| Structure Identification: |
| Journal of Chromatography A,1993,641(1):95-100 | | Isolation and determination of AAL phytotoxins from corn cultures of the fungus Alternaria alternata f. sp. lycopersici[Reference: WebLink] |
METHODS AND RESULTS:
The fungus Alternaria alternata f. sp. lycopersici produces a group of four related host-specific phytotoxins (AAL toxins) which can be divided into two groups (TA and TB), each of which exists as an equilibrium mixture of two structural isomers. The AAL toxins were isolated from corn cultures by aqueous extraction, followed by purification on Amberlite XAD-2 resin, separation of TA from TB on silica gel and final purification on a semi-preparative high-performance liquid chromatographic (HPLC) system. A rapid, sensitive and reproducible method was developed to determine these toxins in culture material in order to monitor toxin production on corn cultures. The method consisted of aqueous extraction, C18 solid-phase extraction clean-up, precolumn derivatization with o-phthaldialdehyde and reversed-phase HPLC with fluorescence detection.
CONCLUSIONS:
An isocratic HPLC system was developed that separated the structural isomers of TA and TB within a chromatographic analysis time of 24 min. | | Journal of Agricultural and Food Chemistry, 1994, 42(2):327-333. | | Structural characterization of three new AAL toxins produced by Alternaria alternata f. sp. lycopersici.[Reference: WebLink] |
METHODS AND RESULTS:
Three new pairs of biologically active regioisomeric toxins (toxins TC, TD, and TE) were isolated from liquid cultures of alternata f.sp. lycopersici, purified using standard chromatographic procedures, and their structures elucidated following interpretation of spectra obtained from and mass spectrometry experiments. Each of the toxin congeners is structurally similar to the toxin TA, which was characterized earlier from culture filtrates of this fungus. toxin TC resembles TA but differs in its lack of at C4 and C5. toxin TE is the N-acetylated form of TC. Spectroscopic data are reported to confirm that TB is similar to TA but lacks a at C5, as suggested earlier. toxin TD is the N-acetylated form of TB.
CONCLUSIONS:
All five pairs of regioisomers arise as products of fungal and do not appear to be generated during isolation. All regioisomeric pairs induce the genotype-specific necrosis characteristic of toxin TA in bioassays but differ markedly in relative toxicity. |
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