Industrial Biotransformations

Amines can be prepared from a variety of precursors. The most common pathway is
from amides through enzymatic hydrolysis [4]. In this route, hydrolysis of amides possessing
an amino moiety on a tertiary carbon atom is very difficult using standard proteases
due to steric hindrance.
Transaminases have been demonstrated, at scale, to convert ketones into amines in
one pot [5]. Amines can also be prepared by reduction of nitro, imine, azide or diazo compounds
using whole cell biotransformations [6].
Chemoenzymatic dynamic kinetic resolution can be used for the preparation of enantiomerically
enriched amines. Here either Pd- or Ru-catalysts have been reported for the
regeneration of racemic amines or ketoximes [7].
R 1
NH2
R 2
R1, R2 = organic substituents
3.4
Alcohols
Pd-, Ru- catalysts
NHAc
NH2
+
R1 R2 R1 R2 3.4 Alcohols
Alcohols can be prepared from a variety of precursors, for example, through hydrolysis
of carboxyl esters, sulfate esters, phosphate esters [8]. Hydrolysis of esters composed of
tert-alcohols can be very difficult by standard carboxyl ester hydrolases.
The reversal reactions are esterification, sulfonylation (sulfotransferases) and phosphorylation
(catalyzed by kinases) [9]. Carbonyl-reduction of aldehyde or ketone precursors
can also be carried out on a practical scale [10].
As for hydroxylation of alkanes, most reactions are carried out under whole cell conditions,
although some recombinant P450s or monooxygenases are available commercially
[11].
Several approaches have been developed for the dynamic resolution of enzyme-catalyzed
resolution of alcohols. For example, Ru-catalysts have been used to racemize the
wrong enantiomeric allylic alcohol [12].
65