A facile stereoselective synthesis of α-glycosyl ureas

Article abstract of DOI:10.1016/j.carres.2006.03.042

α-Glycosyl ureas can be synthesised directly from tetra-O-benzyl glycosyl azides and isocyanates, using a one-pot procedure that is simple and general in scope. The benzyl protecting groups are easily removed from the urea products by catalytic hydrogenat

Full text of DOI:10.1016/j.carres.2006.03.042

Carbohydrate Research 341 (2006) 1438–1446
A facile stereoselective synthesis of a-glycosyl ureas
Aldo Bianchi, Davide Ferrario and Anna Bernardi*
`
Dipartimento di Chimica Organica e Industriale, Universita degli Studi di Milano, via Venezian 21, 20133 Milano, Italy
Received 6 December 2005; received in revised form 22 March 2006; accepted 30 March 2006
Available online 2 May 2006
Abstract—a-Glycosyl ureas can be synthesised directly from tetra-O-benzyl glycosyl azides and isocyanates, using a one-pot proce-
dure that is simple and general in scope. The benzyl protecting groups are easily removed from the urea products by catalytic hydro-
genation. The synthesised a-glycosyl ureas represent a new class of neo-glycoconjugates with the potential of being resistant towards
carbohydrate processing enzymes.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Carbohydrates; Glycosyl azides; Glycosyl ureas; Neo-glycoconjugates; Synthetic methods
1. Introduction
and chemical properties and biological activity. In fact,
because glycosyl derivatives can be highly sensitive to
chemical or enzymatic hydrolysis, it is particularly inter-
esting to have access to new modified structures that
could be endowed with an increased stability.
Glycosyl ureas are generally prepared starting from
glycosyl isocyanates (Scheme 1).7,8 These substrates can
react directly with amines7 (Scheme 1a) or with imino-
phosphoranes8 generated by reduction of azides9
(Scheme 1b). In the latter case, carbodiimides are ini-
tially obtained and subsequently hydrolysed to the cor-
Glycosyl ureas are found in nature in the aminoglycos-
idic antibiotics.1,2 They have also been used as stable
N-linked-glycopeptide mimics3 and for the synthesis of
polyvalent glycoconjugates.4 However, only a few meth-
ods for the synthesis of glycosyl ureas have been
reported,5–8 and in particular, a practical synthesis of
anomeric a-glycosyl ureas is still lacking.3b,7d Yet, these
compounds could constitute an interesting new class of
neo-glycoconjugates, with virtually unexplored physical
OAc
O
OAc
O
H
N
H
N
AcO
AcO
AcO
AcO
NCO
RNH2
+
R
a.
b.
OAc
OAc
O
H2O
OAc
O
OAc
O
AcO
AcO
N C O
O
PPh3
AcO
AcO
O
PPh3
N R
N C N R
OAc
PPh3
OAc
Glc N C N R
Glc N C
R
N3
+
Ph3P O
R
N PPh3
Scheme 1. Synthesis of b-glycosyl ureas from glycosyl isocyanates: (a) direct synthesis using amines,3,7 (b) synthesis via carbodiimides, using
iminophosphoranes.8
*
Corresponding author. Tel.: +39 02 5031 4092; fax: +39 02 5031 4072; e-mail: anna.bernardi@unimi.it
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.03.042

A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
1439
temperature led to the corresponding iminophosphor-
anes. The in situ reaction of these compounds with car-
bon disulfide under mild conditions led to the
symmetrical glycosyl carbodiimides. The procedure
worked effectively starting from b-azides and the
expected products were obtained in good yields as stable
crystalline solids. However, from a-azides, complex
reaction mixtures were formed and the expected prod-
ucts could not be isolated (Scheme 3).
Here we report that, on the contrary, 2,3,4,6-tetra-O-
benzyl-glycosyl azides give iminophosphoranes that do
react productively with isocyanates without anomeric
isomerisation. Hence, a one-pot stereoselective synthesis
of a-glycosyl ureas from a-glycosyl azides can be easily
achieved, provided that tetra-O-benzyl a-glycosyl azides
are used as starting material.11 The benzyl protecting
groups are then simply removed from the urea products
by catalytic hydrogenation. In general, the resulting a-
glycosyl ureas were found to be configurationally stable,
but one exception was found. Thus, a new class of neo-
glycoconjugates becomes available for further studies.
OAc
O
OAc
O
AcO
AcO
AcO
AcO
N3
N
PPh3
OAc
PPh3
OAc
MeN=C=O
2 h
+
toluene
110°
OAc
OAc
O
H
N
H
O
AcO
AcO
AcO
AcO
N
Me
N C N Me
OAc
OAc
40 %
O
Scheme 2. Reaction of tetra-O-acetyl-glucopyranosyl iminophospho-
rane with isocyanates.8a
responding ureas, most conveniently in a one-pot proce-
dure (Scheme 1b).8a The starting glycosyl isocyanates
can be synthesised either from glycosyl halides, follow-
ing the classical Fischer procedure,6 or from the corre-
sponding azides,3,7 using multi-step sequences that
involve glycosyl isonitriles3,7a–c or glycosyl carbamates7d
as intermediates. The stereoselectivity of these transfor-
mations is complete for b azides, but 4:1 a/b ratios are
typically obtained starting from the a anomers.7
Direct conversion of glycosyl azides to ureas could in
principle be achieved by inverting the reaction partners
of the carbodiimide reaction, as shown in Scheme 2.
Thus, a glycosyl azide could be transformed with phos-
phines into a glycosyl iminophosphorane, which could
react with isocyanates to give ureas through a carbo-
diimide intermediate (Scheme 2).
2. Results and discussion
The low reactivity observed for anomeric glycosyl imino-
phosphoranes is likely due to the electron withdrawing
effect of the pyranose moiety, which stabilises the nega-
tive charge on the ylide nitrogen (Scheme 2) and reduces
its nucleophilicity.8a This effect is maximised for acety-
lated (disarmed12) pyranoses but it should be greatly
reduced if the hydroxyl groups of sugar are protected
as benzyl ethers (armed12). Therefore, we reasoned that
the iminophosphoranes obtained by reduction of the
2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl azide 111a,13
(Scheme 4) ought to react with alkyl isocyanates. The
reaction of 1 with triphenylphosphine in dry dichloro-
methane at room temperature followed by treatment
with benzyl isocyanate afforded a complex mixture of
reaction intermediates that contained the a anomer of
carbodiimide 2 (20% yield). The reaction of 1 with
trimethylphosphine was much faster. After disappear-
ance of the starting material, benzyl isocyanate was
added to the mixture and complete conversion of the
intermediate into the corresponding carbodiimide 2
However, in practice,8a anomeric glycosyl iminophos-
phoranes of tetra-O-acetyl pyranoses react very slug-
gishly with isocyanates.8a For instance, at room
temperature no reaction occurred between 2,3,4,6-tetra-
O-acetyl-b-D-glucopyranosyl phosphinimine and methyl
isocyanate, while at 110 ꢁC the reaction proceeded in
two hours in low yield (Scheme 2). With more complex
isocyanates, the reaction is even slower and gives rise to
various side products.8a
´
In a recent example, Gyo¨rgydeak and co-workers em-
ployed a similar procedure for the synthesis of symmet-
rical and unsymmetrical glycosyl carbodiimides.10 The
reaction of peracetylated glycosyl azides with 1 equiv
of trimethylphosphine in dry dichloromethane at room
OAc
O
OAc
AcO
1) PMe3, CH2Cl2, r.t.
2) CS2
O
OAc
OAc
y = 80 %
AcO
AcO
AcO
AcO
N3
N C N
O
OAc
OAc
AcO
OAc
O
1) PMe3, CH2Cl2, r.t.
2) CS2
AcO
AcO
complex mixture
AcO
N3
Scheme 3. Synthesis of symmetrical carbodiimides from tetra-O-acetyl-glucopyranosyl azides.10

1440
A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
OBn
O
OBn
O
1) PPh3
BnO
BnO
BnO
BnO
reaction by-products
+
+
2) PhCH2NCO
BnO
BnO
Ph
N3
N C
N
2
1
20 %
OBn
O
OBn
O
OBn
O
1) PMe3
BnO
BnO
BnO
BnO
BnO
BnO
H
N
2) PhCH2NCO
BnO
BnO
BnO
NH
Ph
N3
N C
N
Ph
1
2
3
15 %
64 %
O
Scheme 4. Synthesis of N0-benzyl-N-2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl carbodiimide 2 and of urea 3 from azide 1.
OBn
O
1) PMe3
BnO
3
a.
b.
BnO
2) PhCH2NCO
3) HCO2H/ H2O
BnO
N3
α only, y = 71 %
1
BnO
BnO
BnO
BnO
OBn
O
OBn
O
1) PMe3
2) PhCH2NCO
3) HCO2H/ H2O
H
N
BnO
N3
BnO
NH
Ph
5
4
O
α only, y = 70 %
Scheme 5. One-pot synthesis of N0-benzyl-N-tetra-O-benzyl-a-D-glucopyranosyl urea 3 from a-glucopyranosyl azide 1 (a) and of N0-benzyl-N-tetra-
O-benzyl-a-D-galactosyl urea 5 from a-galactosyl azide 4 (b).
was achieved in one hour (Scheme 4). This compound
could be isolated in 64% yield by flash chromatography
even if, during the purification, partial hydrolysis was
observed and 15% of urea 3 was formed. The a config-
uration was assigned to the anomeric carbon of 2 and
3 by 1H NMR, on the basis of the value of the coupling
constant of the anomeric proton (J1,2 = 4.1 Hz). The
reaction was found to be completely a-stereoselective.
Trimethylphosphine, used as a 1 M toluene solution,
has the further advantage that the corresponding tri-
methylphosphinoxide can be easily removed from the
reaction mixture by simple aqueous work-up.
Acid-catalysed hydrolysis of 2 in aqueous THF and in
the presence of different protic acids (Amberlite-IR120,
acetic acid, formic acid) proved to be slow and incom-
plete. Better results were obtained following a slight
modification of the one-pot procedure introduced by
chromatographic purification in 71% overall yield and with
complete retention of the anomeric configuration (Scheme
5a). The a-galactosyl azide 411,13 reacted under the same
conditions with benzyl isocyanate to afford the corre-
sponding a-galactosyl urea 5 in 70% yield (Scheme 5b).
These optimised conditions were then used for the
reactions of 1 with a series of commercially available iso-
cyanates; the results are collected in Table 1. All the
reactions examined proceeded with total retention of
the a configuration at the anomeric centre, as deter-
1
mined by H NMR. The reactions with phenyl isocya-
nate (entry 2) and allyl isocyanate (entry 3) gave the
corresponding ureas 6 and 7 with 74% and 67% yield,
respectively. On the contrary, using phenyl isothiocya-
nate (entry 4) phenyl urea 6 was isolated with only
19% yield and the formation of various side products
was observed. The reaction with 1,4-diisocyanobutane
(entry 5) also proved to be highly efficient and afforded
divalent neo-glycoconjugate 8 in 60% global yield start-
ing from azide 1.
Removal of the benzyl ether protecting groups was
achieved by catalytic hydrogenation (Scheme 6). After
some investigation, we found that the reaction per-
formed consistently well using a 85:10:5 N,N-dimethyl-
acetamide/H2O/AcOH mixture and a slight H2 pressure
(3 atm).14 The deprotected glycosyl ureas could be
isolated in good yields (85–90%) by filtration from the
´
´
Ortiz Mellet, Garcia-Fernandez and co-workers in
20008b (Scheme 5). Thus, after the formation of carbodii-
mide, formic acid and water (2:1) were added to the
reaction mixture, which was stirred for an additional
30 min. The urea product 3 was then isolated after
The use of acetic acid and water (2:1), as in the original procedure,
resulted in much slower conversion of the diimide, and partially
hydrolysed by-products were obtained (12%) even after 18 h of
reaction.

A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
1441
Table 1. One-pot synthesis of glycosyl ureas from 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl azide 1
Entry
Electrophile
Yielda (%)
Product
a/b Ratiob
OBn
O
BnO
BnO
1
PhCH2–NCO
71
P97:3
P97:3
P97:3
H
N
BnO
HN
Ph
3
O
OBn
O
BnO
BnO
2
3
Ph–NCO
74
67
H
N
BnO
HN
Ph
6
O
OBn
O
BnO
BnO
CH2–CH@CH2–NCO
H
N
BnO
HN
7
O
4
5
Ph–NCS
19
6
P97:3
P97:3
OBn
O
OBn
BnO
O
BnO
BnO
OBn
O
H
60c
BnO
OCN–(CH2)4–NCO
N
N
NH
OBn
H
N
H
O
8
a Yield after flash chromatography. General conditions: 1.2 equiv of PMe3 in CH2Cl2, then 1.2 equiv of iso(thio)cyanate for 1 h, at rt, followed by 2:1
v/v HCO2H/H2O (30 min).
b Determined by 1H NMR on the crude reaction mixtures.
c 2.2 mol of sugar per mol of isocyanate 1 h at rt, followed by 2:1 v/v HCO2H/H2O (1.5 h).
OBn
O
OH
O
BnO
BnO
HO
HO
H2 (3 atm)/ Pd-C
H
N
BnO
H
N
HO
NH
NH
85:10:5
R
R
DMA, AcOH, H2O
O
O
OBn
OBn
OH
BnO
HO
6 R = -Ph
7 R = -CH2-CH=CH2
-CH -CH -CH -CH NHCONH
9 R = -Ph
10 R = -CH2-CH2-CH3
-CH -CH -CH -CH NHCONH
OH
O
O
OBn
HO
11 R =
8 R =
2
2
2
2
2
2
2
2
Scheme 6. Hydrogenolitic removal of the protecting groups.
reaction mixtures, and further purified by flash chroma-
tography, reverse phase HPLC or gel permeation
chromatography.
2,3,4,6-tetra-O-benzyl-glucopyranosyl urea derivative
by reaction of 1 with trimethylphosphine and n-propyl
isocyanate (Scheme 7).
Surprisingly, deprotection of N0-allyl urea 7 occurred
with simultaneous anomerisation, and N0-propyl urea
10 was initially isolated as a 1:1 mixture of the two
anomeric a- and b-N-propyl anomers that slowly inter-
converted to the pure b-anomer. Examples of anomerisa-
tion of glycosyl thioureas have been reported to occur,
but only in basic media.15 The behaviour of the propyl
derivative was rather puzzling, so, at the suggestion of a
referee, we independently synthesised the N0-propyl-N-
To our surprise, a 3.2:1 mixture of the a and b isomers
was formed. Moreover, both a- to b- and b- to a-iso-
merisation were found to occur on silica gel during flash
chromatography. Slow anomer interconversion (4 days)
was also observed in CDCl3 solution in the NMR tube.
This behaviour was not observed for any of the other
compounds described in this paper, which were all
found to be stable on silica gel, and configurationally
stable for months at 4 ꢁC, nor was it reported for similar

1442
A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
OBn
O
OBn
O
OBn
O
H
N
1) PMe3
BnO
BnO
BnO
BnO
NH
BnO
BnO
+
H
N
2) PrNCO
3) HCO2H, H2O
BnO
NH
BnO
13
BnO
N3
O
12
1
O
Scheme 7. Reaction of 1 with n-propyl isocyanate.
OH
O
OAc
O
Ac2O, py, DMAP
Ph
HO
AcO
AcO
HO
H
N
H
N
HO
AcO
NH
NH
9
14
Ph
O
O
Scheme 8. Acetylation of urea 9.
(unprotected) b-glucopyranosyl azides recently de-
scribed in the literature.16 These results suggest that sim-
ple N-alkyl, N0-glycosyl ureas may undergo anomeric
equilibration under slightly acidic conditions and that
the composition of the a-b equilibrium mixture may
depend on the oxygen substitution of sugar.
involved in the best procedure previously reported.
Neo-glycoconjugates are of great interest for medicinal
chemistry due to their potential biological activities,
their resistance towards enzymatic degradation, and
their expected greater half-life in biological systems.17
This protocol opens the way to a straightforward syn-
thesis of an interesting class of neo-glycoconjugates,
whose chemical and biological properties can now be
explored in detail.
Finally, to confirm the product configuration, N0-phenyl
urea 9 was acetylated (Ac2O, pyridine, DMAP catalyst)
and product 14 was fully characterised by NMR spec-
troscopy confirming the a configuration of the anomeric
4
centre and the C1 conformation of the pyranose ring
(Scheme 8).
4. Experimental
4.1. General
3. Conclusions
The solvents were dried by standard procedures: CH2Cl2
In conclusion, the reaction of a-glycosyl azides of per-
benzylated monosaccharides with trimethylphosphine
and isocyanates followed by one pot hydrolysis affords
the corresponding a-glycosyl ureas with complete ste-
reocontrol and good yields. Peracetylated compounds
show little reactivity under these conditions,8a and this
difference can be explained considering the arming-dis-
arming effect of the protecting groups.12 Trimethylphos-
phine was used as a 1 M solution in toluene and it was
found to be more effective than triphenylphosphine in
this reaction in terms of yield.
The procedure reported here works effectively for a
series of isocyanates, both on the gluco and galacto ser-
ies. The resulting a-glycosyl ureas appear to adopt a 4C1
chair conformation, and the anomeric configuration can
be established by coupling constant analysis. Removal
of the benzyl protecting groups is obtained by catalytic
hydrogenation, and leads to configurationally stable a-
ureas, with the exception of N0-propyl urea 11. Com-
pared to the literature reports,7d this method allows
the direct transformation of a-glycosyl azides into the
corresponding ureas in a one-pot facile reaction, avoid-
ing the four steps and one chromatographic separation
over CaH2, pyridine and N,N-dimethylacetamide
(DMA) over activated 4 A molecular sieves. Reactions
˚
involving trimethylphosphine were performed under
1
argon. H and 13C spectra were recorded at 300 K on
a Bruker AVANCE-400 or a Bruker AVANCE-600
spectrometer. Chemical shifts d for 1H and 13C are
expressed in parts per million relative to internal
(CH3)4Si as standard. Signals were abbreviated as s,
singlet; br s broad singlet; d, doublet; t, triplet; q,
quartet; m, multiplet. Mass spectra were obtained with
a MALDI-TOF (OMNIFLEX Bruker) or an ESI
(LCQ Advantage Termofinnigan) apparatus, and
HRMS with a FT-ICR (APEXTM II Bruker Daltonics).
Optical rotations [a]D were measured in a cell of 1 dm
pathlength and 1 mL capacity with a Perkin–Elmer
241 polarimeter. IR spectra were recorded on a JASCO
FT/IR-300E spectrometer, and frequencies are
expressed in cmꢀ1. Thin layer chromatography (TLC)
was carried out with precoated Merck F254 silica gel
plates. Flash chromatography (FC) was carried out with
Macherey-Nagel Silica Gel 60 (230–400 mesh). Tetra O-
benzyl a-glycosyl azides 1 and 4 were synthesised follow-
ing the reported procedures.11,13

A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
1443
4.2. General procedure for the synthesis of glycosyl ureas
3 and 5–7
J4,5 = 8.3 Hz); 13C NMR (100.6 MHz, CDCl3): 156.14,
138.35, 138.29, 137.92, 137.50, 137.00, 129.19–127.80
(9 peaks), 123.75, 123.34, 120.64, 119.96, 81.84, 78.65,
78.03, 77.46, 75.87, 75.02, 73.50, 73.08, 69.86, 68.74;
MALDI-TOFMS m/z: 659.2 (M+H+), 681.2 (M+Na+),
697.2 (M+K+).
Trimethylphosphine (1.2 equiv, 1 M solution in toluene)
was added, at rt and under argon, to a 0.1 M solution of
the a-azide (1 equiv) in dry CH2Cl2. The mixture was
stirred for 1 h until the disappearance of the starting
material from the TLC plate (4:1, toluene/EtOAc).
The iso(thio)cyanate (1.2 equiv) was added and the solu-
tion was stirred for 1.5 h. A 2:1 v/v solution of formic
acid and H2O was then added (5 equiv of formic acid)
and the hydrolysis of the carbodiimide was monitored
by TLC (4:1, toluene/EtOAc). After 1.5 h, the solution
was diluted with CH2Cl2 and washed with H2O, satd
aq NaHCO3 and H2O again. The organic layer was
dried (Na2SO4) and concentrated. The crude product
was purified by flash chromatography.
4.5. N0-Propenyl-N-2,3,4,6-tetra-O-benzyl-a-D-gluco-
pyranosyl urea (7)
Flash chromatography: 3:1 toluene/EtOAc; yield: 67%;
25
1
½aꢁD +21.7 (c 1.0, CHCl3); IR (nujol): 1678 mC@O; H
NMR (400 MHz, CDCl3): 7.30–7.20 (m, 18H, aromat-
ics), 7.15–7.04 (m, 2H, aromatics), 5.75–5.65 (m, 1H,
@CH), 5.60 (t, 1H, NHCH2, J = 5.4), 5.16 (br s, 1H,
NH,) 5.04 (d, 1H, H-1, J1,2 = 4.0 Hz), 5.06–5.04 (m,
1H, @CH2), 4.98–4.94 (m, 1H, @CH2), 4.80 (d, 1H,
CH2Ph, J = 11 Hz), 4.71 (d, 1H, CH2Ph, J = 11 Hz),
4.69 (d, 1H, CH2Ph, J = 11 Hz), 4.55 (AB system, 2H,
CH2Ph), 4.45 (d, 1H, CH2Ph, J = 12 Hz), 4.38 (d, 1H,
CH2Ph, J = 11 Hz), 4.34 (d, 1H, CH2Ph, J = 12 Hz),
3.86–3.84 (m, 1H, H-5), 3.71–3.60 (m, 4H, H-2, H-3,
CH2N) 338–3.52 (m, 2H, H-6, H-60), 3.43 (dd, 1H, H-
4, J4,3 = J4,5 = 5.3 Hz); 13C NMR (100.6 MHz, CDCl3):
158.51, 138.36, 138.06, 137.69, 137.14, 134.99, 128.58–
127.73 (six peaks), 115.44, 81.91, 80.41, 78.32, 78.19,
77.89, 77.43, 75.80, 74.94, 73.45, 72.99, 69.66, 68.63,
42.40; MALDI-TOFMS m/z: 623.4 (M+H+), 645.4
(M+Na+), 661.4 (M+K+).
4.3. N0-Benzyl-N-2,3,4,6-tetra-O-benzyl-a-D-gluco-
pyranosyl urea (3)
Flash chromatography: 4:1, toluene/EtOAc; yield: 71%;
25
1
½aꢁD +62.9 (c 1.0, CHCl3); IR (nujol): 1652 mC@O; H
NMR (400 MHz, CDCl3): 7.30–7.10 (m, 23H, aromat-
ics), 7.10–7.05 (m, 2H, aromatics), 5.83 (t, 1H, NHCH2,
J = 7.5 Hz), 5.15 (br s, 1H, NH), 5.13 (dd, 1H, H1,
J1,2 = 4.6 Hz, J1-NH = 8.0 Hz), 4.82 (d, 1H, CH2Ph,
J = 11 Hz), 4.70 (AB system, 2H, CH2Ph, J = 6 Hz),
4.55 (AB system, 2H, CH2Ph, J = 12 Hz), 4.38 (AB sys-
tem, 1H, CH2Ph, J = 11 Hz), 4.36 (AB system, 1H,
CH2Ph, J = 12 Hz), 4.24–4.22 (m, 2H, NCH2Ph), 4.21
(AB system, 1H, CH2Ph, J = 11 Hz), 3.81 (m, 1H, H-
5), 3.70–3.60 (m, 2H, H-2, H-3), 3.50–3.40 (m, 2H, H-
4.6. N0-Benzyl-N-2,3,4,6-tetra-O-benzyl-a-D-galacto-
pyranosyl urea (5)
4 H-6), 3.37 (d, 1H, H-60, J6,6 = 8 Hz, J5,6 = 0 Hz);
13C NMR (100.6 MHz, CDCl3, selected peaks): 158,
139.27, 138.49, 138.18, 137.77, 137.29, 128.79–127.39
(12 peaks), 82.07, 78.49, 78.34, 77.47, 76.04, 75.16,
73.56, 73.25, 69.78, 68.52, 44.13. ESIMS m/z: 673.3
(M+H+), 695.3 (M+Na+), 711.3 (M+K+).
Flash chromatography: 4:1, toluene/EtOAc; yield: 70%;
0
0
25
1
½aꢁD +48.8 (c 1.0, CHCl3); IR (nujol): 1652 mC@O; H
NMR (400 MHz, CDCl3): 7.35–7.18 (m, 25H, aromat-
ics), 6.06 (t, 1H, NHCH2, J = 5.3 Hz), 5.10 (br s, 1H,
NHCO), 5.10 (d, 1H, H-1, J1,2 = 4.9 Hz), 4.84 (d, 1H,
CH2Ph, J = 11 Hz), 4.71–4.55 (m, 4H, CH2Ph), 4.44
(d, 1H, CH2Ph, J = 11 Hz), 4.30 (dd, 1H, CH2NH,
J = 5.3 Hz, 14.3 Hz), 4.21–4.18 (m, 2H, CH2Ph), 4.10
(dd, 1H, CH2NH J = 5.3, 14.3 Hz), 4.02 (dd, 1H, H-2,
J2,1 = 4.9 Hz, J2,3 = 9.5 Hz), 3.95–3.90 (m, 1H, H-5),
3.74 (br s, 1H, H-4), 3.56 (dd, 1H, H-3, J3,4 = 2.3 Hz,
4.4. N0-Phenyl-N-2,3,4,6-tetra-O-benzyl-a-D-gluco-
pyranosyl urea (6)
Flash chromatography: 9:1, toluene/EtOAc; yield: 74%.
25
1
0
½aꢁD +120.8 (c 1.0, CHCl3); IR (nujol): 1665 mC@O; H
NMR (400 MHz, CDCl3): 7.55 (br s, 1H, NHPh),
7.30–7.27 (m, 20H, aromatics), 7.13 (t, 2H, aniline Hm,
J = 7.3 Hz), 7.09–7.07 (m, 2H, aromatics), 6.92 (t, 1H,
aniline Hp, J = 7.3 Hz), 5.33 (br s, 1H, NH), 5.18 (br
s, 1H, H-1, J1,2 = 4.6 Hz), 4.82 (d, 1H, CH2Ph,
J = 11 Hz), 4.74 (d, 1H, CH2Ph, J = 11 Hz), 4.72 (d,
1H, CH2Ph, J = 11 Hz), 4.59 (AB system, 2H, CH2Ph),
4.48 (d, 1H, CH2Ph, J = 12 Hz), 4.43 (d, 1H, CH2Ph,
J = 11 Hz), 4.42 (d, 1H, CH2Ph, J = 12 Hz), 3.92–3.90
(m, 1H, H-5), 3.70–3.64 (m, 2H, H-2, H-3), 3.60–3.52
J2,3 = 9.5 Hz), 3.34 (dd, 1H, H-6, J6,5 = J6,6 = 9.1 Hz),
3.21 (dd, 1H, H-60, J6 ,5 = 5.1 Hz, J6,6 = 9.1 Hz); 13C
NMR (100.6 MHz, CDCl3): 159.4, 139.3, 138.4, 137.8,
137.7, 128.7–727.2 (10 peaks), 79.1, 78.6, 75.2, 74.8,
74.5, 73.6, 73.5, 69.4, 69.2, 44.0; ESIMS m/z: 673.9
(M+H+), 695.9 (M+Na+), 711.9 (M+K+).
0
0
4.7. Synthesis of the N,N00-butane-1,4-diylbis[(N0-2,3,4,6-
tetra-O-benzyl-a-D-glucopyranosyl)urea] (8)
Trimethylphosphine (2.4 equiv, 1 M solution in toluene)
was added, at rt and under argon, to a 0.1 M solution of
(m, 2H, H-6, H-60), 3.45 (dd, 1H, H-4, J4,3
=

1444
A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
a-azide 1 (2.2 equiv) in dry CH2Cl2. The mixture was
stirred for 1 h until the disappearance of the starting
material from the TLC plate (4:1, toluene/EtOAc).
The 1,4-diisocyanobutane (1 equiv) was added and the
solution was stirred for 1.5 h. A 2:1 v/v solution of for-
mic acid and H2O was then added (5 equiv of formic
acid) and the hydrolysis of the carbodiimide was moni-
tored by TLC (4:1, toluene/EtOAc). After 1.5 h, the
solution was diluted with CH2Cl2 and washed with
H2O, satd aq NaHCO3 and H2O again. The organic
layer was dried (Na2SO4) and concentrated. The crude
product was purified by flash chromatography (3:1, tol-
4.10. N0-Propyl-N-D-glucopyranosyl urea (10)
Flash chromatography 61:35:4 CHCl3/MeOH/H2O, on
silica gel; yield = 86%; Mixtures of a and b anomers
were obtained, with variable composition, depending
on the reaction time. The two isomers could be identified
in the crude NMR spectra (CD3OD) by the signals of
their anomeric protons at 5.30 ppm (a isomer, J1,2
=
4.0 Hz) and 4.76 ppm (b isomer, J1,2 = 9.4 Hz). These
1
two signals correlated in the HETCOR H–13C spec-
trum with the two anomeric carbons (82.0 ppm C-1b
and 78.5 ppm C-1a). ESI mass spectrometry showed
two peaks at m/z 287.3 (M+Na+) and 303.3 (M+K+),
which are consistent with the N0-propyl-N-D-glucopyr-
anosyl urea structure.
25
uene/EtOAc); yield: 60%; ½aꢁD +41.5 (c 1.0, CHCl3); IR
1
(nujol): 1651 mC@O; H NMR (400 MHz, CDCl3): 7.30–
7.15 (m, 2 · 18H, aromatics), 7.09–7.07 (m, 2 · 2H, aro-
matics), 5.51 (t, 2H, 2 · NHCH2, J = 5.3 Hz), 5.06 (br s,
2H, 2 · NH), 5.03 (d, 2H, 2 · H-1, J = 5.0 Hz), 4.80 (d,
2H, 2 · CH2Ph, J = 11 Hz), 4.68 (d, 2H, 2 · CH2Ph,
J = 11 Hz), 4.66 (d, 2H, 2 · CH2Ph, J = 11 Hz), 4.51
(AB system, 4H, 2 · CH2Ph), 4.43 (d, 2H, 2 · CH2Ph,
J = 12 Hz), 4.38 (d, 2H, 2 · CH2Ph, J = 11 Hz), 4.31
(d, 2H, 2 · CH2Ph, J = 12 Hz), 3.81–3.78 (m, 2H,
2 · H-5), 3.66–3.63 (m, 4H, 2 · H-2, 2H-3), 3.53–3.49
(m, 4H, 2 · H-6, 2 · H-6), 3.40 (dd, 2H, 2 · H-4,
J4,2 = J4,3 = 9.2 Hz), 3.03–3.01 (m, 2H, 2 · CH2NH),
2.94–2.92 (m, 2H, 2 · CH2NH), 1.33–1.29 (m, 4H,
2 · CH2CH2); 13C NMR (100.6 MHz, CDCl3): 158.66,
138.36, 138.06, 137.68, 137.15, 128.56–627.72 (six
peaks), 81.90, 78.21, 77.61, 77.46, 75.77, 74.93, 73.46,
72.91, 69.56, 68.78, 39.76, 27.32; MALDI-TOFMS:
m/z 1219.2 (M+H+), 1241.2 (M+Na+), 1257.1 (M+K+).
4.11. N,N00-Butane-1,4-diylbis[N0-(a-D-glucopyranos-
yl)urea] (11)
The compound was purified by gel permeation (Sepha-
dex LH20, CH3OH) chromatography. An analytical
sample was purified by reverse phase HPLC (XterraTM
C18, 95:5 H2O/CH3CN with 0.1% TFA); yield: 70%;
1H NMR (400 MHz, CD3OD): 5.24 (d, 2H, 2 · H-1,
J1,2 = 5.4 Hz), 3.75 (dd, 2H, 2 · H-6, J5,6 = 2.1 Hz,
0
J6,6 = 11.4 Hz), 3.56–3.49 (m, 4H, 2 · H-2 and 2 · H-
60), 3.49–3.45 (m, 2H, 2 · H-5), 3.38 (dd, 2H, 2 · H-3,
J2,3 = J3,4 = 9.6 Hz), 3.17–3.08 (m, 6H, 2 · H-4 and
2 · CH2NH), 1.45–1.42 (m, 4H, 2 · CH2); 13C
NMR (100.6 MHz, CDCl3, HETCOR): 78.7, 73.7,
72.3, 70.5, 70.0, 61.6, 38.8, 26.9; ESIMS m/z: 521.4
(M+Na+).
4.8. General procedure for the debenzylation; synthesis of
glycosyl ureas 9–11
4.12. Synthesis of N0-propyl-N-2,3,4,6-tetra-O-benzyl-a-
D-glucopyranosyl urea (12) and N0-propyl-N-2,3,4,6-
tetra-O-benzyl-b-D-glucopyranosyl urea (13)
A 0.01 M solution of the protected urea in 85:15:5
DMA/AcOH/H2O was prepared. The catalyst (10%
Pd/C, 1:1 w/w with the substrate) was added and the
mixture was stirred for 12–36 h under a H2 atmosphere
(3 atm). The reaction was monitored by TLC (4:1 tolu-
ene/EtOAc and 60:35:5 CHCl3/CH3OH/H2O). The mix-
ture was filtered on a Celite pad, washed several times
with CH3OH and then evaporated to dryness.
Trimethylphosphine (2.0 equiv, 1 M solution in toluene)
was added, at rt and under argon, to a 0.1 M solution of
a-azide 1 (1 equiv) in dry CH2Cl2. The mixture was stir-
red for 1.5 h until the disappearance of the starting
material from the TLC plate (4:1, toluene/EtOAc).
The propylisocyanate (1.2 equiv) was added and the
solution was stirred for 1.5 h. A 2:1 v/v solution of for-
mic acid and H2O was added (5 equiv of formic acid)
and the hydrolysis of the carbodiimide was monitored
by TLC (4:1, toluene/EtOAc). After 1 h, the solution
was diluted with CH2Cl2 and washed with H2O, satd
aq NaHCO3 and H2O again. The organic layer was
dried (Na2SO4) and concentrated. The crude product
was purified by flash chromatography (4:1 toluene/
EtOAc).
4.9. N0-Phenyl-N-a-D-glucopyranosyl urea (9)
Flash chromatography 64:35:1 CHCl3/MeOH/H2O, on
1
silica gel; yield = 85%; H NMR (400 MHz, CD3OD):
7.35 (d, 2H, aniline Ho, J = 8.4 Hz), 7.21 (7, 2H, aniline
Hm, J = 7.9 Hz), 6.95 (t, 1H, aniline Hp, J = 7.9 Hz),
5.44 (d, 1H, H-1, J1,2 = 5.4 Hz), 3.77 (dd, 1H, H-6,
0
J5,6 = 1.9 Hz, J6,6 = 11.8 Hz), 3.68–3.60 (m, 2H, H-2,
H-60), 3.53–3.43 (m, 2H, H-3, H-5), 3.27 (dd, 1H, H-4,
J4,3 = J4,5 = 9.3 Hz); 13C NMR (100.6 MHz, CDCl3,
HETCOR): 128.6, 122.5, 118.9, 78.5, 74.1, 72.6, 70.3,
70.2, 61.5; ESIMS m/z: 321.3 (M+Na+).
4.12.1.
N0-Propyl-N-2,3,4,6-tetra-O-benzyl-a-D-gluco-
1
pyranosyl urea (12). Yield: 54%; H NMR (600 MHz,
CD3Cl3): 7.34–7.29 (m, 18H, aromatics), 7.17–7.14 (m,

A. Bianchi et al. / Carbohydrate Research 341 (2006) 1438–1446
1445
2H, aromatics), 5.6 (br s, 1H, NH), 5.3 (br s, 1H, NH),
5.1 (d, 1H, H-1, J1,2 = 4.6 Hz), 4.93 (d, 1H, CH2Ph,
J = 11 Hz), 4.83 (d, 1H, CH2Ph, J = 11 Hz), 4.79 (d,
1H, CH2Ph, J = 11 Hz), 4.68 (AB system, 2H, CH2Ph),
4.56 (d, 1H, CH2Ph, J = 12 Hz), 4.50 (d, 1H, CH2Ph,
J = 11 Hz), 4.44 (d, 1H, CH2Ph, J = 12 Hz), 3.94–3.92
(m, 1H, H-5), 3.76 (dd, 1H, H3, J3,2 = J3,4 = 9.2 Hz),
3.71 (dd, 1H, H2, J2,1 = 4.6 Hz, J2,3 = 9.2 Hz), 3.65–
3.63 (m, 2H, H-66, H-60), 3.54 (dd, 1H, H-4,
J4,3 = J4,5 = 9.2 Hz), 3.30–3.27 (m, 2H, NHCH2),
1.42–1.38 (m, 2H, CH2CH3), 0.85 (t, 1H, CH2CH3,
J = 7.8 Hz); 13C NMR (125 MHz, CDCl3, HETCOR):
82.5, 79.5, 78.3, 77.9, 76.8, 75.8, 74.1, 73.8, 70.1, 69.0,
42.0, 24.0, 13.0.
155.00, 137.81, 129.10, 124.02, 119.98, 77.33, 69.78,
68.84, 68.22, 67.66, 61.92, 20.56; ESIMS: m/z calcd
for [C21H26N2O10]Na+: 489.14797. Found: 489.14627;
m/z calcd for 2[C21H26N2O10]Na+: 955.30671. Found:
955.31064.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2006.03.042.
References
4.12.2. N0-Propyl-N-2,3,4,6-tetra-O-benzyl-b-D-glucopyr-
anosyl urea (13). Yield: 17%; 1H NMR (600 MHz,
CD3Cl3): 7.34–7.29 (m, 18H, aromatics), 7.17–7.14 (m,
2H, aromatics), 5.6 (br s, 1H, NH), 5.3 (br s, 1H,
NH), 4.93 (d, 1H, CH2Ph, J = 11 Hz), 4.86 (d, 1H,
CH2Ph, J = 11 Hz), 4.83 (d, 1H, CH2Ph, J = 11 Hz),
4.80 (br s, 1H, H-1, J1,2 = 8.0 Hz), 4.71 (AB system,
2H, CH2Ph), 4.58 (d, 1H, CH2Ph, J = 12 Hz), 4.52 (d,
1H, CH2Ph, J = 11 Hz), 4.47 (d, 1H, CH2Ph,
J = 12 Hz), 3.76 (dd, 1H, H-3, J3,2 = J3,4 = 9.0 Hz),
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0
3.71 (dd, 1H, H-6, J6,5 = 10.6 Hz, J6,6 = 2.1 Hz), 3.68–
3.66 (m, 2H, H-4, H-60), 3.54 (dd, 1H, H-4, J4,3
=
J4,5 = 9.2 Hz), 3.38 (t, 1H, H-2, J2,1 = J2,3 = 8.0 Hz),
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pyranosyl urea 14
A solution of urea 9 (0.03 mmol) in dry pyridine
(0.3 mL) was prepared. Ac2O (0.5 mmol) and N,N-di-
methylaminopyridine (0.1 equiv) were added. The solu-
tion was stirred at rt for 18 h and the reaction was
monitored by TLC (4:1, toluene/EtOAc). The solution
was then concentrated, the residue was taken up with
CH2Cl2 and washed with 5% HCl, 5% NaHCO3 and
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´
´
8. Synthesis via carbodiimides: (a) Garcıa-Fernandez, J. M.;
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25
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4.22–4.19 (m, 3H, H-5, H-6, H-60), 2.07 (s, 3H, CH3CO),
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