Sweet switches : Azobenzene glycosides as photosensitive lectin inhibitors in solution and on surfaces
Non-covalent interactions between carbohydrate ligands and their lectin receptors are accompanied by conformational changes between the interacting partners. Such changes might reflect a principal conformational control of carbohydrate-protein interactions, which has received only little attention until to date. Hence, the central focus of this thesis is to synthesize photoswitchable glycomimetics and investigate the role of light-induced conformational changes in carbohydrate recognition. Thus azobenzene glycoconjugates are principal target molecules of our research. Photoirradiation of azobenzene glycosides at ~ 365 nm induces E→Z isomerization leading to a certain E/Z ratio in the photostationary state (PSS). The special features of azobenzene glycoconjugates featuring an E→Z→E isomerization option in solution will eventually allow us to utilise this type of molecules with -D-mannose-specific lectins. In this context, a new class of azobenzene glycosides were synthesized and their photochromic properties were studied in solution by 1H NMR and UV-Vis spectroscopy and they were tested as inhibitors for type 1 fimbriae-mediated bacterial adhesion, such as the bacterial lectin FimH.. To mimic the cell surface glycocalyx, azobenzene glycosides were immobilised on gold surfaces to form photoswitchable glyco-SAMs. Photoisomerization was performed on the gold surface and monitored by IRRAS and UV-Vis spectroscopy. To get insight in the conformational control of carbohydrate recognition in a multivalence context, photosensitive glyconanopartices were also prepared and binding efficiency of different isomers was tested with the lectin ConA.