Atazanavir Enzymatic Synthesis of S -Tertiary Leucine

The desired (S)-neopentylglycine was obtained with 95% conversion and 99% ee at substrate concentrations of up to 88g/l. Spiroheterocyclic compounds (morpho-line-4-carboxylic acid amides and neopentylglycine derivatives and their analogs) are reversible inhibitors of cysteine proteases such as cathepsin S and, therefore, useful in treating a variety of autoimmime diseases [43]. 

Leucine dehydrogenase and an FDH from C. boidinii were used to reduce 2-ketocarboxylic acids enzymatically while regenerating the NADH cofactor in situ, and this constitutes an industrially established method for preparing optically active (S)-a-amino acids particularly (S)-fcrf-leucine, which is produced on the ton scale using a membrane reactor. The method is described in detail in the literature [48,49]. However, this method required isolated enzymes in purified form. 

Recently, Groger et al. [51] developed a process for preparing (S)-tertiary leucine 22 by reacting the corresponding keto acid 23 with an ammonium ion donor in the presence of a whole cell of E. coli expressing amino acid dehydrogenase and cofactor-regenerating enzyme FDH. The substrate addition was metered such that the stationary concentration of 2-ketocarboxylic acid remains 500 mM and the external addition of cofactor, based on the total input of substrate, corresponds to 0.0001 equivalents. In this process, a reaction yield of 84% and ee of 99% were obtained for (S)-tertiary leucine at 130 g/1 substrate input. 

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