Dihydroxynaphthoic acid

An example of a biological Friedel-Crafts reaction occurs during the biosynthesis of phylloquinone, or vitamin Kl( the human blood-clotting factor. Phylloquinone is formed by reaction of 1,4-dihydroxynaphthoic acid with phytyl diphosphate. Phytyl diphosphate first dissociates to a resonance-stabilized allylic carbocation, which then substitutes onto the aromatic ring in the typical way. Several further transformations lead to phylloquinone (Figure 16.10). 

Figure 16.10 Biosynthesis of phylloquinone (vitamin K-j) from 1,4-dihydroxynaphthoic acid. The key step that joins the 20-carbon phytyl side chain to the aromatic ring is a Friedel-Crafts-like electrophilic substitution reaction.

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... 

Chung etal. [121] studied both the isothermal and non-isothermal crystallization phenomena in the random copoly(ester amide) Vectra B-950 from Hoechst-Celanese, which is composed of 2,6-dihydroxynaphthoic acid (HNA), p-amino phenol (AP), and terephthaUc acid (TA) with the molar ratio of 60 0/20. The molar mass of the average repeating units is 149.8 g/mole. 

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-... 

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