| Summary: | Clovane and isocaryolane derivatives have been proven to show several levels of activity against the phytopathogenic fungus <i>Botrytis cinerea</i>. Both classes of sesquiterpenes are reminiscent of biosynthetic intermediates of botrydial, a virulence factor of <i>B. cinerea</i>. Further development of both classes of antifungal agent requires exploration of the structure–activity relationships for the antifungal effects on <i>B. cinerea</i> and phytotoxic effects on a model crop. In this paper, we report on the preparation of a series of alkoxy-clovane and -isocaryolane derivatives, some of them described here for the first time (<b>2b</b>, <b>2d</b>, <b>2f</b>–<b>2h</b>, and <b>4c</b>–<b>4e</b>); the evaluation of their antifungal properties against <i>B. cinerea</i>, and their phytotoxic activites on the germination of seeds and the growth of radicles and shoots of <i>Lactuca sativa</i> (lettuce). Both classes of compound show a correlation of antifungal activity with the nature of side chains, with the best activity against <i>B. cinerea</i> for <b>2d</b>, <b>2h</b>, <b>4c</b> and <b>4d</b>. In general terms, while 2-alkoxyclovan-9-ols (<b>2a</b>–<b>2e</b>) exert a general phytotoxic effect, this is not the case for 2-arylalkoxyclovan-9-ols (<b>2f</b>–<b>2i</b>) and 8-alkoxyisocaryolan-9-ols (<b>4a</b>–<b>4d</b>), where stimulating effects would make them suitable candidates for application to plants.
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