Direct chromatographic resolution and isolation of the four stereoisomers of meta -hydroxyphenylpropanolamine

Methods for the direct chiral chromatographic separation of the four stereoisomers of meta -hydroxyphenylpropanolamine (MHPA) on an analytical and preparative scale are described. Separations were carried out on a Crownpak CR (+) chiral column with 113 mM aqueous perchloric acid as the mobile phase. Baseline resolution of the more retained (+)-stereoisomers (1S configuration) and partial resolution of the less retained (−)-stereoisomers (1R configuration) were obtained under these chromatographic conditions. Removal of the bulk of the (1R,2S)-stereoisomer (metaraminol) from the initial crude mixture by fractional crystallization as the (+)-bitartarate salt substantially improved the peak resolution factors (Rs) of the remaining three stereoisomers. Semipreparative chromatographic resolution of the latter isomeric mixture provided milligram quantities of each stereoisomer in >97% enantiomeric excess. Subsequent recrystallization of their bitartarate or fumarate salts gave enantiomeric purities >99%. Chirality 11:684–688, 1999. © 1999 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35056/1/3_ftp.pd

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered

Stereoselective adsorption and trans-membrane transfer of propranolol enantiomers using cellulose derivatives

Cellulose tris(phenyl carbamate), cellulose tris(3,5-dimethylphenyl carbamate) and cellulose tris(3,5-dichlorophenylcarbamate), which are known for their ability to resolve enantiomers when used as chromatographic stationary phases, were examined in terms of their ability to adsorb differentially the enantiomers of propranolol hydrochloride and consequent differential transfer when used as excipients in aqueous donor vehicles. Over a range of conditions investigated, optimum stereospecificity was found at pH 7.4, an incubation temperature of 32°C and propranolol concentration of 1 mgml−1 with 1 mg adsorbent. The ratios of S/R bound was 1.35, 2.65 and 2.31, respectively. The permeation rates of propranolol enantiomers were determined through Silastic membrane in the presence and absence of vehicular cellulose tris(3,5-dimethylphenyl carbamate) and cellulose tris(3,5-dichlorophenyl carbamate). When pure propranolol enantiomers were used, permeation rates of propranolol enantiomers were significantly different, both numerically and statistically (steady-state flux ratios, R/S = 1.70 and 1.68; P = 0.03 and 0.001, respectively). In the absence of adsorbent permeation rates were not significantly different. When racemic propranolol was used, the flux ratios were less, but still of statistical and numerical significance (steady-state flux ratios, R/S 1.14 and 1.14; P = 0.04 and 0.01, respectively) considering the differential activities of propranolol enantiomers. These results demonstrate the potential of enantioselective retardation in transmembrane transfer as an alternative methodology for administering single enantiomers

Direct resolution of propranolol and bupranolol by thin-layer chromatography using cellulose derivatives as stationary phase

Cellulose triphenylcarbamate derivatives have been used as stationary phases for resolution of the enantiomers of the β-blockers propranolol and bupranolol by TLC. The derivatives examined were: cellulose trisphenylacarbamate (1), cellulose tris(2,3-dichlorophenyl carbamate) (2), cellulose tris(2,4-dichlorophenyl carbamate) (3), cellulose tris(2,6-dichlorophenyl carbamate) (4), cellulose tris (2,3-dimethylphenyl carbamate) (5), cellulose tris(3,4-dichlorophenyl carbamate) (6), cellulose tris(3,5-dichlorophenyl carbamate) (7), and cellulose tris(3,5-dimethylphenyl carbamate) (8). A variety of mobile phases were used to achieve useful separations and the effects of solvent polarity are also discussed. The best resolution of rac-propranolol was obtained on CSP 8 (RfR = 0.26, RfS = 0.06, α = 4.33) in mobile phase hexane:propan-2-ol (80:20 v/v). The best resolution of rac-bupranolol was obtained on CSP 5 (RfR = 0.29, RfS = 0.09, α = 3.22) in mobile phase hexane:propan-2-ol (80:20 v/v). These results demonstrated the potential of cellulose triphenylcarbamates as chiral stationary phases in TLC and indicate that this is potentially a useful method for the direct, simple, and rapid (within 30 min) resolution of racemates in the analytical control of enantiomeric purity. Physical aspects such as problems in cracking of the CSP, adhesion to plate, and interference of spot detection due to triphenylcarbamate chromphores are also discussed, along with the method employed to overcome them