Formation of cyclic diterpenoids
OHOH
Labdane
+ - H+
Pimarane
H+
+
- H+
+
+- H
+
Kaurane Abietane
OHGeranylgeraniol
OH
H
+
labdane cation
OH
H+
•Acyclic diterpenoids are characterized by six methyl group equivalents including 5 2ndry, 1 primary methyl groups.•Labdanes are characterized by six methyl group equivalents including 3 3ry, 2 2ndry, 1 primary methyl groups.•Pimaranes and abietanes are characterized by five methyl group equivalents including 4 3ry and a vinyl group in pimaranes, 3 3ry and an isopropyl group in abietanes.•Kauranes are characterized by four methyl group equivalents including 3 3ry and 1 2ndry methyl groups.