3-dehydroquinic acid

The initial step in the pathway is the condensation of erythrose-4-phosphale with phosphoenolpyruvate, yielding dehydroquinic acid, which by elimination of the elements of water affords dehydroshikimic acid reduction of the 3-keto group to hydroxyl gives shikimic acid. 

Some biochemical processes involve alcohol dehydration as a key step. An exanple is the conversion of a compound called 3-dehydroquinic acid to 3-dehydroshikimic acid. 

Dehydroquinic acid and [l,6-14C]-D-shikimic acid methyl ester were not incorporated, indicating a very early branch from the shikimate pathway. The intermediacy of 4-amino-3,4-dideoxy-D-araf>ino-heptulosonic acid 7-phosphate (37) was proposed, consistent with later findings on the role of the variant aminoshikimate pathway [94]. 

The shikimate pathway begins with a coupling of phosphoenolpyruvate (PEP) and D-erythrose 4-phosphate to give the seven-carbon 3-deoxy-D-arabino-heptulo-sonic acid 7-phosphate (DAHP) through an aldol-type condensation. Elimination of phosphoric acid from DAHP, followed by an intramolecular aldol reaction, generates the first carbocyclic intermediate, 3-dehydroquinic acid. Shikimic acid (394) is... 

TDP-streptose Biosynthesis and 5-Dehydroquinic Acid Synthetase The question mark in the above title should indicate that the next two examples are only a tempting, though hopefully constructive, speculation to demonstrate that TDP-streptose biosynthesis as well as 5-dehydro-quinic synthetase are possible candidates for this group of enzymes with identical initiation of enzyme catalysis by hydrogen transfer to form enzyme-NADH. 

Dehydroquinic acid synthetase ° Predicted, but not experimentally verified. 5 5 47... 

Fourthly, biotransformations have been used for the synthesis of 3-deoxy-2-glyculosonic acids, using whole cells or purified enzymes. For instance, 3-deoxy-D-araZu rao-heptulosonic acid (DAH) and its 7-phosphate (DAHP, 122) have been produced directly from D-glucose by mutants of E. coli JB-5, that lack dehydroquinate synthase, the enzyme that converts DAHP into the cyclic intermediate dehydroquinic acid (DHQ, Scheme 14). Both DAH and DAHP are secreted into the medium. The dephosphorylated product could be generated in vivo by a phosphatase acting on DAHP.312... 

Neither shikimic acid66 nor its methyl ester, nor dehydroquinic acid,65 were precursors of mitomycin, so it is likely that deviation to mitomycin biosynthesis occurs from DAHP (150) via, it has been suggested,65 (151), as shown in Scheme 12. 

FIGURE 3.2 The common aromatic pathway to chorismate in Escherichia coli K12, where 5 is phosphoe-nolpyruvate, 6 is erythrose 4-phosphate, 7 is 3-deoxy-D-arabinoheptulose 7-phosphate, 8 is 3-dehydroquinic acid, 9 is 3-dehydroshikimic acid, 10 is shikimic acid, 11 is shikimic acid 3-phosphate, and 12 is 5-enolpyru-vylshikimic acid 3-phosphate. 

Fig. 4-2. Simplified reaction route illustrating the formation of lignin precursors. 1, 5-Dehydroquinic acid 2, shikimic acid 3, phenylpyruvic acid 4, phenylalanine 5, cinnamic acid 6, ferulic acid (Ri=H and R2=OCH3), sinapic acid (R,= R2=OCH3), and p-coumaric acid (R1=R2 = H) 7, coniferyl alcohol (Ri = H and R2=OCH3), sinapyl alcohol (Rj = R2=OCH3), and p-coumaryl alcohol (R =R2=H) 8, the corresponding glucosides of 7.

This product is dehydroquinic acid and is an intermediate on the way to shikimic acid. It is also in equilibrium with quinic acid, which is not an intermediate on the pathway but which appears in some natural products like the coffee ester caffeyl quinic acid. 

V. Formation of 5-Dehydroquinic Acid from 3-Deoxy-D-oro6fno-heptulosonic... 

The synthetic 3-deoxy-D-arabmo-heptulosonic acid 7-phosphate was converted quantitatively to 5-dehydroquinic acid by bacterial extracts, as will be discussed below. It was also used as an aid in identifying the structure of the product formed from enolpyruvate phosphate plus D-erythrose... 

Fio. 7.—Tentative Mechanism for the Enzymic Conversion of 3-Deoxy-n-aro5mo-heptulosonic Acid 7-Phoaphate to 6-Dehydroquinic Acid. (DPN denotes diphosphopyridine nucleotide and DPNH is reduced diphosphopyridine nucleotide.)... 

The route to shikimic acid In plants Involves, as the final steps, the dehydration of dehydroquinic acid and then reduction of the carbonyl group. Doing the reactions this way round means that the dehydration can be ElcB—much preferred under biological conditions. This Is what happens. 

Davis concluded that shikimic acid was a common precursor of phenylalanine, tyrosine, tryptophan, p-aminobenzoic acid, p-hydroxybenzoic acid, and an unknown sixth factor, and he next set out to determine other substances lying on the biosynthetic pathway. The various mutants were therefore tested for syntrophism, i.e., for the ability of one mutant to produce a substance necessary for the growth of another mutant. There was thus found a thermolabile substance, X, which was a true precursor of shikimic acid (184). X was isolated from culture filtrates and identified as 5-dehydroshikimic acid (744). Similar experiments revealed a substance, W, which was a true precursor of substance X (187, 193). This also was isolated and shown to be 5-dehydroquinic acid (906). The enzyme, named 5-dehydroquinase, converting dehydroquinic acid to dehydroshikimic acid has been partially purified (606). It is fairly stable, has a high specificity, appears to have no cofactors, and is of wide occurrence in bacteria, algae, yeasts, and plants but, as expected, could not be found in mammalian liver. 

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