organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
reported by Toshima (2000) and updated in the more recent
review by Carmona et al. (2008). Interest in glycosyl fluorides
has increased since Hayashi et al. (1984) developed a reliable
and safe method for the preparation of these compounds by
exposing suitably protected sugars to a 50–70% mixture of
hydrogen fluoride in pyridine. The stability of glycosyl fluor-
ides in their deprotected form also makes them important
compounds for use as mechanistic probes in the elucidation of
enzyme mechanisms and as reagents for enzymatic synthesis
ISSN 0108-2701
Peracetylated a-D-glucopyranosyl
fluoride and peracetylated a-maltosyl
fluoride
(reviewed by Williams & Withers, 2000). Extending our
interest in the impact of fluorine substitution on carbohydrate
biotransformations (Errey et al., 2009) and the generation of
amylose mimetics (Marmuse et al., 2005; Nepogodiev et al.,
a
b
a
Simone Dedola, David L. Hughes * and Robert A. Field
a
Department of Biological Chemistry, John Innes Centre, Colney Lane, Norwich
2
007; Cl e´ et al., 2008), we had cause to investigate glucosyl
fluorides. In this paper, we report the crystal structures of the
,3,4,6-tetra-O-acetyl-ꢀ-d-glucopyranosyl fluoride, (I), and the
b
NR4 7UH, England, and School of Chemistry, University of East Anglia, Norwich
NR4 7TJ, England
2
corresponding maltose derivative 2,3,4,6-tetra-O-acetyl-ꢀ-d-
glucopyranosyl-(1!4)-2,3,6-tri-O-acetyl-ꢀ-d-glucopyranosyl
fluoride, (II). The crystal structures obtained integrate with
the published series of ꢀ-glycosyl halide derivatives; X-ray
structures of peracetylated ꢀ-glucosyl chloride (James & Hall,
Received 23 November 2009
Accepted 29 January 2010
Online 3 February 2010
The X-ray analyses of 2,3,4,6-tetra-O-acetyl-ꢀ-d-glucopyran-
osyl fluoride, C H FO , (I), and the corresponding maltose
1969) and bromide (Takai et al., 1976) have been reported
1
4
19
9
previously and the members of this series show most clearly
the anomeric effect, where the preference for the axial
orientation of the halogen atom renders synthesis of the
equatorial counterpart a synthetic challenge. Results from
X-ray analyses typically allow direct evaluation of the impact
of the anomeric effect on sugar structure.
derivative 2,3,4,6-tetra-O-acetyl-ꢀ-d-glucopyranosyl-(1!4)-
2,3,6-tri-O-acetyl-ꢀ-d-glucopyranosyl fluoride, C H FO ,
26
35
17
(II), are reported. These add to the series of published
ꢀ
ꢀ
-glycosyl halide structures; those of the peracetylated
-glucosyl chloride [James & Hall (1969). Acta Cryst. A25,
S196] and bromide [Takai, Watanabe, Hayashi & Watanabe
1976). Bull. Fac. Eng. Hokkaido Univ. 79, 101–109] have been
reported already. In our structures, which have been
(
determined at 140 K, the glycopyranosyl ring appears in a
4
regular C chair conformation with all the substituents, except
1
for the anomeric fluoride (which adopts an axial orientation),
in equatorial positions. The observed bond lengths are
consistent with a strong anomeric effect, viz. the C1—O5
4
The glucosyl unit in (I) (Fig. 1) adopts a C chair confor-
1
(
carbohydrate numbering) bond lengths are 1.381 (2) and
˚
.381 (3) A in (I) and (II), respectively, both significantly
mation. All bond lengths and angles conform with the values
found in acetylated glucose. Values for the bond lengths which
are affected by the anomeric effect, together with results from
the X-ray crystal structures of other acetylated glucosyl
halides, are summarized in Table 1. The conformational
properties of pyranosyl halides have been explored by a
number of theoretical studies using model compounds such as
2-fluorotetrahydropyran or 2-chlorotetrahydropyran. The
theoretical approaches to generate three-dimensional struc-
tures rely on experimental data to generate the necessary set
of parameters. In this context, good agreement was obtained
by Tvaroska & Carver (1994) by comparison of their theore-
tical results with experimental ones obtained for the acetyl
and benzoyl d-xylopyranose fluorides. To our knowledge, no
crystal structure of anomeric aldohexosyl fluorides has been
reported to date. The structural data reported herein are in
agreement with the theoretical data obtained by Tvaroska &
Carver (1994), supporting the theoretical methodology
reported in their study.
1
shorter than the C5—O5 bond lengths, viz. 1.448 (2) A in (I)
˚
˚
and 1.444 (3) A in (II).
Comment
Glycosyl fluorides are widely used in carbohydrate chemistry
and biochemistry. The F atom is comparable in size with a
hydroxy group, hence the steric demand upon introduction of
this group is quite small (O’Hagan 2008; Howard et al., 1996).
The popularity of glycosyl fluorides in chemical synthesis is
due to their remarkable stability yet ease of chemospecific
activation in performing glycosylation reactions. One notable
advantage in using glycosyl fluorides as glycosyl donor is their
high thermal stability compared with glycosyl chlorides,
bromides or iodides. The utilization of carbohydrate fluorides
as glycosyl donors originates from the work by Mukaiyama et
al. (1981) on the synthesis of simple glucosides and disac-
charides. Progress made in the utilization of glycosyl fluorides
as donors in the synthesis of O- and C-glycosides has been
Influences on the bond lengths in a series of X-ray crystal
structures of glycopyranosides have been examined by Briggs
o124 # 2010 International Union of Crystallography
doi:10.1107/S0108270110003641
Acta Cryst. (2010). C66, o124–o127
Dedola, Simone
