The cooperative action of two boronic acids is indispensable to the selective binding of saccharides in aqueous solution and the binding process can be spectrophotometrically monitored by using porphyrins as a chromophoric probe. It is not so easy, however, to synthesize porphyrins that satisfy these prerequisites, i.e., porphyrins bearing two appropriately-arranged boronic acid groups within a molecule. In this paper, we report that such a diboronic-acid-based porphyrin receptor can be easily designed by utilizing the self-assembling nature of a Zn(II) porphyrin and an axial ligand: That is, a mixture of boronic-acid-appended Zn(II) porphyrin (1-Zn) and 3-pyridylboronic acid (2) self-organizes to create a novel diboronic acid system for saccharide (S) recognition. Thus, the 1-Zn·2·S ternary complexes give the CD spectral pattern inherent to saccharide absolute configuration. The present study is a new example for sugar sensing using a boronic acid-porphyrin self-assembly system.
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