Combination of biophysical and structural techniques allowed characterizing and uncovering the mechanisms underlying increased binding affinity of lactosamine derivatives for galectin 3. In particular, complementing information gathered from X-ray crystallography, native mass spectrometry and isothermal microcalorimetry showed favorable enthalpic contribution of cation-pi interaction between lactosamine aryl substitutions and arginine residues from the carbohydrate recognition domain, which resulted in two log increase in compound binding affinity. This incrementing strategy allowed individual contribution of galectin inhibitor moieties to be dissected. Altogether, our results suggest that core and substituents of these saccharide-based inhibitors can be optimized separately, providing valuable tools to study the role of galectins in diseases. (C) 2017 Elsevier Inc. All rights reserved.