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.

1

2

4

15

56

7

8910

11

1213

14

OH3

1617

1819

20

Labdane

1

2

4

15

56

7

8910

11

1213

14

COOH

3

1617

1819

20

1

2

4

15

56

7

8910

11

12 13

14

OH

HO3

16

17

1819

20

Abietane

1

2

415

56

7

8910

11

12 13

14

COOGluc(Ac)4

OHOAc

3

16 17

1819

20

Kaurane

OH

OO

1

2

34

5

67

89

10

11

12 1314

15

1617

18

19

20

Clerodane