Heptuloses

Phenylalanine- and Tyrosine-Derived Alkaloids. Carbohydrate metaboHsm leads via a seven-carbon sugar, ie, a heptulose, derivative to shikimic acid [138-59-0] (57), C H qO, which leads in turn to prephenic acid [126-49-8] (58), (43). 

Since the equilibrium reaction mixture contains at least four products, workup can be difficult and therefore, it may be helpful to bring the reaction to completion. For example, in the transketolase-catalyzed reaction of [l-13C]D-ribosc 5-phosphate and [l-l3C]D-i/ /w-2-pen-tulose 5-phosphatc to [l,3-13C]n-a/b,o-2-heptulose 7-phosphate and D-glyceraldehyde 3-phos-... 

Fig. 4.—Difference-Circular Dichroism Spectra or-D-manno-Heptulose minus...

The taste properties of various other ketoses, including 2-pentuloses, 2-hexuloses, and 2-octuloses, have also been studied (see Table XV) to determine the significance of the 2-hydroxyl-2-hydroxymethyl arrangement of 2-ketopyranoses. Some of these, for example, a-D-tagatose (25), -d-g/uco-2-heptulose (26), a-D-mnMno-2-heptulose (27), a-D-fa/o-2-heptulose (28), a-D-a/tro-2-heptulose (29), and D-g/ycero-a-D-g/ co-2-octulose (30),... 

Figure 1. Schematic outline of various products and associated enzymes from the shikimate and phenolic pathways in plants (and some microorganisms). Enzymes (1) 3-deoxy-2-oxo-D-arabino-heptulosate-7-phosphate synthase (2) 5-dehydroquinate synthase (3) shikimate dehydrogenase (4) shikimate kinase (5) 5-enol-pyruvylshikimate-3-phosphate synthase (6) chorismate synthase (7) chorismate mutase (8) prephenate dehydrogenase (9) tyrosine aminotransferase (10) prephenate dehydratase (11) phenylalanine aminotransferase (12) anthranilate synthase (13) tryptophan synthase (14) phenylalanine ammonia-lyase (15) tyrosine ammonia-lyase and (16) polyphenol oxidase. (From ACS Symposium Series No. 181, 1982) (62).

LaForge and Hudson194 prepared an osone from the phenylosazone obtained from sedoheptulose (D-aZ(ro-heptulose). The osone reduced Fehling solution strongly, formed the original osazone with phenylhydrazine, and gave a crystalline derivative with o-phenylenediamine. 

D-afe-o-Heptulose (sedoheptulose) (XXXVII) has been synthesized from D-erythrose (XXXVIII) plus triose phosphate, using an aldolase preparation from peas.169 Aldolases from yeast and from rat liver also form heptu-lose phosphate from these substrates.7S(o) 170(a) Crystalline muscle aldolase causes the formation of L-jrZwco-heptulose (XXXVIIa) from a mixture of L-erythrose (XXXVTIIa) and hexose diphosphate.170(b)... 

The enzyme also catalyzes the reversible reaction of dihydroxyacetone phosphate with D-erythrose 4-phosphate to produce D-oZ[Pg.218]

I, 7-diphosphate.170 1 (f> This tetrose phosphate is involved with phosphoenol pyruvate in the formation of shikimic acid via 3-deoxy-2-keto-D-ara6ino-heptonic acid 7-phosphate and, hence, of aromatic compounds.170(d) A synthesis of the tetrose phosphate has been described.170 1 Aldolase shows a high affinity for the heptulose diphosphate and, compared with that for D-fructose 1,6-diphosphate, the rate of reaction is about 60 %. The enzyme transaldolase, purified 400-fold from yeast, catalyzes the following reversible reaction by transfer of the dihydroxyacetonyl group.l70(o>... 

D-alJro-Heptulose 7-phosphate + D-glycerose 3-phosphate D-fructose 6-phosphate + D-erythrose 4-phosphate... 

D-aZbacterial polysaccharides.174- 176(al Plants show heptulokinase activity176 1 the purification of D-aZfro-heptulose phosphate from Sedum spectabile has been described.176 1 The occurrence of D-wumno-heptulose phosphate in... 

D-erythro-Pentulose 5-phosphate (XLIV) has been formed by the action of transketolase on hydroxypyruvate (XLII) and D-glycerose 3-phosphate, the hydroxypyruvate being decarboxylated196 to active glycolaldehyde which then reacts with the triose phosphate by an acyloin reaction.28 The active glycolaldehyde is also formed from L-glycero-tetrulose, d-altro-heptulose 7-phosphate, D-fructose 6-phosphate, and D-i/ireo-pentulose 5-phosphate and it reacts with various aldehydes (acceptors) to give ketoses.198, 200 Thus, substitution of L-gfh/cero-tetrulose for hydroxypyruvate in the above experiment also resulted in formation of D-en/i/iro-pentulose... 

The above transketolase and transaldolase reactions were found inadequate to explain the metabolism of D-ribose 5-phosphate, because of the non-accumulation of tetrose phosphate, the 75 % yield of hexose phosphate, and the results of experiments with C14 (the distribution of which differed markedly from the values predicted for such a sequence). 24(b) Thus, with D-ribose-l-C14, using rat-liver enzymes, any hexose formed should have equal radioactivity at Cl and C3, whereas, actually, 74% appeared at Cl. Furthermore, D-ribose-2,3-Cl42 should have given material having equal labels at C2 and C4 in the resultant hexose, whereas, in fact, it had 50% of the activity at C4, C3 was nearly as active as C2, and Cl had little activity. Similar results were obtained with pea-leaf and -root preparations.24 The following reactions, for which there is enzymic evidence,170(b) were proposed, in addition to those involving D-aftro-heptulose, to account for these results.24(b) (o) 200... 

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