Methyl 3-O-α-l-fucopyranosyl β-d-glucopyran­oside tetra­hydrate

Lars Eriksson; Göran Widmalm

doi:10.1107/S1600536812041992

. 2012 Oct 20;68(Pt 11):o3180–o3181. doi: 10.1107/S1600536812041992

Methyl 3-O-α-l-fucopyranosyl β-d-glucopyranoside tetrahydrate

Lars Eriksson ^a,^*, Göran Widmalm ^b

PMCID: PMC3515273 PMID: 23284493

Abstract

The title compound, C₁₃H₂₄O₁₀·4H₂O, is the methyl glycoside of a disaccharide structural element present in the backbone of the capsular polysaccharide from Klebsiella K1, which contains only three sugars and a substituent in the polysaccharide repeating unit. The conformation of the title disaccharide is described by the glycosidic torsion angles ϕ_H = 51.1 (1)° and ψ_H = 25.8 (1)°. In the crystal, a number of O—H⋯O hydrogen bonds link the methyl glycoside and water molecules, forming a three-dimensional network. One water molecule is disordered over two positions with occupancies of 0.748 (4) and 0.252 (4).

Related literature

For a background to capsular polysaccharides (CPS), see: Jansson et al. (1988 ▶); Erbing et al. (1976 ▶); Gloaguen et al. (1999 ▶); Cescutti et al. (2005 ▶). For details of the puckering analysis, see: Cremer & Pople (1975 ▶). For the synthesis, see: Baumann et al. (1988 ▶). For a related structure, see: Eriksson & Widmalm (2012 ▶).

Experimental

Crystal data

C₁₃H₂₄O₁₀·4H₂O
M _r = 412.39
Monoclinic,
a = 9.6150 (2) Å
b = 7.1362 (1) Å
c = 13.9716 (2) Å
β = 100.1180 (18)°
V = 943.75 (3) Å³
Z = 2
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 100 K
0.15 × 0.05 × 0.03 mm

Data collection

Oxford Xcalibur 3 diffractometer with Sapphire 3 CCD
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008 ▶) T _min = 0.976, T _max = 0.996
37858 measured reflections
4836 independent reflections
4644 reflections with I > 2σ(I)
R _int = 0.030

Refinement

R[F ² > 2σ(F ²)] = 0.028
wR(F ²) = 0.073
S = 1.08
4836 reflections
294 parameters
16 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.44 e Å⁻³
Δρ_min = −0.26 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2008 ▶); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 1999 ▶); software used to prepare material for publication: PLATON (Spek, 2009 ▶).

Supplementary Material

Click here for additional data file.^{(33.4KB, cif)}

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812041992/is5198sup1.cif

e-68-o3180-sup1.cif^{(33.4KB, cif)}

Click here for additional data file.^{(236.8KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812041992/is5198Isup2.hkl

e-68-o3180-Isup2.hkl^{(236.8KB, hkl)}

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2F—H2FA⋯OW2	0.84	1.89	2.7326 (10)	176
O3F—H3FA⋯O2F	0.84	2.56	2.8696 (10)	103
O3F—H3FA⋯OW1ⁱ	0.84	1.92	2.7049 (10)	156
O4F—H4FA⋯O3F ⁱⁱ	0.84	1.85	2.6836 (10)	172
O6G—H6G⋯OW3ⁱⁱⁱ	0.84	1.86	2.6546 (11)	157
O2G—H2G1⋯OW1	0.84	1.87	2.6981 (10)	168
O4G—H4G1⋯O6G ^iv	0.84	2.00	2.7884 (11)	155
OW1—H11⋯O2F	0.84 (2)	1.92 (2)	2.7522 (10)	172 (2)
OW1—H12⋯O4F ⁱ	0.83 (2)	1.94 (2)	2.7646 (10)	178 (2)
OW2—H21⋯O6G ^iv	0.81 (2)	2.09 (2)	2.8897 (10)	170 (2)
OW2—H22⋯O5F ^v	0.86 (2)	1.91 (2)	2.7682 (11)	176 (2)
OW3—H31⋯OW4A ⁱ	0.81 (2)	2.04 (2)	2.8424 (16)	176 (2)
OW3—H32⋯O7M ^vi	0.87 (2)	2.00 (2)	2.8559 (13)	169 (2)
OW4A—H41A⋯O2G	0.83 (2)	2.10 (2)	2.8615 (16)	151 (3)
OW4A—H42A⋯OW2^vii	0.83 (2)	2.11 (2)	2.9390 (15)	174 (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

Many polysaccharides are built of repeating units of oligosaccharides often having four or five sugar residues in their repeats. They may also carry substituents such as O-acetyl groups and/or pyruvic acids as for the Klebsiella capsular polysaccharides (CPS) termed S-53 and K1, respectively (Jansson et al., 1988; Erbing et al., 1976). The CPS of Klebsiella K1 contains a repeating unit consisting of → 4)-β-D-GlcpA-(2,3-Pyr)-(1→ 4)-α-L-Fucp-(1→ 3)-β-D-Glcp-(1→ (Erbing et al., 1976). More recently the CPS S-53 from Klebsiella pneumoniae ATCC 31488 (Jansson et al., 1988) was investigated, which, in addition, contained O-acetyl groups at positions 2 and 3 of the fucosyl residue. The disaccharide structural element is also present in the CPS produced by the thermophilic cynaobacterium Mastigocladus laminosus (Gloaguen et al., 1999) and the exopolysaccharide from Enterobacter amnigenus (Cescutti et al., 2005). The three-dimensional structure of the title compound, as a methyl glycoside model compound, represents an important part in these polysaccharides and may be used as a suitable starting point in modeling of the polymeric structures.

The major degrees of freedom in an oligosaccharide are the torsion angles φ_H, ψ_H, and ω. For the title compound (I) the two former are present at the glycosidic α-(1 → 3)-linkage. Furthermore, for the glucose residue the φ_H torsion angle is also important. The ω torsion angle describes the conformation of the hydroxymethyl group in the glucose residue. In the title compound both of the φ_H torsion angles in the structure are described by the exo-anomeric conformation with φ_H = 51.1 (1)° for the fucose residue and φ_H = 45.3 (1)° for the glucose residue (Fig. 1). The torsion angle conformation of ψ_H = 25.8 (1)°.

The conformation of the hydroxymethyl group is described by one of the three rotamers, gauche-trans, gauche-gauche, or trans-gauche with respect to the conformation of C6–O6 to C5–O5 and to C5–C4, respectively. In the present case the glucose residue has the gt conformation with ω = 77.02 (9)°, i.e., shifted away somewhat from a canonical gauche conformation. Extensive water-water hydrogen bonding was observed (Table 1) for the four water molecules present in the crystal. Partial occupancy was observed for one of the water molecules, in a 3:1 relative ratio between OW4A and OW4B, with a distance of 0.90 Å in between the disordered water molecules.

The calculated Cremer & Pople (1975) parameters for the two different rings are: ring O5f → C5f [Q=0.5682 (9) Å, θ=172.92 (9) ° and φ=58.2 (7) °], ring O5g → C5g [Q=0.5822 (9) Å, θ=6.17 (9) ° and φ=279.5 (8) °]; consequently, the conformation of both rings can be described as chair-forms.

The crystal structure of methyl 3-O-α-L-fucopyranosyl α-D-galactopyranoside was recently determined (Eriksson & Widmalm, 2012), but in contrast to the title compound it did not crystallize as a hydrate. Two stereochemical differences are present between the compounds: firstly at the reducing end where the O-methyl group is located equatorially (β-configuration) in the title compound but axially (α-configuration) in methyl 3-O-α-L-fucopyranosyl α-D-galactopyranoside; secondly, and more interesting, the configuration at the C4 atom of the hexopyranose residue is different, equatorial in the title compound but axial in the previously investigated disaccharide, i.e., from gluco- to galacto-configuration. For the φ_H dihedral angle the conformation at the glycosidic linkage is almost identical with φ_H = 51° herein and φ_H = 55° in methyl 3-O-α-L-fucopyranosyl α-D-galactopyranoside. However, the conformation at the ψ_H dihedral angle differs significantly with ψ_H = 26° herein, compared to ψ_H = -24° in the previously determined compound, i.e., a difference of 50°. Whether the difference of ca 25° from an eclipsed conformation at the ψ_H dihedral angle represents an intrinsic difference at the glycosidic linkage between 3-O-substituted glucose and galactose residues, or is just due to packing/hydration effects, remains to be elucidated. We note that in water solution the ¹³C NMR glycosylation shifts (Δδ_C), i.e., differences in chemical shifts between the disaccharide and its constituent monosaccharides, for both the C1 and C3 atoms at the glycosidic linkage are lower by ca 1 p.p.m. in the title compound (Δδ_C ~7.2 p.p.m.) compared to those in methyl 3-O-α-L-fucopyranosyl α-D-galactopyranoside (Δδ_C ~8.3 p.p.m.) (Baumann et al., 1988). These ¹³C NMR chemical shift differences may be related to different conformational preferences at the ψ_H dihedral angle.

Experimental

The synthesis of the title compound was described by Baumann et al. (1988) in which the fucose and glucose residues have the L and D absolute configurations, respectively. The compound was crystallized by slow evaporation of a mixture of water and ethanol (1:1) at ambient temperature.