OXIDATION OF THE 8'-POSITION OF A BIOLOGICALLY ACTIVE ABSCISIC ACID ANALOGUE

Article abstract of DOI:10.1016/S0031-9422(00)90687-3

The metabolism of a biologically active abscisic acid (ABA) analogue, (+)-1'S,2'S)-2',3'-dihydroabscisic acid <(+)-4-(1E,3Z)-(4S,5S)-4-(4-carboxy-3-methyl-1,3-butadienyl)-4-hydroxy-3,3,5-trimethylcyclohexanone>, which cannot form phaseic acid was studied in a cell suspension culture of bromegrass (Bromus inermis).The analogue induced freezing tolerance in bromegrass cells similar to (S)-(+)-ABA and was oxidized to (1'S,2'S)-8'-hydroxy-2',3'-dihydroabscisic acid <4-(1E,3Z)-(3R,4S,5S)-4-(4-carboxy-3-methyl-1,3-butadienyl)-4-hydroxy-3-hydroxymethyl-3,5-dimethylcyclohexanone>.The enantiomer (-)-(1'R,2'R)-2',3'-dihydroabscisic acid, which was inactive in inducing freezing tolerance, was converted to two metabolites, viz., the corresponding enantiomeric (1'R,2'R)-8'-hydroxy-2',3'-dihydroabscisic acid <4-(1E,3Z)-(3S,4R,5R)-4-(4-carboxy-3-methyl-1,3-butadienyl)-4-hydroxy-3-hydroxymethyl-3,5-dimethylcyclohexanone> and reduction product (-)-(1E,3Z)-(1R,4S,6R)-1-(4carboxy-3-methyl-1,3-butadienyl)-2,2,6-trimethylcyclohexan-1,4-diol.Both enantiomers of the analogue were transformed to the glucose esters.The structures of the metabolites were established by both spectrometric analyses and chemical synthesis.The metabolite 8'-hydroxy-2',3'-hydroxyabscosic acid is a cyclohexanone analogue of 8'-hydroxyabscisic acid, the transient oxidation product in the metabolism of ABA to phaseic acid.Like phaseic acid, the racemic form of 8'-hydroxy-2',3'-dihydroabscisic acid was inactive in inducing freezing tolerance in bromegrass cells, suggesting that ABA and (+)-(1'S,2'S)-2',3'-dihydroabscisic acid were the active compounds.