Biologically active constituents of Melaleuca leucadendron: inhibitors of induced histamine release from rat mast cells.

Chloroform and methanol extracts of the fruits of Melaleuca leucadendron strongly inhibited histamine release from rat mast cells induced by compound 48/80 or concanavalin A. Ursolic acid, a triterpene, was the most active compound contained in the chloroform extract and two stilbenes, piceatannol and oxyresveratrol, were isolated as active compounds from the methanol extract. Several other stilbenes and related compounds were examined to obtain information on the structure activity relationships of stilbenes.