Dihydroxypyridine ligands

Trinuclear macrocycles, which contain the dihydroxypyridine ligands L3-L5, represent analogues of 12-crown-3. When investigated for their ability to bind alkali metal ions, it was found that the complexes display a very high affinity for lithium and sodium salts [13,17] (Eq. 1). Simple salts such as LiCl and NaCl are bound extremely strong competition experiments have shown that in chloroform, the binding constants are comparable to those of cryptands [17]. 

It was found that the presence of an amino or aldehyde groups in the meta-position of the arylboronic acid did not interfere in the macrocyclization reaction. This allowed the effective assembly of functionalized boronic acids, dihydroxypyridine ligands, and amines or aldehydes, respectively, in a multicomponent procedure affording pen-tameric boronic acid macrocycles (Scheme 4.7) and tetramer derivatives (Scheme 4.8). 

Key L = ligand (5-chloro-2,3-dihydroxypyridine). Stationary phase Mixture of silica gel G and p-toludine (50 1, w/w). Mobile phase M, = Acetonitrile M2 = methanol M3 = acetonitrile-methanol (1 1). Detection Self colored complexes vizualized on chromatoplate with the help of UV-visible lamp. Conditions Ascending technique, layer thickness 0.5 mm, drying of plates at 40°C for 24 h., run 11 cm, development time 30-40 min. Remarks The values are in the order of Co > Fe > Mn > Cr. Reversed phase HPLC separation of the complexes was also carried out on Zorbax ODS column with acetonitrile-methanol-water (6 1 3) eluent using UV-visible detector. 

Key L = ligand (S-chloro-2,3-dihydroxypyridine). Stationary phase Mixture of silica gel C and p-toludine (50 1, w/w). Mobile phase = Acetonitrile =... 

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