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anticancer (Cerqueira et al., 2004; Nyila et al., 2009; Gaspar-Marques et al., 2002) and
antimalarial activity (van Zyl et al., 2008). Compound 124 also has antioxidant activity
(Narukawa et al., 2001). Compound 36 has a royleanone-type structure while the other
two compounds (123-124) have a vinylogous quinone-type structure. In the three studies
that were done on coleon-type and royleanone-type compounds (Mei et al., 2002;
Cerqueira et al., 2004; Gaspar-Marques et al., 2002), it was found that the coleon-type
compounds were more effective as anticancer agents than the royleanone-type
compounds.
When Kabouche et al. (2007) tested the antioxidant activity of royleanone and coleon-
type compounds, they found that the presence of a carbonyl group at C-7 led to higher
activity as apposed to compounds having no substituent at this position or having a
substituent other than a carbonyl at C-7. When the hydroxyl group at C-12 is replaced by
a methoxy group as in 176, the activity is increased as well (Kabouche et al., 2007). In
studies where coleon (compounds where ring C is aromatic) and royleanone-type (where
ring C has a 12-hydroxy-p-benzoquinone moeity) compounds were isolated, the coleon-
type compounds proved to be more active than the royleanone-type compounds
(Kabouche et al., 2007; Cerqueira et al., 2004; Mei et al., 2002; Gaspar-Marques et al.,
2002; Narukawa et al., 2001). However there has been one instance were a royleanone-
type diterpene (Coleon U quinone (44)) showed potent antifeedant activity whereas the
coleon-type diterpene (coleon U (149)) displayed no activity as an antifeedant (Wellsow
et al., 2006).
O
R
12
O
OCCH 3
O
R
(175) OH
(176) OCH3
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