Chromogenic Meroterpenoids from the Mushrooms Russula ochroleuca and R. viscida

The spirodioxolactone ochroleucin A1 (1) is responsible for the red colour produced when the stalk base of Russula ochroleuca and R. viscida is treated with aqueous KOH. The labile chromogen rearranges easily into the isomeric dilactoneochroleucin A2 (2). Ochroleucin A1 is accompanied by the biosynthetically related hemiacetal ochroleucin B (5). The new compounds, whose structures were established by MS and NMR methods, appear to be derived biosynthetically by oxidative condensation of two monomeric units. One of them, 2,5‐dihydroxy‐4‐(3‐methylbut‐3‐en‐1‐ynyl)benzaldehyde (6), was detected in the crude toadstool extract by GC/MS comparison with a synthetic sample. The absolute configurations of the ochroleucins A1 and B have been determined by quantum chemical calculation of their CD spectra. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)