2 - The Chemistry of Intermediates in the Shikimate Pathway

Abstract

Prior to the discovery of the shikimate pathway, the natural product chemists had assiduously pursued the chemistry of (—)-shikimic acid and (—)-quinic acid for over half a century. These substances were regarded as of considerable intrinsic interest from the chemical point of view; however, as with many other natural products, it was not apparent until much later that they served exceedingly important functions in living systems. This chapter describes the chemical details for the principal intermediates and related compounds in the pathway. 3-dehydroshikimic acid was first isolated by Salamon and Davis from cultures of Escherichia coli 83-2 by chromatography on charcoal. Improved preparative procedures have since been described by several groups and in all of these the product is separated, prior to crystallization, by ion-exchange chromatography. 3-dehydroshikimic acid readily undergoes conversion to protocatechuic acid by treatment with acid or upon heating. This latter property gives rise to a characteristic double melting point 151–152° followed by 198–200°.