NMR structural characterization from one-bond 13 C13 C couplings: Complete assignment of a hydrogen-poor depsidone.

Abstract

The connectivity, conformation, tautomeric form, and dynamics of a new depsidone (perisalazinic acid) were characterized using one-bond 13 C13 C NMR scalar couplings (1 JCC ) obtained from the INADEQUATE experiment. Characterization of perisalazinic acid using more conventional NMR techniques is problematic due to the extremely limited number of CH protons present. In the present study, 81 candidate structures were considered and a best fit structure was selected by comparing computed 1 JCC values for each candidate to 15 experimental values. Of the six flexible moieties in perisalazinic acid, three are adequately represented by a single orientation stabilized by intramolecular hydrogen bonding. The three remaining groups are present as mixtures of conformers with two sites consisting of a pair of conformations and another disordered over six orientations. This study demonstrates the feasibility of complete three-dimensional structural characterization of an unknown using only theoretical and experimental 1 JCC values.