Two ambuic acid dimers derived from homo- endo Diels-Alder reaction from Pestalotiopsis versicolor .

Two new dimers of ambuic acid, pestaloversicoloric acids A ( 1 ) and B ( 2 ), and a known derivative, 13( S )-hydroxyambuic acid ( 3 ), were isolated from the static fermentation product of Pestalotiopsis versicolor . The structural identification was accomplished via analyses on the data of HR-MS, 1 D and 2 D NMR, and ECD. Different from the well-known exo -type dimer, torreyanic acid, compounds 1 and 2 represent the first example of endo -type product derived from the intermolecular Diels-Alder reaction of two molecules of ambuic acid derivative with the identical absolute stereochemistry.