STUDIES IN THE BIOCHEMISTRY OF MICROORGANISMS: PART 117. SEPEDONIN, A TROPOLONE METABOLITE OF SEPEDONIUM CHRYSOSPERMUM FRIES

Abstract

Two yellow substances were isolated from culture filtrates of the fungus Sepedonium chrysospermum Fries. One of these, named sepedonin, predominates in growing cultures and is believed to be the direct product of metabolism. The second, an anhydro derivative of sepedonin, was probably formed spontaneously in the culture filtrate, and during the isolation process, by chemical dehydration. Sepedonin, C11H12O5with one C-methyl group, gave two dimethyl ethers with diazomethane and has the spectral characteristics of a substituted tropolone. Dehydration under mild conditions afforded anhydrosepedonin, from which a monomethyl ether and two dimethyl ethers were prepared. One of the latter was unstable and rearranged slowly to a third dimethyl ether. By fusion with alkali, anhydrosepedonin was converted to a mixture from which two substituted benzoic acids and a product formulated as 6-hydroxy-4-methyltropolone were separated. The bathochromic displacement of the peaks in the ultraviolet spectrum of anhydrosepedonin compared with those in sepedonin indicated an unsaturated group conjugated to the tropolone ring, confirmed by catalytic reduction to a dihydro derivative. By careful oxidation of one of the dimethyl ethers of anhydrosepedonin with permanganate a substance believed to be a tropolone containing ester and carboxyl substituents was obtained, together with a second product formulated as the 3,4-cyclic anhydride. From these results and supporting n.m.r. and spectral evidence anhydrosepedonin is considered to be a 6-hydroxytropolone with a 2′-methylpyran ring fused at the 4,5,4′,5′-positions. Sepedonin differs only by having a 2′-hydroxy-2′-methyldihydropyran ring as the heterocyclic moiety.