**2. Diterpene biosynthesis**

Diterpenoid biosynthesis has been studied in plants, bacteria, and fungi [16]; still lots of work are required to clone many important respective genes to characterize and engineer diterpenoid pathways in these representative organisms which remain a big challenge [17]. Fungal di-TPS enzymes show homology to plant enzymes in terms of its size and the combination of biochemical studies with molecular genetics. This also facilitated the comparison of plant and fungal biochemical pathways leading to the formation of gibberellins in plants and fungi [18].

The first committed step in diterpenoid biosynthesis is the cyclization of GGPP to produce the diterpene scaffold, which occurs via a carbocation cascade. Classically, activation of the carbocation cascade by terpene synthases corresponds to the removal of the pyrophosphate group from the linear substrate. This ionization-dependent reaction is catalyzed by class I terpene synthases [19]. Fusicoccanes are potent phytotoxins known to be synthesized by a few fungal species. *P. amygdali* was the first monofunctional diterpene synthase cloned and characterized in *E. coli* [20, 21]. Diterpenoids cyclized by the first, one-step route involves a monofunctional class I diterpene synthase that catalyzes ionization-dependent diphosphate cleavage and subsequent carbocation migration and quenching using a mechanism similar to sesquiterpene synthases, except the prenyl chain is now longer by one isoprene unit [22].

Biosynthesis of labdane-type diterpenoids requires a two-step cyclization pathway involving first a protonation dependent cyclization of GGPP to form the characteristic labdane bicycle and, in the second step, ionization-dependent cyclization at a separate active site to generate the final cyclic product (**Figure 1**). Cyclization of GGPP to ent-CDP and then to the tetracyclic ent-kaurene generates the precursor for gibberellin (gibberellic acids, GA) phytohormones that are major regulators of plant growth and development. It is believed that because of its essential role in plants, ent-kaurene represents the ancestral diterpenoid cyclization pathway from which alternative cyclization routes evolved to generate the large diversity of labdanetype compounds known today [22]. In fact, it has been shown that single amino acid changes are sufficient to alter the product profile of the class I ent-kaurene synthase to form new cyclic scaffolds [23, 24].

**Figure 1.** Overview of diterpenoid biosynthesis: (a) monofunctional-2,10(14)-diene is modified into different fusicoccane compounds and (b) bifunctional diterpene synthases make different labdane-related scaffolds that are modified into

Diterpenes from Different Fungal Sources and Their 13C-NMR Data

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bioactive compounds.

Diterpenes from Different Fungal Sources and Their 13C-NMR Data http://dx.doi.org/10.5772/intechopen.79186 113

As the largest group of documented natural products, terpenoids have attracted attention from a broad scientific community and have been heavily investigated due to their interesting

Fungi are important source of potential bioactive compounds which play an important role in pharmacology industry [7–11]. Among fungi, mushrooms are the most attractive sources of bioactive compounds both of chemical and biomedical interests. Approximately 2000 mushrooms are safe for human consumption, and about 650 of them have medicinal properties out of 15,000 documented species of mushrooms [12]. These are also important in industrial processes to enhance composition of bioactive compounds in fermented grain assays [13–15].

Diterpenoid biosynthesis has been studied in plants, bacteria, and fungi [16]; still lots of work are required to clone many important respective genes to characterize and engineer diterpenoid pathways in these representative organisms which remain a big challenge [17]. Fungal di-TPS enzymes show homology to plant enzymes in terms of its size and the combination of biochemical studies with molecular genetics. This also facilitated the comparison of plant and fungal biochemical pathways leading to the formation of gibberellins in plants

The first committed step in diterpenoid biosynthesis is the cyclization of GGPP to produce the diterpene scaffold, which occurs via a carbocation cascade. Classically, activation of the carbocation cascade by terpene synthases corresponds to the removal of the pyrophosphate group from the linear substrate. This ionization-dependent reaction is catalyzed by class I terpene synthases [19]. Fusicoccanes are potent phytotoxins known to be synthesized by a few fungal species. *P. amygdali* was the first monofunctional diterpene synthase cloned and characterized in *E. coli* [20, 21]. Diterpenoids cyclized by the first, one-step route involves a monofunctional class I diterpene synthase that catalyzes ionization-dependent diphosphate cleavage and subsequent carbocation migration and quenching using a mechanism similar to sesquiterpene synthases, except the prenyl chain

Biosynthesis of labdane-type diterpenoids requires a two-step cyclization pathway involving first a protonation dependent cyclization of GGPP to form the characteristic labdane bicycle and, in the second step, ionization-dependent cyclization at a separate active site to generate the final cyclic product (**Figure 1**). Cyclization of GGPP to ent-CDP and then to the tetracyclic ent-kaurene generates the precursor for gibberellin (gibberellic acids, GA) phytohormones that are major regulators of plant growth and development. It is believed that because of its essential role in plants, ent-kaurene represents the ancestral diterpenoid cyclization pathway from which alternative cyclization routes evolved to generate the large diversity of labdanetype compounds known today [22]. In fact, it has been shown that single amino acid changes are sufficient to alter the product profile of the class I ent-kaurene synthase to form new cyclic

structural characteristics and profound biological effects [3–6].

**2. Diterpene biosynthesis**

is now longer by one isoprene unit [22].

and fungi [18].

112 Terpenes and Terpenoids

scaffolds [23, 24].

**Figure 1.** Overview of diterpenoid biosynthesis: (a) monofunctional-2,10(14)-diene is modified into different fusicoccane compounds and (b) bifunctional diterpene synthases make different labdane-related scaffolds that are modified into bioactive compounds.
