Preparation of Bioactive Isorhapontigenin Dimers through Chemical Transformation of Bisisorhapontigenin A

Two new stilbene dimers, bisisorhapontigenin E (2) and bisisorhapontigenin F (3), and two novel cyclooligostilbenes, bisisorhapontigenin G (4) and 13b-methoxyl bisisorhapontigenin G (5) were prepared through isomerization reaction of bisisorhapontigenin A with sulfuric acid as a catalyst. Their structures and relative stereochemistry were elucidated on the basis of spectral analysis and their possible formation mechanisms were proposed. The pharmacological activities on anti-inflammation and anti-oxidant of 2-4 have been tested. All of them exhibited potent anti-oxidant activities.