Structure and Ethanol Complexation of Cyclic Tetrasaccharide in Aqueous Solution Studied by NMR and Molecular Mechanics

Abstract

Relatively few examples are known of cyclic oligosaccharides, the best known being cyclodextrin.1,2) Other cyclic oligosaccharides have been prepared by means of enzymes and chemical syntheses. 3-6) Cyclo-[→6]-a -D-glucopyranosyl-(1→3)-a -D-glucopyranosyl-(1→6)-a -D-glucopyranosyl-(1→3)-a -D-glucopyranosyl-(1→), a cyclic tetrasaccharide (CTS), is prepared by enzymic hydrolysis of the polysaccharide alternan.3) Recently, CTS has also been synthesized by glycosyltransferase.6) This tetrasaccharide attracts increased interest due to relative resistance to microbial and enzymic degradation. Most of the signals in proton and carbon NMR spectra were assigned.3) The structure of CTS was determined by X-ray analysis of single crystals and molecular dynamics simulations: CTS has a plate shape. 7)Cyclodextrins can entrap many compounds in their cavities. As a result, cyclodextrin is an interesting host compound from the academic viewpoint and is applied in chemicals, pharmaceuticals and foods industries. 1,2,[8][9][10][11][12][13][14] Cyclogentiotetraose peracetate, a cyclic tetrasaccharide, can bind alkali cations in organic solvents.15) The ability of CTS to bind metal cations in aqueous solutions has very recently been investigated.16) To our knowledge, there is no report on the affinity of CTS (Fig. 1) to organic compounds.In the present work, we aimed to estimate the three-dimensional structure of CTS in aqueous solution by proton NMR and molecular mechanics calculations as well as the inclusion property of CTS. The assignment of H6S and H6R was established by spectral simulations and the vicinal spin-spin coupling constants 3 J 5-6S and 3 J 5-6R were determined. These data revealed a clear difference in the internal rotation of the C5-C6 bond between the crystal and solution structures. The rotating frame nuclear Overhauser effect spectroscopy (ROESY) spectrum of CTS was compared with the crystal structure and the structures predicted by molecular mechanics in the presence and absence of water. Because the cavity of CTS is very small, large organic compounds will be not accommodated therein. Therefore we chose ethanol, a relatively small organic molecule and investigated complex formation between it and CTS on the basis of chemical shift data. ExperimentalMaterials The used specimen of CTS · 5H 2 O was 99.97% pure. 6) Commercial samples of tetramethylammonium chloride (Nacalai Tesque Co.), ethanol (Wako Pure Chemicals Co.), and 99.9 atom% deuterium oxide (Aldrich) were used.NMR Measurements All proton NMR experiments were carried out in deuterium oxide at 298.2Ϯ0.1 K. The spectra were recorded on a JEOL Lambda 500 spectrometer. The proton chemical shift and spin-spin coupling constant were determined by Nuts data processing software (Acorn NMR Inc.). The chemical shift of 1 mmol dm Ϫ3 (mM) tetramethylammonium chloride at 3.176 ppm was used as the internal standard. 13,14) Chemical shifts of CTS protons in 10.8 mM CTS solution were determined as a function of the ethanol concentration.Two-dimensional ROESY of a 20 mM...

Purification, Characterization, and Gene Cloning of a Novel Maltosyltransferase from anArthrobacter globiformisStrain That Produces an Alternating α-1,4- and α-1,6-Cyclic Tetrasaccharide from Starch

“…An X-ray crystal structure analysis has shown that CA is shaped like a plate with a depression on one side and has a shallow cavity in the center of its ring (5). CA can complex with ethanol on both the concave and convex sides (9). The oxidation of CA to the dicarboxylic acid yields a selective chelator for Pb 2ϩ , Fe 2ϩ , and Fe 3ϩ (8).…”

Supramolecular Photochirogenesis with Novel Cyclic Tetrasaccharide: Enantiodifferentiating Photoisomerization of (Z)‐Cyclooctene with Cyclic Nigerosylnigerose‐Based Sensitizers

“…The X‐ray crystallographic analysis revealed that this tetrasaccharide possesses only a shallow saucer‐like shape with a small concave at the center . As a supramolecular host, CNN is known to interact with ethanol, whereas a dicarboxylic acid derivative of CNN can selectively chelate some cations …”

“…[26][27][28] The X-ray crystallographic analysis revealed that this tetrasaccharide possesses only a shallow saucer-like shape with a small concave at the center. 29 As a supramolecular host, CNN is known to interact with ethanol, 30 whereas a dicarboxylic acid derivative of CNN can selectively chelate some cations. 31 We became interested in the use of CNN as a potential supramolecular host for the enantiodifferentiating photoisomerization of 1Z because of its inherent chirality and unique chemical structure with a shallow cavity.…”

Enzymatic synthesis of a 2-O-α-d-glucopyranosyl cyclic tetrasaccharide by kojibiose phosphorylase

“…7 CTS binds ethanol on both the concave and convex sides. 8 These properties of CTS open the potential for further applications, for example, as a carrier in drug delivery systems or a base that removes toxic metal cations.…”