Dihydroxyacetone formation from glycerol

The Pt/C catalyst, compared with Pd/C, showed not only enhanced activity (vide supra) but also reduced selectivity for glyceric acid (only 55% at 90% conversion), favoring dihydroxyacetone formation up to 12%, compared with 8% for the Pd case [48]. The Pt/C catalyst promoted with Bi showed superior yields of dihydroxyacetone (up to 33%), at lower pHs. Glyceric and hydroxypyruvic acids, apparently, are formed as by-product and secondary product, respectively [48], The addition of Bi seems to switch the susceptibility of glycerol oxidation from the primary towards the secondary carbon atoms. 

Fig. 10.9 Formation of Phosphatidic Acid from Glycerol or Dihydroxyacetone Phosphate and its Conversion to Triacylglycerol or Phospholipids.

Ricinine.—Ricinine (49), the alkaloid of castor bean plants, is derived from nicotinic acid (28) and quinolinic acid (48), and its formation is intimately associated with the pyridine nucleotide cycle cf. ref. 6. Quinolinic acid is built from a C3 fragment that is formed from glycerol via glyceraldehyde and a C4 unit that is related to succinic or aspartic acids. A recent investigation has confirmed this pathway for ricinine (49) and indicated that dihydroxyacetone phosphate lies between glycerol and glyceraldehyde (loss of tritium from C-2 of labelled glycerol). ... 

In these anaerobic conditions, the citric acid cycle cannot be completed since the succinodehydro-genase activity requires the presence of FAD, a strictly respiratory coenzyme. The chain of reactions is therefore interrupted at succinate, which accumulates (0.5-1.5 g/1). The NADH generated by this portion of the Krebs cycle (from oxaloacetate to succinate) is reoxidized by the formation of glycerol from dihydroxyacetone. 

Synthesis of Fats from Fatty Acids. The above biossoithesis releases fatty acids in the form of the acyl-CoA derivatives. They are then stored as glycerol esters, i.e. as neutral fats. Esterification does not take place on the glycerol molecule itself, but rather on glycerol phosphate, which could have arisen, e.g., from reduction of dihydroxyacetone phosphate (cf. Chapt. XVIII-2). There is an enzyme which is responsible for the formation of diglyceride phosphate (also called phosphatidic acid) from glycerol phosphate and 2 moles of activated fatty acid. CoA—SH is released in the process. It is important for the organism to have the coenzyme A available for other reactions. 

Loss of two hydrogens by glycerol leads to the formation of glyceraldehyde or dihydroxyacetone, depending on whether the two hydrogens are lost from the end or middle position, respectively. 

Reduction of dihydroxyacetone phosphate yields sn-glycerol 3-phosphate, the starting compound for formation of the glycerol-containing lipids (Fig. 21-4 step Transfer of two acyl groups from ACP or... 

The major pathways for triacylglycerol synthesis are shown in Fig. 11.17. The formation of phos-phatidic acid by the glycerol phosphate pathway or the dihydroxyacetone phosphate pathway has already been discussed (Section 11.2.11). In addition, see reviews by Gurr (1980) and O Doherty (1978). Phosphatidic add can also be formed from... 

Speciation of A. aceti and A. pasteurianus requires the ability to detect oxidation of glycerol to dihydroxyacetone, a property called ketogenesis (see Procedure 2.3.4), as well as the formation of 5-ketogluconic acid from D-glucose. Table 2-4 summarizes expected results for the three important species. 

To provide better understanding of the reactions taking place when sugars are heated at 250°C in the presence or absence of H2SO4, the aqueous phase chemistry of glycerol, 2-propanol, 1,4-butanediol, tetrahydrofuran, glyceraldehyde, pyruvaldehyde, and dihydroxyacetone under these conditions has been examined. In a related study, focussed on the formation of 5-hydroxymethyl-2-furfuraldehyde from D-fructose or sucrose in aqueous... 

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