Detoxification of Plant Aromatic Abietanoids via Cleavage of the Benzene Ring into 11,12-<i>Seco</i>-diterpene Polyenes by a Specialist Insect of <i>Leucosceptrum canum</i>

Leaves of <i>Leucosceptrum canum</i> harbor abundant toxic aromatic abietanoids, and they are rarely attacked by insect herbivores, except for the larvae of <i>Nacna malachitis</i>. The excrements of the insect that fed on <i>L. canum</i> leaves were investigated, leading to the isolation and identification of two unprecedented 11,12-<i>seco</i>-abietane diterpene polyenes: nacnabietanins A (<b>1</b>) and B (<b>2</b>). This discovery heralds a unique detoxification mechanism of plant aromatic abietanoids by insects through enzymatic cleavage of stable benzene rings into more easily degraded polyenes.