A substrate structure rule to predict the enantioselectivity of Candida rugosa lipase (CRL) towards $ alpha$-substituted carboxylic acids is proposed. Lipase from Candida rugosa resolved methyl $ alpha$-substituted phenylacetates -5. These substrates were examined to understand the influence of steric and the electronic nature of the substituents at the chiral center on the enantioselectivity. Crude CRL was partially enantioselective towards substrates -3, and highly selective towards and, E $>$ 100. Partial purification of crude CRL by 2-propanol extraction and separation by an ion exchange chromatography, dramatically improved the enantioselectivity towards -3, E $>$ 100. One main lipase fraction, F$ sb{ rm C}$ was obtained with 58 fold purification and 62% yield. This improvement in enantioselectivity was achieved with a simple dialysis against deionized water or 50% 2-propanol extraction. Lauric acid (10 mM), partially reversed the increase in the enantioselectivity. The absolute configuration of the favored enantiomer for crude and partially purified lipase preparations, was S. Other lipases with opposite stereoselectivities were not identified. / Based on literature and our results, it is believed that the size of the substituents at the stereogenic carbon center can account for the enantioselectivity of CRL catalyzed hydrolysis. The opposite configuration is not preferred when the electronic nature of the medium size substituent is varied. The rule can predict the selectivity data for partially purified CRL preparations. We believe that the accuracy of the rule can be improved if more examples of partially purified CRL reactions are examined.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.68151 |
| Date | January 1993 |
| Creators | Ahmed, Sharmin Nayela |
| Contributors | Kazlauskas, R. J. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001397730, proquestno: AAIMM94408, Theses scanned by UMI/ProQuest. |
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