Glycoaldehyde intermediate

The formose reaction leads to the production of many sugars with the exception of ribose, which occurs in very low concentrations and it is hard to see how this could be increased. A variation on the formose reaction starting at the phospho-rylated glycoaldehyde intermediate, with the addition of base or in the presence of mineral substrate, produced a surprisingly large amount of ribose but this still... 

Figure 20.21. Transketolase Mechanism. The carbanion of thiamine pyrophosphate (TPP) attacks the ketose substrate. Cleavage of a carbon-carbon bond frees the aldose product and leaves a two-carbon fragment joined to TPP. This activated glycoaldehyde intermediate attacks the aldose substrate to form a new carbon-carbon bond. The ketose product is released, freeing the TPP for the next reaction cycle.

This activated glycoaldehyde intermediate attacks the aldose substrate to form a new carbon-carbon bond. The ketose product is released, freeing the TPP for the next reaction cycle. 

Important intermediates in this process are glycoaldehyde, glycolate, and glyoxalate ... 

Now it is possible to consider the mechanism of the molecular elimination process (eq. 23) in light of a new isomeric intermediate, hydroxymethylene (hCoH). In the low-temperature matrix photolysis of formaldehyde at 15 K, three sets of photochemical products were found (1) methanol and CO in solid formaldehyde (2) glycoaldehyde in a dilute Ar matrix and (3) hydroxyketene in a CO matrix (227). These observations were... 

The compound (54) has been enzymatically converted into a phosphorylated derivative of (E)-2-methylbut-2-ene-l,4-diol, which most probably represents a novel intermediate in the methylerythritol phosphate pathway of isoprenoid biosynthesis. The use of a photolabile acetal protecting group enables the synthesis of glycoaldehyde di-, and triphosphates (55) and (56) respectively. 

Thiamine pyrophosphate is also an important cofactor for the transketolase reactions in the pentose phosphate pathway of carbohydrate metabolism (Fignre 15-3). These reactions are important in the reversible transformation of pentoses into the glycolytic intermediates fructose 6-phosphate and glyc-eraldehyde 3-phosphate. Again, it is the reactive carbon on the thiazole ring of TPP that reacts with a ketose phosphate (xylnlose 5-phosphate) to canse the release of an aldose phosphate with two fewer carbons (glyceraldehyde 3-phosphate). The TPP-bonnd glycoaldehyde unit is then transferred to a different aldose phosphate (ribose 5-phosphate or erythrose 4-phosphate) to produce a ketose phosphate that has two carbons more (sedoheptulose 7-phosphate or fructose 6-phosphate). 

A review in Russian on the synthesis of carbohydrates from formaldehyde has appeared. An investigation of the formose reaction by g.c.-n.m.r. has shown that intermediate glycoaldehyde, glyceraldehyde, and dihydroxyacetone are present as mixtures of monomers, e.g. hydroxy carbonyl compounds, epoxides and hydrates, and dimers such as half and full acetals. Further study of the barium chloride-catalysed formose reaction at pH 12 has shown that the main product forming 33% of the total sugars is the branched pentulose (1). The sugar yield reached a constant value at 70% completion of the reaction, i.e., within... 

We have traced the metabolic pathways channelling metabolites towards the fluorometabolites in S. cattleya and an overview of these relationships is shown in Figure 13. We believe that the substrate for the fluorination process is either a C3 phosphorylated glycolytic intermediate such as dihydroxyacetone phosphate or glyceraldehyde-3-phosphate, or alternatively a C2 metabolite such glycoaldehyde phosphate, derived from these compounds. Fluoroacetaldehyde appears to be a strong candidate for the role of common intermediate to both fluoroacetate and 4-fluorothreonine. 

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