Xanthones and Quinolones Derivatives Produced by the Deep-Sea-Derived Fungus Penicillium sp. SCSIO Ind16F01

Chemical investigation of the fungus Penicillium sp. SCSIO Ind16F01 derived from deep-sea sediment sample afforded a new xanthone, 3,8-dihydroxy-2-methyl-9-oxoxanthene-4-carboxylic acid methyl ester (1) and a new chromone, coniochaetone J (2), together with three known xanthones, 8-hydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester (3), 7,8-dihydroxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester (4), 1,6,8-trihydroxy-3-(hydroxymethyl)anthraquinone (5), three known chromones, coniochaetone B (6), citrinolactones B (7), epiremisporine B (8), and four reported rare class of N-methyl quinolone lactams: quinolactacins B (9), C1 (10), and C2 (11), and quinolonimide (12). The structures of new compounds were determined by analysis of the NMR and MS spectroscopic data. Those isolated compounds were evaluated for their antiviral (EV71 and H3N2) and cytotoxic activities.


Introduction
Marine microorganisms, especially the marine fungi, tend to produce structurally unique and biologically active natural products which have been documented in recent years [1][2][3][4]. Recently, microorganisms from deep-sea habitats, including the hydrothermal vents, have become an interesting and newly emerging source of novel bioactive compounds, which play an important role in drug discovery [5].
As a part of our progressive program to explore the antiviral potential of marine fungi, the secondary metabolites of the strain SCSIO Ind16F01 were examined.
The isolated compounds were evaluated for their antiviral (H3N2 and EV71) and cytotoxic activities (Table S1). Among them, compounds 2 and 8 exhibited weak inhibitory activity against EV71 in vitro, with IC 50 values of 81.6 and 19.8 µM. In addition, compound 8 also exhibited inhibitory activity against H3N2 with IC 50 values of 24.1 µM, and cytotoxic effects on the tested cancer cell lines (K562, MCF-7, and SGC7901) with IC 50 values of 16.6, 16.3, and 15.8 µM, respectively.

Materials and Methods
General experimental procedures. 1  The total rice solid culture was crushed and extracted with acetone three times. The acetone extract was evaporated under reduced pressure to afford an aqueous solution, and then the aqueous solution was extracted with EtOAc to yield 62 g of a crude gum. The H 2 O layer (120 g) was further partitioned n-Butyl alcohol to yield n-Butyl alcohol (55.6 g) fractions.
Anti-EV71 was assayed on Vero cells with the CCK8 (DOjinDo, Kumamoto, Japan) method [19]. Ribavirinwas used as the positive control with an IC 50 value of 0.60 µM. Vero cells (2 × 10 3 cells/well) were seeded with DMEM medium (2% FBS) into a 384-wellplate. After 24 h, 1000 fold serial dilution of the compound was added in triplicate to the 348-well plate. After incubation at 37 • C for 30 min, a twofold dilution 100× the 50% tissue culture infectious dose (TCID50) of EV71 virus in DMEM supplemented with 2% FBS was added to each well. The plate was incubated at 37 • C for 72-96 h when the viral control cells showed complete CPE, the cell survival was quantified using CCK-8. The A450 of the well was measured with a microtiter platereader (Envision, PerkinElmer, Waltham, MA, USA). The 50% inhibitory concentration (IC 50 ) of the testing compound was calculated using the GraphPad Prism software.

Conclusions
The chemical investigation of the deep-sea-derived fungus Penicillium sp. SCSIO Ind16F01 has led to twelve compounds, including two new metabolites. Their structures were elucidated by the detailed analysis of spectroscopic data. All compounds were evaluated for their antiviral (H3N2 and EV71) and cytotoxic effects. Among them, compounds 2 and 8 exhibited anti-EV71 activities in vitro, with IC 50 values of 81.6 and 19.8 µM. In addition, compound 8 also exhibited inhibitory activity against H3N2 with IC 50 values of 24.1 µM, and cytotoxic effects on the tested cancer cell lines (K562, MCF-7, and SGC7901) with IC 50 values of 16.6, 16.3, and 15.8 µM, respectively. Compound 8 was a unique cyclopentachromone dimer.
Supplementary Materials: Supplementary materials are available online.