Elsevier

Fitoterapia

Volume 128, July 2018, Pages 213-217
Fitoterapia

Four novel antibacterial sesquiterpene-α-amino acid quaternary ammonium hybrids from the mycelium of mushroom Stereum hirsutum

https://doi.org/10.1016/j.fitote.2018.05.026Get rights and content

Highlights

  • Jin'er is used as food and crude medicine in Chinese society.

  • The mycelium of Stereum hirsutum was fermented in YMG broth.

  • Four novel stereumamides (A-D) were isolated from the fermentation extracts.

  • Stereumamide would be the first occurring hybrids by sesquiterpene-α-amino acid.

  • Stereumamides A and D (1 and 4) showed antimicrobial activity.

Abstract

The mushroom Stereum hirsutum is parasitized by Tremella aurantia to form a heterogeneous basidiocarp Jin'er, which has been used as food and folk medicine in Chinese society. In present work, the S. hirsutum was fermented in YMG broth, and four novel mixed terpenes, stereumamides A-D (14), which are sesquiterpenes combined with α-amino acids to form quaternary ammonium hybrids, were isolated from the Stereum hirsutum FP-91666 and their structures were elucidated by spectroscopic data analysis. Stereumamides A and D showed antibacterial activity against Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium, with the minimum inhibitory concentration (MIC) values of 12.5–25.0 μg/mL. The stereumamides A-D should be apparently the first example of naturally occurring a quaternary ammonium compound (QAC) conjugated by sesquiterpene with an α-amino acid. QAC is a common antibacterial agent in food industry, which is found in the mycelium of Stereum hirsutum would suggest that the complex basidiocarp is a functional food and veritable folk medicine.

Introduction

The Stereum fungus belongs to the Stereaceae family (basidiomycetes) and is widely distributed throughout the world, which can produce diversiform secondary metabolites. The mushroom Stereum hirsutum is very widely distributed and lives on dead wood of limbs and trunks of both hardwoods and conifers, and plays an important role in the wood deterioration process. However, it is parasitized by the fungus Tremella aurantia to form a heterogeneous complex basidiocarp Jin'er (golden jelly fungus) [1,2], which has been traditionally used as food and crude medicine in Chinese society.

The fermented mycelia of S. hirsutum have been reported to produce abundantly active secondary metabolites, including phytotoxic active acetylenic compounds [3], multiple active sesquiterpenoids [[4], [5], [6]], antibacterial epidioxysterols [7], and benzoate derivatives [[8], [9], [10]]. In the process of studying the biosynthesis of bioactive vibralactone [11], we found that S. hirsutum could produce vibaralactone type compounds [12], and based on genome data information S. hirsutum would produce more secondary metabolites. To further explore its potential in the production of biologically active metabolites, the OSMAC (one strain-many compounds) strategy was applied to maximize the chemical diversity of this fungus [13]. In the research on the secondary metabolites of S. hirsutum FP-91666, we have isolated four novel skeletal mixed terpenoids, stereumamides A-D, which are combination of sesquiterpenes and α-amino acids to form quaternary ammonium hybrids (Fig. 1). Herein, we describe the isolation, structural determination and antibacterial activity of these compounds.

Section snippets

General methods

Column chromatography was carried out on silica gel (200–300 mesh, silica gel H and GF254) (Qingdao Marine Chemical 132 Factory, Qingdao, China) and Sephadex LH-20 (Pharmacia Fine Chemicals, Uppsala, Sweden). Precoated silica gel GF254 plates (Qingdao Marine Chemical Factory, 134 Qingdao, China) were used for thin layer chromatography (TLC). Some fractions were purified by the LC3000 Semi-preparation Gradient HPLC (Beijing Chuangxintongheng Science & Technology Co., Ltd., Beijing, China) on RP C

Results and discussion

The molecular formula of stereumamide A (1), which was obtained as a pale brown amorphic mass, was determined to be C19H23NO5 by HR-ESI-MS at m/z 346.1656 ([M + H]+, calcd. 346.1654), requiring nine degrees of unsaturation. The 1H NMR, 13C NMR, DEPT, and HSQC spectra of 1 revealed 19 carbon signals that represent four methyls, one methylene, seven methines including four olefinic methines, and seven quaternary carbons including three olefinic and one oxygenated carbons, and two carbonyl groups (

Conflict of interest statement

The authors declare that there are no conflicts of interest.

Acknowledgments

This study was financially supported by National Key R&D Program of China (2017YFD0201104), the National Natural Science Foundation of China (31760018, 31560016), and the Applied Basic Research Foundation of Yunnan Province (2018FA0XX).

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  • Sesquiterpene-α-amino acid quaternary ammonium hybrids from Stereum complicatum (Steraceae)

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    sp NN048997 and recently found in the ethyl acetate partition of S. complicatum (Jian-Fang et al., 2014; Perera et al., 2020) (Fig. 1). The hybrid compounds 2–6 have been recently isolated from the n-butanol extract of S. hirsutum (Yuan-Chang et al., 2018; Qian-Hu et al., 2020). The HR-ESI-MS of the sesquiterpene-α-amino acid quaternary ammonium hybrids were also examined.

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1

These authors contributed equally to this work.

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