organic compounds
1,3,4-Tri-O-acetyl-2-N-(trifluoroacetyl)-β-L-fucose
aDepartment of Chemistry, Youngstown State University, 1 University Plaza, Youngstown, OH 44555-3663, USA
*Correspondence e-mail: pnorris@ysu.edu
The title compound, C14H18F3NO8, was produced through conjugation of 1,3,4-tri-O-acetyl-2-azidodeoxy-α,β-L-fucose with trifluoroacetyl chloride in the presence of bis(diphenylphosphino)ethane in tetrahydrofuran at room temperature. The X-ray reveals that the β-anomer of the product mixture crystallizes from ethyl acetate/hexanes. The compound exists in a typical chair conformation with the maximum possible number of substituents, four out of five, located in the sterically preferred equatorial positions. The major directional force facilitating packing of the molecules are N—H⋯O hydrogen bonds involving the amide moieties of neighboring molecules, which connect molecules stacked along the a-axis direction into infinite strands with a C11(4) graph-set motif. Formation of the strands is assisted by a number of weaker C—H⋯O interactions involving the methine and methyl H atoms. These strands are connected through further C—H⋯O and C—H⋯F interactions into a three dimensional network
CCDC reference: 979173
Related literature
Information related to the synthesis of N-acetyl-L-fucosamine analogues may be found in Alhassan et al. (2012). Rao et al. (1998) describe conformations of carbohydrate molecules.
Experimental
Crystal data
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Data collection: SMART (Bruker, 2002); cell SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008) and SHELXLE (Hübschle et al., 2011); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).
Supporting information
CCDC reference: 979173
10.1107/S1600536813034958/bv2229sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536813034958/bv2229Isup2.hkl
The title compound was synthesized from 1,3,4-tri-O-acetyl-2-azidodeoxy-α,β-L-fucoses (anomeric α/β ratio of 3:2 by NMR) by Staudinger-type synthesis with trifluoroacetyl chloride in the presence of bis(diphenylphosphino)ethane following a previously reported procedure (Alhassan et al., 2012). (silica gel, 2:1 hexanes-EtOAc) yielded a 3:2 anomeric α/β mixture (by NMR) of the title compound as a colorless syrup in an overall yield of 37%. The β-anomer was selectively isolated as a crystalline solid by vapor diffusion from ethyl acetate and hexanes, m.p. 157–159 °C.
1H NMR (400 MHz, CDC13): 1.25 (d, 3H, H-6, J = 6.40 Hz); 2.02 (s, 3H, COCH3); 2.12 (s, 3H, COCH3); 2.21 (s, 3H, COCH3); 3.94 (dq, 1H, H-5, J = 0.96, 6.44 Hz); 4.47 (ddd, 1H, H-2, J = 9.28, 9.28, 11.12 Hz); 5.14 (dd, 1H, H-3, J = 3.28, 11.28 Hz); 5.25 (dd, 1H, H-4, J = 0.78, 3.30 Hz); 5.74 (d, 1H, H-1, J = 8.76 Hz); 6.56 (d, 1H, N—H, J = 9.44 Hz).
13C NMR (100 MHz, CDC13): 16.03 (C-6); 20.45 (COCH3); 20.63 (COCH3); 20.68 (COCH3); 50.48 (C-2); 69.18 (C-4); 70.28 (C-3); 70.75 (C-5); 92.40 (C-1); 157.44 (COCF3); 157.81 (COCF3); 169.64 (COCH3); 170.43 (COCH3); 170.90 (COCH3).
MS: m/z calculated: 385.1 m/z found (ESI): 408.2 (+Na+).
H atoms attached to carbon and nitrogen atoms were positioned geometrically and constrained to ride on their parent atoms, with carbon hydrogen bond distances of 1.00 and 0.98 Å for C—H and CH3 and 0.88 Å for N—H moieties, respectively. Methyl H atoms were allowed to rotate but not to tip to best fit the experimental electron density. Uiso(H) values were set to a multiple of Ueq(C/N) with 1.5 for CH3 and 1.2 for C—H and N—H units, respectively. Reflection 0 1 1 was affected by the beam stop and was omitted from the refinement.
The title compound, 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-β-L-fucose, was synthesized during a project focused on the production of glycomimetic analogs of the bacterial aminosugar, N-acetyl-L-fucosamine (Alhassan et al., 2012). Beginning with an anomeric mixture of 1,3,4-tri-O-acetyl-2-azidodeoxy-α,β-L-fucoses, treatment with trifluoroacetyl chloride in the presence of bis(diphenylphosphino)ethane in THF at room temperature afforded a mixture of 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-α,β-L-fucoses as a colorless syrup. The mixture of was purified by and one of the two was selectively isolated by vapor diffusion crystallization using ethyl acetate and hexanes, with the other anomer remaining in solution. The crystals (m.p. 157–159 °C) were initially identified as the β-anomer by 1H NMR spectroscopy. Single-crystal diffraction was then employed in order to unambiguously confirm the configuration of the anomer isolated by crystallization.
Figure 1 shows a depiction of one molecule of 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-β-L-fucose as present in the solid state. From the it was confirmed that the isolated and crystallized fraction is indeed the β anomer, as had been already suspected based on 1H NMR shifts and coupling constants. The molecule crystallizes in a chair conformation as typical for pyranose sugar derivatives (Rao et al., 1998) with the choice of the chair conformation – from the two that are possible – being apparently the result of sterical interactions. The maximum possible number of substituents, four out of five, are located in the sterically preferred equatorial positions. Only the O-acetyl group at carbon atom C4 is, out of necessity to be able to maintain the overall chair conformation, forced into an axial position. This conformation is in agreement with the observed solution conformation as determined from the 1H NMR coupling constants (see experimental section). The acetyl and amide groups are, as expected, nearly perfectly planar – the r.m.s. deviation from planarity for the five atoms of the amide group is only 0.0052. Those for the four atoms of each acetate group at C1, C3 and C4 are 0.0196, 0.0087 and 0.0475, respectively – and they are tilted to variable degrees against the average plane of the pyranose moiety (48.17 (9)° at C1, 57.98 (9)° at C3, 79.04 (7)° at C4, and 71.97 (8)° for the amide group).
This conformation allows for dense packing of the molecules in the solid state, with no significant distortions of the molecules or voids present in the solid state. The major directional force facilitating packing of the molecules are N—H···O hydrogen bonds involving the amide moieties of neighboring molecules. Through these interactions, molecules stacked along the direction of the a-axis (created through translation from each other) are connected into infinite strands, with a C11(4) graph set motif for the N—H···O hydrogen bonds. Formation of the strands is assisted by a number of weaker but nevertheless still attractive C—H···O interactions involving the methine and methyl hydrogen atoms, with three of these interactions featuring H···O separations of 2.5 Å or less (2.38, 2.41 and 2.45 Å, involving H14A, H8B and H3, respectively. See Table 1 for details and symmetry operators). These strands, Figure 2, are in turn connected with each other through further C—H···O and C—H···F interactions into a three dimensional network, Figure 3 and Table 1. The stabilizing and directional effect of the C—H···F interactions might also have contributed to the ordered nature of the trifluoro methyl group. No signs of rotational disorder, as often observed for CF3 groups, is evident for this structure.
Information related to the synthesis of N-acetyl-L-fucosamine analogues may be found in Alhassan et al. (2012). Rao et al. (1998) describe conformations of carbohydrate molecules.
Data collection: SMART (Bruker, 2002); cell
SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2008) and SHELXLE (Hübschle et al., 2011); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).Fig. 1. : Thermal ellipsoid plot, with atom labels for non-hydrogen atoms and 50 percent probability ellipsoids. | |
Fig. 2. : Major packing interactions, viewed roughly perpendicular to the a axis direction showing the strands parallel to [1 0 0]. Blue dotted lines denote N—H···O hydrogen bonds and assisting C—H···O interactions. Symmetry codes: (i) x - 1, y, z; (iv) x + 1, y, z. | |
Fig. 3. : View along the a axis direction, showing C—H···O and C—H···F interactions connecting parallel strands with each other. For atoms involved and symmetry operators, see Table 1. |
C14H18F3NO8 | Dx = 1.494 Mg m−3 |
Mr = 385.29 | Melting point = 430.5–432.5 K |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 6913 reflections |
a = 5.1818 (10) Å | θ = 2.4–30.5° |
b = 16.968 (3) Å | µ = 0.14 mm−1 |
c = 19.484 (4) Å | T = 100 K |
V = 1713.1 (6) Å3 | Block, colourless |
Z = 4 | 0.48 × 0.31 × 0.30 mm |
F(000) = 800 |
Bruker AXS Smart Apex CCD diffractometer | 4232 independent reflections |
Radiation source: fine-focus sealed tube | 3869 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
ω scans | θmax = 28.3°, θmin = 2.1° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | h = −6→6 |
Tmin = 0.839, Tmax = 0.958 | k = −22→21 |
11394 measured reflections | l = −22→25 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.037 | H-atom parameters constrained |
wR(F2) = 0.088 | w = 1/[σ2(Fo2) + (0.0424P)2 + 0.1715P] where P = (Fo2 + 2Fc2)/3 |
S = 1.06 | (Δ/σ)max < 0.001 |
4232 reflections | Δρmax = 0.30 e Å−3 |
239 parameters | Δρmin = −0.17 e Å−3 |
0 restraints | Absolute structure: Flack parameter determined using 1493 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.4 (3) |
C14H18F3NO8 | V = 1713.1 (6) Å3 |
Mr = 385.29 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 5.1818 (10) Å | µ = 0.14 mm−1 |
b = 16.968 (3) Å | T = 100 K |
c = 19.484 (4) Å | 0.48 × 0.31 × 0.30 mm |
Bruker AXS Smart Apex CCD diffractometer | 4232 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2007) | 3869 reflections with I > 2σ(I) |
Tmin = 0.839, Tmax = 0.958 | Rint = 0.029 |
11394 measured reflections |
R[F2 > 2σ(F2)] = 0.037 | H-atom parameters constrained |
wR(F2) = 0.088 | Δρmax = 0.30 e Å−3 |
S = 1.06 | Δρmin = −0.17 e Å−3 |
4232 reflections | Absolute structure: Flack parameter determined using 1493 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
239 parameters | Absolute structure parameter: 0.4 (3) |
0 restraints |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.3282 (4) | 0.43097 (12) | 0.65855 (10) | 0.0225 (4) | |
H1 | 0.1566 | 0.4327 | 0.6351 | 0.027* | |
C2 | 0.3854 (4) | 0.50942 (11) | 0.69399 (10) | 0.0190 (4) | |
H2 | 0.5626 | 0.5077 | 0.7143 | 0.023* | |
C3 | 0.1889 (4) | 0.52308 (11) | 0.75081 (10) | 0.0209 (4) | |
H3 | 0.0174 | 0.5351 | 0.7297 | 0.025* | |
C4 | 0.1619 (4) | 0.45132 (12) | 0.79776 (11) | 0.0239 (4) | |
H4 | 0.0089 | 0.4585 | 0.8284 | 0.029* | |
C5 | 0.1274 (5) | 0.37669 (12) | 0.75536 (11) | 0.0284 (5) | |
H5 | −0.0392 | 0.3801 | 0.7296 | 0.034* | |
C6 | 0.1278 (6) | 0.30211 (14) | 0.79839 (12) | 0.0417 (7) | |
H6A | 0.1026 | 0.2563 | 0.7685 | 0.063* | |
H6B | −0.0124 | 0.3046 | 0.8321 | 0.063* | |
H6C | 0.2934 | 0.2973 | 0.8223 | 0.063* | |
C7 | 0.4717 (4) | 0.36394 (12) | 0.55954 (11) | 0.0255 (5) | |
C8 | 0.6856 (5) | 0.35718 (14) | 0.50908 (11) | 0.0306 (5) | |
H8A | 0.7102 | 0.3017 | 0.4968 | 0.046* | |
H8B | 0.8448 | 0.3779 | 0.5294 | 0.046* | |
H8C | 0.6427 | 0.3875 | 0.4678 | 0.046* | |
C9 | 0.5799 (4) | 0.60760 (12) | 0.61779 (10) | 0.0201 (4) | |
C10 | 0.5121 (4) | 0.67368 (12) | 0.56627 (11) | 0.0231 (4) | |
C11 | 0.0942 (5) | 0.63360 (13) | 0.82140 (11) | 0.0274 (5) | |
C12 | 0.2160 (6) | 0.70111 (14) | 0.85856 (13) | 0.0361 (6) | |
H12A | 0.0826 | 0.7392 | 0.8716 | 0.054* | |
H12B | 0.3424 | 0.7268 | 0.8285 | 0.054* | |
H12C | 0.3029 | 0.6816 | 0.8999 | 0.054* | |
C13 | 0.3851 (4) | 0.47114 (12) | 0.90408 (11) | 0.0247 (4) | |
C14 | 0.6170 (4) | 0.44563 (14) | 0.94350 (11) | 0.0306 (5) | |
H14A | 0.7671 | 0.4764 | 0.9287 | 0.046* | |
H14B | 0.6492 | 0.3895 | 0.9351 | 0.046* | |
H14C | 0.5873 | 0.4542 | 0.9926 | 0.046* | |
F1 | 0.4052 (3) | 0.64366 (8) | 0.50988 (6) | 0.0343 (3) | |
F2 | 0.7207 (3) | 0.71321 (8) | 0.54797 (7) | 0.0374 (3) | |
F3 | 0.3429 (3) | 0.72485 (8) | 0.59280 (7) | 0.0373 (4) | |
N1 | 0.3700 (3) | 0.57409 (10) | 0.64480 (8) | 0.0203 (4) | |
H1A | 0.2170 | 0.5916 | 0.6325 | 0.024* | |
O1 | 0.3363 (3) | 0.36940 (8) | 0.70706 (7) | 0.0269 (3) | |
O2 | 0.5281 (3) | 0.41733 (8) | 0.61054 (7) | 0.0236 (3) | |
O3 | 0.2779 (3) | 0.59116 (8) | 0.78734 (7) | 0.0230 (3) | |
O4 | 0.3917 (3) | 0.44154 (8) | 0.83929 (7) | 0.0241 (3) | |
O5 | 0.2690 (3) | 0.32900 (9) | 0.55792 (9) | 0.0338 (4) | |
O6 | 0.8048 (3) | 0.59089 (9) | 0.62873 (8) | 0.0272 (3) | |
O7 | −0.1313 (3) | 0.61666 (11) | 0.82064 (9) | 0.0382 (4) | |
O8 | 0.2109 (3) | 0.51128 (9) | 0.92552 (8) | 0.0292 (4) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0229 (11) | 0.0235 (9) | 0.0210 (10) | 0.0005 (8) | −0.0013 (8) | 0.0021 (8) |
C2 | 0.0170 (9) | 0.0221 (9) | 0.0181 (9) | −0.0001 (8) | −0.0011 (8) | 0.0034 (7) |
C3 | 0.0173 (9) | 0.0235 (9) | 0.0220 (10) | −0.0017 (8) | −0.0006 (8) | 0.0003 (8) |
C4 | 0.0200 (10) | 0.0290 (10) | 0.0228 (10) | −0.0037 (9) | −0.0008 (8) | 0.0028 (8) |
C5 | 0.0312 (12) | 0.0276 (10) | 0.0265 (11) | −0.0090 (9) | −0.0003 (10) | 0.0044 (8) |
C6 | 0.0604 (18) | 0.0305 (12) | 0.0342 (13) | −0.0151 (13) | 0.0019 (13) | 0.0073 (10) |
C7 | 0.0296 (12) | 0.0216 (10) | 0.0251 (11) | 0.0053 (9) | −0.0062 (9) | 0.0005 (8) |
C8 | 0.0313 (12) | 0.0330 (11) | 0.0275 (11) | 0.0063 (10) | −0.0004 (10) | −0.0045 (9) |
C9 | 0.0193 (10) | 0.0229 (9) | 0.0181 (9) | −0.0008 (8) | 0.0011 (8) | −0.0001 (7) |
C10 | 0.0237 (10) | 0.0225 (10) | 0.0233 (10) | −0.0010 (8) | 0.0014 (8) | −0.0006 (8) |
C11 | 0.0282 (12) | 0.0292 (11) | 0.0247 (11) | 0.0061 (9) | 0.0019 (9) | 0.0026 (8) |
C12 | 0.0418 (15) | 0.0329 (12) | 0.0335 (12) | 0.0019 (11) | 0.0022 (11) | −0.0054 (10) |
C13 | 0.0235 (11) | 0.0270 (10) | 0.0237 (10) | −0.0045 (9) | 0.0001 (9) | 0.0037 (8) |
C14 | 0.0259 (11) | 0.0385 (12) | 0.0275 (11) | 0.0003 (10) | −0.0032 (10) | 0.0007 (9) |
F1 | 0.0460 (9) | 0.0312 (6) | 0.0258 (7) | 0.0004 (6) | −0.0113 (6) | 0.0026 (5) |
F2 | 0.0354 (8) | 0.0380 (8) | 0.0389 (8) | −0.0104 (6) | 0.0042 (7) | 0.0133 (6) |
F3 | 0.0483 (9) | 0.0295 (6) | 0.0342 (7) | 0.0157 (7) | 0.0119 (7) | 0.0063 (5) |
N1 | 0.0159 (8) | 0.0237 (8) | 0.0214 (8) | 0.0009 (7) | −0.0009 (7) | 0.0041 (6) |
O1 | 0.0334 (9) | 0.0230 (7) | 0.0243 (7) | −0.0011 (7) | −0.0003 (7) | 0.0038 (6) |
O2 | 0.0216 (7) | 0.0260 (7) | 0.0233 (7) | 0.0006 (6) | −0.0002 (6) | −0.0022 (6) |
O3 | 0.0210 (7) | 0.0241 (7) | 0.0240 (7) | −0.0021 (6) | 0.0018 (6) | −0.0021 (6) |
O4 | 0.0231 (8) | 0.0286 (7) | 0.0206 (7) | 0.0004 (6) | −0.0021 (6) | 0.0029 (6) |
O5 | 0.0306 (9) | 0.0324 (9) | 0.0385 (9) | −0.0035 (7) | −0.0044 (7) | −0.0076 (7) |
O6 | 0.0177 (7) | 0.0354 (8) | 0.0286 (8) | −0.0002 (6) | −0.0004 (6) | 0.0061 (6) |
O7 | 0.0234 (9) | 0.0477 (10) | 0.0435 (10) | 0.0088 (8) | 0.0017 (8) | −0.0075 (8) |
O8 | 0.0268 (8) | 0.0343 (8) | 0.0265 (8) | 0.0018 (7) | 0.0003 (7) | −0.0004 (6) |
C1—O1 | 1.410 (2) | C8—H8A | 0.9800 |
C1—O2 | 1.415 (3) | C8—H8B | 0.9800 |
C1—C2 | 1.528 (3) | C8—H8C | 0.9800 |
C1—H1 | 1.0000 | C9—O6 | 1.218 (3) |
C2—N1 | 1.459 (2) | C9—N1 | 1.335 (3) |
C2—C3 | 1.522 (3) | C9—C10 | 1.545 (3) |
C2—H2 | 1.0000 | C10—F2 | 1.321 (2) |
C3—O3 | 1.433 (2) | C10—F1 | 1.332 (2) |
C3—C4 | 1.529 (3) | C10—F3 | 1.338 (2) |
C3—H3 | 1.0000 | C11—O7 | 1.203 (3) |
C4—O4 | 1.449 (3) | C11—O3 | 1.366 (3) |
C4—C5 | 1.523 (3) | C11—C12 | 1.495 (3) |
C4—H4 | 1.0000 | C12—H12A | 0.9800 |
C5—O1 | 1.440 (3) | C12—H12B | 0.9800 |
C5—C6 | 1.518 (3) | C12—H12C | 0.9800 |
C5—H5 | 1.0000 | C13—O8 | 1.205 (3) |
C6—H6A | 0.9800 | C13—O4 | 1.359 (3) |
C6—H6B | 0.9800 | C13—C14 | 1.490 (3) |
C6—H6C | 0.9800 | C14—H14A | 0.9800 |
C7—O5 | 1.207 (3) | C14—H14B | 0.9800 |
C7—O2 | 1.376 (3) | C14—H14C | 0.9800 |
C7—C8 | 1.486 (3) | N1—H1A | 0.8800 |
O1—C1—O2 | 107.48 (16) | C7—C8—H8B | 109.5 |
O1—C1—C2 | 109.69 (16) | H8A—C8—H8B | 109.5 |
O2—C1—C2 | 107.42 (17) | C7—C8—H8C | 109.5 |
O1—C1—H1 | 110.7 | H8A—C8—H8C | 109.5 |
O2—C1—H1 | 110.7 | H8B—C8—H8C | 109.5 |
C2—C1—H1 | 110.7 | O6—C9—N1 | 127.7 (2) |
N1—C2—C3 | 109.07 (16) | O6—C9—C10 | 120.00 (18) |
N1—C2—C1 | 110.34 (15) | N1—C9—C10 | 112.33 (17) |
C3—C2—C1 | 109.37 (16) | F2—C10—F1 | 108.16 (17) |
N1—C2—H2 | 109.3 | F2—C10—F3 | 108.13 (16) |
C3—C2—H2 | 109.3 | F1—C10—F3 | 107.12 (18) |
C1—C2—H2 | 109.3 | F2—C10—C9 | 110.97 (18) |
O3—C3—C2 | 105.59 (16) | F1—C10—C9 | 110.66 (16) |
O3—C3—C4 | 111.98 (16) | F3—C10—C9 | 111.64 (17) |
C2—C3—C4 | 112.03 (17) | O7—C11—O3 | 123.0 (2) |
O3—C3—H3 | 109.0 | O7—C11—C12 | 126.8 (2) |
C2—C3—H3 | 109.0 | O3—C11—C12 | 110.2 (2) |
C4—C3—H3 | 109.0 | C11—C12—H12A | 109.5 |
O4—C4—C5 | 107.73 (17) | C11—C12—H12B | 109.5 |
O4—C4—C3 | 110.49 (17) | H12A—C12—H12B | 109.5 |
C5—C4—C3 | 110.39 (16) | C11—C12—H12C | 109.5 |
O4—C4—H4 | 109.4 | H12A—C12—H12C | 109.5 |
C5—C4—H4 | 109.4 | H12B—C12—H12C | 109.5 |
C3—C4—H4 | 109.4 | O8—C13—O4 | 123.3 (2) |
O1—C5—C6 | 106.8 (2) | O8—C13—C14 | 126.1 (2) |
O1—C5—C4 | 109.73 (17) | O4—C13—C14 | 110.56 (19) |
C6—C5—C4 | 113.17 (18) | C13—C14—H14A | 109.5 |
O1—C5—H5 | 109.0 | C13—C14—H14B | 109.5 |
C6—C5—H5 | 109.0 | H14A—C14—H14B | 109.5 |
C4—C5—H5 | 109.0 | C13—C14—H14C | 109.5 |
C5—C6—H6A | 109.5 | H14A—C14—H14C | 109.5 |
C5—C6—H6B | 109.5 | H14B—C14—H14C | 109.5 |
H6A—C6—H6B | 109.5 | C9—N1—C2 | 122.31 (17) |
C5—C6—H6C | 109.5 | C9—N1—H1A | 118.8 |
H6A—C6—H6C | 109.5 | C2—N1—H1A | 118.8 |
H6B—C6—H6C | 109.5 | C1—O1—C5 | 110.62 (16) |
O5—C7—O2 | 121.8 (2) | C7—O2—C1 | 115.46 (16) |
O5—C7—C8 | 126.4 (2) | C11—O3—C3 | 116.22 (17) |
O2—C7—C8 | 111.75 (19) | C13—O4—C4 | 117.13 (17) |
C7—C8—H8A | 109.5 | ||
O1—C1—C2—N1 | −178.28 (17) | N1—C9—C10—F3 | 50.2 (2) |
O2—C1—C2—N1 | 65.2 (2) | O6—C9—N1—C2 | 0.2 (3) |
O1—C1—C2—C3 | −58.3 (2) | C10—C9—N1—C2 | 179.05 (16) |
O2—C1—C2—C3 | −174.82 (16) | C3—C2—N1—C9 | 137.83 (19) |
N1—C2—C3—O3 | −67.37 (19) | C1—C2—N1—C9 | −102.0 (2) |
C1—C2—C3—O3 | 171.87 (15) | O2—C1—O1—C5 | −176.42 (15) |
N1—C2—C3—C4 | 170.49 (16) | C2—C1—O1—C5 | 67.1 (2) |
C1—C2—C3—C4 | 49.7 (2) | C6—C5—O1—C1 | 171.70 (18) |
O3—C3—C4—O4 | −48.1 (2) | C4—C5—O1—C1 | −65.3 (2) |
C2—C3—C4—O4 | 70.4 (2) | O5—C7—O2—C1 | −2.9 (3) |
O3—C3—C4—C5 | −167.13 (18) | C8—C7—O2—C1 | 176.33 (17) |
C2—C3—C4—C5 | −48.7 (2) | O1—C1—O2—C7 | 81.6 (2) |
O4—C4—C5—O1 | −65.9 (2) | C2—C1—O2—C7 | −160.48 (16) |
C3—C4—C5—O1 | 54.8 (2) | O7—C11—O3—C3 | −1.2 (3) |
O4—C4—C5—C6 | 53.2 (3) | C12—C11—O3—C3 | 178.36 (17) |
C3—C4—C5—C6 | 173.9 (2) | C2—C3—O3—C11 | 154.73 (16) |
O6—C9—C10—F2 | −10.1 (3) | C4—C3—O3—C11 | −83.1 (2) |
N1—C9—C10—F2 | 170.94 (18) | O8—C13—O4—C4 | −7.8 (3) |
O6—C9—C10—F1 | 110.0 (2) | C14—C13—O4—C4 | 171.13 (17) |
N1—C9—C10—F1 | −69.0 (2) | C5—C4—O4—C13 | −142.17 (18) |
O6—C9—C10—F3 | −130.8 (2) | C3—C4—O4—C13 | 97.2 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O6i | 0.88 | 2.14 | 2.959 (2) | 155 |
C3—H3···O6i | 1.00 | 2.45 | 3.308 (3) | 144 |
C6—H6B···F3ii | 0.98 | 2.63 | 3.487 (3) | 147 |
C8—H8A···O5iii | 0.98 | 2.48 | 3.445 (3) | 169 |
C8—H8B···O5iv | 0.98 | 2.41 | 3.206 (3) | 137 |
C8—H8C···O8v | 0.98 | 2.64 | 3.443 (3) | 139 |
C14—H14A···O8iv | 0.98 | 2.38 | 3.292 (3) | 155 |
Symmetry codes: (i) x−1, y, z; (ii) −x, y−1/2, −z+3/2; (iii) x+1/2, −y+1/2, −z+1; (iv) x+1, y, z; (v) −x+1/2, −y+1, z−1/2. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O6i | 0.88 | 2.137 | 2.959 (2) | 155.2 |
C3—H3···O6i | 1.00 | 2.445 | 3.308 (3) | 144.1 |
C6—H6B···F3ii | 0.98 | 2.628 | 3.487 (3) | 146.5 |
C8—H8A···O5iii | 0.98 | 2.479 | 3.445 (3) | 168.7 |
C8—H8B···O5iv | 0.98 | 2.414 | 3.206 (3) | 137.4 |
C8—H8C···O8v | 0.98 | 2.643 | 3.443 (3) | 138.9 |
C14—H14A···O8iv | 0.98 | 2.375 | 3.292 (3) | 155.3 |
Symmetry codes: (i) x−1, y, z; (ii) −x, y−1/2, −z+3/2; (iii) x+1/2, −y+1/2, −z+1; (iv) x+1, y, z; (v) −x+1/2, −y+1, z−1/2. |
Acknowledgements
DCM and PN thank the School of Graduate Studies and Research at Youngstown State University for financial support. The diffractometer was funded by NSF grant No. 0087210, by Ohio Board of Regents grant No. CAP-491 and by YSU.
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
The title compound, 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-β-L-fucose, was synthesized during a project focused on the production of glycomimetic analogs of the bacterial aminosugar, N-acetyl-L-fucosamine (Alhassan et al., 2012). Beginning with an anomeric mixture of 1,3,4-tri-O-acetyl-2-azidodeoxy-α,β-L-fucoses, treatment with trifluoroacetyl chloride in the presence of bis(diphenylphosphino)ethane in THF at room temperature afforded a mixture of 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-α,β-L-fucoses as a colorless syrup. The mixture of anomers was purified by column chromatography, and one of the two anomers was selectively isolated by vapor diffusion crystallization using ethyl acetate and hexanes, with the other anomer remaining in solution. The crystals (m.p. 157–159 °C) were initially identified as the β-anomer by 1H NMR spectroscopy. Single-crystal diffraction was then employed in order to unambiguously confirm the configuration of the anomer isolated by crystallization.
Figure 1 shows a depiction of one molecule of 1,3,4-tri-O-acetyl-2-N-(trifluoro)acetyl-β-L-fucose as present in the solid state. From the crystal structure, it was confirmed that the isolated and crystallized fraction is indeed the β anomer, as had been already suspected based on 1H NMR shifts and coupling constants. The molecule crystallizes in a chair conformation as typical for pyranose sugar derivatives (Rao et al., 1998) with the choice of the chair conformation – from the two that are possible – being apparently the result of sterical interactions. The maximum possible number of substituents, four out of five, are located in the sterically preferred equatorial positions. Only the O-acetyl group at carbon atom C4 is, out of necessity to be able to maintain the overall chair conformation, forced into an axial position. This conformation is in agreement with the observed solution conformation as determined from the 1H NMR coupling constants (see experimental section). The acetyl and amide groups are, as expected, nearly perfectly planar – the r.m.s. deviation from planarity for the five atoms of the amide group is only 0.0052. Those for the four atoms of each acetate group at C1, C3 and C4 are 0.0196, 0.0087 and 0.0475, respectively – and they are tilted to variable degrees against the average plane of the pyranose moiety (48.17 (9)° at C1, 57.98 (9)° at C3, 79.04 (7)° at C4, and 71.97 (8)° for the amide group).
This conformation allows for dense packing of the molecules in the solid state, with no significant distortions of the molecules or voids present in the solid state. The major directional force facilitating packing of the molecules are N—H···O hydrogen bonds involving the amide moieties of neighboring molecules. Through these interactions, molecules stacked along the direction of the a-axis (created through translation from each other) are connected into infinite strands, with a C11(4) graph set motif for the N—H···O hydrogen bonds. Formation of the strands is assisted by a number of weaker but nevertheless still attractive C—H···O interactions involving the methine and methyl hydrogen atoms, with three of these interactions featuring H···O separations of 2.5 Å or less (2.38, 2.41 and 2.45 Å, involving H14A, H8B and H3, respectively. See Table 1 for details and symmetry operators). These strands, Figure 2, are in turn connected with each other through further C—H···O and C—H···F interactions into a three dimensional network, Figure 3 and Table 1. The stabilizing and directional effect of the C—H···F interactions might also have contributed to the ordered nature of the trifluoro methyl group. No signs of rotational disorder, as often observed for CF3 groups, is evident for this structure.