New polychlorinated bibenzyls from Rhododendron minutiflorum

Five new polychlorinated bibenzyls (1-5) along with 3 known compounds (6-8) were isolated from the stems and leaves of Rhododendron minutiflorum. The chemical structures of all the isolates were determined by spectroscopic methods, and compounds 1 and 2 were further verified by single-crystal X-ray diffraction analyses. Compounds 1-5 were halogenated compounds which bear three to five chlorine atoms in their chemical structures. Biologically, compounds 2, 5 and 6 showed varying degrees of toxicity toward the Asian citrus psyllid (Diaphorina citri) with LD₅₀ values 27.15, 17.02 and 16.20 mg/L, respectively. These values were comparable to the positive control matrine (LD₅₀ = 11.86 mg/L), which were calculated using observations on day 6. Meanwhile, compound 4 had α-glucosidase inhibitory activity with IC₅₀ value of 17.87 ± 0.74 μM.