One-Bond C,H Coupling Constants, a New Parameter in Conformational Studies of Peptides? The Cyclo-Sarcosyls

Summary

Carbon-hydrogen spin coupling constants over one bond, ¹J(C,H),were determined for a number of simple open-chain model peptides as well as for cyclo-disarcosyl, cyclo-tetra-sarcosyl and cyclo-octasarcosyl. The dependence of ¹J(Cα,H) on the ionization state of the amino and carboxyl ends of an open-chain peptide and the relative orientation of C-H bond and p_z-orbital of the amide nitrogen is demonstrated. The solution conformation of the cyclo-sarcosyl peptides is discussed as a test case for the new parameter. In peptide systems containing N-methyl groups, the conformational information obtained from ¹J(C,H) can be corroborated by the vicinal coupling constant ³J(C,H) between N-methyl carbon and α-CH proton.

¹³C-NMR spectroscopy, Part XX, for Part XIX see [1].