Furanosesquiterpenes and Related Natural Products from Myoporum Species: Isolation and Semisynthesis

Myoporum species are recognized as toxic plants. Essential oils from the leaves of these species contain furanosesquiterpenes, which comprise the active toxins. In this report, natural products isolation studies of three Myoporum species (M. insulare, M. parvifolium, and M. montanum) afforded two previously unreported furanosesquiterpenes (24 and 25) and three unprecedented γ-lactone-containing analogues (26–28), along with nine previously reported furanosesquiterpenes and five other natural products. Among the 14 furanosesquiterpenes and related compounds isolated in this study, we observed three distinct types of furanosesquiterpene structures isolated from each of these Myoporum species. Semisyntheses of four sesquiterpene natural products were completed from (−)-ngaione over two steps in each case. This included the synthesis of the lactam-containing sesquiterpene myoporumine A.