Abstract
Mangrove-derived endophytes are rich in bioactive secondary metabolites with a variety of biological activities. Recently, a fungus Pseudofusicoccum sp. J003 was first isolated by our research group from mangrove species Sonneratia apetala Buch.-Ham. The subsequent chemical investigation of the methanol extract of the culture broth of this strain has led to the isolation of a new sesquiterpenoid named acorenone C (1), two alkaloids (2–3), four phenolic compounds (4–7), and four steroid derivatives (8–11). The new structure of 1 was established by extensive spectroscopic analysis, including 1D, 2D NMR spectroscopy, and HRESIMS. Its absolute configuration was elucidated by experimental ECD and ECD calculation. The in vitro AChE inhibitory, anti-inflammatory, and cytotoxic activities of the selected compounds were evaluated. The results showed that compound 1 showed mild AChE inhibitory activity, with an inhibition rate of 23.34% at the concentration of 50 μM. Compound 9 exerted a significant inhibitory effect against nitric oxide (NO) production in LPS-stimulated RAW 264.7 mouse macrophages, with an inhibition rate of 72.89% at the concentration of 25 μM, better than that of positive control L-NMMA. Compound 9 also displayed obvious inhibition effects on the growth of two human tumor cell lines, HL-60 and SW480 (inhibition rates 98.68 ± 0.97% and 60.40 ± 4.51%, respectively). The antimicrobial activities of the compounds (1–11) against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa were also tested; however, none of them showed antimicrobial activities.
Highlights
The great diversity of creatures in the ocean was found to be a rich reservoir of candidates for drug development (Sigwart et al, 2021)
Its molecular formula was determined to be C15H24O2 based on the deprotonated ion peak [M + Na]+ at m/z 259.1679 [M + Na]+ in the (+)-HRESIMS, indicating 4 degrees of unsaturation
Apart from the two degrees of unsaturation occupied by the carbonyl group and a double bond, the remaining degrees of unsaturation suggested that compound 1 should be a dicyclic sesquiterpenoid (Amandine et al, 2017)
Summary
The great diversity of creatures in the ocean was found to be a rich reservoir of candidates for drug development (Sigwart et al, 2021). More than 35,000 marine natural products have already been discovered, which have a higher rate of successful drug discovery than other naturally occurring compounds (Lyu et al, 2021; Sigwart et al, 2021). The ingredients produced by mangrove plant species may play a role in helping them survive from universally unfavorable factors (Bandaranayake, 2002). Our research group aimed at structurally diverse natural products from the mangroves and their endophytes for pharmaceutical drug discovery. As a small- to medium-sized columnar true mangrove, the plant species Sonneratia apetala Buch.-Ham. is native to South Asia and Southeast Asia and has been cultivated in Guangdong and Hainan provinces, China (Hossain et al, 2016).
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