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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)

It is now more than 23 years since the first two articles about the new antitumor antibiotic fredericamycin A (FM-A, NSC-305263) with the fascinating unique spirostructure were published in this journal1,2). Shortly after the structure of fredericamycin A (1) was elucidated by X-ray analysis3) and later on confirmed by NMR experiments4,5).