CD AND FTIR SPECTROSCOPIC STUDIES OF AMADORI COMPOUNDS RELATED TO THEOPIOID-PEPTIDES

Circular dichroism (CD) and Fourier transform infrared (FTIR) spectros copy have been used to investigate conformational effects of glycation on the secondary structure of opioid peptide Leuenkephalin and on str ucturally related peptides in 2,2,2-trifluoroethanol (TFE) solution, C D spectral analysis of Leu-enkephalin-related Amadori compounds reveal ed that attachment of the protected or free sugar may influence not on ly the distribution of the backbone but also the side-chain conformati on of the Tyr moiety. The amide I region of the FTIR spectra analysed by self-deconvolution and curve-fitting methods revealed that Leu-enke phalin is present as a mixture of beta-sheet and gamma-turn conformers in TFE solution, while its methyl ester likely adopts a beta-turn con formation, FTIR spectroscopy has shown that no major spectral changes occur in the peptide part of glycated (Amadori) compounds as compared to parent peptides, The structurally related Tyr-Gly-Gly tripeptide de rivatives contain amide I components at ca. 1630 and ca, 1645 cm(-1) c onsistent with the presence of gamma-turns with strong and weak 1 <-- 3 H-bondings, respectively, The attachment of the protected or free su gar moiety to pentapeptides appears to destabilize beta-turns but not to affect H-bonded gamma-turns. In the spectra of Amadori compounds co ntaining a free sugar moiety, the component band at ca. 1730 cm(-1) su ggests the presence of the open-chain sugar form, Based on the studies presented herein, FTIR spectroscopy is shown to be a powerful tool fo r the structural analysis of glycated peptides, in particular for the detection of the keto form of the sugar and turn conformations of the peptide part of the molecule.