Dihydroxyacetone conditions

This reaction is followed by another phosphorylation with ATP catalyzed by the enzyme phosphofructoki-nase (phosphofructokinase-1), forming fructose 1,6-bisphosphate. The phosphofructokinase reaction may be considered to be functionally irreversible under physiologic conditions it is both inducible and subject to allosteric regulation and has a major role in regulating the rate of glycolysis. Fructose 1,6-bisphosphate is cleaved by aldolase (fructose 1,6-bisphosphate aldolase) into two triose phosphates, glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are inter-converted by the enzyme phosphotriose isomerase. 

Dihydroxyacetone is not stable under the basic conditions preferred for oxidation of the primary function to give hydroxypyruvic acid (reaction e). Under acidic conditions the rate of oxidation of a 1 mol I l aqueous solution is veiy slow (5 mol h l mol i(Pt)). On platinum the initial rate of conversion for reduced concentrations of the starting material (0.3 mol whilst retaining the same amount of catalyst, was 42 mol h mol-i(Pt), as might be expected under non-favourable acidic conditions. Hydroxypyruvic acid is evolved with a selectivity of 82% at 40% conversion (see Figure 11). 

A tandem enzymatic aldol-intramolecular Homer-Wadsworth-Emmons reaction has been used in the synthesis of a cyclitol.310 The key steps are illustrated in Scheme 8.33. The phosphonate aldehyde was condensed with dihydroxyacetone phosphate (DHAP) in water with FDP aldolase to give the aldol adduct, which cyclizes with an intramolecular Horner-Wadsworth-Emmons reaction to give the cyclo-pentene product. The one-pot reaction takes place in aqueous solution at slightly acidic (pH 6.1-6.8) conditions. The aqueous Wittig-type reaction has also been investigated in DNA-templated synthesis.311... 

Hypothesis (A) is in contradiction with the experimental evidence, since glycolaldehyde andl, 3-dihydroxy-2-propanone (dihydroxyacetone)9 16 react in the same way as do the sugars. It is evident that these compounds do not possess two contiguous hydroxyl groups. Moreover, when methyl trans-0-(/3-D-glucopyranosyl)acetoacetate enol (LXIV) was treated with zinc chloride under the conditions used by West and by Garda Gonzalez, a... 

Enzymes are very sophisticated systems that apply sound chemical principles. The side-chains of various amino acids are used to supply the necessary bases and acids to help catalyse the reaction (see Section 13.4). Thus, the enzyme aldolase binds the dihydroxyacetone phosphate substrate by reacting the ketone group with an amine, part of a lysine amino acid residue. This forms an imine that becomes protonated under normal physiological conditions. 

Glyceraldehyde phosphate and dihydroxyacetone phosphate react in the presence of aldolase to yield fructose diphosphate as the only product under physiolocial conditions. 

Different enzymes often operate under similar conditions, enabling two or more enzymes to be combined in one pot. In the example shown in Figure 5.28, dihydroxyacetone is phosphorylated and then coupled to an aldehyde, resulting in a C—C coupled product with two new stereocenters. Wever and co-workers carried out this reaction by combining two isolated enzymes an acid phosphatase and a... 

A mixture of ketohexoses, from which D-sorbose and D-fructose were isolated in crystalline condition,29 was also obtained by barium hydroxide treatment of D-glyceraldehyde alone, or with dihydroxyacetone. 

Glycerol (propan-1,2,3-triol) is a readily available raw material from biosus-tainable sources such as rape-seed and sunflower the many products that can be formed from it by oxidation find economic use as intermediates in the fine chemicals industry. However, its oxidation constitutes a complicated scenario by reason of the parallel and sequential reaction paths that can be followed (Scheme 8.3) obtaining a desired product therefore constitutes a considerable challenge. The mono-aldehyde readily isomerises under basic conditions to dihydroxyacetone, but fortunately it is less easily oxidised, so that glyceric acid (HOCH2-CH(OH)-CC>2H) is frequently a major product. Gold catalysts, as in other reactions, do not suffer from deactivation, nor do... 

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