Mevalonic acid phosphate

Mevalonic acid 5-pyrophosphate [1492-08-6] M 258,1, Purified by ion-exchange chromatography on Dowex-1 formate [Bloch et al. JBC 234 2595 7959], DEAE-cellulose [Skilletar and Kekwick, AB 20 171 7967], on by paper chromatography [Rogers et al. BJ99 381 7966]. Likely impurities are ATP and mevalonic acid phosphate. Stored as a dry powder or as a slightly alkaline (pH 7-9) soln at -20°. 

I schcsche and co-workers " employed the I.emieux-Rudlolf procedure for oxidation of the carbinol phosphate (6) to Di.-mevalonic acid 5-phosphate (7). At the end of the reaction excess periodate was destroyed with ethylene glycol, iodate ion was precipitated as barium Iodate, and cations were removed with Dowex-50. Mevalonic acid phosphate (7) was then isolated ai the crystulline tricyclohexylnmmonlum... 

In keeping with its biogenetic origin m three molecules of acetic acid mevalonic acid has six carbon atoms The conversion of mevalonate to isopentenyl pyrophosphate involves loss of the extra carbon as carbon dioxide First the alcohol hydroxyl groups of mevalonate are converted to phosphate ester functions—they are enzymatically phosphorylated with introduction of a simple phosphate at the tertiary site and a pyrophosphate at the primary site Decarboxylation m concert with loss of the terti ary phosphate introduces a carbon-carbon double bond and gives isopentenyl pyrophos phate the fundamental building block for formation of isoprenoid natural products... 

Mevalonic acid 5-phosphate [1189-94-2] M 228.1, pKes,(d 1.5 (PO4H2), pKEst(2) 4.4 (CO2H), pKEst(3) (P04H ). Purified by conversion to the tricyclohexylammonium salt (m 154-156°) by treatment with cyclohexylamine. Crystd from water/acetone at -15°. Alternatively, the phosphate was chromatographed by ion-exchange or paper (Whatman No 1) in a system isobutyric acid/ammonia/water (66 3 30 Rp 0.42). Stored as the cyclohexylammonium salt. 

The isoprenoid side chains of quinones are biosynthesized mainly by the mevalonic acid pathway from acetyl-CoA. Another pathway to biosynthesizing isoprenoids is the so-called non-mevalonate ronte by which isopentenyldiphosphate (IPP) is formed from glyceraldehyde 3-phosphate and pyrnvate. The key molecule is the famesyl-diphosphate (FPP) that accepts other IPP molecules to form polyprenyl diphosphates. 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

The CPPase substrate DMAPP (15) is formed from isopentenyl pyrophosphate (IPP) (14) via the IPP isomerase reaction. It had been assumed that IPP was generated only via mevalonic acid (12) (Fig. 2), but Rohmer discovered another route, 2-C-methyl-D-erythritol 4-phosphate (13) (MEP) pathway (Fig. 2) [22, 23]. A key step in the MEP pathway is the reaction catalyzed by 1-deoxy-D-xylulose 5-phosphate synthase (DXS), which combines hydroxyethyl thiamine pyrophosphate (hydroxyethyl TPP) generated from pyruvic acid (17) and TPP with glyceral-dehyde 3-phosphate (18) to yield 1-deoxy-D-xylulose 5-phosphate (19) containing five carbons. The mevalonate pathway operates in the cytosol of plants and animals, whereas the MEP pathway is present in the plastid of plants or in eubacteria [24-27]. 

Fig. 2 Two possible biosynthetic pathways to pyrethrolone. The [l-13C]D-glucose-derived 13C labels that occur in the mevalonic acid and 2-C-methyl-D-erythritol 4-phosphate (13) pathways are colored in red and green, respectively. The phosphate moiety is indicated as P ...

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... 

Alkaloid biosynthesis needs the substrate. Substrates are derivatives of the secondary metabolism building blocks the acetyl coenzyme A (acetyl-CoA), shikimic acid, mevalonic acid and 1-deoxyxylulose 5-phosphate (Figure 21). The synthesis of alkaloids starts from the acetate, shikimate, mevalonate and deoxyxylulose pathways. The acetyl coenzyme A pathway (acetate pathway) is the source of some alkaloids and their precursors (e.g., piperidine alkaloids or anthraniUc acid as aromatized CoA ester (antraniloyl-CoA)). Shikimic acid is a product of the glycolytic and pentose phosphate pathways, a construction facilitated by parts of phosphoenolpyruvate and erythrose 4-phosphate (Figure 21). The shikimic acid pathway is the source of such alkaloids as quinazoline, quinoline and acridine. 

Bhat, C.S. and Ramasarma, T., Effect of phenyl and phenolic acids on mevalonate-5-phosphate kinase and mevalonate-5-pyrophosphate decarboxylase of the rat brain, J. Neurochem., 32, 1531, 1979. 

MEP/DXPpathway. 2-C-methyl-D-erythritol4-phosphate/r-de-oxy-D-xylulose s-phosphate pathway, first reported in the late 1980s, is also known as non-mevalonate pathway or mevalonic acid independent pathway (MEP). This pathway is located in the plastids of plants and in the stmcture known as the api-complexan in protozoa as well as in many bacteria. 

Terpenes, biogenetically, arise from two simple five-carbon moieties. Isoprenyl-diphosphate (IPP) and dimethylallyldiphosphate (DMAPP) serve as universal precursors for the biosynthesis of terpenes. They are biosynthesised from three acetylcoenzyme A moieties through mevalonic acid (MVA) via the so-called mevalonate pathway. About 10 years ago, the existence of a second pathway leading to IPP and DMAPP was discovered involving l-deoxy-D-xylulose-5-phos-phate (DXP) and 2C-methyl-D-erythritol-4-phosphate (MEP). This so-called non-mevalonate or deoxyxylulose phosphate pathway starts off with the condensation of glyceraldehyde phosphate and pyruvate affording DXP. Through a series of reactions as shown in Fig. 4.1, IPP and DMAPP are formed, respectively [3,7, 42, 43]. 

Mevalonic acid lactone. Mevalonic acid 5-phosphate, Mevalonic acid 5-pyrophosphate... 

Mevalonic acid is converted to 5-pyrophosphomevalonate in two steps, each of which transfers a phosphate group from ATP. 

Elimination usually involves loss of a proton together with a nucleophilic group such as -OH, -NH3+, phosphate, or pyrophosphate. However, as in Eq. 13-18, step c, electrophilic groups such as -COO-can replace the proton. Another example is the conversion of mevalonic acid-5-pyrophosphate to isopentenyl pyrophosphate (Eq. 13-19) This is a key reaction in the biosynthesis of isoprenoid compounds such as cholesterol and vitamin A (Chapter 22). The phosphate ester formed in step a is a probable intermediate and the reaction probably involves a carbo-cationic intermediate generated by the loss of phosphate prior to the decarboxylation. 

Until 1993, all terpenes were considered to be derived from the classical acetate/mevalonate pathway involving the condensation of three units of acetyl CoA to 3-hydroxy-3-methylglutaryl CoA, reduction of this intermediate to mevalonic acid and the conversion of the latter to the essential, biological isoprenoid unit, isopentenyl diphosphate (IPP) [17,18,15]. Recently, a totally different IPP biosynthesis was found to operate in certain eubacteria, green algae and higher plants. In this new pathway glyceradehyde-3-phosphate (GAP) and pyruvate are precursurs of isopentenyl diphosphate, but not acetyl-CoA and mevalonate [19,20]. So, an isoprene unit is derived from isopentenyl diphosphate, and can be formed via two alternative pathways, the mevalonate pathway (in eukaryotes) and the deoxyxylulose pathway in prokaryotes and plant plastids [16,19]. 

It is difficult to identify the lipid moiety as a polyprenol, because of the small amounts present in tissues. Nevertheless, some information can be obtained by using glycosylated lipids labelled in the sugar moiety. The first indication of the presence of polyprenyl glycosyl phosphates comes from study of the properties just mentioned, namely, lability to mild acid, stability to mild alkali, and acidic properties. Information on the polyprenyl nature of the lipid may be obtained by labelling the lipid with radioactive 2,4-dideoxyO-C-methyl-D-g/ycero-pentono-l.S-lactone (mevalonic acid ). 

In addition to acetyl-CoA, shikimic acid, mevalonic acid, and deoxyxylulose phosphate, other building blocks based on amino acids are frequently employed in natural product synthesis. Peptides, proteins, alkaloids, and many antibiotics are derived from amino acids, and the origins of the most important amino acid components of these are briefly indicated in Figure 2.1. Intermediates from the glycolytic pathway and the Krebs cycle are used in constructing many of them, but the aromatic amino acids phenylalanine, tyrosine,... 

The biochemical isoprene units may be derived by two pathways, by way of intermediates mevalonic acid (MVA) (Figure 5.4) or 1-deoxy-D-xylulose 5-phosphate (deoxyxylulose phosphate DXP) (Figure 5.6). Mevalonic acid, itself a product of acetate metabolism, had been established as a precursor of the animal sterol cholesterol, and... 

O Reaction of mevalonic acid with three equivalents of ATP converts one hydroxy group to a pyrophosphate group and the other to a phosphate group. 

This brief survey of natural products derived from the 3-deoxy-D-oro6iTk>-heptulosonic acid 7-phosphate pathway illustrates the economy of fimda-mental biosynthetic pathways. The relative economy and simplicity of the biological degradative and energy-yielding reactions is paralleled in the biosynthetic reactions. For example, 3-deoxy-D-oroW o-heptulosonic acid 7-phosphate is a precursor of a host of aromatic products mevalonic acid is the progenitor of the terpenoids and steroids, and 5-aminolevulinic acid of the porphyrins. 

---