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.     

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).     

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.     

1‐(β‐d‐Erythrofuranosyl)adenosine

The title compound, also known as β‐erythroadenosine, C₉H₁₁N₅O₃, (I), a derivative of β‐adenosine, (II), that lacks the C5′ exocyclic hydroxymethyl (–CH₂OH) substituent, crystallizes from hot ethanol with two independent molecules having different conformations, denoted (IA) and (IB). In (IA), the furanose conformation is ^OT₁–E₁ (C1′‐exo, east), with pseudorotational parameters P and τ_m of 114.4 and 42°, respectively. In contrast, the P and τ_m values are 170.1 and 46°, respectively, in (IB), consistent with a ²E–²T₃ (C2′‐endo, south) conformation. The N‐glycoside conformation is syn (+sc) in (IA) and anti (−ac) in (IB). The crystal structure, determined to a resolution of 2.0 Å, of a cocrystal of (I) bound to the enzyme 5′‐fluorodeoxyadenosine synthase from Streptomyces cattleya shows the furanose ring in a near‐ideal ^OE (east) conformation (P = 90° and τ_m = 42°) and the base in an anti (−ac) conformation.     

具有β-(1→6)-半乳吡喃糖骨架和α-L-(1→3)-阿拉伯呋喃糖侧链的阿拉伯半乳寡糖的简易合成

4-Methoxyphenyl glycoside of β-D-Galp-(1→6)-[α-L-Araf-(1→3)-]β-D-Galp-(1→6)-β-D-Galp-(1→6)-{β-D-Galp-(1→6)-[α-L-Araf-(1→3)-]β-D-Galp-(1→6)-β-D-Galp-(1→6)-}2β-D-Galp-(1→6)-[α-L-Araf-(1→)3)-]β-D-Galp-(1→)6)-β-D-Galp was synthesized with 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (1), 6-O-acetyl-2,3,4-tri-O-benzoyl-α-D-galactopyranosyl trichloroacetimidate (11), 4-methoxyphenyl 3-O-allyl-2,4-tri-O-benzoyl-β-D-galactopyranoside (2),isopropyl 3-O-allyl-2,4-tri-O-benzoyl--thio-β-D-galactopyranoside (12),4-methoxyphenyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside (5), and 2,3,5-tri-O-benzoyl-α-L-arabinofuranosyl trichloroacetimidate (8) as the key synthons.     

Highly Efficient Regio- and Stereoselective Synthesis of β-（1 →6）-Branched β-（1 →3）-Linked Glucohexaose and Its Analogue

A β-（1→）6）-branched β-（1→）3）-linked glucohexaose （1） and its lauryl glycoside （2）, present in many biologically active polysaccharides from traditional herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, were highly efficiently synthesized. Coupling of 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl- （1--）3）-2-O-benzoyl-4,6-O-benzylidene-a-D-glucopyranosyl trichloroacetimidate （7） with 3,6-branched acceptors 8 and 12 gave β-（1→）3）-linked pentasaccharides （9） and （13）, then via simple chemical transformation 4＇,6＇-OH pentasaccharide acceptors 10 and 14 were obtained. Regio- and stereoselective coupling of 3 with 10 and 14 gave β-（1→）3）-linked hexasaccharides （11） and （15） as the major products. Deprotection of 11 and 15 provided the target sugar 1 and 2. Thus, a new method for the preparation of this kind of compounds was developed.     

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 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.     

1‐(β‐d‐Erythrofuranos­yl)cytidine (β‐erythrocytidine)

1‐(β‐d ‐Erythrofuranosyl)cytidine, C₈H₁₁N₃O₄, (I), a derivative of β‐cytidine, (II), lacks an exocyclic hydroxy­methyl (–CH₂OH) substituent at C4′ and crystallizes in a global conformation different from that observed for (II). In (I), the β‐d ‐erythrofuranosyl ring assumes an E₃ conformation (C3′‐exo; S, i.e. south), and the N‐glycoside bond conformation is syn. In contrast, (II) contains a β‐d ‐ribofuranosyl ring in a ³T₂ conformation (N, i.e. north) and an anti‐N‐glycoside linkage. These crystallographic properties mimic those found in aqueous solution by NMR with respect to furan­ose conformation. Removal of the –CH₂OH group thus affects the global conformation of the aldofuranosyl ring. These results provide further support for S/syn–anti and N/anti correlations in pyrimidine nucleosides. The crystal structure of (I) was determined at 200 K.     

Methyl 4‐O‐β‐d‐galactopyranosyl α‐d‐mannopyranoside methanol 0.375‐solvate

Methyl β‐d ‐galactopyranosyl‐(1→4)‐α‐d ‐mannopyranoside methanol 0.375‐solvate, C₁₃H₂₄O₁₁·0.375CH₃OH, (I), was crystallized from a methanol–ethanol solvent system in a glycosidic linkage conformation, with ϕ′ (O5_Gal—C1_Gal—O1_Gal—C4_Man) = −68.2 (3)° and ψ′ (C1_Gal—O1_Gal—C4_Man—C5_Man) = −123.9 (2)°, where the ring is defined by atoms O5/C1–C5 (monosaccharide numbering); C1 denotes the anomeric C atom and C6 the exocyclic hydroxymethyl C atom in the βGalp and αManp residues, respectively. The linkage conformation in (I) differs from that in crystalline methyl α‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐α‐d ‐glucopyranoside], (II) [Pan, Noll & Serianni (2005). Acta Cryst. C 61 , o674–o677], where ϕ′ is −93.6° and ψ′ is −144.8°. An intermolecular hydrogen bond exists between O3_Man and O5_Gal in (I), similar to that between O3_Glc and O5_Gal in (II). The structures of (I) and (II) are also compared with those of their constituent residues, viz. methyl α‐d ‐mannopyranoside, methyl α‐d ‐glucopyranoside and methyl β‐d ‐galactopyranoside, revealing significant differences in the Cremer–Pople puckering parameters, exocyclic hydroxymethyl group conformations and intermolecular hydrogen‐bonding patterns.     

Regioisomeric 4‐nitroindazole N1‐ and N2‐(β‐d‐ribonucleosides)

The structures of the isomeric nucleosides 4‐nitro‐1‐(β‐d ‐ribo­furan­osyl)‐1H‐indazole, C₁₂H₁₃N₃O₆, (I), and 4‐nitro‐2‐(β‐d ‐ribo­furan­osyl)‐2H‐indazole, C₁₂H₁₃N₃O₆, (II), have been determined. For compound (I), the conformation of the gly­cosylic bond is anti [χ = −93.6 (6)°] and the sugar puckering is C2′‐exo–C3′‐endo. Compound (II) shows two conformations in the crystalline state which differ mainly in the sugar pucker; type 1 adopts the C2′‐endo–C3′‐exo sugar puckering associated with a syn base orientation [χ = 43.7 (6)°] and type 2 shows C2′‐exo–C3′‐endo sugar puckering accompanied by a somewhat different syn base orientation [χ = 13.8 (6)°].     

Synthesis of β-（ 1→6）-Branched （ 1→3）-Glucononaoside with Alter-nate β- and α-Bonds in the Backbone

Lauryl glycoside of β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]α-D-Glcp-(1→3)-β-D-Glcp-(1→3)-[β-D-Glcp-(1→6)-]β-D-Glcp was synthesized through 3 3 3 strategy. 3-O-Allyl-2,4,6-tri-O-benzoyl-β-D-glucopyranosyl-(1→3)- -[2, 3, 4, 6-tetra-O-benzoyl-β-D-glucopyranosyl-(1→6)-] 1,2-O-isopropylidene-α-D-glucofuranose was used as the key intermediate which was converted to the corresponding trisaccharide donor and acceptor readily.     

Regioselective Lactonization of α‐(2→8)‐Trisialic Acid

A simple and selective method has been developed to obtain both monolactones of the title compound, a model compound for biologically important polyneuraminic acid derivatives: acidic lactonization and alkaline hydrolysis of dilactone 1 . The two monolactonized trimers can be separated by capillary electrophoresis, and then distinguished by enzymatic hydrolysis with neuraminidase; only the 2‐monolactone undergoes reaction.     

pH Dependent Thermal Stabilization of DNA by Glcβ(1→3)GlcNAcβ1→STol

A disaccharide, Glcβ(1→3)GlcNAcβ1→STol (GGS, 1 ), was synthesized and demonstrated to stabilize ct‐DNA during the denaturing process. GGS at 50 μM shifted T_m of ct‐DNA by 23 °C and the behavior was pH dependent. Poly(dA‐dT)₂ was found to be the preferable type of DNA for GGS stabilization by circular dichroism spectroscopy study.     

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).