(+)- And (-)-Alternarilactone A: Enantiomers With A Diepoxy-Cage-Like Scaffold From An Endophytic Alternaria Sp.

The enantiomers (+)- and (-)-alternarilactone A (1), the first examples of dibenzo-a-pyrones bearing a diepoxy-cage-like moiety, were isolated from the endophytic fungus Alternaria sp. hh930. The deficiency in H-1-H-1 COSY and HMBC correlations caused by the highly oxidized caged system of 1 and the deceptive and ambiguous signals such as "W" couplings in NMR data increased the risk of structure misassignment of 1. By performing a quantum chemical calculation of the NMR chemical shifts together with a DP4+ probability analysis and single-crystal X-ray crystallographic experiment, their structures were unambiguously determined, and their absolute configurations were determined by ECD calculations.