Prenols, poly

As shown in Scheme 1, two other pathways lead to the formation of dolichol phosphate. These are (a) phosphorylation of the free poly-prenol, and (b) dephosphorylation of dolichol diphosphate. A dolichol phosphate-cleaving phosphatase has been described as occurring in Tetrahymena pyriformis,15 human lymphocytes,18 calf brain,17 and rat-nerve tissue.18 The protozoal enzyme was a soluble acid phosphatase, although it was clearly different from the bulk phosphatase activity, whereas the mammalian enzymes had optima at neutral pH and were membrane-bound. 

Much of the current interest in poly terpenoids is concerned with their biological role. The C55 prenol (68 n = 3, m = 8) from Staphylococcus aureus was shown ... 

Ruthenium complexes generated from the amphiphilic phosphines 24 (see also Section 7.5) were used for the selective hydrogenation of 3-methyl-2-butenal (pre-nal) to 3-methyl-2-butenol (prenol) in isopropanol/water mixtures [49]. High conversions of up to 100% and selectivities of 90-96% were achieved with ligands of the type 24 containing long poly ether chains [49]. 

The arrangement of the trans and cis units in typical polyprenols was determined according to information obtained from the 13C NMR study of acyclic terpenes mentioned above. Poly-prenol-11 C(55), isolated from the leaves of Ficus elastica, was found to contain the -terminal unit, three internal trans units, six internal cis units, and a cis a-terminal unit from 1H NMR observations. Polyprenol-12 C(60), isolated from Ficus etastica and silkworm feces, showed a similar composition except that there were seven internal cis units. 

Two well-known natural materials are rubber and gutta percha which are cis and trans polyiso-prene, respectively (11.116). Other examples of terpenes are provided by poly prenols (10.63), vitamin A (10.64), certain components of essential oils and the closely related sterols. Terpenes are widespread in nature and many are cyclic compounds. 

All P. are unbranched molecules, and the double bonds may be cis or irons (Fig.). For the biosynthesis of P. see Terpenes. With the exception of certain Poly-prenols (see), P. are found only in plants, in latex and... 

All ra 5-polyprenols are believed to be formed from GFPP by the chain extension process already discussed (Sect. 8.1.1.2), followed by hydrolysis by appropriate phosphatases. There is evidence to show that synthesis of all- raAi -poly-prenol pyrophosphates occurs in mitochondrial membranes and chloroplasts. Biosynthetic studies have shown that c/5, ra 5-polyprenols are synthesized from FPP or GGPP by cw-prenylation by IIP (189, 369, 392). 

The dolichol moiety of lipid-intermediates is not homogeneous but a mixture of 14-20 isoprene units [71-73]. For the yeast OST it was shown that the enzyme hardly discriminates specific isoprene chain lengths [74]. Whether unsaturated poly-prenols, preferred in eubacterial cell wall synthesis, will be accepted is not known. However, the formation of the DolPP-GlcNAc, i.e. the first step in lipid-linked precursor formation shows an absolute dependency for saturation of the a-isoprenoid unit, i.e for dolichol-type polyprenols [74], what seems to be generally true for other eukaryotic glycosyltransferases involved in lipid-linked sugar formation [75, 76]. 

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