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

摘要

A series of singly branched a-dextrins with dp greater than or equal to 5 was prepared by treating amylopectin with an alpha-amylase (Termamyl) and then with beta-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 6(2)-alpha-maltotriosyl-maltotriose, 6(3)-alpha-maltosyl-maltotetraose and 6(2)-alpha-maltosyl-maltotetraose. H-1 and C-13 NMR parameters of these compounds and of dp5, 6(2)-alpha-maltosyl-maltotriose, are discussed in relation to the linkage pattern of the different glucose units and compared with similar parameters in the linear maltodextrins. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 27]