Formation of N-(carboxymethyl)fumonisin B1, following the reaction of fumonisin B1 with reducing sugars

The fumonisins are mycotoxins produced by fungi that contaminate primarily corn and are toxic through interruption of intracellular sphingolipid synthesis. Several reports have indicated that fumonisin B(1) concentrations decreased when heated in aqueous solutions of reducing sugars. The incubation of fumonisin B1 with D-glucose resulted in the formation of N-(carboxymethyl)fumonisin BL, which was characterized by NMR and electrospray mass spectroscopy. We determined the methylene carbon of the carboxymethyl group is derived from C1 on glucose, while the carbonyl carbon is derived from the C2 of glucose, using (13)C glucose. Apparently N-(carboxymethyl)fumonisin B1 arises from Schiffs base formation, Amadori rearrangement to a B-ketoamine, and oxidation with molecular oxygen. N-(Carboxymethyl)fumonisin B1 formation is favored by alkaline conditions (pH > 7), requires molecular oxygen, and is catalyzed by several reducing sugars. N-(carboxymethyl)fumonisin B(1) was detected in raw corn samples that contained fumonisin B(1) (0.5-1.4 ppm) at an average of 4% of the fumonisin B(1) levels.