The thiourea group has been exploited to link two or four carbohydrate units at the upper rim of tetrapropoxycalixarene derivatives in the cone conformation. Two synthetic methodologies were used, the first one consisting of the condensation of di- and tetraminocalixarenes with the isothiocyanate of monosaccharides in dry CH2Cl2 at room temperature and the second one exploiting the condensation of an aminolactoside with a calixarene isothiocyanate. The first method allows the glycoconjugates to be obtained in 75-80% overall yields. The difunctionalised derivatives exist in a closed flattened cone conformation in CDCl3 and CD3OD due to the formation of intramolecular hydrogen bonds involving the thiourea groups which are broken in DMSO-d(6) to give an open flattened cone conformation. The thiourea groups act not only as linkers but also as binding units for anionic substrates as evidenced by solution H-1 NMR and ESI-MS experiments. Turbidimetric analysis indicates that the tetraglucoside and tetragalactoside clusters give specific interactions with Concanavalin A (Con A) and peanut lectin (PNA), respectively Both features show that the neoglycoconjugates could also be used as site specific molecular delivery systems.
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