Isoprenyl-1,4-naphthoquinone

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. 

OSB, and 1,4-dihydroxynaphthoic acid, or its diketo tautomer, have been implicated in the biosynthesis of a wide range of plant naphthoquinones and anthraquinones. There are parallels with the later stages of the menaquinone sequence shown in Figure 4.55, or differences according to the plant species concerned. Some of these pathways are illustrated in Figure 4.58. Replacement of the carboxyl function by an isoprenyl substituent is found to proceed via a disubstituted intermediate in Catalpa (Bignoniaceae) and... 

As shown in Figure 5.1, compounds with vitaminK activity have a 2-methyl-1,4-naphthoquinone ring. There are two naturally occurring vitamers phylloqui-none (from plants) has a phytyl side chain, whereas the menaquinones (from bacteria) have a polyisoprenyl side chain, with up to 15 isoprenyl units (most commonly 6 to 10), shown by menaquinone- n. Bacteria also form a variety of... 

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. 

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,... 

A rather unique branch of the shikimate pathway operates in the biosynthesis of naphthoquinones related to vitamin K (menaquinone) (Fig. 30). Seven of the ten carbon atoms of the naphthoquinone ring system are derived from the seven carbon atoms of shikimic acid. The remaining three carbons are provided by the three center carbon atoms of a-ketoglutaric acid in a reaction leading to the unique intermediate o-succinylbenzoic acid. Cyclization of the latter produces the intermediate 1,4-dihydroxynaphthoic acid, the substrate for an isoprenylation reaction which occurs with simultaneous loss of COa Methylation of the 3 position then completes the reaction sequence. Studies by Meganathan and Bentley had indicated that chorismic acid is the substrate for the thiamine pyrophosphate-... 

The K homologues [1] are a family of 2-methyl-l,4-naphthoquinones possessing cofactor activity for y-glutamylcarboxylase and differ in the side chain attached at C3. Phylloquinone (vitamin Ki) has a phytyl side chain and occurs in green plants. Vitamin K2 includes a group of compounds s)mthesized by bacteria and characterized by a polyisoprene side chain each of them is designated menaquinone-n (MK-n, with n from 4 to 13) according to the number of isoprenyl units. Menadione (vitamin K3), menadiol (vitamin K4), and vitamin Ki(2s) are synthetic forms [1,4]. 

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