Synthesis of 9-deoxy-15-hydroxycotylenol and its germination-stimulating activity on lettuce seeds

Cotylenins and fusicoccins, fungal diterpenoid glycosides, are know to have identical, yet unique, plant growth regulating activities. These compounds widen the stomatal pore, stimulate cell enlargement, break seed dormancy, and stimulate rhizogenesis. Because of these plant-hormone like activities, fusicoccin, a representative of this family, has been widely utilized in plant physiology. During the course of our study on the structure-activity relationships of this class of compounds, 9-deoxy-15-hydroxycotylenol and its 15-methoxymethyl ether were synthesized in order to clarify the role of the 9 alpha-hydroxy group of cotylenol, a common aglycon of cotylenins. Since these cotylenol analogs retained germination-stimulating activity on lettuce seeds, it has been clarified that the 9 alpha-hydroxy group of cotylenol is not essential for its biological activities. This finding is informative in designing useful tools for targeting the 14-3-3 protein, which has recently been identified as the binding protein of fusicoccin.