Transpiration-inhibiting abscisic acid analogs

Synthetic analogs of abscisic acid (ABA) and their inhibiting effect on transpiration rates of detached barley leaves are presented. By systematically varying the carbon skeleton of ABA, the influence of structural changes on biological activity was investigated. The results show that a properly substituted cyclohexane unit and a six-carbon side chain seem to be indispensable for high ABA-like activity, whereas the oxidation state of the terminal carbon atom in the side chain appears to be less essential. Thus, synthetic compounds have been created that exhibit biological activities comparable both in type and strength with ABA itself. On the basis of molecular models, a hypothesis of the geometric arrangement of essential substructural units is proposed.