A novel diaza-18-crown-6-based saccharide receptor (4) bearing two boronic acid groups has been developed. In 4 boronic acid groups in the side arms interact as Lewis acids with amines and boron atoms are changed to sp(3) hybridization through the B ... N interaction. Because of this hybridization, the boronic acid groups can bind saccharides even in a neutral pH region. Judging from the distance between two boronic acid groups in 4 assuming a syn conformation, one can expect that 4 forms 1:1 cyclic complexes with monosaccharides. These are confirmed by circular dichroism spectroscopy of 4 in the presence of glucose and allose. UV photometric titration studies showed that the boronic acid groups and metal cation bound to the crown cavity competitively interact as Lewis acids with the crown amines. As a result, saccharides and metal cations "communicate" with each other in an allosteric manner. It was shown that added metal cations can affect the saccharide binding ability of 4 through the competitive interaction with the crown amines and the conformational change of the crown ether ring.