Two Classes of Enzymes of Opposite Stereochemistry in an Organism:  One for Fluorinated and Another for Nonfluorinated Substrates

Abstract

Reduction of methyl ketones by dried cells of Geotrichum candidum (APG4) afforded (S)-alcohols in excellent enantiomeric excess (ee), whereas the reduction of trifluoromethyl ketones gave the corresponding alcohols of the opposite configuration also in excellent ee. The replacement of the methyl moiety with a trifluoromethyl group alters both the bulkiness and the electronic properties, the effect of which on the stereoselectivity was examined. No inversion in stereochemistry was observed in the reduction of hindered ketones such as isopropyl ketone, while the stereoselectivity was inverted in the reduction of ketones with electron-withdrawing atoms such as chlorine. The mechanism for the inversion in stereochemistry was investigated by enzymatic studies. Several enzymes with different stereoselectivities were isolated; one of them catalyzed the reduction of methyl ketones, and another with the opposite stereoselectivity catalyzed the reduction of trifluoromethyl ketones. Furthermore, both APG4 and the isolated enzyme were applied to the reduction of fluorinated ketones on a preparative scale, which resulted in the synthesis of chiral fluorinated alcohols with excellent ee.

Didymosphaeria igniaria: a new microorganism useful for the enantioselective reduction of aryl-aliphatic ketones

“…Moreover, 2 was more efficiently reduced than 1. The similar difference was described for reduction of fluorinated and nonfluorinated substrates by two enzymes with opposite stereochemical preferences contained in the acetone powder of yeast of Geotrichum candidum [40].…”

Enzymatic reactions in supercritical CO2: carboxylation, asymmetric reduction and esterification

“…In our case, very high enantioselectivities (>99% ee) were obtained for the reduction with the majority of the substrates tested, while slightly lower enantioselectivities (96, 97% ee) were observed for a few of them. The enantioselectivities obtained in this system are superior to or at least equal to those for most other biocatalytic and chemical systems [62][63][64][65][66][81][82][83]. The immobilized resting cell of G. candidum was also used as a catalyst for the reduction of ketones in a semi-continuous flow process using supercritical CO 2 [51].…”

“…The resting cells of a fungus, Geotrichum candidum [81][82][83], were employed for the reduction of various ketones in supercritical CO 2 [50,51]. The advantage of alcohol dehydrogenase catalyzed reactions in supercritical CO 2 is the ease of the product isolation from CO 2 .…”

Expanding the Scope of Alcohol Dehydrogenases towards Bulkier Substrates: Stereo‐ and Enantiopreference for α,α‐Dihalogenated Ketones

“…Then, the influence of electron donating (Me or OMe) or electron withdrawing substituents (Cl or NO2), at different positions in the aromatic ring was studied for α,α-dichloroacetophenone derivatives 2b-i. Clear trends were observed as follows: (i) ADHs led to good levels of activity and stereoselectivity to those substrates with the presence of substituents in the meta-or para-position (entries [8][9][10][11][12][13][14][15][16][17][18][19][20], while for ortho-substituted acetophenones 2b,c (entries 4-7), only the Prelog enzyme RasADH (entries 4 and 6) allowed the isolation of the corresponding (R)-alcohols in quantitative yield and enantiopure form. This is especially relevant since the bioreduction of ortho-substituted acetophenones remains usually hampered.…”

“…[16 The lipase-catalysed resolution of 2,2-dichloro-1-phenylethanol (3a) was achieved with Amano Pseudomonas cepacia lipase (PSL), but 44% conversion of the final product was reached after 142 h. [17] On the other hand, the bioreduction of the α,α-dihalo ketone precursor 2a has been tested with whole cells from Geotrichum candidum APG4 [18] and baker's yeast, [19] but stereoselectivities remained modest (<55% ee). Based on the high selectivities displayed by alcohol dehydrogenases (ADHs), [20] and since α-monohalogenated ketones are excellent substrates for these enzymes, [21] the bioreduction of a series of bulkier α,α-dihalogenated acetophenones is here presented.…”