NMR structural characterization from one‐bond 13C?13C couplings: Complete assignment of a hydrogen‐poor depsidone

The connectivity, conformation, tautomeric form, and dynamics of a new depsidone (perisalazinic acid) were characterized using one‐bond ¹³C? ¹³C NMR scalar couplings (¹J_CC) 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 ¹J_CC 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 ¹J_CC values.