Stereochemical studies on ascaulitoxin: a J-based NMR configurational analysis of a nitrogen substituted system

The J-based NMR configurational analysis was applied to the determination of relative stereochemistry of the ascaulitoxin molecule (1), a phytotoxic metabolite with herbicidal activity against Chenopodium album. This method is particularly suitable for acyclic structures containing hydroxy(alkoxy) groups, because in this kind of system, besides 3JH–H and 3JC–H, 2JC–H values can also be used to extract additional angular information. Ascaulitoxin (1), with its bis-amino acid side chain containing four stereocenters, two of which with nitrogen substituents, required a more careful analysis of heteronuclear J-couplings, also in comparison with theoretical values obtained by ab initio methods.