university of kwazulu-natal faculty of science and agriculture school ...

H
1,3 H + migration
H
H
12
13
14
D
H
16
15
Intermediate II
H
H
D
16
15
13
C
sandaracopimarenyl cation
H
H
H
8
(Intermediate I)
-H (17)
19
16
4
17
15
-H + (16)
H H
HO
16
14
H H
12
CH 2OH
15
13
17
13
12 17
15
9,16-bond formation
8
14
1,2 H + loss of CH2 11
20 H
9
shift
18
Atisirene
(atisane type compound)
16
Beyerol
(beyerane type diterpene)
CH 2OH
15
-H (12)
12,15-bond
formation
19
4
20
18
19
4
18
20
aconane type compound
12
17
15 13
16
9
8
trachylobane type diterpene
15
16
9
8
Figure 11: Biosynthesis of beyerane, trachylobane, atisane and aconane diterpenes
(Manitto, 1981)
The loss of a proton at C-14 in the sandaracopimarenyl cation leads to the formation of a
double bond between C-8 and C-14 after which a methyl migration from C-17 to C-15
yields an abietenyl cation, which loses a proton at C-7 to produce abietadiene (figure 12).
H
H
8
14
16
H
17
H
8
sandaracopimarenyl cation (-)-sandaracopimaradiene
H
15
17
14
H
H
H
7
H
16
15
abietenyl cation O (-)-abietadiene
Figure 12: Synthesis of abietadiene (reproduced from Dewick, 2002)
H
H
13