Structure of a mycotoxin produced by Fusarium nivale: 4-acetamido-2-buten-4-olide

Abstract

C6H7NO3, M r = 141.13, monoclinic, P2~/c, a = 8.790 (4), b = 5.314 (2), c = 14.264 (3)A, fl = 96.47 (3) °, Z = 4, U = 662.03 A 3, D e = 1.415 Mg m -3, Cu K~, ~, = 1.5418 A, g = 0.994 mm-k Final R = 0.039 for 963 observed reflexions (I > 20(I)). Both o and L enantiomers appear in the structure. Bond lengths and angles are in agreement with expected values. The lactone ring is planar; mean value of the ring torsion angles is 0.7 (3) ° . The molecules are connected by hydrogen bonds N-H... O (3.000 (4) ,/k) forming infinite chains along b. Introduction. Toxic metabolites produced by the mould Fusarium nivale on tall fescue (Festuca arundinacea Schreb.) cause various maladies in cattle (Tookey, Yates, Ellis, Grove & Nichols, 1972). Among the three isolated toxins (a butenolide, an unknown toxin, and a sesquiterpenoid), the butenolide is the most abundant (ratios 87:8:3) (Yates, Tookey, Ellis & Burkhardt, 1968). The structure of the butenolide, assigned as 4-acetamido-2-buten-4-olide on the basis of the IR, UV and NMR spectra, is in agreement with the X-ray structure determination. Although the butenolide pos- sesses a chiral centre at the y-carbon, the lack of optical rotation between 600 and 290 nm (Yates et al., 1968) suggests isomerization or racemization during isolation and purification. An X-ray structure determination o(0) revealed the presence of both enantiomers in the c(1)