Polyprenols synthesis

Solanesol and other prenyl alcohols are important as metabolites in mulberry and tobacco leaves and in the synthesis of isoprenoid quinones. Hence, Sato and collaborators107 have developed a stereoselective synthesis of all-trans-polyprenol alcohols up to C50. Construction of the requisite skeletons was accomplished by the alkylation of a p-toluenesulphonyl-stabilized carbanion, followed by reductive desulphonylation of the resulting allylic sulphonyl group. This was achieved most efficiently by the use of a large excess of lithium metal in ethylamine (equation (43)), although all reaction conditions led to mixtures. The minor product results from double bond rearrangement. 

If the synthesis starts from glucose molecules, then the initial step is the transfer of glucose residues from UDP-glucose onto an intermediary acceptor-dolichol phosphate (membrane-bound polyprenol phosphate). Dolichol phosphate assists in the synthesis of an... 

The structures of polyprenyl diphosphate-linked intermediates of Salmonella O-specific-polysaccharide biosynthesis were confirmed by chemical synthesis of their analogs derived from the plant polyprenols ficaprenol and moraprenol (structurally related to bacterial polyprenol57) with the following study of their behavior as substrates of enzymic reactions. Synthetic polyprenyl a-D-galactopyranosyl diphosphate291,292 was found to serve as an effective acceptor for the transfer of L-rhamnosyl groups.293"295 Two synthetic, isomeric disaccharide derivatives,292 13 and296 14, were tested as acceptors for enzymic D-mannosyl transfer from GDP-Man, but only the former was found to be an efficient substrate.294... 

Grange and Adair73 isolated 2,3-dehydrodolichyl phosphate from in vitro studies on hen oviduct. It may be derived from 2,3-dehydrodolichyl diphosphate, a likely intermediate in the biosynthesis of dolichyl phosphate. Many questions still remain unanswered, such as is the substrate for the a-isoprene reductase, the diphosphate or the monophosphate of 2,3-dehy-drodolichol Are the unsaturated polyprenols a reserve pool for the synthesis of dolichol in plants What is the function of unsaturated, plant polyprenols How is the synthesis of saturated and unsaturated polyprenols regulated ... 

Asymmetric hydrogenation of allylic alcohols (14, 39-40).1 Mammalian dol-ichols (2) are terminal dihydropolyisoprenols which are involved in glycoprotein synthesis. They contain one terminal chiral primary allylic alcohol group. The polyprenols 3 present in plants correspond to dolichols except that they lack the terminal double bond considered to be (Z). They can be obtained by hydrogenation of 2 catalyzed by (bistrifluoroacetate)ruthenium(II) and (S)-l, which affects only the terminal double bond to provide (S)-3 in >95% ee. 

In Phytophthora cactorum the polyprenols are all trans in the ubiquinones-8 and -9 (112) whereas dolichols-13 to -16 (113) all have three double bonds trans and the rest cis. This stereochemistry was shown in the usual way by the incorporation of tritium from [2- C,31 ,4/ - H]- and [2- C,3/ ,4S- H]-mevalonic acid. The incorporation of mevalonate into various polyprenols has been reported. Polyprenols are involved in bacterial cell-wall synthesis. Some of the enzymes involved in this process have been studied. 

Dolichol phosphate, which is a crucial intermediate, has been shown to be synthesised in a variety of tissues and subcellular fractions, of which mitochondrial outer membranes are especially active. These are also a major store of dolichol. The synthesis can start from isopentenyl pyrophosphate or its precursor, mevalonic acid (see the reviews of Beytia and Porter, 1976 Daleo and Pont-Lezica, 1977 Daleo etaiy 1977). In one case the product was the a-unsaturated polyprenol phosphate (dehydrodolichol phosphate), which suggests that a-saturation may occur after phosphorylation, at least in tissues such as hen oviduct (Grange and Adair, 1977 Adair and Keller, 1982). 

Waechter, C.J. and Lennarz, W.J. (1976). The Role of Polyprenol-Linked Sugars in Glycoprotein Synthesis . Annual Reviews of Biochemistry, 45, 95-112. 

Waechter, C. j. and W. J. Lennarz, The role of polyprenol-linked sugars in glycoprotein synthesis, Annu. Rev. Biochem., 45, 95-112(1976). 

A polyprenol phosphate such as dolichol phosphate (10.63) can react with a nucleoside diphosphate sugar in one of two ways (11.119) and (11.120). As an example of a synthesis proceeding... 

The role of undecaprenyl phosphate (C55, allylic) as a carrier of glycosyl units in the biosynthesis of bacterial cells walls is well established. Dolichyl phosphate plays a similar role in the synthesis of glycoproteins in animal systems. Evidence that prenyl lipids serve as glycosyl carriers in the biosynthesis of glycoproteins in plants is accumulating rapidly (Pont Lezica et al., 1976 Delmer al., 1978 Erickson et al., 1978). Several authors have recently reviewed the literature on the role of polyprenols as glycosyl carriers in plants (Hemming, 1978 Pont Lezica, 1979 Elbein, 1979). 

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