Recombinant Baker's Yeast as a Whole-Cell Catalyst for Asymmetric Baeyer−Villiger Oxidations

Abstract

Cyclohexanone monooxygenase (E. C. 1.14.13.22) from Acinetobacter sp. NCIB 9871 has been expressed in baker's yeast (Saccharomyces cereVisiae) to create a general reagent for asymmetric Baeyer-Villiger oxidations. This "designer yeast" approach combines the advantages of using purified enzymes (single catalytic species, no overmetabolism, etc.) with the benefits of whole-cell reactions (experimentally simple, no cofactor regeneration necessary, etc.). The yeast reagent was used to systematically examine a series of 2-, 3-, and 4-substituted cyclohexanones (R ) Me, Et, n-Pr, i-Pr, allyl, n-Bu), almost all of which were oxidized to the corresponding -caprolactones in good yields and high enantioselectivities (typically g 95%). Mesomeric 4-substituted cyclohexanones were oxidized to -caprolactones in g 92% ee. The engineered yeast strain also effected kinetic resolutions of 2-substituted cyclohexanones with enantioselectivity values g 200 for substituents larger than methyl. The behavior of 3-substituted cyclohexanones depended upon the size of the substituent. The engineered yeast strain cleanly converted the antipodes of 3-methyl-and 3-ethylcyclohexanone to divergent regioisomers. On the other hand, for cyclohexanones with larger substituents (n-Pr, allyl, n-Bu), both antipodes were oxidized by the enzyme to a single regioisomer. In these cases, the observed enantioselectivities were due to a combination of a modest preference for one enantiomer by the enzyme and an unfavorable conformational preequilibrium required prior to binding of the less-favored antipode, a phenomenon we refer to as substrate-assisted enantioselectivity.

Asymmetric synthesis of chiral amines with ?-transaminase

“…Asymmetric synthesis has been one of the central themes in biotransformation (Klibanov, 1990;Koskinen and Klibanov, 1996;Margolin, 1993;Santaniello et al, 1993;Sheldon, 1996;Stewart et al, 1998;Stinson, 1997;Wong and Whitesides, 1994) as well as in modern organic chemistry (Aitken and Kilenyi, 1992;Chan, 1993;Juaristi et al, 1998;Kajiro et al, 1998;Larsen et al, 1989;Myers et al, 1997;Sonawane et al, 1992). Asymmetric synthesis of chiral compounds using prochiral precursors is usually favored over kinetic resolution using racemic mixtures, because the theoretical yield is 100% and achiral precursors are usually less expensive than racemic mixtures (Sheldon, 1996).…”

Enzymatic Baeyer–Villiger Oxidation of Benzaldehydes

“…[52] Such a whole-cell system is of particular interest from a preparative point of view because it avoids expensive cofactor recycling. [53,54] Therefore, with proper upscaling and downstream processing, [41,55 -58] HAPMO may develop as an environmentally benign alternative for the synthesis of fluorophenols.…”

Reduções enantiosseletivas de cetonas utilizando-se fermento de pão

“…Por outro lado, células inteiras de microorganismos podem produzir enzima(s) de interesse, e são mais apropriadas do que enzimas que exigem adição de cofatores, em particular aquelas que catalisam reações redox 14 . Uma solução para estes problemas de existência de mais de uma enzima competitiva foi proposta por Stewart e colaboradores empregando fermento de pão recombinante 15 . A enantiosseletividade na redução de grupos carbonílicos por fermentos é também fortemente influenciada pela concentração do substrato e do produto formado 16 .…”