Structure-activity relationship of α hormones, the mating factors of phytopathogen Phytophthora

The mating hormones alpha 1 and alpha 2 induce sexual reproduction of the phytopathogenic genus Phytophthora. To demonstrate the structural elements responsible to hormonal activity, 17 derivatives of alpha 1 and alpha 2 were synthesized and their hormonal activity (oospore-inducing activity) was evaluated. The terminal ester derivatives of alpha 1 (diacetate and dibenzoate) retained the hormonal activity, whereas a dicarbamate derivative completely suppressed the activity. Even monocarbamates showed weak activities; among them the 1-O-carbamate was less active than 16-O-carbamate, suggesting that the 1-OH group is a little more important than 16-OH. Dihydro, dehydro, and demethyl derivatives exhibited the minimum level of activity. Surviving activity of 15-epi-alpha 1 suggested a less importance of this stereochemistry. Contrary to alpha 1, not only the terminal diacetate derivative but also monoacetates of alpha 2 exhibited no or little activity. Among the monoacetates, 1-O-acetyl-alpha 2 exhibited little yet relatively better activity than the others. No activity was observed for mono- and dicarbamoyl derivatives of alpha 2. Dihydro alpha 2 with the saturated double bond lost most of the activity. These findings suggest that both the mating hormones alpha 1 and alpha 2 require most of the functional (hydroxyl, keto, and olefinic) groups they possess in their natural form for inducing the sexual reproduction of Phytophthora. (C) 2011 Elsevier Ltd. All rights reserved.