Thioester Transamination

Conversion to the Aldehyde. This transformation is accomplished through a two-step procedure. One such variant requires reduction to the alcohol (e.g. LiAllTt, H2O) and subsequent oxidation (e.g. Swem conditions). Alternatively, Wein-reb transamination " followed by Diisobutylaluminum Hydride or conversion to the thioester (see below) and subsequent Triethylsilane reduction, afford the desired aldehyde in excellent yields. Weinreb transamination proceeds with minimal endocyclic cleavage when there is a p-hydroxy moiety free for internal direction of the aluminum species. 

Isoleucine and valine. The first four reactions in the degradation of isoleucine and valine are identical. Initially, both amino acids undergo transamination reactions to form a-keto-/T methyl valerate and a-ketoiso valerate, respectively. This is followed by the formation of CoA derivatives, and oxidative decarboxylation, oxidation, and dehydration reactions. The product of the isoleucine pathway is then hydrated, dehydrogenated, and cleaved to form acetyl-CoA and propionyl-CoA. In the valine degradative pathway the a-keto acid intermediate is converted into propionyl-CoA after a double bond is hydrated and CoA is removed by hydrolysis. After the formation of an aldehyde by the oxidation of the hydroxyl group, propionyl-CoA is produced as a new thioester is formed during an oxidative decarboxylation. 

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