Elsevier

Phytochemistry Letters

Volume 36, April 2020, Pages 1-6
Phytochemistry Letters

New azaphilone, isocoumarin and α-pyrone derivatives from the marine-derived gut fungus Paraphaeosphaeria sp. XZD2-1

https://doi.org/10.1016/j.phytol.2019.12.010Get rights and content

Highlights

  • The first report about lunatoic acids from a marine-derived Paraphaeosphaeria sp. fungus.

  • Four new isocoumarin and α-pyrone derivatives from the fungus.

  • Experimental and calculated ECD were used to elucidate the absolute configurations of new compounds.

  • The antimicrobial activity and cytotoxicity of isolated compounds were examined.

Abstract

Six new compounds including two azaphilones, lunatoic acids D–E (1, 2), three isocoumarins, lunatinins B–D (3-5), and one α-pyrone derivative, lunatinin E (6), as well as four known ones, lunatoic acid A (7), lunatinin (8), penicipyran D (9) and chaetoquadrin F (10) were isolated from the rice medium of the gut fungus Paraphaeosphaeria sp. XZD2-1. Their planar structures were elucidated by analysis of 1D and 2D NMR as well as HRESIMS spectroscopic data. The absolute configurations of compounds 1-3 were assigned by experimental and calculated ECD data and an ester hydrolysis reaction. Compounds 4 and 5 were a pair of enantiomeric excess mixture. Structure of compound 6 was further confirmed by comparing optical rotation with known compounds according to literature. The antimicrobial activity and cytotoxicity of compounds 1-10 were examined.

Graphical abstract

Six new compounds including two azaphilones, lunatoic acids D–E (1, 2), three isocoumarins, lunatinins B–D (3-5), and one α-pyrone derivative, lunatinin E (6), as well as four known ones, lunatoic acid A (7), lunatinin (8), penicipyran D (9) and chaetoquadrin F (10) were isolated from the rice medium of the gut fungus Paraphaeosphaeria sp. XZD2-1.

  1. Download : Download high-res image (167KB)
  2. Download : Download full-size image

Introduction

In the research and development process of lead compounds for drugs, marine-derived fungi are an abundant source for their novel and bioactive secondary metabolites (Blunt et al., 2018). The genus Paraphaeosphaeria which has reported to yield many new metabolites were often found as plant endophytic fungi (de Amorim et al., 2019; Huang et al., 2017), insect gut fungi (Shao et al., 2016) or marine-derived fungi (Tsuda et al., 2003). In our study for new natural products from marine-derived fungi, one strain Paraphaeosphaeria sp. XZD2-1 was isolated from the gut of a sea shrimp. OSMAC strategy indicated the fungus mainly produced diketopiperazine alkaloids in T.G. + salt liquid medium (Figure S64), but showed rich secondary metabolites when cultured on solid rice medium. A chemical investigation of the EtOAc extract from the rice medium resulted in the isolation of six new compounds, lunatoic acids D–E (1, 2), lunatinins B–E (3-6). The remaining four known compounds were identified as lunatoic acid A (7) (Nukina and Marumo, 1977), (+)-lunatinin (8) (Cai et al., 2018; Yamaguchi et al., 2004), penicipyran D (9) (Ma et al., 2017) and chaetoquadrin F (10) (Fujimoto et al., 2003), as shown in Fig. 1, by comparison of their NMR, MS data and optical rotations (Table S3) with those reported.

Section snippets

Results and discussion

Lunatoic acid D (1) was obtained as a yellowish oil. HRESIMS analysis gave an ion peak at m/z 405.1551 [M−H], indicating a molecular formula of C21H26O8, corresponding to 9 degrees of unsaturation. The IR spectrum showed the presence of a hydroxyl (3242 cm-1) and a conjugated carbonyl (1648 cm-1). The 1H NMR spectrum (Table 1) showed four olefinic proton signals (δH 6.12, 6.31, 6.42, 7.11), and four methyl signals (δH 0.84, 0.85, 1.05, 1.70). The 13C NMR spectrum exhibited two ketone carbonyls

General experimental procedures

Optical rotations were measured on a Rudolph Research Analytical Autopol I automatic polarimeter. UV spectra were recorded on a Shimadzu UV-1800 spectrophotometer. IR spectra were taken on a Thermo Scientific Nicolet iS10 spectrometer using an attenuated total reflectance (ATR) method. CD spectra were measured on a JASCO J-1500 CD spectrometer. HRESIMS spectra were performed on an Agilent 6224 TOF LC-MS spectrometer. NMR spectra were recorded on a JEOL 600 MHz NMR spectrometer with TMS as an

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

Acknowledgment

This work was supported by the National Natural Science Foundation of China (NSFC No.41406141). We thank Jianyang Pan (Pharmaceutical Informatics Institute, Zhejiang University) and Ying Liu (Ocean College, Zhejiang University) for performing NMR spectrometry.

References (18)

There are more references available in the full text version of this article.

Cited by (4)

  • Marine natural products

    2022, Natural Product Reports
  • Bioactive compounds from marine-derived fungi and their potential applications

    2021, Fungi Bio-prospects in Sustainable Agriculture, Environment and Nano-technology: Volume 3: Fungal Metabolites, Functional Genomics and Nano-technology
  • Natural isocoumarins: Structural styles and biological activities, the revelations carry on ….

    2021, Phytochemistry
    Citation Excerpt :

    Their planar structures were elucidated by analysis of 1D and 2D NMR as well as HRESIMS spectroscopic data. The compounds 236 and 237 were obtained as pair of enantiomers (Sun et al. 2020). Image 70Lunatinin B (235) Lunatinin C (236) Lunatinin D

View full text