Search Results

You are looking at 1 - 10 of 19 items for :

  • "Racemates" x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All

Abstract  

It is shown from experiments on leucine, that is possible to obtain pure enantiomer tracers of amino acids by using radioactive racemates only. The resolution takes place in a single crystallization step after mixing the active racemate with the inactive enantiomer, due to an absolute stereoselection.

Restricted access

Resolution of racemic metoprolol, propranolol, carvedilol, bisoprolol, salbutamol, and labetalol, commonly used β-blockers, into their enantiomers has been achieved by TLC on silica gel plates impregnated with optically pure L -Glu and L -Asp. Acetonitrile-methanol-water-dichloromethane and acetonitrile-methanol-water-glacial acetic acid mobile phases in different proportions enabled successful separation. The spots were detected with iodine vapor. The detection limits were 0.23, 0.1, 0.27, 0.25, 0.2, and 0.2 μg for each enantiomer of metoprolol, propranolol, carvedilol, bisoprolol, salbutamol, and labetalol, respectively.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: A. Sykuła-Zając, E. Łodyga-Chruścińska, B. Pałecz, R. E. Dinnebier, U. J. Griesser, and V. Niederwanger

Molecular formula of bupivacaine hydrochloride (C 18 H 28 N 2 O·HCl, H 2 O, 342.99 g mol −1 ) The drug is still clinically available as a racemate which consists of “left-handed” S (−)- and “right-handed” R (+)- [ 3

Open access

Abstract  

The physicochemical characterization of the solid-state enantiomers and racemate of efaroxan hydrochloride (C13H17N2O+Cl-, M=252.5 g mol-1) was performed by thermoanalytical methods (differential scanning calorimetry, thermogravimetry and thermomicroscopy) and spectral methods (infrared spectrometry and X-ray diffractometry). The efaroxan enantiomers and racemate were shown to be unstable near the melting point. At the beginning of the decomposition, a loss of hydrogen chloride was observed. However when sealed pans were used, the compounds decomposed at higher temperature, allowing a precise evaluation of the melting enthalpies by means of differential scanning calorimetry. The nature of the racemate and its thermal stability were assessed by evaluating its free formation enthalpy. An enantiotropic solid-solid transformation (II→I) was noted for the racemate; the reverse process (I→II) follows zero-order kinetics.

Restricted access

Racemic compound formation-conglomerate formation

Part 4. Optical resolution and determination of the melting phase diagrams of 2′,6′-pipecoloxylidide and four 1-alkyl-2′,6′-pipecoloxylidides

Journal of Thermal Analysis and Calorimetry
Authors: Katalin Nemák, Mária Ács, D. Kozma, and E. Fogassy

The phenomena of conglomerate formation-racemic compound formation were investigated in a series of five (N-alkyl)-2′,6′-pipecoloxylidides. The optically active enantiomers were prepared by optical resolution of the racemates using 2R,3R-tartaric acid and 0,0′-dibenzoyl-2R,3R-tartaric acid as resolving agent. By DSC measurement of the racemates and the enantiomer the binary phase diagrams were determined.

Restricted access

The scientific development in the area of enantioseparation during the last few decades has centered on the production of new chiral stationary phases (CSPs) and new chiral derivatizing reagents (CDRs) for use in liquid chromatography, and in particular high-performance liquid chromatography (HPLC) only. Both CSPs and CDRs have several limitations which, in general, are ignored. Little attention has been paid to thin-layer chromatography (TLC) despite its many advantages compared to HPLC in pharmaceutical and drug analysis and the areas of natural products chemistry and organic synthesis, particularly enantioselective synthesis in purification of the product prior to establishing enantiomeric ratio by different method(s). TLC provides a rapid, easy, aff ordable, and simple approach in all these situations. The demonstrated capability and effi- ciency of TLC in direct resolution of the racemate clearly establish its superiority, and the methodology should allow its application in the resolution of several other racemates, irrespective of the functional group, in a very short time along with the recovery of native enantiomers (for further use).

Restricted access

Abstract  

There is no statistically significant difference in the response of the enantiomers and the racemate of -alanine to -radiation (60Co) and accelerated electrons (10 MeV). The response was measured by the yield of ammonia, one of the separated final products of solid alanine radiolysis and the concentration of free radical CH3·CH·COO, the intermediate product of radiolysis. Some of the properties of the racemate may affect the precision of measurements. TheDL-alanine shows different crystal structure, morphology of crystals, specific density and bulk density than the enantiomers. The response ofL andDL alanines built into composites may be different because of different reactivity of the enantiomer and the racemate with components during the processing and irradiation.

Restricted access

Abstract  

The 4-nitrobenzyl ester of acetylphenylhydroxyacetic acid differs in its melting behaviour from other nitrobenzyl esters of phenylhydroxyacetic or acetylphenylhydroxyacetic acids, the racemate having a higher melting point than the enantiomers. By means of thermal analysis, IR spectroscopy and X-ray diffractometry the ester can be shown to occur in two crystalline modifications. In the process of solidification of the molten mass, at first a modification of higher energy is formed, obviously being caused by an excess of one enantiomer, which is then exothermally rearranged in the lattice of the racemate.

Restricted access

Enantioresolution of three active pharmaceutical ingredients (APIs), namely, atenolol, betaxolol, and orciprenaline, marketed as racemic mixture, has been achieved in a direct mode using (S)-glutamic acid as chiral additive in thin-layer chromatography. Two different approaches were adopted: (1) (S)-glutamic acid was mixed in the silica gel slurry for making thin-layer plates, or (2) it was added in the mobile phase and plain plates without any chiral additive were used. Both (1) and (2) were capable of separating enantiomers of all the three racemates, but different combinations and proportions of solvents were found successful in the two cases. Good resolution was achieved in both cases, and the results are compared for these two sets of studies among themselves and with other literature reports. Iodine was used to locate the spots of the corresponding enantiomers. The detection limits for each enantiomer were found in the range of 1.4–1.9 μg (per spot).

Restricted access

Abstract  

The gelation of a powder coating and its matrix based on a saturated carboxyl functional polyester resin and triglycidyl isocyanurate of different diastereomer racemate composition was investigated by rotational viscometry. The iso-T cure diagrams have been determined directly by isothermal viscometric measurements and the gelation curves for the TTT-diagram have been constructed. To the measured section of the gelation curves power functions could be fitted and with their help the reactivity of the investigated systems were compared. The ratio of the two diastereomer racemates of TGIC has a significant effect on the reactivity of the coating, as it was also supported by DSC measurements. β-TGIC is of highest reactivity, and by increasing its ratio in TGIC, reactivity increases, and adversely effects the performance of the powder coating. Commercial TGIC-s have similar reactivity, comparable to that of high α-TGIC. The reactivity of the matrix is higher than that of the powder.

Restricted access