NMR structural studies of fumonisin B1 and related compounds from Fusarium moniliforme.

Fumonisin B1 (FB1) is the primary mycotoxin produced by Fusarium moniliforme and appears to be responsible for the varied toxigenic effects associated with ingestion of this mold, particularly that of the inhibition of sphingolipid biosynthesis. Understanding the structure and biosynthesis of fumonisins is a key factor in determining structure/activity relationships. To this end, Nuclear Magnetic Resonance (NMR) methods have been used to identify various derivatives of FB1, both naturally occurring and synthetic. With accurate chemical shift assignments, NMR may be used to determine the level of impurities in toxicological grade FB1 preparations. Specifically enriched FB1 was prepared from F. moniliforme cultures using 13C-enriched acetate as well as several 13C-enriched amino acids. 13C NMR analysis indicates that the biosynthesis of fumonisins involves the addition of methionine-derived methyl functions, glutamate-derived tricarballylic ester functions and alanine to an 18 carbon hydrocarbon backbone that is likely polyketide in origin. With the goal of obtaining a crystalline compound for the determination of absolute configuration, several derivatives of FB1 have been prepared, and NMR analysis used to determine the relative and absolute configuration of the 10 stereocenters present in this molecule.