| Abstract | The conformations of fourteen thiopeptides in three solvents (acetonitrile, methylene chloride, DMSO) are discussed as inferred by interpretation of the amide infrared absorptions. The spectra indicate that the enhanced acidity of the thioamide NH proton (and hence the stronger hydrogen-bonding donor potential) promotes the formation of C5 ring structures that are not often found in unsubstituted peptides, and strong C(S)NH → OC hydrogen bonds render both C, (γ-turn) and C10 (β-turn) structures more stable than their oxoamide counterparts. The ability of infrared spectra to discriminate among C5, C7, and C10 structures is evaluated and discussed. |
|---|
