Binding of para-substituted phenyl glycosides to concanavalin a

The binding of para-substituted phenyl glycopyranosides of α- D-glucose, β- D-glucose, and α- D-mannose by concanavalin A has been related to the electronic and hydrophobic nature of the substituents by multiparameter regression analysis. Hydrophobicity is an important factor for the binding of the β- D-glucosides, especially in the p-alkyl series; a smaller but mutually comparable dependence on hydrophobicity is noted for each of the p-halogeno, p-alkoxy, and p-acyl substituent series. In the last two series, an additional substituent interaction with the protein might occur. The more tightly bound α- D-mannosides and α- D-glucosides show a constant binding ratio for all p-phenyl substituents. Here, hydrophobic contributions are negligible when compares with electronic effects. Hammett relations ( p−= 0.5) are valid for α- D-glucosides and α- D-mannosides, and can be improved by considering inductive and mesomeric contributions of the substituents. These observations are compatible with crystallographic data at a resolution of 2 Å. Their relevance for the α- D-anomeric specificity, governed by a protein electrophile, is discussed.