Dehydroquinate pathway structures

The w-CyN unit described was shown to be incorporated in the biosynthesis of both the ansamycins and also other related antibiotics, such as pactamycin and other compounds [188-190]. With respect to other naturally occurring compounds which contain a partial structure derived from the m-CyN unit in the molecule, asukamycin [191] is a possible shunt metabolite from 3-dehydroquinic acid in the shikimate pathway. Incorporation of [l - 3C]-AHBA (118) into the C-6 methyl group of porfiromycin (120) (a mitomycin group antibiotic) was reported (Fig. 6) [192], and the participation of a m-CyN unit in this biosynthetic pathway and the antibiotics containing a m-CyN unit were reviewed [178,188,190]. 

The structure of 3-dehydroquinic acid as a cyclic aldol made it appear probable that its six-membered ring is formed from an acyclic precursor through an intramolecular aldoli-zation it would then be the first compound in the pathway in which the ring of phenylalanine, tyrosine, tryptophan, etc., is already present, although not yet aromatic. Not long afterwards, this interpretation was shown to be correct when Sprinson and his coworkers at Columbia University isolated DAHP, the acyclic earliest intermediate, and studied its cyclization to 3-dehydroquinic acid. 

Simple benzoic acids are synthesized in plants via the shikimate pathway, which is derived from shikimic acid, which is itself derived from quinic acid via 3-dehydroquinic and 3-dehydroshikimic acids (Scheme 68.1). In fact, shikimic, but not quinic, acid has been described in the leaves and stems of this species [14]. The simplest benzoic acids are protocatechuic acid (3,4-dihydroxybenzoic acid) and gallic acid (3,4,5-trihydroxybenzoic acid). The latter proved to be present in the tissues of C. roseus, in addition to vanillic acid (4-hydroxy-3-methoxybenzoic acid) [15]. The quantitative composition of C. roseus in benzoic acids can be seen in Table 68.1, and the structures of these compounds are represented in Fig. 68.1. 

---