A simple and convenient synthesis of fl-D-galactopyranose derivatives selectively modified at C-l and C-6 is described. A key feature is the selective protection of the 6-OH group of methyl-, allyl-, and (p-nitrophenyl)-|S-D-galactopyranosides using tert-butyldiphenylsilyl chloride, yielding silyl ethers 4-6. After protection of the remaining hydroxyl groups with acetyl, benzoyl, or p-phenylbenzoyl functions, the glycosidic methyl group can be easily split by 1,1-dichloromethyl methyl ether (DCMME) to give galactosyl chlorides 17-19, retaining the temporary protection at C-6. When benzoates or p-phenylbenzoates are used as permanent protection, the tert-butyldiphenylsilyl group (such as in compounds 8-11) can be selectively removed to give 6-OH galactosides 13-16. Some of these were coupled with tetraacetylor tetrabenzoylgalactosyl bromide to yield disaccharides 20-23. Compounds 21 and 22 could be reacted with DCMME to give digalactosyl chlorides 24 and 25. These are useful glycosyl donors for further chain expansion. The coupling of chloride 18 or 19 with nucleophile 14 or 15 under silver triflate/sym-collidine mediated conditions afforded disaccharides 26 and 27 bearing silyl protecting groups at C-6. The latter can be selectively removed, resulting in nucleophiles 28 and 29, which can be coupled with tetraacetylgalactosyl bromide (to give trisaccharide 30) or with chloride 18 to yield trisaccharide 31. The latter one has again a tert-butyldiphenylsilyl function at C"-6, allowing further expansion of the chain from the nonreducing end. The structures of mono-, di-, and trisaccharides were confirmed by and 13C NMR spectra.

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The binding of four monoclonal immunoglobulins, two with specificity for beta(1-->6)-linked D-galactopyranans (IgA X24 and IgA J539) and two with specificity for the chain terminus of alpha(1-->6)-linked d-glucopyranans (IgA W3129 and IgA 16.4.12E), was measured with a number of their homologous oligosaccharide ligands at different temperatures. The results show a linear relationship between lnKa and 1/T, where Ka is the affinity constant and T is the absolute temperature. The unitary free energy of binding, DeltaGu, is virtually independent of T, and the DeltaSu is small when compared with DeltaGu. The enthalpy changes derived from van't Hoff plots are large and negative, indicating an exothermic binding effect, whereas the entropy changes are small and negative, indicating minor overall hydrophobic contributions. Measurements of the free energies of binding, in low and high salt buffers, of methyl beta-d-galactopyranoside and the methyl glycoside of beta(1-->6)-D-galactopyranotetraose with anti-galactan IgA X24 indicate that the monosaccharide has no hydrophobic interaction with the highest affinity subsite of IgA, whereas the tetraoside might have a modest hydrophobic interaction with the three other hapten-binding subsites of IgA. The standard entropy change of binding of the two groups (galactosyl and glucosyl) of oligosaccharides to the two respective sets (anti-galactan and anti-dextran) of antibodies shows a distinct, differing correlation with the hapten chain length within each set. This correlation agrees with the type of association previously established between the antibodies and either the interior determinants of the antigen (in the case of the anti-galactans) or the chain terminus (in the case of the anti-dextrans).