Synthesis of novel heterobranched β-cyclodextrins from 42-O-β-D-galactosy-maltose and β-cyclodextrin by the reverse action of pullulanase, and isolation and characterization of the products

From the mixture of 4(2)-O-beta-D-galactosyl-maltose (Gal-G2) and beta-cyclodextrin (beta CD), novel heterobranched beta CDs, (Gal-G2)-beta CD and (Gal-G2)(2)-beta CDs, were synthesized by the reverse action of debranching enzyme. The optimum conditions for the production of (Gal-G2)(2)-beta CDs were examined. A mixture of (Gal-G2)(2)-beta CDs was produced in about 4% yield when Aerobacter aerogenes pullulanase (64 units per 1 g of Gal-G2) was incubated with 1.6 M Gal-G2 and 0.16 M beta CD at 50 degrees C for 4 days. The reaction products, (Gal-G2)(2)-beta CDs, were separated into three peaks by HPLC analysis on a Hypercarb S column. Their structures were analyzed by fast atom bombardment mass spectroscopy and NMR spectroscopies, and confirmed by comparison of their hydrolyzates by beta-galactosidase with the authentic (G2)(2) -beta CDs. The structures of (Gal-G2)(2)-beta CD and three components of (Gal-G2)(2)-beta CDs were identified as 6-O-(Gal-G2)-beta CD, 6(1),6(2)-, 6(1),6(3)- and 6(1),6(4)-di-O-(Gal-G2)(2)-beta CD, respectively.