Main content area

Study on the racemization of synephrine by off-column chiral high-performance liquid chromatography

Pellati, Federica, Cannazza, Giuseppe, Benvenuti, Stefania
Journal of chromatography 2010 v.1217 no.21 pp. 3503-3510
Citrus aurantium, EDTA (chelating agent), bioactive properties, cellulose 1,4-beta-cellobiosidase, energy, half life, high performance liquid chromatography, ionic strength, pH, phenethylamine, secondary metabolites, sodium phosphate, solvents, temperature
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, 100mm×4.0mm i.d., 5μm). The mobile phase was 10mM sodium phosphate buffer (pH 6.0)-2-propanol (95:5, w/w), with 50μM disodium EDTA, at 0.8mL/min. The column was thermostatted at 20°C and detection was set at 225nm. 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.