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

when a methyl group migrates to an adjacent carbon atom and “seco” refers to a bond
that has been broken on the skeletal structure. The numbers preceding “abeo” refers to
the carbon atoms involved in the migration e.g. (10→5) abeo indicates that a methyl has
migrated from C-10 to C-5 and the numbers preceding “seco” refers to the carbon atoms
in which the bond has been broken e.g. in 4,5-seco the bond has been broken between C-
4 and C-5. Figure 5 includes examples of these.
1
2 10
3
4
19
20
13
12
11
9
8
5
6
7
14
16
15
17
20
4 5
(a) 18-nor (b) 4,5-seco-20(10→5)abeoabietane
Figure 5: Examples of the use of the prefix “nor”, “abeo” and “seco”
1.3 Biosynthesis
The acyclic diterpenes (Class 1), for example phytane (1) (Figure 1a) is formed by the
addition of four molecules of IPP (isopentenyl diphosphate). The formation of IPP can
follow either one of two biosynthetic pathways, the methylerythritol phosphate pathway
(MEP), also known as the 1-deoxy-D-xylulose (DOX) pathway and the mevalonic acid
(MVA) pathway. The MVA pathway is the only pathway used by animals, while both
pathways are present in plants. The enzymes involved in the MVA pathway are found in
the cytosol while those in the MEP or DOX pathway are found in the chloroplast of the
plant.
10
7