Abstract
Four new indolediketopiperazine derivatives (1–4), along with nine known congeners (5–13), were isolated and identified from the culture extract of Eurotium cristatum EN-220, an endophytic fungus obtained from the marine alga Sargassum thunbergii. The structures of thesecompounds were elucidated on the basis of extensive spectroscopic analysis and the absolute configurations of compounds 1–4 were established by NOESY experiments and by chiral HPLC analyses of their acid hydrolysates. The absolute configuration of C-8 (a quaternary carbon substituted with a hydroxyl group) in 5 of preechinulin class was firstly determined by electronic circular dichroism (ECD) calculations. All these compounds were evaluatedfor brine shrimp (Artemia salina) lethality and nematicidal activity as well as antioxidativeand antimicrobial potency.
Highlights
Marine algicolous fungi, an ecologically defined group of marine-derived microorganisms, have recently attracted much attention for natural product researchers due to their potential to produce structurally unique and biologically active metabolites [1]
Most of the algicolous fungi distributed in the genera of Aspergillus and Penicillium, which belong to the facultative marine fungi that were frequently discovered from different groups of algae [1,2]
A literature searching result showed that only two indolediketopiperazine derivatives of preechinulin class, rubrumline
Summary
An ecologically defined group of marine-derived microorganisms, have recently attracted much attention for natural product researchers due to their potential to produce structurally unique and biologically active metabolites [1]. Compared to its unknown ecological role, the fungal genus Eurotium has attracted more interests on its profilic source of indolediketopiperazine derivatives containing L-tryptophan and L-alanine units, generally characterized by a reverse isoprene chain at C-2 of the indole nucleus [3,7,8,9,10]. These compounds were reported to possess antibacterial [3,9], nematicidal [11], antioxidative (DPPH assay) [12,13], moderate immunosuppressive [14], and anti.
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