Source
Major diterpenes
Common name
Botanical name (Family)
Yew tree
Taxus brevifolia (Taxaceae)
Paclitaxol
Sawada fungus
Gibberella fujikuroi
Gibberellins
Coleus
Coleus forskohlii (Lamiaceae)
Forskolin
Stevia
Stevia rebaudiana (Asteraceae)
Stevioside
Ginkgo
Ginkgo biloba (Ginkgoaceae)
Ginkgolides
6.5.6 Triterpenes
The triterpenoids encompass a large and diverse group of naturally occurring
30-carbon-atom-containing compounds derived from squalene or, in the case
of 3b-hydroxytriterpenoids, the 3S-isomer of squalene 2,3-epoxide. Two
molecules of farnesyl pyrophosphate are joined tail-to-tail to yield squalene.
The conformation that all-trans-squalene 2,3-epoxide adopts, when the initial
cyclization takes place, determines the stereochemistry of the ring junctions
in the resulting triterpenoids. The initially formed cation intermediate may
undergo a series of 1,2-hydride and methyl migrations, commonly called
backbone rearrangements, to provide a variety of skeletal types.
A number of triterpenoids are bioactive compounds and are used
in medicine. For example, fusidic acid is an antimicrobial fungal metabolite,
isolated from Fusidium coccineum, and cytotoxic dimeric triterpenoids,
crellastatins, are isolated from marine sponges Crella species.
O
Squalene 2,3-epoxide
O
O
H
O
H
H
O
H
H
OAc
Fusidic acid
An antimicrobial agent
H
O
H
H
CHO
H
H
OH
COOH
Quillaic acid
A triterpene from Quillaja
O
H
O
H
H
OH
H
H
OH
Panaxatriol
A triterpene from Panax ginseng
Squalene
Formed from tail-to-tail combination of 2 FPP
Tail
Tail
6.5 TERPENOIDS
347