A unique benzofuran named suillusin was isolated from the methanolic extrac
t of the fruiting body of the mushroom Suillus granulatus. Its structure wa
s assigned on the basis of various spectroscopic analyses as a highly subst
ituted novel 1H-cyclopenta[b]benzofuran (1). Suillusin is suggested to be b
iogenerated from polyporic acid.