Synthesis,resolution, and chiroptical properties of hemicryptophane cage controlling the chirality of propeller arrangement of a C3 triamide unit

The five‐steps synthesis of a hemicryptophane cage combining a benzene‐1,3,5‐tricarboxamide unit and a cyclotriveratrylene (CTV) moiety is described. Chiral high‐performance liquid chromatography (HPLC) was used to resolve the racemic mixture. The absolute configuration of the isolated enantiomers was assigned by comparison of the experimental electronic circular dichroism (ECD) spectra with the calculated ones. X‐ray molecular structures reveal that the capped benzene‐1,3,5‐tricarboxamide unit adopts a structurally chiral conformation in solid state: the chirality of CTV moiety controls the Λ or Δ orientation of the three amides.     

Enantiomeric impurities in chiral catalysts,auxiliaries, and synthons used in enantioselective syntheses. Part 5

The enantiomeric excess of chiral starting materials is one of the important factors determining the enantiopurity of products in asymmetric synthesis. Fifty‐one commercially available chiral reagents used as building blocks, catalysts, and auxiliaries in various enantioselective syntheses were assayed for their enantiomeric purity. The test results were classified within five impurities level (ie, <0.01%, 0.01%‐0.1%, 0.1%‐1%, 1%‐10%, >10%). Previously from 1998 to 2013, several reports have been published on the enantiomeric composition of more than 300 chiral reagents. This series of papers is necessitated by the fact that new reagents are forthcoming and that the enantiomeric purity of the same reagent can vary from batch to batch and/or from supplier to supplier. This report presents chiral liquid chromatography (LC) and gas chromatography (GC) methods to separate enantiomers of chiral compounds and evaluate their enantiomeric purities. The accurate and efficient LC analysis was done using newly introduced superficially porous particle (SPP 2.7 μm) based chiral stationary phases (TeicoShell, VancoShell, LarihcShell‐P, and NicoShell).     

Separation of ephedrine and pseudoephedrine enantiomers using a polysaccharide‐based chiral column: A normal phase liquid chromatography–high‐resolution mass spectrometry approach

Chiral considerations are found to be very much relevant in various aspects of forensic toxicology and pharmacology. In forensics, it has become increasingly important to identify the chirality of doping agents to avoid legal arguments and challenges to the analytical findings. The scope of this study was to develop an liquid chromatography–mass spectrometry (LCMS) method for the enantiomeric separation of typical illicit drugs such as ephedrines (ie, 1S,2R(+)‐ephedrine and 1R,2S(?)‐ephedrine) and pseudoephedrine (ie, R,R(?)‐pseudoephedrine and S,S(+)‐pseudoephedrine) by using normal phase chiral liquid chromatography–high‐resolution mass spectrometry technique. Results show that the Lux i‐amylose‐1 stationary phase has very broad and balancing‐enantio‐recognition properties towards ephedrine analogues, and this immobilized chiral stationary phase may offer a powerful tool for enantio‐separation of different types of pharmaceuticals in the normal phase mode. The type of mobile phase and organic modifier used appear to have dramatic influences on separation quality. Since the developed method was able to detect and separate the enantiomers at very low levels (in pico grams), this method opens easy access for the unambiguous identification of these illicit drugs and can be used for the routine screening of the biological samples in the antidoping laboratories.     

Application of force field calculations to the prediction of chirally discriminating chromatographic behaviour for β-CDs

β-Cyclodextrin and its derivatives have been utilised to effect chiral separation in HPLC and CZE, both as stationary phases and mobile phase additives. The basis of the method is assumed to depend upon the formation of inclusion complexes of differing stabilities between enantiomeric analytes and the cyclodextrin, resulting in a differential dynamic distribution between chromatographic phases. In this study, force field calculations have been employed to model the inclusion complexes of enantiomeric brompheniramine, ephedrine, pseudoephedrine, ibuprofen, mandelic acid, methylphenobarbitone, and hexobarbitone with β-cyclodextrin. The resulting values for Δ(ΔH), the difference in enthalpy of complex formation between enantiomeric pairs has been compared with literature chromatographic data to explain the ability of the systems to achieve enantiomeric separations. © 1996 Wiley-Liss, Inc.     

Unusual amino acids VI. Substituted arylamino acids by asymmetric hydrogenation of N-Cbz and N-Boc protected dehydroamino acid derivatives

Substituted N-Cbz and N-Boc protected arylamino acrylic acids and esters have been prepared and used in asymmetric hydrogenations catalyzed by PROPRAPHOSRh. Stereoselectivities > 90% ee could be achieved, the rate of which is dependent on the position of the substituent in the aromatic ring. The N-Boc derivatives provide advantages compared with the N-Cbz analogues. The amino acid derivatives were fully characterized by ¹⁹F, ¹³C, and ¹H NMR spectroscopy. © 1996 Wiley-Liss, Inc.     

Considerations about the chirality of the saturated six-membered rings with two or more heteroatoms

The chirality of the title heterocycles is discussed considering their genesis by desymmetrization of the corresponding adamantanes. Some rules for the specification of the absolute configurations of the enantiomers (R or S) for this type of compounds are proposed. © 1996 Wiley-Liss, Inc.     

Synthesis and analysis of the enantiomers of calmidazolium,and a 1H NMR demonstration of a chiral interaction with calmodulin

Calmidazolium {R24571, 1-[bis(4-chlorophenyl)methyl]-3-[2-(2,4-dichlorophenyl)-2-[(2,4-dichlorophenyl)methoxy]ethyl]-1H-imidazolium chloride} is a potent calmodulin inhibitor. This paper describes the synthesis and properties of the enantiomers of calmidazolium from the enantiomers of miconazole {1(N)-(2-(2,4-dichlorobenzyloxy)-2-(2,4-dichlorophenyl))-ethyl imidazole}, prepared from the racemate by chiral preparative scale high performance liquid chromatography. Overlap between ligand and protein resonances in the aromatic region of the ¹H NMR spectrum of the calmidazolium-calmodulin complexes has been obviated by preparation of the protein with all of its nine phenylalanine rings deuterated (Phe-d₅ calmodulin). This has been accomplished by the overexpression of calmodulin derived from Trypanosoma brucei rhodiesiense in E. coli in a medium supplemented with ring-deuterated phenylalanine. The kinetics of binding of each enantiomer are slow on the ¹H NMR time scale as judged by the behaviour of the H2 resonance of Histidine-107, which is clearly visible under the sample conditions used. The aromatic spectral regions of the protein-bound (+) and (−) enantiomers contrast strikingly, reflecting differences in bound environment and/or conformation. Chirality 8:545–500, 1996. © 1997 Wiley-Liss, Inc.     

Kinetic resolution of chiral amines with omega-transaminase using an enzyme-membrane reactor

A kinetic resolution process for the production of chiral amines was developed using an enzyme-membrane reactor (EMR) and a hollow-fiber membrane contactor with (S)-specific omega-transaminases (omega-TA) from Vibrio fluvialis JS17 and Bacillus thuringiensis JS64. The substrate solution containing racemic amine and pyruvate was recirculated through the EMR and inhibitory ketone product was selectively extracted by the membrane contactor until enantiomeric excess of (R)-amine exceeded 95%. Using the reactor set-up with flat membrane reactor (10-mL working volume), kinetic resolutions of alpha-methylbenzylamine (alpha-MBA) and 1-aminotetralin (200 mM, 50 mL) were carried out. During the operation, concentration of ketone product, i.e., acetophenone or alpha-tetralone, in a substrate reservoir was maintained below 0.1 mM, suggesting efficient removal of the inhibitory ketone by the membrane contactor. After 47 and 32.5 h of operation using 5 U/mL of enzyme, 98.0 and 95.5% ee of (R)-alpha-MBA and (R)-1-aminotetralin were obtained at 49.5 and 48.8% of conversion, respectively. A hollow-fiber membrane reactor (39-mL working volume) was used for a preparative-scale kinetic resolution of 1-aminotetralin (200 mM, 1 L). After 133 h of operation, enantiomeric excess reached 95.6% and 14.3 g of (R)-1-aminotetralin was recovered (97.4% of yield). Mathematical modeling of the EMR process including the membrane contactor was performed to evaluate the effect of residence time. The simulation results suggest that residence time should be short to maintain the concentration of the ketone product in EMR sufficiently low so as to decrease conversion per cycle and, in turn, reduce the inhibition of the omega-TA activity.     

Production of L-2,3-butanediol by a new pathway constructed in Escherichia coli

AIMS: A metabolic pathway for L-2,3-butanediol (BD) as the main product has not yet been found. To rectify this situation, we attempted to produce L-BD from diacetyl (DA) by producing simultaneous expression of diacetyl reductase (DAR) and L-2,3-butanediol dehydrogenase (BDH) using transgenic bacteria, Escherichia coli JM109/pBUD-comb. METHODS AND RESULTS: The meso-BDH of Klebsiella pneumoniae was used for its DAR activity to convert DA to L-acetoin (AC) and the L-BDH of Brevibacterium saccharolyticum was used to reduce L-AC to L-BD. The respective gene coding each enzyme was connected in tandem to the MCS of pFLAG-CTC (pBUD-comb). The divided addition of DA as a source, addition of 2% glucose, and the combination of static and shaking culture was effective for the production. CONCLUSIONS: L-BD (2200 mg l(-1)) was generated from 3000 mg l(-1) added of DA, which corresponded to a 73% conversion rate. Meso-BD as a by-product was mixed by 2% at most. SIGNIFICANCE AND IMPACT OF THE STUDY: An enzyme system for converting DA to L-BD was constructed with a view to using DA-producing bacteria in the future.     

Effective use of preparative chiral HPLC in a preclinical drug synthesis

Access to a key 3-aryl-delta-lactone intermediate in enantiopure form using preparative chiral chromatography allowed expedited preparation of an important drug discovery target. A preclinical drug discovery strategy that combines rapid route discovery with effective use of preparative chiral chromatography can result in significant savings of both time and labor.