Lipase mediated sequential resolution of aromatic β-hydroxy esters using fatty acid derivatives

Chemoenzymatic Synthesis of Optically Active Alcohols Possessing 1,2,3,4-Tetrahydroquinoline Moiety Employing Lipases or Variants of the Acyltransferase from Mycobacterium smegmatis

The enzymatic kinetic resolution (EKR) of racemic alcohols or esters is a broadly recognized methodology for the preparation of these compounds in optically active form. Although EKR approaches have been developed for the enantioselective transesterification of a vast number of secondary alcohols or hydrolysis of their respective esters, to date, there is no report of bio- or chemo-catalytic asymmetric synthesis of non-racemic alcohols possessing 1,2,3,4-tetrahydroquinoline moiety, which are valuable building blocks for the pharmaceutical industry. In this work, the kinetic resolution of a set of racemic 1,2,3,4-tetrahydroquinoline-propan-2-ols was successfully carried out in neat organic solvents (in the case of CAL-B and BCL) or in water (in the case of MsAcT single variants) using immobilized lipases from Candida antarctica type B (CAL-B) and Burkholderia cepacia (BCL) or engineered acyltransferase variants from Mycobacterium smegmatis (MsAcT) as the biocatalysts and vinyl acetate as irreversible acyl donor, yielding enantiomerically enriched (S)-alcohols and the corresponding (R)-acetates with E-values up to 328 and excellent optical purities (>99% ee). In general, higher ee-values were observed in the reactions catalyzed by lipases; however, the rates of the reactions were significantly better in the case of MsAcT-catalyzed enantioselective transesterifications. Interestingly, we have experimentally proved that enantiomerically enriched 1-(7-nitro-3,4-dihydroquinolin-1(2H)-yl)propan-2-ol undergoes spontaneous amplification of optical purity under achiral chromatographic conditions.

Enantioselective Synthesis of 3-Aryl-3-hydroxypropanoic Esters as Subunits for Chiral Liquid Crystals

Chiral liquid crystals (LCs) with their unique optical and mechanical properties are perspective functional soft materials for fundamental science and advanced technological applications. Herein, we introduce the chiral 3-aryl-3-hydroxypropanoic ester moiety as a versatile building block for the preparation of LC compounds. Three chiral subunits differing in the aromatic part were obtained through asymmetric transfer hydrogenation using Ru(II) complexes with ee from 98% to >99%. Chiral LC compounds of diverse topologies were further prepared without deterioration of the ee during the synthesis. The mesomorphic behavior of rod-shaped, bent-shaped flexible dimeric, and polycatenar LCs is consistent with their topology─chiral nematic and smectic phases were identified as well as the rarely observed twist grain boundary A and blue phases. The utilization of synthetic chiral building blocks offers the possibility of fine tuning the intermolecular interactions by subtle changes in the molecular structure as well as the preparation of the corresponding racemic forms. This paves the way for the study of self-organization and the structure-property relationship in chiral soft materials.

Evaluation of a new protocol for enzymatic dynamic kinetic resolution of 3-hydroxy-3-(aryl)propanoic acids

The application of tandem metal–enzyme dynamic kinetic resolution (DKR) is a powerful tool for the manufacture of high-value chemical commodities.

Access to optically pure β-hydroxy esters via non-enzymatic kinetic resolution by a planar-chiral DMAP catalyst

The development of new approaches to obtain optically pure β-hydroxy esters is an important area in synthetic organic chemistry since they are precursors of other high value compounds. Herein, the kinetic resolution of racemic β-hydroxy esters using a planar-chiral DMAP derivative catalyst is presented. Following this procedure, a range of aromatic β-hydroxy esters was obtained in excellent selectivities (up to s = 107) and high enantiomeric excess (up to 99% ee). Furthermore, the utility of the present method was demonstrated in the synthesis of (S)-3-hydroxy-N-methyl-3-phenylpropanamide, a key intermediate for bioactive molecules such as fluoxetine, tomoxetine or nisoxetine, in its enantiomerically pure form.