Crownpak CR Research Articles

Excitatory amino acid receptor antagonists: Resolution, absolute stereochemistry, and pharmacology of (S)‐ and (R)‐2‐amino‐2‐(5‐tert‐butyl‐3‐hydroxyisoxazol‐4‐yl)acetic acid (ATAA)

We have previously shown that (RS)-2-amino-2-(5-tert-butyl-3-hydroxyisoxazol-4-yl)acetic acid (ATAA) is an antagonist at N-methyl-D-aspartic acid (NMDA) and (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors. We have now resolved ATAA via diastereomeric salt formation using N-BOC protected ATAA and (R)- and (S)-phenylethylamine. Enantiomeric purities (ee > 98%) of (R)- and (S)-ATAA were determined using the Crownpak CR(−) and CR(+) columns, respectively. The absolute configuration of (R)-ATAA was established by an X-ray crystallographic analysis of the (R)-phenylethylamine salt of N-BOC-(R)-ATAA. Like ATAA, neither (R)- nor (S)-ATAA significantly affected (IC50 > 100 μM) the receptor binding of tritiated AMPA, kainic acid, or (RS)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, the latter being a competitive NMDA antagonist. Electrophysiological experiments, using the rat cortical wedge preparation, showed the NMDA antagonist effect as well as the AMPA antagonist effect of ATAA to reside exclusively in the (R)-enantiomer (Ki = 75 ± 5 μM and 57 ± 1 μM, respectively). Neither (R)- nor (S)-ATAA significantly reduced kainic acid-induced excitation (Ki > 1,000 μM). Chirality 9:529–536, 1997. © 1997 Wiley-Liss, Inc.

Excitatory amino acid receptor antagonists: resolution, absolute stereochemistry, and pharmacology of (S)- and (R)-2-amino-2-(5-tert-butyl-3-hydroxyisoxazol-4-yl)acetic acid (ATAA).

We have previously shown that (RS)-2-amino-2-(5-tert-butyl-3-hydroxyisoxazol-4-yl)acetic acid (ATAA) is an antagonist at N-methyl-D-aspartic acid (NMDA) and (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors. We have now resolved ATAA via diastereomeric salt formation using N-BOC protected ATAA and (R)- and (S)-phenylethylamine. Enantiomeric purities (ee > 98%) of (R)- and (S)-ATAA were determined using the Crownpak CR(-) and CR(+) columns, respectively. The absolute configuration of (R)-ATAA was established by an X-ray crystallographic analysis of the (R)-phenylethylamine salt of N-BOC-(R)-ATAA. Like ATAA, neither (R)- nor (S)-ATAA significantly affected (IC50 > 100 microM) the receptor binding of tritiated AMPA, kainic acid, or (RS)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid, the latter being a competitive NMDA antagonist. Electrophysiological experiments, using the rat cortical wedge preparation, showed the NMDA antagonist effect as well as the AMPA antagonist effect of ATAA to reside exclusively in the (R)-enantiomer (Ki = 75 +/- 5 microM and 57 +/- 1 microM, respectively). Neither (R)- nor (S)-ATAA significantly reduced kainic acid-induced excitation (Ki > 1,000 microM).

Development and validation of chiral high-performance liquid chromatographic methods for the quantitation of valsartan and of the tosylate of valinebenzyl ester.

A stereospecific HPLC method for the quantitation of CGP 49309 in samples of its corresponding enantiomer valsartan has been developed and validated. The enantiomeric separation was achieved on a 5 micron silica-bonded, alpha 1-acid glycoprotein column (Chiral AGP) with a phosphate buffer, pH 7, containing 2% (v/v) 2-propanol as a mobile phase. The linearity was established in the range 0.1-4% (r > 0.999). The limit of quantitation was 0.1% and the limit of detection was 0.04%. The accuracy of the method was found to be 96.7% (average). For the precision (repeatability), a relative standard deviation value of 2.4% was found. Similarly, a stereoselective HPLC method was also developed and validated for the quantitation of the enantiomer of the starting material used for the synthesis of valsartan, namely (R)-valinebenzyl ester tosylate. Baseline resolution of the enantiomers of valinebenzyl ester tosylate could be achieved on the chiral crown ether column Crownpak CR (Daicel) at 50 degrees C using water-methanol-trifluoroacetic acid (850:150:1, v/v) as a mobile phase. The linearity was established in the range 0.5-5% (r > 0.999). The accuracy of the method was found to be 100.5% (average). For the precision (repeatability), a relative standard deviation value of 3.4% was found. Both methods were found to be suitable for the analysis of the respective analytes.

Direct separation of tranylcypromine enantiomers and their profile in an atypical depressive patient.

An isocratic and simple high-performance liquid chromatographic method is developed for the direct resolution of the tranylcypromine (TCP) enantiomers. The method involves the use of an S-18-crown-6-ether chiral stationary phase known as the Crownpak CR (+) column. The stereochemical separation factor (alpha) obtained was 1.30 and the stereochemical resolution factor (Rs) was 0.69 when using a mobile phase consisting of 0.1 N perchloric acid containing 12% methanol at 23 degrees C. The method has been used to monitor and identify, qualitatively, the profile of enantiomers of TCP in urine of an atypical depressive patient. It was found that the (-)-S-TCP concentration is significantly higher than the (+)-R-enantiomer.

HPLC Chiral Optimization of a Unique β-Amino Acid and Its Ester

Abstract Enantiomeric optimization of a unique s-amino acid (s-amino-3-pyridylpropionic acid) and its ethyl ester was achieved with a Daicel Crownpak CR (+) column requiring no derivatization. Using this column, the pH of the mobile phase was adjusted with perchloric acid and studied to determine the optimum pH. A plot of the capacity factor as a function of pH for the amines showed the critical pH required for chiral recognition. From this data, the retention of the amines shift from a hydrophobic non-enantioselective retention mechanism (pH > 2) to complex formation between the crown ether and the amines causing enantioselectivity (pH ≤ 2). At pH 1, lowering the column temperature from ambient to sub-ambient temperatures caused increased retention and enantiomeric separation of the amines. At pH 1 and a column temperature of ∼7°C, concurrent enantiomeric baseline resolution (Rs > 1.5) of the s-amino acid and ester was achieved. The addition of methanol under these conditions caused a decrease in retenti...

Direct Chiral Liquid Chromatographic Separation of Tocainide Enantiomers on a Crownpak (Cr) Column and its Application to Pharmaceutical Formulations and Biological Fluids

Abstract Direct chiral liquid chromatographic resolution of racemic tocainide was accomplished without any derivatization using a crownpak CR(+) column as a chiral stationary phase. The stereochemical resolution (R) with symmetrical peaks was 0.97 and a separation factor (α) of 1.44 were obtained. Optimization of separation was achieved using different concentrations of perchloric acid.