Polyprenyl pyrophosphate

The first stage of the synthesis is the preparation of the substrate for enzymatic polymerization, the polyprenyl pyrophosphate-galactosy1-rhamnosy1-mannose XXI. Since the most convenient way to control the polycondensation reaction is the use of isotopic methods, a procedure for incorporation of tritium into trisaccharide I was developed (2 5). Labelled trisaccharide was then converted into the glycosyl phosphate XIX through interaction of its peracetate III with anhydrous phosphoric acid (26). Conditions were found under which the reaction is accompanied by minimal destruction and yields the Ot-phosphate of the trisaccharide. 

The synthesis of XXI was accomplished by direct condensation of XIX with moraprenyl phosphoimidazo1id-ate XX in a THF-DMSO-mixture under mild conditions (27). This new method makes it possible to prepare polyprenyl pyrophosphate oligosaccharides directly from unprotected phosphates of oligosaccharides, thus avoiding the need for de-protection procedures which may be accompanied by extensive destruction of polyprenyl pyrophosphate sugars. 

L. L. Danilov, S. D. Maltsev, V. N. Shibaev, and N. K. Kochetkov, Synthesis of polyprenyl pyrophosphate sugars from unprotected mono- and oligo-saccharide phosphates, Carbohydr. Res., 88 (1981) 203-211. 

Polyterpenoids.—A series of polyprenyl acetates (231) has been isolated from Pinus sylvestris needles. Homologues with 10—19 isoprene units mainly with the cis-configuration were detected.110 A method for the preparation of [l-3H]polyprenyl pyrophosphates (232) has been described. The reaction products (phosphate and pyrophosphate esters and inorganic phosphate) are separated on a diethylaminoethoxylated form of lipophilic Sephadex.111 P -Dolichyl-P a-D-mannopyranosyl pyrophosphate (233) has been prepared from P -dolichyl-P2-diphenyl pyrophosphate (234) and 2,3,4,6-tetra-O-acetyl-a-D-mannopyranosyl... 

Several papers report new findings on ubiquinone biosynthesis. A mitochondrial membrane-rich preparation from baker s yeast can convert 4-hydroxybenzoate and isopentenyl pyrophosphate into the ubiquinone precursor 3-all-trans-hexaprenyl-4-hydroxybenzoate (234). Details of the cell-free system are presented. With preformed polyprenyl pyrophosphates, the system catalysed the polyprenylation of several aromatic compounds, e.g. methyl 4-hydroxybenzoate, 4-hydroxybenzaldehyde, 4-hydroxybenzyl alcohol, and 4-hydroxycinnamate. No evidence was obtained for the involvement of 4-hydr-oxybenzoyl-CoA or 4-hydroxybenzoyl-S-protein in the reaction. With shorter-chain prenyl pyrophosphates a shorter prenyl side-chain was introduced, e.g. geranyl and farnesyl pyrophosphates gave products with a 3-diprenyl and 3-triprenyl side-chain respectively. A crude enzyme preparation from E. coli... 

Other - Farnesylpyrophosphate synthetase has been used in asymmetric synthesis of isoprenoids. Potato acid phosphatase has been applied to mild hydrolysis of polyprenyl pyrophosphates. Sulfatase-catalyzed hydrolysis of /9-napthol sulfate has been used to separate a- and 8-napthols. NAD and flavin adenine dinucleotide have been made by enzymic coupling reactions. 

Some aspects of the mechanism of 0-specific polysaccharide biosynthesis in Salmonella newport and S. Kentucky have been reported. Cell envelope and soluble glycosyltransferase preparations from both organisms catalysed the formation of polyprenyl pyrophosphate oligosaccharides with carbohydrate units corresponding to the structures of the main-chain polysaccharides (Scheme 1). The D-glucosylation reaction occurs before the polymerization of the repeating units to the polysaccharide. 

The biosynthesis of polyprenyl quinones presumably involves condensation of polyprenyl pyrophosphates with some member of the shikimic acid... 

Chemoselective Hydrolysis of Phosphate Esters. Chemical hydrolysis of polyprenyl pyrophosphates is hampered by side reactions due to the lability of the molecule. Hydrolysis catalyzed by acid phosphatase - an enzyme named because it displays its pH-optimum in the acidic range - readily afforded the corresponding dephosphorylated products in acceptable yields [511]. 

The isoprenoid quinones, e.g. the ubiquinones 5.36), are essential metabolites, being involved in electron transport in living systems. In the ubiquinones a particular chain length is favoured from n = 6 in certain micro-organisms to w = 10 in most mammals. Mevalonic acid (5.55) is well established as the source of polyprenyl side-chains in these metabolites. It is probable that the side-chain is assembled as a polyprenyl pyrophosphate which then couples with the aromatic fragment. The evidence is that polyprenyl pyrophosphate synthetases and 4-hydroxybenzoate polyprenyltransferases have been isolated from living systems and ubiquinones co-occur with polyprenyl alcohols [as (5.57)] [26, 27]. 

The major difference between the IPPSs and the terpene cyclases lies in the fact that terpene cyclases do not bind IPP. The first step in the terpene cyclase-catalysed reaction is still in most cases the loss of the pyrophosphate group with the formation of a polyprenyl cation in the active site. This time, however, it is an electron-rich double bond elsewhere in the molecule which serves as an internal nucleophile, with the result being formation of a cychc structure. The active sites of terpene cyclase enzymes are tailored to fold the polyprenyl pyrophosphates into the optimum conformation for intramolecular attack to take place, with hydrophobic residues to force the prenyl chain into the desired conformation, and aromatic residues such as tyrosine to stabilize the positive charge on the intermediate carbocation (Starks etal.1997). Initial isomerization, for example to linalyl or nerohdyl pyrophosphate (vide infra), is often important to present the correct geometry at the electron-accepting end of the molecule to allow cychzation to occur (Bohhnann et al. 1998). 

Fujii H, Koyama T, Ogura K. Essential protein factors for polyprenyl pyrophosphate synthetases. Separation of heptaprenyl pyrophosphate synthetase into two components. FEBS Lett, 1983 161 257-260. 

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