Prenyl quinones

The brown algal order Fucales accounts for just over a third of known chemistry, with the genus Cystoseira accounting for more than 100 reported structures (Munro and Blunt 2005). The compounds are primarily prenylated quinones and hydroqui-nones, ranging from simple and linear to often complex and polycyclic forms as seen in cystoketal (sis to ke tal) (Fig. 1.61) (Amico et al. 1984) from C. balearica and from C. stricta (Fig. 1.6m)[B2] (Amico et al. 1987). 

The molecular target site of triketone herbicides is the enzyme -hydroxyphenylpyruvate dioxygenase (HPPD). Inhibition of this enzyme disrupts the biosynthesis of carotenoids and causes a bleaching (loss of chlorophyll) effect on the foliage similar to that observed with inhibitors ofphytoene desaturase (e.g. norflurazon). However, the mechanism of action of HPPD inhibitors is different. Inhibtion of HPPD stops the synthesis of homogen tisate (HGA), which is a key precursor of the 8 different tocochromanols (tocopherols and tocotrienols) and prenyl quinones. In the absence of prenylquinone plastoquinone, phytoene desaturase activity is interrupted. The bleaching of the green tissues ensues as if these compounds inhibited phytoene desaturase. 

Prenylated quinones and hydroquinones Polyketides Polyphenols Fatty acids Prostaglandins Peptides (including cyclic) Alkaloids... 

Marine invertebrates have proved to be a rich source of biologically active prenylated heterocyclic natural products, with several prenylated quinones and chromenols having been discovered from ascidian species (sea squirts). Conicaquinones A and B (Figure 8) were isolated from the marine ascidian Aplidium conicum in 2003 (03EJO898), and are clearly related to the previously mentioned benzoquinone thiazine counterparts, the aplidinones (05EJ(35024). However, unlike the aplidinones, these... 

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. 

Potassium hydroxide in acetonitrile solution with dicyclohexyl-18-crown-6 gives good yields of aj8-unsaturated nitriles from a variety of aldehydes and ketones, including benzophenone. One consequence of the rate enhancement of the [3,3] sigmatropic rearrangement of certain enolates reported last year by Evans is a new route to prenylated quinones (Scheme 14). A development in the synthesis of olefins by the boron mediated cross-coupling reaction is the use of the boronic... 

Prenyllipid biosynthesis under the influence of sethoxydim Most of the C-label was found in the sterol fraction, whereby the highest mol-specific radioactivity was detected in the 4-dimethyl and 4-methyl sterols, which are known as biosynthetic precursors of the desmethyl sterols (Table 6). High label was also found in the mitochondrial ubiquinone, which in maize leaves consists of the two homologues Q-9 and Q-10 (29). Much less radioactivity is found in the chloroplast prenyllipids (chlorophylls, carotenoids, prenyl-quinones) as is expected and known, since exogeneously applied mevalonic... 

Fu X, Hossain MB, van der Helm D, Schmitz FJ. Longithor-one A unprecedented dimeric prenylated quinone from the tunicate Aplydium longithorax. J. Am. Chem. Soc. 1994 116 12125-12126. 

Cimino, G De Stefano, S and Minale, L. (1972f) Prenylated quinones in marine sponges Ircinia sp. Experientia, 28,1401-1408. 

Prenylated Quinones in marine sponges Ircinia sp. Experientia 28,1401 (1972). 

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. 

Quinones represent a very large and heterogeneous class of biomolecules. Three major biosynthetic pathways contribute to the formations of various quinones. The aromatic skeletons of quinones can be synthesized by the polyketide pathway and by the shikimate pathway. The isoprenoid pathways are involved in the biosynthesis of the prenyl chain and in the formation of some benzoquinones and naphthoquinones. ... 

The shikimate pathway is the major route in the biosynthesis of ubiquinone, menaquinone, phyloquinone, plastoquinone, and various colored naphthoquinones. The early steps of this process are common with the steps involved in the biosynthesis of phenols, flavonoids, and aromatic amino acids. Shikimic acid is formed in several steps from precursors of carbohydrate metabolism. The key intermediate in quinone biosynthesis via the shikimate pathway is the chorismate. In the case of ubiquinones, the chorismate is converted to para-hydoxybenzoate and then, depending on the organism, the process continues with prenylation, decarboxylation, three hydroxy-lations, and three methylation steps. - ... 

The third pathway involved in the quinones biosynthesis is the isoprenoid route. This pathway is primarily important for the formation of prenyl side chains of prenylquinones (ubiquinone, menaquinone, plastoquinones, etc.). The side chains of ubiquinones and prenylated naphthoquinones derive from polyprenyl diphosphates. 

The ort/zo-quinone cyclization to the carbazole-3,4-quinones carbazoquinocin C 51 and ( )-carquinostatin A ( )-55a is more convergent than the previous approaches to these natural products, which required transformation to the ort/zo-quinone and/or introduction of substituents (prenyl or heptyl) following the carbazole ring formation (cf. Schemes 20,21, and 37). 

Fu, X. Hossain, M.B. Schmitz, F.J. van der Helm, D. (1997) Longithorones, unique prenylated para- and metacyclophane type quinones from the tunicate Aplidium longithorax. J. Org. Chem., 62, 3810-19. 

In 1955, R. A. Morton and associates in Liverpool announced the isolation of a quinone which they named ubiquinone for its ubiquitous occurrence.484 485 It was characterized as a derivative of benzoquinone attached to an unsaturated polyprenyl (isoprenoid) side chain (Fig. 15-24). In fact, there is a family of ubiquinones that from bacteria typically contains six prenyl units in its side chain, while most ubiquinones from mammalian mitochondria contain ten. Ubiquinone was also isolated by F. L. Crane and associates using isooctane extraction of mitochondria. These workers proposed that the new quinone, which they called coenzyme Q, might participate in electron transport. As is described in Chapter 18, this function has been fully established. Both the name ubiquinone and the abbreviation Q are in general use. A subscript indicates the number of prenyl units, e.g., Q10. Ubiquinones can be reversibly reduced to the hydro-quinone forms (Fig. 15-24), providing a basis for their function in electron transport within mitochondria and chloroplasts.486 490... 

Another important family of quinones, related in structure to those already discussed, are the vitamins K (Fig. 15-24, Box 15-F). These occur naturally as two families. The vitamins K, (phylloquinones) have only one double bond in the side chain and that is in the prenyl unit closest to the ring. This suggests again the possibility of chromanol formation. In the vitamin K2 (menaquinone) series, a double bond is present in each of the prenyl units. A synthetic compound menadione completely lacks the polyprenyl side chain and bears a hydrogen in the corresponding position on the ring. Nevertheless, menadione serves as a synthetic vitamin K, apparently because it can be converted in the body to forms containing polyprenyl side chains. 

PQQ See Pyrroloquinoline quinone Preproteins 519-522. See also Proenzyme(s) peroxisomal 521 Precursor activation 540 Prenatal diagnosis 26 Prenyl diphosphate (pyrophosphate) 390s Prenylation 402... 

The phenolics include anthocyanins, anthraquinones, benzofurans, chromones, chromenes, coumarins, flavonoids, isoflavonoids, lignans, phenolic acids, phenylpropanoids, quinones, stilbenes and xanthones. Some phenolics can be very complex in structure through additional substitution or polymerization of simpler entities. Thus xanthones can be prenylated and flavonoids, lignans and other phenolics can be glycosylated. Condensed tannins involve the polymerization of procyaninidin or prodelphinidin monomers and hydrolysable tannins involve gallic acid residues esterified with monosaccharides. As detailed in this review, representatives of some major classes of plant-derived phenolics are potent protein kinase inhibitors. 

---