A Novel Caffeic Acid Derivative and Other Constituents of Populus Bud Excretion and Propolis (Bee-Glue)

The bud exudates of Populus nigra, P. trichocarpa, and P. grandidentata × tremuloides were analyzed for the presence of phenolics and flavonoids. A novel natural product, caffeic acid y.y-dimethylallyl ester, was identified from P. nigra, along with further phenolics such as ρ-hydroxy-acetophenone, dimethyl caffeic acid, cinnamoyl cinnamata and vanillin. The flavonoid aglycones correspond to those reported earlier. Propolis samples from the Sonoran Desert were shown to exhibit the flavonoid pattern that is typical for poplar bud exudates, thus confirming this material as the major source for bee-glue. Only a single flavonoid might originate from the leaf exudate of a desert shrub.