A new fumonisin has been isolated from liquid cultures of Fusarium moniliforme. The new compound was separated from fumonisin B₁ by preparative hplc and characterized by liquid sims, gc-ms analysis of TMSi and TFA derivatives, and ¹H and ¹³C nmr. The new compound, fumonisin C₁ [2], lacked the amino-end terminal-methyl group of fumonisin B₁ [1] and is the diester of 13,14-propane-1,2,3-tricarboxylic acid and 1-amino-11,15-dimethyl-2,4,9,13,14-pentahydroxynonadecane. Fumonisins are a recently discovered class of fungal mycotoxins implicated in a number of animal diseases (1-3). Epidemiological studies have indicated that fumonisins may cause human esophageal cancer (4). Fumonisins are produced by several species of Fusaria within section Liseola, but the most copious producers are found within the species Fusarium moniliforme Sheldon (5). Fumonisin B₁ [1] was first characterized in 1988 (6) and typically accounts for 70% of the total fumonisins produced. Three other fumonisins, (A₁, A₂, and B₂) were reported by Bezuidenhout et al. (6). The A-series fumonisins are acetylated on the amino group while the B-fumonisins have a free amine. The A-fumonisins have, so far, not been reported by other investigators and may be artifacts of the isolation procedure employed by Bezuidenhout et al. (6). Fumonisin B₂ is produced in lesser quantities than [1] and usually accounts for 20-30% of the total fumonisins. In 1992, Plattner et al. (7) reported a third fumonisin, B₃, which is a structural isomer of B₂. In this paper we report the isolation of a new fumonisin designated C₁ [2]. Preparative hplc of liquid culture extracts of F. moniliforme M-2326 under three mobile phase conditions yielded 21 mg of [2]. Compound [2] was analyzed by liquid sims, ms/ms, hydrolysis followed by gc-ms (9), and ¹H and ¹³C nmr. A mol wt of 707 was determined by fabms in a glycerol matrix (M⁺H⁺ 708). The mol wt of [1] is 721, yielding a difference of 14 daltons between [1] and [2], indicating loss of a methyl group. A comparison of ms/ms spectra of [1] and [2] showed that the backbone of [2] was 14 daltons less than [1], suggesting a methyl group was lost on the fumonisin backbone. Hydrolysis of [1] and [2] in base was followed by derivatization to form trifluoroacetates (TFA) and trimethylsilyl (TMSi) derivatives which were analyzed by electron ionization gc-ms (9). The mol wt observed as the molecular anion in negative cims of the TFA derivative of [2] was 967, compared to 981 for [1], and again indicated the loss of a methyl group as suggested by the liquid sims spectrum. In eims the TFA derivative of [1] showed an intense fragment at m/z 140 which arises from cleavage between C-2 and C-3. In the eims of the TFA derivative of [2] this signal shifted to m/z 126, indicating that loss of the methyl group occurred on the amino-end of the fumonisin backbone. Similarly in the spectra of the TMSi derivatives the signal from cleavage between C-2 and C-3 of [1] was observed at m/z 116 in [1], and the signal from cleavage between C-1 and C-2 in [2] was at m/z 102. These data together strongly suggest that the difference between [1] and [2] is that the amino terminal carbon in [1] is absent from [2]. The ¹³C- (Table 1) and ¹H-nmr data (data not shown) provide further evidence for the structural assignment of [2]. The chemical shifts of [1] (7) compared to [2] show that signal for C-1 is absent in the spectrum of [2]. The shift for the amino-bearing carbon in compound [2] moved upfield 8 ppm as expected. The ¹H-nmr spectrum of [2] is similar to that of [1] except that the doublet for C-1 at 1.3 ppm is missing in [2]. Thus, the structure of [2] is consistent with the ms and nmr data presented.