Erythrose isomerization

Pearson and Lin (52) developed an elegant approach to the synthesis of optically active ( )-swainsonine (247) from isopropylidene-D-erythrose (242) (Scheme 9.52). Wittig reaction of the acetonide 242 led to the (Z) alkene 252 in 86% yield. The chloro alcohol 252 was converted to the azide 253 in 76% yield, which subsequently underwent 1,3-dipolar cycloaddition, isomerization and hydroboration-oxidation to give the indolizidine 255 in 70% overall yield. Cleavage of the acetonide unit in 255 using 6 N HCl gave the target molecule 247 in 85% yield. 

The six-carbon chain of ManNAc 6-P can be extended by three carbon atoms using an aldol-type condensation with a three-carbon fragment from PEP (Eq. 20-7, step c) to give N-acetylneuraminic acid (sialic acid).48 Tire nine-carbon chain of this molecule can cyclize to form a pair of anomers with 6-membered rings as shown in Eq. 20-7. In a similar manner, arabi-nose 5-P is converted to the 8-carbon 3-deoxy-D-manno-octulosonic acid (KDO) (Fig. 4-15), a component of the lipopolysaccharide of gram-negative bacteria (Fig. 8-30), and D-Erythrose 4-P is converted to 3-deoxy-D-arafrmo-heptulosonate 7-P, the first metabolite in the shikimate pathway of aromatic synthesis (Fig. 25-1).48a The arabinose-P used for KDO synthesis is formed by isomerization of D-ribulose 5-P from the pentose phosphate pathway, and erythrose 4-P arises from the same pathway. 

The discovery of enzyme systems by which D-glucose could be isomerized directly to D-fructose was a key factor in the development of commercial-scale isomerization-processes. These direct systems were developed from fundamental studies of carbohydrate metabolism, in which was identified for the first time an enzyme that catalyzes the isomerization of an unsubstituted sugar, namely, the isomerization of D-erythrose to D-g/ycero-tetrulose.31... 

Synthesis from erythrose An efficient approach for the synthesis of (-l-)-trihy-droxyheliotridane (180) via a chiral erythrose derivative has been reported (Scheme 16). Wittig reaction of 2,3-(9-isopropylidene-L-erythrose (172) with Ph3P=CHCH=CHC02Et produced a 1 5 mixture of the ( , )-173 and (Z,A)-174 isomeric dienes, respectively. The diene 173 could be quantitatively obtained by isomerization of 174 with E. The diene 174 was converted to the azide 177, which upon boiling in benzene gave the vinyl aziridine 176. Pyrolysis of 176 furnished the pyrrolizidine 178. On the other hand, the diene 173 was... 

In a similar manner, the isomeric oxadiazine carbaldehydes (155 R = CHO) and (156 R = CHO), which are synthetic equivalents of 2,4-deoxy-2-amino-L-erythrose and 2,4-deoxy-2-amino-L-threose, respectively, have been prepared from the oxadiazine-5-carboxylates (155 R = C02Et) and (156 R = COjEt) <89TL5511>. 

Fructose 6-phosphate, Neuberg ester an intermediate in Glycolysis (see) produced by isomerization of glucose 6-phosphate. It is also formed from erythrose 4-phosphate by transketolation. 

Preparation (4, 4S). D-Ribose may be synthesized from D-arabinose by alkaline isomerization, by the glycal synthesis, or through the pyridine-catalyzed epimerization of D-arabonic acid followed by reduction. The sugar also has been prepared by the oxidative degradation of calcium D-altronate (44) and by the nitromethane synthesis from D-erythrose (4 ). 

Briefly, two of the five glyceraldehyde 3-phosphates are isomerized to glycerone phosphate, one of which reacts with a third glyceraldehyde 3-phosphate under the influence of fructose-bisphosphate aldolase (Section 11.2) to yield fructose 1,6-bis-phosphate which is dephosphorylated.to fructose 6-phosphate (Section 11.7). Transketolase catalyses a two-carbon unit transfer between fructose 6-phosphate and a fourth glyceraldehyde 3-phosphate to yield erythrose 4-phosphate and xylulose 5-phosphate. An aldol condensation of erythrose 4-phosphate with the second glycerone phosphate, catalyst by fructose-bisphosphate aldolase, produces sedoheptulose 1,7-bisphosphate which on dephosphorylation yields sedoheptulose 7-phos-phate. A second transketolase reaction utilizes sedoheptulose 7-phosphate and a flfth glyceraldehyde 3-phosphate to produce xylulose 5-phosphate and ribose 5-phosphate. The epimerization of both xylulose 5-phosphates and the isomerization of ribose 5-phosphate (Section 11.9) produces ribulose 5-phosphates which are phosphorylated to regenerate three ribulose 1,5-bisphosphate molecules. 

---