Prenylated cinnamate and stilbenes from Kangaroo Island propolis and their antioxidant activity.

A prenylated cinnamic acid derivative as well as six prenylated tetrahydroxystilbenes were isolated from the ethyl acetate extract of propolis that originated from Kangaroo Island, Australia. Furthermore, six known stilbenes and two known flavanones were also identified from the same sample. Stilbenes are not common in propolis; therefore, Kangaroo Island propolis is considered a unique type of propolis that is rich in prenylated stilbenes. Stilbene propolis from Kangaroo Island showed a stronger scavenging activity towards DPPH free radical than Brazilian green propolis. This strong activity can be explained by the presence of large number of stilbenes, most of them showed strong free radical scavenging activity.