Isoprenoid naphthoquinones

Naphthoquinones Isoprenoid naphthoquinones (D 8.1) Coenzymes of glutamic acid carboxylase (D 17), vitamins for humans (vitamins and Kg)... 

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 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. 

Ubiquinone (UQ), also known as coenzyme Q, has a benzoquinone structure with a long side chain. The name ubiquinone is for the ubiquitous nature of the quinone. Some bacteria also contain menaquinone (vitamin K2), either in addition to ubiquinone or in place of it. For instance, the reaction center of Rhodopseudomonas viridis contains one ubiquinone and one menaquinone, while in some other bacterial reaction centers both quinones are ubiquinones. Menaquinone has a naphthoquinone structure with a long isoprenoid side chain. The long hydrocarbon side chains in ubiquinone and menaquinone render a high degree of hydrophobicity to these molecules. 

Figure 1 Structures of major isoprenoid quinones found in E. coli. (1) Q-8, ubiquinone (2) MK-8, menaquinone (3) DMK-8, demethylmenaquinone. in the structure of MK, the A ring and B ring of the naphthoquinone are shown.

Vitamin K comprises derivatives of 1,4-naphthoquinone. Naturally occurring forms are equipped with structures possessing the unsaturated isoprenoid side chain linked to naphthoquinone at carbon-3 (Figure 7.5). Vitamin Kj, phylloquinone (2 methyl-3 phytyl-1,4-naphthoquinone), is one of the natural forms. Similar to compounds belonging to the vitamin E family, those included in the vitamin K group have the isoprenoid side chain consisting of 20 carbon atoms with one double bond. This side chain is derived from plant diterpenoic alcohol (C20H39OH). These compounds have been detected in alfalfa oil. 

Pennock (1965) has given a detailed review of the infrared and NMR spectra of quinones and related compounds, covering the prenyl-substituted benzo- and naphthoquinones, related chromenes, chromanes, and some isoprenoid hydrocarbons and alcohols. Table 19.16 presents the main frequencies of the substituted quinone nuclei of some naturally occurring isoprene-substituted quinones. Additional bands are also accounted for in the work of others cited by Pennock. Table 19.17 shows absorption frequencies of quinones in the region 1350-1250 cm . ... 

Chemical structure (Figure 5). Derivatives of naphthoquinone natural forms contain an unsaturated isoprenoid side chain on C-3 parent compound 2-methyl-1,4-naphthoquinone (menadione, not thought to occur naturally) green plants contain 2-methyl-3-phytyl-l,4-naphthoquinone (phylloquinone, vitamin Ki) with one double bond in the side chain. 

Phylloquinone (V.K antihemorrhagic V. coagulation V.) is a group of fat-soluble naphthoquinone compounds, with varying sizes of isoprenoid side chain. Mammals can synthesize the side chain but not the naphthoquinone moiety. VK is plentiful in green plants. V.K2 (famoquinone menaquinone-6 2-methyl-l,4-naphthoquinone) is found chiefly in... 

Dehydroquinic acid, shikimic acid, and chorismic acid are carboxylated compounds containing a six-membered carbocyclic ring with one or two double bonds (Fig. 143). The secondary products derived from these substances either still contain the ring and the C -side chain of the acids (see the structure of the benzoic acid derivatives, of anthranilic and 3-hydroxyanthranilic esters, D 8, D 8.2, D 8.4 and D 8.4.1) or have additional rings (see the formulae of naphthoquinones and anthraquinones, D 8.1, of quinoline, acridine, and benzodiazepine alkaloids, D 8.3.2). The carbon skeletons may be substituted by isoprenoid side chains (see the structure of ubiquinones, D 8.3) and may carry different functional groups, e.g., hydroxy, carboxy, methoxy, and amino groups. 

Naphthoquinones and anthraquinones are derivatives of the bicyclic and tricyclic aromatic compounds, naphthene and anthracene. The naphthoquinones of the vitamin K type possess a long isoprenoid side chain. Other naphthoquinones are devoid of a side chain, e.g., juglone (Fig. 144) or are substituted only by an isoprene residue, e.g., deoxylapachol. A typical representative of the anthraquinone derivatives is alizarin (Fig. 144). 

Naphthoquinones with a long isoprenoid side chain are formed in microorganisms (menaquinones, vitamins Kg) and in higher plants (phylloquinone, vitamin K ). Naphthoquinone derivatives with short or absent side chains as well as anthraquinones of the ahzarin type are produced by a few families of higher plants, e.g., Balsaminaceae, Juglandaceae, Rubiaceae. 

AU naturally occurring compounds that show vitamin K activity (the coagulation vitamin) are derivatives of menadione (2-methyl-1,4-naphthoquinone) with an isoprenoid unsaturated side chain at the C-3 position of the aromatic ring. Today, essentially two types of active substances are recognised. The other compounds with vitamin K activity are synthetic derivatives. 

Vitamin Kp also known as vitamin Kk20)> phylloquinone or phytylmenaquinone, contains a hexahydrotetraprenyl chain (2-methyl-3-phytyl-l,4-naphthoquinone, 5-44). Phylloquinone occurs in foods of plant origin. The side chain derived from phytol has 20 carbon atoms (four isoprenoid units, of which three are reduced). The isomer with a cis-configuration in the side chain is not biologically active. The systematic name of vitamin Kj is (2 ,7 R,ll R)-2-methyl-3-(3, 7Ml, 15 -tetramethyUiexadecyl)naphtho-l,4-quinone. The second compound with the activity of vitamin K is vitamin K2 (5-45), also known as vitamin K2( ), menaquinone, menaquinone-n, MK-n or 2-methyl-3-multiprenyl-l,4-naphthoquinone (n = 0-13). The most common menaquinones contain 4-10 isoprene units, such as MK-7, additionally called pharnoquinone. Vitamin K2 is produced by many bacteria and actinomycetes. A multiprenyl side chain... 

Phylloquinone (vitamin K), the antihemorrhagic vitamin, is composed of a naphthoquinone with an isoprenoid side chain. Besides phylloquinone (vitamin... 

Vitamin K (antihemorrhagic vitamin, phyUoquinone) is a naphthoquinone with an isoprenoid side chain. The side chain can be synthesized by the mammalian organism (Chapt. XIV-1, 9). For this reason, menadione (= 2-methyl-l,4-naphtho-quinone) has phyUoquinone activity. Biochemically, vitamin K seems to be involved as a redox catalyst in the respiratory chain (Chapt. X-4), but the question is not yet solved. 

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