LAUSR

Olean is the chiral spiroacetal sex pheromone of the female olive fruit fly Bactrocera oleae. Laboratory tests have demonstrated that the (R)-(-)-olean enantiomer is active on males, whereas females respond to (S)-(+)-olean. Here we present the first HPLC enantioseparation of olean using polysaccharide derivatives as chiral stationary phases and a polarimetric detector equipped with a micro-flow cell capable of detecting optical rotation at six different wavelengths. Unlike blind UV detection, the polarimetric detector allows the chiral spiroacetal, which lacks a chromophore, to be detected as bisegnate peaks, indicating the opposite sign of the optical rotation. The HPLC enantioseparation was optimized on the coated type amylose-based Chiralpak AS-H CSP using a mobile phase consisting of n-hexane-2-propanol 99.99:0.01 (v/v). These conditions were scaled up to a semi-preparative level and allowed resolution of 2.5 mg of racemic sample in 5 min. Multiwavelength optical rotation detection during HPLC enantioseparation of racemic samples provides a direct readout of the stereochemistry of olean and allows tracking of virtual optical rotation dispersion curves without the need for preliminary collection of enantiomeric samples by semi-preparative HPLC.