Novel approach towards C-C-linked carbohydrate dimers via Claisen rearrangement of a disaccharide allyl ketene acetal

Article abstract of DOI:10.1055/s-2006-942407

A disaccharide derivative was synthesised by coupling tri-O-benzyl-D-glucal with an allylic sugar alcohol in a glycosyloxyselenation reaction. Subsequent oxidation followed by syn-elimination of the selenoxide and in situ rearrangement of the inter-mediat

Full text of DOI:10.1055/s-2006-942407

PAPER
2117
Novel Approach towards C–C-Linked Carbohydrate Dimers via Claisen
Rearrangement of a Disaccharide Allyl Ketene Acetal
C–C-Linked
C
t
arbohy
e
drate
D
ime
f
rs via
C
a
nangement Jürs, Joachim Thiem*
Institut für Organische Chemie der Universität, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
Fax +49(40)428384325; E-mail: joachim.thiem@chemie.uni-hamburg.de
Received 11 April 2006
Dedicated to Prof. Dr. Dieter Hoppe on the occasion of his 65th birthday
To this end, we started from tri-O-acetyl-D-glucal (1),
which was subjected to a Ferrier rearrangement10 to give
the 2,3-dideoxyhex-2-enopyranoside 2 (Scheme 1). Sub-
sequent deacetylation11 and silylation of the primary hy-
Abstract: A disaccharide derivative was synthesised by coupling
tri-O-benzyl-D-glucal with an allylic sugar alcohol in a glycosyl-
oxyselenation reaction. Subsequent oxidation followed by syn-
elimination of the selenoxide and in situ rearrangement of the inter-
mediate allyl ketene acetal gave novel C–C-linked saccharide droxyl function delivered the allylic alcohol 4, the a-
dimers.
anomer of which was coupled with tri-O-benzyl-D-glucal
(5) in a glycosyloxyselenation reaction previously de-
scribed by Sinaÿ et al.12 The anomeric configuration at C-
1¢ of the isolated product 6 proved to be a which suggests
a trans-diaxial nucleophilic opening of an intermediate
seleniranium ion by the allylic alcohol 4. Oxidation of the
selenide 6 to the selenoxide 7 was accomplished with 30%
hydrogen peroxide at –25 °C and delivered a mixture of
products diastereomeric at selenium (ratio: 7a/7b = 3:1).
These compounds proved relatively stable owing to a ki-
netically retarded syn-elimination of phenylselenenic acid
(PhSeOH)13 toward the anomeric centre which consider-
ably facilitated the chromatographic purification. A slow
interconversion of the diastereomers at selenium due to
hydration was likewise noted resulting in a ratio of 7a/
7b = 2:1 after one week in deuterated benzene.
Key Words: mimetics, carbohydrates, selenium, allyl ketene ace-
tals, rearrangements
Oligosaccharides play a central role in intercellular com-
munication and cell-mediated processes. The investiga-
tion of the structural features present in carbohydrate
recognition and binding sites of antibodies and lectins is
of crucial interest and requires the development of saccha-
ride mimetics of naturally occurring carbohydrates.1
In recent years numerous efforts have been directed to-
ward the synthesis of C-disaccharides, the chemical sta-
bility of which renders them particularly useful for
imitating the biological and physical properties of the cor-
responding O-glycosides.2 The replacement of the inter-
glycosidic
oxygen
atom
by
carbonyl3
and
Since a syn-elimination of PhSeOH towards C-3¢ in 7a/b
is impossible due to the trans-diaxial arrangement, it was
expected to proceed between C-1¢ and C-2¢ under en-
hanced thermal conditions14 to give the corresponding al-
lyl ketene acetal 8. In order to subsequently effect the
Claisen rearrangement of the reactive ketene acetal 8 in
situ, the mixture of diastereomers 7a/b was initially heat-
ed in n-butyl vinyl ether with diisopropylamine to 130 °C
in a microwave device to give compounds 9a/b in a mod-
erate yield of 52%. Although n-butyl vinyl ether and relat-
ed compounds are known to act as a scavenger for
PhSeOH,15 the formation of side products from the sol-
vent, PhSeOH and diisopropylamine complicated purifi-
hydroxymethylene4 groups has led to further interesting
disaccharide analogues. A potential application field of
these molecules includes inhibition of biosynthetic path-
ways of glycoproteins which may later result in novel an-
tibacterial,5 antiviral6 or antitumoral agents.7
In a recent contribution from our laboratory we reported
on the synthesis of divalent saccharide structures incorpo-
rating either a spiro or a methylene linkage via a ketene
acetal Claisen rearrangement.8 In this paper we reveal the
first Claisen rearrangement of a disaccharide allyl ketene
acetal incorporating both double bonds in endocyclic po-
sitions. The resulting dimeric saccharide structures fea-
ture a direct linkage of two pyranose rings without a
methylene bridge. Similar compounds have hitherto been
accessible only by acid-catalysed glycal dimerisation.9
cation and hence imposed
a
major drawback.
Considerably better results were obtained by using tolu-
ene instead of n-butyl vinyl ether under similar conditions
resulting in a maximum yield of 91% 9a/b. The purpose
of the added diisopropylamine was to convert PhSeOH
A direct C–C bond formation between two pyranose rings
can be achieved by the [3,3]-sigmatropic rearrangement
of a disaccharide featuring an allyl ketene acetal substruc-
ture which incorporates the glycosidic bond.
13
into the selenenamide PhSeN(i-Pr)2 and thus prevent it
from attacking the double bond in the rearrangement
products.
The inseparable mixture of lactones 9a/b (ratio: 9a/
9b = 10:3) was thoroughly analysed primarily by means
of NMR spectroscopy. Comparisons of coupling con-
stants as well as known conformational structures of their
SYNTHESIS 2006, No. 13, pp 2117–2120
Advanced online publication: 08.06.2006
DOI: 10.1055/s-2006-942407; Art ID: C01306SS
x
x.
x
x
.
2
0
0
6
© Georg Thieme Verlag Stuttgart · New York

2118
S. Jürs, J. Thiem
PAPER
OR'
AcO
O
MeOH, BF3⋅Et2O
O
2: R = R' = Ac
3: R = R' = H
4: R = H, R' = TBDPS
NaOMe, MeOH
87%
TBDPSCl, imidazole
DMF, 58% pure α
AcO
AcO
RO
OMe
80 %
1
α:β = 85:15
BnO
R
BnO
O
BnO
BnO
4α, PhSeCl,
2,4,6-collidine
MeCN
O
BnO
BnO
OTBDPS
O
1'
84%
O
1
5
OMe
H2O2, CH2Cl2,
–25 °C to r.t.
84%
6: R = SePh
7a,b: R = Se(O)Ph
BnO
BnO
BnO
toluene, i-Pr2NH,
MS 4 Å, 130 °C, 1 h
91%
O
OTBDPS
7a,b
O
O
OMe
8
OTBDPS
BnO
OTBDPS
4
O
O
C
O
OBn
2'
OMe
OBn
O
CH2OBn
2'
O
OMe
2
+
C
O
CH2OBn
BnO
3
5
9a, B2,5
9b, 4H3
diastereomeric ratio: 9a:9b = 10:3
Scheme 1
parent compounds, d-D-mannono-1,5-lactone and d-D- Regarding the 2¢,3¢,4¢-trideoxyhex-3¢-enopyranoside part
glucono-1,5-lactone, argue for the proposed conforma- the conformation in both compounds 9a and 9b most like-
tions of 9a and 9b. Both the 2-deoxymannonolactone and ly features a half-chair with the planar substructure incor-
2-deoxygluconolactone residues may either exhibit a half- porating C-2¢ to C-5¢.20 Due to the axial nature of the
chair (4H3) or a boat (B2,5) structure since C-2 must be co- methoxy group the configuration at C-2¢ cannot be exactly
planar with the lactone group. d-D-Mannono-1,5-lactone deduced from the corresponding coupling constant
10 indeed features the boat geometry, which is favoured (3J1¢,2¢ = 4.1 Hz), however, a pseudoequatorial orientation
over the boat form due to the cis arrangement of the hy- is rather likely in order to minimise steric interactions of
droxyl group at C-2 and the hydroxymethylene group at the lactone residue with the TBDPS group.
C-5 (Figure 1).16 By contrast, d-D-glucono-1,5-lactone 11
In this paper we have demonstrated the first Claisen rear-
rangement of a disaccharide ketene acetal with an allyl vi-
nyl ether substructure incorporating the interglycosidic
occurs in a slightly distorted half-chair conformation16,17
caused by the trans orientation of 2-OH and 5-CH2OH.
Furthermore, both of these structures enable bulky substit-
bond and both double bonds in endocyclic positions.
uents at C-2 to adopt pseudoequatorial orientations. The
measured coupling constants of 9a and 9b show similar
HO
H
H
values compared to those of the parent compounds, i.e.
4
3
3J2,3 = 2.2 Hz in 9a versus J2,3 = 3.4 Hz in 10 and
OH
H
OH
5
H
O
O
3J2,3 = 6.3 Hz in 9b versus 3J2,3 = 8.5 Hz in 11.18 Hence, 9a
features the boat geometry (B2,5) and 9b the half-chair ge-
ometry (4H3) of the respective lactone ring. The differenc-
es in the coupling constants may be attributed to the lack
of oxygen at C-2 and the substitution pattern associated
with slight conformational distortions.19
CH2OH
C
O
C
O
HO
HO
CH2OH
H
2
HO
3
10
11
H
H
H
Figure 1 Boat conformation (B2,5) of d-D-mannono-1,5-lactone 10
and half-chair conformation (4H3) of d-D-glucono-1,5-lactone 11
Synthesis 2006, No. 13, 2117–2120 © Thieme Stuttgart · New York

PAPER
C–C-Linked Carbohydrate Dimers via Claisen Rearrangement
2119
(R/S)-(Methyl-6-O-tert-butyldiphenylsilyl-2,3-dideoxy-a-D-
erythro-hex-2-enopyranos-4-yl)-3,4,6-tri-O-benzyl-2¢-deoxy-2¢-
phenylselenoxyl-a-D-mannopyranosides (7a/b)
Within a synthetic sequence of six steps starting from pro-
tected D-glucal derivatives a mixture of diastereomeric
target compounds 9a/b could be isolated in an overall
yield of 26%. These novel compounds exhibit a direct C–
C bond between two pyranose rings and hence belong to
a new class of C–C-disaccharides that are of particular in-
terest with respect to saccharide mimetics and carbohy-
drate-based pharmaceuticals.
A stirred solution of 6 (47 mg, 48 mmol) in CH2Cl2 (3 mL) was treat-
ed with 30% H2O2 (15 mL, 5.0 mg, 147 mmol) at –30 °C and the stir-
ring was continued at –25 °C overnight. The next day, a second
portion of 30% H2O2 (10 mL, 3.3 mg, 98 mmol) was added at –25 °C
and the solution was allowed to warm to r.t. After evaporation of the
solvent, the residue was purified by column chromatography (petro-
leum ether–EtOAc, 1:3) to give 7a/b (mixture of diastereomers, 40
mg, 84%) as a colourless syrup; diastereomeric ratio: a/b = 3:1;
Rf 0.22, 0.26 (petroleum ether–EtOAc, 1:3).
Anhyd solvents were purchased from the manufacturers Fluka and
Merck. The protected D-glucal derivatives were purchased from
Fluka and Sigma-Aldrich. Phenylselenyl chloride was purchased
from Lancaster Synthesis. TLC was performed on silica gel 60-
coated aluminum sheets (Merck or Macherey-Nagel), with detec-
tion by UV at 254 nm and by heating with H2SO4 (10% in EtOH).
Flash chromatography was carried out on silica gel 60 (0.04–0.063
mm; Merck, Macherey-Nagel or ICN). Petroleum ether used refers
to the fraction with bp 50–70 °C. The microwave experiments were
performed in a CEM microwave system (Discover, 300 W maxi-
mum power output) by using sealed tubes with temperature control
via infrared sensor. NMR spectra were recorded on a Bruker AMX-
400 and DRX-500 NMR spectrometer (1H: 400/500 MHz; 13C: 100
MHz) and analysed with the respective solvent peaks as references.
Mass spectra were recorded with a Bruker Biflex III (MALDI-TOF,
positive reflection mode, matrix: 2,5-dihydroxybenzoic acid). IR
spectra were recorded on a Bruker Vector 22 FT-IR spectrometer.
The optical rotations were measured on a Perkin-Elmer 243 or 341
polarimeter at 20 °C.
IR (film): 3031, 2928, 2857, 1454, 1428, 1112, 1046, 967, 742, 700
cm–1.
1H NMR (400 MHz, C6D6): d = 1.15, 1.20 (2 s, 2 × 9 H, 2 × tert-
3
C4H9), 3.30, 3.31 (2 s, 2 × 3 H, 2 × CH3), 3.56 (dd, J1¢,2¢ = 1.3,
3
3
3J2¢,3¢ = 4.8 Hz, 1 H, H-2¢a), 3.65 (dd, J1¢,2¢ = 3.3, J2¢,3¢ = 4.8 Hz, 1
H, H-2¢b), 5.35 (d, 3J1¢,2¢ = 3.3 Hz, 1 H, H-1¢b), 5.55–5.61 (m,
3
3J2,3 = 10.4 Hz, 2 H, H-2a/b), 5.74 (d, J2,3 = 10.4 Hz, 1 H, H-3b),
6.06 (d, 3J2,3 = 10.4 Hz, 1 H, H-3a), 6.17 (s, 1 H, H-1¢a).
13C NMR (100 MHz, C6D6): d = 27.07 [3 C, C(CH3)3b], 27.16 [3 C,
C(CH3)3a], 55.49 (2 × 1 C, CH3a/b), 64.13 (1 C, C-6b), 64.25 (1 C,
C-6a), 65.83 (1 C, C-2¢b), 67.72 (1 C, C-2¢a), 68.93 (1 C, C-6¢b),
69.02 (1 C, C-6¢a), 71.07, 72.26, 72.56, 72.96, 73.18, 73.25, 74.24,
74.91, 75.32, 76.65, 78.02, 79.53, 79.56 (16 C, C-4a/b, C-5a/b
,
C-3¢a/b, C-4¢a/b, C-5¢a/b, PhCH2a/b), 93.28 (1 C, C-1¢a), 93.32 (1 C, C-
1¢b), 95.72 (2 × 1 C, C-1a/b), 127.44–130.75, 136.02, 136.05, 136.31
(2 × 38 C, C-2a/b, C-3a/b, Ara/b).
MALDI-TOF: m/z = 1009.4 [M + Na]+.
(Methyl-6-O-tert-butyldiphenylsilyl-2,3-dideoxy-a-D-erythro-
hex-2-enopyranos-4-yl)-3,4,6-tri-O-benzyl-2¢-deoxy-2¢-phenyl-
selenyl-a-D-mannopyranoside (6)
Anal. Calcd for C56H62O9SeSi (986.23): C, 68.20; H, 6.35. Found:
C, 68.07; H, 6.93.
Under argon, a stirred solution of 5 (106 mg, 254 mmol) in MeCN
(3 mL) was treated at 0 °C with PhSeCl (73 mg, 381 mmol) and
2,4,6-collidine (50 mL, 46 mg, 375 mmol). Subsequently a solution
of 4 (71 mg, 178 mmol) in MeCN (2 mL) was added and stirring
continued overnight. When TLC confirmed the complete conver-
sion of 4, the solvent was evaporated and the residue purified by
column chromatography (petroleum ether–EtOAc, 7:1) to give 6
(145 mg, 84%) as a colourless syrup; [a]546 +79.2 (c = 0.50,
CHCl3); Rf 0.4 (petroleum ether–EtOAc, 3:1).
IR (film): 3030, 2930, 1454, 1428, 1112, 1049, 966, 753, 700 cm–1.
2-Deoxy-2-[(3¢Z)-methyl-6¢-O-tert-butyldiphenylsilyl-2¢,3¢,4¢-
trideoxy-a-D-ribo- or -D-xylo-hex-3¢-enopyranos-2¢-yl]-D-man-
nono-1,5-lactone (9a) and 2-Deoxy-2-[(3¢Z)-methyl-6¢-O-tert-
butyldiphenylsilyl-2¢,3¢,4¢-trideoxy-a-D-ribo- or -D-xylo-hex-3¢-
enopyranos-2¢-yl]-D-glucono-1,5-lactone (9b)
A solution of 7a/b (40 mg, 41 mmol) in toluene (6 mL) was stirred
with molecular sieves 4 Å for 10 min. After addition of i-Pr2NH
(243 mmol, 24.7 mg, 34 mL), the solution was heated to 130 °C for
1 h. Evaporation of the solvent and column chromatography of the
residue (petroleum ether–EtOAc, 12:1) gave a diastereomeric mix-
ture of 9a/b (30.0 mg, 91%) as a colourless syrup; diastereomeric
ratio 9a/9b (2S/2R) = 10:3; Rf 0.34 (petroleum ether–EtOAc, 3:1).
20
1H NMR (400 MHz, C6D6): d = 1.20 (s, 9 H, t-C4H9), 3.30 (s, 3 H,
CH3), 3.55 (dd, 2J6¢a,6¢b = 10.9, 3J5¢,6¢b = 1.5 Hz, 1 H, H-6¢b), 3.74 (dd,
2J6¢a,6¢b = 10.9, 3J5¢,6¢a = 3.8 Hz, 1 H, H-6¢a), 3.93 (dd, 3J1¢,2¢ = 1.8 Hz,
IR (film): 2927, 2856, 1457, 1114 cm–1.
3
3
3J2¢,3¢ = 4.3 Hz, 1 H, H-2¢), 3.96–3.99 (m, J4¢,5¢ = 9.4, J5¢,6¢a = 3.8,
3J5¢,6¢b = 1.5 Hz, 1 H, H-5¢), 4.03–4.10 (m, 2 H, H-6a/b), 4.11–4.15
2S-Diastereomer
1H NMR (500 MHz, C6D6): d = 1.21 (s, 9 H, t-C4H9), 2.92 (dd,
3J2,2¢ = 11.0, 3J2,3 = 2.2 Hz, 1 H, H-2), 3.10 (s, 3 H, CH3), 3.47–3.51
(m, 3J1¢,2¢ = 4.4, 3J2,2¢ = 11.0 Hz, 1 H, H-2¢), 3.91–3.97 (m, 3J2,3 = 2.2
3
3
3
(m, J4,5 = 9.2, J5,6a = 2.3, J5,6b = 4.8 Hz, 1 H, H-5), 4.24 (dd,
3J2¢,3¢ = 4.3, 3J3¢,4¢ = 8.4 Hz, 1 H, H-3¢), 4.28–4.36 (m, 3J4¢,5¢ = 9.4 Hz,
3 H, PhCH2, H-4¢), 4.42–4.48 (m, 3J4,5 = 9.2 Hz, 2 H, PhCH2, H-4),
4.56–4.60 (m, 2 H, PhCH2), 4.72 (d, 3J1,2 = 2.0 Hz, 1 H, H-1), 4.95
(d, 1 H, PhCH2), 5.49 (d, 3J1¢,2¢ = 1.8 Hz, 1 H, H-1¢), 5.56–5.60 (m,
3J1,2 = 2.0, 3J2,3 = 10.4 Hz, 1 H, H-2), 5.68 (d, 3J2,3 = 10.4 Hz, 1 H,
H-3), 6.91–6.96, 7.06–7.35, 7.60–7.62, 7.85–7.90 (4 m, 30 H, Ar).
3
Hz, 1 H, H-3), 4.35 (d, J1¢,2¢ = 4.4 Hz, 1 H, H-1¢), 5.85, 6.35 (2 d,
3J3¢,4¢ = 10.4 Hz, 2 × 1 H, H-3¢, H-4¢).
13C NMR (100 MHz, C6D6): d = 27.12 [3 C, C(CH3)3], 35.41 (1 C,
C-2¢), 44.28 (1 C, C-2), 54.85 (1 C, CH3), 66.95, 69.01, 70.23,
71.70, 73.60 (C-6, C-6¢, PhCH2), 69.29, 74.43, 75.59, 78.38 (4 C, C-
3, C-4, C-5, C-5¢), 97.97 (1 C, C-1¢), 126.24–130.02, 136.08–
136.18 (32 C, C-3¢, C-4¢, Ar), 170.56 (1 C, C-1).
13C NMR (100 MHz, C6D6): d = 19.64 (1 C, CMe3), 27.17 [3 C,
C(CH3)3], 49.80 (1 C, C-2¢), 55.48 (1 C, CH3), 64.18 (1 C, C-6),
67.23 (1 C, C-4), 69.43 (1 C, C-6¢), 71.11 (1 C, C-5), 71.66 (1 C,
PhCH2), 73.44 (1 C, C-5¢), 73.71, 75.17 (2 C, PhCH2), 75.90 (1 C,
C-4¢), 79.72 (1 C, C-3¢), 95.67 (1 C, C-1), 97.71 (1 C, C-1¢), 127.61–
130.01, 135.18, 136.07, 136.32 (38 C, Ar).
2R-Diastereomer
1H NMR (500 MHz, C6D6): d = 1.18 (s, 9 H, t-C4H9), 3.00 (dd,
3J2,2¢ = 3J2,3 = 6.3 Hz, 1 H, H-2), 3.17–3.21 (m, 3J1¢,2¢ = 4.1,
3J2,2¢ = 6.3 Hz, 1 H, H-2¢), 3.24 (s, 3 H, CH3), 3.80 (dd, 3J2,3 = 6.3,
3J3,4 = 10.1 Hz, 1 H, H-3), 4.81 (d, 3J1¢,2¢ = 4.1 Hz, 1 H, H-1¢), 5.81–
5.91 (m, 2 H, H-3¢, H-4¢).
MALDI-TOF: m/z = 993.1 [M + Na]+, 1009.1 [M + K]+.
Anal. Calcd for C56H62O8SeSi (970.23): C, 69.32; H, 6.45. Found:
C, 68.64; H, 6.71.
Synthesis 2006, No. 13, 2117–2120 © Thieme Stuttgart · New York

2120
S. Jürs, J. Thiem
PAPER
(6) Taylor, D. L.; Fellows, L. E.; Farrar, G. H.; Nash, R. J.;
Taylor-Robinson, D.; Mobberley, M. A.; Ryder, T. A.;
Jeffries, D. J.; Tyms, A. S. Antiviral Res. 1988, 10, 11.
(7) Nishimura, Y.; Satoh, T.; Adachi, H.; Kondo, S.; Takeuchi,
T.; Azetaka, M.; Fukuyasu, H.; Iizuka, Y. J. Am. Chem. Soc.
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13C NMR (100 MHz, C6D6): d = 27.10 [3 C, C(CH3)3], 39.20 (1 C,
C-2¢), 47.83 (1 C, C-2), 55.16 (1 C, CH3), 66.73, 68.05, 68.88,
72.65, 73.36, 73.69 (C-6, C-6¢, PhCH2), 69.47, 76.19, 77.26, 77.74
(4 C, C-3, C-4, C-5, C-5¢), 98.51 (1 C, C-1¢), 125.89–130.82, 136.36
(32 C, C-3¢, C-4¢, Ar), 168.60 (1 C, C-1).
MALDI-TOF: m/z = 835.3 [M + Na]+, 851.2 [M + K]+.
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16, 569.
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Acknowledgment
Support of this work by the Deutsche Forschungsgemeinschaft
(GRK 464) and the Fonds der Chemischen Industrie is gratefully
acknowledged.
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Synthesis 2006, No. 13, 2117–2120 © Thieme Stuttgart · New York