Secalonic acid

Secalonic acids are a group of xanthone derivatives closely related to ergoflavin and ergochrysin A that are collectively called ergochromes and belong to a class of mycotoxins initially isolated as major ergot pigments from the fungi Claviceps purpurea that grows parasitically on rye grasses.

[1] During the following decade the structures of secalonic acids A, B, C, D and ergochrysin A were similarly firmly established,[11] and although there was some early contention whether they were 2,2’-, 4,4’- or even 2,4’-linked [1] it was confirmed that they too were all 2,2’- linked between the biphenyl residues.

[1] The tetrahydroxanthone-containing secalonic acids have been demonstrated to be unstable under basic conditions, and they can easily undergo isomerizations arising from ether linkage replacement.

Whalley's synthesis of ergoflavin 3 from hemiergoflavin 1 in 1971 was achieved by a low yield coupling of two protected 2-iodo-hemiegoflavin monomers 2 with copper under the Ullmann reaction conditions, followed by acid deprotection.

[11][12] Similarly more than forty years later Porco's synthesis of the more labile secalonic acid D in 60% yield involved coupling two protected iodo monomers via their stannes with CuCl at room temperature,[14] whereas Tietze achieved a similar synthesis of secalonic acid E by coupling two protected iodo monomers with Pd (OAc)2under Suzuki conditions at 70 °C in 85% yield.