The binding of banana lectin (BanLec) to laminaribiose (Glcb1,3Glc) and a series of novel synthetic analogs was measured by titrn. calorimetry to assess the contribution of the hydroxyl groups of the reducing glycosyl moiety and its 3-O-b-substituent to binding. Key areas of interaction involved the 1, 2, and 6 positions of the reducing-terminal hexose unit. The a-anomeric configuration of the reducing hexose was strongly favored over the b-anomer. The 2-hydroxyl in the axial position (mannose) also enhanced binding, whereas the 6-hydroxymethyl group was essential, because xylopyranose in the reducing position was inactive. The 3-O-b-glucosyl unit of Me a-laminaribioside could be replaced by any of its monodeoxy derivs. However, the 49-deoxy deriv. or axial hydroxy (galactosyl) substitution was somewhat detrimental to binding. 3-O-substitution with the (S)tetrahydropyranyl ring or a benzyl group had similar effect as 49-deoxyglucosyl substitution. Surprisingly, p-nitrobenzyl or b-xylosyl 3-O-substitution greatly enhanced binding of the reducing glucosyl or mannosyl deriv. Chem. syntheses of a no. of novel disaccharides and analogs prepd. for this study are described. [on SciFinder (R)]