The spirodioxolactone ochroleucin A 1 ( 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 A 2 ( 2 ). Ochroleucin A 1 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 A 1 and B have been determined by quantum chemical calculation of their CD spectra. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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Sontag et al. (2005) studied this question.