Direct chiral separation of abscisic acid by high‐performance liquid chromatography with a phenyl column and a mobile phase containing γ‐cyclodextrin

Abscisic acid (2‐ cis ,4‐ trans ‐abscisic acid) is a plant hormone that has an asymmetric carbon atom. We tried to separate the enantiomers of native abscisic acid by HPLC using a phenyl column and a chiral mobile phase containing γ‐cyclodextrin. The optimum mobile phase conditions were found to be 0.8% (w/v) γ‐cyclodextrin, 4% (v/v) acetonitrile, and 20 mM phosphate buffer (pH 6.0). It was found that ( R )‐abscisic acid was earlier detected than ( S )‐abscisic acid. Since γ‐cyclodextrin is hardly retained on a phenyl column, it was suggested that ( R )‐abscisic acid formed a more stable complex with γ‐cyclodextrin than the ( S )‐abscisic acid. Abscisic acid in an acacia honey sample was successfully enantioseparated with the proposed method and only ( S )‐abscisic acid was detected. A biologically inactive 2‐ trans ,4‐ trans ‐abscisic acid, which was prepared by irradiation of abscisic acid with a light‐emitting diode lamp at 365 nm, was partially enantioseparated by the proposed method. Since the irradiation of ( S )‐abscisic acid‐induced cis ‐to‐ trans isomerization to produce one 2‐ trans ,4‐ trans ‐abscisic acid enantiomer, it is reasonable that racemization did not proceed during the cis ‐to‐ trans isomerization. ( S )‐Abscisic acid and probably ( S )‐2‐ trans ,4‐ trans ‐abscisic acid were detected in a honey sample, where the peak area of ( S )‐abscisic acid was 7 times larger than that of ( S )‐2‐ trans ,4‐ trans ‐abscisic acid.