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 Sepedoniuna chrysospermunz Fries. One of these, named sepedonin, predominates in growing cultures and is believed t o 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, C1lH1205 with 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 a n 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 a t the 4,5,4',5'-positions. Sepedonin differs only by having a 2'-hydroxy-2'-methyldihydropyran ring as the heterocyclic moiety.Sepedoniz~m chrysospermz~m (Bull.) Fr., the iinperfect stage of Hypomyces chrysospermus (Bull.) Tul., has been isolated froin soils in Europe and the Ainerican continent and is a coxnnlon parasite of the fleshy fungi. The strain used in the present work was isolated from Boletz~s luridus. Cultures of this hypholnycete developed a yellow color in the broth and the surface inyceliuin showed patches of orange-yellow color after approxiinately 10 days undisturbed growth on Raulin-Thom or Czapek-Dox media. The color of the culture fluid later deepened and, in addition, gave an increasingly strong greenish-brown reaction with ferric chloride. Spectrophotoilletric exaxnination of the solution showed that these changes corresponded with the appearance of a strong absorption peak a t 250-275 n~p and weaker absorption in the region between 300 and 360 n~p . The wavelengths a t which the lnaxixna appeared varied with the pH of the culture filtrate. The

Structure of sepedonin, a tropolone metabolite of Sepedomumchrysospermum Fries

“…Chemical non-equivalence of the hydrogens in each methylene group (both gave characteristic broadened AB quartets, JAB -17 Hz) also indicated that they were either part of a ring system, in which no averaging of the environment occurred due to conformer interconversion, or in an otherwise asymmetric environment. Previous work (1) had also shown that anhydrosepedonin contained two phenolic-type hydroxyl groups (pK --6 and 9) and a masked carbonyl group. These functional groups are also present in sepedonin since they were not involved in its dehydration.…”

“…We have checked and found that the latter belief was unfounded; all three dimethyl ethers are stable and are not interconvertible. The only dimethyl ethers obtained when anhydrosepedonin was treated with base and dimethyl sulfate in acetone, or alternatively with silver oxide and methyl iodide in benzene, were A and B. Sepedonin gave dimethyl ethers A and B when reacted with diazomethane, and these were dehydrated to anhydrosepedonin dimethyl ethers A and B, respectively (1). The structures of all of these derivatives were not determined.…”

“…( I ) Sepedonin (C, , H1205) is easily converted to anhydrosepedonin (C, lH,oO,) by loss of one molecule of water (1). (2) The p.m.r.…”

“…Samples were isolated from cultures of Sepedoni~crtz chrysosper?nlrrn Fries and purified as described previously (1). Anhydrosepedonin was obtained from sepedonin by heating under reflux for 1 h in glacial acetic acid and purified as described (1).…”

Classic fungal natural products in the genomic age: the molecular legacy of Harold Raistrick

“…In the case of citrinin 2 the more reduced aromatic nucleus is stable and does not rearrange. Compounds such as sepedonin 5, 84 another of the Raistraick compounds, feature structural motifs common to both the tropolones and citrinin and it seems likely that the sepedonin BGC will feature both a citB-type and a TropC-type oxidase.…”