Described in this thesis is the isolation of two microorganisms containing a nitrile hydratase and amidase to effect the enantioselective hydrolysis of a-substituted nitriles to their corresponding amides and acids. Isolate NP3854 was identified as an atypical Rhodococcus sp. The nitrile hydratase proved to be non-selective for all the substrates tested. However, carboxylic acids with excellent enantiomeric excess were obtained from a large number of amides. X R~CN H nitr-il-e--h-y-d-r.a~tase ~X amidas.e RH CONH2 X R~"""CO H H 2 Optically active acids with an enantiomeric excess of, generally, >98 %, were obtained when X = NH2, Me and Cl, but proved to be racemic for OH and Br. R could be a variety of aromatic, cyclic and acyclic alkyl residues without adversely affecting the enantioselectivity. The pH-activity profile was determined for the amidase of NP3854 using propionamide as the substrate. From this data, coupled with inhibition studies, it may ,.tentatively be suggested that the amidase has a histidine residue in the active site, which may act as a general base for a serine amino acid. The pH-activity profile was determined for 2-amino-2-phenylacetamide 2b, and this suggested that the unprotonated form of the amine acted as the substrate. Within a pH range of 3 - 9 the enantiomeric excess remains high (>98 %) and experimentally invariant. The amidase was found to have a temperature optimum of 60°C and could tolerate 20 % THF with a loss of only 15 % activity. Attempts made to hydrolyse 4,5,6-amino nitriles and amides to the corresponding amino acids and isolate any reaction intermediates failed. This was presumed to be due to the large fraction of the unprotonated amine due to the higher pKa (- 9 - 10).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:363237 |
| Date | January 1996 |
| Creators | Beard, Timothy Mark |
| Publisher | University of Huddersfield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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