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

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