Abstract
The aromatic substrate profile of the cobalt nitrile hydratase from Rhodococcus rhodochrous ATCC BAA 870 was evaluated against a wide range of nitrile containing compounds (>60). To determine the substrate limits of this enzyme, compounds ranging in size from small (90 Da) to large (325 Da) were evaluated. Larger compounds included those with a bi-aryl axis, prepared by the Suzuki coupling reaction, Morita–Baylis–Hillman adducts, heteroatom-linked diarylpyridines prepared by Buchwald–Hartwig cross-coupling reactions and imidazo[1,2-a]pyridines prepared by the Groebke–Blackburn–Bienaymé multicomponent reaction. The enzyme active site was moderately accommodating, accepting almost all of the small aromatic nitriles, the diarylpyridines and most of the bi-aryl compounds and Morita–Baylis–Hillman products but not the Groebke–Blackburn–Bienaymé products. Nitrile conversion was influenced by steric hindrance around the cyano group, the presence of electron donating groups (e.g., methoxy) on the aromatic ring, and the overall size of the compound.
Highlights
IntroductionThe base or acid conversion of a nitrile to an amide is problematic as the subsequent conversion to the carboxylic acid is faster and hard to prevent
Nitrile hydratase is a well-known success story for biocatalysis
Apart from evaluating a range of readily available small aromatic nitriles, we synthesised a number of more functionalised derivatives for assessing the biocatalytic potential of the purified
Summary
The base or acid conversion of a nitrile to an amide is problematic as the subsequent conversion to the carboxylic acid is faster and hard to prevent. This was initially circumvented through the use of metallic copper heterogeneous catalysts and encouraged the exploration of other metal catalysts [1]. The nitrile hydratase-expressing organism Rhodococcus rhodochrous J1 was selected to convert acrylonitrile into acrylamide [2], which is manufactured at a multi-hundred thousand ton per annum scale with near perfect chemoselectivity (>99.99%). Whole cell nitrile hydratase catalysts have been applied in the production of
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