Isoprenylated Quinones

The best known isoprenylated quinones are the benzoquinone ubiquinone (157) and the naphthoquinone menaquinone (158), which normally occur in natural tissues as a mixture of homologues (isoprenylogues) with different chain lengths. Analysis of the mixtures of ubiquinone or menaquinone isoprenylogues present in various species has been used in the chemotaxonomic characterization of bacteria. 

Mankowski, and T. Chojnacki, Chem. and Phys. Lipids, 1977, 18, 199. 

Fartaczek, W. Tanner, and H. Kauss, Arch. Biochem. Biophys., 1976,175, 419. 

Chemistry.—The chemical structures of several bacterial menaquinones (MKs) with partly saturated isoprenoid side-chains have been studied. Spectroscopic (u.v., i.r., m.s., and H n.m.r.) and chromatographic data have been recorded for the tetrahydro-MK8 and -MK9 mixture of some nocardioform and coryneform bacteria.The main component tetrahydro-MK9 has the second and third iso-prene residues from the quinone ring saturated, i.e. has structure (159), 2- 

The separation of plant isoprenoid lipids, including ubiquinone, phylloquinone [=MK-4(II,III,IV-H6], and plastoquinone (160) by h.p.l.c. has been described. 

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Quinones.—Rules for the nomenclature of isoprenylated quinones have been presented.2... 

Isoprenylated Quinones.—Chemistry. An efficient method has been described for the preparation of ubiquinone-1 (221) and plastoquinone-1 (223) from the parent quinone and allyltributyltin. The synthesis of ubiquinone-10 by isoprenoid chain-elongation of a ubiquinone-1 derivative has been reported.The sul-phone derivative of the protected ubiquinol-1 (224) on reaction with solanesyl bromide (225) and McjCOK gave the sulphone (226) in 90% yield. Benseker reduction to remove the PhCH2- and PhS02-groups, followed by oxidation in air, afforded ubiquinone-10 (222). 

Isoprenylated Quinones.—A review has been published on the chemistry and biochemistry of ubiquinone (236) and plastoquinone (237) in plants.273 Chemistry. Methods have been presented for the preparation of sulphone-function-alized prenylhydroquinones.274 Thus the ubiquinol (238), plastoquinol (239), and... 

Isoprenylated Quinones.—A book has been published dealing with biomedical and clinical aspects of coenzyme Q [ubiquinone (203)]. Other reviews have appeared on the chemistry and biochemistry of ubiquinone,vitamin K [phyl-loquinone (204) and menaquinone (205)], and plastoquinone (206) and on the chemical methods for prenylation of quinones. ... 

Chemistry. Several new methods for the synthesis of isoprenylated quinones have been published. A method for elongation of the isoprenoid side-chain of ubiquinone involves preparation of the chloride (207) by the reaction sequence outlined in Scheme 8 and the condensation of (207) with an aryl sulphone prepared from a prenyl (C5, Cio, or C15) halide, followed by reductive elimination of the sulphone group. Syntheses have been reported of some ubiquinone analogues (208)—(210) and of urinary metabolites of these and of ubiquinone itself. The metabolites were compounds having an abbreviated isoprenoid side-chain (Cg) and containing one or two carboxy-groups, e.g. (211). The preparation... 

Isoprenylated Quinones.—A review has been published on the chemistry, distribution, and functioning of vitamins A new volume in the Methods in Enzymology series contains experimental procedures used in the ubiquinone and vitamin K fields. 

The method could be applied to the synthesis of many natural benzo- and naphthoquinones. The masked quinone (146), which may serve as a general precursor to the menaquinones, was prepared and isoprenylated by a similar series of reactions. 

Regiospecific quinone isoprenylation can be effected by the following scheme used in the synthesis of vitamin K - 9... 

On the other hand. Biggins examined various benzo-, naphtho- and anthraquinones and found a more stringent structural requirement for areplacement quinone to be functional at the A i site. It was specifically noted that among the many types of quinones, only naphthoquinones possessing a hydrocarbon chain at the 3-position, namely, 2-methyl-3-decyl-, 2-methyl-3-(isoprenyl)2- and 2-methyl-3-(isoprenyl)4-naphthoquinones, similar to phylloquinone with the 3-phytyl chain, could provide the required molecular structure for interaction with the hydrophobic domain at the A site, as confirmed by the criterion of P700 /P430 recombination kinetics. All other quinones presumably could oxidize Aq but the reduced quinone then recombined directly with P700. It was also noted that 2,3-dimethyl-1,4-naphthoquinone,... 

Isopentenylhydroquinone, 397, 398 Isopentyl nitrite, 48 Isophorone, 287 oxide, 282, 283, 394 Isoprene dimers, 4-5 Isoprene epoxide, 79 isoprenoid quinones, 250 Isoprenylation, 397-398 N-Isopropylideneanilines, 3 Isopropylidenecarbene. 358 Isup ropy I idenecy do propanes, 358... 

Isoprenylation of quinones. Evans and Hoffmann have developed a useful route to prenylated quinones, which are natural products involved in various biological processes. The process is illustrated in equation (I) for the synthesis of 2-isopentenylhydroquinone (3). Reaction of the protected quinone (1) with the allylic bromide in the presence of Rieke magnesium (5, 419) affords the epimeric quinols (2). On deprotection the initial product (a) undergoes a facile rearrangement, probably a Cope rearrangement, to (3) in high yield. 

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