764. The chemistry of fungi. Part XLVII. The constitution of ergochrysin A, secalonic acid A, and secalonic acid B

Abstract

Ozonolysis of ergochrysin A, C2,H2,012(C02Me), one of the pigments of ergot, yields hemiergoflavin-2-carboxylic acid (VIII), pyrolysis forms the benzoate (IV; R = Me), and fusion with alkali gives the acid (IV; R = H) with the biphenyl (V; R1 = COMe, R2 = H). Vigorous acetylation of ergochrysin A forms the hemiergoflavin (VI; R1 = R2 = Ac), which is degraded by acid to carbon dioxide, the acid (IV; R = H), and the hemiergoflavin (VII; R = H).Tri-O-methylergochrysinone A (X) , formed by oxidation of tri-O-methylergochrysin A (I; R2 = R3 = H, R1 = Me), gives the biphenyl (XI) upon degradation with alkali.Ergochrysin A undergoes mutarotation in pyridine to yield an isomer, isoergochrysin A. These and other observations are rationalised in terms of the structures (I; R2 = R3 = H, R1 = Me) for tri-O-methylergochrysin A and ( I ; R1 = R2 = R3 = H) or ( 111) for ergochrysin A.Constitutions are derived for the closely related colouring matters, secalonic acid A and secalonic acid B.The biosynthesis of the ergot pigments is discussed. c o -~o r k e r s . ~ Secalonic acids B and C have been i ~o l a t e d . ~ The term chrysergonic acid, when used in the present Paper, refers to the mixture of secalonic acid A and secalonic acid B isolated by Stoll et aZ.ll Chrysergonic acid Part XLVI, preceding Paper.

Xanthones from Fungi, Lichens, and Bacteria: The Natural Products and Their Synthesis

“…DeMayo, Aberhart, and co-workers reported in 1965 on the isolation in crystalline form of six compounds from a Portuguese ergot drug . In contrast to earlier reports, ,, these authors found that all compounds gave a positive Gibbs test, possibly indicating the presence of a free para- position to the phenolic moiety and, thus, a 2,2′-linkage . These compounds proved to be secalonic acid B ( 449 , Figure ), secalonic acid C ( 455 ), ergochrysin A ( 451 ), ergochrysin B ( 454 ), ergoflavin ( 448 ), and a novel compound that the authors named ergoxanthin ( 460 ).…”

“…“Ergochromes” is a collective name for a group of compounds including secalonic acids and the closely related ergoflavins, ergochrysins, and chrysergonic acid, all of which can be described as “ergochrome dimers”. The secalonic acids are homodimers of two esters; the ergochrysins are heterodimers of one lactone and one ester, whereas the ergoflavins are homodimers of the lactone species . They are a relatively widespread group of symmetrical or semisymmetrical dimeric xanthone mycotoxins, first reported as a single compound of the formula C 14 H 14 O 6 by Kraft in 1906 after isolation from Claviceps purpurea .…”

Xanthone dimers: a compound family which is both common and privileged

“…Whilst secalonic acids are ester homodimers, other heterodimer ergochromes are known. For example, ergochrysins are lactone/ester heterodimers, ergo-avin is a homodimer, 145 whilst ergoxanthin has undergone structural rearrangement to form a pendant butyrolactone ring on one half of the molecule. 146 Due to the early time at which they were rst studied, modern spectral methods were not applicable to facilitate the structural elucidation of the ergochromes, and early structural assignations on these compounds were frequently revised in later years.…”

Diastereomeric Secalonic Acids

“…Thus 5,5-dimethylhepta-l,3,6-triene is readily rearranged on irradiation into a mixture of cis-and trans-3,3-dimethyl-l,2divinylcyclopropane [6]. The structure of (10) was deduced from infrared and N M R spectra.…”