Malto-oligosaccharide homologues of 3,7-anhydro-2-azi-1,2-dideoxy-D-glycero-D-gulo-octitol+ ++: improved photoaffinity reagents for labelling the malto-oligosaccharide-binding protein of Escherichia coli.

3,7-Anhydro-2-azi-1,2-dideoxy-D-glycero-D-gulo-octitol (2) was synthesized as a beta-D-glucopyranosyl analogue, which could be converted into a series of malto-oligosaccharide derivatives (3-7) by cyclodextrinase-catalyzed glucosyl transfer from alpha-cyclodextrin (cyclomaltohexaose). The pure analogues 3-7 containing 1-5 (1----4)-linked alpha-D-glucose residues inhibited the uptake of maltose via the maltose-binding protein-dependent transport system in Escherichia coli. The concentration of half-maximal inhibition of maltose transport at 60nM decreases with increasing chain-length of the analogue, reaching a minimum at 0.02 mM for 6 (4 glucose residues). 3H-Labelled alpha-cyclodextrin was prepared by partial oxidation and reduction of the aldehyde groups with NaB3H4. Radiolabelled 5a was used to photolabel the binding site of the maltose-binding protein.