Dead oak leaves (100 g) were obtained from a young
tree (ca. 20 years), cut into strips and pulverised in a
Waring blender. The powder was extracted with 2 l of
chilled 50% aqueous methanol for 1 h, followed by ®l-
tration through glass wool and Watman No. 113 ®lter
paper under vacuum. The methanol was removed using
a rotary evaporator at 35C under vacuum. The residue
was freeze-dried, yielding 1.8 g of powder