Biological reaction, alcohol aldehyde reduction

The aldehyde intermediate can be isolated if 1 equivalent of diisobutvl-aluminum hydride (D1BAH) is used as the reducing agent instead of LiAlH4. The reaction has to be carried out at -78 °C to avoid further reduction to the alcohol. Such partial reductions of carboxylic acid derivatives to aldehydes also occur in numerous biological pathways, although the substrate is either a thioester or acyl phosphate rather than an ester. 

NADH (reduced nicotinamide adenine dinucleotide) is utilized in biological reductions to deliver hydride to an aldehyde or ketone carbonyl group (see Box 7.6). A proton from water is used to complete the process, and the product is thus an alcohol. The reaction is catalysed by an enzyme called a dehydrogenase. The reverse reaction may also be catalysed by the enzyme, namely the oxidation of an alcohol to an aldehyde or ketone. It is this reverse reaction that provides the dehydrogenase nomenclature. 

Figure 3-23. Representation of the hydride transfer reaction involved in the biological reduction of aldehydes to alcohols.

In these compounds, there is a marked relationship between molecular geometry and biological activity. From values reported in the literature and according to our own studies, the E isomers, in which the residue originating from the aldehyde is in the transposition to the triazole, are markedly superior to the Z isomers in their biological activity. By suitable control of the reaction conditions, it is possible to achieve an almost complete isomerization to the unsaturated E-triazolylketones. Subsequent reduction leads to the more active E-alcohols. This group of N-vinylazoles includes the triazole derivative S 3308 (Sumitomo), currently under development as... 

Finally the benzyl group was removed, the primary alcohol oxidised to the aldehyde, and an ii-selective Wittig reaction performed with the enantiomerically pure stabilised ylid 137. No racemisation of either partner occurred and the product was almost pure E at the new alkene. Stereoselective reduction gave (+)-pumiliotoxin B 129 identical to the natural product in all respects, including biological effects. 

In general it is aldehydes of aromatic hydrocarbons and of heterocycles that can be subjected to this reaction, named after its discoverer the Cannizzaro reaction but there a similar oxidation-reduction, brought about by an enzyme, plays an important part in biological events in the cell. In the laboratory the Cannizzaro reaction serves for preparation of both acids and alcohols, each normally in 50% yield. As example, the preparation of 2-furoic acid and fur-furyl alcohol from 2-furaldehyde is here recorded.499... 

Aldehydes and ketones are among the most important of all compounds, both in the chemical industry and in biological pathway. In this chapter, we ve looked at some of their typical reactions. Aldehydes are normally prepared in the laboratory by oxidation of primary alcohols or by partial reduction of esters. Ketones are prepared by oxidation of secondary alcohols. 

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