The crystal and molecular structure of the trisaccharide erlose as the monohydrate

Investigating the Potential of Phenolic Compounds and Carbohydrates as Acceptor Substrates for Levansucrase-Catalyzed Transfructosylation Reaction

This study characterizes the acceptor specificity of levansucrases (LSs) from Gluconobacter oxydans (LS1), Vibrio natriegens (LS2), Novosphingobium aromaticivorans (LS3), and Paraburkholderia graminis (LS4) using sucrose as fructosyl donor and selected phenolic compounds and carbohydrates as acceptors. Overall, V. natriegens LS2 proved to be the best biocatalyst for the transfructosylation of phenolic compounds. More than one fructosyl unit could be attached to fructosylated phenolic compounds. The transfructosylation of epicatechin by P. graminis LS4 resulted in the most diversified products, with up to five fructosyl units transferred. In addition to the LS source, the acceptor specificity of LS towards phenolic compounds and their transfructosylation products were found to greatly depend on their chemical structure: the number of phenolic rings, the reactivity of hydroxyl groups and the presence of aliphatic chains or methoxy groups. Similarly, for carbohydrates, the transfructosylation yield was dependent on both the LS source and the acceptor type. The highest yield of fructosylated-trisaccharides was Erlose from the transfructosylation of maltose catalyzed by LS2, with production reaching 200 g/L. LS2 was more selective towards the transfructosylation of phenolic compounds and carbohydrates, while reactions catalyzed by LS1, LS3 and LS4 also produced fructooligosaccharides. This study shows the high potential for the application of LSs in the glycosylation of phenolic compounds and carbohydrates.

Octa-O-propanoyl-β-maltose: crystal structure, acyl stacking, related structures, and conformational analysis

The crystal structure of beta-maltose octapropanoate (1) was solved to improve understanding of di-, oligo-, and polysaccharide conformations. The O6 and O6' atoms are in gg and gt orientations, respectively. Extrapolation of the coordinates of the non-reducing residue and observed linkage bond and torsion angles of 1 [Formula: see text] yields a left-handed helix similar to amylose triacetate I. The phi and psi values of 1 are also similar to those of other crystalline, acylated maltose compounds as well as some hydroxyl-bearing molecules. Acylated maltose moieties are often stabilized by stacking of the carbonyl groups and alpha-carbons on O3 and O2' as well as by the exo-anomeric effect. The conformation of 1 is within the 1-kcal/mol contour on a hybrid energy map built with a dielectric constant of 7.5, but corresponds to higher energies on maps made with lower dielectric constants. In one region of phi,psi space, both hydroxyl-bearing and derivatized maltose moieties are found but no inter-residue, intramolecular hydrogen-bonding occurs. In another region, only hydroxyl-bearing molecules crystallize and O2'...O3 hydrogen bonds are always found. In agreement with the energy surfaces, amylose helices extrapolated from available linkage geometries were almost all left-handed.

Linkage and pyranosyl ring twisting in cyclodextrins

Acylated beta-cyclodextrins (beta-CDs) were studied to gain perspective on maltose octapropanoate, the crystal structure of which was reported in the preceding paper in this issue. Acylated beta-CDs are distorted so we looked at other CDs and gained increased understanding of distortion in CDs and possibly, shapes in starch. Classic CDs have six to eight glucose residues in a doughnut shape that is stabilized by a ring of inter-residue O3,,,O2' hydrogen bonds. On a phi,psi energy map for a maltose analog that does not form hydrogen bonds, classic CD linkages have higher energies than structures that are stabilized by the exo-anomeric effect. In distorted beta-CDs, which lack hydrogen bonding, some linkages attain low-energies from the exo-anomeric effect and acyl stacking. Those linkages result in left-handed helical geometry so other linkages are forced by the CD macrocycle to have counter-balancing right-handed character. Permethylated gamma-CDs have two 'flipping' linkages as do some larger native CDs. Flipping linkages allow two left-handed segments to join into a macrocycle, thus avoiding the higher-energy, right-handed forms. Some glucose rings in derivatized beta-CDs have substantial positive twists of the pseudo torsion angle O1-C1...C4-O4, adding right-handed character to balance the left-handed linkages. In substituted gamma-CD, all residues have negative twists, giving extra left-handed character to the short, pseudo-helical segments. In non-macrocyclic molecules the twists ranged from -14 degrees to +2 degrees , averaging -6.1 degrees. In these beta- and gamma-CDs, the twists ranged from -22 degrees to +16 degrees for (4)C(1) rings, and the (O)S(2) ring in acetylated beta-CD has a twist of +34 degrees . Glucose residues in other CDs were less twisted.

Molecular and crystal structure of galactinol dihydrate [1-O-(alpha-D-galactopyranosyl)-myo-inositol dihydrate]

The crystal structure of galactinol dihydrate has been determined by X-ray diffraction. The crystal belongs to the orthorhombic system, space group P2(1)2(1)2, a = 15.898(6), b = 19.357(5), c = 5.104(4) A, and Z = 4. The structure was refined to R = 0.044 for 1818 observed structure amplitudes. The primary hydroxyl group exhibits twofold orientational disorder. The linkage conformation is close to those of alpha-(1 --> 4) linkages in methyl alpha-maltotrioside tetrahydrate and erlose trihydrate. Although there is no interring hydrogen bond in galactinol, an indirect interring hydrogen bond including a water molecule is present. The observed conformation is additionally stabilized by the indirect interring hydrogen bond. The global minimum in the relaxed-residue energy map based on the MM3(92) force-field is close to the observed conformation in the crystal structure. All hydroxyl, ring and water oxygen atoms are involved in a complex three-dimensional hydrogen-bonding network.

A QM/MM analysis of the conformations of crystalline sucrose moieties

Both ab initio quantum mechanics (QM) and molecular mechanics (MM) were used to produce a hybrid energy surface for sucrose that simultaneously provides low energies for conformations that are observed in crystal structures and high energies for most unobserved structures. HF/6-31G* QM energies were calculated for an analogue based on tetrahydropyran (THP) and tetrahydrofuran (THF). Remaining contributions to the potential energy of sucrose were calculated with MM. To do this, the MM surface for the analogue was subtracted from the MM surface for the disaccharide, and the QM surface for the analogue was added. Prediction of the distribution of observable geometries was enhanced by reducing the strength of the hydrogen bonding. Reduced hydrogen-bonding strength is probably useful because many crystalline sucrose moieties do not have intramolecular hydrogen bonds between the fructose and glucose residues. Therefore, hydrogen bonding does not play a large role in determining the molecular conformation. On the hybrid energy surface that was constructed with a dielectric constant of 3.5, the average potential energy of 23 sucrose moieties from crystal structures is 1.16 kcal/mol, and the population of observed structures drops off exponentially as the energy increases.

The crystal and molecular structure of the trisaccharide erlose trihydrate

Erlose [beta-D-fructofuranosyl O-alpha-D-glucopyranosyl-(1-->4)-D-glucopyranoside] trihydrate, C18H32 O16.3H2O, M(r) = 558.48, is orthorhombic, P2(1)2(1)2(1) with a = 31.164(7), b = 13.111(5), c = 11.636(5) A, and Z = 8. The structure was solved by direct methods, and refined to R = 0.035 for 3926 observed reflections. The unit cell contains two independent molecules having a similar conformation. The conformation of the alpha-(1-->2) glycosidic linkage is similar to that observed in erlose monohydrate, whereas the conformation of the alpha-(1-->4) glycosidic linkage differs significantly. The molecule has no intramolecular hydrogen-bonds except for the minor components of three-center bonds, but indirect intramolecular hydrogen-bonds through the water molecules are formed. The hydrogen-bond system in the crystal structure consists of infinite and finite chains crosslinked by water molecules.

The crystal and molecular structure of beta-D-fructofuranosyl alpha-D-xylopyranoside hemihydrate

The crystal and molecular structure of beta-D-fructofuranosyl alpha-D-xylopyranoside (xylosucrose) hemihydrate, C11H20O10.0.5H2O, is orthorhombic, P2(1)2(1)2, with a = 20.919(5), b = 18.727(2), c = 7.071(1) A, V = 2770.1(2) A3, Z = 8, and Dx = 1.541 g.cm-3. The structure was solved by direct methods and refined to R = 0.040 for 2564 observed reflections. Two independent xylosucrose molecules exist in the unit cell, and their conformations about the 1-->2' glycosidic bond are similar to sucrose. The orientations of the primary hydroxyl groups in the two molecules differ. An O-1'...O-2 intramolecular hydrogen bond was observed in the one molecule, while an O-6'...O-5 intramolecular hydrogen bond was observed in the other involving disorder of O-6'.