Anti-tumour activity of two 19-norclerodane diterpenes, trans-dehydrocrotonin and trans-crotonin, from Croton cajucara - Grynberg,N.F.; Echevarria,A.; Lima,J.E.; Pamplona,S.SR.; Pinto,A.C.; Maciel,M.AM. (Planta Medica, 1999)