2‐Propynyl 2,3,4,6‐tetra‐O‐acetyl‐α‐d‐mannopyranoside

The 2‐propynyl group in the title compound, C₁₇H₂₂O₁₀, adopts an exoanomeric conformation, with the acetylenic group gauche with respect to position C1. Comparison of ¹³C NMR chemical shifts from solution and the solid state suggest that the acetylenic group also adopts a conformation anti to C1 in solution. The pyranose ring adopts a ⁴C₁ conformation. Of the three secondary O‐acetyl groups, that on position O4, flanked by two equatorial groups, adopts a syn conformation, in agreement with recent generalizations [González‐Outeiriño, Nasser & Anderson (2005). J. Org. Chem. 70 , 2486–2493]. The acetyl group on position O3 adopts a gauche conformation, also in agreement with the recent generalizations, but that on position O2 adopts a syn conformation, not in agreement with the recent generalizations.     

Methyl 2‐O‐β‐d‐glucopyranosyl‐α‐l‐rhamnopyranoside

The overall conformation of the title compound, C₁₃H₂₄O₁₀, is described by the glycosidic torsion angles ?_H (H1_g—C1_g—O2_r—C2_r) and ψ_H (C1_g—O2_r—C2_r—H2_r), which have values of 13.6 and 16.1°, respectively. The former is significantly different from the value predicted by consideration of the exo‐anomeric effect (?_H～ 60°) and from that in solution (?_H～ 50°), as determined previously by NMR spectroscopy. An intramolecular O3_r—H?O2_g hydrogen bond may help to stabilize the conformation in the solid state. The orientation of the hydroxy­methyl group of the glucose residue is gauche–gauche, with a torsion angle ω (O5_g—C5_g—C6_g—O6_g) of ?70.4 (4)°. Both pyranose rings are in their expected chair conformations, i.e.⁴C₁ for d ‐glucose and ¹C₄ for l ‐rhamnose.     

Methyl 3‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside trihydrate

The water content of the title compound, C₁₃H₂₄O₁₀·3H₂O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°.     

Conformational analysis of the disaccharide methyl α‐d‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d‐mannopyranoside monohydrate

The crystal structure of methyl α‐d ‐mannopyranosyl‐(1→3)‐2‐O‐acetyl‐β‐d ‐mannopyranoside monohydrate, C₁₅H₂₆O₁₂·H₂O, ( II ), has been determined and the structural parameters for its constituent α‐d ‐mannopyranosyl residue compared with those for methyl α‐d ‐mannopyranoside. Mono‐O‐acetylation appears to promote the crystallization of ( II ), inferred from the difficulty in crystallizing methyl α‐d ‐mannopyranosyl‐(1→3)‐β‐d ‐mannopyranoside despite repeated attempts. The conformational properties of the O‐acetyl side chain in ( II ) are similar to those observed in recent studies of peracetylated mannose‐containing oligosaccharides, having a preferred geometry in which the C2—H2 bond eclipses the C=O bond of the acetyl group. The C2—O2 bond in ( II ) elongates by ～0.02 Å upon O‐acetylation. The phi (?) and psi (ψ) torsion angles that dictate the conformation of the internal O‐glycosidic linkage in ( II ) are similar to those determined recently in aqueous solution by NMR spectroscopy for unacetylated ( II ) using the statistical program MA′AT, with a greater disparity found for ψ (Δ = ～16°) than for ? (Δ = ～6°).     

Methyl 4‐O‐β‐l‐fucopyranosyl α‐­d‐­glucopyranoside hemihydrate

The crystal structure of methyl 4‐O‐β‐l ‐fuco­pyran­osyl α‐d ‐gluco­pyran­oside hemihydrate C₁₃H₂₄O₁₀·0.5H₂O is organized in sheets with antiparallel strands, where hydro­phobic interaction accounts for partial stabilization. Infinite hydrogen‐bonding networks are observed within each layer as well as between layers; some of these hydrogen bonds are mediated by water mol­ecules. The conformation of the disaccharide is described by the glycosidic torsion angles: ?_H = ?6.1° and ψ_H = 34.3°. The global energy minimum conformation as calculated by molecular mechanics in vacuo has ?_H = ?58° and ψ_H = ?20°. Thus, quite substantial changes are observed between the in vacuo structure and the crystal structure with its infinite hydrogen‐bonding networks.     

Methyl 4‐O‐β‐d‐galacto­pyran­osyl α‐d‐gluco­pyran­oside (methyl α‐lactoside)

Methyl α‐lactoside, C₁₃H₂₄O₁₁, (I), is described by glycosidic torsion angles ϕ (O5_gal—C1_gal—O1_gal—C4_glc) and ψ (C1_gal—O1_gal—C4_glc—C5_glc), which have values of −93.52 (13) and −144.83 (11)°, respectively, where the ring atom numbering conforms to the convention in which C1 is the anomeric C atom and C6 is the exocyclic hydroxy­methyl (–CH₂OH) C atom in both residues. The linkage geometry is similar to that observed in methyl β‐lactoside methanol solvate, (II), in which ϕ is −88.4 (4)° and ψ is −161.3 (4)°. As in (II), an inter­molecular O3_glc—H⋯O5_gal hydrogen bond is observed in (I). The hydroxy­methyl group conformation in both residues is gauche–trans, with torsion angles ω_gal (O5_gal—C5_gal—C6_gal—O6_gal) and ω_glc (O5_glc—C5_glc—C6_glc—O6_glc) of 69.15 (13) and 72.55 (14)°, respectively. The latter torsion angle differs substantially from that found for (II) [−54.6 (2)°; gauche–gauche]. Cocrystallization of methanol, which is hydrogen bonded to O6_glc in the crystal structure of (II), presumably affects the hydroxy­methyl conformation in the Glc residue in (II).     

Methyl β‐d‐fructopyranoside

In methyl β‐d ‐fructopyranoside, C₇H₁₄O₆, the thermodynamically most stable methyl glycoside of the ketose d ‐fructose, the pyranose ring is close to being an ideal ²C₅ chair. The compound forms bilayers involving a complex hydrogen‐bonding pattern of five independent hydrogen bonds. Graph‐set analysis was applied to distinguish the hydrogen‐bond patterns at unary and higher level graph sets.     

Methyl β‐d‐galactopyranosyl‐(1→4)‐β‐d‐allopyranoside tetrahydrate

The title compound, C₁₃H₂₄O₁₁·4H₂O, (I), crystallized from water, has an internal glycosidic linkage conformation having ϕ′ (O5_Gal—C1_Gal—O1_Gal—C4_All) = −96.40 (12)° and ψ′ (C1_Gal—O1_Gal—C4_All—C5_All) = −160.93 (10)°, where ring‐atom numbering conforms to the convention in which C1 denotes the anomeric C atom, C5 the ring atom bearing the exocyclic hydroxymethyl group, and C6 the exocyclic hydroxymethyl (CH₂OH) C atom in the βGalp and βAllp residues. Internal linkage conformations in the crystal structures of the structurally related disaccharides methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (II), and methyl β‐cellobioside [methyl β‐d ‐glucopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Ham & Williams (1970). Acta Cryst. B 26 , 1373–1383], (III), are characterized by ϕ′ = −88.4 (2)° and ψ′ = −161.3 (2)°, and ϕ′ = −91.1° and ψ′ = −160.7°, respectively. Inter‐residue hydrogen bonding is observed between O3_Glc and O5_Gal/Glc in the crystal structures of (II) and (III), suggesting a role in determining their preferred linkage conformations. An analogous inter‐residue hydrogen bond does not exist in (I) due to the axial orientation of O3_All, yet its internal linkage conformation is very similar to those of (II) and (III).     

Methyl 2‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside monohydrate: a synchrotron study

The structure of the title compound, C₁₃H₂₄O₁₀·H₂O, is stabilized by hydrogen bonds situated adjacent to the glycoside linkage. A direct intramolecular hydrogen bond is present between the fucopyranosyl ring O atom and a glucopyranoside OH group, and a bridging water molecule mediates a hydrogen‐bond‐based interaction from a fucopyranosyl OH group to the methoxy O atom. The conformation of the disaccharide is described by the glycosidic torsion angles ϕ_H = −41° and ψ_H = −2°.     

Methyl 4‐O‐β‐l‐galactopyranosyl‐β‐d‐glucopyranoside (methyl β‐l‐lactoside)

Methyl β‐l ‐lactoside, C₁₃H₂₄O₁₁, (II), is described by glycosidic torsion angles ϕ (O5_Gal—C1_Gal—O4_Glc—C4_Glc) and ψ (C1_Gal—O1_Gal—C4_Glc—C5_Glc) of 93.89 (13) and −127.43 (13)°, respectively, where the ring atom numbering conforms to the convention in which C1 is the anomeric C atom and C6 is the exocyclic hydroxy­methyl (CH₂OH) C atom in both residues (Gal is galactose and Glc is glucose). Substitution of l ‐Gal for d ‐Gal in the biologically relevant disaccharide, methyl β‐lactoside [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (I), significantly alters the glycosidic linkage inter­face. In the crystal structure of (I), one inter‐residue (intra­molecular) hydrogen bond is observed between atoms H3O_Glc and O5_Gal. In contrast, in the crystal structure of (II), inter‐residue hydrogen bonds are observed between atoms H6O_Glc and O5_Gal, H6O_Glc and O6_Gal, and H3O_Glc and O2_Gal, with H6O_Glc serving as a donor with two intra­molecular acceptors.     

Methyl 4‐O‐β‐D‐mannopyranosyl β‐D‐xylopyranoside

Methyl β‐D‐mannopyranosyl‐(1→4)‐β‐D‐xylopyranoside, C₁₂H₂₂O₁₀, (I), crystallizes as colorless needles from water, with two crystallographically independent molecules, (IA) and (IB), comprising the asymmetric unit. The internal glycosidic linkage conformation in molecule (IA) is characterized by a ϕ′ torsion angle (O5′_Man—C1′_Man—O1′_Man—C4_Xyl; Man is mannose and Xyl is xylose) of −88.38 (17)° and a ψ′ torsion angle (C1′_Man—O1′_Man—C4_Xyl—C5_Xyl) of −149.22 (15)°, whereas the corresponding torsion angles in molecule (IB) are −89.82 (17) and −159.98 (14)°, respectively. Ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH₂OH) C atom in the β‐Xylp and β‐Manp residues, respectively. By comparison, the internal glycosidic linkage in the major disorder component of the structurally related disaccharide, methyl β‐D‐galactopyranosyl‐(1→4)‐β‐D‐xylopyranoside), (II) [Zhang, Oliver & Serriani (2012). Acta Cryst. C 68 , o7–o11], is characterized by ϕ′ = −85.7 (6)° and ψ′ = −141.6 (8)°. Inter‐residue hydrogen bonding is observed between atoms O3_Xyl and O5′_Man in both (IA) and (IB) [O3_Xyl...O5′_Man internuclear distances = 2.7268 (16) and 2.6920 (17) Å, respectively], analogous to the inter‐residue hydrogen bond detected between atoms O3_Xyl and O5′_Gal in (II). Exocyclic hydroxymethyl group conformation in the β‐Manp residue of (IA) is gauche–gauche, whereas that in the β‐Manp residue of (IB) is gauche–trans.     

β‐1‐Acet­amido‐4‐O‐β‐d‐galacto­pyranosyl‐d‐gluco­pyran­ose dihydrate

The crystal structure of the title compound, C₁₄H₂₅NO₁₁·2H₂O, has been determined. The glucose and galactose residues are in a ⁴C₁ conformation. The N‐acetyl group has a Z‐anti conformation.     

Methyl β‐allolactoside [methyl β‐d‐galactopyranosyl‐(1→6)‐β‐d‐glucopyranoside] monohydrate

Methyl β‐allolactoside [methyl β‐d ‐galactopyranosyl‐(1→6)‐β‐d ‐glucopyranoside], (II), was crystallized from water as a monohydrate, C₁₃H₂₄O₁₁·H₂O. The βGalp and βGlcp residues in (II) assume distorted ⁴C₁ chair conformations, with the former more distorted than the latter. Linkage conformation is characterized by ϕ′ (C2_Gal—C1_Gal—O1_Gal—C6_Glc), ψ′ (C1_Gal—O1_Gal—C6_Glc—C5_Glc) and ω (C4_Glc—C5_Glc—C6_Glc—O1_Gal) torsion angles of 172.9 (2), −117.9 (3) and −176.2 (2)°, respectively. The ψ′ and ω values differ significantly from those found in the crystal structure of β‐gentiobiose, (III) [Rohrer et al. (1980). Acta Cryst. B 36 , 650–654]. Structural comparisons of (II) with related disaccharides bound to a mutant β‐galactosidase reveal significant differences in hydroxymethyl conformation and in the degree of ring distortion of the βGlcp residue. Structural comparisons of (II) with a DFT‐optimized structure, (II_C), suggest a link between hydrogen bonding, pyranosyl ring deformation and linkage conformation.     

Methyl 3,6‐di‐O‐pivaloyl‐α‐d‐manno­pyran­oside

The X‐ray crystal structure analysis of the title compound, C₁₇H₃₀O₈, revealed a ⁴C₁ conformation of the pyran­osyl ring [Cremer–Pople puckering parameters of Q = 0.568 (2) Å, θ = 5.1 (2) and ϕ = 218 (3)°]. The structure shows no deviations from the geometric parameters of pyran­oside carbohydrates. The hydroxyl groups participate in O—H⃛O hydrogen bonds, forming a two‐dimensional pattern [O⃛O = 2.811 (3) and 2.995 (3) Å].     

Diaqua[methyl 4‐O‐benzyl‐2,3,6‐tri‐O‐(2‐picolyl)‐α‐d‐mannopyranoside]cobalt(II) bis(perchlorate) monohydrate: partial coordination of a ligand derived from d‐mannose

The title compound, [Co(C₃₂H₃₅N₃O₆)(H₂O)₂](ClO₄)₂·H₂O, contains a cationic complex with a novel facultative hexadentate sugar‐derived ligand coordinated in a tetradentate fashion to give a CoN₂O₄ coordination. The partial coordination is imposed by the rigid conformation of the sugar. The pyridine group that is not bound to the metal is free to participate in intermolecular hydrogen bonding and π–π stacking interactions.     

3‐O‐Acetyl‐4‐deoxy‐4‐iodo‐β‐d‐fructo­furan­osyl 2,3,6‐tri‐O‐acetyl‐4‐chloro‐4‐deoxy‐α‐d‐gluco­pyran­oside

At 160 K, the gluco­pyran­osyl ring of the title compound, C₂₀H₂₈ClIO₁₃, has a near‐ideal ⁴C₁ conformation and the fructo­furan­osyl ring has a twist ⁴T₃ conformation. The two hydroxy groups are involved in intra‐ and intermolecular hydrogen bonds, with the latter interactions linking the mol­ecules into infinite one‐dimensional chains. The absolute configuration of the mol­ecule has been determined.     

Methyl 4‐O‐benzoyl‐2,3‐O‐isopropyl­idene‐α‐l‐rhamnopyran­oside

The title compound, C₁₇H₂₂O₆, has an exocyclic ester group at the hexopyranosyl sugar residue. The carbonyl group shows a conformation that is eclipsed with respect to the adjacent ring C—H bond. The two ester torsion angles are denoted by syn and cis conformations. One of these torsion angles is indicated to have a similar conformation in solution, as analyzed by NMR spectroscopy and a Karplus‐type relationship.     

Disorder and conformational analysis of methyl β‐d‐galactopyranosyl‐(1→4)‐β‐d‐xylopyranoside

Methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐xylopyranoside, C₁₂H₂₂O₁₀, (II), crystallizes as colorless needles from water with positional disorder in the xylopyranosyl (Xyl) ring and no water molecules in the unit cell. The internal glycosidic linkage conformation in (II) is characterized by a ϕ′ torsion angle (C2′_Gal—C1′_Gal—O1′_Gal—C4_Xyl) of 156.4 (5)° and a ψ′ torsion angle (C1′_Gal—O1′_Gal—C4_Xyl—C3_Xyl) of 94.0 (11)°, where the ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH₂OH) C atoms in the β‐Xyl and β‐Gal residues, respectively. By comparison, the internal linkage conformation in the crystal structure of the structurally related disaccharide, methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside], (III) [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], is characterized by ϕ′ = 153.8 (2)° and ψ′ = 78.4 (2)°. A comparison of β‐(1→4)‐linked disaccharides shows considerable variability in both ϕ′ and ψ′, with the range in the latter (∼38°) greater than that in the former (∼28°). Inter‐residue hydrogen bonding is observed between atoms O3_Xyl and O5′_Gal in the crystal structure of (II), analogous to the inter‐residue hydrogen bond detected between atoms O3_Glc and O5′_Gal in (III). The exocyclic hydroxymethyl conformations in the Gal residues of (II) and (III) are identical (gauche–trans conformer).