Diterpenoid diphosphate

Terpenoids are classified according to the number of five-carbon multiples they contain. Monoterpenoids contain 10 carbons and are derived from two isopentenyl diphosphates, sesquiterpenoids contain 15 carbons and are derived from three isopentenyl diphosphates, diterpenoids contain 20 carbons and are derived from four isopentenyl diphosphates, and so on, up to triterpenoids (C30) and tetraterpenoids (C40). Monoterpenoids and sesquiterpenoids are found primarily in plants, bacteria, and fungi, but the higher terpenoids occur in both plants and animals. The triterpenoid lanosterol, for example, is the precursor from which steroid hormones are made, and the tetraterpenoid /3-carotene is a dietary source of vitamin A (Figure 27.6). 

The terpenoid precursor isopentenyl diphosphate, formerly called isopentenyl pyrophosphate and abbreviated IPP, is biosynthesized by two different pathways depending on the organism and the structure of the final product. In animals and higher plants, sesquiterpenoids and triterpenoids arise primarily from the mevalonate pathway, whereas monoterpenoids, diterpenoids, and tetraterpenoids are biosynthesized by the 1-deoxyxylulose 5-phosphate (DXP) pathway. In bacteria,... 

Diterpenoids are derived biosynthetically from geranylgeranyl diphosphate (GGPP), which is itself biosynthesized by reaction of farnesvl diphosphate with isopentenyl diphosphate. Show the structure of GGPP, and propose a mechanism for its biosynthesis horn FPP and IPP. 

The diterpenoids constitute a large group of compounds derived from geranylgeranyl diphosphate. They are found in higher plants, fungi, insects and marine organisms. 

Hemiterpenoids are produced from the isoprenyl diphosphate DMAPP. All other terpenoids are produced from DMAPP and IPP via longer-chain prenyl diphosphate intermediates formed by prenyl transferases. Prenyl transferases (20) catalyze the formation of geranyl diphosphate (GPP), famesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP) from one molecule of DMAPP and one, two, or three molecules of IPP, respectively (Fig. 1). Isoprenyl diphosphates are the substrates for all TPS, which lead to the hemiterpenoids, monoterpenoids, sesquiterpenoids, and diterpenoids, which will be highlighted with selected examples in the following sections. 

Figure 1 Schematic overview of the biosynthesis of the monoterpenoids, sesquiterpenoids, diterpenoids, and triterpenoids. Representatives of these classes with biological relevance are shown. Enzymatic steps are indicated in italics DMADP, dimethylallyl diphosphate CDP, geranyl diphosphate GGDP, geranylgeranyl diphosphate FDP, farnesyl diphosphate IDP, isopentenyl diphosphate.

Generally, terpenoids have been believed to be biosynthesized via acetate-mevalonate pathway. Aphidicolin, a tetracyclic diterpenoid isolated from moulds, Cephalosporium aphidicola [47] and Nigrospora sphaerica [48], was also proved to be biosynthesized from mevanonic acid [49]. In this pathway, isopentenyl pyrophosphate (IPP), geranylgeranyl diphosphate (GGPP), labdane-type and pimarane-type diterpenoids were proposed to be intermediate precursors of aphidicolin [50]. 

GGPP to copalyl diphosphate (CPP), followed by its transformation into abietadiene via 49 in a class I reaction (Scheme 87.20). Notably, the bifunctional plant terpene synthases are generally involved in the biosynthesis of a large superfamily of terpenes, the labdane-related diterpenoids [214]. 

Xu M, Hillwig ML, Prisic S, Coates RM, Peters RJ (2004) Functional identification of rice syn-copalyl diphosphate synthase and its role in initiating biosynthesis of diterpenoid phytoalexin/allelopathic natural products. Plant J 39 309... 

Terpenes are synthesised in organisms by complex mechanisms from isoprene units, isopentenyl phosphate and dimethy-lallyl diphosphate (pyrophosphate). The first product is geranyl diphosphate, which is the universal precursor of monoterpenoids. The reaction of geranyl diphosphate with another molecule of isopentenyl diphosphate yields famesyl diphosphate, which is the precursor of sesquiterpenoids. Further reaction with isopentenyl diphosphate gives geranylgeranyl diphosphate, the precursor of diterpenoids (see Figure 3.10). 

Although not directly involved as odour-active food components, diterpenes are widespread in the plant kingdom, where they mainly occur as components of resins of conifers and juices of the aster (sunflower) family (Asteraceae) and spurge family (Euphorbiaceae) plants. Diterpenic hydrocarbons are precursors of numerous diterpenoids, many of which are biologically active substances. More than 3000 different diterpenoid structures have been defined, aU of which appear to be derived from geranylgeranyl diphosphate. Like monoterpenes and sesquiterpenes, diterpenes are mostly cycHc compounds. Examples of diterpenoid hydrocarbons (8-9) are tri-cychc hydrocarbon (-)-ent-kaur-16-ene, tetracycHc hydrocarbon (-)-abieta-7(8),13(14)-diene and macrocycHc compounds cem-brene, casbene and taxa-4,11-diene. 

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