Cyclic oligomers (macroaldonolactones) from a protected d-galactonic acid monomer

Dicyclohexylcarbodiimide-promoted self-condensation of 2,3:4,5-di-O-isopropylidene-d-galactonic acid (3) led to the macrocyclic oligomeric cyclo(2,3:4,5-di-O-isopropylidene-(1→6)-d-galactonate)₂] (4) and cyclo(2,3:4,5-di-O-isopropylidene-(1→6)-d-galactonate)₃] (5), having, respectively, 14- and 21-membered rings. The macrocycles 4 and 5 were also synthesized by cyclization of the respective linear dimer 11 and trimer 14 ω-hydroxy acids precursors prepared by stepwise additions of 3. Compounds 4 and 5 are biomaterials that may be described as macrolactone-cyclodextrins.