A new sesquiterpene named panal was isolated from Panellus stipticus. Upon treatment with salts of ammonia or the luminous mushroan primary anines, panal yields a substance(s) which emits light in the presence of Fe2+, On the basis of chemical and spectroscopic data, the structure 1 panal, excluding the absolute configuration. H2D2, and surfactants. was assigned to The emission of light by certain fungi has drawn much attention for centuries.l-3 Nonetheless, the chemistry of fungal bioluminescence is still hidden in a veil. We have recently observed that a crude aqueous extract of the luminous mushroom Panellus stipticus yields, upon treatment with salts of ammonia or primary amines, a substance(s) which emits light in the presence of Fe2+, H202, and surfactants.4 This suggests a possibility that the crude aqueous extract may contain the precursor of the light-emitting principle (luciferin) for the bioluminescence of fungi. Thus, we used the chemiluminescent activity for monitoring the "active" substance, resulting in the isolation of a new sesquiterpene, which we have named panal. In this paper, we would like to report the structure of panal. Panal (1; a~ -17') was isolated as an amorphous solid. The molecular formula (C15H1805) was established from the high-resolution mass spectrum. A broad IR absorption at 1700 cm-l, coupled with a UV absorption at 218 RR (E 15,300), suggested the presence of one or more conjugated carbonyl functionalities. The 13C-NMR spectrum exhibited 15 signals, which were assigned to the following groups: 1 x CO (208.58 ppm. s), 1 x CHO (193.34, d). 1 x C02H (170.74. s), 1 x CH-C (141.24, d and 127.30, s). 1 x CHpC (138.11, t and 145.80, s), 1 x CH(OH) (63.83, d), 4 x CH (50.55, d, 42.09, d, 38.31, d. and 32.00. d), 2 x CH2 (47.81, t and 33.06, t), and 1 x CH3 (19.25, q). On the basis of these spectroscopic data, it is evident that pans1 contains the functional groups summarized in Diagram 1. In addition, extensive homo-nuclear spin-decoupling experiments established the proton spin coupling systems summarized in Diagram 2.