IDENTIFICATION OF A PLANT-GROWTH INHIBITING IRIDOID LACTONE FROM DUROIA-HIRSUTA, THE ALLELOPATHIC TREE OF THE DEVILS-GARDEN

Bioactivity-directed fractionation of a root extract of Duroia hirsuta (Rubiaceae), a toxic and potentially allelopathic understory tree fro m the western Amazon, has led to the isolation of the tetracyclic irid oid lactone, plumericin (1). Bioassays showing plumericin strongly inh ibited lettuce radicle elongation at a concentration (IC50) of 35.8 mu m/ml (123 mu M). The isolation of a highly potent inhibitor of plant growth from Duroia hirsuta supports the hypothesis that the lack of ve getation surrounding this tree is the result of allelopathy.