Microbial biotransformations in water/organic solvent system. Enantioselective reduction of aromatic β- and γ-nitroketones

The production of single enantiomers of γ and β-nitroalcohols by microbial bioreduction has been studied. A restricted screening among 14 yeasts was performed using 1-phenyl-4-nitro-1-butanone 1 as substrate. Pichia minuta (CBS 1708) and Pichia etchellsii (CBS 2011) gave the highest enantiopreference for (S)-alcohol 3 formation (e.e. 85% and 80%, respectively), while Kluyveromyces marxianus (CBS 397) was the only strain able to preferentially furnish the (R) enantiomer (e.e. 70%). These three microorganisms, along with baker's yeast, were then employed in reactions performed in water/organic solvent systems using different solvents (hexane, benzene and dibutyl ether) affording alcohol 3 in high enantiomeric excesses (>95-97%). These strains were also employed to reduce 1-phenyl-3-nitro-1- propanone 2, maintaining the same stereobias observed with γ-nitroketone 1 and showing high enantioselectivity in both simple aqueous (>85-97%) and biphasic media (>97%).