Insights into the geometrical features underlying β-O-GIcNAc glycosylation: Water pockets drastically modulate the interactions between the carbohydrate and the peptide backbone

Article abstract of DOI:10.1002/chem.200901204

A novel and simple model was proposed to explain the different relative orientation of the peptide backbone and presentation of beta-N-scetyl-D- glucosamine (β-O-GlcNAc)-Thr and Ser moieties. The sugar-peptide interactions were modulated by the specific hydrogen bonds and the existence of water pockets at key sites. NMR experiments of the interactions were recorded on a Bruker Avance 400 spectrometer at 298 K to verify the investigations. MAD-tar simulations were performed with AMBER 6.0 (AMBER94) that was implemented with GLYCAM 04 parameters to accurately simulate the computational behavior of the sugar moiety. NOE-derived distances were included as time-averaged coupling constraints along with the scalar coupling constants J. Final trajectories were run using an exponential decay constant of 16 ns and a simulation length of 16 ns with water molecules.

Full text of DOI:10.1002/chem.200901204

COMMUNICATION
DOI: 10.1002/chem.200901204
Insights into the Geometrical Features Underlying b-O-GlcNAc
Glycosylation: Water Pockets Drastically Modulate the Interactions between
the Carbohydrate and the Peptide Backbone
[
a]
[a]
[a]
Alberto Fernꢀndez-Tejada, Francisco Corzana,* Jesffls H. Busto,
[a]
[
b]
[c]
Gonzalo JimØnez-OsØs, Jesffls JimØnez-Barbero, Alberto Avenoza, and
[
a]
Jesffls M. Peregrina*
There is an increasing interest in clarifying the role of b-
N-acetyl-d-glucosamine (b-GlcNAc) since the discovery that
it modifies the chemical, biochemical, and biomedical be-
havior of an increasing number of cytoplasmic and nuclear
proteins, such as transcription factors, nuclear pore proteins,
oncogene products, tumor suppressors, and cytoskeletal pro-
glycans. However, in spite of the importance of O-GlcNAc
glycosylation, sparse information has been reported to date
concerning the geometry and dynamics of b-O-GlcNAc-Ser
and b-O-GlcNAc-Thr motifs.
On the contrary, significant progress has been made with
regard to the understanding of the structural properties of
[1]
[1e]
teins. This post-translational glycosylation is highly dynam-
the b-N-GlcNAc-Asn fragment. In fact, while numerous
[
2]
ic and draws comparisons with protein phosphorylation as
a biological control mechanism. It has been implicated in
crystal structures containing this fragment have been report-
[
6a–g]
ed to date,
only one crystal structure with a serine resi-
[
3]
[6h]
gene transcription, nuclear trafficking, protein translation,
due glycosylated with a b-O-GlcNAc has been deposited
in the Protein Data Bank. This crystal structure shows the
complex between a b-O-GlcNAc glycopeptide with the se-
quence FAPSNYPAL (named K3G) and the MHC Class 1
[1a]
signal transduction, regulation of protein–protein interac-
[1]
[4]
tions, and the sensing of nutritional levels within the cell.
Furthermore, there is clear evidence that the aberrant O-
b
GlcNAc modification of proteins is correlated with diabetes,
H-2D antibody. The authors suggested the occurrence of
[1,5]
tumorgenesis, and even with Alzheimerꢀs disease.
two conformations for the O-GlcNAc-Ser glycosidic linkage,
each displaying similar occupancy. This experimental finding
clearly suggests a significant degree of mobility for this
From a structural point of view, O-GlcNAc glycosylation
sites do not show obvious consensus sequences. Additional-
ly, in contrast to ꢁclassicalꢀ protein glycosylation, O-GlcNAc
is not elongated or further modified with a complex array of
[6]
moiety. One of these conformers is shown in Figure 1.
On the other hand, the conformational study in aqueous
solution of glycopeptides containing the b-O-GlcNAc-Ser/
[
a] A. Fernꢂndez-Tejada, Dr. F. Corzana, Dr. J. H. Busto,
Prof. A. Avenoza, Dr. J. M. Peregrina
Departamento de Quꢃmica
Universidad de La Rioja
UA-CSIC. Madre de Dios 51
2
6006 LogroÇo, La Rioja (Spain)
Fax : (+34)941 299 621
E-mail: francisco.corzana@unirioja.es
jesusmanuel.peregrina@unirioja.es
[
b] Dr. G. Jimꢄnez-Osꢄs
Departamento de Quꢃmica Orgꢂnica
ICMA-CSIC-Universidad de Zaragoza
Pedro Cerbuna 12, 50009 Zaragoza (Spain)
[
c] Prof. J. Jimꢄnez-Barbero
Centro de Investigaciones Biolꢅgicas (CSIC)
Ramiro Maeztu 9, 28040 Madrid (Spain)
Figure 1. Unique crystal structure found in the Protein Data Bank
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901204.
(1QLF) containing a glycopeptide which incorporates the b-O-GlcNAc
residue. The structure shows the H-2D /glycopeptide complex.
b
[6h]
Chem. Eur. J. 2009, 15, 7297 – 7301
ꢆ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7297

Thr moiety has been limited to very few studies, which sug-
gest that the glycosylation of Thr or Ser with b-O-GlcNAc
[7]
promotes turnlike structures. However, in these cases,
there is not a clear hypothesis on the mechanism that could
support the key influence of the sugar moiety on the peptide
backbone.
On chemical grounds, one of the key steps to understand
the bioactivity of b-O-GlcNAc-Ser and b-O-GlcNAc-Thr
motifs would be to know their conformational preferences,
as well as their dynamics and their interactions (if any) with
the peptide backbone. The presentation mode of the
GlcNAc moiety could also be of paramount importance for
establishing interactions with the corresponding molecular
entities.
On this basis, we report herein the conformational analy-
sis in aqueous solution, by NMR spectroscopy and molecu-
lar modeling of the simplest model glycopeptides derived
from serine and threonine glycosylated with b-O-GlcNAc
(
Scheme 1). The synthesis of the glycopeptides was achieved
by following the procedure described by Schmidt and co-
workers (see the Supporting Information).
Figure 2. a, b) Sections of the 800 ms 2D NOESY spectrum (400 MHz) in
[8]
H O/D O (9:1) at 258C of compound 2, showing the amide cross-peaks.
2
2
Diagonal peaks and exchange cross-peaks connecting NH protons and
water are negative. The NOE contacts are represented as positive cross-
peaks. c) NOE buildup curves for H1 of compound 1.
Scheme 1. Model glycopeptides synthesized and studied in this work.
Once the assignment of the NMR spectra was completed
(
see Experimental Section), selective 1D-NOESY experi-
ments in D O (258C, pH 5.2) and 2D-NOESY experiments
2
in H O/D O (9/1) (258C, pH 5.2) were then carried out for
2
2
glycopeptides 1 and 2 (Figure 2). From a quantitative point
of view, NOE buildup curves were measured and used to ex-
tract the corresponding proton–proton distances. Distances
involving the key NH protons were semiquantitatively deter-
mined from the integrated volumes of the corresponding
3
cross-peaks. In addition, J coupling constants were mea-
sured from the splitting of the resonance signals in the 1D
spectra (Figure 2).
The conformational behavior of compounds 1 and 2 was
examined by using MD simulations with time-averaged ex-
perimental restraints (MD-tar) using the protocol recently
[9]
described by our group. The results obtained from the
[10]
MD-tar simulations, for both compounds, showed a close
agreement, in numerical terms, between the distances found
in the refined models and the experimental NMR data,
when using a 16 ns MD-tar simulation in explicit water. The
peptide backbone of both derivatives adopted mainly the
PPII-like conformation (47% and 43% for 1 and 2, respec-
tively). Furthermore, around 20% of conformers showed f/
y dihedral values (backbone) corresponding to helix-like
structures (Figure 3a). This result is in good agreement with
the weak-medium NOE observed between the NH protons
Figure 3. a) f/y distributions (backbone) obtained from the MD-tar sim-
ulations for compounds 1 (left) and 2 (right). b) c distributions obtained
1
from the MD-tar simulations for compounds 1 (left) and 2 (right). c) y
distribution (glycosidic linkage) obtained from the MD-tar simulations
for compounds 1 and 2, showing the Newman projection of the Cb O1
bond.
À
7298
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Chem. Eur. J. 2009, 15, 7297 – 7301

b-O-GlcNAc Glycosylation
COMMUNICATION
of the backbone (Figure 2b and Supporting Information).
As additional evidence of the goodness of the obtained con-
formational distribution, the experimental and theoretical
Figure 4a shows the MD-tar ensembles that quantitatively
reproduced the experimental NMR data. These drastically
different y values for compounds 1 and 2 are responsible
3
J(NHGlcNAc,H2) coupling constants were also in good agree-
3
ment. The high value of J (9.4 Hz for both compounds) sug-
gests that the orientation of the N-acetyl group relative to
the sugar framework seems essentially fixed. These results
are in agreement with those reported by other authors for
[
11]
b-O-GlcNAc carbohydrate
derivatives.
or b-O-GalNAc glycopeptide
[12]
1
As far as the lateral chain (c torsion angle) is concerned,
the simulations suggest that the rotation around c in the
1
Thr derivative is to some extent restricted, with values for
this torsion angle close to 608 (Figure 3b). Although we
3
could not experimentally measure the J
value for 2 due
Ha,Hb
3
to overlapping signals in the spectrum, a J
value of
Ha,Hb
1
.8 Hz has been measured for the b-O-GlcNAc-Thr motif in
[7b]
a glycopeptide derived from the RNA polymerase II. In
sharp contrast, the lateral chain of the Ser-containing glyco-
peptide is rather flexible, showing a significant population of
each staggered conformation for this torsion angle. This
3
result is in good agreement with the medium J
values
Ha,Hb
(
6.6 and 5.2 Hz) experimentally observed for derivative 1.
Concerning the glycosidic linkage, the f (O5-C1-O1-Cb)
dihedral angle was found to be rather rigid for both com-
pounds, exhibiting values around À608, in perfect agreement
[13]
with the exo-anomeric effect. However, it is important to
note that the Ser and Thr derivatives showed markedly dif-
ferent behavior in terms of the y (C1-O1-Cb-Ca) dihedral
angle (Figure 3c). In fact, for derivative 2, this angle showed
well-defined values around 1208–1408, resulting in an
eclipsed conformation for the HbÀCb and O1ÀC1 bonds.
Figure 4. a) Calculated ensembles obtained from the MD-tar simulations
for 1 (left) and 2 (right). b) Water pocket between the carbohydrate and
the peptide moieties found for compound 2.
for the existence of a completely different relative orienta-
tion between the carbohydrate and the peptide moieties,
which affects the presentation mode of the GlcNAc residue.
In fact, whereas for Ser-derivative 1, the acetyl group of the
GlcNAc unit is close to the peptide backbone, for its Thr-an-
alogue 2, the hydroxymethyl group of the carbohydrate frag-
ment is closer to the peptide, allowing the formation of a hy-
drogen bond between the hydroxymethyl group of the car-
bohydrate moiety and the carbonyl group of Thr (Fig-
ure 4b). This hydrogen bonding was present about 45% of
the total trajectory time. In contrast, no hydrogen bond was
found above 5% of the total 16 ns trajectory time for com-
pound 1.
This conformer avoids the steric repulsions between the
methyl group at Cb and the anomeric H1 proton, which
would be present when this y angle is close to 1808.
Notably, this conformation has also been observed in the
glycopeptide derived from the RNA polymerase II, support-
ed by the observed strong NOE between H1 and Hb pro-
[7b]
tons, exclusive for this eclipsed conformation. In contrast
to the facts for the Thr-containing molecule (2), y was
found to be more flexible for the Ser-analogue (1), with a
major anti-type arrangement for the GlcNAc residue and
the peptide moiety (Figure 3c). The different conformers
found in these two molecules for the glycosidic linkage were
in good agreement with the adiabatic maps calculated by
On the other hand, important new insights into the role
of water in organizing polysaccharide structure, in protein
folding, and in folding of small nucleic acids are emerging
[14]
using a systematic approach with the AMBER force field
see the Supporting Information). Curiously, although the
(
[11,16]
anomeric linkage and the chemical nature of the sugar is
completely different, it has to be mentioned that an eclipsed
y conformation has been previously reported by our group
from different studies,
which point to a new way toward
visualizing the effects of water on these structures. However,
few examples have been published concerning the role of
water in the modulation of the interactions between the car-
[15]
for glycopeptides containing the a-O-GalNAc-Thr.
This
[9,15]
similar behavior could indicate that the conformational ten-
dencies for y in O-glycopeptides are mainly determined by
the presence (or not) of the b-methyl group in the b-hy-
droxy-a-amino acid residue (Thr or Ser, respectively), irre-
spective of the chemical nature of the carbohydrate moiety
and of the configuration at the anomeric center.
bohydrate and peptide backbone in glycopeptides,
which
could modify the orientation and/or the flexibility features
of the carbohydrate moieties and thus their presentation
ability to interact with their biological targets. Therefore, we
decided to investigate the anisotropy hydration of both com-
pounds 1 and 2 following our previously described proto-
Chem. Eur. J. 2009, 15, 7297 – 7301
ꢆ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7299

J. M. Peregrina et al.
[
9]
col. Normalized two-dimensional radial pair distributions
calcd (%) for C15
7.18, N 11.16.
H
27
N
3
O
8
: C 47.74, H 7.21, N 11.13; found: C 47.66, H
[17]
were calculated for all possible share water density sites.
2
D NMR experiments: NMR experiments were recorded on a Bruker
These calculations lead to water densities higher than the
bulk water density, in regions where structural or semistruc-
tural water molecules are present.
Avance 400 spectrometer at 298 K. Magnitude-mode ge-2D COSY spec-
tra were recorded with gradients and using the cosygpqf pulse program
with 90 degree pulse width. Phase-sensitive ge-2D HSQC spectra were
recorded using z-filter and selection before t1 removing the decoupling
during acquisition by use of invigpndph pulse program with CNST2
Figure 4b shows the 2D radial pair distribution obtained
for the oxygen atom of the acetyl group of GlcNAc and the
Thr-nitrogen of derivative 2. The shared water density found
in the first hydration shell of both atoms revealed the exis-
tence of bridging water molecules between them. The densi-
ty of this shared water site was 7.0 times the bulk density.
Importantly, a water pocket involving the N-acetyl group
has been previously found by ab initio calculations in
GlcNAc carbohydrate. On the other hand, although the
water pocket observed in glycopeptide 2 was also present in
compound 1, in this case, the density of the shared water
site was only about twice that of the bulk. This difference is
likely due to both the distinct flexibility of the lateral chains
and the different orientation of the aglyconic linkages.
Markedly, for both compounds, this water pocket was more
persistent (about 1.5 times) when the helix-like structures
were present. In addition, both the hydrogen bond and a
bridging water molecule were present at the same time
about 20% of the trajectory time.
(
JHC)=145. 2D NOESY experiments were made using phase-sensitive
ge-2D NOESY with WATERGATE for H O/D O (9:1) spectra. Selective
2
2
ge-1D NOESY experiments were carried out using the 1D-DPFGE NOE
pulse sequence. NOEs intensities were normalized with respect to the di-
agonal peak at zero mixing time. Experimental NOEs were fitted to a
Àp1t
Àp2t
double exponential function, f(t)=p
0
A
H
U
G
R
N
U
)
A
H
U
G
E
N
N
0 1 2
, p , and p
[
19]
0 2
p
[11]
ton distances were obtained by employing the isolated spin pair approxi-
mation. The calculated J values were obtained from the simulations by
applying the appropriate Karplus equation
sion angles.
3
[
20]
to the corresponding tor-
Molecular dynamics simulations: MD-tar simulations were performed
[
21]
[22]
with AMBER
6.0 (AMBER94),
which was implemented with
[23]
GLYCAM 04 parameters
behavior of the sugar moiety. NOE-derived distances were included as
time-averaged distance constraints, and scalar coupling constants J as
time-averaged coupling constraints. A <r
the distances and a linear average was used for the coupling constants.
Final trajectories were run using an exponential decay constant of 16 ns
and a simulation length of 16 ns with explicit water molecules (TIP3P).
to accurately simulate the conformational
À6
À1/6
>
average was used for
[24]
Therefore, we propose a novel and simple model for ex-
plaining the different relative orientation of the peptide
backbone and presentation of b-O-GlcNAc-Thr and Ser
moieties. The sugar–peptide interactions are modulated not
only by specific hydrogen bonds but also by the existence
of water pockets at key sites. It is likely that the existence of
these solvent pockets could also have important biological
implications, providing the required presentation of the
GlcNAc moieties to interact with their biological receptors.
Acknowledgements
[18]
We thank the Ministerio de Ciencia e Innovaciꢅn (project CTQ2006-
05825/BQU, Ramꢅn y Cajal contract to F.C. and grant to A.F.-T.) and the
Universidad de La Rioja (project EGI08/06). We also thank CESGA for
computer support.
Keywords: glycopeptides
· glycosylation · hydration ·
molecular dynamics · NMR spectroscopy
Experimental Section
Characterization of compounds 1 and 2: Compound 1: M.p. 235–2378C;
[
1] a) L. Wells, K. Vosseller, G. W. Hart, Science 2001, 291, 2376–2378;
b) J. E. Rexach, P. M. Clark, L. C. Hsieh-Wilson, Nat. Chem. Biol.
2
5
1
[
(
3
a]
D
=À22.7 (c=0.95, H
2
O); H NMR (300 MHz, D
), 3.38–3.56 (m, 3H, H
), 3.81–3.94 (m, 2H, H , H ), 4.01 (dd,
H,H =5.8 Hz, 1H, H
); H NMR (400 MHz, H O/D O, 9:1): d =7.87–
.94 (m, 1H, NHMe), 8.10 (d, JH,H =9.4 Hz, 1H, NHAcGlcNAc), 8.14 ppm
2
O): d =1.93–2.10
m, 6H, 2COCH ), 2.70 (s, 3H, NHCH
.60–3.77 (m, 2H, H
0.8, 6.7 Hz, 1H, H
H,H =8.4 Hz, 1H, H
3
3
4
, H
5
, H
3
),
=
2
008, 4, 97–106; c) N. E. Zachara, G. W. Hart, Chem. Rev. 2002, 102,
3
2
, H
), 4.40 (ꢁtꢀ,
6
b
6
J
H,H
4
31–438; d) R. G. Spiro, Glycobiology 2002, 12, 43R–56R.
3
1
b
J
a
), 4.49 ppm (d,
[2] G. W. Hart, M. P. Housley, C. Slawson, Nature 2007, 446, 1017–1022.
[3] F. I. Comer, G. W. Hart, J. Biol. Chem. 2000, 275, 29179–29182.
[4] N. E. Zachara, G. W. Hart, Biochim. Biophys. Acta Gen. Subj. 2004,
3
1
J
1
2
2
3
7
(
(
6
1
3
13
d,
CH
J
H,H =6.8 Hz, 1H, NHAc); C NMR (100 MHz, D
2
O): d =21.8
), 55.3 (C ), 60.6 (C ),
), 171.6, 174.3,
1
673, 13–28.
5] a) Y. Akimoto, L. K. Kreppel, H. Hirano, G. W. Hart, Diabetologia
000, 43, 1239–1247; b) Y. Akimoto, L. K. Kreppel, H. Hirano,
3
CO), 22.1 (CH
8.1 (C ), 69.8 (C
3
CO), 25.9 (NHCH
3
), 53.8 (C
a
2
6
[
b
4
), 73.6 (C ), 75.8 (C
3
5
), 100.8 (C
1
2
74.5 ppm (3CO); elemental analysis calcd (%) for C14
H
25
N
3
O
8
: C 46.28,
G. W. Hart, Arch. Biochem. Biophys. 2001, 389, 166–175; c) M.
Brownlee, Nature 2001, 414, 813–820; d) K. Vosseller, L. Wells,
M. D. Lane, G. W. Hart, Proc. Natl. Acad. Sci. USA 2002, 99, 5313–
5318.
H 6.93, N 11.56; found: C 46.38, H 6.90, N 11.61.
2
5
1
Compound 2: M.p. 225–2278C; [a]
D
=À30.6 (c=1.15, H
H,H =6.2 Hz, 3H, bCH
2
O); H NMR
3
(
400 MHz, D
2
O): d=1.16 (d,
J
3
), 2.02–2.14 (m,
), 3.38–3.49 (m, 2H, H , H ), 3.54 (ꢁtꢀ,
), 3.63–3.70 (m, 1H, H
6
J
5
H, COCH ), 2.76 (s, 3H, NHCH
3
3
5
4
[6] a) D. Loganathan, U. Aich, T. Lakshmanan, Proc. Indian Natl. Sci.
Acad. 2005, 71A, 213–236; b) D. Sriram, T. Lakshmanan, D. Loga-
nathan, S. Srinivasan, Carbohydr. Res. 1998, 309, 227–236; c) L. T.
Delbaere, Biochem. J. 1974, 143, 197–205; d) J. Ohanessian; D.
Avenel, A. Neuman, H. Gillier-Pandraud, Carbohydr. Res. 1980, 80,
1–13; D. Avenel, A. Neuman, H. Gillier-Pandraud, Carbohydr. Res.
1980, 80, 1–13; e) T. Lakshmanan, D. Sriram, K. Priya, D. Logana-
than, Biochem. Biophys. Res. Commun. 2003, 312, 405–413; f) D.
Loganathan, U. Aich, Glycobiology 2005, 16, 343–348; g) M. M. N.
3
3
H,H =9.1 Hz, 1H, H
3
2
), 3.76 (dd,
J
H,H =12.2,
3
.2 Hz, 1H, H6proR), 3.89 (dd,
m, 2H,
400 MHz, H
.4 Hz, 1H, NHAc), 8.33 ppm (d,
J
H,H =12.2, 2.1 Hz, 1H, H6proS), 4.30–4.39
3
1
(
(
H
b
,
H
a
), 4.50 ppm (d,
J
H,H =8.4 Hz, 1H,
H
1
); H NMR
3
2
O/D
2
O, 9:1): d =7.89–7.96 (m, 1H, NHMe), 8.12 (d, JH,H
=
3
9
JH,H =7.5 Hz, 1H, NHAcGlcNAc);
1
3
C NMR (100 MHz, D
NHCH ), 55.5 (C ), 58.1 (C
5.6 (C ), 100.0 (C ), 172.0, 174.8, 174.8 ppm (3CO); elemental analysis
2
O): d =16.4 (bCH
3
), 21.8, 22.1 (2CH
3
CO), 25.9
), 73.6 (C ), 75.0 (C
(
3
2
a
), 60.7 (C ), 69.7 (C
6
4
3
b
),
7
5
1
7300
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Chem. Eur. J. 2009, 15, 7297 – 7301

b-O-GlcNAc Glycosylation
COMMUNICATION
Ali, U. Aich, B. Varghese, S. Pꢄrez, A. Imberty, D. Loganathan, J.
Am. Chem. Soc. 2008, 130, 8317–8325; h) A. Glithero, J. Tormo,
J. S. Haurum, G. Arsequell, G. Valencia, J. Edwards, S. Springer, A.
Townsend, Y.-L. Pao, M. Wormald, R. A. Dwek, E. Y. Jones, T. El-
liott, Immunity 1999, 10, 63–74.
7] a) W. G. Wu, L. Pasternack, D. H. Huang, K. M. Koeller, C. C. Lin,
O. Seitz, C. H. Wong, J. Am. Chem. Soc. 1999, 121, 2409–2417;
b) E. E. Simanek, D. H. Huang, L. Pasternack, T. D. Machajewski,
O. Seitz, D. S. Millar, H. J. Dyson, C. H. Wong, J. Am. Chem. Soc.
[14] J. Wang, P. Cieplak, P. A. Kollman, J. Comput. Chem. 2000, 21,
1049–1074.
[15] F. Corzana, J. H. Busto, G. Jimꢄnez-Osꢄs, M. Garcꢃa de Luis, J. L.
Asensio, J. Jimꢄnez-Barbero, J. M. Peregrina, A. Avenoza, J. Am.
Chem. Soc. 2007, 129, 9458–9467.
[
[16] a) E. J. Sorin, Y. M. Rhee, V. S. Pande, Biophys. J. 2005, 88, 2516–
2
524; b) A. Almond, J. K. Sheehan, Glycobiology 2003, 13, 255–
2
64; c) Y. M. Rhee, E. J. Sorin, G. Jayachandran, E. Lindahl, V. S.
Pande, Proc. Natl. Acad. Sci. USA 2004, 101, 6456–6461.
17] C. Andersson, S. B. Engelsen, J. Mol. Graphics 1999, 17, 101–105.
18] J. Schuman, A. P. Campbell, R. R. Koganty, B. M. Logenecker, J.
Pept. Res. 2003, 61, 91–108.
[
[
1
998, 120, 11567–11575; c) Y. X. Chen, J. T. Du, L. X. Zhou, X. H.
Liu, Y. F. Zhao, H. Nakanishi, Y. M. Li, Chem. Biol. 2006, 13, 937–
44.
8] U. K. Saha, R. R. Schmidt, J. Chem. Soc. Perkin Trans. 1 1997,
855–1860.
9
[
[
19] T. Haselhorst, T. Weimar, T. Peters, J. Am. Chem. Soc. 2001, 123,
[
[
1
0705–10714.
1
20] a) A. Demarco, M. Llinꢂs, K. Wꢇthrich, Biopolymers 1978, 17, 617–
9] a) F. Corzana, J. H. Busto, S. B. Engelsen, J. Jimꢄnez-Barbero, J. L.
Asensio, J. M. Peregrina, A. Avenoza, Chem. Eur. J. 2006, 12, 7864–
6
7
36; b) G. W. Vuister, A. Bax, J. Am. Chem. Soc. 1993, 115, 7772–
777; c) C. A. G. Haasnoot, F. A. A. M. de Leeuw, C. Altona, Tetra-
7
871; b) F. Corzana, J. H. Busto, G. Jimꢄnez-Osꢄs, J. Jimꢄnez-Bar-
bero, J. L. Asensio, J. M. Peregrina, A. Avenoza, J. Am. Chem. Soc.
006, 128, 14640–14648; c) A. Fernꢂndez-Tejada, F. Corzana, J. H.
Busto, G. Jimꢄnez-Osꢄs, J. M. Peregrina, A. Avenoza, Chem. Eur. J.
008, 14, 7042–7058; d) F. Corzana, J. H. Busto, M. Garcꢃa de Luis,
J. Jimꢄnez-Barbero, A. Avenoza, J. M. Peregrina, Chem. Eur. J.
009, 15, 3863–3874.
hedron 1980, 36, 2783–2792.
[
[
21] a) D. A. Pearlman, D. A. Case, J. W. Caldwell, W. R. Ross, T. E.
Cheatham III, S. DeBolt, D. Ferguson, G. Seibel, P. A. Kollman,
Comput. Phys. Commun. 1995, 91, 1–41; b) P. A. Kollman,
AMBER 6, University of California, San Francisco 1999.
22] W. D. Cornell, P. Cieplak, C. I. Bayly, I. R. Gould, K. M. Merz,
D. M. Ferguson, D. C. Spellmeyer, T. Fox, J. W. Caldwell, P. A. Koll-
man, J. Am. Chem. Soc. 1995, 117, 5179–5197.
2
2
2
[
[
[
10] D. A. Pearlman, J. Biomol. NMR 1994, 4, 1–16.
11] M. Mobli, A. Almond, Org. Biomol. Chem. 2007, 5, 2243–2251.
12] D. M. Coltart, A. K. Royyuru, L. J. Williams, P. W. Glunz, D. Sames,
S. D. Kuduk, J. B. Schwarz, X. T. Chen, S. J. Danishefsky, D. H. Live,
J. Am. Chem. Soc. 2002, 124, 9833–9844.
[
[
23] R. J. Woods, R. A. Dwek, C. J. Edge, B. Fraser-Reid, J. Phys. Chem.
B 1995, 99, 3832–3846.
24] M. W. Mahoney, W. L. Jorgensen, J. Chem. Phys. 2000, 112, 8910–
8
922.
[
13] G. R. J. Thatcher, The Anomeric Effect and Associated Stereoelec-
tronic Effects, ACS, Washington, 1993.
Received: May 6, 2009
Published online: June 19, 2009
Chem. Eur. J. 2009, 15, 7297 – 7301
ꢆ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7301