Isopentyl pyrophosphate

During the second step, mevalonic acid is implicated in a number of enzymic reactions involving ATP, and is converted to isopentyl pyrophosphate and to its isomer 3,3-dimethylallyl pyrophosphate. Actually, the two compounds constitute the active isoprene , which... 

In pepper as in many plants, there are two sources of isoprene monomers the mevalonic acid pathway and the plastidal pool from pymvate and glyceraldehyde-3-phosphate [26], Pepper carotenoid biosynthesis uses the plastidal pathway for the isopentyl pyrophosphate monomers and the resident terpenoid synthases and transferases [27], Using the 5-carbon isoprene pool, the prenyl transferases sequentially... 

Figure 1. A schematic representation of the terpene pathway showing the possible derivation of the musty/earthy "off-flavor" microbial metabolites 2-methylisobomeol and geosmin. Abbreviations PP, pyrophosphate IPP, isopentyl pyrophosphate DMAPP, dimethylally pyrophosphate Pi, inorganic phosphate (Adapted from ref. 42),...

Isopentyl pyrophosphate Geranyl pyrophosphate Carotenoids ---Farnesyl pyrophosphate ... 

Isoprenoid structures for carotenoids, phytol, and other terpenes start biosynthetically from acetyl coenzyme A (89) with successive additions giving mevalonate, isopentyl pyrophosphate, geranyl pyrophosphate, farnesyl pyrophosphate (from which squalene and steroids arise), with further build-up to geranyl geranyl pyrophosphate, ultimately to a- and /3-carotenes, lutein, and violaxanthin and related compounds. Aromatic hydrocarbon nuclei are biosynthesized in many instances by the shikimic acid pathway (90). More complex polycyclic aromatic compounds are synthesized by other pathways in which naphthalene dimerization is an important step (91). 

Two fundamental building-blocks of natural product chemicals are isopentyl pyrophosphate and isoprene [31, 32], Isoprene is incorporated in compounds known as isoprenoids. The function and occurrence of isoprenoids cover a very broad range in nature according to Stryer [31], "-isoprenoids can bring delight by their colour as well as their fragrance. Indeed, isoprenoids can be regarded as the sensual molecules The colour of tomatoes and carrots comes from carotenoids, specifically lycopene and beta-carotene, respectively."... 

In bacteria and plastids of plants, formation of prenyl pyrophosphates, which are the precursors of carotenoids, proceeds via an alternative—the glyceraldehyde-3-phosphate pyruvate pathway. The pathway is apparently the sole source of isoprenoid compounds for the unicellular algae Scenedesmus (Metzler 2003). Initially, pyruvate is decarboxylated by a l-deoxyxylulose-5-phosphate synthase and condensed with D-glyceraldehyde 3-phosphate to form 1-deoxyxylulose 5-phosphate. This product may be the branching point for independent routes to isopentyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). 

The n bond of Isopentyl pyrophosphate functions as a nucleophile and attacks the carbocation... 

The biosynthesis of geranyl pyrophosphate is achieved in just three steps. The first step involves loss of a leaving group (pyrophosphate) to generate a resonance-stabilized carbocation. The second step is a nucleophilic attack in which the carbocation is attacked by the tt bond of isopentyl pyrophosphate to generate a new carbocation. Finally, a proton transfer yields geranyl pyrophosphate. 

The preceding discussion has indicated the sequence of squalene 4.8) biosynthesis as mevalonate 4.13) isopentyl pyrophosphate 4.14) dimethylallyl pyrophosphate 4.15) geranyl pyrophosphate 4.41) farnesyl pyrophosphate 4.19) squalene 4.8). Each stage involves stereochemical change at one or two carbon atoms. The presence of several prochiral centres in the molecules of this sequence meant that for stereochemical changes to be monitored they had to be chirally labelled with deuterium or tritium e.g. the condensation of isopentenyl pyrophosphate 4.14) with dimethylallyl pyrophosphate 4.15) (see Scheme 4.10) involves loss of one of the... 

The mechanics of latex formation in the rubber tree has been the subject of considerable study. It is now known that the monomer isopentyl pyrophosphate is the one used in the biosynthesis of natural rubber. Catalysts for these transformation are enzymes in the latex and tissues of Hevea. The structure for natural-rubber is c/5 -l,4-polyisoprene (1) and the trans form for the structure of gutta... 

MECHANISM FOR THE CONVERSION OF ISOPENTYL PYROPHOSPHATE TO DIMETHYLALLYL PYROPHOSPHATE... 

The pyrophosphate leaving group is expelled to give a resonance-stabilized (allylic) carbocation. The k bond of isopentyl phosphate then functions as a nucleophile and attacks the carbocation. Finally, a basic amino acid residue of the enzyme removes a proton to give the product ... 

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