Study on the racemization of synephrine by off-column chiral high-performance liquid chromatography.
In this study, the racemization kinetic parameters of R-(-)-synephrine, the active phenethylamine alkaloid of Citrus aurantium L., were determined by means of an off-column HPLC method. Enantioseparation was carried out in different buffer solutions and solvents on a chiral stationary phase (CSP) with cellobiohydrolase as the chiral selector (Chiral-CBH, 100 mm x 4.0 mm i.d., 5 microm). The mobile phase was 10 mM sodium phosphate buffer (pH 6.0)-2-propanol (95:5, w/w), with 50 microM disodium EDTA, at 0.8 mL/min. The column was thermostatted at 20 degrees C and detection was set at 225 nm. The influence of pH value, ionic strength, temperature and addition of organic modifier on the rate constant, the half-life of racemization and the free energy barrier of racemization of R-(-)-synephrine were determined. Among the different chemical and physical parameters evaluated as affecting the racemization of naturally occurring R-(-)-synephrine, pH, temperature and addition of an organic co-solvent appear to have the strongest effect, while ionic strength does not exert a significant influence on the racemization rate. The results of the present study indicated that synephrine racemization is possible at high temperature at both acidic and basic pH values; therefore, the extraction procedure of R-(-)-synephrine from the plant material should be carried out under specific conditions to preserve the stereochemical integrity and the biological activity of this secondary metabolite.
Pellati
Federica
F
Department of Pharmaceutical Sciences, University of Modena and Reggio Emilia, Via G. Campi 183, 41100 Modena, Italy. federica.pellati@unimore.it
Cannazza
Giuseppe
G
Benvenuti
Stefania
S
D043366:Cellulose 1,4-beta-Cellobiosidase / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002957:Citrus / Q000737:chemistry; D000431:Ethanol / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D013237:Stereoisomerism; D013578:Synephrine / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
D000431:Ethanol; D043366:Cellulose 1,4-beta-Cellobiosidase; D013578:Synephrine