HPLC with polysaccharide chiral stationary phase in polar-organic phase mode: application to the asymmetric epoxidation of allylic alcohols.

A simple and rapid HPLC method using a polysaccharide-based chiral stationary phase (Chiralpak AD-H) in polar-organic phase mode has been developed for direct resolution of glycidyl nitrobenzoate (GNB) and 2-methyl glycidyl nitrobenzoate (MGNB) enantiomers. ACN and methanol were used as mobile phase and the effects of the addition of ethanol and 2-propanol as organic modifier in the mobile phase, flow rate and the column temperature were tested. The optimized conditions were: methanol/ethanol (80:20) at a flow rate of 0.9 mL/min and 40 degrees C. Analysis time was < or = 13 min and the chiral resolution was > or = 2. The method was validated and resulted to be selective, precise and accurate. The method was found to be linear in 2-300 microg/mL range (R(2) >0.999) with an LOD nearly 0.5 microg/mL for four enantiomers. GNB and MGNB enantiomers were obtained by asymmetric epoxidation of allyl alcohol and 2-methyl allyl alcohol, respectively, using chiral titanium-tartrate complexes as catalyst and dichloromethane as solvent after in situ derivatization of the intermediate glycidols derivatives. The quite simple and rapid validated method was applied successfully for direct determination of the enantiomeric excess (> or = 90%) and yield obtained in real samples of asymmetric epoxidation of allylic alcohols without further purification, workup or solvent removal. The method provides a useful and value-added tool for controlling the enantiomeric purity of the synthesized epoxides.