The isolation and in vivo potent antitumor activity of clerodane diterpenoid from the oleoresin of Brazilian medicinal plant Copaifera langsdorfii Desfon - Ohsaki,A.; Yan,L.T.; Ito,S.; Edatsugi,H.; Iwata,D.; Komoda,Y. (Bioorg Med Chem Lett, 1994)