1 Introduction
Sesterterpenoids are a relatively small group of natural products. Even though they
belong to one of the largest families of natural products, the “terpenoids,” only
around 1000 natural sesterterpenoids have been reported [1–5]. Considering that
over 80,000 terpenoids have already been isolated [6–8], the number of known
sesterterpenoids is quite small. Moreover, in almost all cases, their biological role is
unknown. However, sesterterpenoids have been isolated from many kinds of organisms (e.g., plants, bacteria, fungi, lichens, insects, marine sponges, and other marine
organisms) [1–5]. This fact implies that various organisms have the potential to
produce sesterterpenoids.
In this contribution, we will introduce the chemical structures of sesterterpenoids.
Although the number of sesterterpenoids is not very large, they have a large variety
of simple to complicated chemical structures. Herein, we have classified the
sesterterpenoids based on the number of carbocyclic moieties in their chemical
structures. In addition, we will also explain how the structure of each sesterterpenoid
is formed in Nature.
2 What Are the Sesterterpenoids?
2.1 “Sesterterpenoids” Are Members of the “Terpenoids”
As mentioned above, the sesterterpenoids are a subgroup of the terpenoids. Therefore, we will start by briefly describing the terpenoids. Terpenoids are defined as a
group of natural products composed of simple “C 5 ” units, called isoprene units
(Fig. 1). Thus, terpenoids are also called “isoprenoids.” In this definition, “C 5 ”
means that a compound contains five carbon atoms. This notation will be frequently
used in this chapter, and thus “C 25 ” refers to a compound containing 25 carbon
atoms.
For example, the chemical structure of sesterbrasiliatriene (1), a type of terpenoid,
contains five isoprene units (Fig. 2b) [9]. In another example, four isoprene units
(b) constitute the chemical structure (a) of 2 (Fig. 3) [10].
The origins of the isoprene units are dimethylallyl pyrophosphate (DMAPP) (3)
and isopentenyl pyrophosphate (IPP) (4) (Fig. 4) [6–8]. Both are widely distributed
in Nature, and generated via two kinds of metabolic pathways, known as the MVA
(mevalonate) and MEP (methylerythritol phosphate) pathways [11, 12].
The biosynthesis of all terpenoids starts from condensation reactions of 3 and 4 to
yield polyprenyl diphosphates, which are important intermediates of terpenoids.
Fig. 1 Isoprene unit
Sesterterpenoids
3
Sesterterpenoids are a relatively small group of natural products. Even though they
belong to one of the largest families of natural products, the “terpenoids,” only
around 1000 natural sesterterpenoids have been reported [1–5]. Considering that
over 80,000 terpenoids have already been isolated [6–8], the number of known
sesterterpenoids is quite small. Moreover, in almost all cases, their biological role is
unknown. However, sesterterpenoids have been isolated from many kinds of organisms (e.g., plants, bacteria, fungi, lichens, insects, marine sponges, and other marine
organisms) [1–5]. This fact implies that various organisms have the potential to
produce sesterterpenoids.
In this contribution, we will introduce the chemical structures of sesterterpenoids.
Although the number of sesterterpenoids is not very large, they have a large variety
of simple to complicated chemical structures. Herein, we have classified the
sesterterpenoids based on the number of carbocyclic moieties in their chemical
structures. In addition, we will also explain how the structure of each sesterterpenoid
is formed in Nature.
2 What Are the Sesterterpenoids?
2.1 “Sesterterpenoids” Are Members of the “Terpenoids”
As mentioned above, the sesterterpenoids are a subgroup of the terpenoids. Therefore, we will start by briefly describing the terpenoids. Terpenoids are defined as a
group of natural products composed of simple “C 5 ” units, called isoprene units
(Fig. 1). Thus, terpenoids are also called “isoprenoids.” In this definition, “C 5 ”
means that a compound contains five carbon atoms. This notation will be frequently
used in this chapter, and thus “C 25 ” refers to a compound containing 25 carbon
atoms.
For example, the chemical structure of sesterbrasiliatriene (1), a type of terpenoid,
contains five isoprene units (Fig. 2b) [9]. In another example, four isoprene units
(b) constitute the chemical structure (a) of 2 (Fig. 3) [10].
The origins of the isoprene units are dimethylallyl pyrophosphate (DMAPP) (3)
and isopentenyl pyrophosphate (IPP) (4) (Fig. 4) [6–8]. Both are widely distributed
in Nature, and generated via two kinds of metabolic pathways, known as the MVA
(mevalonate) and MEP (methylerythritol phosphate) pathways [11, 12].
The biosynthesis of all terpenoids starts from condensation reactions of 3 and 4 to
yield polyprenyl diphosphates, which are important intermediates of terpenoids.
Fig. 1 Isoprene unit
Sesterterpenoids
3