New Diels-Alder type adducts from Morus macroura and their anti-oxidant activities

Fractionation of the ethanolic extract of the stem bark of Morus macroura resulted in the isolation of four new Diels-Alder type adducts, named guangsangons K--N (1, 2, 5, 6), together with two known compounds, mulberrofuran G (3) and K (4). Their structures were determined on the basis of spectroscopic analyses and chemical methods. Furthermore, by means of (1)H-NMR variable temperature experiments and the Cotton curves in the circular dichroism (CD) spectra, the stereochemistry of four new compounds was elucidated. The isolated new compounds showed good activity on anti-oxidant in vitro, with the inhibitory rates of MDA being from 91.8 to 100.0% at concentrations of 10(-5) mol/l.