A new diphenyl ether dimethyl 2,3Ј-dimethylosoate (1) together with three known compounds monomethylsulochrin (2), emodin (3), and questin (4) were isolated through bioassay-guided fractionations from the culture of a marine-derived fungus Aspergillus sp. B-F-2. The structures of these compounds were determined by spectroscopic methods. Cytotoxicities of compounds 1 and 2 against K562 cell line were preliminarily evaluated by the MTT method and flow cytometry.Keywords Aspergillus sp., diphenyl ether, asterric acid, anthraquinone, cytotoxicity
IntroductionIn our research for new anticancer microbial metabolites, a culture broth of a marine-derived fungus Aspergillus sp. B-F-2, exerted significant cytotoxic activity against K562 cell line. Bioassay-guided isolation led to one new asterric acid derivative dimethyl 2,3Ј-dimethoxyosoate (1), and three known fungal metabolites monomethylsulochrin (2), emodin (3), and questin (4) (Fig. 1).Asterric acid, possessing a diphenyl ether structure, was the first non-peptide endothelin (ET) binding inhibitor discovered [1,2]. In this paper we mainly report the isolation and structure determination of the new diphenyl ether (1), and its preliminary in vitro cytotoxicity against the K562 cell line. These kinds of compounds are formed biosynthetically from the anthraquinone emodin, via sulochrin, and grisandienes such as geodin was previously reported [3,4].
Materials and Methods
Fungal MaterialThe fungus Aspergillus sp. B-F-2 was isolated from the marine sediments collected in Behai Bay, China. It was preserved in the China Center for Type Culture Collection (patent depositary number: B-F-2 CCTCC M 205148). Working stocks were prepared on Potato Dextrose agar slants stored at 4°C.
Fermentation and ExtractionThe fungus was grown under static conditions at 24°C for 25 days in 1000 mlϫ150 conical flasks containing the liquid medium (300 ml/flask) composed of glucose (20 g/liter), peptone (5.0 g/liter), malt extract (3.0 g/liter) and yeast extract (3.0 g/liter) and sea-water after adjusting its pH to 7.0. The fermented whole broth (45 liter