*3.2.1.1. Tricyclic abietatrienes*

This group of abietane terpenes includes a tricyclic ring, three double bonds on B or C rings. Carboxylic acids are representatives of this group, of which the earliest example is the biologically active dehydroabietic acid (**Figure 6**), which possess an acid group at C-18 [42].

**Figure 4.** Skeleton of labdanes.

**Figure 5.** Classification of tricyclic abietane diterpenes.
