Naphthoquinones and Anthraquinones Derived from Shikimic Acid

1 Naphthoquinones and Anthraquinones Derived from Shikimic Acid 

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. 

The naphthoquinone nucleus of the above-mentioned compounds originates from chorismic acid and y-hydroxybutyryl-2 -thiamine pyrophosphate ( activated succinylsemialdehyde ) derived from oc-ketoglutarate (C 4). An important intermediate is 2-succinylbenzoic acid. Naphthohydroquinone-2-carboxylic acid is the first naphthalene derivative formed. Juglone is synthesized via a symmetrical intermediate, in contrast to the vitamins K, e.g., phylloquinone, and to lawsone. The side chain of phylloquinone derives from phytol (D 6.3). 

3-Prenyl-naphthohydroquinone-2-carboxyhc acid is the key intermediate in the formation of anthraquinones of the alizarin type. (In contrast the A-ring-substituted anthraquinone derivatives found in fungi and certain higher plants, e.g., Rhamnaceae and Polygonaceae, are polyketides, D 3.3.5). In the biosynthesis of alizarin one C-atom of the isoprene residue is lost. In structurally related compounds, however, this C-atom may still be present in the form of a methyl, hydroxymethyl, aldehyde, or carboxy group. 

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D 8.1 Naphthoquinones and Anthraquinones Derived from Shikimic Acid... 

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