Agaricus blazei is an important fungus for producing bioactive compounds. There are some reports of polysaccharides and steroid derivatives from the fruiting bodies of A. blazei. However, the chemical examination of the secondary metabolites of the cultured mycelia of this species has not been reported. Eight compounds, an unprecedented skeleton have been isolated from the cultured mycelia of A. blazei. The structures of the novel compounds each named blazeispirols A (1), B (2), C (3), D (4), E (5) X(6), Y (7) and Z (8) were confirmed by extensive 1D and 2D NMR spectral data and X-ray analysis. Blazeispirols A (1), B (2), C (3), D (4) and E (5) were des-A-ergostane type compounds having spiroacetal structure as a side chain. Blazeispirols X (6) and Y (7) were determined to be (20S, 22S, 23R, 24S)-1 (10→6) abeo-14β, 22:22, 25-diepoxyergosta-5,7,9,11-tetraene-3α,23-diol and (20S, 22S, 23R, 24S)-14β,22:22,25-diepoxy-9,23-dihydroxyergosta-4,7,11-triene-3,6-dione by comparison of extensive 1D and 2D NMR spectral data with that of blazeispirol A. The biosynthesis of blazeispirol A was investigated by feeding ^<13>C-labeled acetates and methionine to the growing cultures of A. blazei. The labeling patterns of 1 derived from singly and doubly ^<13>C-labeled acetates were consistent with that of ergosterol reported previously except for the A-ring and then ^<14>C-labeled ergosterol was incorporated into blazeispirol A. Taking the structures of blazeispirols Z and D into consideration, it can be assumed that blazeispirol A is biosynthesized from ergosterol by the cleavage of C-4, C-5 and C-1, C-10 bonds on retro aldol condensation and Michael reaction via such as intermediate A as shown in Fig. 4. A large number of ergostane-type steroids have been isolated from many fungi. However, blazeispirol A is the first example of a naturally occurring des-A-ergostane-type steroid including a spiroacetal structure moiety as a side chain.
