Confirmation of structures of Semecarpus biflavanones A1 and A2

The biflavanone mixture from Semecarpus anacardium L. was reisolated and dehydrogenated with I2/KOAc in AcOH to yield the corresponding, relatively more stable, biflavone mixture which was methylated using diazomethane. Two biflavone methyl ethers SA1 and SA2 were obtained which confirmed the structures proposed for the parent biflavanones A1 and A2 respectively