Nitrilases Catalyze Key Step to Conformationally Constrained GABA Analogous γ-Amino Acids in High Optical Purity

Me2(CH2CH)SiCN: a bifunctional ethylene equivalent for Diels–Alder reaction based controllable tandem synthesis

A bifunctional silyl reagent Me₂(CH₂CH)SiCN has been developed as a novel ethylene equivalent for the Diels–Alder (DA) reaction. The use of this reagent enables the controllable synthesis of value-added cyclohexenyl ketones or 2-acyl cyclohexancarbonitrile derivatives through a five- or six-step tandem sequence based on a Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence that involves a temporary silicon-tethered intramolecular DA reaction.

We report an unprecedented tandem Wittig/cyanosilylation/DA reaction/retro-cyanosilylation/isomerization sequence by using our designed bifunctional ethylene equivalent Me₂(CH₂CH)SiCN.

Facile synthesis of 2-azaspiro[3.4]octane

Our annulation strategy utilized for the synthesis of 2-azaspiro[3.4]octane is explained. Three successful routes for the synthesis were developed. One of the approaches involved annulation of the cyclopentane ring and the remaining two approaches involved annulation of the four membered ring. All three approaches employ readily available starting materials with conventional chemical transformations and minimal chromatographic purifications to afford the title compound. The merits and limitations of the three approaches are also discussed.

Preparation of chiral 3-oxocycloalkanecarbonitrile and its derivatives by crystallization-induced diastereomer transformation of ketals with chiral 1,2-diphenylethane-1,2-diol

Chiral 3-oxocycloalkanecarbonitriles were prepared by fractional crystallization and crystallization-induced diastereomer transformation (CIDT) of diastereomeric ketals with (1R,2R)-1,2-diphenylethane-1,2-diol. Investigation of the crystal structures by X-ray diffraction analysis revealed that the difference in hydrogen bonds caused the discrepancy of the solubilities between (R) and (S) diastereomers. Furthermore, CIDT to afford the (R)-diastereomer in good yield (95% yield) and with high diastereoselectivity (97% de) was accomplished, which is the first example of CIDT of neutral compounds via formation of the diastereomeric ketal with (1R,2R)-1,2-diphenylethane-1,2-diol.

Chiral 3-oxocyclopentanecarbonitrile was prepared in good yield and with high diastereoselectivity by crystallization-induced diastereomer transformation of the corresponding diastereomeric ketal.

Switching a nitrilase from Syechocystis sp. PCC6803 to a nitrile hydratase by rationally regulating reaction pathways

Based on this mechanism, a nitrilase was engineered to shift the reaction pathway from formation of acid to formation of amide.

The Important Role of Halogen Bond in Substrate Selectivity of Enzymatic Catalysis

The use of halogen bond is widespread in drug discovery, design, and clinical trials, but is overlooked in drug biosynthesis. Here, the role of halogen bond in the nitrilase-catalyzed synthesis of ortho-, meta-, and para-chlorophenylacetic acid was investigated. Different distributions of halogen bond induced changes of substrate binding conformation and affected substrate selectivity. By engineering the halogen interaction, the substrate selectivity of the enzyme changed, with the implication that halogen bond plays an important role in biosynthesis and should be used as an efficient and reliable tool in enzymatic drug synthesis.

Bioconversion of Iminodiacetonitrile to Iminodiacetic acid with whole cells of Lysinibacillus boronitolerans MTCC 107614 (IICT-akl252)

Biotechnological potential of nitrilases are prompting significant interest in finding the novel microbes capable of hydrolyzing nitriles. In this view, we have screened about 450 bacterial strains for nitrilase production using bioconversion of iminodiacetonitrile (IDAN) to iminodiacetic acid (IDA) through hydrolysis and obtained six nitrilase-producing isolates. Among these six isolates, IICT-akl252 was promising which was identified as Lysinibacillus boronitolerans. This is the first report on L. boronitolerans for nitrilase activity. Optimization of various medium and reaction parameters for maximizing the nitrilase production using whole cells in shake flask was carried out for L. boronitolerans IICT-akl252. Sucrose (2 %) as a carbon source attained better nitrilase yield while IDAN appeared to be the preferable inducer (0.2 %). The maximum IDA formation was achieved with 100 mM IDAN and 150 mg/ml cells at 30 °C and pH 6.5. After optimization of the culture and reaction conditions, the activity of nitrilase was increased by 2.3-fold from 27.2 to 64.5 U. The enzyme was stable up to 1 h at 50 °C. The enzyme was able to hydrolyze aliphatic, aromatic and heterocyclic nitrile substrates.

Targeting the substrate binding site of E. coli nitrile reductase QueF by modeling, substrate and enzyme engineering

Nitrile reductase QueF catalyzes the reduction of 2-amino-5-cyanopyrrolo[2,3-d]pyrimidin-4-one (preQ0) to 2-amino-5-aminomethylpyrrolo[2,3-d]pyrimidin-4-one (preQ1) in the biosynthetic pathway of the hypermodified nucleoside queuosine. It is the only enzyme known to catalyze a reduction of a nitrile to its corresponding primary amine and could therefore expand the toolbox of biocatalytic reactions of nitriles. To evaluate this new oxidoreductase for application in biocatalytic reactions, investigation of its substrate scope is prerequisite. We report here an investigation of the active site binding properties and the substrate scope of nitrile reductase QueF from Escherichia coli. Screenings with simple nitrile structures revealed high substrate specificity. Consequently, binding interactions of the substrate to the active site were identified based on a new homology model of E. coli QueF and modeled complex structures of the natural and non-natural substrates. Various structural analogues of the natural substrate preQ0 were synthesized and screened with wild-type QueF from E. coli and several active site mutants. Two amino acid residues Cys190 and Asp197 were shown to play an essential role in the catalytic mechanism. Three non-natural substrates were identified and compared to the natural substrate regarding their specific activities by using wild-type and mutant nitrile reductase.

A short, chemoenzymatic route to chiral beta-aryl-gamma-amino acids using reductases from anaerobic bacteria

A short chemoenzymatic synthesis of beta-aryl-gamma-aminobutyric acids has been developed, based on a highly enantioselective biocatalytic reduction of beta-aryl-beta-cyano-alpha,beta-unsaturated carboxylic acids.

Fungal nitrilases as biocatalysts: Recent developments

Of the numerous putative fungal nitrilases available from protein databases only a few enzymes were purified and characterized. The purified nitrilases from Fusarium solani, Fusarium oxysporum f. sp. melonis and Aspergillus niger share a preference for (hetero)aromatic nitriles, temperature optima between 40 and 50 degrees C and pH optima in the slightly alkaline region. On the other hand, they differ in their chemoselectivity, i.e. their tendency to produce amides as by-products. The production of fungal nitrilases is increased by up to three orders of magnitude on the addition of 2-cyanopyridine to the culture media. The whole-cell and subcellular biocatalysts were immobilized by various methods (LentiKats(R); adsorption on hydrophobic or ion exchange resins; cross-linked enzyme aggregates). Operational stability was examined using continuous stirred membrane bioreactors. Fungal nitrilases appear promising for biocatalytic applications and biodegradation of nitrile environmental contaminants.

Influence of relative configuration of disubstituted cyclopentanes and -hexanes on 13C shifts

(13)C shifts of disubstituted cyclopentane and cyclohexane derivatives were compared in dependence on the relative configuration of the two substituents. A diequatorial substitution correlates with deshielding compared to other substitution patterns. Some novel fluorinated cyclopentanes and -hexanes including their DFT calculation-assisted structure elucidation are described.

An efficient synthesis of gamma-amino acids and attempts to drive its enantioselectivity

Addition of carboxylic acid dianions to bromoacetonitrile lead, in good yields,to the corresponding gamma-cyanoacids, which on hydrogenation yielded gamma-amino acids. This two step methodology improves upon previously described results. Poor e.e's resultedfrom our attempts to drive the enantioselectivity of this transformation by chiral amide induction.