Cytotoxic diterpenoids from Vietnamese medicinal plant Croton tonkinensis Gagnep.

Six new ent-kaurane-type diterpenoids were isolated from the leaves of the endemic Vietnamese medicinal plant Croton tonkinensis GAGNEP. (Euphorbiaceae) together with three known ent-11 alpha-acetoxy-7 beta,14 alpha-dihydroxy-kaur-16-en-15-one (1), ent-kaur-16-en-15-one 18-oic acid (5) and ent-18-hydroxykaur-16-ene (7). Their structures were determined by spectroscopic analyses to be ent-7 beta-acetoxy-11 alpha-hydroxykaur-16-en-15-one (2), ent-18-acetoxy-11 alpha-hydroxykaur-16-en-15-one (3), ent-11 alpha-acetoxykaur-16-en-18-oic acid (4), ent-15 alpha,18-dihydroxykaur-16-ene (6), ent-alpha,18-diacetoxy-7 beta-hydroxykaur-16-en-15-one (8), and ent-(16S)-1 alpha-14 alpha-diacetoxy-7 beta-hydroxy-17-methoxykauran-15-one (14). ent-Kaurane-type diterpenoids from Croton tonkinensis 2-4, 6, and 9-13, were tested for toxicity in the brine shrimp lethality assay. Compounds 9, 10, and 12 demonstrated significant activity, compounds 2, 3, 6, and I I showed weak activity, and compounds 4 and 13 were inactive.