Geranylpyrophosphate

IPP and DMAPP lead to geranylpyrophosphate (GPP), which is an immediate precursor of monoterpenes. The formation of nerylpyrophosphate (NPP) from GPP gives rise to a wide range of acyclic, cyclic, bicyclic or tricyclic skeletons. Reactions like rearrangement, oxidation, reduction and hydration via various terpene cyclases result in the formation of numerous terpene derivatives. Condensation of GPP and IPP leads to farnesylpyrophosphate (FPP), the immediate precursor of sesquiterpenoids. Likewise, FPP and IPP are conducive to diterpenoids. 

Fig. 20.3. Schematic representation of the main pathways in the lipid metabolism of parasitic flatworms. Boxed substrates are supplied by the host. Pathways present in mammalian systems but absent in parasitic flatworms are shown by open arrows. Abbreviations DAG, diacylglycerol CDP-DAG, cytidine diphosphodiacylglycerol Farnesyl PP, farnesyl pyrophosphate Geranyl PP, geranylpyrophosphate Geranylgeranyl PP, geranylgeranylpyrophosphate FlMG-CoA, hydroxymethylglutaryl-CoA TAG, triacylglycerol PA, phosphatidic acid PC, phosphatidylcholine PE, phosphatidylethanolamine PI, phosphatidylinositol PS, phosphatidylserine.

These isomeric C5 units condense to form a Cjq compound isopentenyl pyrophosphate attacks an allylic carbonium ion formed from dimethylallyl pyrophosphate to yield geranylpyrophosphate (Figure 26.9). The same kind of reaction takes place again geranyl pyrophosphate is converted into an allylic carbonium ion, which is attacked by isopentenyl pyrophosphate. The resulting C15 compound is called farnesylpyrophosphate. The same enzyme, geranyl transferase, catalyzes each of these condensations. 

Many other closely related compounds possess vitamin K activity (e.g., menadione [2-methyl-1,4-naphthoquinone] is as active as vitamin K on a molar basis). The synthetic compounds menadione and menadiol are referred to as vitamins Kj and Ke, respectively. Vitamin K is a naphthoquinone derivative containing diterpenoid units biosynthesized by the intermediate geranylpyrophosphate. ... 

Gibberellin biosynthesis is initiated by the activation of MVA, followed by its conversion to isopentenylpyrophosphate (IPP). Stepwise condensation leads to the formation of trans-geranylpyrophosphate (GPP), trans-farnesylpyrophosphate (FPP) and trans-geranylgeranylpyrophosphate (GGPP). 

Chemoenzymatic synthesis. In parallel to the work of the Li group on C7 [43, 219], Edwards and co-workers recently identified, expressed and characterised the bacterial ferf-prenyltransferase LtxB from the marine cyanobacterium Lyngbya majuscula [28]. It was possible to catalyse the 7-tert-geranylation of indolactam V (1) with geranylpyrophosphate (289) affording the natural product lyngbyatoxin (290) (Scheme 55). 

Fig. 95.1 Terpene biosynthesis pathways and their subcellular localization in the plants. Different classes of terpenes are respectively formed in the cytosol or the plastid by two independent pathways in the plants, that is, acetate-mevalonate pathway (MEV) (cytosol) and methylerythritol 4-phosphate (MEP) or deoxyxylulose 5-phosphate pathway (DXP) (plastid). Mraioterpcmes, diterpenes, and tetraterpenes are derived from IPP and DMAPP Irran the plastidial MEP ot DXP pathway. Sesquiterpenes and triterpenes are biosynthesized from IPP and DMAPP from the cytosol pathway. Black square with a white question mark suggests a possible transport of IPP (isopentenylpyrophosphate) from the plastid to the cytosol. Other metabolites involved in the different steps are DMAPP dimethylallylpyrophosphate, FPP famesylpyrophosphate, GASP D- glyceraldehyde- 3-phosphate, GPP geranylpyrophosphate, GGPP geranylgeranylpyro-phosphate. TPSs in the circle correspond to terpene synthases. Broken arrows show several enzymatic steps (Adapted from Aharoni et al. [8] and Sallaud et al. [154])...

Gondensation of this compound with one molecule of isopentylpyrophosphate results in the formation of geranylpyrophosphate, and addition of a second molecule of isopentylpyrophosphate yields famesylpyrophosphate (Fig. 20.19). 

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