Acaricidal Activity of Bufadienolides Isolated from Drimia pancration against Tetranychus urticae, and Structural Elucidation of Arenobufagin-3- O-α -L-rhamnopyranoside.

Chemical characterization of the bulbs of Drimia pancration was conducted to isolate four steroidal saponins ( 1 - 4 ). Earlier, we focused on the structural elucidation of compounds 1 - 3 . Herein, by means of 1 H-NMR, 13 C-NMR, Nuclear Overhauser Effects (NOE), and 2D-NMR spectra, the full stereochemical structure of 4 is reported, and all the 1 H and 13 C signals are assigned. Compounds 1 - 4 were tested for their acaricidal properties against the two-spotted spider mite Tetranychus urticae . Our results showed excellent activity of compound 1, with an LD 50 (µg/cm 2 ) of 0.29 and a LD 90 (µg/cm 2 ) of 0.96, whereas compounds 2 , 3 , and 4 showed moderate activity. Furthermore, the acaricidal and cytotoxic properties of the crude extract were also investigated. Of note, after 96 h of exposure, the acaricidal activity of compound 1 was higher than that of the positive control, hexythiazox. Indeed, for compound 1 , LD 50 and LD 90 were 0.29 and 0.96 µg/cm 2 , respectively, while hexythiazox LD 50(90) was 18.7 (132.5) µg/cm 2 . Additionally, D. pancration extract, after 72 h, induced a high cytotoxic effect in HaCaT and THP-1 cell lines, with an IC 50 of 7.37 ± 0.5 µg/mL and 3.50 ± 0.15 µg/mL, respectively. Overall, D. pancration can be considered as a green source of novel acaricides effective against mites of agricultural importance, such as T. urticae , pending proper field validation and the assessment of non-target effects on other invertebrate species.