STRUCTURAL CHARACTERIZATION OF 3 NEW AAL TOXINS PRODUCED BY ALTERNARIA-ALTERNATA F SP LYCOPERSICI

Three new pairs of biologically active regioisomeric toxins (AAL toxin s TC, TD, and TE) were isolated from liquid cultures of Alternaria alt ernata f. sp. lycopersici, purified using standard chromatographic pro cedures, and their structures elucidated following interpretation of s pectra obtained from NMR and mass spectrometry experiments. Each of th e toxin congeners is structurally similar to the AAL toxin TA, which w as characterized earlier from culture filtrates of this fungus. AAL to xin TC resembles TA but differs in its lack of hydroxyl groups at C-4 and C-5 AAL toxin TE is the N-acetylated form of TC. Spectroscopic dat a are reported to confirm that TB is similar to TA but lacks a hydroxy l group at C-5, as suggested earlier. AAL toxin TD is the N-acetylated form of TB. All five pairs of regioisomers arise as products of funga l biosynthesis and dd not appear to be generated during isolation. All regioisomeric pairs induce the genotype-specific necrosis characteris tic of AAL toxin TA in tomato-bioassays but differ markedly in relativ e toxicity.