Five new secondary metabolites produced by a marine-associated fungus, Daldinia eschscholzii

Abstract

Five new compounds, including a benzopyran ribonic glycoside, daldiniside A (1), two isocoumarin ribonic glycosides, daldinisides B (2) and C (3), and two alkaloids, 1-(3-indolyl)-2R,3-dihydroxypropan-1-one (4) and 3-ethyl-2, 5-pyrazinedipropanoic acid (5), along with five known compounds (6-10), were isolated from the EtOAc extract of the marine-associated fungus, Daldinia eschscholzii. Their structures were elucidated by extensive physicochemical and spectroscopic properties, besides comparison with literature data. The absolute configurations of compounds 1-3 were corroborated by chemical transformation, GC analysis and X-ray crystallographic analysis. Meanwhile, the absolute configuration of compound 4 and the planar structure of compound 6 were also determined based on the X-ray diffraction analysis. The cytotoxicity of compounds 1-10, antifungal and anti-HIV activities of compounds 1-5 and the in vitro assay for glucose consumption of compounds 1-3 were done in the anti-diabetic model, whereas none showed obvious activity.

Figure 1

Structures of compounds 1–10.

Figure 2

Selected ¹H-¹H COSY and HMBC correlations of compounds 1–3.

Figure 3

X-ray structure of compound 1.

Figure 4

Selected ¹H-¹H COSY and HMBC correlations of compounds 4 and 5.

Figure 5

X-ray structure of compound 4.

Figure 6

X-ray structure of compound 6.