Synthesis and characterization of polyaspartic acid-carbohydrate conjugates: Multivalent sialyl lewis

Spacer-separated sialyl LewisX cyclopeptide conjugates as potential E-selectin ligands

Completely protected sialyl LewisX azide was synthesized from a neolactosamine azide precursor carrying a 3-O-allyloxycarbonyl group as the temporary protecting group. After its Pd(0)-catalyzed deprotection and stereoselective alpha-fucosylation, the obtained LewisX azide was subjected to O-deacetylation in the galactose unit and subsequent regio- and stereoselective sialylation. Reduction of the anomeric azido group afforded the sialyl LewisX amine building block. Two molecules of this tetrasaccharide ligand were conjugated to a preformed cyclooctapeptide containing two equidistant l-asparagine units equipped with carboxy-terminated tetraethyleneglycol side chains to give, after deprotection, the target glycopeptide conjugate. Preliminary biological evaluation of the synthesized bivalent sialyl LewisX cyclopeptide conjugate showed only slightly enhanced inhibition of E-selectin binding in spite of the given flexibility of the two linked saccharide determinants.

Fluorophore Appended Saccharide Cyclophane: Self-Association, Fluorescent Properties, Heterodimers with Cyclodextrins, and Cross-Linking Behavior with Peanut Agglutinin of Dansyl-Modified Saccharide Cyclophane

A saccharide cyclophane bearing an environment-sensitive fluorophore (1) was prepared by introducing not only three branches with a terminal galactose residue but also one with a dansyl moiety into a tetraaza[6.1.6.1]paracyclophane skeleton. Self-association behavior of the dansyl-appended saccharide cyclophane was characterized in aqueous media by fluorescence spectroscopy and dynamic light scattering measurements. At least in the concentrations below 1.0 x 10(-5) M, saccharide cyclophane 1 existed in a monomeric state, whereas it tended to form self-aggregated complexes in the higher concentration. Solvent polarity dependency on the emission spectra of 1 was examined by fluorescence spectroscopy. With increasing dioxane contents in dioxane/water solvents, the fluorescence intensity originating from the dansyl moiety of 1 increased along with a concomitant blue shift of the fluorescence maximum (lambda(em)). In the monomeric state of 1 in water, the dansyl moiety of 1 was not fully included into its cyclophane cavity but partially exposed to the bulk aqueous phase. In the higher concentration ranges in an aggregate state, however, the dansyl group of 1 was located in the apolar cyclophane cavity whose microenvironment was equivalent to the polarity of 1-butanol evaluated on the basis of a correlation between lambda(em) and solvent polarity. This indicates an intermolecular inclusion of the dansyl moiety within the cyclophane. When cyclodextrin (CD) was mixed with 1, the dansyl group of 1 was bound to an internal cavity of CD such as gamma-CD, beta-CD, 6-O-alpha-glucosyl-beta-CD, and 6-O-alpha-maltosyl-beta-CD with binding constants of 7.5 x 10(2), 7.8 x 10(2), 7.7 x 10(2), and 6.0 x 10(2) M(-1), respectively. Such a supramolecular assembling of dansyl-modified cyclophane 1 and CDs caused changes of the fluorescence spectra as well as appearance of induced CD bands in aqueous media. Furthermore, saccharide cyclophane 1 was selectively bound to peanut agglutinin (PNA), galactoside-binding lectin, which was readily monitored by a visible turbidity of the solution due to a cross-linking agglutination of these components, as well as by fluorescence spectroscopy.