Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801009710/wn6022sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536801009710/wn6022Isup2.hkl |
CCDC reference: 170764
Compound (I) was prepared according to the procedure of Rosenthal & Nguyen (1967). Suitable crystals were obtained by recrystallization from ether/petroleum ether at room temperature (m.p. 310–311 K).
Crystals of the title compound suffered thermal-shock damage when cooled to low temperatures and it was therefore necessary to record the data at 273 K. The crystals also diffracted quite weakly at this temperature, which lead to a paucity of reflections with significant intensities and a consequent decrease in the precision of the geometric parameters. The methyl H atoms were constrained to an ideal geometry with Uiso(H) = 1.5Ueq(C), but were allowed to rotate freely about the C—C bonds. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with Uiso(H) = 1.2Ueq(C). The absolute configuration could not be determined because of the absence of significant anomalous scatterers in the compound. The enantiomer used in the model was based on the known chirality of D-glucose, from which (I) was synthesized. Friedel pairs were merged before the final refinement.
Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1991); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN (Molecular Structure Corporation, 1999); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
Fig. 1. The molecular structure of the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. |
C16H24O7 | Dx = 1.257 Mg m−3 |
Mr = 328.36 | Melting point = 310–311 K |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71069 Å |
a = 5.929 (2) Å | Cell parameters from 23 reflections |
b = 14.133 (2) Å | θ = 13.0–18.5° |
c = 10.3892 (12) Å | µ = 0.10 mm−1 |
β = 95.065 (16)° | T = 273 K |
V = 867.2 (3) Å3 | Prism, colourless |
Z = 2 | 0.38 × 0.24 × 0.15 mm |
F(000) = 352 |
Rigaku AFC-5R diffractometer | Rint = 0.018 |
Radiation source: Rigaku rotating anode generator | θmax = 25.0°, θmin = 2.9° |
Graphite monochromator | h = 0→7 |
ω–2θ scans | k = 0→16 |
1752 measured reflections | l = −12→12 |
1588 independent reflections | 3 standard reflections every 150 reflections |
891 reflections with I > 2σ(I) | intensity decay: none |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.064 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.200 | H-atom parameters constrained |
S = 1.01 | w = 1/[σ2(Fo2) + (0.1053P)2 + 0.2323P] where P = (Fo2 + 2Fc2)/3 |
1588 reflections | (Δ/σ)max = 0.001 |
213 parameters | Δρmax = 0.47 e Å−3 |
1 restraint | Δρmin = −0.20 e Å−3 |
C16H24O7 | V = 867.2 (3) Å3 |
Mr = 328.36 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 5.929 (2) Å | µ = 0.10 mm−1 |
b = 14.133 (2) Å | T = 273 K |
c = 10.3892 (12) Å | 0.38 × 0.24 × 0.15 mm |
β = 95.065 (16)° |
Rigaku AFC-5R diffractometer | Rint = 0.018 |
1752 measured reflections | 3 standard reflections every 150 reflections |
1588 independent reflections | intensity decay: none |
891 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.064 | 1 restraint |
wR(F2) = 0.200 | H-atom parameters constrained |
S = 1.01 | Δρmax = 0.47 e Å−3 |
1588 reflections | Δρmin = −0.20 e Å−3 |
213 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.2090 (8) | 0.8413 (5) | 0.6644 (5) | 0.0785 (16) | |
O2 | 0.5241 (8) | 0.8790 (4) | 0.7964 (5) | 0.0799 (17) | |
O4 | 0.1001 (9) | 0.7688 (4) | 0.8464 (5) | 0.0764 (15) | |
O5 | 0.0940 (11) | 0.7568 (4) | 1.1958 (5) | 0.0915 (19) | |
O6 | −0.1832 (13) | 0.6510 (5) | 1.1705 (7) | 0.122 (3) | |
O14 | 0.6330 (13) | 1.0228 (5) | 1.0402 (6) | 0.109 (2) | |
O15 | 0.7218 (11) | 0.9627 (4) | 1.2341 (6) | 0.094 (2) | |
C1 | 0.1371 (13) | 0.8554 (6) | 0.7860 (7) | 0.067 (2) | |
H1 | 0.0014 | 0.8952 | 0.7819 | 0.080* | |
C2 | 0.3361 (12) | 0.9031 (6) | 0.8642 (7) | 0.0632 (19) | |
H2 | 0.3160 | 0.9717 | 0.8714 | 0.076* | |
C3 | 0.3455 (10) | 0.8543 (5) | 0.9921 (6) | 0.0520 (16) | |
C4 | 0.1960 (10) | 0.7672 (5) | 0.9768 (6) | 0.0543 (17) | |
H4 | 0.2899 | 0.7105 | 0.9910 | 0.065* | |
C5 | 0.0075 (12) | 0.7646 (6) | 1.0654 (8) | 0.067 (2) | |
H5 | −0.0869 | 0.8213 | 1.0531 | 0.081* | |
C6 | −0.1381 (14) | 0.6756 (6) | 1.0443 (8) | 0.083 (3) | |
H61 | −0.2769 | 0.6890 | 0.9907 | 0.099* | |
H62 | −0.0563 | 0.6257 | 1.0044 | 0.099* | |
C7 | −0.0049 (15) | 0.6799 (6) | 1.2552 (8) | 0.076 (2) | |
C8 | −0.1146 (19) | 0.7170 (9) | 1.3757 (10) | 0.120 (4) | |
H81 | −0.1859 | 0.7768 | 1.3560 | 0.181* | |
H82 | 0.0002 | 0.7246 | 1.4461 | 0.181* | |
H83 | −0.2258 | 0.6724 | 1.3996 | 0.181* | |
C9 | 0.168 (2) | 0.6039 (9) | 1.2926 (14) | 0.146 (5) | |
H91 | 0.1016 | 0.5567 | 1.3438 | 0.219* | |
H92 | 0.2962 | 0.6316 | 1.3416 | 0.219* | |
H93 | 0.2164 | 0.5751 | 1.2159 | 0.219* | |
C10 | 0.4523 (13) | 0.8375 (6) | 0.6747 (7) | 0.070 (2) | |
C11 | 0.5324 (16) | 0.7385 (8) | 0.6738 (10) | 0.101 (3) | |
H111 | 0.6949 | 0.7374 | 0.6849 | 0.152* | |
H112 | 0.4815 | 0.7095 | 0.5928 | 0.152* | |
H113 | 0.4729 | 0.7042 | 0.7430 | 0.152* | |
C12 | 0.5336 (18) | 0.8934 (8) | 0.5685 (8) | 0.102 (3) | |
H121 | 0.4779 | 0.9570 | 0.5724 | 0.153* | |
H122 | 0.4799 | 0.8655 | 0.4873 | 0.153* | |
H123 | 0.6962 | 0.8941 | 0.5765 | 0.153* | |
C13 | 0.4609 (11) | 0.8801 (5) | 1.1028 (7) | 0.0610 (19) | |
H13 | 0.4449 | 0.8425 | 1.1749 | 0.073* | |
C14 | 0.6109 (13) | 0.9627 (6) | 1.1208 (7) | 0.0627 (19) | |
C15 | 0.896 (2) | 1.0330 (8) | 1.2629 (13) | 0.147 (6) | |
H151 | 0.9537 | 1.0532 | 1.1829 | 0.176* | |
H152 | 0.8294 | 1.0878 | 1.3012 | 0.176* | |
C16 | 1.066 (2) | 1.0023 (8) | 1.3420 (15) | 0.153 (6) | |
H161 | 1.0202 | 0.9997 | 1.4283 | 0.230* | |
H162 | 1.1919 | 1.0446 | 1.3395 | 0.230* | |
H163 | 1.1090 | 0.9403 | 1.3158 | 0.230* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.068 (3) | 0.104 (4) | 0.062 (3) | −0.007 (3) | −0.006 (2) | −0.005 (3) |
O2 | 0.054 (3) | 0.123 (5) | 0.063 (3) | −0.025 (3) | 0.006 (2) | −0.020 (3) |
O4 | 0.073 (3) | 0.079 (4) | 0.074 (3) | −0.018 (3) | −0.007 (3) | −0.002 (3) |
O5 | 0.118 (5) | 0.089 (4) | 0.071 (4) | −0.049 (4) | 0.027 (3) | −0.012 (3) |
O6 | 0.137 (6) | 0.123 (6) | 0.104 (5) | −0.070 (5) | 0.005 (5) | 0.007 (4) |
O14 | 0.145 (6) | 0.084 (4) | 0.093 (5) | −0.053 (4) | −0.024 (4) | 0.010 (4) |
O15 | 0.106 (5) | 0.065 (3) | 0.101 (4) | −0.035 (4) | −0.041 (4) | 0.010 (3) |
C1 | 0.059 (4) | 0.075 (5) | 0.065 (5) | 0.004 (4) | −0.003 (3) | −0.008 (4) |
C2 | 0.055 (4) | 0.062 (5) | 0.073 (5) | 0.006 (4) | 0.008 (3) | 0.005 (4) |
C3 | 0.044 (3) | 0.053 (4) | 0.060 (4) | 0.004 (3) | 0.008 (3) | −0.003 (3) |
C4 | 0.044 (3) | 0.055 (4) | 0.064 (4) | 0.006 (3) | 0.007 (3) | 0.004 (3) |
C5 | 0.052 (4) | 0.055 (4) | 0.098 (6) | 0.002 (4) | 0.018 (4) | −0.002 (4) |
C6 | 0.070 (5) | 0.092 (7) | 0.089 (6) | −0.033 (5) | 0.025 (4) | −0.022 (5) |
C7 | 0.092 (6) | 0.055 (4) | 0.080 (5) | −0.019 (5) | 0.010 (5) | −0.004 (4) |
C8 | 0.119 (8) | 0.142 (10) | 0.107 (7) | 0.009 (8) | 0.047 (6) | 0.022 (8) |
C9 | 0.151 (12) | 0.107 (9) | 0.182 (13) | 0.032 (9) | 0.030 (9) | −0.007 (9) |
C10 | 0.072 (5) | 0.086 (6) | 0.052 (4) | −0.008 (5) | 0.001 (3) | −0.009 (4) |
C11 | 0.092 (7) | 0.122 (9) | 0.090 (6) | −0.009 (6) | 0.007 (5) | −0.020 (6) |
C12 | 0.111 (7) | 0.130 (9) | 0.064 (5) | −0.025 (7) | −0.001 (5) | 0.016 (5) |
C13 | 0.055 (4) | 0.064 (5) | 0.064 (4) | −0.003 (4) | 0.006 (3) | 0.003 (4) |
C14 | 0.069 (5) | 0.055 (5) | 0.063 (5) | −0.006 (4) | −0.003 (4) | 0.004 (4) |
C15 | 0.163 (12) | 0.070 (7) | 0.186 (12) | −0.040 (8) | −0.103 (10) | 0.037 (8) |
C16 | 0.124 (9) | 0.094 (9) | 0.226 (15) | −0.027 (8) | −0.065 (10) | −0.016 (9) |
O1—C1 | 1.383 (9) | C7—C9 | 1.512 (14) |
O1—C10 | 1.438 (9) | C7—C8 | 1.552 (13) |
O2—C2 | 1.412 (9) | C8—H81 | 0.9600 |
O2—C10 | 1.424 (8) | C8—H82 | 0.9600 |
O4—C1 | 1.402 (10) | C8—H83 | 0.9600 |
O4—C4 | 1.422 (8) | C9—H91 | 0.9600 |
O5—C7 | 1.403 (9) | C9—H92 | 0.9600 |
O5—C5 | 1.410 (9) | C9—H93 | 0.9600 |
O6—C7 | 1.377 (10) | C10—C12 | 1.472 (12) |
O6—C6 | 1.406 (10) | C10—C11 | 1.479 (14) |
O14—C14 | 1.208 (9) | C11—H111 | 0.9600 |
O15—C14 | 1.296 (9) | C11—H112 | 0.9600 |
O15—C15 | 1.445 (12) | C11—H113 | 0.9600 |
C1—C2 | 1.529 (11) | C12—H121 | 0.9600 |
C1—H1 | 0.9800 | C12—H122 | 0.9600 |
C2—C3 | 1.494 (10) | C12—H123 | 0.9600 |
C2—H2 | 0.9800 | C13—C14 | 1.469 (10) |
C3—C13 | 1.336 (9) | C13—H13 | 0.9300 |
C3—C4 | 1.517 (10) | C15—C16 | 1.315 (14) |
C4—C5 | 1.510 (9) | C15—H151 | 0.9700 |
C4—H4 | 0.9800 | C15—H152 | 0.9700 |
C5—C6 | 1.530 (11) | C16—H161 | 0.9600 |
C5—H5 | 0.9800 | C16—H162 | 0.9600 |
C6—H61 | 0.9700 | C16—H163 | 0.9600 |
C6—H62 | 0.9700 | ||
C1—O1—C10 | 109.0 (5) | H81—C8—H82 | 109.5 |
C2—O2—C10 | 110.8 (5) | C7—C8—H83 | 109.5 |
C1—O4—C4 | 112.0 (6) | H81—C8—H83 | 109.5 |
C7—O5—C5 | 110.6 (6) | H82—C8—H83 | 109.5 |
C7—O6—C6 | 108.9 (7) | C7—C9—H91 | 109.5 |
C14—O15—C15 | 119.0 (7) | C7—C9—H92 | 109.5 |
O1—C1—O4 | 110.9 (7) | H91—C9—H92 | 109.5 |
O1—C1—C2 | 105.2 (6) | C7—C9—H93 | 109.5 |
O4—C1—C2 | 106.9 (6) | H91—C9—H93 | 109.5 |
O1—C1—H1 | 111.2 | H92—C9—H93 | 109.5 |
O4—C1—H1 | 111.2 | O2—C10—O1 | 105.7 (6) |
C2—C1—H1 | 111.2 | O2—C10—C12 | 110.7 (7) |
O2—C2—C3 | 111.3 (6) | O1—C10—C12 | 108.5 (7) |
O2—C2—C1 | 103.6 (6) | O2—C10—C11 | 108.9 (7) |
C3—C2—C1 | 103.6 (6) | O1—C10—C11 | 110.8 (8) |
O2—C2—H2 | 112.6 | C12—C10—C11 | 112.1 (8) |
C3—C2—H2 | 112.6 | C10—C11—H111 | 109.5 |
C1—C2—H2 | 112.6 | C10—C11—H112 | 109.5 |
C13—C3—C2 | 128.0 (7) | H111—C11—H112 | 109.5 |
C13—C3—C4 | 124.2 (6) | C10—C11—H113 | 109.5 |
C2—C3—C4 | 107.8 (6) | H111—C11—H113 | 109.5 |
O4—C4—C5 | 109.0 (6) | H112—C11—H113 | 109.5 |
O4—C4—C3 | 105.5 (5) | C10—C12—H121 | 109.5 |
C5—C4—C3 | 114.4 (6) | C10—C12—H122 | 109.5 |
O4—C4—H4 | 109.2 | H121—C12—H122 | 109.5 |
C5—C4—H4 | 109.2 | C10—C12—H123 | 109.5 |
C3—C4—H4 | 109.2 | H121—C12—H123 | 109.5 |
O5—C5—C4 | 111.2 (6) | H122—C12—H123 | 109.5 |
O5—C5—C6 | 103.1 (6) | C3—C13—C14 | 125.8 (7) |
C4—C5—C6 | 111.8 (6) | C3—C13—H13 | 117.1 |
O5—C5—H5 | 110.2 | C14—C13—H13 | 117.1 |
C4—C5—H5 | 110.2 | O14—C14—O15 | 123.5 (7) |
C6—C5—H5 | 110.2 | O14—C14—C13 | 124.9 (7) |
O6—C6—C5 | 102.8 (7) | O15—C14—C13 | 111.6 (7) |
O6—C6—H61 | 111.2 | C16—C15—O15 | 113.3 (9) |
C5—C6—H61 | 111.2 | C16—C15—H151 | 108.9 |
O6—C6—H62 | 111.2 | O15—C15—H151 | 108.9 |
C5—C6—H62 | 111.2 | C16—C15—H152 | 108.9 |
H61—C6—H62 | 109.1 | O15—C15—H152 | 108.9 |
O6—C7—O5 | 106.0 (7) | H151—C15—H152 | 107.7 |
O6—C7—C9 | 114.7 (9) | C15—C16—H161 | 109.5 |
O5—C7—C9 | 111.2 (9) | C15—C16—H162 | 109.5 |
O6—C7—C8 | 105.3 (8) | H161—C16—H162 | 109.5 |
O5—C7—C8 | 108.3 (8) | C15—C16—H163 | 109.5 |
C9—C7—C8 | 110.9 (9) | H161—C16—H163 | 109.5 |
C7—C8—H81 | 109.5 | H162—C16—H163 | 109.5 |
C7—C8—H82 | 109.5 | ||
C10—O1—C1—O4 | −90.9 (8) | O4—C4—C5—C6 | 61.5 (8) |
C10—O1—C1—C2 | 24.4 (8) | C3—C4—C5—C6 | 179.4 (6) |
C4—O4—C1—O1 | 134.3 (6) | C7—O6—C6—C5 | −29.9 (10) |
C4—O4—C1—C2 | 20.0 (8) | O5—C5—C6—O6 | 21.6 (8) |
C10—O2—C2—C3 | 121.6 (7) | C4—C5—C6—O6 | 141.1 (7) |
C10—O2—C2—C1 | 10.8 (8) | C6—O6—C7—O5 | 26.6 (10) |
O1—C1—C2—O2 | −21.5 (8) | C6—O6—C7—C9 | −96.6 (10) |
O4—C1—C2—O2 | 96.5 (7) | C6—O6—C7—C8 | 141.2 (9) |
O1—C1—C2—C3 | −137.7 (6) | C5—O5—C7—O6 | −11.3 (9) |
O4—C1—C2—C3 | −19.8 (8) | C5—O5—C7—C9 | 114.0 (9) |
O2—C2—C3—C13 | 82.5 (9) | C5—O5—C7—C8 | −123.9 (8) |
C1—C2—C3—C13 | −166.7 (7) | C2—O2—C10—O1 | 3.3 (9) |
O2—C2—C3—C4 | −97.8 (7) | C2—O2—C10—C12 | 120.5 (8) |
C1—C2—C3—C4 | 12.9 (7) | C2—O2—C10—C11 | −115.8 (7) |
C1—O4—C4—C5 | 111.8 (7) | C1—O1—C10—O2 | −18.0 (9) |
C1—O4—C4—C3 | −11.5 (7) | C1—O1—C10—C12 | −136.7 (8) |
C13—C3—C4—O4 | 177.8 (6) | C1—O1—C10—C11 | 99.9 (8) |
C2—C3—C4—O4 | −1.9 (7) | C2—C3—C13—C14 | −1.8 (11) |
C13—C3—C4—C5 | 58.0 (9) | C4—C3—C13—C14 | 178.6 (7) |
C2—C3—C4—C5 | −121.7 (6) | C15—O15—C14—O14 | −5.7 (14) |
C7—O5—C5—C4 | −126.6 (7) | C15—O15—C14—C13 | 173.1 (9) |
C7—O5—C5—C6 | −6.7 (8) | C3—C13—C14—O14 | 7.1 (13) |
O4—C4—C5—O5 | 176.2 (6) | C3—C13—C14—O15 | −171.7 (7) |
C3—C4—C5—O5 | −65.9 (8) | C14—O15—C15—C16 | −147.0 (13) |
Experimental details
Crystal data | |
Chemical formula | C16H24O7 |
Mr | 328.36 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 273 |
a, b, c (Å) | 5.929 (2), 14.133 (2), 10.3892 (12) |
β (°) | 95.065 (16) |
V (Å3) | 867.2 (3) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.10 |
Crystal size (mm) | 0.38 × 0.24 × 0.15 |
Data collection | |
Diffractometer | Rigaku AFC-5R diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1752, 1588, 891 |
Rint | 0.018 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.064, 0.200, 1.01 |
No. of reflections | 1588 |
No. of parameters | 213 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.47, −0.20 |
Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1991), MSC/AFC Diffractometer Control Software, TEXSAN (Molecular Structure Corporation, 1999), SHELXS86 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.
Branched-chain sugars (Yoshimura, 1984) have been found as components of many antibiotics and other natural products which possess interesting biological activities. Many of these compounds have furopyran structures. Examples of these are azadiractin (Broughton et al., 1986; Ley et al. 1987) and miharamycin A and B (Seto et al., 1983; Koul, 1984a). The former is an insect anti-feedant (Koul, 1984a,b; Rembold, 1984) isolated from the neem tree and the latter are active against rice blast disease caused by Pyricularia oryzae (Ley et al., 1987). Our interest is to find convenient and efficient approaches to the synthesis of furopyran and related fused-ring systems from readily available sugars and their derivatives. As part of this programme, the title compound, (I), was synthesized and its structure determined.
Fig. 1 depicts the correct absolute configuration of (I), which was assigned to agree with the known chirality of D-glucose, from which (I) was synthesized. The molecule contains three five-membered rings which exhibit various conformations. The furanoid sugar ring has an envelope conformation puckered at C1, as indicated by the puckering parameter, ϕ2 = 222 (2)° (Cremer & Pople, 1975). Atom C1 lies 0.295 (8) Å from the plane defined by C2, C3 C4 and O4. The 1,2-O-isopropylidene ring also has an envelope conformation [ϕ2 = 208 (2)°] with C1 lying 0.346 (8) Å from the plane through C10, O1, O2 and C2. The 5,6-O-isopropylidene ring has a half-chair conformation [ϕ2 = 93.0 (17)°] with C6 and O6 lying 0.173 (8) and -0.260 (7) Å, respectively, from the plane defined by O5, C5 and C7.
The atomic displacement parameters for O6 and the adjacent methyl groups of the 5,6-O-isopropylidene ring are slightly enlarged, which suggests that the part of the ring containing O6 is quite flexible. However, there are no significant peaks of residual electron density in the vicinity of O6, so that the possibility of the ring having two different envelope conformations can be excluded. This effect has also been observed in the corresponding 3-C-ethoxycarbonylmethyl derivative (Linden et al., 1996). The elongated atomic displacement ellipsoids for the ethyl group of the ester substituent also suggest that this group is disordered. However, the data quality did not enable a sensible model for the disorder to be developed. As an artefact of the untreated disorder, the bond lengths in this region of the molecule appear to be unduly short.