Biologically active abietane and ent-kaurane diterpenoids and other constituents from Erythroxylum suberosum

Bioassay-guided fractionation of the ethanol extract from the branches of Erythroxylum suberosum, which was toxic to brine shrimp larvae, afforded five diterpenes bearing abietane and ent-kaurane-type skeletons from an active fraction. From these, four were new, 7-oxo-16-hydroxy-abiet-15(17)-en-19-al, 16-hydroxyabiet-15(17)-en-7-one, 7α,16-dihydroxy-abiet-15(17)-en-19-al and ent-12α-hydroxy-kaur-16-en-19-al, while methyl ent-7α,15β-dihydroxy-kaur-16-en-19-oate is reported for the first time as a natural product. This is also the first reported occurrence of abietane-type diterpenes in the genus Erythroxylum. The flavonoid ombuin-3-rutinoside was isolated from an inactive fraction, while rutin (quercetin-3-rutinoside) was obtained from the non-toxic ethanol extract of the leaves. The structures of the new and known compounds were established by analyses of 1D- and 2D-NMR and mass spectrometry data.