(±)-Pratenone A (1), the first representative of natural 3-(1-naphthyl)-2-benzofuran-1(3H)-one polyketides, was isolated from a marine-derived Streptomyces pratensis strain KCB-132 together with three other new analogues (2-4). Its structure was assigned by spectroscopic analysis, and the absolute configurations of the two enantiomers separated by high-performance liquid chromatography were determined by single-crystal X-ray diffraction and electronic circular dichroism calculations. The solvent-induced racemization of 1 and a proposed biogenetic pathway to 1-4 from the co-isolated angucyclinone precursor, as well as their biological activity, are also discussed.
Keywords: Streptomyces pratensis; angucyclinone derivatives; chiral separation; electronic circular dichroism; exciton-coupled CD; structure elucidation.
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