1 Hand 13C NMR data of methyl tetra-O-benzoyl-D- pyranosides in acetone-d6

Article abstract of DOI:10.1002/mrc.2400

Complete assignments of ¹H- and ¹³C-NMR resonances of five methyl tetra-O-benzoyl-D-pyranosides based on ¹H, ¹³C, 2D DQF-COSY, HMQC, HMBC and HSQC-TOCSY experiments have been performed. Copyright

Full text of DOI:10.1002/mrc.2400

Spectral Assignments and Reference Data
Received: 14 October 2008
Revised: 9 December 2008
Accepted: 11 December 2008
Published online in Wiley Interscience: 28 January 2009
(www.interscience.com) DOI 10.1002/mrc.2400
1H and 13C NMR data of methyl
tetra-O-benzoyl-D-pyranosides in acetone-d6
a,b
a
b
a∗
ˇ
´
Aslan Esmurziev, Nebojsa Simic, Eirik Sundby and Bård Helge Hoff
Complete assignments of 1H- and 13C-NMR resonances of five methyl tetra-O-benzoyl-D-pyranosides based on 1H, 13C, 2D
c
DQF–COSY, HMQC, HMBC and HSQC–TOCSY experiments have been performed. Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Keywords: NMR; 1H; 13C; HMBC; methyl tetra-O-benzoyl-D-pyranosides
Introduction
Acetone-d6 was chosen as a solvent for all NMR experiments of
compounds 1–5, since there are no overlapping regions with the
target molecules. The NMR assignments of the compounds 1–5
were based on the data obtained from 1D 1H, 13C and various 2D
experiments. Spin systems and connectivity in the pyranose ring
and in the aromatic systems were identified by DQF–COSY, HMQC
and HSQC–TOCSY experiments. The connections between the
pyranose ring and benzoyl groups were identified by the HMBC
technique.TheHMBCspectraallowedfortheidentificationof long-
range correlations between protons H-2, H-3, H-4 and H-6 and the
adjacent carbonyl carbon, and long-range correlation between
the aromatic protons and the same carbonyl carbons (Fig. 2).
Long-range correlations were also observed between protons in
the pyranoside ring and the substituted aromatic carbon.
The importance of complex carbohydrates as vital components
in living systems and medicinal chemistry are well recognised.
Methyl tetra-O-acyl pyranosides are chemical entities suitable
both for construction of natural and artificial carbohydrates,
and for the qualitative and quantitative analysis of sugar
constitutes in oligo- and polysaccharides. As synthetic building
blocks, methyl tetra-O-acyl pyranosides allows for regioselective
deacylation using chemical or enzymatic methods. Alternatively,
the anomeric carbon can be subjected to various reaction
such as halogenation, arylations[1] or allylations.[2] Other possible
reactions includes conversion to carbohydrate ethers,[3] and
oxidative cleavage.[4] If required the remaining ester moieties can
be readily removed under mild conditions. Compared to acetate
pyranosides, benzoates are useful if higher stability towards basic
reagents is required. Benzoate pyranosides are less problematic
in terms of acyl migration, a challenge often encountered for
the corresponding acetates.[5] Also, benzoate pyranosides are
more conveniently analysed by various techniques such as UV
absorption detection and by circular dichroism.[6]
1
The 13C chemical shifts are given in Table 1, the H chemical
shifts are shown in Table 2 and the resolved 1H coupling constants
are presented in Table 3.
1
The small differences in our assignments of both H and 13C
resonances from literature data,[7–14] can be attributed to the use
of different solvents. The use of acetone-d6 gave better overall
appearance of the spectra, which in combination with a stronger
magnetic field than those used for acquiring previously published
NMR data,[12,14] allowed us to distinguish close resonances, even
in the aromatic regions.
In the course of our work on synthesising methyl tetra-O-
benzoylgluco-, galacto-, and mannopyranosides, it was noted
that existing 1H NMR data for the compounds 1–5 (Fig. 1) are
incomplete,[7–14] while 13C NMR data are either not available
(for compounds 2, 4 and 5), or incomplete.[14] At 600 MHz the
structural identity for pure compounds can be deduced from
1H NMR and extracted coupling constants. However, 13C NMR
provides additional identity evidence especially in cases where
low frequency instruments are used. 13C reference spectra are
also useful for aiding the identification of structurally related
compounds, or for analysing mixtures of benzoate pyranosides
having the same core structure and thus similar magnitude of
coupling constants. The aim of this work was therefore to perform
The C-1 chemical shifts of compounds 1–5 depended on the
stereochemistry of the anomeric carbon. The α-anomers reside
at lower ppm values than their β-anomers. Moreover, for methyl
2,3,4,6-tetra-O-benzoyl-α-D-mannopyranoside (3) the shift value
of C-1 increased to 99.5 ppm from 97.9 ppm in 1. The 13C chemical
shift of the methoxy signal is also a strong indication of anomeric
configuration. The α-anomers had shift values between 55.8 and
55.9 ppm, whereas the two β-anomers, 4 and 5, had shift values
near 57 ppm. Also the chemical shift values of C-3 and C-5 seemed
complete assignments of the H and 13C resonances of selected
1
methyl tetra-O-benzoyl-D-pyranosides.
∗
Correspondence to: Bård Helge Hoff, Department of Chemistry, Norwegian
University of Science and Technology (NTNU), NO-7491, Norway.
E-mail: bhoff@chem.ntnu.no
Results and Discussion
Themethyltetra-O-benzoyl-D-pyranosides,1–5,weresynthesised
from the corresponding methyl D-pyranosides using benzoyl
chloride and pyridine. The structures of the molecules are given in
Fig. 1.
a
Norwegian University of Science and Technology, Høgskoleringen 5, NO-7491
Trondheim, Norway
b
Sør-Trøndelag University College, E. C. Dahls gate 2, 7004 Trondheim, Norway
c
Magn. Reson. Chem. 2009, 47, 449–452
Copyright ꢀ 2009 John Wiley & Sons, Ltd.

A. Esmurziev et al.
OBz
OBz
H
OBz
R1
R1
H
BzO
H
O
O
H
O
R
BzO
BzO
BzO
R
BzO
H
H
OMe
H
H
H
OBz
OBz
H
H
H
OMe
OMe
H
1: R= OBz, R1= H
2: R= H, R1= OBz
4: R= OBz, R1= H
5: R= H, R1= OBz
3
Figure 1. Structure of the compounds in the study. 1: Methyl 2,3,4,6-tetra-O-benzoyl-α-D-glucopyranoside; 2: Methyl 2,3,4,6-tetra-O-benzoyl-α-
D-galactopyranoside; 3: Methyl 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranoside; 4: Methyl 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranoside; 5: Methyl
2,3,4,6-tetra-O-benzoyl-β-D-galactopyranoside.
OBz
6
Table 1. 13C NMR chemical shifts (δ, ppm) of 1–5 in acetone-d6 at
298 K using TMS as internal standard
OBz
O
5
H
H
2
4
C
1
2
3
4
5
H
OMe
O
O
OBz
1
H
HMBC
H
3
1
97.9
72.7
71.6
70.4
68.5
63.8
55.8
98.5
70.2
69.4
70.5
67.7
63.4
55.9
99.5
71.0
71.5
67.4
69.5
63.4
55.8
102.3
72.8
74.2
70.5
72.5
63.6
57.0
102.6
70.8
72.8
69.6
71.7
62.8
56.9
H
2
3
4
5
Figure 2. HMBC correlations revealing connectivity between the pyra-
6
noside and benzoyl groups.
OMe
2-OBz
C-1
to depend on the anomeric configuration, both signals appearing
at lower field for the β-anomers.
130.1
130.5
129.5
134.2
165.8
130.3
130.4
129.5
134.4
166.3
130.4
130.4
129.7
134.5
165.8
130.3
130.2
129.3
134.2
165.5
130.4
130.2
129.4
134.2
165.8
C-2,6
C-3,5
C-4
The 1H chemical shift of H-1 depended on the anomeric
configuration and the configuration at C-2. For the α-anomers
1 and 2, the H-1 signal resides at lower ppm values than for
their β-anomers, 4 and 5, and methyl 2,3,4,6-tetra-O-benzoyl-α-
D-mannopyranoside (3). The coupling constant between H-1 and
CO
3-OBz
C-1
1
130.2
130.2
129.4
134.2
166.4
130.3
130.2
129.3
134.2
165.8
130.2
130.2
129.3
134.2
165.9
129.9
130.1
129.2
134.1
166.0
130.0
130.1
129.2
134.2
165.6
H-2 are also of diagnostic value (Table 3). H NMR spectra of all
C-2,6
C-3,5
C-4
compounds have previously been reported in CDCl3 at variable
field strengths.[7–14] For most protons, variance in shift values
between the current study and those reported previously in CDCl3
were only of minor magnitude (<0.1 ppm). However, for methyl
2,3,4,6-tetra-O-benzoyl-β-D-glucopyranoside (4) chemical shifts
for H-1, H-3 and H-5 were increased by ca. 0.3 ppm in acetone-d6,
compared to thatreported in CDCl3.[13] By re-analysing compound
4 in CHCl3, this change in chemical shift could be ascribed to a
solvent effect. The same solvent dependant variation in chemical
shift was also noticed for the signal from H-1 of methyl 2,3,4,6-
tetra-O-benzoyl-β-D-galactopyranoside ( 5).
CO
4-OBz
C-1
130.1
130.4
129.4
134.4
166.1
130.4
130.5
129.7
134.6
166.3
130.2
130.4
129.4
134.4
166.0
130.0
130.3
129.3
134.3
165.7
130.3
130.4
129.6
134.5
166.2
C-2,6
C-3,5
C-4
CO
6-OBz
C-1
130.9
130.3
129.4
134.0
166.4
130.7
130.3
129.4
134.1
166.3
131.1
130.3
129.5
134.1
166.4
130.7
130.2
129.3
133.9
166.3
130.6
130.2
129.4
134.1
166.2
C-2,6
C-3,5
C-4
Experimental
NMR spectroscopy
CO
All NMR data were recorded using a Bruker Avance 600
spectrometer (XWIN-NMR 3.5 software) operating at a proton
frequency of 600.18 MHz with a 5 mm triple-resonance cryo probe
equipped with a z-gradient. The samples containing a solution of
25 mg of substances 1–5 in acetone-d6 were measured at 298 K
with TMS as the internal standard. Following 1D and 2D pulse
sequences from the Bruker user library were used for the NMR
experiments:
1H 1D (600 MHz): π/2 pulse for 1H 8.0 µs, spectral width 7 kHz,
acquisition time 1.14 s, relaxation delay 1.0 s, the 128-transient
free-inductiondecaywascollectedwith16 Kdatapointsmultiplied
by a −0.30 Hz Lorentzian function and zero-filled up to 32 K data
points prior to Fourier transformation.
13C 1D (150 MHz): π/2 pulse for 13C 14.5 µs, spectral width
36 kHz, acquisition time 0.91 s, WALTZ proton decoupling dur-
ing acquisition, relaxation delay 2.0 s, the 1024-transient free-
induction decay was collected with 64 K data points multiplied by
a −0.10 Hz Lorentzian function prior to Fourier transformation.
HMQC (600/150 MHz) - 2D 1H/13C correlation via heteronuclear
zero and double quantum coherence with gradient pulse for
selection: π/2 pulse for 1H 8.0 µs, spectral width in F2 9.6 kHz,
carrier at 4 ppm, acquisition time 0.11 s, relaxation delay 1.0 s, 40
transients per increment, 256 complex data points in F1, spectral
c
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Copyright ꢀ 2009 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2009, 47, 449–452

1H and 13C NMR data of methyl tetra-O-benzoyl-D-pyranosides
suppress one-bond correlations: π/2 pulse for 1H 8.0 µs, spectral
width in F2 9.6 kHz, carrier at 4 ppm, acquisition time 0.21 s,
relaxation delay 1.0 s, 20 transients per increment, 256 real data
points in F1, spectral width in F1 30 kHz, decoupler at 100 ppm,
linear prediction in F1 up to 1 K real points.
1H,1H DQF–COSY (600 MHz) – 2D homonuclear shift correla-
tion, phase sensitive, using gradient pulses for selection and with
multiple quantum filter according to gradient ratio: π/2 pulse for
1H 8.0 µs, spectral width in F2 8 kHz, carrier at 4.7 ppm, acquisition
time 0.26 s, relaxation delay 1.0 s, four transients per increment,
1 K complex data points in F1, spectral width in F1 8 kHz, linear
prediction in F1 up to 2 K real points.
Table 2. 1H chemical shifts (δ, ppm) of 1–5 in acetone-d6 at 298 K
using TMS as internal standard
H
1
2
3
4
5
1
5.32 (d)
5.40 (d)
5.11(d)
5.08 (d)
5.10 (d)
2
5.42 (dd) 5.76 (dd)) 5.74 (dd) 5.51 (dd)
5.78 (dd)
5.80 (dd)
6.06 (dd)
4.71 (ddd)
4.51 (dd)
4.69 (dd)
3.57 (s)
3
6.19 (dd) 6.03 (dd)
5.81 (dd) 6.13 (dd)
5.87 (dd) 6.00 (t)
4
6.19 (t)
5.75 (t)
5
4.57 (m)
4.56 (m)
4.65 (m)
3.55 (s)
4.81 (m)
4.51 (dd)
4.62 (dd)
3.57 (s)
4.58 (m)
4.60 (m)
4.77 (m)
3.60 (s)
4.47(ddd)
4.56 (dd)
4.67 (dd)
3.52 (s)
6a
6b
OMe
2-OBz
C-2,6
C-3,5
C-4
Synthesis
7.95
7.44
7.59
7.96
7.44
7.58
8.06
7.50
7.69
7.96
7.46
7.59
7.96
7.43
7.56
The methyl D-gluco- and D-galactopyranosides were purchased
from Sigma-Aldrich, while methyl a-D-mannopyranoside was
prepared by a known method.[15] Benzoyl chloride and pyridine
were from Fluka. Column chromatography was performed
using silica gel 60A from Fluka, pore size 40–63 µm. Optical
rotations were measured using the sodium D line at 589 nm
on a Perkin–Elmer 243 B polarimeter. All melting points were
determined by a Mettler FP 5 melting point apparatus and are
uncorrected.
3-OBz
C-2,6
C-3,5
C-4
7.87
7.35
7.49
7.79
7.31
7.50
7.81
7.34
7.51
7.82
7.36
7.50
7.74
7.29
7.48
4-OBz
C-2,6
C-3,5
C-4
7.94
7.43
7.57
8.13
7.58
7.71
8.00
7.44
7.58
7.93
7.43
7.57
8.07
7.57
7.71
Synthesis
of
methyl
2,3,4,6-tetra-O-benzoyl-α-D-
glucopyranoside (1). Methyl α-D-glucopyranoside (5.00 g,
0.026 mol) in dry pyridine (20 mL) at 0 ◦C, was treated with
benzoyl chloride (25.60 g, 0.182 mol). After addition the reaction
was stirred at room temperature for 3 days. The reaction was
stopped by addition of water, followed by extraction with
CH2Cl2 (2 × 100 mL). The combined organic fractions were dried
using Na2SO4 and concentrated in vacuum. The crude product
was purified by flash chromatography (toluene/EtOAc, 9 : 1)
yielding yellow foam. Crystallisation from methanol gave 36%
(5.72 g, 9.37 mmol) of a white solid. Melting point 73–74 ◦C [Lit.[16]
72 ◦C]; [α]2D2 = +88.4. (c 0.5, CHCl3), (lit.[17] [α]2D2 = +84 (c 0.95
CHCl3)]. Methyl 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranoside
(2) was prepared from methyl α-D-galactopyranoside (2.00 g
10.30 mmol) as described for 1. After 90 h reaction time extra
benzoyl chloride (1.5 eq.) was added. The reaction was stopped
after 7 days. The product was purified by flash chromatog-
raphy (toluene/EtOAc, 1 : 1), followed by crystallisation from
absolute ethanol yielding 4.5% (0.295 g, 0.48 mol) of a white
solid. Melting point 63–64 ◦C, [α]D21 = +140.2 (c 1.0, CHCl3),
[lit.[9] [α]2D5 = +142.9 (c 0.9, CHCl3)]. The main product was
methyl 2,3,6-tri-O-benzoyl-α-D-galactopyranoside. Methyl 2,3,4,6-
tetra-O-benzoyl-α-D-mannopyranoside (3) was prepared from
methyl-α-D-mannopyranoside (5.00 g, 25.75 mmol) as described
for 1. The reaction time was 2 days. Purification by crystallized
from absolute ethanol and re-crystallisation from methanol gave
38% (6.00 g, 9.83 mmol) of a white solid, mp. 136–137 ◦C [lit.[12]
138–140 ◦C]; [α]2D1 = −66.9, (c 2.5, CHCl3), [lit.[17] [a]D = −67.5 (c
2.5, CHCl3)]. Methyl 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranoside
(4) was prepared as described for 1 starting with methyl β-D-
glucopyranoside (1.50 g, 7.72 mmol). The product was crystallized
from ethanol yielding 54% (2.55 g, 4.18 mmol) of a white solid.
Melting point 157–158 ◦C, [lit. mp.[10] 159–160 ◦C]; [α]2D1 = +25.4
(c 1.0, CHCl3), [lit.[10] [α]D20 = +28.0 (c 1.0, CHCl3)]. Methyl
2,3,4,6-tetra-O-benzoyl-β-D-galactopyranoside (5) was prepared
from methyl β-D-galactopyranoside (600 mg, 3.09 mmol) as
described for 1. The reaction was stopped after 40 h. The crude
product was purified by flash chromatography (toluene/EtOAc,
6-OBz
C-2,6
C-3,5
C-4
8.07
7.49
7.63
8.04
7.49
7.62
8.15
7.56
7.70
8.07
7.50
7.64
8.00
7.48
7.61
Table 3. 1H coupling constants (Hz) resolved for 1–5 in acetone-d6
at 298 K using TMS as internal standard
1
2
3
4
5
H1-H2
H2-H3
H3-H4
H4-H5
H5-H6a
H5-H6b
3.5
10.0
9.5
3.5
10.5
3.5
2.0
3.5
8.0
9.5
7.5
10.5
3.5
10.0
10.0
NR
9.5
9.5
NRa
1.5
9.5
1.0
5.5
5.0
6.0
NR
7.0
NR
3.0
6.5
H
6a-H6b
NR
11.0
NR
12.5
11.0
a NR, not resolved due to overlapping.
width in F1 24 kHz, decoupler at 76 ppm, GARP decoupling, linear
prediction in F1 up to 1 K real points.
HSQC–TOCSY (600/150 MHz) – 2D 1H/13C correlation via dou-
ble inept transfer, using MLEV17 for homonuclear Hartman–Hahn
mixing, phase sensitive using Echo/Antiecho-TPPI gradient selec-
tion, using trim pulses in INEPT transfer spectra: π/2 pulse for
1H 8.0 µs, spectral width in F2 8 kHz, carrier at 4.7 ppm, acquisition
time 0.06 s, relaxation delay 1.5 s, 32 transients per increment,
MLEV-17 spinlock, mixing time 80 ms, 256 complex data points
in F1, spectral width in F1 25 kHz, decoupler at 110 ppm, GARP
decoupling, linear prediction in F1 up to 1 K complex points.
HMBC (600/150 MHz) – 2D 1H/13C correlation via heteronuclear
zero and double quantum coherence; phase sensitive using
Echo/Antiechogradientselection; withtwo-foldlow-passJ-filterto
c
Magn. Reson. Chem. 2009, 47, 449–452
Copyright ꢀ 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/mrc

A. Esmurziev et al.
9 : 1) followed by crystallisation from absolute et◦hanol giving 21%
(400 mg, 0.66 mmol) as a white solid, mp. 51–52 C, [α]2D1 = +97.7
(c 1.0, CHCl3), [α]D21 = +119.1 (c 0.26, CHCl3) [lit.[9] [α]2D5 = +221.1
(c 0.26, CHCl3)].
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Acknowledgements
Sør-Trøndelag University College is gratefully acknowledged for
financial support. NTNU is acknowledged for use of NMR facilities.
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Magn. Reson. Chem. 2009, 47, 449–452