The Resolution by HPLC ofRS-[2-14C]Me 1', 4'-cis-Diol of Abscisic acid and the Metabolism of (−)-R- and (+)-S-Abscisic Acid

Abstract

The R- and S-enantiomers of racemic [2-¹⁴C]Me 1', 4'-cis-diol of abscisic acid have been separated by high performance liquid chromatography on an optically-active Pirkle column. R-[2-¹⁴C]- and S-[2-¹⁴C]abscisic acids, formed from the Me 1', 4'-cis-diol by oxidation and alkyline hydrolysis were fed to tomato shoots and the extracts analysed by reversed phase high performance liquid chromatography. R-[2-¹⁴C]abscisic acid formed mainly the abscisic acid glucose ester (ABAGE), abscisic acid l'-glucoside (ABAGS) and an uncharacterized conjugate. Dihydrophaseic acid 4'-B-D-glucoside, the major metabolite of RS-abscisic acid in tomato shoots, was found to be derived virtually exclusively from the natural, S-abscisic acid. Phaseic acid and conjugates of abscisic acid were also found as products of the naturally occurring enantiomer. The resolution method was used to measure the relative proportions of R and S enantiomers in the free acid liberated from conjugates formed from RS-[2-¹⁴C]ABA fed to shoots. The ratios show an excess of the R-enantiomer: 5.8: 1, ABAGE; 29.4: 1, ABAGE; 8.3: 1 for an uncharacterized conjugate and 6.1: 1 for the residual free [2-¹⁴C]ABA.