Side Chain Conformations of Oxytocin and Vasopressin Studied by NMR Observation of Isotopic Isomers^1a

The side chain conformations of several residues of oxytocin and [8-arginine]vasopressin are compared by using measurements of the circumjacent vicinal couplings of ¹H^α, ¹³C', and ¹⁵N’ to β protons and stereospecific β deuteration in series of 18 specifically designed and synthesized isotopic isomers. The conformation(s) of half-cystyls-1 and -6 and tyrosyl-2 is (are) markedly similar when comparing the two peptides, and other residues show only small differences. Conformational classes of side chain are identified. It is concluded that most of the side chain conformations are largely uninfluenced by the differences in the primary structures of the two peptides.