Enantioseparation of a few commonly administered racemic β-adrenolytics (namely, carvedilol, betaxolol, salbutamol and bisoprolol) has been achieved using a water micellar mobile phase containing surfactants (sodium dodecyl sulphate and Brij-35) without organic solvents as a new approach in RP-HPLC. Two chiral derivatizing reagents based on enantiomerically pure (S)-(-)-levofloxacin were synthesized using N-hydroxysuccinimide and N-hydroxybenzotriazole as the activation auxiliaries. Diastereomeric derivatives of the chosen β-adrenolytics were synthesized under microwave irradiation in a very short reaction time. The (S)-(-)-levofloxacin moiety enhanced molar absorbance of the diastereomeric derivatives resulting in very low limit of detection (1.618 and 4.902 ng/mL, respectively, for diastereomeric derivatives of (RS)-betaxolol and better resolution with lower retention times (for all the analytes), in comparison to literature reports. There was 15-20 times less consumption of mobile phase because of lower retention time.
Developing surfactant-based
aqueous solvents as alternatives to
organic solvents for chromatographic enantioseparation is highly desired.
Surfactants are inexpensive, nontoxic, environmental friendly, and
increase the solubility of organic compounds in aqueous solutions.
In this work, the impact of surfactant-based aqueous solvents on RP-HPLC
enantioseparation of (RS)-mexiletine is studied.
The in situ derivatization of (RS)-mexiletine with
chirally pure moieties [(S)-levofloxacin, (S)-ketoprofen, (S)-ibuprofen)] was carried
out/performed to reduce consumption of organic solvents and side wastes,
and to maintain a green approach. We report the impact of increasing
concentration of surfactants on separation of diastereomeric derivatives
of (RS)-mexiletine on a C18 column of
HPLC. Surfactant in water increased the solubility of a diastereomeric
derivative, provided the lowest elution time (t
R between 2.152 and 10.87 min), and minimized the consumption
of solvent. The use of surfactant-containing aqueous mobile phases
in chromatographic separations is a good alternative for replacement
of organic solvents. The hydrolysis of the synthesized diastereomeric
derivatives was carried out, and native enantiomers of mexiletine
were isolated and characterized. In addition, the lowest-energy optimized
structures were developed using the Gaussian 09 Rev. A.02 program
for determination of elution order, and the method was validated for
linearity, accuracy, limit of detection (LOD), and limit of quantitation
(LOQ).
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