Biochemical reductions keto esters

Metal amalgams may be used for reduction of the keto groups in keto esters provided the medium does not cause hydrolysis of the ester. Because of that aluminum amalgam in ether is preferable to sodium amalgam in aqueous solutions. Diethyl oxalacetate was reduced to diethyl malate by sodium amalgam in 50% yield and with aluminum amalgam in 80% yield [148], Stereospecific reduction of a- and fi-keto esters to optically pure hydroxy esters was achieved by biochemical reduction in moderate to good yields. Saccharomyces cerevisiae converted methyl 2-keto-2-phenylacetate to methyl... 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

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