Bialternacins A–F, Aromatic Polyketide Dimers from an Endophytic Alternaria sp.

Six novel aromatic polyketide dimers, bialternacins A–F (1–6), were isolated from a plant endophytic Alternaria sp. The structures of compounds 1–6 were elucidated on the basis of extensive spectroscopic analysis, single-crystal X-ray diffraction, and electronic circular dichroism analysis. Compounds 1, 2, 5, and 6 were characterized as four pairs of racemic mixtures. Compound (+)-5 was demonstrated to show acetylcholinesterase inhibitory activity with an IC50 value of 15.5 μM. A putative biosynthetic pathway for these compounds was proposed.