Separation and NMR structural characterisation of singly branched α-dextrins which differ in the location of the branch point

A series of singly branched α-dextrins with dp ≥ 5 was prepared by treating amylopectin with an α-amylase (Termamyl) and then with β-amylase. The dextrins were separated by gel filtration chromatography and the composition of the fractions was checked by HPAEC. Each fraction gave essentially a single peak by HPAEC but NMR spectroscopy indicated that only the fraction corresponding to dp5 consisted of one compound. The fractions corresponding to dp6, 7 and 8 were found to be mixtures of isomers. Three isomers of dp6 were separated by reversed phase HPLC and were characterised by NMR spectroscopy. The isomers were identified as 62-α-maltotriosyl-maltotriose, 63-α-maltosyl-maltotetraose and 62-α-maltosyl-maltotetraose. 1H and 13C NMR parameters of these compounds and of dp5, 62-α-maltosyl-maltotriose, are discussed in relation to the linkage pattern of the different glucose units and compared with similar parameters in the linear maltodextrins.