Structural analysis of hydantoins and 2-thiohydantoins in solution using 13C, 1H NMR coupling constants

One-, two- and three-bond carbon-13; proton scalar spin-spin coupling constants (1JC,H,2JC,H,3JC,H) have been determined for a series of hydantoin- and 2-thiohydantoin derivatives in DMSO-d6 solution using one- and two-dimensional NMR techniques. Simultaneous consideration of several coupling data allowed reliable estimates to be deduced for the ring dihedrals equivalent to the ?, ? and ? angles in peptides. These data are in support of a quasi-planar geometry for the hydantoin ring in solution in close agreement with previous results obtained for the solid state. Rotamer population distributions around the C5-C1' bond have been determined for some 5-substituted derivatives. The existence of four-bond couplings between amide NH protons in 1,3-positions of the imidazolidine ring has been demonstrated for the first time.