Resolution of RS-abscisic acid and the separation of abscisic acid metabolites from plant tissue by high-performance liquid chromatography

Attempts to resolve the enantiomers of racemic abscisic acid (ABA) by high-performance liquid chromatograpy on a chiral stationary-phase column were unsuccessful. However, reduction of RS-methyl ABA (RS-Me-ABA) with sodium borohydride generates a new chiral centre and one of the two isomeric products, the RS-Me-1′,4′-cis-diol of ABA, was separated into its enantiomers by high-performance liquid chromatography on an optically active Pirkle column. High-performance liquid chromatography on a μBondapak C18 column separated the metabolites and conjugates of [2-14C]ABA fed to tomato shoots. The resolution method was used to measure the relative proportions of R and S enantiomers in the free acid liberated from conjugates of ABA.