Tawicyclamides A and B, new cyclic peptides from the Ascidian Lissoclinum patella: studies on the solution- and solid-state conformations

Gypsins A−D from Gypsophila arabica

“…The octapeptide skeleton was suggested from the presence of eight carbonyl carbons in the 13 C NMR spectrum ( Table 2) between δ 170.0 and 173.3. The greater number of methylene carbons (12) and unsaturation number (16) suggested additional proline units compared to 1 and 2. Eight amide carbonyls, one aromatic ring, and three proline moieties accounted for 15 degrees of unsaturation, leaving one for the cyclic structure of 3.…”

Three‐dimensional structure of the α‐MSH‐derived candidacidal peptide [Ac‐CKPV]2

“…A qualitative evaluation of the NOE connectivities showed the presence of strong d α N ( i , i + 1) NOEs along the entire peptide, suggesting that all the amide bonds, with exception of the Lys 2 ‐Pro 3 bond, preferentially adopt a trans ‐conformation. With regard to the Lys 2 ‐Pro 3 peptidic bond, analysis of dipolar coupling in NOESY spectra (23) and/or by 13 C‐NMR data (24) in solution can distinguish cis ‐ and trans ‐Pro forms. Thus, the presence of a strong NOE between C α H of Lys 2 and C δ Hs of Pro 3 (23) and the small chemical shift difference between β ‐ and γ ‐carbon atoms (Δ δ C β −C γ ) of the proline residue (24) clearly indicate the trans ‐nature of the Lys 2 ‐Pro 3 peptidic bond as well.…”

“…With regard to the Lys 2 ‐Pro 3 peptidic bond, analysis of dipolar coupling in NOESY spectra (23) and/or by 13 C‐NMR data (24) in solution can distinguish cis ‐ and trans ‐Pro forms. Thus, the presence of a strong NOE between C α H of Lys 2 and C δ Hs of Pro 3 (23) and the small chemical shift difference between β ‐ and γ ‐carbon atoms (Δ δ C β −C γ ) of the proline residue (24) clearly indicate the trans ‐nature of the Lys 2 ‐Pro 3 peptidic bond as well. These observations, along with the lack of conformational heterogeneity suggested by the 1 H‐NMR spectrum, reasonably exclude the possibility of cis / trans ‐isomerism of the Lys 2 ‐Pro 3 peptidic bond.…”

“…A qualitative evaluation of the NOE connectivities showed the presence of strong d aN (i, i + 1) NOEs along the entire peptide, suggesting that all the amide bonds, with exception of the Lys 2 -Pro 3 bond, preferentially adopt a trans-conformation. With regard to the Lys 2 -Pro 3 peptidic bond, analysis of dipolar coupling in NOESY spectra (23) and/or by 13 C-NMR data (24) Further structural information was obtained by studying the temperature dependence in chemical shifts of NH protons. The chemical shifts of exposed protons can be strongly influenced by environmental changes.…”

Synthesis and biological properties of the seven alanine‐modified analogues of the marine cyclopeptide hymenamide C

“…Isomeric cis and trans Xxx-Pro forms can be distinguished in solution by careful analysis of the pattern of dipolar couplings in the ROESY spectra [12]. This 1 H NMR method relies on the observation that cis Xxx-Pro bonds are likely to give Hα-X/Hα-Pro NOE effects with the preceding residue in the sequence (Xxx), whereas an Hα-X/H 2 δ-Pro NOE effect is observed for trans Xxx-Pro bonds.…”