Asymmetric Synthesis of N-Substituted 1,2-Amino Alcohols from Simple Aldehydes and Amines by One-Pot Sequential Enzymatic Hydroxymethylation and Asymmetric Reductive Amination.

The chiral N-substituted 1,2-amino alcohol motif is found in many natural and synthetic bioactive compounds. In this study, enzymatic asymmetric reductive amination of α-hydroxymethyl ketones with enantiocomplementary imine reductases (IREDs) enabled the synthesis of chiral N-substituted 1,2-amino alcohols with excellent ee values (91-99 %) in moderate to high yields (41-84 %). Furthermore, a one-pot, two-step enzymatic process involving benzaldehyde lyase-catalyzed hydroxymethylation of aldehydes and subsequent asymmetric reductive amination was developed, offering an environmentally friendly and economical way to produce N-substituted 1,2-amino alcohols from readily available simple aldehydes and amines. This methodology was then applied to rapidly access a key synthetic intermediate of anti-malaria and cytotoxic tetrahydroquinoline alkaloids.

Asymmetric Synthesis of N-Substituted α-Amino Esters from α-Ketoesters via Imine Reductase-Catalyzed Reductive Amination.

N-Substituted α-amino esters are widely used as chiral intermediates in a range of pharmaceuticals. Here we report the enantioselective biocatalyic synthesis of N-substituted α-amino esters through the direct reductive coupling of α-ketoesters and amines employing sequence diverse metagenomic imine reductases (IREDs). Both enantiomers of N-substituted α-amino esters were obtained with high conversion and excellent enantioselectivity under mild reaction conditions. In addition >20 different preparative scale transformations were performed highlighting the scalability of this system.

Engineered Imine Reductase for Asymmetric Synthesis of Dextromethorphan Key Intermediate.

(S)-1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline ((S)-1-(4-methoxybenzyl)-OHIQ) is the key intermediate of the nonopioid antitussive dextromethorphan. In this study, (S)-IR61-V69Y/P123A/W179G/F182I/L212V (M4) was identified with a 766-fold improvement in catalytic efficiency compared with wide-type IR61 through enzyme engineering. M4 could completely convert 200 mM of 1-(4-methoxybenzyl)-3,4,5,6,7,8-hexahydroisoquinoline into (S)-1-(4-methoxybenzyl)-OHIQ in 77% isolated yield, with >99% enantiomeric excess and a high space-time yield of 542 g L-1 day-1, demonstrating a great potential for the synthesis of dextromethorphan intermediate in industrial applications.

Enantiodivergent Synthesis of 1-Heteroaryl Tetrahydroisoquinolines Catalyzed by Imine Reductases.

Two enantiocomplementary imine reductases (IREDs) with high enantioselectivity were identified with catalytic activity toward the reduction of 1-heteroaryl dihydroisoquinolines through a screening of wild-type IREDs and enzyme engineering. Furthermore, (R)-IR141-L172M/Y267F and (S)-IR40 were applied to access a series of different 1-heteroaryl tetrahydroisoquinolines with high to excellent ee values (82 to >99%) and isolated yields (80 to 94%), thereby providing an effective method to construct this class of pharmaceutically important alkaloids, such as the intermediate of kinase inhibitor TAK-981.

Identification of Phthalates from Artificial Products in Chinese Kindergarten Classrooms and the Implications for Preschool Children's Exposure Assessments.

Phthalates are typical chemical pollutants in kindergarten classrooms since numerous artificial products (e.g., polyvinyl chloride (PVC) floorings, soft polymers and plastic toys) that might contain phthalates are widely distributed in kindergarten classrooms. Although Chinese preschool children spend a considerable amount of their waking hours (>8 h/day) in kindergartens, phthalate exposure in such indoor environment has not been given much attention. In this study, the mass fractions of six phthalates in twenty-six artificial products (fifteen flat decoration materials and eleven plastic toys) commonly found in Chinese kindergarten classrooms were measured. Di-2-ethylhexyl phthalate (DEHP) was the most predominant compound in all materials. The emission characteristics of the DEHP from these materials were further investigated. The measured emission characteristics were used for predicting multi-phase DEHP concentrations in kindergarten classrooms by applying a mass transfer model. The modeled concentrations were comparable with those measured in the real environment, indicating that these products might be the major sources of DEHP in Chinese kindergarten classrooms. Preschool children's exposure to DEHP was found to be 0.42 µg/kg/day in kindergartens under baseline conditions, accounting for 18% of the total exposure to DEHP in Chinese indoor environments.

Asymmetric Synthesis of Fused-Ring Tetrahydroisoquinolines and Tetrahydro-ß-carbolines from 2-Arylethylamines via a Chemoenzymatic Approach.

While chiral fused-ring tetrahydroisoquinoline (THIQ) and tetrahydro-ß-carboline (THßC) scaffolds have attracted considerable interest due to their wide spectrum of biological activities, the synthesis of optically pure chiral fused-ring THIQs and THßCs remains a challenging task. Herein, a group of active imine reductases were identified to convert the imine precursors into the corresponding enantiocomplementary fused-ring THIQs and THßCs with high enantioselectivity and conversion, establishing an efficient and green chemoenzymatic approach to fused-ring alkaloids from 2-arylethylamines.