Norsolorinic acid aflatoxin intermediate

There is considerable indirect and direct evidence that the PKS responsible for the assembly of norsolorinic acid (NSA, 79), the first isolable intermediate in the pathway to the aflatoxins, is primed by a hexanoate starter and, indeed, as discussed above,feeding [l- Cjhexanoic acid to averufin-producing cultures of Aspergillus parasiticus was reported to give some intact incorporation. To study this further we developed a method for production of NSA (79) in shake cultures and fed [2-2H3]hexanoate (Scheme 21) to these cultures in the form of the free acid (76), the ethyl ester (77) and finally the NAC thioester (78) [67]. NMR... 

Norsolorinic acid (NOR) is the first stable aflatoxin intermediate in the pathway (8, 9). The predicted conversion product from PKS in the aflatoxin... 

The biochemical events prior to the elaboration of the aflatoxins were clarified by the use of mutants, and enzyme inhibitors and by incorporation studies of potential precursors. Norsolorinic acid (14), averufin (8), versiconal acetate (19) (from biosynthetic inhibitors), and versicolorin A (21) comply with two of the postulated requirements for an intermediate i.e., they are overproduced by a mutant blocked in aflatoxin synthesis and furthermore are converted into aflatoxin by the wild-type culture of A. parasiticus. In view of the low incorporation of acetate into aflatoxin Bj [relative specific activity (RSA) = 0.24 vs. a maximum of 9.0], the high RSA values and the higher quantities of aflatoxins derived from the above-mentioned four precursors (14, 8, 19, and 21), as compared to acetate, provide strong evidence for their conversion into the aflatoxins without the intermediary formation of acetate (Singh and Hsieh, 1977). 

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