Methyl 3-O-α-d-mannopyranosyl β-d-glucopyran­oside tetra­hydrate

Lars Eriksson; Göran Widmalm

doi:10.1107/S1600536808021454

. 2008 Jul 31;64(Pt 8):o1639–o1640. doi: 10.1107/S1600536808021454

Methyl 3-O-α-d-mannopyranosyl β-d-glucopyranoside tetrahydrate

Lars Eriksson ^a,^*, Göran Widmalm ^b

PMCID: PMC2962246 PMID: 21203328

Abstract

The title compound, C₁₃H₂₄O₁₁·4H₂O, forms extended hydrogen-bonded networks. These are present between disaccharides, but not as inter-residue hydrogen bonds, as well as to water molecules that in addition form an intermolecular chain of hydrogen bonds. The conformation of the disaccharide is described by the glycosidic torsion angles ϕ_H = −34° and ψ_H = −5°. Macroscopically, the disaccharide was observed to be hygroscopic.

Related literature

For related literature, see: Cremer & Pople (1975 ▶); Eriksson & Widmalm (2005 ▶); Eriksson et al. (1997 ▶, 2000 ▶, 2002 ▶); Färnbäck et al. (2003 ▶, 2008 ▶); Hassel & Ottar (1947 ▶); Huskens (2006 ▶); Jansson et al. (1990 ▶); Juaristi & Cuevas (1992 ▶); Odelius et al. (1995 ▶); Vishnyakov et al. (2000 ▶).

Experimental

Crystal data

C₁₃H₂₄O₁₁·4H₂O
M _r = 428.39
Monoclinic,
a = 18.275 (3) Å
b = 7.7293 (12) Å
c = 13.910 (3) Å
β = 97.87 (2)°
V = 1946.4 (6) Å³
Z = 4
Mo Kα radiation
μ = 0.14 mm⁻¹
T = 291 (2) K
0.40 × 0.30 × 0.15 mm

Data collection

Stoe IPDS diffractometer
Absorption correction: numerical (X-RED; Stoe & Cie, 1997 ▶) T _min = 0.95, T _max = 0.98
8973 measured reflections
2017 independent reflections
1706 reflections with I > 2σ(I)
R _int = 0.037

Refinement

R[F ² > 2σ(F ²)] = 0.025
wR(F ²) = 0.059
S = 0.99
2017 reflections
287 parameters
9 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.13 e Å⁻³
Δρ_min = −0.14 e Å⁻³

Data collection: EXPOSE (Stoe & Cie, 1997 ▶); cell refinement: CELL (Stoe & Cie, 1997 ▶); data reduction: INTEGRATE (Stoe & Cie, 1997 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Bergerhoff, 1996 ▶); software used to prepare material for publication: PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808021454/om2251sup1.cif

e-64-o1639-sup1.cif^{(23.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808021454/om2251Isup2.hkl

e-64-o1639-Isup2.hkl^{(99.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected torsion angles (°).

O5m—C5m—C6m—O6m	−64.9 (2)
C4m—C5m—C6m—O6m	57.2 (2)
O5g—C1g—O1g—C7	−71.2 (2)
C2g—C1g—O1g—C7	168.7 (2)
O5m—C1m—O3g—C3g	85.18 (19)
C2m—C1m—O3g—C3g	−151.40 (15)
C4g—C3g—O3g—C1m	112.63 (18)
C2g—C3g—O3g—C1m	−124.11 (18)
O5g—C5g—C6g—O6g	−69.7 (2)
C4g—C5g—C6g—O6g	50.1 (2)
H1m—C1m—O3g—C3g	−34
C1m—O3g—C3g—H3g	−5

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Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2m—H2m1⋯O3mⁱ	0.82	1.96	2.732 (2)	156
O3m—H3m1⋯O6mⁱⁱ	0.82	1.89	2.705 (2)	172
O4m—H4m1⋯OW4ⁱⁱⁱ	0.82	2.03	2.803 (2)	158
O6m—H6m⋯OW3^iv	0.82	2.00	2.796 (2)	166
O2g—H2g1⋯O4m^v	0.82	2.25	2.848 (2)	130
O2g—H2g1⋯O3m^v	0.82	2.43	3.140 (2)	145
O4g—H4g1⋯OW2^vi	0.82	1.91	2.733 (2)	177
O6g—H6g⋯OW1^vi	0.82	2.00	2.794 (2)	162
OW1—H11⋯O4g	0.94 (2)	1.80 (2)	2.736 (2)	174 (4)
OW1—H12⋯OW2	0.97 (2)	1.92 (3)	2.834 (2)	156 (2)
OW2—H21⋯OW3	0.92 (2)	1.98 (2)	2.866 (2)	161 (4)
OW2—H22⋯O2g^vi	0.90 (3)	2.06 (3)	2.915 (2)	159 (4)
OW3—H31⋯O1g^vii	0.91 (3)	1.94 (3)	2.814 (2)	163 (4)
OW3—H32⋯OW4	0.90 (2)	1.92 (2)	2.807 (2)	167 (4)
OW4—H41⋯O6g^vii	0.89 (2)	2.04 (2)	2.916 (2)	168 (3)
OW4—H42⋯O2m^vi	0.89 (2)	1.88 (3)	2.747 (2)	163 (4)

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Acknowledgments

This work was supported by a grant from the Swedish Research Council (VR).

supplementary crystallographic information

Comment

Carbohydrates in biological systems, in the case of N-linked glycans of glycoproteins the result of post-translational modifications, are of functional significance due to e.g. their influence on protein stability. Furthermore, highly specific epitopes are formed by oligosaccharides present as glycoconjugates. The information contents in carbohydrate structures are indeed very large as a consequence of the immense numbers of permutations possible by combining different linkages and anomeric configurations of the sugar residues. It is of particular importance that the often weak carbohydrate interactions function by resorting to multivalent interactions upon cell-cell recognition (Huskens, 2006).

The major degrees of freedom in an oligosaccharide are described by the torsion angles φ_H, ψ_H, and ω. For the title compound the two former are present at the glycosidic α-(1 → 3)-linkage with φ_H being defined by H1m—C1m—O3g—C3g and ψ_H by C1m—O3g—C3g—H3g. The ω torsion angle, defined by O5—C5—C6—O6, refers to the conformation of the hydroxymethyl group of each sugar residue. The structure is described as the exo-anomeric conformation with φ_H = -34°, which, as a result of stereoelectronic effects, is characteristic of sugars in a cyclic form (Fig. 1). For the title compound the presence of the endo-anomeric effect (Juaristi & Cuevas, 1992) is evident from the difference in C—O bond lengths at the anomeric positions of the α-D-Manp residue having the axial bond C1m—O3g = 1.409 (2) Å and the β-D-Glcp residue having the equatorial bond C1g—O1g = 1.402 (2) Å, i.e., the bond with the axial electronegative atom is longer than the corresponding equatorial one, in complete agreement with ab initio data of model compounds (Odelius et al., 1995). At the glycosidic linkage ψ_H = -5°, leading to an almost eclipsed conformation and as a result the inter-residue distance across the glycosidic linkage for the proton pair H1m—H3g becomes short, only 2.12 Å.

The conformations of the hydroxymethyl groups are described by one of the three rotamers, gauche-trans, gauche-gauche, or trans-gauche with respect to the orientation of C6—O6 to C5—O5 and to C5—C4, respectively. In the present case both the mannopyranosyl and the glucopyranosyl residues show the gg conformation for their hydroxymethyl groups with ω = -64.9 (2)° and ω = -69.7 (2)°, respectively. This conformation is one of the two anticipated rotamers for the monosaccharides in the title compound, since both have an equatorial hydroxyl group at C4, which precludes the tg rotamer as a result of a non-favorable 1,3-diaxial interaction known as the Hassel-Ottar effect (Hassel & Ottar, 1947).

The calculated Cremer & Pople (1975) parameters show that both the mannose and glucose rings are close to the expected chair conformation, i.e.⁴C₁. The parameters for the mannose ring are [Q=0.555 (2) Å, θ=3.0 (2) ° and φ=302 (3) °] and for the glucose ring [Q=0.575 (2) Å, θ=10.0 (2) ° and φ=327 (1) °].

The title compound was quite hygroscopic. This fact is consistent with the relatively high water content in the crystal of the title disaccharide. In our previous structural studies on disaccharide crystals the number of water molecules ranged from zero to three per disaccharide (Eriksson et al. 1997, 2000, 2002, 2005; Färnbäck et al. 2003, 2008). All hydroxyl groups and all H atoms of the four water molecules are hydrogen bond donors and the structure is stabilized by an elaborate hydrogen bond network. The four water molecules can be considered as lying in channels along the b-direction between the sugar residues as shown in Fig. 2. Previous conformational studies on the title compound that focused on solution patterns in binary aqueous solvent mixtures indicated that an inter-residue hydrogen bond was present between O6m as the donor atom and O2g as the acceptor atom (Vishnyakov et al. 2000). This was possible when the ω torsion angle of the mannosyl residue had the gt conformation. However, in the present crystal structure the exo-cyclic hydroxymethyl groups of the glucosyl residue as well as that in the mannosyl residue have the gg conformation, the latter of which precludes the intra-molecular hydrogen bond. Further analysis of the hydrogen bonding patterns showed that O6m acts as a donor to OW3. The O6g atom, on the other hand, acts as a donor to OW1, which acts as a donor to OW2, continued in a donor-acceptor relationship to OW3, and in an analogous way to OW4. Finally, the latter water molecule acts as a donor to the acceptor O6g in another molecule. Thus, the water-mediated chain starts from one glucosyl residue and ends at a symmetry related glucosyl residue. Along the 'chain of water molecules' various atoms of the sugar residues act as hydrogen bond donors and acceptors. The close proximity of O2g in one molecule and O3m and O4m in a symmetry related molecule at distances of 3.140 (2) Å and 2.848 (2) Å, respectively, indicate that a bifurcated hydrogen bond is present with O2g as the donor atom. The triangle formed by the three oxygen atoms is almost isosceles with an O3m^v—O2g—O4m^v [symmetry code (v): -x + 1/2,y + 1/2,-z] angle of 56.09 (4)°.

Experimental

The synthesis of the title compound was described by Jansson et al. (1990). The disaccharide was crystallized by slow evaporation from a mixture of water, ethanol and acetonitrile (1:1:1) at ambient temperature. The absolute configuration of each sugar residue is known from the starting compounds used in the synthesis.