The structures of the fumonisins, a family of structurally related mycotoxins isolated from cultures of Fusarium moniliforme, were elucidated by mass spectrometry and 1H and 13C n.m.r. spectroscopy as the diester of propane-lr2,3-tricarboxylic acid and either 2-acetylamino-or 2-amino-1 2,16-dimethyl-3,5,10,14,15-pentahydroxyicosane as well as in each case the C-10 deoxy analogue; in all cases both the C-14 and C-15 hydroxy groups are involved in ester formation with the terminal carboxy group of propane-I ,2,3-tricarboxylic acid.
The structures of xanthocercin A and B, the first isoflavono-lignoids, have been established as 2,3-trans-(3) respectively by spectroscopic methods. These structures have been confirmed by synthesis via phenol oxidative coupling of the appropriate 7,8-dihydroxyisoflavone and respectively sinapyl and coniferyl alcohol. The natural occurrence of xanthocercin A and B as single regioisomers and their regiospecific formation during synthesis presumably originate from marked differences in susceptibility to oxidation of the hydroxy functions in their 'catechol precursors'.
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