Discovery of an unprecedented benz[α]anthraquinone-type heterodimer from a rare actinomycete Amycolatopsis sp. HCa1

The angucylines are a family of aromatic polyketides featuring a tetracyclic benz[a]anthraquinone skeleton. This class of polycyclic aromatic polyketides are exclusively associated with actinomycetes and can undergo many modifications such as oxidation, ring cleavage, glycosylation and dimerization. Here we report the discovery of a new ether-linked benz[a]anthraquinone heterodimer, named mycolatone (1), from a grasshopper-derived actinomycete, Amycolatopsis sp. HCa1. The structure of mycolatone (1) was determined by comprehensive two-dimensional NMR analysis, high-resolution electrospray ionization mass spectrometry and biogenetic consideration. This new heterodimeric molecule is structurally derived from the dimerization of two tetracyclic angucylines, 2-hydroxy-5-O-methyltetragomycin and PD116779, through an ether bond between C-8 and C-8′. This new structural feature enrich the structural diversity of angucylines. Additionally, the surface tension activity and cytotoxic activities of 1 against human cervical cancer cell line (Hela), human gastric adenocarcinoma cell line (SGC-7901) and human lung adenocarcinoma cell line (SPC-A-1) were evaluated.