NADPH-dependent oxidoreductase Q1EQE0 from Streptomyces kanamyceticus catalyzes the asymmetric reduction of the prochiral monocyclic imine 2-methyl-1-pyrroline to the chiral amine (R)-2-methylpyrrolidine with >99% ee, and is thus of interest as a potential biocatalyst for the production of optically active amines. The structures of Q1EQE0 in native form, and in complex with the nicotinamide cofactor NADPH have been solved and refined to a resolution of 2.7 Å. Q1EQE0 functions as a dimer in which the monomer consists of an N-terminal Rossman-fold motif attached to a helical C-terminal domain through a helix of 28 amino acids. The dimer is formed through reciprocal domain sharing in which the C-terminal domains are swapped, with a substrate-binding cleft formed between the N-terminal subunit of monomer A and the C-terminal subunit of monomer B. The structure is related to those of known β-hydroxyacid dehydrogenases, except that the essential lysine, which serves as an acid/base in the (de)protonation of the nascent alcohol in those enzymes, is replaced by an aspartate residue, Asp187 in Q1EQE0. Mutation of Asp187 to either asparagine or alanine resulted in an inactive enzyme.

Critical parameters affecting the stereoselective amination of (hetero)aromatic ketones using transaminases have been studied such as temperature, pH, substrate concentration, cosolvent and source and percentage of amino donor, to further optimize the production of enantiopure amines using both (S)-and (R)-selective biocatalysts from commercial suppliers.Interesting enantiopure amino building blocks have been obtained overcoming some limitations of traditional chemical synthetic methods. Representative processes were scaled-up affording halogenated and heteroaromatic amines in enantiomerically pure form and good isolated yields.

A straightforward chemoenzymatic synthesis of enantiomerically pure rivastigmine has been efficiently carried out under mild reaction conditions, with Candida antarctica lipase B responsible for the stereoselective acetylation of the corresponding (R)-alcohol or amine. An exhaustive enzymatic study has been developed exploring the possibilities of carry out enzyme recycling, scaling up the enzymatic process and development of a dynamic kinetic resolution procedure for the production of adequate enantiomerically pure precursors of rivastigmine. Total chemoenzymatic synthesis of this pharmaceutical has been performed in good overall yield from commercially available 3-methoxyacetophenone.

Abstract:A one-pot chemoenzymatic method has been described for the synthesis of -butyrolactones starting from the corresponding ketones through a Baeyer-Villiger reaction.The approach is based on a lipase-catalyzed perhydrolysis for the formation of peracetic acid, which is the responsible for the ketone oxidation. Optimization studies have been performed in the oxidation of cyclobutanone, finding Candida antarctica lipase type B, ethyl acetate and urea-hydrogen peroxide complex as the best system. The relative ratio of these reagents has also been analyzed in depth. This synthetic approach has been successfully extended to a family of 3-substituted cyclobutanones in high substrate concentration, yielding the corresponding lactones with excellent isolated yields and purities, under mild reaction conditions and after a simple extraction protocol.

Abstract. The synthesis of a family of pyridines bearing a fluorinated substituent on the aromatic ring has been carried out through two independent and highly stereoselective chemoenzymatic strategies. Short chemical synthetic routes toward fluorinated racemic amines and prochiral ketones have been developed, which served as substrates to explore the suitability of lipases and transaminases in asymmetric biotransformations. The lipase-catalyzed kinetic resolution via acylation of racemic amines proceeded smoothly giving conversions close to 50% and excellent enantioselectivities. Alternatively, the biotransamination of the corresponding prochiral ketones was investigated giving access to both optically pure amine enantiomers using transaminases with complementary selectivity. High to quantitative conversion values were achieved, which allowed the isolation of the amines in moderate to high yields (40-88%). A deeper understanding of the latter process was enabled by performing theoretical calculations on thermodynamic and mechanistic aspects. Calculations showed that the biotransamination reactions are highly favoured by the presence of fluorine atoms and the pyridine ring.

Because of the importance of developing stereoselective syntheses for single enantiomers, a selected panel of racemic biologically active 1-aryl- and 1-heteroarylpropan-2-amines has been prepared, followed by a study of their behavior in enzymatic kinetic resolution (KR) processes. For this purpose, lipase B from Candida antarctica (CAL-B) proved to be an ideal biocatalyst allowing the preparation of the corresponding enantioenriched (R)-amides and (S)-amines by aminolysis reactions. Likewise, dynamic kinetic resolutions (DKR) have been successfully achieved combining the use of CAL-B and Shvo's catalyst. This research constitutes the first example of a lipase-catalyzed DKR process of β-substituted isopropylamines.

A wide range of optically active 3-amino-3-arylpropanoic acid derivatives have been prepared by means of a stereoselective chemoenzymatic route. The key step is the kinetic resolution of the corresponding b-amino esters. Although the enzymatic acylations of the amino group with ethyl methoxy-A C H T U N G T R E N N U N G acetate showed synthetically useful enantioselectivities, the hydrolyses of the ester group catalyzed by lipase from Pseudomonas cepacia have been identified as the optimal processes concerning both activity and enantioselectivity. The enantiopreference of this lipase in these reactions has been explained, at the molecular level, by using a fragment-based approach in which the most favoured binding site for a phenyl ring and the most stable conformation of the 3-aminopropanoate core nicely match the (S)-configuration of the major products. The conversion and enantioselectivity values of the enzymatic reactions have been compared in order to understand the influence of the different substitution patterns present in the phenyl ring. This chemoenzymatic route has been successfully applied to the preparation of a valuable intermediate in the synthesis of (S)-dapoxetine, which has been chemically synthesised in excellent optical purity.

A series of α-amino acid derivatives containing the 2,3-dihydroindole or octahydroindole core have been chemoenzymatically synthesized in good overall yields and high enantiomeric purity under mild reaction conditions using lipases for the introduction of chirality. Candida antarctica lipase type A has shown excellent activity and high enantiodiscrimination ability towards the two cyclic amino esters used as substrates. The selectivity of the process proved to be greatly dependent on the alkoxycarbonylating agent. Thus, the enzymatic kinetic resolution of methyl indoline-2-carboxylate has been successfully achieved using 3-methoxyphenyl allyl carbonate, whereas (2R,3aR,7aR)-benzyl octahydroindole-2-carboxylate required the less reactive diallyl carbonate.