Total synthesis of the bacillosamine containing α-l-serine linked trisaccharide of Neisseria meningitidis

Article abstract of DOI:10.1016/j.carres.2014.04.011

Total synthesis of the bacillosamine containing l-serine linked O-trisaccharide of Neisseria meningitidis is described. The synthesis entails installation of two consecutive α-linkages including the coupling of bacillosamine with l-serine derivative.

Full text of DOI:10.1016/j.carres.2014.04.011

Carbohydrate Research xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Total synthesis of the bacillosamine containing
a-L-serine linked
trisaccharide of Neisseria meningitidis
⇑
Madhu Emmadi, Suvarn S. Kulkarni
Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Total synthesis of the bacillosamine containing
described. The synthesis entails installation of two consecutive
losamine with -serine derivative.
L-serine linked O-trisaccharide of Neisseria meningitidis is
Received 24 March 2014
Received in revised form 15 April 2014
Accepted 16 April 2014
Available online xxxx
a
-linkages including the coupling of bacil-
L
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Neisseria meningitides
Stereoselective glycosylation
Aminoacid coupling
Rare sugars
Nucleophilic displacement of triflates
1. Introduction
analysis by acid hydrolysis and mass spectroscopic studies, the ste-
reochemistry at C4 of the rare sugar (DATDH) could not be defined.
The specific function of glycosylation in meningococcus infec-
tion remains obscure.6 It is suggested that glycosylation may con-
stitute bacterial cloaking devices against the host immune
reponses.7 More importantly, Marceau and Nassif demonstrated
that the presence of the glycosylation at serine 63 can influence
the amount of soluble and secreted form of pilin (S-pilin), a mole-
cule which is crucial in establishing infections.8 Since the pilin
O-glycan contains unique deoxy amino sugars which are not present
on the host cell surfaces, the structural differences can be exploited
for the development of target specific therapeutics and vaccines.9
Given the biological importance and the problems associated
with the isolation of the glycoproteins in acceptable amounts
and purity, it is imperative to synthesize the serine-linked trisac-
charide that can be incorporated into the glycoprotein to expedite
the studies probing the exact role of pilin O-glycans in meningitis
and further vaccine development.
Neisseria meningitidis (menigococcus) is a causative bacterium
of the highly contagious disease meningitis which involves inflam-
mation of the protective membranes (meninges) of the brain and
spinal cord.1 Meningitis is most common in children aged 2–18
and has a high mortality rate. It is estimated that about 5–10% of
the total population may be asymptomatic carriers. Most cases
are acquired through the exposure to these carriers. The onset of
symptoms is sudden and death can occur in a few hours. In a men-
ingitis pandemic, about 10% of patients die, while about 15% of the
survivors develop serious neurological disorders. Thus, novel and
more effective vaccines2 are required to control the periodic out-
break of this deadly disease.
It has been well established that meningococcus pili, which are
long polymeric filamentous glycoproteins produced from the sur-
face of pathogenic N. meningitidis are a key virulence factor.3 Pili
play crucial roles as essential adhesins in colonization of this cap-
sular bacterium and contribute to the specificity for the human
host.4 In 1995, Stimson et al.5 showed that the pili are post-trans-
lationally modified by glycosylation of serine 63 with a unusual
The structure of the target O-trisaccharide comprises a digalac-
tosyl moiety, a rare deoxy amino sugar DATDH and L-serine. Since
the stereochemistry at C4 of the rare sugar is not defined, two
trisaccharide Gal-(b 1-4)-Gal(
a
1-3)-2,4-diacetimido-2,4,6-tride-
putative trisaccharides 1 and 2 are possible, one with a 2,4-diace-
oxyhexose [Gal(b 1-4)Gal( 1-3) DATDH] (Fig. 1). Since the struc-
a
tamido 2,4,6-trideoxy
D-galactose (DATDG), and one containing a
ture of the trisaccharide was proposed based on the linkage
2,4-diacetamido 2,4,6-trideoxy
D
-glucose (bacillosamine, Bac),
respectively. The main challenges involved in the synthesis of the
deceptively simple looking trisaccharides are the synthesis of the
rare, deoxyamino glycans10–13 (Bac11 and DATDG12) and installa-
⇑
Corresponding author. Tel.: +91 22 25767166; fax: +91 22 25767152.
E-mail address: suvarn@chem.iitb.ac.in (S.S. Kulkarni).
tion of two consecutive
a-glycosyl linkages. Moreover, obtaining
http://dx.doi.org/10.1016/j.carres.2014.04.011
0008-6215/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Emmadi, M.; Kulkarni, S. S. Carbohydr. Res. (2014), http://dx.doi.org/10.1016/j.carres.2014.04.011

2
M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
OH
HO
AcO
1. Tf2O, Py, DCM
2. TBAN3,CH3CN, -30 ο
AcO
HO
HO
HO
OH
O
O
C
O
O
HO
SPh
SPh
SPh
O
AcO
3. TBANO2
OH
O
N3
10
OH
N3
61% Over 3 steps
9
11
1.0 : 0.16
Inseparable mixture
R2
HO
HO
α-Linkage
O
R1
O
AcHN
AcO
TfO
1. Tf2O, Py, DCM
2. NaN3, DMF
α-Linkage
O
O
O
N3
SPh
SPh
AcO
N3
12
75%
N3
CO2
HN
1.
R1= H, R2= NHAc
R1= NHAc, R2= H
2.
13
11%
Figure 1. Structures of pilin glycans of Neisseria meningitidis.
Separable by column
Scheme 2. Synthesis of bacillosamine thioglycoside donor 12.
complete
a-stereoselectivity in the coupling of L-serine with the
rare trideoxy amino sugars is difficult. Towards this goal, we
recently established a methodology to access the rare bacterial
deoxy amino sugars including DATDH and thereby accomplished
the first synthesis of trisaccharide 1.14 In this article we describe
the total synthesis of the bacillosamine containing trisaccharide 2.
product (15%). In this case, although we did not encounter the
orthoester, instead thioglycoside 3 was obtained as a major side
product (80%), formed presumably via the aglycon transfer of SPh
from acceptor 4 to donor 6. Such aglycon transfers of thioglyco-
sides are well documented in the literature.20 To obviate the agly-
con transfer, the anomeric thiophenyl group was replaced by a
stable methoxy phenyl group (OMP). For this purpose, the corre-
sponding OMP glycoside 7 was prepared in a manner very much
2. Results and discussions
2.1. Synthesis of the left hand disaccharide
For the synthesis of the left hand disaccharide (di-gal), we first
prepared the known thioglycoside donor 315 and acceptor 416
using reported procedures. First, thioglycoside 3 was treated with
bromine in CH2Cl2 and the so formed glycosyl bromide was acti-
vated with AgOTf and orthogonally coupled with acceptor 4 to
afford the desired disaccharide 5, albeit in a modest 32% yield
(Scheme 1). The low yield encountered in this reaction was attrib-
uted to the simultaneous formation of the corresponding orthoes-
ter17 which could not be rearranged to 5 even after prolonged
stirring in the presence of excess TMSOTf. Since, we were not able
to improve the yield of 5 using glycosyl bromide under various
conditions, we decided to try out the corresponding known imi-
date derivative 6,18 with the hope to circumvent the orthoester for-
mation. Glycosylation of imidate 6 with 4 using TMSOTf as an
activator at rt19 did furnish disaccharide 5, but again as a minor
similar to 4 from the known a
-OMP galactoside21 through sequen-
tial 4,6-O-benzylidenation (PhCH(OMe)2, CSA), 2,3-di-O-benzyla-
tion (NaH, BnBr), benzylidene hydrolysis (80% AcOH reflux) and
selective O6 benzoylation (Et3N, Bz2O), in 68% overall yields. Grat-
ifyingly, glycosylation of imidate 6 with acceptor 7 under TMSOTf
activation at rt furnished the desired b-linked disaccharide 8 in 88%
yields.14b
2.2. Synthesis of the Bac building block
The rare Bac building block 12 was prepared from 9 following
our recently established protocol to synthesize rare bacterial sug-
ars (Scheme 2).14 For this purpose, we were required to carry out
a double inversion at C4 of a D-rhamnose derivative to achieve
azide substitution with retention of configuration. First, diol 9
was subjected to triflation followed by a one-pot double serial
inversion which involved a highly regioselective azide displace-
ment of the C2-OTf followed by a nitrite ion mediated displace-
OAc
O
OAc
O
AcO
AcO
AcO
AcO
ment (Lattrell-Dax reaction22
reaction smoothly delivered the
)
of the remaining C4-OTf. The
-fucosamine derivative 10
1. Br2, CH2Cl2
OBz
O
O
SPh
D
AcO
AcO
2. 4, AgOTf, 3 MS,
SPh
BnO
accompanied by a small amount of acetate migration product 11
in a ratio 1:0.16 (as judged by 1H NMR). Since this side product
was inseparable on TLC and by column chromatography, the mix-
ture was subjected as such to a similar C4-triflation and azide dis-
placement sequence, to afford the desired Bac derivative 12 in 75%
isolated yield over two steps. At this stage, the unreacted C3-OTf
13 (well separated on TLC) was isolated in 11% yield.
DCM, -50 °C, 32%
OBn
3
5
OBz
HO
O
SPh
BnO
OBn
4
4, TMSOTf, DCM, RT
5
3
(15%)
(80%)
OAc
O
AcO
AcO
2.3. Stereoselective glycosylation of bacillosamine donor with
serine acceptor
L-
AcO
CCl3
NH
O
OAc
AcO
AcO
With the appropriate building blocks in hand, we turned our
attention to the synthesis of the right hand unit. As anticipated,
the installation of 1,2-cis glycosidic linkage in the coupling of the
6-deoxy monosaccharide with the primary OH of L-serine was very
difficult. In this case, although the C2-azido group, being a non-
participating group, is expected to facilitate the formation of
6
O
OBz
O
O
7, TMSOTf, DCM, RT
AcO
BnO
88%
BnO
OMP
8
OBz
HO
O
BnO
BnO
a
-linkage, remote participation is not available from the C4 and
OMP
C6 functionalities.23 So, we were mindful that various donors and
conditions may need to be tested to achieve selectivity. Strategi-
cally, our rare sugar building blocks being stable thioglycosides,
7
Scheme 1. Synthesis of the left hand side disaccharide unit.
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M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
3
Table 1
Stereoselective coupling of Bac donors with L-serine acceptor
Br2
O
N3
AcO
N3
Br
14
O
N3
SPh
AcO
N3
O
N3
AcO
1. NBS, THF, H2O
12
N
3O
2. CCl3CN, DBU
72% Over 2 steps
CCl3
NH
15
HO
O
N3
O
Conditions
Table 3
N3
AcO
RO
N3
O
X
N3
CbzHN
CO2Me
16
12/14/15
CbzHN
CO2Me
R = Ac
, R = H
17
18
,
α
Et3N, MeOH
80%
Entry
Donor
Promotor
TMSOTf
Ph2SO/Tf2O
TBAI
Temp (°C)
Solvent
Time (h)
a
/b
Yield (%)
1
Imidate 15
Thioglycoside 12
Bromide 14
ꢀ78
ꢀ60
rt
THF
CH2Cl2
CH2Cl2
4
1
10
1.8/1
2.0/1.0
1.0/0
93
78
52
2
3a
a
Yield over 2 steps.
could be easily transformed into other donors such as halides and
imidates.24 Thus, reaction of 12 with Br2 in dichloromethane gen-
erated the corresponding glycosyl bromide 14, whereas treatment
of 12 with aqueous NBS generated the corresponding anomeric
hemiacetals, which were readily converted into imidate 15
(Table 1).
18 under TMSOTf activation failed to give any coupling product
(Scheme 3). The imidate was too reactive and spontaneously decom-
posed even at ꢀ78 °C. Use of AgOTf29 in place of TMSOTf at ꢀ50 °C
also gave similar results. So, we resorted to the corresponding
glycosyl chlorides which could be generated from the OMP glyco-
sides.30 A combination of AcCl, BF3ꢁOEt2 and cat. ZnI2 converted the
Earlier, we were successful in achieving a complete
lectivity in the glycosylation of a 3-O-AcCl, 4-O-Ac, 6-O-TBDPS
-GalN3 thioglycoside25 with
-serine derivative 16, using diphenyl
a
-stereose-
a-anomeric OMP in 8 into chloride to afford the donor 20 in 72%
yield.14b Chloride 20 underwent a facile AgOTf promoted glycosyla-
tion with the Bac acceptor 18, to afford exclusively -linked product
21(1HNMRd 4.76, d, J1 ,2 = 3.7 Hz, H-10), in82%yield(Scheme3). The
-selectivity in this case is presumably arising through the interme-
D
L
a
0
0
sulfoxide and Tf2O combination, essentially under Boons’ condi-
tions.26 Subsequently we found that these reaction conditions did
not work well for DATDH and after screening several donors and
a
diacy of the a highly reactive glycosyl b-triflate or more likely a
reaction conditions, we were able to achieve excellent
a-selectivity
solvent separated contact ion pair,28c which undergoes a nucleophilic
using trichloroacetimidate donor under TMSOTf activation condi-
tions and using THF as a participating solvent27 at ꢀ78 °C.14b In
continuation of these studies, we employed the same conditions
for glycosylation of the bacillosamine derivative 12. To our dismay,
the corresponding imidate 15 under the same conditions of solvent
participation did not give good selectivity (Table 1, entry 1). The
displacement with acceptor 18 from
a-face to afford the desired
trisaccharide 21 with exclusive -selectivity.
a
Deprotection of 21 involving Staudinger reduction of azide gen-
erated the corresponding amine, which was treated with acetic
anhydride to afford the desired N-acetylated product 22 in 72%
yields. Then benzyl groups were oxidatively31 removed in the pres-
ence of Cbz group under Iadonisi’s conditions using NaBrO3 and
Na2S2O4 to obtain the diol 23 in 85% yield. Finally de-O-acetylation
and simultaneous hydrolysis of methyl ester32 afforded the target
molecule 24, in 89% yield.
desired product 17 was obtained as 1.8:1 a:b mixture (93%) which
was inseparable on TLC. Activation of thioglycoside 12 using
Ph2SO/Tf2O combination as promoter also showed similar results
(Table 1, entry 2). For practical purpose, since the isomers could
not be separated by column chromatography, it was necessary to
get only a-product in this glycosylation. The exclusive a-selectivity
3. Conclusion
was finally achieved using glycosyl bromide under in situ anomer-
ization conditions.28 Accordingly, thioglycoside 12 was converted
Bacterial glycoproteomics is an emerging area of research.9,33
Synthesis of the O-glycans of N. meningitidis is a crucial step
towards understanding the role of pilin glycosylation in pathogen-
esis. We have carried out the first total synthesis of the bacillos-
into corresponding
pling with acceptor 16 in the presence of TBAI to afford the desired
-isomer 17 in 52% yields over 2 steps (Table 1, entry 3). Selective
a-bromide 14, which underwent a facile cou-
a
removal of the acetyl group in 17 using Et3N and methanol combi-
nation revealed 3-OH acceptors 18 (80%).
amine containing L-serine linked trisaccharide present on the pili
of N. meningitidis in an efficient manner. Final compound 24 is well
suited for incorporation into the protein for the synthesis of the
glycoprotein which can be further used for studying the biological
role of the pilin glycans. The total synthesis entails two consecutive
2.4. Synthesis of the L-serine linked O-trisaccharides
With the left hand disaccharide unit 8 and right hand glycosyl
amino acid acceptor 18 in hand, the stage was now set for the crucial
[2+1] relay glycosylation. First the OMP glycoside was hydrolysed by
using ceric ammonium nitrate (CAN) and the so formed anomeric
hemiacetal was smoothly converted into an imidate 19 (76% over 2
steps). Unfortunately, glycosylation of imidate 19 with the acceptor
a
-glycosylations involving the bacterial rare deoxy amino sugar
Bac. In this endeavour, we also studied for the first time the cou-
pling of bacillosamine with -serine derivative and established
the conditions to obtain exclusive -selectivity. These studies will
L
a
be useful for the synthesis of other Bac containing bacterial
glycans.
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M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
OAc
AcO
O
1.CAN, H2O
OBz
O
O
AcO
2.CCl3CN, DBU
18, TMSOTf
No
AcO
BnO
19
product
76% Over 2 steps
BnO
O
CCl3
NH
8
OAc
O
AcO
AcO
18
, AgOTf, MS, Sym
AcCl, BF3-Et2O,
cat. ZnI2
collidine, -30 °C,
OBz
O
O
CH2Cl2
AcO
72%
BnO
82%
BnO
Cl
20
OAc
AcO
OAc
O
AcO
AcO
O
OBz
O
OBz
O
O
AcO
O
AcO
BnO
1. PPh3, H2O, Py, THF
2. AcCl, Py
AcO
BnO
BnO
BnO
N3
72% Over 2 steps
O
AcHN
O
O
O
AcHN
N3
O
O
22
21
CbzHN
CO2Me
CbzHN
CO2Me
OH
OAc
O
HO
HO
AcO
AcO
O
OH
OBz
O
O
O
O
HO
AcO
HO
HO
NaOMe, MeOH,
H2O, 55 οC, 89%
HO
HO
NaBrO3, Na2S2O4,
H2O, EtOAc, 85%
O
O
AcHN
AcHN
O
O
AcHN
AcHN
O
O
24
23
CbzHN
CO2H
CbzHN
CO2Me
Scheme 3. Synthesis of the trisaccharide 24.
added, the mixture was concentrated and the residue was co-evap-
orated twice with toluene.
4. Experimental section
4.1. General methods
The residue which was obtained after solvent removal was dis-
solved in CH2Cl2 (3 mL) and added to a solution of acceptor 416
(0.0.28 g, 0.5 mmol) in CH2Cl2 (3 mL) containing 3 Å MS (0.6 g).
The mixture was stirred under nitrogen for 30 min at rt, after
which the temperature was lowered to ꢀ50 °C and AgOTf (0.19 g,
0.75 mmol) was added. After 2 h Et3N was added, and the stirring
was continued for 10 min. The mixture was diluted with CH2Cl2,
filtered through celite and concentrated. The residue was purified
by silica gel chromatography (20% ethyl acetate/petroleum ether)
to give the desired product 5 as a yellowish liquid (0.17 g, 32%).
All reactions were conducted under a dry nitrogen atmosphere.
Solvents (CH2Cl2 >99%, THF 99.5%, acetonitrile 99.8%, DMF 99.5%)
were purchased in capped bottles and dried under sodium or
CaH2. All other solvents and reagents were used without further
purification. All glassware used were oven dried before use. TLC
was performed on pre-coated Aluminum plates of Silica Gel 60
F254 (0.25 mm, E. Merck). Developed TLC plates were visualized
under a short-wave UV lamp and by heating plates that were
dipped in ammonium molybdate/cerium (IV) sulfate solution. Sil-
ica gel column chromatography was performed using Silica Gel
(100-200 mesh) and employed a solvent polarity correlated with
TLC mobility. NMR experiments were conducted on 400 MHz
instrument using CDCl3 (D, 99.8%) or (CD3)2CO (D, 99.9%) or CD3OD
(99.8%) as solvents. Chemical shifts are relative to the deuterated
solvent peaks and are in parts per million (ppm). 1H–1H COSY
was used to confirm proton assignments. Mass spectra were
acquired in the ESI mode using Q-TOF analyser. Specific rotation
experiments were measured at 589 nm (Na) and 20 °C. IR spectra
were recorded on an FT-IR spectrometer using CsCl plates.
4.2.2. Through imidate
TMSOTf (0.03 mL, 0.16 mmol) was added drop wise to a solu-
tion of imidate 618 (0.39 g, 0.79 mmol), acceptor 416 (0.3 g,
0.55 mmol) and 3 Å MS (0.6 g) at rt and the reaction mixture was
allowed to stir at the same temperature for 4 h. After 4 h the mix-
ture was diluted with CH2Cl2, filtered through celite and concen-
trated. The residue was purified by silica gel chromatography
(20% ethyl acetate/petroleum ether) to give the desired product 5
20
as a yellowish liquid (0.07 g, 15%): [
a]
+8.9 (c 0.31, CHCl3); IR
D
(CHCl3)
m
3020, 2927, 1751, 1422, 1216, 1048, 669 cmꢀ1 1H
;
NMR (400 MHz, CDCl3) d 8.08 (d, J = 7.0 Hz, 2H, ArH), 7.63–7.28
(m, 15H, ArH), 7.19–7.10 (m, 3H, ArH), 5 .37 (d, J = 3.2 Hz, 1H,
H-40), 5.28 (ap.t, J = 10.0, 7.8 Hz, IH, H-20), 5.05 (dd, J = 10.0,
3.2 Hz, 1H, H-30), 4.90–4.62 (m, 7H, H-1, H-10, H-6a, ArH), 4.53–
4.48 (m, 1H, H-6b), 4.12 (d, J = 6.8 Hz, 2H, H-60), 4.05
(d, J = 3.0 Hz, 1H, H-4), 3.82 (t, J = 6.4, Hz, IH, H-50), 3.78–3.75 (m,
1H, H-5), 3.69 (t, J = 10.0, Hz, IH, H-2), 3.58 (dd, J = 10.0,
J = 3.0 Hz, 1H, H-3), 2.18 (s, 3H, CH3), 2.03 (s, 6H, CH3), 1.92
4.2. Phenyl 2,3,4,6-tetra-O-acetyl-b-
D-galctopyranosyl-(1?4)-6-
O-benzoyl-2,3-dibenzyl-1-thio- -galactopyranoside (5)
a-D
4.2.1. Through glycosyl bromide
Bromine (0.09 mL, 1.7 mmol) was added to a solution of 315
(0.35 g, 0.79 mmol) in CH2Cl2 (9 mL). After 30 min, toluene was
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M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
5
(s, 3H, CH3); 13C NMR (100 MHz, CDCl3) d170.6, 170.5, 170.4, 169.5,
166.5, 138.1, 137.9, 134.7, 133.3, 131.3, 130.1, 129.8, 129.7, 128.9,
128.7, 128.6, 128.4, 128.3, 128.1, 127.2, 102.2, 88.5, 83.2, 77.8,
76.1, 75.9, 75.5, 73.7, 71.0, 70.5, 69.1, 67.0, 64.9, 61.5, 21.0, 20.85,
20.82, 20.8; HR-ESI-MS (m/z): [M+Na]+ calcd for C47H50O15SNa,
909.2768; found, 909.2761.
4.68 (dd, J = 10.0, 3.0 Hz, 1H, H-3), 4.50 (d, J = 10.0 Hz, 1H, H-1),
3.76–3.70 (m, 2H, H-2
& H-5), 2.13 (s, 3H, CH3), 1.26
(d, J = 6.4 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3) d 169.7, 133.9,
130.5, 129.2, 129.0, 120.0, 116.8, 86.7, 85.3, 73.2, 69.8, 59.8, 20.4,
16.7; HR-ESI-MS (m/z): [M+Na]+ calcd for C15H16F3N3O6NaS2,
478.0325; found, 478.0322.
4.3. Phenyl 2-azido-3-O-acetyl-2,6-dideoxy-1-thio-b-
D-
4.5. 3-O-Acetyl-2,4-diazido-2,4,6-trideoxy-a-D-glucopyranosyl
galactopyranoside (10)
trichloroacetimidate (15)
Tf2O (11.4 mL, 67.5 mmol) and pyridine (11.8 mL, 146.4 mmol)
were added sequentially at ꢀ10 °C to a stirred solution of 9 (3.36 g,
11.2 mmol) in CH2Cl2 (150 mL). Then the reaction mixture was
gradually warmed to 10 °C over 2 h. After complete consumption
of the starting material, the reaction mixture was diluted with CH2-
Cl2 and washed successively with 1 M HCl, aq. NaHCO3 and brine.
Separated organic layer was dried over Na2SO4 and concentrated.
The crude product which was obtained after removal of sol-
vents was dissolved in acetonitrile (200 mL) and to this, TBAN3
(3.1 g, 10.0 mmol) was added at ꢀ30 °C and the reaction was stir-
red at the same temperature for 20 h. TBANO2 (4.8 g, 16.9 mmol)
was added and the reaction mixture stirred at rt for 1 h. The reac-
tion mixture was diluted with EtOAc and washed with water. Sep-
arated organic layer was dried over Na2SO4 and concentrated in
vacuo. The crude product was purified by column chromatography
on silica gel (1:9 ethyl acetate/pet ether) to obtain 10 as a pale yel-
lowish viscous liquid (2.3 g, 61%): 1H NMR (400 MHz, CDCl3) d
7.62–7.58 (m, 2H, ArH), 7.37–7.31 (m, 3H, ArH), 5.12 (d,
J = 3.0 Hz, 1H, H-4 of 11), 4.79 (dd, J = 10.0, 3.0 Hz, 1H, H-3), 4.46
(d, J = 10.0 Hz, 1H, H-1), 3.85 (d, J = 3.0 Hz, 1H, H-4), 3.74–3.63
(m, 2H, H-2 & H-5), 3.50 (t, J = 10.0 Hz, 1H, H-2 of 11), 2.15 (s,
3H, CH3), 1.42 (d, J = 6.4 Hz, 3H, CH3 of 11), 1.33 (d, J = 6.4 Hz, 3H,
CH3); 13C NMR (100 MHz, CDCl3) d 170.2, 133.5, 133.2, 131.4,
129.2, 129.0, 128.6, 128.3, 86.5, 76.0, 74.7, 73.4, 73.0, 72.2, 69.3,
62.5, 59.4, 21.12, 16.9, 16.7; HR-ESI-MS (m/z): [M+Na]+ calcd for
NBS (1.0 g, 6.0 mmol) was added at 0 °C to a cooled solution of
12 (0.7 g, 2.0 mmol) in THF/H2O (30 mL, 4:1). After 10 min. reac-
tion mixture was brought to rt and stirred for 30 min. Then sol-
vents were evaporated and the crude product was purified by
column chromatography on silica gel (20% ethyl acetate/pet ether)
to afford the desired hemiacetal as a viscous liquid (0.45 g, 88%).
DBU (70
l
L, 0.47 mmol) was added at ꢀ5 °C to the solution of
hemiacetal (0.4 g, 1.56 mmol) and Cl3CCN (1.9 mL, 19.0 mmol) in
CH2Cl2 (10 mL) and the reaction mixture was stirred at the same
temperature for 1 h. The mixture was concentrated under reduced
pressure and the crude product was purified by column chroma-
tography on silica gel (10% ethyl acetate/pet ether) to afford 15
as a white foam (0.45 g, 72%): 1H NMR (400 MHz, CDCl3) d 8.77
(s, 1H, NH), 6.39 (d, J = 3.5 Hz, 1H, H-1), 5.49 (t, J = 10.0 Hz, 1H,
H-3), 3.91 (q, J = 6.4 Hz, 1H, H-5), 3.59 (dd, J = 10.0, 3.5 Hz, 1H,
H-2), 3.27 (t, J = 10.0 Hz, 1H, H-4), 2.20 (s, 3H, CH3), 1.35 (d,
J = 6.4 Hz, 3H).
4.6. N-(Benzyloxycarbonyl)-O-(3-O-acetyl-2,4-diazido-2,4,6-
trideoxy-a-D-glucopyranosyl)-L-serine methylester (17)
Bromine (0.12 mL, 0.2.4 mmol) was added to a solution of 12
(0.45 g, 1.09 mmol) in CH2Cl2 (14 mL). After 1 h, toluene was
added, the mixture was concentrated and the residue was co-evap-
orated twice with toluene.
C
14H17N3O4NaS, 346.0832; found, 346.0827.
The residue in CH2Cl2 (2.5 mL) was added to a solution of ami-
noacid acceptor 16 (0.0.41 g, 0.1.6 mmol), 3 Å MS (0.5 g) and TBAI
(1.2 g, 3.3 mmol) in CH2Cl2 (2.5 mL). After 8 h the mixture was
diluted with CH2Cl2, filtered through celite and concentrated. The
residue was purified by silica gel chromatography to give the
4.4. Phenyl 2,4-diazido-3-O-acetyl-2,4,6-trideoxy-1-thio-b-D-
glucopyranoside (12)
Tf2O (0.9 mL, 5.38 mmol) was added drop wise at ꢀ10 °C to a
stirred solution of 10 (1.45 g, 4.48 mmol) and pyridine (2.2 mL,
26.9 mmol) in CH2Cl2 (20 mL) and this solution was gradually
brought to 10 °C over 2 h. After complete consumption of starting
material, reaction mixture was concentrated in vacuo and the
crude product was used for the next step without purification.
The crude product which was obtained in above step was dis-
solved in DMF (30 mL) and to this, NaN3 (2.9 g, 44 mmol) was
added. The reaction mixture was stirred at rt for 10 h and then it
was diluted with EtOAc and washed with water. Separated organic
layer was dried over Na2SO4 and concentrated in vacuo. The crude
product was purified by column chromatography (10% ethyl ace-
tate/pet ether) to afford 12 as a white solid (1.17 g, 75%) and in this
desired product 17 as a pasty white solid (0.28 g, 52% over 2 steps,
20
only
a
-isomer): [
a]
+86.6 (c 0.74, CHCl3); IR (CHCl3)
m
3019,
D
2928, 2109, 1750, 1714, 1512, 1216, 1042, 669 cmꢀ1
;
1H NMR
(400 MHz, CDCl3) d 7.37–7.29 (m, 5H, ArH), 5.75 (d, J = 8.0 Hz,
1H, NH), 5.32 (t, J = 10.0 Hz, 1H, H-3), 5.13 (s, 2H, CH2 of Cbz),
4.87 (d, J = 3.5 Hz, 1H, H-1), 4.57–4.54 (m, 1H, –CH), 4.01 (dq,
J = 10.5, 3.1 Hz, 1H, –CH2), 3.78 (s, 3H, CH3), 3.74–3.63 (m, 1H,
H-5), 3.15 (t, J = 10.0 Hz, 1H, H-4), 3.07 (dd, J = 10.0, 3.5 Hz, 1H,
H-2), 2.16 (s, 3H, CH3), 1.27 (d, J = 6.2 Hz, 3H, CH3); 13C NMR
(100 MHz, CDCl3) d 170.1, 169.9, 156.0, 136.2, 128.7, 128.4,
128.3, 98.9, 70.4, 69.0, 67.3, 66.8, 66.2, 61.2, 54.4, 53.1, 20.9,
18.2; HR-ESI-MS (m/z): [M+Na]+ calcd for C20H25N7O8Na,
514.1657; found, 514.1658.
reaction 13 was obtained as side product in 11% yield. Data of 12:
20
[
a]
ꢀ41.5 (c 0.61, CHCl3); IR (CHCl3)
m
3020, 2927, 2111, 1759,
4.7. N-(Benzyloxycarbonyl)-O-(2,4-diazido-2,4,6-trideoxy-
a-D-
D
1216, 1047, 669 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d 7.56–7.54 (m,
glucopyranosyl)- -serine methylester (18)
L
2H, ArH), 7.35–7.32 (m, 3H, ArH), 5.02 (t, J = 10.0 Hz, 1H, H-3),
4.47 (d, J = 10.0 Hz, 1H, H-1), 3.36–3.28 (m, 2H, H-2 & H-5), 3.12
(t, J = 10.0 Hz, 1H, H-4), 1.38 (d, J = 6.2 Hz, 3H, CH3); 13C NMR
(100 MHz, CDCl3) d 169.7, 133.8, 130.8, 129.2, 128.8, 85.9, 75.0,
74.6, 65.4, 63.1, 20.8, 18.6; HR-ESI-MS (m/z): [M+Na]+ calcd for
Et3N (1 mL) was added to a clear solution of 17 (0.2 g, 0.4 mmol)
in MeOH (4 mL) and the reaction mixture kept for stirring at rt
overnight in the dark. After complete consumption of starting
material solvents were removed in vacuo and the crude product
was chromatographed by silica gel column chromatography (30%
C
14H16N6O3NaS, 371.0897; found, 371.0889; Data of 13 (pale
20
yellowish viscous liquid): [
a
]
ꢀ36.8 (c 1.83, CHCl3); IR (CHCl3)
ethyl acetate/pet ether) to afford 18 as a viscous liquid (0.15 g,
D
20
m
2988, 2855, 2117, 1755, 1419, 1245, 1220, 1142, 1077, 892,
80%): [
a
]
+158.5 (c 0.19, CHCl3); IR (CHCl3)
m
3430, 3020,
1H NMR (400 MHz,
CDCl3) d 7.37–7.29 (m, 5H, ArH), 5.87 (d, J = 8.0 Hz, 1H, NH), 5.12
D
749, 693, 617 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d 7.64–7.62
2934, 2110, 1721, 1216, 1042, 669 cmꢀ1
;
(m, 2H, ArH), 7.37–7.33 (m, 3H, ArH), 5.36 (d, J = 3.0 Hz, 1H, H-4),
Please cite this article in press as: Emmadi, M.; Kulkarni, S. S. Carbohydr. Res. (2014), http://dx.doi.org/10.1016/j.carres.2014.04.011

6
M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
(s, 2H, CH2 of Cbz), 4.80 (d, J = 3.4 Hz, 1H, H-1), 4.57–4.55 (m, 1H, –
CH), 3.95 (d, J = 2.8 Hz, 2H, –CH2), 3.94 (t, J = 10.0 Hz, 1H, H-3), 3.77
(s, 3H, CH3), 3.61–3.51(m, 1H, H-5), 3.15 (dd, J = 10.0, 3.4 Hz, 1H,
H-2), 3.04 (t, J = 10.0 Hz, 1H, H-4), 1.25 (d, J = 6.2 Hz, 3H, CH3);
13C NMR (100 MHz, CDCl3) d 170.37, 156.1, 136.1, 128.7, 128.4,
128.3, 98.5, 70.3, 68.5, 68.7, 67.3, 67.0, 63.1, 54.4, 53.0, 18.2;
HR-ESI-MS (m/z): [M+Na]+ calcd for C18H23N7O7Na, 472.1551;
found, 472.1548.
20.7, 20.6, 18.2; HR-ESI-MS (m/z): [M+Na]+ calcd for C59H67O22N7
Na, 1248.4231; found, 1248.4244.
4.10. N-(Benzyloxycarbonyl)-O-(2,3,4,6-tetra-O-acetyl-b-
galctopyranosyl-(1?4)-6-O-benzoyl-2,3-dibenzyl-
galactopyranosyl-(1?3)-2,4-diacetimido-2,4,6-trideoxy-
glucopyranosyl)- -serine methylester (22)
D-
a-D-
a-D-
L
Pyridine (0.15 mL, 1.9 mmol) and water (35 lL, 1.9 mmol) were
4.8. 2,3,4,6-Tetra-O-acetyl-b-
benzoyl-2,3-dibenzyl- -galactopyranosyl
Trichloroacetimidate (19)
D
-galctopyranosyl-(1?4)-6-O-
added to a clear solution of trisaccharide 21 (0.23 g, 0.19 mmol)
and PPh3 (0.2 g, 0.77 mmol) in THF (4 mL) and then the reaction
mixture was kept for reflux for 4 h at 70 °C. Then solvents were
removed in vacuo and the crude product was dissolved in pyridine
(3 mL) and Ac2O (0.36 mL, 3.8 mmol) was added. After stirring the
reaction mixture at rt for 10 h solvents were removed under
reduced pressure and the crude product was chromatographed
a-D
CAN (0.6 g) was added at ꢀ10 °C to a cooled solution of 8 (0.5 g,
0.55 mmol) in CH3CN (15 mL) and water (3 mL). After stirring at
the same temperature for 2 h, the reaction mixture was neutralized
with aq. NaHCO3 and extracted with EtOAc (50 mL). Separated
organic layer was dried over Na2SO4, filtered and
chromatographed.
on silica gel (60% ethyl acetate/pet ether) to obtain 22 as a foam
20
(0.175 g, 72%): [
a]
+29.1 (c 1.0, CHCl3); IR (CHCl3)
m
3210,
D
3020, 2923, 1747, 1679, 1517, 1371, 1216, 1056 cmꢀ1
;
1H NMR
DBU (24
l
L, 0.14 mmol) and CCl3CN (0.29 mL, 5.8 mmol) were
(400 MHz, CDCl3) d 8.03 (d, J = 7.4 Hz, 2H, ArH), 7.67–7.28 (m,
18H, ArH), 6.21 (d, J = 8.4 Hz, 1H, NH), 5.89 (d, J = 9.4 Hz, 1H, NH),
5.81 (d, J = 7.0 Hz, 1H, NH), 5.29 (d, J = 3.0 Hz, 1H, H-400), 5.17 (ap.t,
J = 10.0, 7.8 Hz, IH, H-200), 5.11–5.07 (m, 2H, CH2 of Cbz), 5.00 (d,
J = 2.0 Hz, 1H, H-1), 4.95 (dd, J = 10.0, 3.4 Hz, 1H, H-300), 4.78–4.54
(m, 9H), 4.29–4.13 (m, 2H), 4.06–3.93 (m, 3H), 3.87–3.78 (m,
5H), 3.74 (s, 3H, CH3), 3.69–3.66 (m, 2H), 3.54 (t, J = 10.0 Hz, 1H,),
2.09 (s, 3H, CH3), 1.97 (s, 3H, CH3), 1.87 (s, 3H, CH3), 1.83 (s, 3H,
CH3), 1.79 (s, 3H, CH3), 1.60 (s, 3H, CH3), 1.10 (d, J = 6.2 Hz, 3H,
CH3); 13C NMR (100 MHz, CDCl3) d 170.9, 170.6, 170.4, 170.3,
170.1, 169.9, 166.6, 156.2, 138.0, 136.2, 133.4, 132.2, 132.16,
132.10, 129.9, 128.9, 128.7, 128.64, 128.60, 128.5, 128.2, 128.1,
102.3, 98.9, 78.3, 75.9, 74.5, 73.7, 70.9, 70.3, 69.3, 68.8, 67.9,
67.2, 66.7, 62.7, 60.9, 67.6, 54.5, 53.0, 52.8, 23.3, 23.2, 21.0, 20.7,
20.6, 1801; HR-ESI-MS (m/z): [M+Na]+ calcd for C63H75O24N3Na,
1280.4633; found, 1280.4670.
added at ꢀ5 °C to a cooled solution of hemiacetal in CH2Cl2
(8 mL). After 1 h, solvents were removed under reduced pressure
and chromatographed on silica gel (30% ethyl acetate /petroleum
ether) to give the desired imidate 19 as a foam (0.39 g, 76% over
2 steps): 1H NMR (400 MHz, CDCl3) d 8.51 (s, 1H, NH), 7.95 (d,
J = 7.2 Hz, 2H, ArH), 7.56–7.52 (m, 1H, ArH), 7.43–7.27 (m, 12H,
ArH), 6.51 (d, J = 3.0 Hz, 1H, H-1), 5.36 (d, J = 3.2 Hz, 1H, H-40),
5.19 (ap.t, J = 10.0, 7.8 Hz, 1H, H-20), 5.01 (dd, J = 10.0, 3.2 Hz, 1H,
H-30), 4.83–4.59 (m, 6H), 4.41–4.37 (m, 1H), 4.30–4.27 (m, 1H),
4.16 (d, J = 1.3 Hz, 1H, H-4), 4.07–3.97 (m, 4H), 3.82 (t, J = 6.4 Hz,
IH), 2.14 (s, 3H, CH3), 1.997 (s, 3H, CH3), 1.995 (s, 3H, CH3), 1.83
(s, 3H, CH3); 13C NMR (100 MHz, CDCl3): d 170.6, 170.5, 170.4,
169.9, 166.4, 161.1, 138.3, 138.2, 133.2, 130.1, 129.8, 128.7,
128.6, 128.5, 128.3, 128.1, 128.04, 128.0, 127.8, 127.5, 102.3,
94.8, 91.4, 76.3, 76.0, 73.9, 73.3, 71.2, 70.9, 70.6, 69.1, 67.0, 64.7,
61.6, 20.9, 20.8, 20.8.
4.11. N-(Benzyloxycarbonyl)-O-(2,3,4,6-tetra-O-acetyl-b-
galctopyranosyl-(1?4)-6-O-benzoyl- -galactopyranosyl-
-glucopyranosyl)-L-
D-
4.9. N-(Benzyloxycarbonyl)-O-(2,3,4,6-tetra-O-acetyl-b-
galctopyranosyl-(1?4)-6-O-benzoyl-2,3-dibenzyl-
galactopyranosyl-(1?3)-2,4-diazido-2,4,6-trideoxy-
glucopyranosyl)- -serine methylester (21)
D
-
a-D
a
-
a
D
-
D
(1?3)-2,4-diacetimido-2,4,6-trideoxy-
a
-
D
-
-
serine methylester (23)
L
A solution of NaBrO3 (0.07 g, 0.47 mmol) in water (1.5 mL) was
added to a clear solution of 22 (0.1 g, 0.08 mmol) in EtOAc
(1.1 mL). To this biphasic layer a solution of Na2S2O4 (0.07 g,
0.0.4 mmol) in water (2 mL) was added dropwise over 5 min.
After 45 min. the reaction mixture was quenched with aq Na2S2O3
solution and extracted with EtOAc (30 mL ꢂ 3). Combined organic
layers were dried over Na2SO4, concentrated and chromato-
AgOTf (0.18 g, 0.7 mmol) was added to a premixed solution of
glycosyl chloride 2014b (0.28 g, 0.35 mmol), acceptor 18 (0.13 g,
0.29 mmol), sym. collidene (45 lL, 0.32 mmol) and 3 Å MS in CH2-
Cl2 (8 mL) at ꢀ30 °C and the reaction mixture was stirred at the
same temperature for 3 h. The reaction mixture was quenched
with Et3N and the mixture was filtered through celite. Filtrate
was concentrated in vacuo and chromatographed on silica gel
graphed on silica gel (5% methanol/ethyl acetate) to afford the
20
(35% ethyl acetate/pet ether) to obtain 21 as a foam (0.29 g,
desired product 23 as a white solid (72 mg, 85%): [
a]
+51.3
D
20
82%): [
a]
+54.2 (c 0.55, CHCl3); IR (CHCl3)
m
3020, 2928, 2108,
(c 0.59, MeOH); IR (MeOH)
m
;
3409, 2946, 2833, 2518, 2043,
D
1748, 1216, 1052, 669 cmꢀ1
;
1H NMR (400 MHz, CDCl3) d 8.01 (d,
1740, 1663, 1450, 1030 cmꢀ1
1H NMR (400 MHz, CD3OD) d
J = 7.2 Hz, 2H, ArH), 7.55 (t, J = 7.2 Hz, 1H, ArH), 7.46–7.28 (m,
17H, ArH), 5.72 (d, J = 8.0 Hz, 1H, NH), 5.33–5.29 (m, 2H, H-1 &
H-400), 5.19 (ap.t, J = 10.0, 7.8 Hz, 1H, H-200), 5.12 (s, 2H, CH2 of
Cbz), 4.97 (dd, J = 10.0, 3.4 Hz, 1H, H-300), 4.83–4.77 (m, 3H), 4.76
8.05 (d, J = 7.4 Hz, 2H, ArH), 7.62 (t, J = 7.4 Hz, 1H, ArH), 7.50 (t,
J = 7.4 Hz, 2H, ArH), 7.36–7.27 (m, 5H, ArH), 5.26 (d, J = 2.6 Hz,
1H), 5.10–5.06 (m, 4H), 5.00 (d, J = 3.8 Hz, 1H), 4.67–4.61 (m,
4H), 4.45 (t, J = 4.0 Hz, 1H), 4.19–4.06 (m, 4H), 3.94–3.74 (m,
7H), 3.70 (s, 3H, CH3), 3.58 (dd, J = 10.0, 3.8 Hz, 1H), 3.49–3.46
(m, 1H), 2.09 (s, 3H, CH3), 2.89 (s, 3H, CH3), 1.97 (s, 3H, CH3),
1.92 (s, 3H, CH3), 1.81 (s, 3H, CH3), 1.78 (s, 3H, CH3), 1.13
(d, J = 6.4 Hz, 3H, CH3); 13C NMR (100 MHz, CD3OD) d 174.3,
173.6, 172.4, 172.3, 172.2, 171.8, 171.6, 167.5, 158.6, 137.9,
134.7, 131.1, 130.8, 129.9, 129.6, 129.3, 129.2, 103.3, 102.2,
99.9, 78.0, 77.6, 72.3, 71.3, 70.8, 70.3, 69.4, 69.0, 68.5, 68.3,
68.1, 63.4, 62.1, 58.5, 56.0, 54.5, 53.1, 23.2, 23.0, 21.2, 20.6,
20.4, 18.1; HR-ESI-MS (m/z): [M+H]+ calcd for C49H64O24N3Na,
1078.3879; found, 1078.3871.
(d, J1 ,2 = 3.7 Hz, IH, H-10), 4.73–4.63 (m, 3H), 4.49–4.47 (m, 1H,
CH), 4.40–4.32 (m, 2H), 4.16 (d, J = 1.6 Hz, 1H), 4.01–3.86 (m,
5H), 3.77–3.72 (m, 3H), 3.70 (s, 3H, CH3), 3.67–3.37 (m, 1H),
3.09–3.00 (m, 2H, H-2 & H-4), 2.11 (s, 3H, CH3), 1.97 (s, 3H, CH3),
1.92 (s, 3H, CH3), 1.76 (s, 3H, CH3), 1.24 (d, J = 6.4 Hz, 3H, CH3);
13C NMR (100 MHz, CDCl3) d 170.46, 170.4, 170.3, 170.1, 169.7,
166.3, 155.9, 138.5, 138.4, 136.2, 133.1, 130.3, 129.7, 128.66,
128.61, 128.5, 128.48, 128.3, 128.2, 128.0, 127.8, 127.7, 127.6,
102.0, 99.2, 99.0, 78.0, 76.1, 75.8, 75.5, 73.9, 73.6, 70.9, 70.4, 69.2,
69.0, 68.9, 68.7, 67.2, 67.1, 66.8, 64.0, 61.9, 61.2, 54.3, 53.0, 20.8,
0
0
Please cite this article in press as: Emmadi, M.; Kulkarni, S. S. Carbohydr. Res. (2014), http://dx.doi.org/10.1016/j.carres.2014.04.011

M. Emmadi, S. S. Kulkarni / Carbohydrate Research xxx (2014) xxx–xxx
7
J. Am. Chem. Soc. 2005, 127, 13766–13767; (d) Amin, M. N.; Ishiwata, A.; Ito, Y.
Carbohydr. Res. 2006, 341, 1922–1929; (e) Bedini, E.; Esposito, D.; Parrilli, M.
Synlett 2006, 825–830; (f) Leonori, D.; Seeberger, P. H. Org. Lett. 2012, 14, 4954–
4957.
4.12. N-(Benzyloxycarbonyl)-O-(b-
galactopyranosyl-(1?3)-2,4-diacetimido-2,4,6-trideoxy-
glucopyranosyl)- -serine (24)
D-galctopyranosyl-(1?4)-a-D-
a-D-
L
12. For previous synthesis of DATDG see (a) Hermans, J. P. G.; Elie, C. J. J.; van der
Marel, G. A.; van Boom, J. H. J. Carbohydr. Chem. 1987, 6, 451–462; (b) Liav, A.;
Jacobsen, I.; Sheinblatt, M.; Sharon, N. Carbohydr. Res. 1978, 66, 95–101; (c)
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1–4.
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(2 mL) at 50 °C (pH 10). After stirring the reaction mixture at the
same temperature for 20 h, the reaction mixture was neutralized
with AcOH until the pH adjusted to 6. Then solvents were removed
under reduced pressure and the crude product was chromato-
13. For previous synthesis of other rare sugars AAT and FucNAc see: (a) Lönn, H.;
Lönngren, J. Carbohydr. Res. 1984, 132, 39–44; (b) Smid, P.; Jörning, W. P. A.; van
Duuren, A. M. G.; Boons, G. J. P. H.; van der Marel, G. A.; van Boom, J. H. J.
Carbohydr. Chem. 1992, 11, 849–865; (c) Medgyes, A.; Farkas, E.; Lipták, A.;
Pozsgay, V. Tetrahedron 1997, 53, 4159–4178; (d) Liang, H.; Grindley, T. B. J.
Carbohydr. Chem. 2004, 23, 71–82; (e) van den Bos, L. J.; Boltje, T. J.; Provoost,
T.; Mazurek, J.; Overkleeft, H. S.; van der Marel, G. A. Tetrahedron Lett. 2007, 48,
2697–2700; (f) Cai, Y.; Ling, C.-C.; Bundle, D. R. J. Org. Chem. 2009, 74, 580–589;
(g) Pedersen, C. M.; Figueroa-Perez, I.; Lindner, B.; Ulmer, A. J.; Zähringer, U.;
Schmidt, R. R. Angew. Chem., Int. Ed. 2010, 49, 2585–2590; (h) Iynkkaran, I.;
Bundle, D. R. Carbohydr. Res. 2010, 345, 2323–2327; (i) Pragani, R.; Stallforth,
P.; Seeberger, P. H. Org. Lett. 2010, 12, 1624–1627; (j) Pragani, R.; Seeberger, P.
H. J. Am. Chem. Soc. 2011, 133, 102–107; (k) Christina, A. E.; Blas Ferrand, V. M.;
de Bordes, F.; Spruit, W. A.; Overkleeft, H. S.; Codée, J. D. C.; van der Marel, G. A.
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Beilstein J. Org. Chem. 2013, 9, 332–341; (p) Danieli, E.; Proietti, D.; Brogioni, G.;
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references cited therein.
graphed on silica gel (7:2:1 ethyl acetate/MeOH/H2O) to afford
20
the desired product 24 as a white solid (22 mg, 89%): [
+43.8 (c 0.32, MeOH); IR (MeOH)
1415, 1032, 688 cmꢀ1 1H NMR (400 MHz, CD3OD) d 7.38–7.29
a]
D
m
3544, 2831, 2522, 1661, 1449,
;
(m, 5H, ArH), 5.10 (d, J = 6.5 Hz, 2H), 4.97 (d, J = 2.8 Hz, 1H),
4.65–4.61 (m, 1H), 4.42 (d, J = 8.0 Hz, 1H), 4.22–4.16 (m, 1H),
4.06–4.03 (m, 2H), 3.88–3.33 (m, 16H), 2.03, 1.96 (2s, 3H, CH3),
1.89 (s, 3H, CH3), 1.05 (d, J = 6.4 Hz, 3H, CH3); 13C NMR
(100 MHz, CD3OD) d 180.3, 176.8, 174.1, 158.0, 129.6, 129.2,
129.0, 107.1, 102.2, 101.9, 99.4, 98.9, 80.5, 79.5, 78.2, 77.6, 77.1,
75.3, 73.4, 71.9, 71.6, 71.0, 70.5, 70.2, 68.3, 68.0, 67.8, 62.6, 61.1,
60.9, 58.2, 58.1, 57.7, 54.7, 24.2, 23.2, 18.2; HR-ESI-MS (m/z):
[M+Na]+ calcd for C33H48O19N3Na2, 836.2672; found, 836.2675.
Acknowledgements
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This work was supported by the Department of Science and
Technology (Grant No. SR/S1/OC-40/2009 and Council of Scientific
and Industrial Research (Grant No. 01(2376)/10/EMR-II). M.E.
thanks CSIR-New Delhi for a fellowship.
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Please cite this article in press as: Emmadi, M.; Kulkarni, S. S. Carbohydr. Res. (2014), http://dx.doi.org/10.1016/j.carres.2014.04.011