New Antifeedant C₂₀ Terpenoids from <i>Leucosceptrum canum</i>

Three novel C₂₀ terpenoids, norleucosceptroids A–C (<b>1</b>–<b>3</b>), were isolated from the leaves and flowers of <i>Leucosceptrum canum</i> (Labiatae) and were identified by comprehensive spectroscopic analysis and, in the case of <b>1</b>, single-crystal X-ray diffraction. Structurally, compounds <b>1</b>–<b>3</b> should be categorized as pentanor-sesterterpenoids rather than diterpenoids. Moderate antifeedant activity of <b>1</b>–<b>3</b> against the generalist plant-feeding insect <i>Helicoverpa armigera</i> was detected, suggesting that they might also be involved in the plant defense against insect herbivores

Biologically Active Dichapetalins from <i>Dichapetalum gelonioides</i>

A phytochemical investigation of the toxic tropical plant <i>Dichapetalum gelonioides</i> led to the isolation and identification of 14 new dichapetalins (<b>1</b>–<b>14</b>) and the known dichapetalins A (<b>15</b>) and K (<b>16</b>). The structures of the new compounds were determined by analyses of their NMR, MS, electronic circular dichroism, and X-ray diffraction data. The esterification at C-25 by 4-hydroxyphenylpropanoic acid and the hydroxylation at C-2′ are unique in this unusual class of natural products. In addition to the known cytotoxicity, an array of biological activities, including antifeedant, nematicidal, antifungal, and NO and AChE inhibitory activities, were observed for this class of compounds. These findings suggested that dichapetalin hybrid triterpenoids as a class have broad biologically active cellular functions including defense against insect herbivores and pathogens

Peltate Glandular Trichomes of <i>Colquhounia coccinea</i> var. <i>mollis</i> Harbor a New Class of Defensive Sesterterpenoids

A new class of unique sesterterpenoids, colquhounoids A–C (<b>1</b>–<b>3</b>), were identified from the peltate glandular trichomes of <i>Colquhounia coccinea</i> var. <i>mollis</i> (Lamiaceae) through precise laser-microdissection coupled with UPLC/MS/MS and spectroscopic analyses and X-ray diffraction. Very interestingly, their structural features and defensive function are closely related to leucosceptroid-class sesterterpenoids harbored by the glandular trichomes of another Lamiaceae taxon, <i>Leucosceptrum canum</i>, even though this is morphologically distinct and taxonomically distant

Unraveling the Metabolic Pathway in <i>Leucosceptrum canum</i> by Isolation of New Defensive Leucosceptroid Degradation Products and Biomimetic Model Synthesis

Seven new leucosceptroid degradation products possessing a C₂₀, C₂₁, or C₂₅ framework, norleucosceptroids D–H (<b>1</b>–<b>5</b>), leucosceptroids P (<b>6</b>), and Q (<b>7</b>), have been isolated from <i>Leucosceptrum canum</i>. Their structures were determined by comprehensive NMR, MS, and single-crystal X-ray diffraction analyses. Discovery of these key intermediates, together with the biomimetic oxidation of a model system, supports the hypothesis that two biosynthetic pathways are operative. Antifeedant activity was observed for compounds <b>1</b>–<b>3</b>