Synthesis of Photoactive α‐Mannosides and Mannosyl Peptides and Their Evaluation for Lectin Labeling

Abstract

AbstractAdhesion to the glycosylated surface of eukaryotic cells, mediated by lectins for example, plays an important role in inflammation and other cellular processes of living organisms. To elucidate the mechanisms involved in the adhesion to cell surfaces and their biological consequences, the investigation of the molecular interactions between carbohydrate recognition domains of lectins and their ligands is of relevance. In this work, we have selected the photoaffinity labeling technique for the exploration of the ligand binding to mannose‐specific lectins, particularly the α‐mannose‐specific adhesin FimH, which is expressed at the tips of type 1 fimbriae of Escherichia coli bacteria. We have designed and synthesized a series of mannosides and glycopeptides derived thereof that are equipped with a photoactive functional group. It was our goal to compare the properties and labeling potencies of different types of photolabile residues, and therefore, photolabeled mannosides with an azide, a diazirine, and a benzophenone moiety were synthesized. Their crosslinking activity was investigated by photolysis in the presence of six different amino acids and with three model peptides, angiotensin II, PTHIKWGD, and pentaglycine as well. The crosslinked adducts so obtained were analyzed by mass spectrometry. In addition, difunctionalized mannosides were sought that contained a photolabel and a biotin marker to facilitate the isolation and the eventual identification, respectively, of the photolabeled peptides and proteins. To realize this concept, we have employed orthogonally functionalized glycoamino acid building blocks, which could be utilized as scaffold molecules for the synthesis of our bifunctional target molecules. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)