Excellent Ee Research Articles

Asymmetric Bioreduction of 4-hydroxy-2-butanone by Carbonyl Reductases PFODH and CpSADH Delivers 1,3-butanediol Enantiomers with Excellent R- and S-enantioselectivity

Chiral 1,3-butandiol (1,3-BD) is a very important intermediate for the synthesis of pharmaceutically valuable compounds. In this study, biocatalysts were developed to deliver optically pure R- and S-1,3-BD enantiomers at high conversions. Based on the catalytic activity and enantioselectivity toward 4-hydroxy-2-butanone (4H2B), two carbonyl reductases, PFODH from Pichia finlandica and CpSADH from Candida parapsilosis were screened out from a library of 20 reductases. PFODH was discovered as a new biocatalyst for reducing the 4H2B to the corresponding R-product while CpSADH was used for the first time to reduce the target substrate with strict Sselectivity, and both showed high substrate/product tolerance and good catalytic activity (with conversions of 81-90%) without requirement of external cofactors. Regeneration of cofactor NADH was facilitated by the substrate-coupled system using isopropyl alcohol as a cosubstrate. The substrate spectra of PFODH and CpSADH were further investigated by expanding to various substituted aryl ketones. Almost all of the analyzed ketones were reduced asymmetrically into their corresponding chiral alcohols with excellent ee values of 97-99%. PFODH easily reduced the substrates which are substituted adjacent to the carbonyl group or those substituted on the meta-position of the phenyl ring, while CpSADH hardly reduced those with substituents adjacent to the carbonyl group. These results demonstrate the industrial potential of PFODH and CpSADH in biosynthesis of optically pure 1,3-butanediol and other valuable chiral alcohols.

Nickel-Catalyzed Chemoselective Asymmetric Hydrogenation of α,β-Unsaturated Ketoimines: An Efficient Approach to Chiral Allylic Amines.

An efficient synthetic route to chiral allylic amines has been developed by nickel/(S,S)-Ph-BPE complex catalyzed chemoselective asymmetric hydrogenation of α,β-unsaturated ketoimines. Varieties of α,β-unsaturated ketoimines have been well tolerated in this transformation to give chiral allylic amines with high yields and excellent ee values (up to 99% yield, up to 99% ee). A gram-scale reaction with 0.2 mol % catalyst loading has also been achieved.

An Ammonium-Formate-Driven Trienzymatic Cascade for ω-Transaminase-Catalyzed (R)-Selective Amination.

(R)-Amination mediated by (R)-specific ω-transaminases generally requires costly d-alanine in excess to obtain the desired chiral amines in high yield. Herein, a one-pot, trienzymatic cascade comprising an (R)-specific ω-transaminase, an amine dehydrogenase, and a formate dehydrogenase was developed for the economical and eco-friendly synthesis of (R)-chiral amines. Using inexpensive ammonium formate as the sole sacrificial agent, the established cascade system enabled efficient ω-transaminase-mediated (R)-amination of various ketones, with high conversions and excellent ee (>99%); water and CO2 were the only waste products.

Kinetic Resolution via Rh-Catalyzed C-C Activation of Cyclobutanones at Room Temperature.

Herein we describe the development of a highly selective kinetic resolution of cyclobutanones via a Rh-catalyzed "cut-and-sew" reaction with selectivity factor up to 785. This reaction takes place at room temperature with excellent efficiency. Various trans-5,6-fused bicycles and C2-substituted cyclobutanones were obtained with excellent ee's that can be further used as chiral building blocks. DFT calculations reveal the crucial roles of the DTBM-segphos ligand in stabilizing the rate- and enantioselectivity-determining C-C oxidative addition transition state via favorable ligand-substrate dispersion interactions.

Enantioselective Rhodium-Catalyzed Addition of Arylboroxines to N-Unprotected Ketimines: Efficient Synthesis of Cipargamin.

Highly enantioselective rhodium-catalyzed addition of arylboroxines to N-unprotected ketimines is realized for the first time by employing chiral BIBOP-type ligands with a Rh loading as low as 1 mol %. A range of chiral α-trifluoromethyl-α,α-diaryl α-tertiary amines or 3-amino-3-aryloxindoles were formed with excellent ee values and yields by employing either WingPhos or PFBO-BIBOP as the ligand. The method has enabled an efficient enantioselective synthesis of cipargamin.

Enantioselective Rhodium‐Catalyzed Addition of Arylboroxines to N‐Unprotected Ketimines: Efficient Synthesis of Cipargamin

AbstractHighly enantioselective rhodium‐catalyzed addition of arylboroxines to N‐unprotected ketimines is realized for the first time by employing chiral BIBOP‐type ligands with a Rh loading as low as 1 mol %. A range of chiral α‐trifluoromethyl‐α,α‐diaryl α‐tertiary amines or 3‐amino‐3‐aryloxindoles were formed with excellent ee values and yields by employing either WingPhos or PFBO‐BIBOP as the ligand. The method has enabled an efficient enantioselective synthesis of cipargamin.

BINOL-phosphoric acid catalyzed asymmetric Mannich addition of β-ketoesters to indolenines generated in situ by DDQ

An asymmetric Mannich addition of β-ketoesters to indolenines that were generated in situ from 3-indolinone-2-carboxylates by DDQ has been developed using a catalytic amount of chiral BINOL-phosphoric acid. The corresponding chiral 3-indolinone-2-carboxylate derivatives were obtained in good yields with excellent ee (up to 99%). This is the first report on the enantioselective addition of β-ketoesters to indolenines using a chiral Brønsted acid.

One‐Pot Three‐Step Consecutive Transformation of L‐α‐Amino Acids to (R)‐ and (S)‐Vicinal 1,2‐Diols via Combined Chemical and Biocatalytic Process

AbstractOptically pure vicinal 1,2‐diols are versatile chiral building blocks in the fine chemical and pharmaceutical industries. L‐α‐amino acid is a good feedstock source for high value‐added product production since it is inexpensive and renewable. However, conversion of L‐α‐amino acids to enantioenriched vicinal 1,2‐diols remains a significant challenge. In this study, combining a simple chemical process and a three‐enzyme cascade biocatalysis system, we have successfully implemented a one‐pot sequential process for the transformation of L‐α‐amino acids into enantiopure vicinal 1,2‐diols in aqueous medium. Firstly, the NaBH4‐H2SO4 system converted L‐α‐amino acids to (S)‐amino alcohols via amino acid carboxyl reduction. Secondly, the three‐enzyme (transaminase, carbonyl reductase and glucose dehydrogenase) cascade biocatalysis system converted amino alcohols to enantiopure vicinal 1,2‐diols via amino alcohol deamination, α‐hydroxy ketone asymmetric reduction and cofactor regeneration. Taking advantage of the two different reaction systems, chiral vicinal 1,2‐diols could be obtained from L‐α‐amino acids with high yields (69–90 %) and excellent ee values (91–>99 % ee).

Enantioselective Synthesis of β‐Methyl Amines via Iridium‐Catalyzed Asymmetric Hydrogenation of N‐Sulfonyl Allyl Amines

AbstractThe iridium‐catalyzed asymmetric hydrogenation of several N‐sulfonyl allyl amines is reported. All substrates can be easily obtained by the Ir‐catalyzed isomerization of N‐tosylaziridines reported previously. The commercially available threonine‐derived phosphinite (UbaPHOX) iridium complex has been found to be the best catalyst for this catalytic application, affording β‐methyl amines with good to excellent ee values (up to 94%). The synthetic potential of this novel methodology was demonstrated by the formal synthesis of Lorcaserin and LY‐404187.magnified image

Chiral Gating for Size- and Shape-Selective Asymmetric Catalysis.

A poor or mediocre stereoselectivity is a key roadblock for a chiral catalyst to find practical adoptions. We report a facile method to create a tunable chiral space near a chiral catalyst to augment its selectivity. The space was created rationally through templated polymerization within cross-linked micelles, using readily available amino acid derivatives. It provided gated entrance of reactants to the catalyst, enabling a mediocre prolinamide to catalyze aldol condensation in water with excellent yields and ee, in a size- and shape-selective manner.

Diastereo- and Enantioselective 1,6-Conjugate Addition of 2-Azaarylacetamides to para-Quinone Methides.

A chiral Mg(II)/N,N'-dioxide complex was found to be highly effective in promoting the diastereo- and enantioselective 1,6-conjugate addition of various azaarylacetamides to p-quinone methides under mild reaction conditions. Various chiral azaarene derivatives containing gem(1,1)-diaryl skeletons were obtained in good yields, dr, and excellent ee values. Meanwhile, on the basis of insight gained from the control experiments as well as the single-crystal structure of the Mg(II)/N,N'-dioxide complex and product, a possible transition state was proposed to explain the origin of coordination and stereoinduction.

Asymmetric Catalytic Formal 1,4‐Allylation of β,γ‐Unsaturated α‐Ketoesters: Allylboration/Oxy‐Cope Rearrangement

AbstractA highly enantioselective formal conjugate allyl addition of allylboronic acids to β,γ‐unsaturated α‐ketoesters has been realized by employing a chiral NiII/N,N′‐dioxide complex as the catalyst. This transformation proceeds by an allylboration/oxy‐Cope rearrangement sequence, providing a facile and rapid route to γ‐allyl‐α‐ketoesters with moderate to good yields (65–92 %) and excellent ee values (90–99 % ee). The isolation of 1,2‐allylboration products provided insight into the mechanism of the subsequent oxy‐Cope rearrangement reaction: substrate‐induced chiral transfer and a chiral Lewis acid accelerated process. Based on the experimental investigations and DFT calculations, a rare boatlike transition‐state model is proposed as the origin of high chirality transfer during the oxy‐Cope rearrangement.

Asymmetric Catalytic Formal 1,4-Allylation of β,γ-Unsaturated α-Ketoesters: Allylboration/Oxy-Cope Rearrangement.

A highly enantioselective formal conjugate allyl addition of allylboronic acids to β,γ-unsaturated α-ketoesters has been realized by employing a chiral NiII /N,N'-dioxide complex as the catalyst. This transformation proceeds by an allylboration/oxy-Cope rearrangement sequence, providing a facile and rapid route to γ-allyl-α-ketoesters with moderate to good yields (65-92 %) and excellent ee values (90-99 % ee). The isolation of 1,2-allylboration products provided insight into the mechanism of the subsequent oxy-Cope rearrangement reaction: substrate-induced chiral transfer and a chiral Lewis acid accelerated process. Based on the experimental investigations and DFT calculations, a rare boatlike transition-state model is proposed as the origin of high chirality transfer during the oxy-Cope rearrangement.

Tandem Chiral Cu(II) Phosphate‐Catalyzed Deoxygenation of Nitrones/Enantioselective Povarov Reaction with Enecarbamates

A new catalytic enantioselective tandem deoxygenation/aza‐Diels‐Alder reaction of nitrones with enecarbamates was serendipitously discovered in the presence of chiral copper(II) diphosphate complexes. This process affords a wide range of 4‐aminotetrahydroquinolines in respectable yields under mild conditions with good to excellent ee values.

Biosynthesis of D-danshensu from L-DOPA using engineered Escherichia coli whole cells.

D-Danshensu (D-DSS), a traditional Chinese medicine, is used to treat cardiovascular and cerebrovascular diseases. However, current isolation protocols for D-DSS both natural and synthetic are not ideal; therefore, in this study, we have developed a whole-cell biotransformation method to produce D-DSS from L-DOPA. This was done by co-expressing L-amino acid deaminase (aadL), D-lactate dehydrogenase (ldhD), and glucose dehydrogenase (gdh). To begin to optimize the production of D-DSS, varying copy number plasmids were used to express each of the required genes. The resulting strain, Escherichia coli ALG7, which strongly overexpressed aadL, ldhD, and weakly overexpressed gdh, yielded a 378% increase in D-DSS production compared to E. coli ALG1. Furthermore, the optimal reaction conditions for the production of D-DSS were found to be a pH of 7.5, temperature at 35°C, and 50g/L wet cells for 12h. Under these optimized conditions, the D-DSS amount achieved 119.1mM with an excellent ee (> 99.9%) and a productivity of 9.9mM/h.

Switchable Skeletal Rearrangement of Dihydroisobenzofuran Acetals with Indoles.

The switchable skeletal rearrangement for the construction of amino indanones and tetrahydroisoquinolones frameworks had been developed. In the presence of a chiral phosphoric acid catalyst, the reaction gave the amino indanones in high yields and good to excellent ee (85-98%), while the methoxyl substituent at the 5-position of dihydroisobenzofuran acetal selectively gave isoquinolinones products in good to excellent ee (46-98%). Furthermore, DFT calculations were performed to explain the regioselectivity of the switchable transformation pathways.

Production of enantiomerically pure (S)-phenyl(pyridin-2-yl)methanol with Lactobacillus paracasei BD101

Asymmetric reduction studies of heteroaryl ketones, including phenyl(pyridin-2-yl)methanone in enantioselective form with biocatalysts are very few, and chiral heteroaryl alcohols have been synthesized generally in the small scale. In this study, seven bacterial strains have been used to produce the (S)-phenyl(pyridin-2-yl)methanol in high enantiomeric excess and yield. Among the tested strains, Lactobacillus paracasei BD101, was found to be the best biocatalyst for the reducing phenyl(pyridin-2-yl)methanone to the (S)-phenyl(pyridin-2-yl)methanol at gram scale. The asymmetric bioreduction conditions were systematically optimized using L. paracasei BD101, which demonstrated excellent enantioselectivity and high level of conversion for the bioreduction reaction. (S)-phenyl(pyridin-2-yl)methanol, which is an analgesic, was produced enantiomerically pure form in the first time on gram scale using a biocatalyst. In total, 5.857 g of (S)-phenyl(pyridin-2-yl)methanol in enantiomerically pure form (>99% enantiomeric excess) was obtained in 52 h with 93% yield using whole cells of L. paracasei BD101. Enantiomerically pure (S)-phenyl (pyridin-2-yl)methanol, which is an analgesic, was first produced in the gram scale using a biocatalyst with excellent ee (>99%) and yield (93%).

Axially Chiral Cyclic Phosphoric Acid Enabled Enantioselective Sequential Additions.

Efficient axially chiral cyclic phosphoric acid catalyzed enantioselective sequential additions of 2-aryl-3 H-indol-3-ones, aldehydes, and diethyl 2-aminomalonate have been developed, and a new type of nitrogen-containing heterocyclic compounds, 2,3-dihydro-1 H-imidazo[1,5- a]indol-9(9a H)-one derivatives, were prepared in good yields and excellent ee values with a wide functional group tolerance, in which the reactivity and enantioselectivity of the substrates were enabled by our newly developed axially chiral cyclic phosphoric acid, ( R)-CYC-9-CPA. Furthermore, the corresponding 1 H-imidazo[1,5- a]indol-9(9a H)-ones were constructed through the easy oxidation of 2,3-dihydro-1 H-imidazo[1,5- a]indol-9(9a H)-one derivatives.

Kinetic Resolution and Dynamic Kinetic Resolution of Chromene by Rhodium-Catalyzed Asymmetric Hydroarylation.

A highly efficient kinetic resolution and dynamic kinetic resolution of chromene is reported for the first time and they procced by a rhodium-catalyzed asymmetric hydroarylation pathway. This new approach offers versatile access to various chiral 2,3-diaryl-chromanes containing vicinal stereogenic centers, as well as the recovered chiral flavenes, in high yields with excellent ee values (s factor up to 532). Particularly noteworthy is that this strategy can be further extended to the establishment of a dynamic version of the kinetic resolution of chromene acetals and allows complete access to chiral isoflavanes and α-aryl hydrocoumarins.

Kinetic Resolution and Dynamic Kinetic Resolution of Chromene by Rhodium‐Catalyzed Asymmetric Hydroarylation

AbstractA highly efficient kinetic resolution and dynamic kinetic resolution of chromene is reported for the first time and they procced by a rhodium‐catalyzed asymmetric hydroarylation pathway. This new approach offers versatile access to various chiral 2,3‐diaryl‐chromanes containing vicinal stereogenic centers, as well as the recovered chiral flavenes, in high yields with excellent ee values (s factor up to 532). Particularly noteworthy is that this strategy can be further extended to the establishment of a dynamic version of the kinetic resolution of chromene acetals and allows complete access to chiral isoflavanes and α‐aryl hydrocoumarins.