation for the new compound rubrumol (1) (Figure 1) and bioactivities for compounds 1–5 were present. Several errors on the coupling constants of the known coniothyrinone A (6) were pointed out in this note.17