Ester-linked glycopeptides as tools for studies of biological phenomena

Modifications of plasma proteins, structural proteins and other macromolecu les by glycation (the Maillard reaction) contribute to the development of a ccelerated atherosclerosis and other complications in diabetes and are also involved in the pathogenesis of aging. Monosaccharide esters, which mimic the reactivity of sugar 6-phosphate esters in nonenzymatic glycations, were prepared from endogenous opioid peptide leucine-enkephalin (Tyr-Gly-Gly-Ph e-Leu), smaller peptides of different lengths (Tyr-Pro-Phe-Val, Tyr-Pro-Phe , Tyr-Pro) and from only one amino acid (Tyr) and were used as model compou nds for a study of the Maillard reaction in vitro. It was found that these compounds readily undergo intramolecular reactions leading to different typ es of products, such as Amadori compounds, imidazolidinones, glycosylamine, diketopiperazine, pyrrololactone, etc. The obtained results demonstrate th at the chemical properties of the glycopeptides studied are determined by t he structure and length of the peptide chain, suggesting that similar produ cts may be also generated in the early stages of the Maillard reaction in v ivo.