Characterization and Synthesis of Alkaloidal Butenolides with Seed Germination Stimulating Properties from <i>Angelica dahurica</i>

Two novel alkaloids, dahurine G (<b>1</b>) and its epimer dahurine H (<b>2</b>) were isolated from the roots of <i>Angelica dahurica</i>. The planar structures of <b>1</b> and <b>2</b> were elucidated through a comprehensive analysis of their spectroscopic and spectrometric data, including nuclear magnetic resonance (NMR), infrared (IR), and high-resolution electrospray ionization mass spectrometry (HRESIMS). Biomimetic synthesis, initiated with (2<i>S</i>,3<i>R</i>,4<i>S</i>)-4-hydroxyisoleucine, enabled the unequivocal determination of the absolute configurations of <b>1</b> and <b>2</b>, while also yielding an unnatural analogue (<b>3</b>) as a byproduct. Compounds <b>1</b>, <b>2</b> and the synthetic analogue <b>3</b> all contain a distinctive butenolide moiety, which is commonly observed in plant signaling molecules such as strigolactones (SLs) and karrikins (KARs). Further experiments demonstrated that all three compounds significantly promote seed germination in both model plants (<i>Arabidopsis thaliana</i> and <i>Nicotiana benthamiana</i>) and vital crops (<i>Zea mays</i> and <i>Oryza sativa</i>), as well as radicle elongation in <i>Z. mays</i> and <i>O. sativa</i>. The findings suggest that compounds <b>1</b>-<b>3</b> may play a significant role in seedling germination and early root development, thereby demonstrating considerable potential for agricultural applications.