The chemistry of fungi. Part LXV. The structures of ergochrysin A, isoergochrysin A, and ergoxanthin, and of secalonic acids A, B, C, and D

Abstract

The linear structure for the ergot pigment, ergochrysin A, has been confirmed; isoergochrysin A has the corresponding angular structure. The synthesis of various relevant biphenyls, including 3-acetyl-4-hydroxy-2,2′,4′-trimethoxybiphenyl, 3,3′-diacetyl-4,4′-dihydroxy-2,2′-dimethoxybiphenyl, and derivatives is described. Iodination of 2′-hydroxy-6′-methoxyacetophenone gives 2′-hydroxy-3′-iodo-6′-methoxyacetophenone and not 2′-hydroxy-5′-iodo-6′-methoxyacetophenone as previously claimed. Similarly the compounds previously described as 8-iodo-5-methoxy-2-methylchromone and 8,8′-bis-(5-methoxy-2-methylchromone) are 6-iodo-5-methoxy-2-methylchromone and 6,6′-bis-(5-methoxy-2-methylchromone), respectively.

By n.m.r. spectroscopy and by chemical degradation it has been established that the linkage between the two halves of the secalonic acids A, B, C, and D is 2,2′- and not 4,4′- as previously suggested. The 2,2′-linkage is also present in ergoxanthin and ergochrysin B.

Ullmann condensation of 5-O-benzoyl-2-iodo-1,9-di-O-methylhemiergoflavin gave 5,5′-di-O-benzoyl-1,1′,9,9′-tetra-O-methylergoflavin, which on demethylation and debenzoylation gave ergoflavin, thereby constituting a partial synthesis of this metabolite.