Obscuroside E: A Novel Alkaloid Glycoside from <i>Clematis obscura</i> as an Insecticide Lead Candidate against <i>Acyrthosiphon pisum</i> and <i>Plutella xylostella</i>

To discover insecticide lead compounds from the insecticidal plant <i>Clematis</i>, a new alkaloid glycoside obscuroside E (<b>1</b>) and 17 known compounds (<b>2</b>-<b>18</b>) were identified from <i>Clematis obscura</i> and <i>Clematis tibetana</i> var. <i>vernayi</i>. Compound <b>1</b> displayed remarkable oral toxicities against <i>Acyrthosiphon pisum</i> (<i>A. pisum</i>) and <i>Plutella xylostella</i> (<i>P. xylostella</i>) with half-lethal concentration (LC₅₀) values of 0.11 and 0.85 mg/mL, respectively, as well as potential antifeedant activity. Compound <b>1</b> inhibited α-amylase (α-AL) of <i>A. pisum</i> and <i>P. xylostella</i> with inhibition rates of 32.82 and 23.80% at LC₇₀, respectively. It bound tightly to the crystal structure of α-AL in <i>P. xylostella</i> through five hydrogen bonds and three alkyl/pi alkyl interactions. Besides, compound <b>1</b> destroyed the microstructure of the midguts of <i>A. pisum</i> and <i>P. xylostella</i>, particularly the microvilli and nucleus. This study provides valuable insight into the better utilization of compound <b>1</b> as an insecticide lead candidate for the biocontrol of <i>A. pisum</i> and <i>P. xylostella</i>.