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

摘要

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 ~3J_(H-H) and ~3J_(C-H), ~2J_(C-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.