Absolute Configuration of Sesquiterpenes from Crossopetalum tonduzii and Their Inhibitory Effects on Epstein−Barr Virus Early Antigen Activation in Raji Cells

Two new sesquiterpenoids (<BO>1 </BO>and<BO> 2</BO>) with a dihydro-β-agarofuran skeleton were isolated from Crossopetalum tonduzii. Their structures were elucidated on the basis of spectral analysis, including homonuclear and heteronuclear correlation NMR experiments (COSY, ROESY, HSQC, and HMBC). Their absolute configurations were determined by CD studies on <BO>3</BO>, the benzoylated derivative of <BO>1</BO>. Chemical correlations have allowed the absolute configurations of <BO>4</BO> and <BO>5</BO>, two previously known dihydro-β-agarofuran analogues, to be reported for the first time. Compounds <BO>1</BO>, <BO>2</BO>, and <BO>5 </BO>showed strong antitumor-promoting effects on Epstein−Barr virus early antigen (EBV-EA) activation.