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ISSN: 2056-9890

5-Azido-4-benz­yl­oxy-2-meth­­oxy-6-methyl­perhydro­pyran-3-ol

aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia, bSyngene International Ltd, Biocon Park, Plot Nos. 2 & 3, Bommasandra 4th Phase, Jigani Link Rd, Bangalore 560 100, India, cDepartment of Printing, Manipal Institute of Technology, Manipal 576 104, India, and dDepartment of Chemistry, National Institute of Technology-Karnataka, Surathkal, Mangalore 575 025, India
*Correspondence e-mail: hkfun@usm.my

(Received 20 July 2009; accepted 20 July 2009; online 25 July 2009)

In the title compound, C14H19N3O4, the perhydro­pyran ring adopts a chair conformation. An intra­molecular C—H⋯O hydrogen bond generates an S(6) ring motif. In the crystal packing, mol­ecules are linked by O—H⋯O hydrogen bonds, forming infinite chains along [100].

Related literature

For background to D-perosamine, see: Jacquinet (2006[Jacquinet, J. C. (2006). Carbohydr. Res. 341, 1630-1644.]). For the synthesis of D-perosamine, see: Krishna & Agrawal (2000[Krishna, N. R. & Agrawal, P. K. (2000). Adv. Carbohydr. Chem. Biochem. 56, 201-234.]). For metabolites, see: Grond et al. (2000[Grond, S., Langer, H. J., Henne, P., Sattler, I., Thiericke, R., Grabley, S., Zähner, H. & Zeeck, A. (2000). Eur. J. Chem. pp. 929-937.]). For ring conformations, see: Cremer & Pople (1975[Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354-1358.]). For hydrogen-bond motifs, see: Bernstein et al. (1995[Bernstein, J., Davis, R. E., Shimoni, L. & Chang, N.-L. (1995). Angew. Chem. Int. Ed. Engl. 34, 1555-1573.]). For bond-length data, see: Allen et al. (1987[Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1-19.]). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986[Cosier, J. & Glazer, A. M. (1986). J. Appl. Cryst. 19, 105-107.]).

[Scheme 1]

Experimental

Crystal data
  • C14H19N3O4

  • Mr = 293.32

  • Orthorhombic, P 21 21 21

  • a = 4.6662 (2) Å

  • b = 15.3356 (8) Å

  • c = 20.9273 (12) Å

  • V = 1497.54 (13) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.10 mm−1

  • T = 100 K

  • 0.27 × 0.11 × 0.08 mm

Data collection
  • Bruker SMART APEXII CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2005[Bruker (2005). APEX2 SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.773, Tmax = 0.980

  • 13029 measured reflections

  • 1742 independent reflections

  • 1334 reflections with I > 2σ(I)

  • Rint = 0.096

Refinement
  • R[F2 > 2σ(F2)] = 0.049

  • wR(F2) = 0.103

  • S = 1.09

  • 1742 reflections

  • 196 parameters

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.23 e Å−3

  • Δρmin = −0.20 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O2—H1O2⋯O2i 0.88 (4) 1.91 (3) 2.757 (2) 161 (3)
O2—H1O2⋯O3i 0.88 (3) 2.49 (3) 3.063 (3) 124 (3)
C7—H7B⋯O2 0.97 2.58 3.180 (4) 120
Symmetry code: (i) [x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z].

Data collection: APEX2 (Bruker, 2005[Bruker (2005). APEX2 SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2005[Bruker (2005). APEX2 SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]).

Supporting information


Comment top

4-Amino-4,6-dideoxy-D-mannose (D-perosamine) was first discovered in the polyene macrolide antibiotic perimycin and was later recognized to be present in the lipopolysaccharide (LPS) of Vivrio cholera (Jacquinet, 2006). Methyl 3-benzyloxy-4-azido-α-D-rhamnopyranoside is an important intermediate in the synthesis of D-perosamine (Krishna & Agrawal, 2000). Rhamnopyranosides were detected as metabolites from five different strains of Streptomycetes (Grond et al., 2000).

The bond lengths (Allen et al., 1987) and angles in the molecule (Fig. 1) are within normal ranges. The perhydropyran ring adopts a chair conformation. The puckering parameters (Cremer & Pople, 1975) are Q = 0.540 (3) Å; Θ = 8.0 (3)° and ϕ = 8.0 (2)°. Intramolecular C7—H7B···O2 hydrogen bonds formed a six-membered ring, producing an S(6) ring motif (Bernstein et al., 1995). The dihedral angle formed between the benzene (C1—C6) and perhydropyran (C8—C10/O4/C11/C12) rings is 57.32 (16)°.

In the crystal packing (Fig. 2), the molecules are linked by intermolecular O2—H1O2···O2 and O2—H1O2···O3 hydrogen bonds (Table 1) into an infinite one-dimensional chains along the [100] direction.

Related literature top

For background to D-perosamine, see: Jacquinet (2006). For the synthesis of D-perosamine, see: Krishna & Agrawal (2000). For metabolites, see: Grond et al. (2000). For ring conformations, see: Cremer & Pople (1975). For hydrogen-bond motifs, see: Bernstein et al. (1995). For bond-length data, see: Allen et al. (1987). For the stability of the temperature controller used for the data collection, see: Cosier & Glazer (1986).

Experimental top

To a stirred mixture of methyl 3-benzyloxy-4-methoxysulfonyl-α-D-rhamnopyranoside (0.50 g, 1.4 mmol) in DMF (5.0 ml) was added sodium azide (0.18 g, 2.8 mmol). The reaction mixture was stirred further at room temperature for 12 h. TLC (30% EtOAc/hexane, Rf-0.5) analysis showed complete conversion. The reaction mixture was concentrated under vacuum and the residue was purified by column chromatography using 25% ethylacetate in petroleum ether to get pure product as colourless crystals (yield: 300.0 mg, 71%, M.p. 376–378 K).

Refinement top

Atom H1O2 was located in a difference map and was refined freely. Other H atoms were positioned geometrically [C—H = 0.93 to 0.98 Å] and was refined using a riding model, with Uiso(H) = 1.2 or 1.5 Ueq(C). A rotating-group model was applied for the methyl groups. In the absence of significant anomalous dispersion, 1187 Friedel pairs were merged for the final refinement.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom numbering scheme. Intramolecular interaction is shown by dashed line.
[Figure 2] Fig. 2. The crystal packing of the title compound, viewed along a axis. Intermolecular hydrogen bonds are shown by dashed lines.
5-Azido-4-benzyloxy-2-methoxy-6-methylperhydropyran-3-ol top
Crystal data top
C14H19N3O4F(000) = 624
Mr = 293.32Dx = 1.301 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 1880 reflections
a = 4.6662 (2) Åθ = 2.4–29.9°
b = 15.3356 (8) ŵ = 0.10 mm1
c = 20.9273 (12) ÅT = 100 K
V = 1497.54 (13) Å3Block, colourless
Z = 40.27 × 0.11 × 0.08 mm
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer
1742 independent reflections
Radiation source: fine-focus sealed tube1334 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.096
ϕ and ω scansθmax = 26.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)
h = 55
Tmin = 0.773, Tmax = 0.980k = 1817
13029 measured reflectionsl = 2525
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.049Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.103H atoms treated by a mixture of independent and constrained refinement
S = 1.09 w = 1/[σ2(Fo2) + (0.0499P)2]
where P = (Fo2 + 2Fc2)/3
1742 reflections(Δ/σ)max < 0.001
196 parametersΔρmax = 0.23 e Å3
0 restraintsΔρmin = 0.20 e Å3
Crystal data top
C14H19N3O4V = 1497.54 (13) Å3
Mr = 293.32Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 4.6662 (2) ŵ = 0.10 mm1
b = 15.3356 (8) ÅT = 100 K
c = 20.9273 (12) Å0.27 × 0.11 × 0.08 mm
Data collection top
Bruker SMART APEXII CCD area-detector
diffractometer
1742 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)
1334 reflections with I > 2σ(I)
Tmin = 0.773, Tmax = 0.980Rint = 0.096
13029 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0490 restraints
wR(F2) = 0.103H atoms treated by a mixture of independent and constrained refinement
S = 1.09Δρmax = 0.23 e Å3
1742 reflectionsΔρmin = 0.20 e Å3
196 parameters
Special details top

Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.0881 (4)0.40074 (13)0.13521 (10)0.0229 (5)
O20.0911 (5)0.28256 (14)0.02574 (11)0.0251 (5)
O30.3176 (5)0.39026 (14)0.06657 (9)0.0236 (5)
O40.0200 (5)0.49881 (14)0.04434 (10)0.0250 (5)
N10.3572 (6)0.56890 (17)0.10102 (12)0.0260 (7)
N20.3482 (6)0.56020 (18)0.16023 (14)0.0306 (7)
N30.3680 (9)0.5600 (2)0.21422 (15)0.0537 (11)
C10.2228 (8)0.2487 (2)0.26646 (17)0.0341 (9)
H1A0.35170.21000.24790.041*
C20.1203 (8)0.2318 (2)0.32682 (17)0.0389 (9)
H2A0.17950.18200.34850.047*
C30.0706 (8)0.2888 (3)0.35523 (17)0.0379 (9)
H3A0.14050.27760.39600.045*
C40.1561 (9)0.3619 (2)0.32269 (16)0.0362 (9)
H4A0.28560.40030.34130.043*
C50.0489 (8)0.3786 (2)0.26165 (16)0.0314 (9)
H5A0.10510.42890.24020.038*
C60.1390 (7)0.3216 (2)0.23289 (15)0.0245 (7)
C70.2586 (8)0.3380 (2)0.16733 (16)0.0309 (9)
H7A0.45410.35900.17080.037*
H7B0.26070.28400.14310.037*
C80.1803 (7)0.4219 (2)0.07207 (14)0.0209 (7)
H8A0.38370.40730.06750.025*
C90.1415 (7)0.51995 (19)0.06387 (14)0.0193 (7)
H9A0.04980.53610.07910.023*
C100.1727 (7)0.5493 (2)0.00515 (14)0.0215 (7)
H10A0.37030.53970.01930.026*
C110.0416 (7)0.4086 (2)0.04432 (15)0.0241 (8)
H11A0.09650.37940.07230.029*
C120.0088 (7)0.37161 (19)0.02287 (15)0.0214 (7)
H12A0.19410.37540.03470.026*
C130.3436 (8)0.4054 (3)0.13393 (15)0.0361 (9)
H13A0.53090.38800.14800.054*
H13B0.31590.46620.14270.054*
H13C0.20120.37200.15620.054*
C140.0949 (9)0.6437 (2)0.01442 (16)0.0364 (9)
H14A0.11460.65880.05870.055*
H14B0.22030.67950.01070.055*
H14C0.09970.65300.00120.055*
H1O20.060 (8)0.251 (2)0.0151 (15)0.028 (10)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0225 (12)0.0219 (12)0.0243 (11)0.0014 (10)0.0055 (10)0.0037 (10)
O20.0200 (12)0.0185 (12)0.0368 (13)0.0030 (11)0.0015 (11)0.0055 (10)
O30.0222 (11)0.0283 (13)0.0205 (11)0.0038 (11)0.0013 (10)0.0046 (10)
O40.0249 (12)0.0218 (12)0.0282 (12)0.0030 (11)0.0041 (10)0.0033 (10)
N10.0301 (16)0.0255 (17)0.0224 (16)0.0079 (14)0.0009 (14)0.0004 (12)
N20.0360 (17)0.0250 (17)0.0307 (19)0.0096 (14)0.0032 (15)0.0024 (13)
N30.084 (3)0.049 (2)0.0274 (18)0.028 (2)0.0075 (19)0.0015 (15)
C10.036 (2)0.032 (2)0.035 (2)0.0072 (17)0.0014 (17)0.0053 (17)
C20.044 (2)0.032 (2)0.040 (2)0.003 (2)0.000 (2)0.0127 (18)
C30.040 (2)0.045 (2)0.0295 (19)0.002 (2)0.0026 (18)0.0106 (18)
C40.040 (2)0.036 (2)0.0329 (19)0.0034 (19)0.0131 (19)0.0041 (17)
C50.038 (2)0.0257 (19)0.0300 (19)0.0002 (18)0.0039 (18)0.0061 (16)
C60.0246 (18)0.0220 (18)0.0267 (17)0.0019 (16)0.0029 (16)0.0018 (15)
C70.0305 (19)0.031 (2)0.0315 (19)0.0135 (17)0.0029 (16)0.0033 (16)
C80.0170 (16)0.0213 (18)0.0244 (17)0.0001 (15)0.0013 (15)0.0015 (14)
C90.0197 (16)0.0150 (16)0.0233 (16)0.0001 (14)0.0031 (15)0.0037 (13)
C100.0238 (17)0.0185 (17)0.0224 (16)0.0001 (15)0.0005 (15)0.0037 (14)
C110.0224 (16)0.0213 (18)0.0286 (18)0.0019 (15)0.0045 (15)0.0047 (15)
C120.0153 (15)0.0157 (16)0.0333 (18)0.0017 (14)0.0013 (15)0.0062 (14)
C130.035 (2)0.052 (2)0.0214 (17)0.004 (2)0.0043 (18)0.0014 (17)
C140.052 (2)0.028 (2)0.0291 (19)0.0020 (19)0.0024 (19)0.0017 (16)
Geometric parameters (Å, º) top
O1—C71.418 (4)C5—H5A0.9300
O1—C81.427 (4)C6—C71.502 (4)
O2—C121.420 (3)C7—H7A0.9700
O2—H1O20.88 (4)C7—H7B0.9700
O3—C111.398 (4)C8—C121.515 (4)
O3—C131.434 (4)C8—C91.524 (4)
O4—C111.412 (4)C8—H8A0.9800
O4—C101.443 (4)C9—C101.520 (4)
N1—N21.247 (4)C9—H9A0.9800
N1—C91.477 (4)C10—C141.505 (4)
N2—N31.134 (4)C10—H10A0.9800
C1—C21.375 (5)C11—C121.524 (4)
C1—C61.376 (5)C11—H11A0.9800
C1—H1A0.9300C12—H12A0.9800
C2—C31.382 (5)C13—H13A0.9600
C2—H2A0.9300C13—H13B0.9600
C3—C41.371 (5)C13—H13C0.9600
C3—H3A0.9300C14—H14A0.9600
C4—C51.396 (5)C14—H14B0.9600
C4—H4A0.9300C14—H14C0.9600
C5—C61.378 (5)
C7—O1—C8115.1 (2)N1—C9—C10106.5 (2)
C12—O2—H1O2107 (2)N1—C9—C8111.2 (3)
C11—O3—C13111.9 (2)C10—C9—C8112.8 (2)
C11—O4—C10113.5 (2)N1—C9—H9A108.7
N2—N1—C9116.5 (3)C10—C9—H9A108.7
N3—N2—N1171.1 (4)C8—C9—H9A108.7
C2—C1—C6121.5 (3)O4—C10—C14107.0 (3)
C2—C1—H1A119.2O4—C10—C9108.8 (2)
C6—C1—H1A119.2C14—C10—C9112.6 (3)
C1—C2—C3120.0 (3)O4—C10—H10A109.5
C1—C2—H2A120.0C14—C10—H10A109.5
C3—C2—H2A120.0C9—C10—H10A109.5
C4—C3—C2119.4 (3)O3—C11—O4112.6 (3)
C4—C3—H3A120.3O3—C11—C12109.0 (3)
C2—C3—H3A120.3O4—C11—C12110.2 (3)
C3—C4—C5120.1 (3)O3—C11—H11A108.3
C3—C4—H4A120.0O4—C11—H11A108.3
C5—C4—H4A120.0C12—C11—H11A108.3
C6—C5—C4120.7 (3)O2—C12—C8108.5 (2)
C6—C5—H5A119.6O2—C12—C11111.7 (2)
C4—C5—H5A119.6C8—C12—C11112.6 (3)
C1—C6—C5118.3 (3)O2—C12—H12A107.9
C1—C6—C7119.8 (3)C8—C12—H12A107.9
C5—C6—C7121.9 (3)C11—C12—H12A107.9
O1—C7—C6109.8 (3)O3—C13—H13A109.5
O1—C7—H7A109.7O3—C13—H13B109.5
C6—C7—H7A109.7H13A—C13—H13B109.5
O1—C7—H7B109.7O3—C13—H13C109.5
C6—C7—H7B109.7H13A—C13—H13C109.5
H7A—C7—H7B108.2H13B—C13—H13C109.5
O1—C8—C12110.8 (2)C10—C14—H14A109.5
O1—C8—C9107.0 (2)C10—C14—H14B109.5
C12—C8—C9111.3 (3)H14A—C14—H14B109.5
O1—C8—H8A109.2C10—C14—H14C109.5
C12—C8—H8A109.2H14A—C14—H14C109.5
C9—C8—H8A109.2H14B—C14—H14C109.5
C9—N1—N2—N3177 (2)C12—C8—C9—C1047.1 (4)
C6—C1—C2—C30.2 (6)C11—O4—C10—C14175.5 (3)
C1—C2—C3—C40.0 (6)C11—O4—C10—C962.7 (3)
C2—C3—C4—C50.5 (6)N1—C9—C10—O4176.0 (2)
C3—C4—C5—C61.2 (6)C8—C9—C10—O453.7 (3)
C2—C1—C6—C50.9 (5)N1—C9—C10—C1465.6 (3)
C2—C1—C6—C7179.4 (3)C8—C9—C10—C14172.2 (3)
C4—C5—C6—C11.4 (5)C13—O3—C11—O470.6 (3)
C4—C5—C6—C7179.8 (3)C13—O3—C11—C12166.9 (2)
C8—O1—C7—C6179.9 (3)C10—O4—C11—O359.5 (3)
C1—C6—C7—O1163.7 (3)C10—O4—C11—C1262.4 (3)
C5—C6—C7—O117.8 (5)O1—C8—C12—O271.0 (3)
C7—O1—C8—C1298.3 (3)C9—C8—C12—O2170.1 (3)
C7—O1—C8—C9140.2 (3)O1—C8—C12—C11164.8 (2)
N2—N1—C9—C10173.4 (3)C9—C8—C12—C1145.9 (3)
N2—N1—C9—C863.3 (4)O3—C11—C12—O251.3 (3)
O1—C8—C9—N172.2 (3)O4—C11—C12—O2175.3 (2)
C12—C8—C9—N1166.7 (2)O3—C11—C12—C871.1 (3)
O1—C8—C9—C10168.2 (2)O4—C11—C12—C852.9 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H1O2···O2i0.88 (4)1.91 (3)2.757 (2)161 (3)
O2—H1O2···O3i0.88 (3)2.49 (3)3.063 (3)124 (3)
C7—H7B···O20.972.583.180 (4)120
Symmetry code: (i) x1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaC14H19N3O4
Mr293.32
Crystal system, space groupOrthorhombic, P212121
Temperature (K)100
a, b, c (Å)4.6662 (2), 15.3356 (8), 20.9273 (12)
V3)1497.54 (13)
Z4
Radiation typeMo Kα
µ (mm1)0.10
Crystal size (mm)0.27 × 0.11 × 0.08
Data collection
DiffractometerBruker SMART APEXII CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2005)
Tmin, Tmax0.773, 0.980
No. of measured, independent and
observed [I > 2σ(I)] reflections
13029, 1742, 1334
Rint0.096
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.049, 0.103, 1.09
No. of reflections1742
No. of parameters196
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.23, 0.20

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H1O2···O2i0.88 (4)1.91 (3)2.757 (2)161 (3)
O2—H1O2···O3i0.88 (3)2.49 (3)3.063 (3)124 (3)
C7—H7B···O20.97002.58003.180 (4)120.00
Symmetry code: (i) x1/2, y+1/2, z.
 

Footnotes

Thomson Reuters ResearcherID: A-3561-2009.

Acknowledgements

HKF and WSL thank Universiti Sains Malaysia (USM) for the Research University Golden Goose Grant (1001/PFIZIK/811012). WSL thanks USM for a student assistantship.

References

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