Polyprenyl compounds

FIGURE 8.18 Dolichol phosphate is an initiation point for the synthesis of carbohydrate polymers in animals. The analogous alcohol in bacterial systems, undecaprenol, also known as bactoprenol, consists of 11 isoprene units. Undecaprenyl phosphate delivers sugars from the cytoplasm for the synthesis of cell wall components such as peptidoglycans, lipopolysaccharides, and glycoproteins. Polyprenyl compounds also serve as the side chains of vitamin K, the ubiquinones, plastoquinones, and tocopherols (such as vitamin E). 

Reaction type 6B of Table 10-1 is allylic rearrangement with simultaneous condensation with another molecule. The reaction, which is catalyzed by prenyl-transferases,3073 occurs during the polymerization of polyprenyl compounds (Fig. 22-1,Eqs. 22-2,22-3). Experimental evidence favors a carbocation mechanism for all of these reactions.308 309 See Chapter 22. 

Isoprenoid alcohol phosphokinase 409 Isoprenoid compounds. See also Polyprenyl compounds... 

Polypeptide(s) 56 - 59. See also Proteins antibiotics 66 chemical synthesis 85 conformation of 59 - 61, 78 definition of 51 torsion angles 59-62 Polypeptides. See also Peptides Polyphosphates 302, 303 Polyprenyl compounds... 

Figure 22-1 Outline of biosynthetic pathways for polyprenyl compounds. Steps e,f, and g and many subsequent steps are catalyzed by isoprenyl diphosphate synthases.

The chain length of the polyprenyl compounds appears to be determined by the protein structure of... 

Chain elongation during polymerization of prenyl units can be terminated in one of a number of ways. The pyrophosphate group may be hydrolyzed to a monophosphate or to a free alcohol. Alternatively, two polyprenyl compounds may join "head to head" to form a symmetric dimer. The C30 terpene squalene, the precursor to cholesterol, arises in this way from two molecules of famesyl diphosphate as does phy-toene, precursor of the Qo carotenoids, from E,E,E geranylgeranyl diphosphate. The phytanyl groups of archaebacterial lipids (p. 385) arise rather directly from geranylgeranyl diphosphate by transfer of the poly-... 

Another polyprenyl compound formed by a head to head condensation is chrysanthemic acid. This monoterpene component of the pyrethrum insecticides is formed by chrysanthemums from two molecules of dimethyallyl-PP via an intermediate analogous to presqualene alcohol-PP.118a... 

Polyprenyl compounds are formed by condensation of isoprene units that are derived from acetate by reductive trimerization and decarboxylation. These compounds include terpenes, carotenoids, sterols, and steroids (Coscia, 1984 Hobkirk, 1979). 

This paper describes the structural analysis of naturally occurring ois-1,4 polyisoprenes using 13C NMR spectroscopy. First, the structural characterization of polyprenols, which are linear isoprenoid compounds containing 30 to 100 carbons, was carried out on the basis of information obtained from acyclic terpenes having various ois and trans isoprene units as model compounds. This method was also applied to the structural analysis of polyisoprenes. The elucidation of the structure of the end groups and the arrangement of isoprene units provides information on the mechanism of the biosynthesis of polyprenyl compounds in nature. 

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