Studies On Turn Structure Of Peptide Chain Constructed By Amino Acids

The turn conformation widely exists in proteins and bioactive polypeptide structure,and the common types of turn structure are ?-,?-,?-and ?-turn which are composed of 3,4,5 and 6 of amino acids respectively.Studies have shown that endogenous peptides containing innate ?-turn or the ones with ?-turn modified segments can be applied as enzyme inhibitors and antagonists to different target proteins,that make them as lead compounds for a new generation of pesticides in agriculture.Herein,seven polypeptides chains consisting of ?-amino acid and three polypeptides chains consisting of simulated ?-amino acid were constructed using liquid-phase peptide synthetic method and were confirmed via ¹H,¹³ C NMR and MS analysis.Constant--gradient and variable-temperature ¹H NMR spectra detected the formation of intram--olecular hydrogen bond in polypeptides.Results indicated that five of them?Boc-Gly--L-Pro-Gly-Aniline,Boc-Gly-Gly-L-Pro-Gly-Aniline,Boc-Gly-L-Pro-Gly-Gly-Aniline,Boc-Gly-L-Pro-Gly-Ben,Boc-Gly-Gly-Gly-Aniline?formed intramolecular hydrogen bond while the other two?Boc-L-Pro-Gly-Gly-Gly-Aniline and Boc-Gly-Gly-L-Pro--Aniline?did not,suggesting that peptides with-Gly-L-Pro-Gly-fragments are prone to facilitate intramolecular hydrogen bond formation and the aniline at the terminus exerts no influence on it,and that the cis-conformation of L-Pro can be passed on to the next amino acid,resulting in conformation changes possibly from ?-turn to ?-turn.Besides,another three polypeptides consisting of simulated ?-amino acids were obtained,and results showed that Boc-Gly-Atc-Gly-Aniline and Boc-Gly-Gly-Atc-Gly-Aniline had no intramolecular hydrogen bond formed while the other Boc-Gly-Ant-Gly-Aniline did,indicating that 2-aminobenzoic acid of the side chain may provide cis-transformation for turn conformation which 3-amino-thiophene-2-caboxylic acid ring cannot.