Abstract
Four 4-hydroxy-α-pyrones including three new ones named nipyrones A–C (1–3) together with one known analogue germicidin C (4) were discovered from a marine sponge-derived fungus Aspergillus niger cultivated in a solid rice culture. Their structures and absolute configurations were elucidated through a combination of spectroscopic data and electronic circular dichroism (ECD) calculations as well as comparison with literature data. Compounds 1–4 were evaluated for their antibacterial activities against five pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Bacillus subtilis, methicillin-resistant Staphylococcus aureus, and Mycobacterium tuberculosis). Compound 3 showed promising activity against S. aureus and B. subtilis, with minimum inhibitory concentration (MIC) values of 8 μg/mL and 16 μg/mL, respectively, and displayed weak antitubercular activities against M. tuberculosis, with MIC value of 64 μg/mL, while compounds 1 and 2 exhibited moderate antibacterial efficacy against four pathogenic bacteria with MIC values of 32–64 μg/mL.
Highlights
In recent years, sponge-derived fungi have represented a potential resource for discovery of novel bioactive molecules [1,2]
Its UV absorption at 290 nm indicated the presence of a conjugated α-pyrone unsaturation
Three new 4-hydroxy-α-pyrone derivatives, nipyrones A–C (1–3) along with one known analogue germicidin C (4) were isolated from a marine sponge-derived fungus A. niger grown on a solid rice culture
Summary
Sponge-derived fungi have represented a potential resource for discovery of novel bioactive molecules [1,2]. Numerous secondary metabolites with a broad spectrum of bioactivities have been isolated from sponge-derived fungi, inclusive of alkaloids [3], terpenoid [4], polyketides [5], and peptides [6]. Α-Pyrones can be widely found in the fungi and actinomycetes [8–10], and these molecules demonstrated a wide range of extraordinary biological activities, such as antimicrobial [11], anti-inflammatory [12], cytotoxic [13], and quorum sensing signaling molecules [14,15]. Members of the genus Aspergillus are well known to produce chemically diverse secondary metabolites, many of which have been developed to therapeutic leads for human health [16–19]. During our ongoing search for sponge-derived fungi capable of producing antibiotics, a sponge-derived fungus Aspergillus niger LS24 showed antimicrobial activities.
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