Esters oxidations

Two and twelve moles of ATP are produced, respectively, per mole of glucose consumed in the glycolytic pathway and each turn of the Krebs (citrate) cycle. In fat metaboHsm, many high energy bonds are produced per mole of fatty ester oxidized. Eor example, 129 high energy phosphate bonds are produced per mole of palmitate. Oxidative phosphorylation has a remarkable 75% efficiency. Three moles of ATP are utilized per transfer of two electrons, compared to the theoretical four. The process occurs via a series of reactions involving flavoproteins, quinones such as coenzyme Q, and cytochromes. 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

Example Ester (59) was needed for a photochemical synthesis of chrysanthemate ester (60), a component of the pyrethrin insecticides. The a,B disconnection (59a) gives synthon (61) and aldehyde (62). This 8,y-unsaturated compound could be made by dehydration of (63) as the double bond can appear in only the required position. On page T 149 we discussed the synthesis of (62) by the aldol dimerisation of (64), An alternative strategy is to work at the ester oxidation level (65) which means synthon (66) is needed to combine with (64). 

The initial condensation is best carried out at tr.-, ester oxidation level to take advantage of the Reformatsky method of control. Oxalic acid hydrolyst-s (36) to (31) without moving the double bond into conjugation. ... 

Although substituted phenols (e.g., para-iodophenol, para-phenylphenol, firefly luciferin, coumaric acid) are popular enhancers, in both luminol and acridan ester oxidation, enhancers with other functional groups [24], e.g., phe-nylboronic acids [25-28], phenothiazines [29], are also useful. As an example the structure of the phenothiazine enhancer used in the Supersignal substrate family is shown in Figure 6. 

In accordance with this scheme, the rate of ester oxidation was found to obey the equation ... 

As in the case of the oxidation of saturated esters, the rate of chain copolymerization monomer and dioxygen obeys the equation similar to that for aliphatic ester oxidation. 

The accumulation of hydroperoxide accelerates the ester oxidation. As in hydrocarbon oxidation, this acceleration is the result of hydroperoxide decomposition into free radicals. The most probable is the bimolecular reaction of hydroperoxide with the weakest C—H bond of saturated ester (see Chapter 4). 

Chain propagation proceeds in ester oxidation via the reaction of the ester peroxyl radical with weakest C—H bond of the ester. Is the activity of the ester peroxyl radical same as alkyl peroxyl radical Let us compare the rate constants of two different peroxyl radicals reactions with the same ester group, namely, RCH2C(0)0CH2R. 

The advent of sulfamate ester oxidative cyclization makes available a myriad of oxathia-zinane derivatives from simple alcohol precursors. These unusual heterocycles have enjoyed only sparing use despite their potential as electrophiHc azetidine equivalents. By contrast, five-membered ring sutfamidates and cycHc sulfates are broadly recog-... 

Scheme 17.43 Bromopyrrole alkaloid assembly, highlighting sulfamate ester oxidation.

Carbenes, dioxirane preparation, 1132 Carbocations, antimalarial endoperoxides, 1309 Carbohydrate hydroperoxides, Mo-catalyzed olefin epoxidation, 432, 436 Carbohydrates, TBARS assay, 669 Carbonate esters, oxidative ozonolysis, 737, 738... 

Retinyl esters and the P-carotene are incorporated into chylomicrons and taken up mainly by hepatocytes. In the liver retinol may be stored in stellate cells as retinyl esters, oxidized to retinoic acid or liberated into cells bound to retinol-binding proteins (RBP). All E retinoic acid and its 9Z isomer have an affinity for nuclear receptors. They activate the transcription and bind as dimers to specific nucleotide sequences, present in promoters of target genes. 

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