Pyranoside-into-Furanoside Rearrangement of 4-Pentenyl Glycosides in the Synthesis of a Tetrasaccharide-Related to Galactan I of Klebsiella pneumoniae

Article abstract of DOI:10.1002/ejoc.201601413

An efficient strategy for synthesis of a spacer-armed tetrasaccharide related to galactan I of Klebsiella pneumoniae is described, which uses newly developed acid-free conditions for the pyranoside-into-furanoside (PIF) rearrangement of a digalactoside bearing a 4-pentenyl group at the anomeric position. The 4-pentenyl aglycon was successfully used both as a leaving group in the glycosylation of 3-(trifluoroacetamido)propanol, and as a temporary anomeric protecting group, allowing conversion into an imidate donor. Regioselective coupling of the disaccharide blocks gave the desired tetrasaccharide sequence required for investigation of the interaction of galactan I with immune-system proteins.

Full text of DOI:10.1002/ejoc.201601413

A Journal of
Accepted Article
Title: Pyranoside-into-furanoside rearrangement of 4-pentenyl
glycoside in the synthesis of tetrasaccharide related to galactan I
of Klebsiella pneumoniae
Authors: Stella A. Verkhnyatskaya, Vadim B. Krylov, and Nikolay E.
Nifantiev
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201601413
Link to VoR: http://dx.doi.org/10.1002/ejoc.201601413
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
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Pyranoside-into-furanoside rearrangement of 4-pentenyl
glycoside in the synthesis of tetrasaccharide related to galactan I
of Klebsiella pneumoniae
Stella A. Verkhnyatskaya, Vadim B. Krylov, and Nikolay E. Nifantiev*[a]
Abstract: An efficient strategy for synthesis of spacer-armed
tetrasaccharide related to galactan I of Klebsiella pneumoniae was
Results and Discussion
reported employing newly developed acid-free conditions for
pyranoside-into-furanoside (PIF) rearrangement of a digalactoside
Previously, preparative protocol for the PIF rearrangement of
different glycosides bearing allyl as a temporary protective group
at anomeric position was developed.[12-17] In this communication
we expand the scope of this process by using an aglycon which
can act as a leaving group during glycosylation. Latest studies
revealed that the PIF rearrangement efficiently proceeded for
substrates bearing electron donating aglycon in equatorial
orientation.[13] Thus herein, the applicability in PIF
rearrangement of thioglycosides, which are widely employed in
glycosylation reactions[18-19] was studied first.
bearing 4-pentenyl group at anomeric position. The 4-pentenyl
aglycon was successfully used both as
a leaving group in
glycosylation of 3-trifluoroacetamidopropanol, and as a temporary
anomeric protection, permitting its conversion into the imidate donor.
Regioselective coupling of the disaccharide blocks afforded the
desired tetrasaccharide sequence required for investigation of
interaction of galactan I with immune system proteins.
Introduction
Gram-negative bacterium Klebsiella pneumoniae is responsible
for different diseases including pneumonia, bacteremia, urinary
tract infections, and pyogenic liver abscess with high incidence
2]
and mortality.[1,
This bacterium is a frequent cause of
nosocomial infections and may be responsible for as much as
20% of respiratory infections in neonatal intensive care units.[3]
The most common serotype of K. pneumoniae O1[4] consists
of two O-antigens: galactan I (repeating units [→3)-α-D-Galp-
(1→3)-β-D-Galf-(1→]) and galactan II (repeating units [→3)-α-D-
Galp-(1→3)-β-D-Galp-(1→]).[5] In other K. pneumoniae
serotypes the structure of galactan I is decorated by acetyl
groups and monosaccharide branches [α-D-Galp(1→2) or α-D-
Galp(1→4)]. The lipopolysaccharides (LPS) of K. pneumoniae
Scheme 1. Reagents and conditions: a) PySO3, HSO3Cl, DMF, 20C; b)
DMF:Dioxane = 1:5, IR120(H+), 60°С, 67% for 6.
are important virulence determinants[6-9] and synthetic
Treatment of thioethyl galactoside 1[20] under standard
conditions for PIF rearrangement[12] with PySO3 complex and
HSO3Cl gave totally O-sulfated pyranoside derivative 2 in 30 min
(Scheme 1). Unfortunately, prolongation of reaction time
resulted in formation of a complex mixture of decomposition
products with dominant product 3, which could be connected
with instability of thioethyl group even under mild oxidative
conditions. Direct sulfation of L-fucose by PySO3 complex in
DMF gave analogous mixture. Unsatisfactory results obtained
for the thioethyl glycoside led us to studying of 4-n-pentenyl
,
oligosaccharides[10-12]
representing
these
carbohydrate
sequences are required as model substrates for investigation of
the LPS O-chain recognition by immune system and for vaccine
design.
Recently, we reported pyranoside-into-furanoside (PIF)
rearrangement as an original and useful tool for preparation of a
variety of protected furanosides from corresponding
pyranosides.[12-15] Herein, we describe the use of PIF
rearrangement for the efficient synthesis of tetrasaccharide
related to galactan I motif.
[21-22]
glycosides which were proposed by Fraser-Reid’s et al.
and which could be activated under similar conditions with
thioglycosides. PIF rearrangement of pentenyl β-glycoside 4[23]
smoothly gave totally O-sulfated furanoside 5, which was further
subjected to solvolytic desulfation producing monosaccharide 6
in a good yield. Encouraged by this result, we developed a
synthetic scheme towards the spacer-armed tetrasaccharide
related to galactan I of K. pneumoniae using anomeric 4-n-
pentenyl as a leaving group and a temporary protection.
[a]
MSc. S.A. Verkhnyatskaya, Dr. V.B. Krylov, Prof. N.E. Nifantiev
Laboratory of Glycoconjugate Chemistry, N.D. Zelinsky Institute of
Organic Chemistry, Russian Academy of Sciences, Leninsky
prospect 47, 119991 Moscow (Russian Federation). E-mail:
nen@ioc.ac.ru; http://zioc.ru/institute/laboratories/glycoconjugates
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
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Scheme 2. Retrosynthetic scheme of target tetrasaccharide 7.
Assembling of target tetrasaccharide
7
was planned
Lemieux conditions,[33] which was not efficient - even after 3
days of treatment with Bu4NBr the conversion of the bromide
11a was low (TLC control). Size exclusion column
chromatography was successfully applied for separation of the
disaccharide fraction from monosaccharides, which could not be
efficiently performed using chromatography on silica gel due to
similar retention time of desired product 9 and the byproduct of
the donor hydrolysis. Thus, after filtration of reaction mixture
crude material was loaded on the Bio-beads SX-3 to give a
disaccharide fraction consisting mainly of three disaccharides
12-14 (Scheme 3) with total yield of 39% (entry 1 in Table 1).
According to the integral intensities in 1H NMR spectrum (Figure
1) the ratio of disaccharides 12 : 13 : 14 was 6 : 3 : 1 with the
prevalence of desired α-(1→3)-linked product 12.
according to [2+2]-synthetic scheme using disaccharide
precursor 8 both for the preparation of donor and acceptor
blocks (Scheme 2). The key step of the synthesis was PIF-
rearrangement of digalactoside 9 bearing 4-n-pentenyl aglycon.
Preparation of disaccharide 9 was planned by regio- and
stereoselective coupling of readily available monosaccharide
building blocks 10[23] and 11.[24-26]
Regioselective glycosylation of 4,6-O-benzylidene protected
acceptors with two free hydroxyls at C-2 and C-3 is a well-known
procedure for di- or oligosaccharide substrates,[27-29] but in case
of monosaccharide acceptors it can be less regioselective.[30-32]
Hence our synthesis was started with optimization of
glycosylation conditions for monosaccharide diol 10[23] (Scheme
3). First, the glycosylation by bromide 11a[24] was studied under
Scheme 3. Glycosylation of diol 10 with donors 11a-c.
Table 1. Reaction conditions in diol 10 glycosylations by donors 11a-c.
Entry
Donor
Activation conditions
Ratio of
12 : 13 : 14
Total yield of
disaccharides
(Yield of 12)[a]
1
2
3
4
11a
11a
11b
11c
Bu4NBr, MS-4Å
DMF, rt, 72 h
AgOTf, MS-4Å
CH2Cl2, -20C, 1 h
Tf2O, DTBMP, MS-4Å
CH2Cl2, -50 °C, 2.5 h
TfOH, MS-4Å
6 : 3 : 1
39% (23%)
51% (32%)
61% (44%)
79% (64%)
4.2 : 1.5 : 1
7.3 : 1.8 : 1
25 : 1 : 5
THF:CH2Cl2, -80
 -50 °C, 1 h
Figure 1. Parts of 1H NMR spectra of disaccharide fractions obtained in
glycosylations of diol 10 by donors 11a-c and subsequent separation of
disaccharide fractions by SX-3 gel-filtration of reaction mixtures. Numbers in
parentheses correspond to entries in Table 1.
[a] NMR yield
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10.1002/ejoc.201601413
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Scheme 4. Reagents and conditions: a) TFAaq 90%, CH2Cl2; for persulfation and O-desulfation conditions see Table 2 below.
The structures of disaccharides 12-14 were established on
by the addition of ammonium bicarbonate (NH4HCO3), which
could be then easily evaporated. The new procedure led to
increase the overall yield of compound 16 (Table 2, entry 2) up
to 38%. In continue, we also perform the reaction without harsh
chlorosulfonic acid but under the heating at 80 °C. This new
high-temperature rearrangement protocol permitted to increase
further the yield of 16 up to 53% (Table 2, entry 3).
1
the basis of H and 13C NMR data. Thus stereochemistry of the
newly formed bond in 12 was confirmed by the characteristic
coupling constant J1,2 = 3.7 Hz for α-galactopyranoside and the
value of chemical shift of the anomeric carbon (δ 94.7 ppm). The
site of glycosylation in disaccharide 12 was confirmed by
downfield shift of C-3I carbon (δ 76.9 ppm), whereas the
chemical shift of C-2I was found to be virtually unchanged (δ
69.3 ppm). Disaccharide 13 was similarly proved to have α-
configuration of glycoside bond (J1,2 = 3.9 Hz and δ C-1II = 96.6
ppm), however, the position of glycosylation (at O2) was
confirmed by the downfield chemical shift of the C-2I carbon (δ
79.4 ppm). The β-(1→3)-linkage in 14 was proved by coupling
constant J1,2 = 7.7 Hz and δ C-1II – 103.0 ppm typical for β-
galactopyranoside and downfield shift of C-3I signal (δ C-3I –
79.6 ppm and δ C-2I – 67.0 ppm).
To improve the yield of desired disaccharide 12, different
conditions for 1,2-cis glycosylation were studied. Coupling of diol
10 and bromide 11a was performed in presence of AgOTf at -
20 °C to give the mixture of disaccharides (12-14) with total yield
of 51% and the ratio of 12:13:14 to be 4.2 : 1.5 : 1. (Table 1,
entry 2, see also Figure 1). The use of sulfoxide donor[34] 11b in
the presence of triflic anhydride (Tf2O) and 2,6-di-tert-butyl-4-
methylpyridine (DTBMP) gave disaccharides 12-14 in 61% yield
and the component ratio 7.3 : 1 : 1.8 (Table 1, entry 3).
Schmidt’s glycosylation[35] with glycosyl trichloroacetimidate 11c
activated by catalytic amount of triflic acid (TfOH) in mixed
solvent system THF - CH2Cl2 (v/v, 6/1)[36] at -80 °C produced a
mixture of disaccharides with good 79% yield and ratio of
disaccharides 12 : 13 : 14 was 25 : 5 : 1 (Table 1, entry 4). After
purification by column chromatography target disaccharide 12
was isolated from the reaction mixture in 62% yield. These
conditions were further chosen for the preparative synthesis of
disaccharide 12.
Next, the benzylidene group of disaccharide 12 was
removed of under the treatment with 90% aq. TFA in CH2Cl2 (v/v,
1/10), which produced disaccharide 9 in 96% yield. It was further
subjected to the PIF rearrangement (Scheme 4). The standard
protocol for this rearrangement, which was successfully applied
in syntheses of oligosaccharides related to polysaccharides from
Aspergillus fumigatus,[15,17] Enterococcus feacalis,[14] Chordaria
flagelliformis[16], included the treatment by Py∙SO3/HSO3Cl
mixture followed by neutralization with NaHCO3 and solvolytic
desulfation in presence of acidic resins IR-120(H+).
Unfortunately, under these conditions substrate 9 gave only 27%
of target disaccharide 16 (Scheme 4, Table 2, entry 1). To avoid
the use of excess of NaHCO3, which can interfere with the
desulfation step, neutralization of the reaction mixture was done
Table 2 Optimization of PIF-rearrangement conditions.
Entry
1
Conditions for O-persulfation
Conditions for
O-desulfation
Isolated
yield of 16
1) Py·SO3 (3.2 equiv./OH-
group), HSO3Cl (1.2
equiv./OH-group), DMF, rt, 24 h;
2) NaHCO3
1) Py·SO3 (3.2 equiv./OH-
group), HSO3Cl
(1.2 equiv./OH-group), DMF, rt,
24 h; 2) NH4HCO3
DMF:Dioxane,
27%
38 %
53 %
IR120-H+,
60 °С, 3 h
2
3
DMF:Dioxane,
IR120-H+,
60 °С, 3 h
1) Py·SO3 (4.7 equiv./OH-
group), DMF, 80 °С, 1.5 h;
2) NH4HCO3
DMF:Dioxane,
IR120-H+,
90 °С, 10 min
ESI-HRMS analysis indicated that 9 and 16 were isomeric
compounds, but NMR spectra revealed considerable differences
in the monosaccharide unit at the reducing end. Characteristic
location of C-1I (107.9 ppm) while of C-2I, C-3I and C-4I signals
at 80-90 ppm confirmed the presence of a 3-O-substituted
furanoside ring in disaccharide 16, which agreed with the data in
literature.[37]
Disaccharide 16 was per-O-benzoylated with BzCl in
presence of pyridine to give product 8, which was further
converted into both glycosyl donor and acceptor blocks (Scheme
5). To synthesize donor 19, precursor 8 was transformed into
hemiacetal 17 by treatment with NIS and excess of TFA in
CH2Cl2. Further imidation under the treatment with ClC(NPh)CF3
and cesium carbonate gave 19. For preparation of acceptor 20,
N-trifluoroacetic 3-aminopropan-1-ol was glycosylated by 4-
pentenyl glycoside 8 in presence of TMSOTf-NIS (818), and
then subjected to catalytic hydrogenolysis, and 4,6-O-
benzylidenation (1820). Unfortunately, glycosylation of
acceptor 20 with 4-pentenyl donor 8 yielded hardly separable
mixture of products containing less than 10% of desired
tetrasaccharide 21. Coupling of acceptor 20 with imidate donor
19 at low temperature predominantly yielded β-(13)-linked
tetrasaccharide 21 (42%), though formation of β-(12)-linked
tetrasaccharide (19%) and branched (12)- and (13)-linked
hexasaccharide (18%) was also observed. The structure of
tetrasaccharide 21 was confirmed by analysis of 1H and 13C
NMR spectra together with ESI-HRMS data. The β-configuration
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10.1002/ejoc.201601413
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of the newly formed bond was established by the characteristic
chemical shift of C-1III (δ = 107.9 ppm). The downfield shift of
C3II (δ = 77.4 ppm) together with spatial proximity of H-1III and
H-3II observed in NOE experiments confirmed the formation of
(13)-bond. The removal of blocking groups in 21 gave desired
spacer-armed oligosaccharide 7.
diol 10 were achieved by the use of trichloroacetimidate donor
11c in the mixture of solvents THF-CH2Cl2, which afforded α-
(1→3)-linked digalactopyranoside 12. A new, high-temperature,
acid-free PIF rearrangement protocol was developed for the
preparation of the disaccharide with a furanoside residue at the
reducing end. Further biological investigations of the reported
compounds are in progress and their results will be published
elsewhere.
Experimental Section
General: All solvents were distilled and dried if necessary according to
standard procedures[38] (CH2Cl2, MeOH, Toluene) or purchased as dry
(DMF, Pyridine, CH3CN Sigma-Aldrich). Commercial chemicals were
used without purification unless noted. All reactions involving air- or
moisture-sensitive reagents were carried out using dry solvents under Ar
atmosphere. All glycosylation reactions were carried out under dry Ar.
Molecular sieves 4Å for glycosylation reactions were activated prior to
application at 180 ºC in vacuum of an oil pump during 2 h. Analytical thin-
layer chromatography (TLC) was performed on Silica Gel 60 F254
aluminium sheets (Merck), and visualization was accomplished using UV
light or by charring at ~150 ºC with 10% (v/v) H3PO4 in ethanol. Column
chromatography was performed on Silica Gel 60, 40–63 m (Merck).
Preparative HPLC was performed on a Supelcosil LC-SI, 25 cm× 21.2
mm, 5 µm at a flow rate of 8 mL/min with a UV/VIS-155 detector (Gilson).
Gel-filtration was performed on a SX-3 gel colnmn (500  23 mm) by
elution with toluene and TSK-40 HW(S) column (400  17 mm) by elution
with 0.1 M AcOH in water at a flow rate of 0.5 mL/min. Optical rotation
values were measured using a JASCO P-2000 polarimeter at the
ambient temperature in solvents specified. 1H and 13C NMR spectra were
recorded on Bruker AMX-400, Bruker DRX-500, and Bruker Avance 600
spectrometers. Chemical shifts were referenced to residual solvent
signals. Signal assignment in 1H and 13C NMR spectra was made using
COSY, TOCSY, and 1H–13C HSQC techniques. Monosaccharide
residues in oligosaccharides are numbered by the Roman numerals
starting from the reducing end. High-resolution mass spectra (HR MS)
were measured on a Bruker micrOTOF II instrument using electrospray
ionization (ESI).[39] The measurements were performed in a positive ion
mode (interface capillary voltage –4500 V); mass range from m/z 50 to
m/z 3000 Da; external or internal calibration was made with Electrospray
Calibrant Solution (Fluka). A syringe injection was used for solutions in a
mixture of acetonitrile and water (50:50 v/v, flow rate 3 L/min). Nitrogen
was applied as a dry gas; interface temperature was set at 180 C.
Acid-promoted sulfation of ethyl 1-thio-β-D-galactopyranoside (1).
To a stirred solution of pyranoside 1 (10 mg, 0.04 mmol) in DMF (0.5 mL)
PySO3 (81 mg, 0.51 mmol) and HSO3Cl (13 μl, 0.20 mmol) were added.
The resulting solution was kept for 30 min. (24 h) at room temperature,
and then reaction mixture was neutralized by the addition of aqueous
solution of NaHCO3 (136 mg, 1.70 mmol in 2 ml of H2O). The solution
was concentrated in vacuo and then co-evaporated with H2O and then
with D2O. The residue was dissolved in D2O and used for recording NMR
spectra. NMR data for sodium salt of ethyl 2,3,4,6-tetra-O-sulfonato-
1-thio--D-galactopyranoside (2) (reaction time 30 min). 1H NMR (400
MHz, D2O): δ = 5.10 (d, J 3.0 Hz, 1H, H-4), 4.79 (d, J 9.7 Hz, 1H, H-1),
4.58 (dd, J 9.6, 3.0 Hz, 1H, H-3), 4.42 (t, J 9.6 Hz, 1H, H-2), 4.26 (dd, J
9.8, 2.1 Hz, 1H, H-6a), 4.23 – 4.13 (m, 2H, H-5, H-6b), 2.85 – 2.68 (m, 2H,
CH2),1.27 ppm (t, J 7.4 Hz, 1H, CH3). 13C NMR (101 MHz, D2O) δ = 88.1
(C-1), 81.1 (C-3), 80.1 (C-5), 79.8 (C-4), 78.7 (C-2), 72.1 (C-6), 29.2
(CH2), 18.8 (CH3). NMR data for sodium salt of 1,2,3,4,6-penta-O-
Scheme 5. Reagents and conditions: a) BzCl, Py, CH2Cl2, 93%; b) 1) NIS,
TFA, CH2Cl2, 60%; c) TMSOTf, NIS, CH2Cl2, HO(CH2)3NHTFA, 79%; d)
ClC(NPh)CF3, Cs2CO3, CH2Cl2, 95% e) 1) H2, Pd(OH)2/C, AcOH, EtOAc 2)
PhCH(OMe)2, 58% f) TfOH, CH2Cl2, -60 °C, 42%; g) 1) H2, Pd(OH)2/C, AcOH,
EtOAc 2) MeONa, MeOH, H2O, 40 °C, 63%.
Conclusions
A convergent synthesis of spacer-armed tetrasaccharide 7
structurally related to galactan I from K. pneumoniae was
performed. High regio- and stereoselectivity in glycosylation of
1
sulfonato-α-D-galactopyranoside 3 (reaction time 24 h) H NMR (600
MHz, D2O): δ = 6.11 (d, J 3.7 Hz, 1H, H-1), 5.23 (d, J 3.2 Hz, 1H, H-4),
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4.80 (dd, J 10.6, 3.1 Hz, 1H, H-3), 4.72 (dd, J 10.5, 3.7 Hz, 1H, H-2),
4.61 (dd, J 8.0, 4.0 Hz, 1H, H-5), 4.37 (dd, J 11.3, 4.1 Hz, 1H, H-6a), 4.25
(dd, J 11.2, 7.9 Hz, 1H, H-6b). 13C NMR (101 MHz, D2O) δ 96.7 (C-1),
76.9 (C-4), 73.21 (C-3), 72.53(C-2), 71.1 (C-5), 68.5 (C-6).
mg, 0.11 mmol) was added. When the TLC analysis indicated complete
consumption of donor, the mixture was quenched by a drop of pyridine.
Then it was diluted with CH2Cl2 and washed with 5% Na2S2O3 and water.
The organic layer was dried over Na2SO4 and concentrated in vacuo. The
mixture was loaded on the SX-3 gel to afford mixture disaccharides 12,
13 and 14 (13 mg, ratio 12 : 13 : 14 = 4.2 : 1.5 : 1).
PIF rearrangement of pent-4-enyl β-D-galactopyranoside (4).To a
stirred solution of pyranoside 4 (10 mg, 0.04 mmol) in DMF (0.5 mL)
PySO3 (81 mg, 0.51 mmol) and HSO3Cl (13 μl, 0.20 mmol) were added.
The resulting solution was kept for 24 h. at room temperature, after which
the mixture was neutralized by the addition of aqueous solution of
NaHCO3 (136 mg, 1.70 mmol in 2 ml of H2O) and evaporated twice with
water. The solid residue was dissolved in a minimal amount of water and
then an excess of MeOH was added to result in precipitation of inorganic
salts, the mixture was filtrated, the solid was washed with MeOH, and the
filtrate was concentrated to give per-O-sulfated furanoside 5 which was
used in desulfation step without additional purification. NMR data for the
intermediate 5: 1H NMR (600 MHz, CDCl3): δ = 5.95 – 5.87 (m, 1H,
CH=CH2), 5.37 (s, 1H, H-1), 5.14 – 5.09 (m, 1H, CH=CH2), 5.04 – 5.01
(m, 2H, H-3, CH=CH2), 4.90 (ddd, J 7.6, 5.1, 2.4 Hz, 1H, H-5), 4.84 (s,
1H, H-2), 4.46 (dd, J 4.6, 2.4 Hz, 1H, H-4), 4.35 (dd, J 10.3, 5.2 Hz, 2H,
H-6a), 4.25 (dd, J 10.3, 7.7 Hz, 2H, H-6b), 3.77 (dt, J = 10.1, 6.7 Hz, 1H,
OCH2-pent), 3.63 (dt, J 10.1, 6.1 Hz, 1H, OCH2-pent), 2.15 ppm (q, J 7.1
Hz, 2H, CH2-pent), 1.75 – 1.68 (m, 2H, CH2-pent). 13C NMR (151 MHz,
D2O): δ = 115.03 (CH=CH2), 105.02 (C-1), 84.45 (C-2), 81.07 (C-3, C-4),
74.06 (C-5), 67.08 (OCH2-pent), 65.78 (C-6), 29.58 (CH2-pent), 27.81
ppm (CH2-pent). The crude material was dissolved in DMF : dioxane (1/5,
v/v, 6 mL) and IR-120H+ was added until acidic pH. The reaction mixture
was stirred for 3 h. at 60°С, after which it was filtrated from the resin and
washed with EtOAc. Filtrate was concentrated in vacuo. The residue was
purified by column chromatography (silica gel, 6/1 CHCl3/MeOH, Rf =
0.33) to give furanoside 6 (6.7 mg, 67%). 1H NMR (400 MHz, CD3OD): δ
= 5.90 – 5.77 (m, 1H, CH=CH2), 5.02 (d, J 17.0 Hz, 1H, CH=CH2), 4.95 (d,
J 10.1 Hz, 1H, CH=CH2), 4.85 (d, J 1.5 Hz, 1H, H-1), 4.00 (dd, J 6.5, 4.1
Hz, 1H, H-3), 3.96 – 3.89 (m, 2H, H-2, H-4), 3.76 – 3.68 (m, 2H, H-5,
OCH2-pent), 3.64 – 3.59 (m, 2H, H-6), 3.43 (dt, J 9.6, 6.6 Hz, 1H, OCH2-
pent), 2.18 – 2.10 (m, 2H, CH2-pent), 1.73 – 1.63 ppm (m, 2H, CH2-pent).
13C NMR (101 MHz, CD3OD): δ = 115.18 (CH=CH2), 109.47 (C-1), 84.24
(C-4), 83.45 (C-2), 78.78 (C-3), 72.48 (C-5), 68.23 (OCH2-pent), 64.61
(C-1), 31.39 (CH2-pent), 30.07 ppm (CH2-pent). HRMS (ESI): [M+Na]+
m/z calcd for C11H20O6: 271.1152, found: 271.1151.
Procedure 3: glycosylation with sulfoxide donor 11b
A solution of sulfoxide donor 11b (20 mg, 0.03 mmol) and 2,6-di-tert-
butyl-4-methylpyridine (16 mg, 0.085 mmol), molecular sieves (100 mg)
in CH2Cl2 (1 mL) was stirred for 15 min and then cooled to -50°С.
Trifluoromethanesulfonic anhydride (7 μl, 0.04 mmol) was added to the
resulted solution and the mixture was stirred for 10 min. Then the
solution of acceptor 10 in CH2Cl2 (11 mg in 0.5 mL, 0.03 mmol) was
added dropwise. The mixture was stirred for 2.5 h, diluted with CH2Cl2
and washed with sat. aq. NaHCO3. The organic layer was dried over
Na2SO4 and concentrated in vacuo. The residue was loaded on the SX-3
gel to afford mixture disaccharides 12, 13 and 14 (17 mg, 61%, ratio 12 :
13 : 14 = 7.3 : 1.8 : 1).
Procedure 4: glycosylation with trichloroacetimidate 11c
A mixture of donor 11c (26 mg, 0.04 mmol), acceptor 10 (13 mg, 0.04
mmol), and 4Å molecular sieves (200 mg) in THF-CH2Cl2 (5:1, v/v, 2.8
mL) was stirred for 15 min at room temperature and cooled to -80 °C.
Trifluoromethanesulfonic acid (10 μl, 0.1 mmol) was added and the
reaction mixture was stirred for 1 h then allowed to warm to -50 °C and
quenched with triethylamine and filtrated. The filtrate was concentrated in
vacuo to give a residue, which was purified by gel-filtration on the SX-3
gel to afford mixture of disaccharide 12, 13 and 14 (26 mg, 79%, ratio 12
: 13 : 14 = 25 : 1 : 5).
Pent-4-enyl 2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→3)-4,6-О-
benzylidene-β-D-galactopyranoside (12): 1H NMR (600 MHz, CDCl3): δ
= 7.53 – 7.10 (m, 25H, CHar 5Ph), 5.82 (m, 1H, CH=CH2 Pent), 5.49 (s,
1H, CHPh), 5.19 (d, J 3.7 Hz, 1H, H-1II), 5.03 (dd, 1H, CH=CH2 Pent),
4.93 (d, 1H, CH2Ph), 4.82 (d, 1H, CH2Ph), 4.71 (d, 1H, CH2Ph), 4.59 (m,
3H, CH2Ph), 4.46 (q, 2H, CH2Ph), 4.29 (m, 1H, H-6Ia), 4.25 (d, J 3.7 Hz,
1H, H-4I), 4.23 (m, 2H, H-5II, CH2 Pent), 4.21 (d, J 7.7 Hz, 1H, H-1I), 4.09
(dd, J 10.0, 3.6 Hz, 1H, H-2II), 4.05 – 3.99 (m, 3H, H-3II, H-4II, H-6Ib), 3.98
(dd, J 9.8, 7.7 Hz, 1H, H-2I), 3.94 (m, 2H, H-6IIa), 3.66 (dd, J 9.8, 3.5 Hz,
Glycosylation of diol 10
1H, H-3I), 3.61 – 3.56 (m, 1H, CH=CH2 Pent), 3.52 (m, 2H, H-6II ), 3.46
b
Procedure 1: glycosylation with bromide 11a under Lemieux conditions
(dd, J 9.7, 5.9 Hz, 1H, CH2 Pent), 3.28 (s, 1H, H-5I), 2.14 (m, 2H, CH2
Pent), 1.75 ppm (m, 2H, CH2 Pent). 13C NMR (151 MHz, CDCl3): δ =
129.0 - 126.5 (С 5Ph), 114.93 (CH Pent), 103.2 (C-1I), 101.3 (CHPh),
94.7 (C-1II), 78.9 (C-3II), 76.9 (C-3I), 76.4 (C-2II), 75.3 (C-4II), 74.9
(CH2Ph), 73.36 (CH2Ph), 72.7 (C-4I), 72.6 (CH2Ph), 69.9 (C-5II), 69.5 (C-
6I), 69.4 (CH2 Pent), 69.3 (C-2I), 69.1 (C-6II), 66.7 (C-5I), 30.3, 28.9 ppm
(2CH2 Pent).
A solution of Br2 in CH2Cl2 (50μl, 3 v %) was added to the solution of
ethyl tetra-2,3,4,6-О-benzyl-1-thio-β-D-galactopyranoside (17 mg, 0.03
mmol) in CH2Cl2 (2 mL). After 10 min the mixture was co-evaporated
twice with toluene and the residue was dried in vacuo to give bromide
11a which was used for glycosylation without additional purification. A
mixture of bromide 11a (see above) and acceptor 10 (10 mg, 0.03 mmol)
was dissolved in DMF (0.5 mL), 4Å molecular sieves were added
(100 mg) and the solution was stirred for 15 min. Then Bu4NBr (66 mg,
0.21 mmol) was added and the resulting solution was stirred for 3 days.
The mixture was filtrated through silica gel and after the solvent was
removed under reduced pressure, obtained syrup was loaded on the SX-
3 gel to afford mixture disaccharides 12, 13 and 14 (10 mg, 39%, ratio 12
: 13 : 14 = 6 : 3 : 1).
Pent-4-enyl 2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→2)-4,6-О-
benzylidene-β-D-galactopyranoside (13): 1H NMR (600 MHz, CDCl3): δ
= 7.53 – 7.10 (m, 25H, CHar 5Ph), 5.77 – 5.71 (m, 1H, CH=CH2 Pent),
5.56 (d, J 3.9 Hz, 1H, H-1II), 5.54 (s, 1H, CHPh), 5.00 (dd, 2H, CH=CH2
Pent), 4.96 (d, 1H, CH2Ph), 4.92 (d, 1H CH2Ph), 4.77 (d, 2H CH2Ph),
4.71 (d, 2H, CH2Ph), 4.59 (d, 1H, CH2Ph), 4.58 (d, J 7.3 Hz, 1H, H-1I),
4.34 – 4.24 (m, 3H, H-6Ia, H-5II, H-4II), 4.22 (dd, J 7.8, 4.7 Hz, 1H, H-3II),
4.16 (d, J 3.2 Hz, 1H, H-2II), 4.11 – 3.87 (m, 3H, H-6II, H-2I, H-4I), 3.85
(dd, J 6.2, 2.7 Hz, 1H, H-3I), 3.56 – 3.43 (m, 3H, H-6Ib, CH2 Pent), 3.42
(s, 1H, H-5I), 2.33 – 2.28 (m, 2H, CH2 Pent), 2.04 – 1.96 ppm (m, 2H,
CH2 Pent). 13C NMR (151 MHz, CDCl3): δ = 138.0 - 126.6 (С 5Ph),
138.2 (CH=CH2 Pent), 114.9, 138.2 (CH=CH2 Pent),103.0 (C-1I), 101.3
(CHPh), 96.6 (C-1II), 79.4 (C-2I), 76.4 (C-3II), 76.2 (C-2II), 75.2 (C-3I),
74.8 (C-4I), 74.3 (CH2Ph), 73.6 (CH2Ph), 73.5 (CH2Ph), 72.6 (CH2Ph),
Procedure 2: glycosylation with bromide 11a in a presence of AgOTf
A solution of bromide 11a (prepared from tetra-2,3,4,6-О-benzyl-1-thio-β-
D-galactopyranoside (17 mg, 0.03 mmol) of as describe above), acceptor
10 (10 mg, 0.03 mmol) and 4Å molecular sieves (100 mg) in CH2Cl2 (1
mL) was stirred for 15 min. Then it was cooled to -20 °C and AgOTf (27
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
FULL PAPER
71.7 (C-4II), 69.9 (C-6II), 69.2 (C-6I), 68.90 (C-5II), 66.7 (CH2 Pent), 66.4
(C-5I), 29.0, 24.1 ppm (2CH2 Pent).
added resulting the precipitation of inorganic salts. The precipitate was
centrifugated at 3000 rpm and the supernatant was concentrated. The
crude material was dissolved in DMF : dioxane (1/5, v/v, 6 mL) and IR-
120H+ was added until acidic pH. The reaction mixture was stirred for 3 h.
at 60°С, after which it was diluted with EtOAc and washed with H2O and
sat. aq. NaCl. The organic layer was dried over Na2SO4 and concentrated
in vacuo. The product was purified by HPLC (Supelcosil LC-SI, 25 cm
21.2, 5 µm, eluted with EtOAc) to give furanoside 16 (11 mg, 37%).
Pent-4-enyl 2,3,4,6-tetra-О-benzyl-β-D-galactopyranosyl-(1→3)-4,6-О-
benzylidene-β-D-galactopyranoside (14): 1H NMR (600 MHz, CDCl3): δ
= 7.52 – 7.10 (m, 25H, 5Ph), 5.78 – 5.69 (m, 1H, CH=CH2 Pent), 5.46
(s, 1H, CHPh), 5.03 (m, 1H, CH=CH2 Pent), 4.96 (d, 1H, CH2Ph), 4.92 (d,
1H, CH2Ph), 4.85 (d, J 7.8 Hz, 1H, H-1I), 4.77 (d, 3H, CH2Ph), 4.71 (d,
2H, CH2Ph), 4.59 (d, 1H, CH2Ph), 4.30 – 4.21 (m, 4H, H-4I, H-6Ia, H-5I,
H-1II), 4.06 – 3.84 (m, 5H, H-2II, H-3II, H-6Ib, H-2I, H-4II, CH2 Pent), 3.74
(dd, J 9.9, 3.4 Hz, 1H, H-3I), 3.58 – 3.42 (m, 2H, H-6II, CH=CH2 Pent),
3.35 (s, 1H, H-5I), 2,34 – 2,28 (m, 2H, CH2 Pent), 2,09 - 1,96 ppm (m,
2H, CH2 Pent). 13C NMR (151 MHz, CDCl3): δ = 138.0 - 126.6 (С 5Ph),
104.4 (С-1I), 103.0 (C-1II), 100.8 (PhC), 82.60, 79.6 (C-3I), 76.8 (C-2II),
76.8 (C-3II), 76.2 (C-4I), 74.8 (CH2Ph), 74.0 (CH2Ph), 73.9 (C-4II), 73.7
(CH2Ph), 73.6 (CH2Ph), 70.6 (C-6II) 69.2 (C-6I), 67.0 (C-2I), 66.8 (C-5I),
66.7, 29.9, 24.1 ppm (3CH2 Pent).
Procedure 3
To a stirred solution of disaccharide 9 (310 mg, 0.42 mg) in DMF (9 mL)
PySO3 (950 mg, 6.0 mmol) was added. The reaction mixture was stirred
for 1.5 h at 80 °C, then it was neutralized by the addition of aqueous
solution of NH4HCO3 (0.95 g, 12 mmol) and coevaporated twice with
water. The residue was dissolved in minimal amount of water and then
excess of methanol was added resulting the precipitation of inorganic
salts. The precipitate was centrifugated at 3000 rpm and the supernatant
was concentrated. The resulting crude was dissolved in DMF:dioxane
(1/5, v/v, 9 mL), then IR-120H+ was added until acidic pH and the
resulting solution was heated to 90 °C. After 10 min the mixture was
filtrated and the filtrate was diluted with CH2Cl2 and washed with water
and sat. aq. NaCl. Organic layer was dried over Na2SO4 and
concentrated in vacuo. Purification using the column chromatography on
silica gel gave the title compound (164 mg, 53%). Rf 0.18 (toluene /
EtOAc, 1:1); [α]D20 +3.53° (c 1.0, EtOAc). 1H NMR (600 MHz, CDCl3): δ =
7.40 – 7.19 (m, 20H, CHar 4Ph), 5.81 (m, 1H, CH=CH2 Pent), 5.02 (m,
1H, CH=CHH), 4.96 (m, 1H, CH=CHH), 4.91 – 4.88 (m, 3H, CH2Ph, H-1II,
H-1I), 4.83 – 4.79 (m, 2H, CH2Ph), 4.72 (d, 1H, CH2Ph), 4.67 (d, 1H,
CH2Ph), 4.51 (m, 2H, CH2Ph), 4.40 (d, 1H, CH2Ph), 4.11 – 4.05 (m, 2H,
H-2II, H-2I), 3.98 (dd, J 9.0, 2.8 Hz, 1H, H-5I), 3.87 (dd, J 10.1, 2.8 Hz, 1H,
H-4I), 3.79 (dd, J 8.8, 5.6 Hz, 2H, H-3II, H-3I), 3.69 (m, 4H, H-4II, H-5II, H-
6IIab, CHH Pent), 3.59 – 3.54 (m, 1H, C-6Ia), 3.43 (dt, J = 9.6, 6.6 Hz, 1H,
CHH Pent), 3.14 (dd, J 9.8, 3.1 Hz, 1H, H-6Ib), 2.12 (dd, J 14.7, 6.9 Hz,
2H, CH2 Pent), 1.68 (dt, J 13.8, 6.8 Hz, 2H, CH2 Pent). 13C NMR (151
MHz, CDCl3): δ = 138.5 - 137.1 (cq Сar 4Ph), 131.2 (CH=CH2), 128.6 -
127.6 (CHar 4Ph), 115.0 (CH=CH2), 107.9 (C-1I), 99.9 (C-1II), 87.8 (C-3I),
81.5 (C-2I), 81.0 (C-4I), 79.1 (C-3II), 75.7 (C-2II), 75.1 (C-5II), 74.6, 74.1,
73.7, 73.3 (4CH2Ph), 72.3 (C-4II), 71.0 (C-5I), 70.0 (C-6I), 67.9 (CH2
Pent), 64.0 (C-6II), 30.34, 29.02 ppm (2CH2 Pent). HRMS (ESI):
[M+Na]+ m/z calcd for C45H54O11: 793.3558, found: 793.3552.
Preparative synthesis of disaccharide 12. The glycosylation of
acceptor 10 (1.17 g, 3.5 mmol) with donor 11c (3.67 g, 5.4 mmol) as
described in Procedure 4, followed by purification by column
chromatography (Toluene/EtOAc, 5:1, Rf = 0.38) gave disaccharide 12
(1.87 g, 62%). [α]D20 +65.38 (c 1.0, EtOAc). HRMS (ESI): [M+Na]+ m/z
calcd for C52H58O11: 881.3871, found: 881.3878.
Pent-4-enyl 2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→3)-β-D-
galactopyranoside (9). Disaccharide 12 (1.87 g, 2.18 mmol) (438 mg,
0.59 mmol) was dissolved in CH2Cl2 (4 mL) and treated with TFAaq 90%
(4.4 mL) at room temperature for 1 hour. The mixture was diluted with
methanol (40 mL) and triethylamine was added until pH neutral. The
reaction mixture was concentrated in vacuo. The title compound was
purified by column chromatography, yielding 1.62 g (96 %). Rf=0.29
(toluene/EtOAc,1:1). [α]D20 +14.59 (c 1.0, CHCl3).
1H NMR (600 MHz, CDCl3): δ = 7.41 – 7.22 (m, 20H, CHar 4Ph), 5.80 (m,
1H, CH=CH2), 5.02 (m, 1H, CH2 Pent), 4.97 – 4.94 (m, 1H, CH2 Pent),
4.92 (d, 1H, CH2Ph), 4.89 4.85 (m, 2H, CH2Ph, H-1II), 4.75 (s, 2H,
CH2Ph), 4.65 (d, 1H, CH2Ph), 4.56 (d, 1H, CH2Ph), 4.48 (d, 1H, CH2Ph),
4.42 (d, 1H, CH2Ph), 4.29 (t, J 6.6 Hz, 1H, H-5II), 4.18 (d, J 7.8 Hz, 1H,
H-1I), 4.07 (dd, J 10.2, 3.7 Hz, 1H, H-2II), 4.01 – 3.98 (m, 2H, H-3II, H-4II),
3.96 – 3.88 (m, 3H, H-6II , H-6Ia, CH2 Pent), 3.80 (d, J 3.5 Hz, 1H, H-4I),
a
3.76 (dd, J 11.7, 4.7 Hz, 1H, H-6Ib), 3.71 (dd, J 9.3, 7.9 Hz, 1H, H-2I),
Pent-4-enyl 2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→3)-2,5,6-
tri-O-benzoyl-β-D-galactofuranoside (8). To a solution of disaccharide
16 (1.46 g, 1.9 mmol) in CH2Cl2 (10 mL) BzCl (2 mL, 17 mmol) and
pyridine (1.37 mL, 17 mmol) were added. The reaction mixture was kept
overnight, then it was diluted with CH2Cl2, washed with sat. aq. NaHCO3
and with 1M HCl. The organic layer was dried over Na2SO4 and
concentrated in vacuo. Purification using column chromatography
afforded the title compound as a white solid (1.94 g, 93%). Rf = 0.31
3.57 – 3.49 (m, 3H, H-3I, H-6II , CH2 Pent), 3.44 (t, J 5.6 Hz, 1H, H-5I),
b
2.13 (q, J = 7.3 Hz, 2H, CH2 Pent), 1.77 – 1.68 ppm (m, 2H, CH2 Pent).
13C NMR (151 MHz, CDCl3): δ = 138.6 - 137.9 (cq, Сar 4Ph), 138.2
(CH=CH2 Pent), 128.5 - 127.5 (Сar 4Ph), 114.9 (CH=CH2 Pent), 103.2
(C-1I), 95.9 (C-1II), 79.4 (C-3II), 79.3 (C-3I), 76.1 (C-2II), 74.8 (C-4II), 74.7
(CH2Ph), 74.6 (CH2Ph), 74.1 (C-5I), 73.3 (CH2Ph), 72.7 (CH2Ph), 69.9
(C-5II), 69.8 (C-2I), 69.2 (C-6II), 68.8 (CH2 Pent), 66.4 (C-4I), 62.6 (C-6I),
30.1, 28.80 ppm (2CH2 Pent).. HRMS (ESI): [M+Na]+ m/z calcd for
C45H54O11: 793.3558, found: 793.3552.
20
(petroleum ether / EtOAc, 5:1). [α]D +15.01° (c 1.0, EtOAc). 1H NMR
(600 MHz, CDCl3): δ = 8.17 – 8.14 (m, 2H, o-Har Bz1), 8.02 – 8.00 (m, 2H,
o-Har Bz2), 7.93 – 7.89 (m, 2H, o-Har Bz3), 7.66 – 7.18 (m, 29H, CHar
7Ph), 5.93 (dt, J = 7.6, 3.8 Hz, 1H, H-5I), 5.84 (m, 1H, CH=CH2), 5.47 (d,
J = 2.1 Hz, 1H, H-2I), 5.17 (s, 1H, H-1I), 5.15 (d, J = 3.8 Hz, 1H, H-1II),
5.07 (m, 1H, CH=CHH), 5.00 (dd, J = 10.3, 1.4 Hz, 1H, CH=CHH), 4.95
(d, 1H, CH2Ph), 4.85 – 4.80 (m, 3H, CH2Ph), 4.79 – 4.71 (m, 2H, CH2Ph),
4.71 – 4.66 (m, 2H, H-6Iab), 4.58 – 4.54 (m, 1H, H-4I, CH2Ph), 4.34 (d, 1H,
CH2Ph), 4.31 (dd, J 6.7, 2.0 Hz, 1H, H-3I), 4.24 (d, 1H, CH2Ph), 4.19 –
4.13 (m, 1H, H-5II), 4.11 (dd, J 10.1, 3.8 Hz, 1H, H-2II), 4.06 (d, J 2.2 Hz,
1H, H-4II), 3.99 (dd, J 10.1, 2.8 Hz, 1H, H-3II), 3.76 (m, 1H, CH2 Pent),
PIF
rearrangement:
pent-4-enyl
2,3,4,6-tetra-О-benzyl-α-D-
galactopyranosyl-(1→3)-β-D-galactofuranoside (16)
Procedure 1
The pyranoside-into-furanoside (PIF) rearrangement of disaccharide 9
(30 mg, 0.04 mmol) as described for monosaccharie 6 gave 8 mg of
furanoside 16 (27%).
3.56 – 3.51 (m, 2H, H-6II , CH2 Pent), 3.38 (dd, J = 9.0, 5.4 Hz, 1H, H-6IIb),
a
2.22 – 2.15 (m, 2H, CH2 Pent), 1.80 – 1.71 (m, 2H, CH2 Pent) ppm. 13C
NMR (151 MHz, CDCl3): δ = 166.0, 165.4, 162.3 (3PhC(O)), 134.5
(CH=CH2), 133.3 - 127.3 (Car 7Ph), 114.9 (CH=CH2), 105.8 (C-1I), 99.6
(C-1II), 83.6 (C-3I), 82.5 (C-2I), 80.2 (C-4I), 78.8 (C-3II), 76.2 (C-2II), 74.9
(C-4II), 74.8, 73.3, 73.2, 72.9 (4CH2Ph), 70.2 (C-5I), 69.8 (C-5II), 68.1
(C-6II), 66.9 (OCH2 Pent), 63.9 (C-6I), 30.2, 28.7 ppm (2CH2
Pent).HRMS (ESI): [M+Na]+ m/z calcd for C66H66O14: 1105.4345, found:
1105.4329.
Procedure 2
To a stirred solution of 9 (30 mg, 0.04 mmol) in DMF (0.5 mL) PySO3
(60.4 mg, 0.38 mmol) and HSO3Cl (10 μl, 0.15 mmol) were added. The
resulting solution was kept for 24 h at room temperature, after which the
mixture was neutralized by the addition of aqueous solution of NH4HCO3
(95 mg, 1.23 mmol). and coevaporated twice with water. The residue was
dissolved in minimal amount of water and then excess of methanol was
2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→3)-2,5,6-tri-O-
benzoyl-β-D-galactofuranoside (17). To a solution of 8 (190 mg, 0.17
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
FULL PAPER
mmol) in CH2Cl2 / H2O (99/1, v/v, 20 mL) NIS (80 mg, 0.34 mmol) and
excess of TFA (205 μl, 2.68 mmol) were added. The mixture was stirred
overnight, then it was diluted with CH2Cl2 and washed with aqueous
solutions of Na2S2O3 and NaHCO3. The organic layer was dried over
Na2SO4 and concentrated in vacuo. Purification using column
chromatography afforded 17 as a yellowish syrup (107 mg, 60%). Rf =
0.37 (toluene / EtOAc, 5:1). Hemiacetals were obtained as a mixture of
anomers, ratio βα = 2/1. 1H NMR (400 MHz, CDCl3): δ = 8.16 – 7.91 (m,
12H, o-H Bz), 7.63 – 7.12 (m, 58H, CHar Ph), 5.87 (dt, J = 7.9, 4.0 Hz, 1H,
H-5Iβ), 5.84 – 5.78 (m, 1H, H-5Iα), 5.73 (t, J = 4.4 Hz, 1H, H-1Iα), 5.60 (s,
1H, H-2Iβ), 5.39 (s, 1H, H-1Iβ), 5.32 (dd, J 6.6, 4.4 Hz, 1H, H-2Iα), 5.15 (d,
J 3.8 Hz, 1H, H-1IIβ), 5.12 (d, J 3.8 Hz, 1H, H-1IIα), 4.95 (d, 1H, CH2Ph),
4.93 – 4.86 (m, 2H, CH2Ph), 4.83 – 4.80 (d, 1H, CH2Ph), 4.78 – 4.65 (m,
7H, H-6Iβab, H-4Iβ, H-3Iα, CH2Ph, H-6Iα), 4.65 – 4.49 (m, 4H, CH2Ph), 4.41
(d, 1H, CH2Ph), 4.38 (d, J 5.5 Hz, 1H, H-3Iβ), 4.32 (d, 1H, CH2Ph), 4.25 –
4.02 (m, 4H, CH2Ph, H-5IIβ, H-2IIβ), 4.02 – 3.88 (m, 6H, H-5IIα, H-4IIα, H-2IIα,
H-4IIβ H-3IIβ, H-3α), 3.78 (br s, 1H, OHβ), 3.53 – 3.40 (m, 3H, H-6Iαb, OHα,
H-6IIβab), 3.28 ppm (dd, J 8.9, 5.3 Hz, 1H, H-6IIαb). 13C NMR (101 MHz,
CDCl3) δ 166.4 - 165.5 (PhC(O)), 138.7 - 138.4 (q Car Ph), 133.3 - 127.4
(Car Ph), 100.8 (C-1Iβ), 99.0 (C-1IIa), 98.1 (C-1IIβ), 95.4 (C-1Iα), 82.6 (C-3Iβ),
81.7 (C-2I β), 81.6 (C-4Iβ), 80.6 (C-3Ia), 78.8 (C-3IIβ, C-4Iα), 78.4 (C-2Iα),
76.3 (C-2Iβ), 76.1 (C-2IIβ), 74.9 (C-2IIα), 74.6 (C-4IIβ), 73.7, 73.6, 73.6,
73.3, 73.1, 72.8 (CH2Ph), 72.5 (C-5Iα), 70.6 (C-5Iβ), 70.0 (C-5IIα, C-5IIβ),
69.3 (C-6IIβ), 68.1 (C-6IIα), 63.8 (C-6Iβ), 63.3 ppm (C-6Iα).HRMS (ESI):
[M+Na]+ m/z calcd for C61H58O14: 1037.3719, found: 1037.3710.
1H, H-3II), 3.53 (t, J 8.3 Hz, 1H, H-6II ), 3.43 ppm (dd, J 9.0, 5.8 Hz, 1H,
a
H-6IIb). 13C NMR (151 MHz, CDCl3): δ = 165.9 - 165.1 (PhC(O)), 138.8 -
138.1 (q Car Ph), 133.4 - 127.4 (CHar Ph), 124.3 (p-C NPh), 119.6 (o-C
NPh, 102.4 (C-1I), 99.8 (C-1II), 83.14 (C-3I), 83.12 (C-4I), 81.4 (C-2I),
78.8 (C-3II), 76.2 (C-2II), 75.0 (C-4II), 74.8, 73.5, 73.3, 73.0 (CH2Ph), 70.2
(C-5II), 69.9 (C-5I), 68.4 (C-6II), 63.6 ppm (C-6I).HRMS (ESI): [M+Na]+
m/z calcd for C69H62F3O14: 1208.4015, found: 1208.3990.
3-trifluoroacetimipropyl
4,6-О-benzylidene-α-D-galactopyranosyl-
(1→3)-2,5,6-tri-O-benzoyl-β-D-galactofuramoside (20). To a solution of
disaccharide 18 (342 mg, 0.29 mmol) in EtOAc (5 mL), 10% Pd(OH)2/C
(355 mg) and AcOH (40 μl) were added. The resulting mixture was
stirred overnight under hydrogen atmosphere at room temperature. Then
the mixture was filtrated through celite and the filtrated was concentrated
in vacuo. The debenzylated product was dissolved in CH3CN (3 mL) and
treated by PhCH(OMe)2 (70 μl, 0.46 mmol) and CSA (30 mg). After 2 h
stirring the mixture was quenched by the addition of triethylamine (50 μl)
and concentrated. Purification using column chromatography gave the
title product (152 mg, 58%). Rf 0.15 (toluene/EtOAc, 2:1). [α]D20 +25.05°
(c 1.0, EtOAc). 1H NMR (400 MHz, CDCl3): δ = 8.13 – 8.08 (m, 2H, o-Har
Bz1), 8.00 – 7.95 (m, 2H, o-Har Bz2), 7.95 – 7.87 (m, 2H, o-Har Bz3), 7.63
– 7.29 (m, 14H, CHar 4Ph), 5.89 – 5.83 (m, 1H, H-5I), 5.51 (s, 1H,
CHPh), 5.31 (d, J 2.4 Hz, 1H, H-2I), 5.15 (d, J 2.4 Hz, 1H, H-1II), 5.11 (s,
1H, H-1I), 4.74 (m, 2H, H-6Iab), 4.53 (dd, J 7.0, 3.6 Hz, 1H, H-4I), 4.33 (dd,
J 7.0, 3.2 Hz, 1H, H-3I), 4.28 (s, 1H, H-3II), 4.11 – 3.84 (m, 6H, H-2II, H-5II,
H-4II, H-6IIab, OCHHCH2CH2N), 3.66 – 3.39 (m, 3H, OCH2CH2CH2N,
OCHHCH2CH2N), 1.98 – 1.84 ppm (m, 2H, OCH2CH2CH2N). 13C NMR
(101 MHz, CDCl3): δ = 166.4, 166.3, 166.1 (PhC(O)), 137.6 - 133.5 (q Car
Ph), 130.2 - 126.4 (Car Ph), 106.4 (C-1I), 101.3 (CHPh), 100.9 (C-1II),
83.2 (C-2I), 82.7 (C-3I), 80.1 (C-4I), 75.9 (C-3II), 70.1 (C-5I), 69.6 (C-2II),
69.5 (C-4II), 69.3 (C-5II), 66.5 (OCH2CH2CH2N), 64.1 (C-6II), 63.5 (C-6I),
38.2 (OCH2CH2CH2N), 28.3 ppm (OCH2CH2CH2N).HRMS (ESI): [M+Na]+
m/z calcd for C45H44F3NO15: 918.2555, found: 918.2554.
3-trifluoroactimidopropyl
galactopyranosyl-(1→3)-2,5,6-tri-O-benzoyl-β-D-galactofuranoside
(18). mixture of donor (400 mg, 0.37 mmol), 3-
2,3,4,6-tetra-О-benzyl-α-D-
A
8
trifluoroacetimidopropan-1-ol (316 mg, 1.85 mmol), and molecular sieves
AW300 (500 mg) in CH2Cl2 (5 mL) was stirred for 15 minutes at room
temperature and then cooled to -40 °C. NIS (203 mg, 0.90 mmol) and
TfOH (35 μl, 0.19 mmol) were added, the reaction mixture was allowed to
attain to room temperature, then the mixture was diluted with CH2Cl2,
quenched with aqueous Na2S2O3 and washed with H2O. The organic
layer was dried over Na2SO4 and concentrated in vacuo. Purification
using column chromatography afforded spacer-armed disaccharide as a
3-trifluoroacetimidopropyl
galactopyranosyl-(1→3)-2,5,6-tri-O-benzoyl-β-D-galactofuranosyl-
(1→3)-4,6-О-benzylidene- α-D-galactopyranosyl-(1→3)-2,5,6-tri-O-
2,3,4,6-tetra-O-benzyl-α-D-
20
white solid (342 mg, 79%). Rf = 0.21 (toluene / EtOAc, 10:1); [α]D
benzoyl-β-D-galactofuranoside (21). A solution of donor 19 (78 mg,
0.07 mmol), acceptor 20 (59 mg, 0.07 mmol), MS-4Å (170 mg) in CH2Cl2
(0.8 mL) was stirred for 15 min and cooled to -80 °C. TfOH (2 μl, 0.02
mmol) was added and when the TLC analysis indicated the complete
consumption of the starting donor the reaction mixture was loaded on the
column. Purification using column chromatography afforded 21 as a
white solid. (52 mg, 42%). Rf 0.21 (toluene/EtOAc, 5:1). 1H NMR (600
MHz, CDCl3): δ = 8.14 – 8.10 (m, 2H, o-H Bz1), 8.06 (d, J 7.2 Hz, 2H, o-H
Bz2), 7.98 – 7.91 (m, 8H, o-H Bz3-6), 7.61 – 7.13 (m, 43H, CHar Ph), 5.92
– 5.88 (m, 1H, H-5I), 5.86 (dt, J 7.9, 4.0 Hz, 1H, H-5III), 5.64 (d, J 2.3 Hz,
1H, H-2III), 5.43 (s, 1H, CHPh), 5.42 (s, 1H, H-1III), 5.33 (d, J 2.9 Hz, 1H,
H-2III), 5.19 (d, J 3.8 Hz, 1H, H-1II), 5.18 (d, J 3.9 Hz, 1H, H-1IV), 5.15 (s,
1H, H-1I), 4.86 (d, 1H, CH2Ph), 4.81 (dd, J 12.0, 3.9 Hz, 1H, H-6Ia), 4.76
– 4.65 (m, 5H, H-6Ib, H-6IIIa, H-4III, CH2Ph), 4.61 – 4.56 (m, 3H, H-6IIIb, H-
4I, CH2Ph), 4.50 (d, 1H, CH2Ph), 4.45 – 4.41 (m, 2H, H-3I, CH2Ph), 4.37
(d, J 3.6 Hz, 1H, H-4II), 4.35 (d, 1H, CH2Ph), 4.31 (dd, J 6.2, 2.3 Hz, 1H,
H-3III), 4.27 – 4.22 (m, 2H, H-3II, CH2Ph), 4.14 (dd, J 13.2, 6.7 Hz, 1H, H-
+19.35 (c 1.0, EtOAc). 1H NMR (600 MHz, CDCl3): δ = 8.15 – 8.11 (m,
2H, o-Har Bz1), 8.01 – 7.95 (m, 2H, o-Har Bz2), 7.95 – 7.89 (m, 2H, o-Har
Bz3), 7.62 – 7.11 (m, 29H, CHar 7Ph), 5.89 – 5.84 (m, 1H, H-5I), 5.31 (d,
J = 2.5 Hz, 1H, H-2I), 5.12 – 5.10 (m, 2H, H-1I, H-1II), 4.91 (d, 1H,
CH2Ph), 4.83 – 4.70 (m, 4H, 2CH2Ph), 4.70 – 4.63 (m, 2H, H-6Iab), 4.55
– 4.49 (m, 2H, H-4I, CH2Ph), 4.34 (dd, J = 7.1, 3.0 Hz, 1H, H-3I), 4.21 (d,
1H, CH2Ph), 4.13 (d, 1H, CH2Ph), 4.09 (dd, J 10.1, 3.8 Hz, 1H, H-2II),
4.09 (dd, J 10.1, 3.8 Hz, 1H), 4.04 – 3.99 (m, 2H, H-5II, H-4II), 3.93 (dd, J
10.2, 2.7 Hz, 1H, H-3II), 3.91 – 3.85 (m, 1H, OCHHCH2CH2N), 3.55 –
3.42 (m, 4H, H-6II , OCHHCH2CH2N, OCH2CH2CH2N), 3.30 (dd, J 9.1,
a
5.5 Hz, 1H, H-6IIb), 1.91 – 1.83 ppm (m, 2H, OCH2CH2CH2N). 13C NMR
(151 MHz, CDCl3): δ = 166.1 - 165.9 (3PhC(O), 138.7 - 137.8 (cq Car
Ph), 133.5 (o-Car Bz1), 133.4 (o-Car Bz2), 133.1 (o-Car Bz3), 129.9 - 127.3
(Car Ph), 106.4 (C-1I), 99.5 (C-1II), 83.5 (C-2I), 82.6 (C-3I), 80.0 (C-4I),
78.8 (C-3II), 76.1 (C-2II), 74.8 (CH2Ph), 74.7 (C-4II), 73.5, 73.2, 72.8
(3CH2Ph), 70.1 (C-5II, C-5I), 68.3 (C-6II), 66.0 (OCH2CH2CH2N), 63.7
(C-6I), 37.7 (OCH2CH2CH2N), 27.8 ppm (OCH2CH2CH2N).HRMS (ESI):
[M+Na]+ m/z calcd for C66H64F3NO15: 1190.4120, found: 1190.4094.
5IV), 4.05 – 4.00 (m, 2H, H-2IV, H-6II ), 3.99 (dd, J 10.1, 3.4 Hz, 1H, H-3II),
a
3.92 – 3.88 (m, 1H, OCHHCH2CH2N), 3.82 – 3.76 (m, 4H, H-3IV, H-6II ,
b
H-5II, H-4IV), 3.58 (m, J 12.4, 6.1 Hz, 1H, OCH2CH2CHHN), 3.55 – 3.49
(m, 1H, OCHHCH2CH2N), 3.44 – 3.35 (m, 3H, H-6IVab, OCH2CH2CHHN),
1.98 – 1.86 ppm (m, 2H, OCH2CH2CH2N). 13C NMR (151 MHz, CDCl3) δ
166.1 - 165.8 (PhC(O)), 138.8 - 137.7 (cq Car Ph), 133.7 -126.2 (Car Ph),
107.9 (C-1III), 106.1 (C-1I), 100.6 (C-1II), 99.3 (C-1IV), 83.6 (C-3III), 83.3
(C-2I), 82.5 (C-3I), 82.1 (C-2III), 80.8 (C-4III), 80.4 (C-4I), 79.1 (C-3IV), 77.4
(С-3II), 76.2 (C-2IV, C-4IV), 74.9 (C-4II), 74.7, 73.4, 73.3, 72.7 (CH2Ph),
70.5 (C-5III), 70.3 (C-5I), 70.0 (C-5IV), 69.0 (C-6II), 68.9 (C-6IV), 67.0 (C-
2II), 65.8 (OCH2CH2CH2N), 63.7 (C-5II), 63.6 (C-6III), 63.4 (C-6I), 37.9
(OCH2CH2CH2N), 27.9 ppm (OCH2CH2CH2N).HRMS (ESI): [M+Na]+ m/z
calcd for C106H100F3NO28: 1914.6276, found: 1914.6241.
2,3,4,6-tetra-О-benzyl-α-D-galactopyranosyl-(1→3)-2,5,6-tri-O-
benzoyl-β-D-galactofuranoside N-phenyltrifluoroacetamide (19).
Hemiacetals 17 (107 mg, 0.11 mmol) were dissolved in CH2Cl2 (2 mL),
followed by the addition of N-phenyl trifluoroacetimidoyl chloride (35 μl,
0.21 mmol) and Cs2CO3. After stirring intensively for 30 min at room
temperature the mixture was loaded on the column with silica gel
(toluene, 1% Et3N). Purification of the product using column
chromatography (toluene / EtOAc 25/1, 1% Et3N) gave 19 as yellowish oil
(125 mg, quantitative yield). Rf 0.61 (toluene / EtOAc, 10:1). 1H NMR
(600 MHz, CDCl3): δ = 8.15 – 8.06 (m, 2H, o-H Bz1), 8.03 – 7.95 (m, 2H,
o-H Bz2), 7.90 (d, J 7.7 Hz, 2H, o-H Bz3), 7.62 – 7.35 (m, 8H, CHar Ph),
7.33 (t, J 7.8 Hz, 2H, m-H NPh), 7.31 – 7.12 (m, 10H, CHar Ph), 7.10 (t, J
7.4 Hz, 1H, p-H NPh), 6.86 (d, J 7.5 Hz, 1H, o-H NPh), 6.49 (br s, 1H, H-
1I), 5.93 – 5.89 (m, 1H, H-5I), 5.77 (s, 1H, H-2I), 5.17 (d, J 3.2 Hz, 1H, H-
1II), 4.95 (d, 1H, CH2Ph), 4.84 (dd, 2H, CH2Ph), 4.78 – 4.73 (m, 3H,
CH2Ph, H-4I), 4.73 – 4.63 (m, 2H H-6Iab), 4.56 (d, 1H, CH2Ph), 4.45 (d,
1H, J 3.9 Hz, 1H, H-3I), 4.37 (d, 1H, CH2Ph), 4.27 (d, 1H, CH2Ph), 4.21 –
Aminopropyl
α-D-galactopyranosyl-(1→3)-β-D-galactofuranosyl-
(7).
(1→3)-α-D-galactopyranosyl-(1→3)-β-D-galactofuranoside
Tetrasaccharide 21 (26 mg, 0.01mmol) was dissolved in EtOAc (1 mL)
and catalyst 10% Pd(OH2)/C (28 mg) and AcOH (15 μl) were added. The
resulting mixture was stirred overnight under hydrogen atmosphere, after
which the mixture was filtrated through celite and the filtrate was
concentrated in vacuo. Obtained product was suspended in MeOH (1
4.08 (m, 2H, H-5II H-2II), 4.04 (s, 1H, H-4II), 3.99 (dd, 1H, J 3.2, 10.2 Hz,
,
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
FULL PAPER
mL) and treated with NaOMe (1 M solution, 100 μl). After 30 min the
solution was diluted with H2O (200 μl) and the excessive amount of
NaOMe (1M solution, 300 μl) was added. The resulting mixture was
stirred at 40 °C and after 5 min it was neutralized by the addition of 0.1 M
AcOH (4 mL). The solution was concentrated in vacuo and the residue
was purified by gel-chromatography on TSK-40 HW to give desirable
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1664.
1
product as a white powder (6.2 mg, 63%). H NMR (600 MHz, D2O): δ =
5.21 (d, J 1.4 Hz, 1H, H-1III), 5.07 (d, J 3.9 Hz, 1H, H-1II), 5.05 (d, J 3.5
Hz, 1H, H-1IV), 5.03 (d, J 1.9 Hz, 1H, H-1I), 4.41 (dd, J 3.0, 1.4 Hz, 1H, H-
2III), 4.28 (dd, J 3.0, 2.0 Hz, 1H, H-2I), 4.24 (dd, J 6.3, 4.2 Hz, 1H, H-4III),
4.18 (dd, J 6.2, 4.1 Hz, 1H, H-4I), 4.13 (d, J 2.8 Hz, 1H, H-4II), 4.11 (t, J
6.3 Hz, 1H, H-5I), 4.09 – 4.03 (m, 2H, H-3I, H-5III, H-3III, ), 3.99 (d, J 2.4
Hz, 1H, H-4IV), 3.95 (dd, J 10.5, 3.9 Hz, 1H, H-2II), 3.91 – 3.81 (m, 6H, H-
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Eur. J., 2015, 21, 1749-1754.
3II, H-5II, H-3IV, H-5IV, H-2IV, OCHHCH2CH2N), 3.78 – 3.73 (m, 4H, H-6III
,
ab
H-6Iab), 3.73 – 3.63 (m, 5H, H-6IIab, H-6IVab, OCHHCH2CH2CH2N), 3.12 (t,
J 7.2 Hz, 2H, OCH2CH2CH2N), 2.02 – 1.95 (m, 2H, OCH2CH2CH2N). 13
C
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10.1021/acs.orglett.6b02735.
NMR (151 MHz, D2O): δ = 109.3 (C-1III), 107.5 (C-1I), 99.7 (C-1IV), 99.5
(C-1II), 84.7 (C-3III), 84.3 (C-3I), 81.8 (C-4III, C-4I), 79.7 (C-2III), 79.5 (C-2I),
76.9 (C-3II), 71.5 (C-5III), 71.4 (C-5I), 70.9 (C-5II), 70.8 (C-3IV), 69.3 (C-
2IV), 69.2 (C-4IV, C-4II), 68.2 (C-5IV), 67.2 (C-2II), 65.6 (OCH2CH2CH2N),
62.8 (C-6II), 62.7(C-6IV), 61.3 (C-6III), 61.1 (C-6I), 37.5 (OCH2CH2CH2N),
26.8 (OCH2CH2CH2N) ppm. HRMS (ESI): [M+Na]+ m/z calcd for
C27H49NO21: 746.2689, found: 746.2675.
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Acknowledgements
This work was supported by RSF grant 14-23-00199 (NEN). We
thank Dr. A.S. Dmitrenok for recording NMR-spectra and Dr. A.O.
Chizhov for recording high resolution mass spectra at the
Department of Structural Studies of the Zelinsky Institute of
Organic Chemistry, Moscow. We thank Dr. A.G. Gerbst for
careful reading of manuscript and valuable comments.
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Keywords: carbohydrates • glycosylation • galactofuranose •
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•
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10.1002/ejoc.201601413
European Journal of Organic Chemistry
FULL PAPER
Entry for the Table of Contents
Oligosaccharide Synthesis
FULL PAPER
Extending of scope: The acid-free
conditions for pyranoside-into-
furanoside (PIF) rearrangement of 4-
pentenyl glycosides were developed
and applied for the synthesis of
spacer-armed tetrasaccharide related
to galactan I of Klebsiella
Stella A. Verkhnyatskaya, Vadim B.
Krylov, Nikolay E. Nifantiev*
Page No. – Page No.
Pyranoside-into-furanoside
rearrangement of 4-pentenyl
glycoside in the synthesis of
tetrasaccharide related to galactan I
of Klebsiella pneumoniae
pneumoniae, demanded for biological
investigation.
This article is protected by copyright. All rights reserved.