Quinone/hydroquinone meroterpenoids with antitubercular and cytotoxic activities produced by the sponge-derived fungus Gliomastix sp. ZSDS1-F7

Abstract Fifteen compounds, including six quinone/hydroquinone meroterpenoids, purpurogemutantin (1), macrophorin A (2), 4′-oxomacrophorin (3), 7-deacetoxyyanuthone A (4), 2,3-hydro-deacetoxyyanuthone A (5), 22-deacetylyanuthone A (6), anicequol (7), three roquefortine derivatives, roquefortine C (8), (16S)-hydroxyroquefortine C (9), (16R)-hydroxyroquefortine C (10), dihydroresorcylide (11), nectriapyrone (12), together with three fatty acid derivatives, methyl linoleate (13), phospholipase A2 (14), methyl elaidate (15), were isolated from the sponge-derived fungus Gliomastix sp. ZSDS1-F7 isolated from the sponge Phakellia fusca Thiele collected in the Yongxing island of Xisha. Their structures were elucidated mainly by extensive NMR spectroscopic and mass spectrometric analyses. Among these compounds, compounds 1–3 and 5–7 showed significant in vitro cytotoxicities against the K562, MCF-7, Hela, DU145, U937, H1975, SGC-7901, A549, MOLT-4 and HL60 cell lines, with IC50 values ranging from 0.19 to 35.4 μM. And compounds 2–4 exhibited antitubercular activity with IC50 values of 22.1, 2.44 and 17.5 μM, respectively. Furthermore, compound 7 had anti-enterovirus 71 activity with MIC value of 17.8 μM. To the best of our knowledge, this is the first report to product two quinone/hydroquinone meroterpenoids skeletons (linear skeleton and drimane skeleton) from the same fungal strain.


Introduction
Infectious diseases have seriously threatened the human health worldwide (Morens et al. 2004). One of the more alarming recent trends in infectious diseases has been the increasing frequency of tuberculosis (TB), exacerbated by the prevalence of multi-(MDR-TB), extensively (XDR-TB) and totally (TDR-TB) drug-resistant strains (Wang et al. 2013). Marine microorganisms are recognised as important sources of pharmacologically active metabolites. In particular, a growing number of marine-derived fungi have been reported to produce novel bioactive secondary metabolites (Blunt et al. 2015). Meroterpenoids are hybrid natural products of both terpenoid and non-terpenoid origin, and more than 330 naturally occurring meroterpenoids have been isolated from various fungal sources. (Geris & Simpson 2009;Wang et al. 2016). Quinone/hydroquinone sesquiterpenes having a normal drimane or a rearranged drimane skeleton represent a prominent class of mixed biogenesis metabolites that incorporate the biocyclic or prenylated sesquiterpene unit coupled to a quinine or hydroquinone moiety (Marcos et al. 2010a;Sunassee & Davies-Coleman 2012). Most of them have been isolated from the marine sponge, brown algae and fungi, and they display a wide range of biological activities, including cytotoxic, antiviral and especially antimicrobial activities against methicillin-resistant and multidrug-resistant strains (Fujimoto et al. 2001;Rateb & Ebel 2011;Fu et al. 2015).
As part of our investigations aimed at exploring bioactive secondary metabolites from fungal species inhabiting unique environments (Wang, Wei, et al. 2014;Wang et al. 2015;Wang et al. 2016). A subculture of an isolate of fungal strain Gliomastix sp. ZSDS1-F7, obtained from the sponge Phakellia fusca Thiele collected in the Yongxing island of Xisha, was grown in a rice culture medium. Its ethyl acetate extract displayed significant cytotoxic and antitubercular activities at a concentration of 100 μg/mL, and different secondary metabolites with similar UV absorptions at 220 and 240 nm were detected by HPLC analysis with diode array detection.
Quinone/hydroquinone sesquiterpenes with drimane or rearranged drimane skeleton are very interesting not only for their biological activities, but also for the diverse structures that they present, which have stimulated many total synthesis programmes (Mehta & Pan 2005;Marcos et al. 2010b;Fang et al. 2012;Göhl & Seifert 2014;Serra et al. 2014). Among the six isolated quinone/hydroquinone meroterpenoids (1-6), compounds (4-6) are the special sample possessing a linear sesquiterpenoid moiety. Biogenetically, the linear quinone/hydroquinone meroterpenoids (4-6) are proposed to be the key biosynthetic intermediates leading to the quinone/hydroquinone sesquiterpenes (1-3) with drimane or rearranged drimane skeleton (Scheme 1). To the best of our knowledge, this is the first report to product two quinone/hydroquinone meroterpenoids skeletons (linear skeleton and drimane skeleton) from the same fungal strain.

Conclusion
The investigation of bioactive natural products from the fermentation products of the sponge-derived fungus ZSDS1-F7 has led to the isolation of six quinone/hydroquinone meroterpenoids (1-6), one ergostane derivatives (7), three roquefortine derivatives (8-10), two polyketides (11 and 12), together with three fatty acid derivatives (13-15). Among them, compounds 1-3 and 5-7 showed significant in vitro cytotoxicities. And compounds 2-4 exhibited antitubercular activity. In addition, compound 7 had anti-enterovirus 71 activity. To the best of our knowledge, this is the first report that describes the isolation of two h y d r a t io n 2 c y c l iz a t io n ring opening OH HO Scheme 1. the postulated biogenetic pathway for quinone/hydroquinone meroterpenoids (1-6).
quinone/hydroquinone meroterpenoids possessing either linear skeleton or drimane skeleton from the same fungal strain.

Supplementary material
The physicochemical data of the known compounds (1-15) and experimental details relating to this article are available online.