Isolation of novel indole diterpenes and dihydrodibenzofuran from the marine fungus Aspergillus sp.

Abstract

Twelve secondary metabolites were earlier isolated from two marine-derived fungal strains, Aspergillus sp. AF-119 and Aspergillus sp. JQG a-6f. The objectives of this investigation were to isolate and purify natural products produced in these fungi, and identify possible drug candidates. The chemical structures of these compounds were elucidated and characterized by the analysis of 1D and 2D NMR spectra, UV, optical rotation and mass
spectroscopy data. Three of the isolated compounds are novel derivatives of indole diterpenes (1& 2), and dihydrodibenzofuran, namely, 9-hydroxy-7-methyl-2, 3-dihydrodibenzo [b, d] furan-1, 4-dione (3). The rest of the compounds were also determined from spectroscopy data to be known. These included three indole diterpenes – paspalinine (4), paspalicine (5) and paspaline (6); two ditetopiperazines –fumitremorgin B and lanosulin (7 & 8); methyl 2,8-dihydroxy-6-methyl-9-oxo-9H-xanthene-1 carboxylate (9); 1,3,8-trihydroxy-6-methylanthracene-9,10- dione (10); terphenyl (11) and 2-(3-chloro-2-hydroxyphenyl)-5-hydroxy-3,7,8-trimethoxy-4H-chromen-4-one (12). Paper disc diffusion assays showed that the novel compounds exhibit antibacterial activity on S. aureus, B. subtilis, and E. coli, but no activity on C. niger. MTT assays showed that the three novel compounds have antibacterial activity in vitro. These findings further enhanced the concept that natural products synthesized by marine-derived fungi possessed high structural diversity, antimicrobial and antitumor activities. Hence, they are a rich resource for drug discovery.

Keywords: Marine Fungi; Natural product; Indole diterpenes; Cytotoxicity Assay