Thiols aldehyde oxidation

Fig. 13. Aldehyde dehydrogenases utilize thiol-mediated reactions in either of two ways. The top pathway demonstrates the capture of the energy of aldehyde oxidation through formation of a car-boxylate-phosphoric acid anhydride, which can subsequently generate ATP. The bottom pathway shows the hydrolysis of the active site thioester to the thermodynamically favored carboxylate.

The catalysis of the oxidation of aldehydes to carboxylates by alcohol dehydrogenases raises questions regarding the function of the active site thiols found in most aldehyde dehydrogenases. Clearly a free thiol is not mechanistically essential for aldehyde oxidation. For example, pig heart lactate dehydrogenase catalyzes the facile oxidation of glyoxalate to oxalate (71), glucose-6-... 

Thiols are oxidized by NH2CI to disulfides (Ingols et al., 1953). Monochloramine reacts with aldehydes (although in many cases the reaction is slow Hauser and Hauser, 1930 Conyers and Scully, 1993) to form N-chloroimines (R-CH = NC1) which then undergo further reactions (elimination of HCl to the nitrile hydrolysis to aldehydes polymerization etc.)... 

Alcohols are oxidized to aldehydes and ketones, whereas thiols are oxidized to disulfides. 

Write balanced chemical equations for the combustion, dehydration, and oxidation of alcohols. Write balanced chemical equations for the oxidation and reduction of thiols, aldehydes, and ketones. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

Barrett and coworkers have explored hetero-substituted nitroalkenes in organic synthesis. The Michael addition of nucleophiles to 1-alkoxynitroalkenes or 1-phenylthionitroalkenes followed by oxidative Nef reaction (Section 6.1) using ozone gives a-substituted esters or thiol esters, respectively.41 As an alternative to nucleophilic addition to l-(phenylthio)-nitroalkenes, Jackson and coworkers have used the reaction of nucleophiles with the corresponding epoxides (Scheme 4.4).42 Because the requisite nitroalkenes are readily prepared by the Henry reaction (Chapter 3) of aldehydes with phenylthionitromethane, this process provides a convenient tool for the conversion of aldehydes into ot-substituted esters or thiol esters. 

From the oxidative synthesis of thioesters from aldehyde and thiol ... 

Williams and Rastetter also accomplished an elegant synthesis of ( )-hyalodendrin (83) in 1980 [39]. Beginning with the sarcosine anhydride-derived enolic aldehyde 78, silyl protection of the enal enabled alkylation of the glycine center with benzyl bromide and thiolation using LDA and monoclinic sulfur a la Schmidt. After protection of the thiol with methylsulfenyl chloride and deprotection of the silyl ether, the enol was sulfenylated with triphenylmethyl chlorodisulfide to afford bis(disulfide) 82 as a 2 1 mixture of diastereomers favoring the anti isomer. Reduction of the disulfides with sodium borohydride and oxidation with KI3 in pyridine afforded ( )-hyalodendrin (83) in 29 % yield (Scheme 9.4). 

Figure 10.3 Antibody molecules oxidized with sodium periodate to create aldehyde groups on their polysaccharide chains can be modified with PDPH to produce thiols after reduction of the pyridyl disulfide. Direct labeling of the sulfhydryls with "Tc produces a radioactive complex.

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