Synthesis and biological activity of tetralone abscisic acid analogues

Bicyclic analogues of the plant hormone abscisic acid (ABA) were designed to incorporate the structural elements and functional groups of the parent molecule that are required for biological activity. The resulting tetralone analogues were predicted to have enhanced biological activity in plants, in part because oxidized products would not cyclize to forms corresponding to the inactive catabolite phaseic acid. The tetralone analogues were synthesized in seven steps from 1-tetralone and a range of analogues were accessible through a second route starting with 2-methyl-1-naphthol. Tetralone ABA 8 was found to have greater activity than ABA in two bioassays. The absolute configuration of (+)- 8 was established by X-ray crystallography of a RAMP hydrazone derivative. The hydroxymethyl compounds 10 and 11, analogues for studying the roles of 8'- and 9'-hydroxy ABA 3 and 6, were also synthesized and found to be active.