A cyclic tetrasaccharide, cycloisomaltotetraose, was enzymatically produced from dextran and its crystal structure was determined.

Two bacterial strains isolated from soil, namely Agreia sp. D1110 and Microbacterium trichothecenolyticum D2006, were found to produce a novel oligosaccharide. The oligosaccharide was enzymatically produced from dextran using the culture supernatant of Agreia sp. D1110 or M. trichothecenolyticum D2006. LC-MS and NMR analysis identified the novel oligosaccharide as cyclo-{→6)-α-d-Glcp-(1→6)-α-d-Glcp-(1→6)-α-d-Glcp-(1→6)-α-d-Glcp-(1→}, which was named cycloisomaltotetraose, and abbreviated as CI4. CI4 was subsequently crystalized and its X-ray crystallographic structure was determined. CI4 crystals were shown to be pentahydrate, with the CI4 molecules in the crystal structure displaying a unique 3D structure, in which two glucosyl residues in the molecule were facing each other. This unique 3D structure was quite different from the 3D structure of known cyclic tetrasaccharides. This is the first report of CI4 molecules and their unique crystal structure.