Comomonas acidovorans

A key step in the synthesis of the /3-lactamase inhibitor cilastatin (Bayer, Leverkusen, Germany) is the preparation of (S)-2,2-dimethylcyclopropane carboxamide. The chemically synthesized corresponding nitrile, l-cyano-2,2-dimethylcyclopropane, is hydrolyzed by a highly active but enanhounspecific nitrile hydratase to the racemic carboxamides. An amidase from Comomonas acidovorans overexpressed in E. coli selectively hydrolyzes the undesired (R)-isomer to the acid. The remaining (S) enantiomer is obtained with > 99% e.e. and 48% conversion (the resulting E value thus exceeds 100). The (R)-acid is recycled by chemical amidation with thionyl chloride and ammonia. The process has been developed by Lonza (Visp, Switzerland) and runs on a 15 m3 scale (Rasor, 2001). 

Asano et al. have also purified a D-stereospecific amino acid amidase from another Ochrobadrum anthropi isolate137, 38i. Recently, a new amidase from Comamonas acidovorans has been reported that exhibits a broad substrate specificity and also d-amino acid amidase activity1391. In addition, a D-specific amidase has been identified in Arthrobacter sp. NJ-261401. In contrast to the D-selective enzymes of Ochrobadrum sp. and Comomonas acidovorans, the D-amide hydrolase identified in Arthrobacter sp. NJ-26 was very substrate specific a good hydrolysis rate was only observed for d-alanine amide. 

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