Biosynthesis of vitamin K and other natural naphthoquinones
Compounds with vitamin K activity, menaquinone and phylloquinone, are biosynthesized from shikimic acid (or a close relative) and either 2-ketoglutaric acid or glutamic acid. The mechanism of the condensation and the nature of possible intermediates are discussed. Flaviolin (produced by Aspergillus niger) and 2,7-dimethoxynaphthazarin (produced by Streptomycete 12396) are shown to be typical acetate polymalonate compounds. Other routes to naturally occurring naphthoquinones are briefly reviewed.