Page 279 - Cascade_Biocatalysis_Integrating_Stereoselective_and_Environmentally_Friendly_Reactions

11.2 Natural Cascades 255

CH OCH CH OCH
2 3 2 3
Nitrile hydratase Amidase
CN CONH 2
Fe Fe No product
R. rhodochrous PA-34 R. rhodochrous PA-34
whole cells whole cells
(Inductor: acetonitrile) (Inductor: acetonitrile)
(±) (+)-(Sp)
Yield 32%, ee 83%
COOH
CH 2 OCH 3 CH 2 OCH 3 CONH 2
Nitrile hydratase Amidase
CN CONH 2 + Fe CH 2 OCH 3 CH 2 OCH
Fe Fe Fe 3
R. rhodochrous PA-34 R. rhodochrous PA-34
whole cells whole cells
(Inductor: BuCN or valeronitrile) (Inductor: BuCN or valeronitrile)
(±) (+)-(Sp) (–)-(Rp) (Rp)
Yield 8%, ee 53% Yield 2.5%, ee 96%
Figure 11.7 Hydrolysis of racemic 1-cyano-2-methoxymethyl ferrocene to the correspond-
ing optically active amide by Rhodococcus rhodochrous PA-34 whole cells. Only one isomer is
drawn for racemic compounds.
that the ferrocene scaffold can be recognized by the bienzymatic NHase/amidase
system expressed by R. erythropolis A4 and R. rhodochrous PA-34 whole cells, and
that this strategy can be potentially used to synthesize building blocks for the
production of valuable molecules, such as the antimalarian ferroquine or the
antiproliferative agents of the ferrocifen series. The main parameters leading to
molecular recognition were the specific structure features and the inducers adopted
during the growth of the strains. Even more noteworthy, the same work group
has observed the first example of enantiorecognition of a NHase/amidase system
toward substrates with planar chirality such as the 1,2 disubstituted ferrocenes; in
the presence of R. rhodochrous PA-34 whole cells, racemic 1-cyano-2-methoxymethyl
ferrocene was hydrolyzed to the corresponding optically active amide (ee 83%,
Figure 11.7). Again, the use of different inducers during the bacterial growth
phase, permitted a partial modulation of the enzymatic activities both in term of
conversion values and of enantioselectivity features (manuscript in preparation).
In addition to synthetic applications, the NHase/amidase cascade can also be
used in post-production processes, like enhancing structure and properties of
(poly)acrylic fibers. Tauber et al. [43] showed that the NHase and amidase of R.
rhodochrous NCIMB 11216 were able to hydrolyze nitrile groups of both granular
polyacrylonitriles (PANs) and acrylic fibers. The acrylic fibers became more
hydrophilic because of the enzymatic modification, enhancing the adsorption
of dyes.
11.2.2
Aldoxime Dehydratase–Nitrile Hydratase–Amidase
Aldoximes are formed in many plants by the action of specific cytochromes
P450 from amino acids and are important as intermediates in the synthesis
of glucosinolates and certain phytohormones [44]. It is therefore not surprising
+
that the ability to degrade aldoximes is widely distributed among Gram -and
−
Gram -bacteria, yeasts, and fungi [45]. In all the microorganisms studied, the
aldoximes are converted by heme-containing aldoxime dehydratases to nitriles,