Mannoside dimers

Scheme 4. Palladium(0)-catafyzed syntheses of mannoside dimers using Sonogashira cross-coupling reactions.

Scheme 6. Comparative structures of mannoside dimers prepared in this study.

Scheme 7. Synthesis of other mannosides dimers using a tethering unit.

Diacetylene-bridged dimers 18, 25, and 28 were more conveniently prepared (47-68% yields after Zemplen treatment) by a modified Glaser (27) oxidative homocoupling under Hay s conditions (28) of the corresponding ethynylphenyl mannosides using copper(II) acetate in refluxing pyridine (48 h.). 

To further expand the family of mannoside clusters obtainable from the alkyne derivatives, we also prepared cyclotrimerized hexamers using dicobalt octacarbonyl according to a known strategy (34). Thus dimer 37 and 30 were treated with Co2(CO)8 in refluxing dioxane to provide 48 and 50 in 61% and 42% yield, respectively (Scheme 9). 

A schematic representation of the cross-linked behavior of the best dimeric candidate (18) is illustrated (Fig. 2). The hypothetical lattice structure shown was based on the general behavior of natural (39) as well as non-natural (41) mannosides. The above cross-linking process is suggested to be analogous to the... 

The 5- or 6-coordinate tin which is present in the solid dioxastannolanes and di-oxastannananes shows high-field 119Sn signals in the solid state NMR spectrum. For example, the dimer of the ethylidene equivalent of 14-9 shows signals at -126 and -129 ppm for the 5-coordinate tin (-125 in CDCI3 solution), and the mannoside pentamer shows signals at -119 and -127 ppm for the two terminal 5-coordinate tin atoms, and -223 and -234 ppm for the inner 6-coordinate tin atoms. 

New research on conformational properties of carbohydrates was carried out by Elli et al. who chose fully sulfated maltotriose alpha-beta C-C linked dimer as the object of study. Leino et al. focused their attention on phosphorylated p-(l-> 2) linked mannosides (mannotriose and tetraose) similar to those found in nature on the cell surface of C. albicans fungus. Conformational flexibility of 5g losides with aromatic aglycon moiety was studied by Widmalm et al. The NMR studies were carried out in different solvents in order to gain information on conformational equilibria of the saccharide units that may exist in enzyme active sites of polarity similar to appropriate solvent. Perez and Widmalm et al. elucidated conformational preferences of the E. call O-antigen polysaccharides using NMR analysis of intra and inter-residue proton-proton distances from NOESY experiments. The linear tetra-... 

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