After the fundamental carbon skeleton of the terpenoids is formed by the
prenyltransferases and terpene cyclases, the intermediates of the terpenoids are
converted into the final products by tailoring enzymes. A typical tailoring enzyme
is cytochrome P450, which catalyzes an oxidation reaction. For instance, casbene (9)
is converted to the oxidized products 10–12 by means of cytochrome P450 (Fig. 8)
[13]. However, in addition to cytochrome P450, various other enzymes are also
involved in the biosynthesis of terpenoids and expand their structural diversity.
For example, many kinds of tailoring enzymes (prenyltransferase, oxidase, aminotransferase, methyltransferase, sugar transferase, and ligase) are involved in the
biosynthesis of brasilicardin A (13), a terpenoid with potent immunosuppressive
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OPP
OPP
OPP
H
+
+ H
+
– H
+
H
2
protonation to initiate
the cyclization reaction
deprotonation to finalize
the cyclization reaction
Fig. 7 Cyclization reaction
to form 2. This reaction is
catalyzed by the
type 2 terpene cyclase
9
OH
O
O
O
11
12
10
P450
Fig. 8 Compound 9 could
be oxidized by a cytochrome
P450, forming 10–12
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T. Mitsuhashi and I. Abe