Abstract
Three novel cyclic hexapeptides, sclerotides C–E (1–3), and a new lipodepsipeptide, scopularide I (4), together with a known cyclic hexapeptide sclerotide A (5), were isolated from fermented rice cultures of a soft coral-derived fungus: Aspergillus sclerotiorum SCSIO 41031. The structures of the new peptides were determined by 1D and 2D NMR spectroscopic analysis, Marfey’s method, ESIMS/MS analysis, and single crystal X-ray diffraction analysis. Scopularide I (4) exhibited acetylcholinesterase inhibitory activity with an IC50 value of 15.6 μM, and weak cytotoxicity against the human nasopharyngeal carcinoma cell line HONE-EBV with IC50 value of 10.1 μM.
Highlights
Marine microorganisms are generally considered to be a significant new chemical resource of secondary metabolites [1,2]
Sclerotides present a unique hexapeptide containing both anthranilic acid and dehydroamino acid residues, which are rarely reported in nature
These results revealed that compound 3 consisted of cyclo (Thr-Ala-Phe-Ser-anthranilic acid (AA)-ADPAT)
Summary
Marine microorganisms are generally considered to be a significant new chemical resource of secondary metabolites [1,2]. These organisms thrive in the hostile and competitive oceanic environment and produce a variety of chemically diverse and biologically active compounds [3–5], which have attracted great attention in biomedical research [6,7]. Representatives include lucentamycins [8] and marthiapeptide A [9] from marine actinomycetes, sclerotiotides A-K [10], JBIR-15 [11], maribasins [12] and sclerotides A and B [13] from marine fungi. Of these representatives, sclerotides present a unique hexapeptide containing both anthranilic acid and dehydroamino acid residues, which are rarely reported in nature. In our ongoing studies discovering structurally novel and bioactive natural hybrid peptides from soft coral-derived fungi [14], three novel cyclic hexapeptides, sclerotides C–E (1–3) and a new lipodepsipeptide scopularide I (4), along with a known cyclic hexapeptide, sclerotide A (5) [13], were obtained from Aspergillus sclerotiorum SCSIO 41031 (Figure 1)
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