The Cyanopivaloyl Ester: A Protecting Group in the Assembly of Oligorhamnans

Article abstract of DOI:10.1002/ejoc.201600956

Protecting groups play a vital role in the assembly of oligosaccharides. The pivaloyl (Piv) ester is commonly used to ensure 1,2-trans-selective glycosylation reactions. A significant drawback of the Piv ester is its stability, necessitating strong alkali

Full text of DOI:10.1002/ejoc.201600956

A Journal of
Accepted Article
Title: The Cyanopivaloyl Ester: A New Protecting Group in the Assembly of Oligor-
hamnans
Authors: Anne Geert Volbeda; Niels Reintjens; Herman Overkleeft; Gijs Van Der
´
Marel; Jeroen Codee
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201600956
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European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
The Cyanopivaloyl Ester: A New Protecting Group in the
Assembly of Oligorhamnans
Anne Geert Volbeda,[a] Niels R.M. Reintjens,[a] Herman S. Overkleeft,[a] Gijsbert A. van der Marel[a] and
Jeroen D. C. Codée*[a]
Abstract: Protecting groups play a vital role in the assembly of
oligosaccharides. The pivaloyl (Piv) ester is commonly used to
ensure 1,2-trans selective glycosylation reactions. A significant
drawback of the Piv-ester is its stability, necessitating strong alkaline
conditions for its removal. We here present the cyanopivaloyl
(CNPiv) group: a modified pivaloyl group, having a cyano group
appended to the tert-butyl moiety. The CNPiv benefits from the
profitable features of the Piv-group (stability and effective
neighboring group participation with minimal orthoester formation
during glycosylation reactions) but can be removed under mild
conditions (reduction of the cyano function followed by mild base
treatment). The applicability of the CNPiv group is demonstrated in
the assembly of two rhamnose oligosaccharides: a hexarhamnan
that represents a fragment of the capsular polysaccharide of
Enterococcus faecium and a tetrarhamnan that is part of the
polyrhamnose backbone of the Lancefield group A carbohydrate
(GAC).
To enable cleavage of Piv-type esters under less strenuous
conditions, various Piv-analogues[7] have been introduced
bearing a masked nucleophile four or five atoms away from the
Piv-carbonyl group. Liberating this nucleophile sets the stage for
intramolecular attack allowing the smooth deprotection of the Piv
ester. Figure 1 depicts some members of the relay-cleavage
pivaloyl family. 2,2-Dimethylpentenoate 1[8] can be cleaved by
hydroboration of the double bond and ensuing base mediated
cleavage. Piv-analogues 2[9] and 3[10,11] bear a distal, masked
hydroxyl group that can be liberated by either fluoride or
methanolate to release the internal nucleophile. We have
recently introduced a para-methoxyphenyl caged Piv-ester 4[12]
and azido-Piv group 5[12] that can be removed under oxidative
(4) and reductive (5) conditions, respectively. We exploited the
mutual orthogonality of these Piv-groups in the assembly a
Streptococcus mutans oligosaccharide and also showed the
applicability of the azido-Piv group in the solid phase assembly
of a -glucan oligomer.[13] We here introduce a new relay-
cleavage pivaloyl family member: the cyanopivaloyl (CNPiv)
group (6, Figure 1). This group was developed to streamline the
global deprotection of oligosaccharides. We reasoned that a
pivaloyl group that is removable under hydrogenation conditions,
commonly employed to remove benzyl esters in the final stage
of an oligosaccharide synthesis, could abridge the endgame. As
described here, the reagents to introduce the CNPiv-goup,
cyanopivalic acid 8[14] and the corresponding acid chloride (9,
CNPivCl) can be readily synthesized on large scale and the
protective group can be easily introduced on carbohydrate
building blocks. It is stable under commonly used reaction
conditions and can be removed through reduction of the cyano-
function. We have applied the CNPiv group in the assembly of
Introduction
The success of an oligosaccharide or glycoconjugate synthesis
campaign hinges on the protecting group strategy followed.[1,2]
Protecting groups are key to discriminate the different hydroxyl
and amino groups on the carbohydrate rings and have an
important effect on the reactivity of the carbohydrate building
block.[3–6] As well, they can be decisive in the stereochemical
outcome of a glycosylation. Neighboring group participation by a
C-2-O-acyl group is an extremely powerful means to ensure the
stereoselective formation of 1,2-trans-glycosidic linkages. Of all
ester-type protecting groups, the pivaloyl (Piv) ester is least
prone to provide orthoester side products, formed by attack of
the nucleophile at the dioxolenium carbon instead of the
anomeric center. The neopentylic nature of the pivaloyl
dioxolenium ion makes this intermediate significantly less
susceptible to nucleophilic attack. Where this steric protection is
beneficial during a glycosylation reaction, the bulk of the Piv
group can pose a problem during the removal of this protecting
group, necessitating harsh nucleophilic conditions for its removal.
two bacterial rhamnan structures:
a
tetrasaccharide,
representing part of the backbone structure of the
exopolysaccharide of Group A Streptococcus[15,16], and an
Enterococcus faecium[17,18] derived hexarhamnoside.
[a]
Codée, J.D.C., van der Marel, G.A., Overkleeft, H.S., Reintjens,
N.R.M., Volbeda, A.G.
BioOrganic Synthesis, Leiden Institute of Chemistry
Leiden University
Einsteinweg 55, 2333CC, Leiden, The Netherlands
E-mail: jcodee@chem.leidenuniv.nl
Figure 1. Pivaloyl analogues and new CNPiv 6.
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
Results and Discussion
The assembly of the building blocks is depicted in Scheme 3.
Known diol 16[28] can be selectively alkylated on the C-3-OH
through the intermediacy of the cyclic tin ketal,[29] with either
The synthesis of required reagents, cyanopivalic acid and the
corresponding chloride (CNPiv-Cl) is depicted in Scheme 1.
They can be generated through a three or four step reaction
sequence in multigram quantities. Reaction of methyl isobutyrate
with bromoacetonitrile under the influence of freshly prepared
LDA, resulted in cyanide 7. Saponification of the methyl ester
then provided acid 8, which can be reacted with oxalylchloride to
yield acid chloride 9. Both reagents can be used without further
purification.
benzylbromide
or
para-methoxybenzylchloride
to
give
rhamnosides 17 and 18 in 86% and 73% yield respectively.
Esterification of the C-2-hydoxyl group in 17 with levulinic acid
yields donor 13 in excellent yield (96%). Thioglycoside 13 can
be converted into the corresponding hemiacetal 19 by N-
bromosuccinimide driven hydrolysis (78%). Installation of the N-
phenyltrifluoroacetimidate group[30] on the anomeric alcohol then
delivers 20 in high yield (99%). PMB protected rhamnoside 18 is
treated with acid chloride 9 and pyridine at elevated temperature
to provide fully protected compound 21 in 72% yield. Under
standard esterification conditions, applying the CNPiv acid 8 in
concert
with
di-iso-propylcarbodiimide
(DIC)
and
Scheme 1. Synthesis of CNPiv acid 8 and CNPiv chloride 9.
dimethylaminopyridine (DMAP), compound 21 was obtained in
good yield (74%). To remove the PMB ether, we initially
explored deprotection conditions using trifluoroacetic acid and a
thiol scavenger.[12] Besides the desired alcohol 22, these
conditions also provided deoxy-L-glucoside 23, bearing the
CNPiv group at its C-3-OH and a C-2-thiophenol group, as a
prominent side product. This product is likely the result of the
mechanism depicted in Scheme 3B. Under the acidic conditions
used, the CNPiv ester can be protonated and subsequently
attacked by the neighboring C-3-alcohol. Migration of the CNPiv
ester to the C-3 position can be caused by the participating
anomeric thiophenol moiety to provide an intermediate
episulfonium ion. This is attacked at the anomeric center to
provide deoxy-L-glucoside 23.[31–33]
With acid 8 and chloride 9 in hand, the introduction of the CNPiv
ester and its use as a protecting group in oligosaccharide
synthesis was explored. Two bacterial rhamnan structures, the
backbone structure of the exopolysaccharide of Group A
Streptococcus, and an Enterococcus faecium capsular
polysaccharide derived hexarhamnoside, were chosen as
synthetic targets to validate the performance of the CNPiv group
in oligosaccharide assembly.[19–26] The Enterococcus faecium
capsular polysaccharide is composed of trisaccharide repeating
units featuring α-(1,3)- and α-(1,2)-rhamnosyl linkages, whereas
the Group A Streptococcus repeating unit is a dirhamnoside with
α-(1,3) and α-(1,2)-linkages. The target structures for the current
study are depicted in Scheme 2. Tetrasaccharide 10 and
hexasaccharide 11 each contain two repeating units of the
respective capsular polysaccharides. It was envisaged that
these two target structures could be assembled from building
blocks 12, 13 and 14, which are equipped with a levulinoyl group,
that serves as a temporary protecting group, to be removed to
allow elongation of the rhamnan chains, and/or a CNPiv group,
which serves as a permanent participating protecting group.
Linker 15[27] is used to cap the reducing end of the target
rhamnans and can serve as a handle for future conjugation
chemistries.
We recently showed that
a catalytic amount of HCl in
2,2,2,3,3,3-hexafluoro-iso-propanol (HFIP) could be used to
cleave electron rich benzyl ethers in a mild and fast manner.[34]
Application of these conditions proved effective here to remove
the C-3-O-PMB from rhamnoside 21. The reaction time had to
be carefully controlled as a prolonged reaction time led to
activation of the anomeric thiophenol function. The liberated
alcohol in compound 22 was masked with a levulinoyl group to
provide building block 12. Rhamnoside 22 was also used to
generate disaccharide building block 14. To this end, N-
phenyltrifluoroacetimidate rhamnoside 20 and thiorhamnoside
acceptor 22 were combined in a chemoselective glycosylation
reaction to provide the dirhamnoside 14 in high yield (93%) and
with complete stereoselectivity.
Scheme 2. Target compounds and retrosynthetic analysis
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European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
Scheme 3. Building block synthesis.
Having assembled the required building blocks, we turned to the
Next the levulinoyl ester was removed to provide the
construction of the two target oligosaccharides (Scheme 4). First, monosaccharide
acceptor
building
block
25.
This
the linker-functionalized rhamnoside was generated in
a
monosaccharide was elongated with monorhamnoside 13 to
give dimer 26 in 93% yield. Liberation of the C-2”-OH by
treatment of 26 with hydrazine set the stage for the next
stereoselective, NIS/TMSOTf-mediated glycosylation[35] of donor
12 with protected aminohexanol 15.
Scheme 4. Synthesis of the fully protected tetra- and
hexasaccharide targets.
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European Journal of Organic Chemistry
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FULL PAPER
glycosylation. In this condensation the dimers 14 and 27 were Conclusions
united to provide the fully protected target tetrasaccharide 28 in
high yield.
Herein we have described the introduction of the cyanopivaloyl
ester as a novel hydroxyl protecting group. It features a cyano
moiety appended two atoms away from the ester carbonyl to
allow for a relay-cleavage of the pivaloyl type ester. This
cleavage mechanism alleviated one of the major drawbacks of
the pivaloyl ester, that is, its difficult removal.
Next the assembly of the protected hexarhamnan 34 was
undertaken. To this end linker bearing monorhamnose 25 and
dirhamnoside 14 were coupled under the agency of
NIS/TMSOTf to provide trisaccharide 30 in 52% yield.
Delevulinuylation of 30 was followed by a glycosylation with
monorhamnose donor 12 to provide the tetrasaccharide 32 in
75% yield. Removal of the Lev-ester then paved the way for the
final glycosylation in which tetramer 33 was elongated with
dirhamnoside 14 giving the fully protected hexarhamnan in 88%
yield.
We have shown the applicability of the novel protecting group in
the assembly of two bacterial oligorhamnans. It represents a
robust protecting group that tolerates many functional group
manipulations and withstands both (Lewis) acidic as well as mild
basic conditions. It is a new member of the family of pivaloyl-
type protecting groups and may be used in combination with
other pivaloyl type esters, such as the recently introduced
With the two fragments in hands, we commenced the
deprotection sequence. First the levulinoyl groups were removed.
Next all benzyl ethers and cyano groups were reduced by
hydrogenolysis using Pd(OH)2/C. The reduction was achieved in
azidopivaloyl group, as
a (semi)-orthogonal pair for the
streamlined synthesis of carbohydrates and other complex
(bio)molecules.
two stages, the first of which was executed in
a
THF/tBuOH/H2O/AcOH solvent system. After filtration the
partially deprotected material was taken up in water and
subjected to
a
second hydrogen event. During the
Experimental Section
hydrogenation AcOH was added to prevent deactivation of the
catalyst. Reduction of the cyano-groups released the primary
amines of the Piv-like esters, which under the reaction
conditions used are protonated. To affect ring closure, release
the 2,2-dimethyl-γ-butyrolactam and complete the removal of the
CNPiv esters the crude products were treated with triethylamine
in water. The release of the 2,2-dimethyl-γ-butyrolactam could
be easily followed by NMR analysis using the characteristic
triplets of the liberated lactam. After completion of the reaction,
the crude tetra- and hexasaccharide were purified by size
exclusion chromatography to provide Group A Streptococcus
tetrarhamnan 10 and Entrococcus faecium hexarhamnan 11 in
100% and 80% respectively.
General experimental procedures. All chemicals were used as
received unless stated otherwise. 1H and 13C NMR spectra were
recorded on a 400/100 MHz, 500/125 MHz, 600/150 MHz or a 850/214
MHz spectrometer. Chemical shifts (δ) are given in ppm relative to
tetramethylsilane as internal standard. Coupling constants are given in
Hz. All individual signals were assigned using 2D-NMR spectroscopy,
HH-COSY, HSQC and HMBC. IR spectra are reported in cm−1. Flash
chromatography was performed on silica gel 60 (0.04 – 0.063 mm). TLC-
analysis was followed by detection by UV-absorption (254 nm) where
applicable and by spraying with 20% sulfuric acid in ethanol followed by
charring at ~150 °C or by spraying with a solution of (NH4)6Mo7O24·H2O
(25 g/l) and (NH4)4Ce(SO4)4·2H2O (10 g/l) in 10% sulfuric acid in water
followed by charring at 50 °C. LC-MS standard eluents used were A:
100% H2O, B: 100% acetonitrile, C: 1% TFA in H2O. The column used
was a C18 column (4.6 mmD × 50 mmL, 3μ particle size). All analyses
were 13 min, with a flow-rate of 1 ml/min. High-resolution mass spectra
were recorded on a LTQ-Orbitrap equipped with an electrospray ion
source in positive mode (source voltage 3.5 kV, sheath gas flow 10,
capillary temperature 275ºC) with resolution R=60.000 at m/z=400 (mass
range = 150-4000) and dioctylphthalate (m/z=391.28428) as "lock mass".
High resolution mass measurements were performed on a Synapt G2-Si
MALDI-TOF mass spectrometer equipped with a 355-nm laser. 1 uL
samples were spotted on the MALDI-plate, followed by applying 1 uL of
the the matrix solution (2,5-dihydroxybenzoic acid 100 mg/mL dissolved
in H2O : ACN : dimethylaniline 1 : 1 : 0.02). A laser frequency of 1000 Hz
(power set at 60%) was used.
Methyl 3-cyano-2,2-dimethylpropanoate (7) A solution of LDA was
prepared by adding n-butyllithium in hexanes (1.6 M, 134.8 mL, 215.7
mmol, 1 equiv.) drop wise to a solution of diisopropylamine (33.4 mL, 238
mmol, 1.1 equiv.) in THF (310 mL) at -78°C under argon. After 45 min no
more bubbles appeared and methyl isobutyrate (28.2 mL, 246 mmol,
1.13 equiv.) was added. After 1h of stirring at -78°C, bromoacetonitrile
(19.5 mL, 280 mmol, 1.26 equiv.) was added. The resulting dark mixture
was allowed to warm up gradually to room temperature and stirred
overnight. The reaction was neutralized by the addition of 1M HCl (90
mL) and 2M HCl (240 mL) at 0 °C. The mixture was diluted with brine,
followed by extraction with Et2O (3x). The combined organic layers were
washed with sat. aq. NaHCO3 (6x), H2O (6x) and brine (1x), dried over
MgSO4, and concentrated in vacuo. Purification by column
Scheme 5. Deprotection of the tetra- and hexasaccharide.
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European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
chromatography (19:1 PE/EtOAc to 4:1 PE/EtOAc) and coevaporation
with CHCl3 resulted in the title compound as a light yellow oil (13.45 g,
95.3 mmol). Analytical data are identical to literature precendence.[36]
equiv.), N,N’-diisopropylcarbodiimide (4.92 mL, 31.4 mmol, 1.4 equiv.)
and 4-dimethylaminopyridine (0.31 g, 2.54 mmol, 0.1 equiv.) were added
at 0 °C. After 1.5h the reaction was allowed to warm up to room
temperature and stirred overnight. After TLC-MS showed complete
consumption of the starting material, the mixture was filtered over Celite
and the filtrate was washed with sat. aq. NaHCO3 (2x) and brine (1x).
The organic layer was dried over MgSO4, concentrated in vacuo and
coevaporated with anhydrous toluene. Purification by column
chromatography (3:1 PE/EtOAc) and coevaporation with CHCl3 (2x)
resulted in the title compound as a yellow oil (11.50 g, 21.51 mmol, 96%).
Rf = 0.38 (7:2 PE/EtOAc); IR (neat): 2968, 1728, 1472, 1439, 1358, 1300,
1198, 1132, 1098, 1051, 1022, 903, 835, 783, 733, 689 cm-1; 1H NMR
(400 MHz, CDCl3) δ: 7.44-7.26 (m, 15H, CHarom), 5.59 (m, 1H, H-2), 5.41
(d, 1H, J = 1.2 Hz, H-1), 4.93 (d, 1H, J = 10.8 Hz, CH2 Bn), 4.70 (d, 1H, J
= 11.2 Hz, CH2 Bn), 4.63 (d, 1H, J = 10.8 Hz, CH2 Bn), 4.54 (d, 1H, J =
11.2 Hz, CH2 Bn), 4.22 (dq, 1H, J = 9.4, 6.2 Hz, H-5), 3.90 (dd, 1H, J =
9.3, 3.3 Hz, H-3), 3.48 (t, 1H, J = 9.4 Hz, H-4), 2.76-2.69 (m, 4H, 2x CH2
Lev), 2.16 (s, 3H, CH3 Lev), 1.33 (d, 3H, J = 6.2 Hz, CH3-6); 13C NMR
(100 MHz, CDCl3) δ: 206.3 (C=O Lev ketone), 172.1 (C=O Lev), 138.5,
137.9, 134.0 (Cq Carom), 131.9, 129.2, 128.5, 128.5, 128.3, 128.2, 128.0,
127.9, 127.8 (CHarom), 86.1 (C-1), 80.3 (C-4), 78.4 (C-3), 75.6 (CH2 Bn),
71.8 (CH2 Bn), 70.9 (C-2), 69.1 (C-5), 38.1 (CH2 Lev), 30.0 (CH3 Lev),
28.3 (CH2 Lev), 18.0 (CH3-6); HRMS calculated for [C31H34O6S + NH4]+:
552.24144, found 552.24165.
3-cyano-2,2-dimethylpropanoic acid (8) A suspension was formed by
the addition of H2O (205 mL) and EtOH (35 mL) to compound 7 (13.45 g,
95.3 mmol, 1 equiv.). Lithium hydroxide (98%) (5.85 g, 244 mmol, 2.5
equiv.) was added and the mixture was refluxed at 95°C for 5.5h. The
mixture was cooled to 0 °C, quenched with 1M HCl to pH = 1, diluted with
H2O and extracted with EtOAc (2x). The combined organic layers were
washed with brine, dried over MgSO4 and concentrated in vacuo.
Coevaporation with DCM and CHCl3 resulted in an oil that crystallized out
as a light yellow solid (10.41 g, 81.89 mmol, 33% in two steps). IR (neat):
3368, 3192, 2971, 2936, 2884, 2544, 2264, 1699, 1661, 1585, 1474,
1449, 1412, 1398, 1366, 1308, 1240, 1231, 1202, 1184, 1140, 1020, 974,
937, 922, 899, 874, 858, 831, 797, 773, 750, 648 cm-1; 1H NMR (400
MHz, CDCl3) δ: 11.12 (bs, 1H, OH), 2.63 (s, 2H, CH2), 1.42 (s, 6H, CH3).
13C NMR (100 MHz, CDCl3) δ: 181.5 (C=O), 117.4 (CN), 41.0 (Cq), 27.8
(CH2), 24.7 (CH3). HRMS calculated for [C6H9NO2 + H]+: 128.07061,
found 128.07055.
3-cyano-2,2-dimethylpropanoyl chloride (9) After coevaporation with
anhydrous toluene, acid 8 (5.53 g, 43.5 mmol, 1 equiv.) was dissolved in
DCM (110 mL). Oxalylchloride (8.4 mL, 97.8 mmol, 2.2 equiv.) was
added at room temperature and the solution was refluxed at 40 °C for 40
min allowing the gases produced during the reaction to be stripped by a
stream of argon, after which the water cooling was closed and the DCM
was allowed to evaporate at 50 °C for 2h. The reaction mixture was
cooled and concentrated in vacuo. The obtained oil was used directly
without further purification. 1H NMR (400 MHz, CDCl3) δ: 2.70 (s, 2H,
CH2), 1.49 (s, 6H, CH3). 13C NMR (100 MHz, CDCl3) δ: 177.6 (C=O),
116.3 (CN), 50.6 (Cq), 27.8 (CH2), 24.5 (CH3).
3,4-di-O-benzyl-2-O-levulinoyl-α/β-L-rhamnopyranoside
(19)
Compound 13 (1.07 g, 2.00 mmol, equiv.) was dissolved in
1
acetone/water 3:1 (10 mL) and cooled to 0 °C. N-bromosuccinimide (1.08
g, 6.07 mmol, 3 equiv.) was added and the mixture was stirred at 0 °C.
The reaction was allowed to warm up to room temperature after 100 min
and stirred overnight. The reaction was quenched by addition of sat. aq.
Na2S2O3, diluted with EtOAc and the organic layer was washed with sat.
aq. NaHCO3 (2x), H2O (1x) and brine (1x). The organic layer was dried
over MgSO4 and concentrated in vacuo. Purification by column
chromatography (3:1 to 1:1 PE/EtOAc) yielded hemiacetal 19 (0.692 g,
1.56 mmol, 78%). Rf = 0.53 (1:1 PE/EtOAc); IR (neat): 1738, 1717, 1362,
1207, 1155, 1063, 1042, 1028, 988, 912, 837, 735, 696 cm-1; NMR
assignment for the major isomer: 1H NMR (400 MHz, CDCl3) δ: 7.33-7.2
(m, 10H, CHarom), 5.25 (m, 1H, H-2), 5.03 (s, 1H, H-1), 4.91-87 (m, 1H,
CH2 Bn), 4.72-4.58 (m, 2H, CH2 Bn), 4.51-4.45 (m, 1H, CH2 Bn), 4.00-
3.93 (m, 2H, H-3, H-5), 3.40 (t, 1H, J = 9.2 Hz, H-4), 2.76-2.60 (m, 4H, 2x
CH2 Lev), 2.11 (s, 3H, CH3 Lev), 1.27 (d, 3H, J = 6.2 Hz, CH3-6); 13C
NMR (100 MHz, CDCl3) δ: 206.9 (C=O Lev ketone), 172.1 (C=O Lev),
138.3, 137.9 (Cq Carom), 128.3, 128.2, 128.2, 128.1, 128.0, 128.0, 127.7,
127.6, 127.6 (CHarom), 91.9 (C-1), 80.0 (C-4), 77.4 (C-3), 75.2 (CH2 Bn),
71.4 (CH2 Bn), 69.6 (C-2), 67.3 (C-5), 37.9 (CH2 Lev), 29.7 (CH3 Lev),
28.0 (CH2 Lev), 18.0 (CH3-6). HRMS calculated for [C25H30O7 + NH4]+:
460.23298, found 460.23299.
Phenyl 4-O-benzyl-1-thio-α-L-rhamnopyranoside (16) A solution of
80% acetic acid (950 mL) was added to phenyl 4-O-benzyl-2,3-di-O-
isopropylidene-1-thio-α-L-rhamnopyranoside (73.8 g, 191 mmol) and
heated to 70 °C and stirred overnight after which TLC analysis showed
complete consumption of the starting material. The reaction was cooled
down to 0 °C, neutralized with Et3N, diluted with H2O and extracted with
EtOAc (2x). The combined organic layers were washed with sat. aq.
NaHCO3 (5x) and brine (1x), dried over MgSO4 and concentrated in
vacuo. Crystallization (EtOH) at -20 °C resulted in the title compound as
a white solid (58.3 g, 168.3 mmol, 88%). Rf = 0.51 (2:1 PE/EtOAc).
Analytical data are identical to literature precendence.[28]
Phenyl 3,4-di-O-benzyl-1-thio-α-L-rhamnopyranoside (17) Diol 16
(3.47 g, 10.0 mmol, 1 equiv.) was coevaporated with anhydrous toluene
two times under argon and dissolved in anhydrous toluene (100 mL).
Dibutyltin oxide (3.00 g, 12.1 mmol, 1.2 equiv.) was added and the white
suspension was heated to 105°C. The reaction was stirred overnight
after which the clear solution was cooled down and concentrated in
vacuo. After three times coevaporation with anhydrous toluene under
argon, the oil was dissolved in DMF (100 mL). BnBr (1.6 mL, 13.5 mmol,
1.3 equiv.) and CsF (3.05 g, 20.1 mmol, 2 equiv.) were added. After 6h,
TLC-MS and TLC analysis showed complete reaction and the reaction
mixture was diluted with EtOAc, washed with H2O (2x), brine (2x), dried
over MgSO4 and concentrated in vacuo. Purification by column
chromatography (PE to 2:1 PE/EtOAc) yielded the title compound as a
colorless oil (3.76 g, 8.62 mmol, 86%). Rf = 0.77 (2:1 PE/EtOAc).
Analytical data are identical to literature precendence.[29]
3,4-di-O-benzyl-2-O-levulinoyl-1-(N-[phenyl]-trifluoroacetimidoyl)-
α/β-L-rhamnopyranoside (20) To a solution of compound 19 (0.65 g,
1.47 mmol, 1 equiv.) in acetone (7.4 mL), were added ClC(=NPh)CF3
(0.27 mL, 1.78 mmol, 1.2 equiv.) and Cs2CO3 (0.72 g, 2.21 mmol, 1.5
equiv.) at
0 °C. The reaction was allowed to warm up to room
temperature after 40 min and stirred for an additional 20 min. TLC
analysis showed complete consumption of starting material. The reaction
was diluted with EtOAc and the organic layer was washed with H2O (2x)
and brine (1x). The organic layer was dried over MgSO4 and
concentrated in vacuo. Purification by column chromatography (7:1
PE/EtOAc to EtOAc) yielded the title compound in a 4:1 α/β-ratio (0.894
g, 1.456 mmol, 99%). Rf = 0.54 (4:1 PE/EtOAc); IR (neat): 2922, 1740,
1717, 1454, 1364, 1312, 1207, 1153, 1119, 1072, 1028, 985, 943, 920,
839, 735, 696 cm-1; NMR assignment for the major isomer: 1H NMR (400
MHz, CDCl3) δ: 7.35-7.23 (m, 12H, CHarom), 7.09-7.06 (m, 1H, CHarom),
6.86-6.80 (m, 2H, CHarom), 6.17 (bs, 1H, H-1), 5.49 (s, 1H, H-2), 4.92 (d,
1H, J = 10.8 Hz, CH2 Bn), 4.71 (d, 1H, J = 11.2 Hz, CH2 Bn), 4.63 (d, 1H,
Phenyl 3,4-di-O-benzyl-2-O-levulinoyl-1-thio-α-L-rhamnopyranoside
(13) After coevaporation with anhydrous toluene (2x) under argon,
compound 17 (9.79 g, 22.5 mmol, 1 equiv.) was dissolved in freshly
distilled DCM and cooled to 0 °C. Levulinic acid (6.38 mL, 62.9 mmol, 2.8
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
J = 10.8, CH2 Bn), 4.55 (d, 1H, J = 11.2 Hz, CH2 Bn), 3.98 (dd, 1H, J =
9.2, 2.8 Hz, H-3), 3.90 (m, 1H, H-5), 3.50 (t, 1H, J = 9.2 Hz, H-4), 2.75-
2.63 (m, 4H, 2x CH2 Lev), 2.08 (s, 3H, CH3 Lev), 1.36 (d, 1H, J = 6.0 Hz,
CH3-6); 13C NMR (100 MHz, CDCl3) δ: 205.8 (C=O Lev ketone), 171.6
(C=O Lev), 143.2, 138.0, 137.5 (Cq Carom), 128.7, 128.3, 128.3, 128.2,
128.0, 128.0, 127.8, 127.8, 124.4, 199.3 (CHarom), 94.2 (C-1), 79.1 (C-4),
77.2 (C-3), 75.5 (CH2 Bn), 71.9 (CH2 Bn), 70.4 (C-5), 67.6 (C-2), 37.7
(CH2 Lev), 29.6 (CH3 Lev), 27.9 (CH2 Lev), 17.9 (CH3-6). TLC-MS: m/z =
636.35 (M+Na+).
CNPiv), 1.36 (s, 6H, 2x CH3 CNPiv), 1.32 (d, 3H, J = 6.0 Hz, H-6); 13C
NMR (100 MHz, CDCl3) δ: 174.1 (C=O CNPiv), 159.5, 138.3, 133.7 (Cq
Carom), 132.1, 132.1 130.0, 129.8 (CHarom), 129.3 (Cq Carom), 128.5, 128.3,
128.0, 127.9, 127.8 (CHarom), 117.6 (CN), 114.0, 113.9 (CHarom), 86.0 (C-
1), 79.9 (C-4), 78.1 (C-3), 75.5 (CH2 Bn), 71.6 (CH2 PMB), 71.4 (C-2),
69.1 (C-5), 55.4 (CH3 PMB), 41.2 (Cq CNPiv), 28.1 (CH2 CNPiv), 24.9,
24.8 (CH3 CNPiv), 18.0 (CH3-6); HRMS calculated for [C33H37NO6S +
NH4]+: 593.26798, found 593.26838.
Phenyl 4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-1-thio-α-L-
Phenyl
4-O-benzyl-3-O-p-methoxybenzyl-1-thio-α-L-
rhamnopyranoside (22)
rhamnopyranoside (18) Diol 16 (6.94 g, 20.0 mmol, 1 equiv.) was
coevaporated with anhydrous toluene two times under argon and
dissolved in anhydrous toluene (200 mL). Dibutyltin oxide (5.99 g, 24.1
mmol, 1.2 equiv.) was added to the mixture, which was stirred overnight
at 105°C. The clear solution was cooled to 0 °C, concentrated in vacuo
and two times coevaporated with anhydrous toluene under argon. The oil
was dissolved in DMF (200 mL), followed by the addition of p-
methoxybenzyl chloride (3.1 mL, 22.9 mmol, 1.12 equiv.) and CsF (6.08
g, 40.0 mmol, 2 equiv.). After heating the mixture to 80 °C for 5h, TLC
analysis showed complete reaction, and the reaction mixture was cooled
to 0 °C, diluted with H2O and extracted two times with EtOAc. The
combined organic layers were washed with H2O (2x) and brine (2x). The
organic layer was dried over MgSO4 and concentrated in vacuo.
Purification by column chromatography (PE to 2:1 PE/EtOAc) and (5:1
PE/EtOAc to 2:1 PE/EtOAc) resulted in the title compound as a clear oil
(6.83 g, 14.6 mmol, 73%). Rf = 0.75 (2:1 PE/EtOAc). Analytical data are
identical to literature precendence.[29]
Method A: To a solution of compound 21 (8.47 g, 14.72 mmol, 1 equiv.)
in DCM (75 mL), thiophenol (1.65 mL, 16.12 mmol, 1.1 equiv.) was
added and the mixture was cooled down to
0 °C, after which
trifluoroacetic acid (7.5 mL) was added. The reaction mixture was stirred
for 3h, after which TLC-MS analysis showed complete consumption of
the starting material. The mixture was diluted with Et2O, washed with sat.
aq. NaHCO3 (4x), H2O (1x) and brine (1x). The organic layer was dried
over MgSO4 and concentrated in vacuo. Purification by column
chromatography (7:1 PE/EtOAc to 3:1 PE/EtOAc) and coevaporation with
DCM and CHCl3 resulted in the title compound as a clear oil (5.38 g, 10.8
mmol, 73%).
Method B: Compound 21 (3.085 g, 5.35 mmol) is dissolved in 27 mL
DCM and 27 mL HFIP. The mixture was cooled to 0 °C and TES (2.56
mL, 16.05 mmol, 3 equiv.) was added. 26.8 mL of a freshly prepared
HCl/HFIP solution (0.2 M, 1 equiv.) was added and the reaction was
stirred for 7 minutes after which it was quenched with sat. aq. NaHCO3.
Purification by column chromatography (PE/EtOAc 1:0  8:1) yielded 22
as a colorless oil (0.08 g, 0.175 mmol, 76%). Rf = 0.38 (7:2 PE/EtOAc);
IR (neat): 3435, 2974, 2880, 1732, 1471, 1298, 1198, 1136, 1078, 1024,
968, 847, 772, 739, 691 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.48-7.45 (m,
2H, CHarom), 7.36-7.27 (m, 8H, CHarom), 5.40 (m, 1H, H-2), 5.37 (d, 1H, J
= 1.2 Hz, H-1), 4.79 (d, 2H, J = 4.4 Hz, CH2 Bn), 4.27 (dq, 1H, J = 9.4,
6.2 Hz, H-5), 4.09 (dd, 1H, J = 9.2, 2.8 Hz, H-3), 3.44 (t, 1H, J = 9.2 Hz,
H-4), 2.59 (d, 2H, J = 4.8 Hz, CH2 CNPiv), 2.05 (bs, 1H, OH), 1.39 (s, 6H,
2x CH3 CNPiv), 1.38 (s, 3H, CH3-6). 13C NMR (100 MHz, CDCl3) δ: 174.3
(C=O CNPiv), 138.0, 133.7 (Cq Carom), 132.1, 129.2, 128.7, 128.3, 128.2,
127.9 (CHarom), 118.0 (CN), 85.8 (C-1), 81.5 (C-4), 75.3 (CH2 Bn), 74.9
(C-2), 70.8 (C-3), 68.9 (C-5), 41.3 CNPiv), 28.0 (CH2 CNPiv), 25.0, 25.0
(CH3 CNPiv), 18.1 (CH3-6); HRMS calculated for [C25H29NO5S + Na]+:
478.16586, found 478.16531.
Phenyl
4-O-benzyl-3-O-p-methoxybenzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-1-thio-α-L-rhamnopyranoside (21)
Method A: Crude chloride 9 (5.53 g, 43.5 mmol, 2 equiv.) was cooled to
0 °C and dissolved in pyridine (20 mL). A solution of compound 18 (10.14
g, 21.7 mmol, 1 equiv.) in pyridine (2x 20 mL) was added to the crude
chloride. After an addition of another 50 mL pyridine, the resulting dark
mixture was heated to 110 °C. After 1h, TLC and TLC-MS analysis
showed complete reaction and the mixture was cooled to 0 °C. The
reaction mixture was diluted with EtOAc and washed with H2O (1x), 1M
HCl (2x) and brine (2x). The organic layer was dried over MgSO4,
concentrated in vacuo and coevaporated with toluene. Purification by
flash column chromatography (8:1 PE/EtOAc  3:1 PE/EtOAc) and (10:1
PE/EtOAc  EtOAc) and coevaporation with CHCl3 resulted in the title
compound as an oil (9.04 g, 15.7 mmol, 72%), which contained 5%
byproduct.
Phenyl
4-O-benzyl-3-O-(3-cyano-2,2-dimethylpropanoyl)-1-thio-2-
thiophenyl-α-L-rhamnopyranoside (23) Rf = 0.61 (7:1 PE/EtOAc); IR
(neat): 2968, 2847, 1728, 1582, 1472, 1439, 1300, 1198, 1132, 1096,
1051, 1020, 783, 733, 689 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.67-7.61
(m, 2H, CHarom), 7.47-7.42 (m, 2H, CHarom), 7.35-7.23 (m, 11H, CHarom),
5.28 (dd, 1H, J = 10.7, 8.2 Hz, H-3), 4.61 (s, 2H, CH2 Bn), 4.35 (d, 1H, J
= 10.6 Hz, H-1), 3.35-3.25 (m, 2H, H-4, H-5), 3.03 (t, 1H, J = 10.7 Hz, H-
2), 2.54 (d, 2H, J = 8.7 Hz, CH2 CNPiv), 1.42 (s, 6H, 2x CH3 CNPiv), 1.29
(d, 3H, J = 5.6 Hz, CH3-6); 13C NMR (100 MHz, CDCl3) δ: 174.2 (C=O
CNPiv), 137.5 (Cq Carom), 135.0 (CHarom), 132.7 (Cq Carom), 132.5 (CHarom),
130.1 (Cq Carom), 129.2, 129.0, 128.9, 128.6, 128.1, 127.9, 127.5 (CHarom),
117.6 (CN), 86.5 (C-1), 83.0 (C-4), 75.7 (C-3), 75.3 (C-5), 74.8 (CH2 Bn),
52.1 (C-2), 41.0 (Cq CNPiv), 28.0 (CH2 CNPiv), 25.0, 24.8 (CH3 CNPiv),
18.3 (CH3-6); HRMS calculated for [C31H33NO4S2 + NH4]+: 565.21893,
found 565.21935.
Method B: Acid 8 (3.49 g, 27.5 mmol, 2 equiv.) and compound 18 (6.41
g, 13.75 mmol, 1 equiv.) were coevaporated twice with anhydrous
toluene after which they were dissolved in dry DCM (35 mL). The solution
was cooled to 0 °C and DIC (2.37 mL, 15.13 mmol, 1.1 equiv.) and
DMAP (0.17 g, 1.37 mmol, 0.1 equiv.) were added. The reaction was
allowed to stir overnight, after which TLC analysis showed conversion of
the starting material in a higher running spot. Filtration over Celite
followed by washing with sat. aq. NaHCO3, the organic layer was dried
over MgSO4 and concentrated. Purification by flash column
chromatography (PE/EtOAc 1:0
 4:1) yielded the fully protected
rhamnopyranoside as a yellow oil (5.86 g, 10.2 mmol, 74%). Rf = 0.68
(3:1 PE/EtOAc); IR (neat): 2974, 2874, 1734, 1612, 1514, 1472, 1454,
1300, 1246, 1136, 1098, 1084, 1030, 820, 739, 691 cm-1; 1H NMR (400
MHz, CDCl3) δ: 7.46-7.43 (m, 2H, CHarom), 7.32-7.22 (m, 10H, CHarom),
6.87-6.84 (m, 2H, CHArom), 5.62 (m, 1H, H-2), 5.37 (d, 1H, J = 1.2 Hz, H-
1), 4.90 (d, 1H, J = 10.8 Hz, CH2 Bn), 4.64 (d, 1H, J = 10.8 Hz, CH2 Bn),
4.60 (d, 1H, J = 10.8 Hz, CH2 PMB), 4.47 (d, 1H, J = 10.4 Hz, CH2 PMB),
4.24 (dq, 1H, J = 9.4, 6.2 Hz, H-5), 3.90 (dd, 1H, J = 9.2, 3.2 Hz, H-3),
3.80 (s, 3H, OCH3 PMB), 3.42 (t, 1H, J = 9.2 Hz, H-4), 2.56 (s, 2H, CH2
Phenyl
4-O-benzyl-3-O-levulinoyl-2-O-(3-cyano-2,2-
(12) After
dimethylpropanoyl)-1-thio-α-L-rhamnopyranoside
coevaporation of compound 22 (2.47 g, 5.42 mmol, 1 equiv.) with
anhydrous toluene (2x) under argon, it was dissolved in distilled DCM
(13.5 mL) and cooled to 0 °C. Levulinic acid (1.54 mL, 15.2 mmol, 2.8
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
equiv.), N,N’-diisopropylcarbodiimide (1.2 mL, 7.7 mmol, 1.4 equiv.) and
a catalytic amount of 4-dimethylaminopyridine (0.066 g, 0.54 mmol, 0.1
equiv.) were added. After 30 min, TLC-MS analysis showed complete
reaction and the mixture was filtered over Celite. The filtrate was washed
with sat. aq. NaHCO3 (2x), dried over MgSO4 and concentrated in vacuo.
Purification by column chromatography (2:1 PE/EtOAc) and
coevaporation with DCM and CHCl3 resulted in the title compound as an
oil (2.97 g, 5.36 mmol, 99%). Rf = 0.59 (2:1 PE/EtOAc); IR (neat): 2976,
1740, 1717, 1474, 1362, 1300, 1204, 1150, 1132, 1099, 1084, 912, 741,
692 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.46-7.43 (m, 2H, CHarom), 7.37-
7.24 (m, 8H, CHarom), 5.54 (m, 1H, H-2), 5.36 (d, 1H, J = 1.2 Hz, H-1),
5.31 (dd, 1H, J = 9.6, 3.2 Hz, H-3), 4.78 (d, 1H, J = 11.2 Hz, CH2 Bn),
4.34 (dq, 1H, J = 9.4, 6.0 Hz, H-5), 3.64 (t, 1H, J = 9.6 Hz, H-4), 2.77-
2.64 (m, 2H, CH2 Lev), 2.59 (d, 2H, J = 1.6 Hz, CH2 CNPiv), 2.56-2.44 (m,
2H, CH2 Lev), 2.14 (s, 3H, CH3 Lev), 1.39 (s, 6H, 2x CH3 CNPiv), 1.36 (s,
3H, CH3-6); 13C NMR (100 MHz, CDCl3) δ: 206.0 (C=O Lev ketone),
173.6, 171.7 (C=O CNPiv, Lev), 137.7, 133.1 (Cq Carom), 131.9, 129.0,
128.9, 128.3, 128.0, 127.8 (CHarom), 117.4 (CN), 85.2 (C-1), 78.1 (C-4),
74.8 (CH2 Bn), 72.2, 72.2 (C-2, C-3), 68.9 (C-5), 41.0 (Cq CNPiv), 27.5
(CH2 Lev), 29.5 (CH3 Lev), 27.7, 27.6 (CH2 Lev, CH2 CNPiv), 24.7, 24.6
(CH3 CNPiv), 17.8 (CH3-6); HRMS calculated for [C30H35NO7S + Na]+:
576.20264, found 576.20209.
equiv.) were added. After 1h, TLC analysis showed fast conversion of the
donor and the mixture was allowed to warm to room temperature for 30
min, after which is was quenched with Et3N. The mixture was diluted with
Et2O and washed with H2O (2x) and brine (2x). The organic layer was
dried over MgSO4 and concentrated in vacuo. Purification by size
exclusion (1:1 DCM/MeOH) and coevaporation with CHCl3 resulted in the
title compound as a yellow oil (0.957 g, 1.24 mmol, 82%). Rf = 0.35 (2:1
PE/EtOAc); IR (neat): 1738, 1694, 1360, 1300, 1207, 1126, 1063, 1028,
976, 912, 733, 696 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.36-7.24 (m, 14H,
CHarom), 7.18-7.16 (m, 1H, CHarom), 5.30 (dd, 1H, J = 9.6, 3.2 Hz, H-3),
5.24 (s, 1H, H-2), 5.17 (d, 2H, J = 13.2 Hz, CH2 Cbz), 4.72 (d, 1H, J =
11.2 Hz, CH2 Bn), 4.65-4.63 (m, 2H, CH2 Bn, H-1), 4.49-4.48 (m, 2H,
CH2 Bn), 3.80 (m, 1H, H-5), 3.60-3.55 (m, 1H, CH2), 3.50 (t, 1H, J = 9.6
Hz, H-4), 3.34 (m, 1H, CH2), 3.26 (m, 1H, CH2), 3.20 (m, 1H, CH2), 2.76-
2.64 (m, 2H, CH2 Lev), 2.61 (d, 2H, J = 1.2 Hz, CH2 CNPiv), 2.53-2.46 (m,
2H, CH2 Lev) 2.14 (s, 3H, CH3 Lev), 1.54- 1.48 (m, 4H, 2x CH2), 1.40 (s,
6H, 2x CH3 CNPiv), 1.35 (d, 3H, J = 12.8 Hz, CH3-6), 1.26 (m, 2H, CH2);
13C NMR (100 MHz, CDCl3) δ: 206.3 (C=O Lev ketone), 173.9, 171.8
(C=O CNPiv, Lev), 137.9, 137.8 (Cq), 128.5, 128.4, 128.2, 128.1, 127.9,
127.8, 127.2 (CHarom), 117.5 (CN), 97.0 (C-1), 78.3 (C-4), 75.0 (CH2 Bn),
72.2 (C-3), 71.0 (C-2), 67.7 (CH2), 67.5 (C-5), 67.1 (CH2 Cbz), 50.5, 50.2
(CH2 Bn), 47.1, 46.1 (CH2), 41.2 (Cq CNPiv), 37.8 (CH2 Lev), 29.8 (CH3
Lev), 29.0 (CH2), 27.9 (CH2 CNPiv, Lev), 27.5 (CH2), 24.9, 24.9 (CH3
CNPiv), 23.3 (CH2), 18.1 (CH3-6). HRMS calculated for [C44H54N2O10
Na]+: 793.36707, found 793.36653.
+
Phenyl 3-O-(3,4-di-O-benzyl-2-O-levulinoyl-α-L-rhamnopyranosyl)-4-
O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-1-thio-α-L-
rhamnopyranoside (14) Imidate donor 20 (0.353 g, 0.575 mmol, 1.2
equiv.) and acceptor 22 (0.219 g, 0.481 mmol,
1
equiv.) were
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-4-O-benzyl- 2-O-(3-
cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranoside (25)
coevaporated two times with anhydrous toluene under an argon
atmosphere before being dissolved in distilled DCM (4.8 mL) and the
mixture was stirred at room temperature for 15 min over activated
molecular sieves (3Å). The reaction was cooled to 0 °C and triflic acid
(4.5 µL, 0.051 mmol, 0.1 equiv.) was added. After 20 min the reaction
was quenched by addition of 0.1 mL Et3N. The reaction mixture was
diluted with Et2O and washed with H2O (2x) and brine (2x). The organic
layer was dried over MgSO4 and concentrated in vacuo. Purification by
size exclusion (1:1 DCM/MeOH) resulted in the title compound as a
yellow oil (0.394 g, 0.448 mmol, 93%). Rf = 0.64 (7:2 PE/EtOAc); IR
(neat): 2974, 2930, 1740, 1717, 1452, 1364, 1204, 1136, 1117, 1082,
1028, 989, 922, 845, 731, 700 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.45-
7.20 (m, 20H, CHarom), 5.40 (m, 1H, H-2’), 5.31 (s, 2H, H-1, H-2), 5.07 (s,
1H, H-1’), 4.93 (d, 1H, J = 11.2 Hz, CH2 Bn), 4.79 (d, 1H, J = 10.8 Hz,
CH2 Bn), 4.65-4.59 (m, 3H, CH2 Bn), 4.49 (d, 1H, J = 12 Hz, CH2 Bn),
4.22 (q, 1H, J = 6.0 Hz, H-5), 4.12 (dd, 1H, J = 9.6, 2.4 Hz, H-3), 3.80 (dd,
1H, J = 9.2, 3.2 Hz, H-3’), 3.60 (q, 1H, J = 6.0 Hz, H-5’), 3.53 (t, 1H, J =
9.6 Hz, H-4), 3.42 (t, 1H, J = 9.2 Hz, H-4’), 2.70-2.63 (m, 4H, 2x CH2 Lev),
2.45 (q, 2H, J = 14.0 Hz, CH2 CNPiv), 2.13 (s, 3H, CH3 Lev), 1.29 (m,
12H, CH3-6, CH3-6’, 2x CH3 CNPiv); 13C NMR (100 MHz, CDCl3) δ: 206.0
(C=O Lev ketone), 173.9, 171.7 (C=O CNPiv, Lev), 138.5, 137.8, 137.6,
133.2 (Cq Carom), 132.1, 131.9, 129.1, 128.8, 128.4, 128.3, 128.3, 128.2,
128.1, 128.1, 127.9, 127.8, 127.7, 127.7, 127.6, 127.5 (CHarom), 117.2
(CN), 99.7 (C-1’), 85.3 (C-1), 80.2 (C-4), 79.4 (C-4’), 77.05 (C-3), 76.8
(C-3’), 75.5 (CH2 Bn), 74.9 (CH2 Bn), 74.6 (C-2), 71.1 (CH2 Bn), 69.2 (C-
5), 68.9 (C-2’), 68.5 (C-5’), 40.9 (Cq CNPiv), 37.9 (CH2 Lev), 29.7 (CH3
Lev), 28.0 (CH2 Lev), 27.6 (CH2 CNPiv), 24.7, 24.6 (CH3 CNPiv), 17.8,
17.8 (C-6, C-6’); HRMS calculated for [C50H57NO11S + Na]+: 902.35445,
found 902.35458.
Compound 24 (0.212 g, 0.275 mmol, 1 equiv.) was dissolved in pyridine
(2.2 mL) and AcOH (0.55 mL). Hydrazine acetate (0.130 g, 1.41 mmol, 5
equiv.) was added and the mixture was stirred for 30 min, after which
TLC analysis showed complete reaction. The reaction mixture was
quenched with acetone and diluted with EtOAc. The organic layer were
washed with H2O (3x) and brine (1x), dried over MgSO4, concentrated in
vacuo. Purification by column chromatography (2:1 PE/EtOAc) and
coevaporation with CHCl3 resulted in the title compound as an oil (0.135
g, 0.200 mmol, 73%). Rf = 0.52 (2:1 PE/EtOAc); IR (neat): 2934, 1734,
1694, 1472, 1454, 1422, 1368, 1300, 1227, 1128, 1061, 1028, 976, 734,
696 cm-1; 1H NMR (400 MHz, CDCl3) δ: 7.35-7.24 (m, 14H, CHarom), 7.17-
7.16 (m, 1H, CHarom), 5.16 (d, 2H, J = 12.4 Hz, CH2 Cbz), 5.09 (s, 1H, H-
2), 4.82 (d, 1H, J = 11.2 Hz, CH2 Bn), 4.69 (d, 1H, J = 11.2 Hz, CH2 Bn),
4.64 (s, 1H, H-1), 4.48 (d, 2H, J = 6.8 Hz, CH2 Bn), 4.07 (bs, 1H, H-3),
3.70 (m, 1H, H-5), 3.57 (m, 1H, CH2), 3.32 (t, 1H, J = 6.4 Hz, H-4), 3,31
(m, 1H, CH2), 3.30-3.18 (m, 2H, CH2), 2.58 (d, 2H, J = 6.0 Hz, CH2
CNPiv), 1.54-1.48 (m, 4H, 2x CH2), 1.39 (s, 6H, 2x CH3 CNPiv), 1.33 (d,
3H, J = 6.0 Hz, CH3-6), 1.26 (m, 2H, CH2); 13C NMR (100 MHz, CDCl3) δ:
174.5 (C=O CNPiv), 138.1, 137.9 (Cq Carom), 128.6, 128.6, 128.5, 128.2,
128.1, 128.0, 127.9, 127.3, 127.2 (CHarom), 117.9 (CN), 97.1 (C-1), 81.3
(C-4), 75.2 (CH2 Bn), 73.5 (C-2), 70.2 (C-3), 67.7 (CH2), 67.5 (C-5), 67.2
(CH2 Cbz), 50.5, 50.3 (CH2 Bn), 47.1, 46.1 (CH2), 41.2 (Cq CNPiv), 29.7,
29.1 (CH2), 28.0 (CH2 CNPiv), 27.5 (CH2), 25.0, 24.9 (CH3 CNPiv), 23.4
(CH2), 18.2 (CH3-6); HRMS calculated for [C39H48N2O8 + Na]+: 695.33358,
found 695.32958.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3,4-di-O-
benzyl-2-O-levulinoyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-
cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranoside (26) Acceptor
25 (0.358 g, 0.533 mmol, 1 equiv.) and donor 13 (0.352 g, 0.658 mmol,
1.2 equiv.) were coevaporated three times with anhydrous toluene before
being dissolved in distilled DCM (7.6 mL) under an argon atmosphere
and stirred at room temperature for 20 min over activated molecular
sieves (3Å). The reaction was cooled to 0 °C, followed by the addition of
NIS (0.178 g, 0.791 mmol, 1.44 equiv.) and a solution of TMSOTf in
distilled DCM (0.221 M, 0.24 mL, 0.053 mmol, 0.1 equiv.) were added.
After 40 min, TLC and TLC-MS showed complete consumption of the
acceptor and the reaction was quenched with 0.1 mL Et3N. The mixture
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-4-O-benzyl-3-O-
levulinoyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-
rhamnopyranoside (24) Donor 12 (0.843 g, 1.52 mmol, 1 equiv.) and
acceptor 15 (1.552 g, 4.74 mmol, 3 equiv.) were coevaporated three
times with anhydrous toluene before being dissolved in distilled DCM (17
mL) under an argon atmosphere. Activated molecular sieves (3Å) were
added and the mixture was cooled to 0 °C. The mixture was stirred for 15
min, followed by the addition of NIS (0.42 g, 1.9 mmol, 1.2 equiv.) and a
solution of TMSOTf in distilled DCM (0.221 M, 0.68 mL, 0.15 mmol, 0.1
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
was diluted with Et2O and the organic layer was washed with H2O (2x)
and brine (2x), dried over MgSO4 and concentrated in vacuo. Purification
by size exclusion (1:1 DCM/MeOH) resulted in the title compound as a
yellow oil (0.544 g, 0.496 mmol, 93%). Rf = 0.64 (7:2 PE/EtOAc); 1H
NMR (400 MHz, CDCl3) δ: 7.36-7.20 (m, 24H, CHarom), 7.15 (m, 1H,
CHarom), 5.39 (m, 1H, H-2’), 5.15 (d, 2H, J = 13.2 Hz, CH2 Cbz), 5.04 (s,
2H, H-1’, H-2), 4.93 (d, 1H, J = 11.6 Hz, CH2 Bn), 4.77 (d, 1H, J = 10.8
Hz, CH2 Bn), 4.64-4.56 (m, 4H, H-1, 2x CH2 Bn), 4.49-4.46 (m, 3H, CH2
Bn), 4.11 (d, 1H, J = 8.8 Hz, H-3), 3.81 (dd, 1H, J = 9.2, 3.2 Hz, H-3’),
3.74 (m, 1H, H-5), 3.68-3.52 (m, 2H, H-5’, CH2), 3.44-3.38 (m, 2H, H-4,
H-4’), 3.33-3.18 (m, 3H, CH2), 2.71-2.63 (m, 4H, 2x CH2 Lev), 2.48 (q, 2H,
J = 6.8 Hz, CH2 CNPiv), 2.11 (s, 3H, CH3 Lev), 1.53-1.43 (m, 4H, CH2),
1.31-1.27 (m, 14H, CH3-6, CH3-6’, 2x CH3 CNPiv, CH2). 13C NMR (100
MHz, CDCl3) δ: 205.9 (C=O Lev ketone), 174.0, 171.6 (C=O CNPiv, Lev),
156.6 (C=O Cbz), 138.5, 137.8, 137.7, 137.6, 136.7 (Cq Carom), 128.9,
128.8, 128.4, 128.4, 128.2, 128.1, 128.1, 128.0, 127.9, 127.8, 127.7,
127.6, 127.5, 127.4, 127.1 (CHarom), 117.2 (CN), 99.6 (C-1’), 96.4 (C-1),
80.1 (C-4), 79.4 (C-4’), 77.4 (C-3), 76.7 (C-3’), 75.5, 74.7 (CH2 Bn), 73.1
(C-2), 71.0 (CH2 Bn), 68.9 (C-2’), 68.2 (C-5’), 67.5 (C-5), 67.5 (CH2), 66.9
(CH2 Cbz), 50.4, 50.1 (CH2 Bn), 46.9, 46.0 (CH2), 40.8 (Cq CNPiv), 37.8
(CH2 Lev), 29.6 (CH3 Lev), 28.9 (CH2), 28.0, 27.8, 27.5, 27.3 (CH2 CNPiv,
CH2 Lev, CH2), 24.7, 24.5 (CH3 CNPiv), 23.2 (CH2), 17.9, 17.7 (CH3-6,
CH3-6’). HRMS calculated for [C64H76N2O14 + NH4]+: 1114.56348, found
1114.56494.
(0.0703 g, 0.312 mmol, 1.2 equiv.) and a solution of TMSOTf in distilled
DCM (0.221 M, 0.12 mL, 0.026 mmol, 0.1 equiv.) were added. After 50
min, TLC and TLC-MS showed complete consumption of the acceptor
and the reaction was quenched with 0.1 mL Et3N. The mixture was
diluted with Et2O and the organic layer was washed with H2O (1x) and
brine (2x), dried over MgSO4 and concentrated in vacuo. Purification by
size exclusion (1:1 DCM/MeOH) and coevaporation with CHCl3 resulted
in the title compound as a yellow oil (0.320 g, 0.181 mmol, 94%). Rf = 0.5
(2:1 PE/EtOAc); IR (neat): 2932, 1736, 1697, 1452, 1362, 1206, 1128,
1072, 980, 914, 893, 733, 696 cm-1; 1H NMR (400 MHz, CDCl3): δ 7.34-
7.15 (m, 40H, CHarom), 5.41 (s, 1H, H-2’’’), 5.23 (s, 1H, H-2’’), 5.16 (d, 2H,
J = 9.6 Hz, CH2 Cbz), 5.07 (s, 1H, H-1’’’), 5.0 (s, 1H, H-2), 4.97 (s, 1H, H-
1’), 4.96-4.86 (m, 2H, CH2 Bn), 4,84 (s, 1H, H-1’’), 4.75 (d, 1H, J = 10.8
Hz, CH2 Bn), 4.65-4.56 (m, 8H, H-1, 4x CH2 Bn), 4.54-4.44 (m, 4H, 2x
CH2 Bn), 4.18 (dd, 1H, J = 9.6, 3.2 Hz, H-3’’), 4.02 (d, 1H, J = 9.2 Hz, H-
3), 3.83-3.77 (m, 3H, H-2’, H-3’’’, H-5*), 3.72-3.68 (m, 3H, H-3’, H-5*, H-
5*), 3.60-3.46 (m, 1H, CH2), 3.45-3.32 (m, 5H, H-4, H-4’, H-4’’, H-4’’’, H-
5*), 3.31-3,14 (m, 3H, CH2), 2.71-2.63 (m, 4H, 2x CH2 Lev), 2.55-2.35 (m,
4H, 2x CH2 CNPiv), 2.14 (s, 3H, CH3 Lev), 1.58 – 1.16 (m, 28H); 13C
NMR (100 MHz, CDCl3): δ 206.1 (C=O Lev ketone), 174.2, 173.8, 171.8
(C=O 2x CNPiv, Lev), 138.7, 138.6, 138.2, 138.0, 137.9 (Cq Carom), 128.8,
128.5, 128.4, 128.4, 128.3, 128.3, 128.3, 128.2, 128.1, 128.1, 127.9,
127.9, 127.8, 127.7, 127.7, 127.7, 127.6, 127.6, 127.5, 127.3 (CHarom),
117.4 (CN), 101.4 (C-1’), 99.4 (C-1’’’), 98.5 (C-1’’), 96.5 (C-1), 80.3, 80.0,
79.9, 79.6 (C-4, C-4’, C-4’’, C-4’’’), 78.6 (C-3’), 78.2 (C-3), 77.4, 77.1 (C-
2’, C-3’’’), 75.8 (C-3’’), 75.6, 75.5, 75.0, 75.0 (CH2 Bn), 73.4 (C-2), 73.0
(C-2’’), 72.0, 71.2 (CH2 Bn), 69.0 (C-2’’’), 68.7, 68.5, 68.4 (C-5*), 67.8
(CH2), 67.6 (C-5*), 67.1 (CH2 Cbz), 50.6, 50.3 (CH2 Bn), 47.1, 46.1 (CH2),
40.9 (Cq CNPiv), 38.0 (CH2 Lev), 29.9 (CH3 Lev), 29.0, 28.1, 27.9, 27.8,
27.7, 27.5 (2x CH2 CNPiv, CH2 Lev, 2x CH2), 24.8, 24.7, 24.7 (CH3
CNPiv), 23.3 (CH2), 18.1, 18.0, 17.8, 17.8 (CH3-6, CH3-6’, CH3-6’’, CH3-
6’’’); HRMS calculated for [C103H121N3O23 + NH4]+: 1786.87623, found
1786.87609. *The difference between 5, 5’, 5’’, 5’’’ could not be
determined.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3,4-di-O-
benzyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-α-L-rhamnopyranoside (27) Compound 26 (0.526
g, 0.479 mmol, 1 equiv.) was dissolved in pyridine (3.8 mL), cooled to
0 °C and AcOH (0.96 mL) was added, followed by the addition of
hydrazine acetate (0.228 g, 2.48 mmol, 5 equiv.). The mixture was
allowed to warm up to room temperature and stirred for 1h. The reaction
mixture was quenched with acetone and diluted with EtOAc. The organic
layer were washed with H2O (3x) and brine (1x), dried over MgSO4,
concentrated in vacuo. Purification by column chromatography (2:1
PE/EtOAc) and coevaporation with DCM and CHCl3 resulted in the title
compound as an oil (0.433 g, 0.433 mmol, 90%). Rf = 0.64 (7:2
PE/EtOAc); IR (neat): 2972, 2932, 2872, 1734, 1695, 1472, 1452, 1422,
1366, 1300, 1248, 1209, 1126, 1072, 1028, 914, 837, 733, 696 cm-1; 1H
NMR (400 MHz, CDCl3) δ: 7.36-7.20 (m, 24H, CHarom), 7.15 (m, 1H,
CHarom), 5.16 (d, 2H, J = 12.8 Hz, CH2 Cbz), 5.07 (s, 2H, H-1’, H-2), 4.88
(d, 1H, J = 11.6 Hz, CH2 Bn), 4.69-4.57 (m, 6H,H-1, 3x CH2 Bn), 4.48 (d,
2H, J = 8.4 Hz, CH2 Bn), 4.11 (m, 1H, H-3), 3.91 (s, 1H, H-2’), 3.71-3.68
(m, 2H, H-3’, H-5), 3.60-3.54 (m, 2H, H-5, CH2), 3.49-3.38 (m, 2H, H-4,
H-4’), 3.37-3.3.13 (m, 3H, CH2), 2.64 (bs, 1H, OH), 2.49 (q, 2H, J = 14.8
Hz, CH2 CNPiv), 1.53 - 1.22 (m, 16H); 13C NMR (100 MHz, CDCl3) δ:
174.0 (C=O CNPiv), 138.6, 137.8, 136.8 (Cq Carom), 128.5, 128.4, 128.2,
128.0, 127.9, 127.9, 127.8, 127.7, 127.5, 127.5, 127.2 (CHarom), 117.3
(CN), 101.6 (C-1’), 96.6 (C-1), 80.3 (C-4), 79.6 (C-4’), 79.0 (C-3’), 77.3
(C-3), 75.5 (CH2 Bn), 74.8 (CH2 Bn), 73.3 (C-2), 71.6 (CH2 Bn), 68.6 (C-
2’), 68.0 (C-5’), 67.7 (CH2), 67.6 (C-5), 67.1 (CH2 Cbz), 50.5, 50.2 (CH2
Bn), 47.0, 46.0 (CH2), 40.9 (Cq CNPiv), 28.9 (CH2), 27.7 (CH2 CNPiv),
27.4 (CH2), 24.8, 24.7 (CH3 CNPiv), 23.2 (CH2), 18.0, 17.7 (CH3-6, CH3-
6’). HRMS calculated for [C59H70N2O12 + NH4]+: 1016.52670, found
1016.52807.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(2-O-(3-O-(3,4-
di-O-benzyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-α-L-rhamnopyranosyl)-3,4-di-O-benzyl-α-L-
rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-
α-L-rhamnopyranoside (29) Compound 28 (0.185 g, 0.104 mmol, 1
equiv.) was dissolved in pyridine (0.82 mL) and AcOH (0.2 mL).
Hydrazine acetate (0.050 g, 0.52 mmol, 5 equiv.) was added and the
mixture was stirred for 1h. TLC and TLC/MS analysis showed complete
consumption of the starting material after which the reaction mixture was
quenched with acetone and diluted with EtOAc. The organic layer were
washed with H2O and brine (1x), dried over MgSO4, concentrated in
vacuo. Purification by column chromatography (PE/EtOAc 4:1  2:1)
resulted in the title compound as an oil (0.167 g, 0.099 mmol, 96%) Rf =
0.59 (7:2 PE/EtOAc); IR (neat): 2970, 1926, 1736, 1697, 1472, 1454,
1422, 1364, 1298, 1207, 1126, 1072, 1059, 982, 912, 837, 733, 696 cm-
1
;
1H NMR (400 MHz, CDCl3): δ 7.38-7.15 (m, 40H, CHarom), 5.26 (s, 1H,
H-2’’), 5.16 (d, 2H, J = 10.0 Hz, CH2 Cbz), 5.11 (s, 1H, H-1’’’), 4.99 (s, 1H,
H-2), 4.97 (s, 1H, H-1’), 4.91-4.87 (m, 3H, H-1’’, CH2 Bn), 4.69-4.54 (m,
10H, H-1, 5x CH2 Bn), 4.52-4.47 (m, 3H, 2x CH2 Bn), 4.17 (dd, 1H, J =
9.6, 3.2 Hz, H-3’’), 4.02 (d, 1H, J = 7.2 Hz, H-3), 3.92 (s, 1H, H-2’’’), 3.84
(s, 1H, H-2’), 3.82-3.76 (m, 1H, H-5*), 3.72-3.66 (m, 4H, H-3’, H-3’’’, H-5*,
H-5*), 3.58-3.49 (m, 1H, CH2), 3.47-3.31 (m, 5H, H-4, H-4’, H-4’’, H-4’’’,
H-5*), 3.28-3,14 (m, 3H, CH2), 2.56-2.44 (m, 4H, 2x CH2 CNPiv), 1.57 -
1.16 (m, 28H); 13C NMR (100 MHz, CDCl3) δ: 174.2, 173.7 (C=O 2x
CNPiv), 138.7, 138.6, 138.3, 137.9, 137.9 (Cq Carom), 128.6, 128.4, 128.4,
128.3, 128.1, 128.1, 128.0, 127.9, 127.8, 127.8, 127.7, 127.7, 127.6,
127.3 (CHarom), 117.5, 117.4 (CN), 101.4 (C-1’), 101.2 (C-1’’’), 98.5 (C-
1’’), 96.5 (C-1), 80.4, 80.0, 79.9, 79.7 (C-4, C-4’, C-4’’, C-4’’’), 79.2 (C-
3’’’), 78.7 (C-3’), 78.3 (C-3), 76.2 (C-3’’), 75.7 (C-2’), 75.6, 75.5, 75.1,
75.0 (CH2 Bn), 73.4 (C-2), 73.1 (C-2’’), 72.0, 71.8 (CH2 Bn), 68.7 (C-2’’’,
C-5*), 68.5, 68.1 (C-5*), 67.8 (CH2), 67.6 (C-5*), 67.2 (CH2 Cbz), 50.6,
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(2-O-(3-O-(3,4-
di-O-benzyl-2-O-levulinoyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-
cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-3,4-di-O-
benzyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-α-L-rhamnopyranoside (28) Acceptor 27 (0.191 g,
0.193 mmol, 0.8 equiv.) and donor 14 (0.220 g, 0.250 mmol, 1 equiv.)
were coevaporated three times with anhydrous toluene before being
dissolved in distilled DCM (3.6 mL) under an argon atmosphere and
stirred at room temperature for 20 min over activated molecular sieves
(3Å). The reaction was cooled to 0 °C, followed by the addition of NIS
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
50.3 (CH2 Bn), 47.1, 46.2 (CH2), 41.0, 40.9 (Cq CNPiv), 29.8 (CH2), 29.4,
29.1 (CH2), 27.8, 27.8 (2x CH2 CNPiv), 24.9, 24.9, 24.8 (CH3 CNPiv),
23.3 (CH2), 18.1, 18.0, 17.8 (CH3-6, CH3-6’, CH3-6’’, CH3-6’’’). HRMS
calculated for [C99H115N3O21 + NH4]+: 1688.83945, found 1688.84017.
*The difference between 5, 5’, 5’’, 5’’’ could not be determined.
CH2 CNPiv, CH2 Lev, CH2), 25.0, 24.9, 24.8, 24.7 (CH3 CNPiv), 23.4
(CH2), 18.1, 17.9 (CH3-6, CH3-6’, CH3-6’’). HRMS calculated for
[C83H99N3O19 + NH4]+: 1459.72110, found 1459.72186.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(3,4-di-O-
benzyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
5-aminopentanyl-3-O-(2-O-(3-O-(α-L-rhamnopyranosyl)-α-L-
dimethylpropanoyl)-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-
2,2-dimethylpropanoyl)-α-L-rhamnopyranoside (31) Compound 30
(0.195 g, 0.135 mmol, 1 equiv.) was dissolved in pyridine (1.2 mL) and
AcOH (0.3 mL). Hydrazine acetate (0.065 g, 0.69 mmol, 5 equiv.) was
added and the mixture was stirred for 45 min, after which TLC-MS
analysis showed complete reaction. The reaction mixture was quenched
with acetone and diluted with EtOAc. The organic layer were washed
with H2O (3x) and brine (1x), dried over MgSO4, concentrated in vacuo.
Purification by column chromatography (2:1 PE/EtOAc) and
coevaporation with DCM and CHCl3 resulted in the title compound as an
oil (0.141 g, 0.105 mmol, 78%). Rf = 0.59 (2:1 PE/EtOAc). IR (neat):
2970, 2930, 1736, 1695, 1454, 1422, 1362, 1298, 1207, 1128, 1072,
1042, 1028, 982, 917, 837, 733, 696 cm-1. 1H NMR (400 MHz, CDCl3) δ:
7.39-7.23 (m, 29H, CHarom), 7.15 (m, 1H, CHarom), 5.17-5.15 (m, 3H, H-2’,
CH2 Cbz), 5.06 (m, 1H, H-2), 5.03 (s, 1H, H-1’’), 4.99 (s, 1H, H-1’’), 4.86-
4,81 (m, 2H, CH2 Bn), 4.67 (d, 1H, J = 11.2 Hz, CH2 Bn), 4.61-4.59 (m,
6H, H-1, 3x CH2 Bn), 4.49-4.47 (m, 2H, CH2 Bn), 4.13 (dd, 1H, J = 9.2,
2.4 Hz, H-3), 4.02 (dd, 1H, J = 9.6, 3.2 Hz, H-3’), 3.83 (m, 1H, H-2’’),
3.69-3.53 (m, 5H, H-3’’, H-5, H-5’, H-5’’’, CH2), 3.47-3.37 (m, 3H, H-4, H-
4’, H-4’’), 3.27-3.18 (m, 3H, CH2), 2.58 (q, 2H, J = 8.4 Hz, CH2 CNPiv),
2.44 (q, 2H, J = 8.8 Hz, CH2 CNPiv), 1.52 - 1.14 (m, 25H). 13C NMR (100
MHz, CDCl3): δ 174.4, 173.8, (C=O CNPiv), 138.6, 138.1, 138.0, 137.9,
137.7 (Cq Carom), 128.5, 128.5, 128.1, 128.0, 127.9, 127.9, 127.7, 127.6,
127.3 (CHarom, 117.4, 117.4 (CN), 101.8 (C-1’’), 98.8 (C-1’), 96.7 (C-1),
80.4, 80.0, 79.5 (C-4, C-4’, C-4’’), 79.0 (C-3’’), 76.9 (C-3’), 76.6 (C-3),
75.5, 75.2, 74.9 (CH2 Bn), 73.2 (C-2, C-2’), 71.8 (CH2 Bn), 68.7 (C-2’’),
68.7, 68.1, 67.8 (C-5, C-5’, C-5’’), 67.7 (CH2), 67.2 (CH2 Cbz), 50.6, 50.3
(CH2 Bn), 47.1, 46.1 (CH2), 41.2, 40.9 (Cq CNPiv), 29.8, 29.4, 29.1 (CH2),
27.9, 27.7 (CH2 CNPiv), 25.0, 24.9, 24.8, 24.7 (CH3 CNPiv), 23.4 (CH2),
18.1, 17.9, 17.8 (CH3-6, CH3-6’, CH3-6’’). HRMS calculated for
[C78H93N3O17 + NH4]+: 1361.68432, found 1361.68484.
rhamnopyranosyl)-α-L-rhamnopyranosyl)-α-L-rhamnopyranoside
(10) Tetrasaccharide 29 (0.0345 g, 0.0206 mmol) was dissolved in
H2O/THF/tBuOH (3 mL:1.3 mL:1.3 mL) and several drops of acetic acid
were added. The solution was purged with argon for 5 minutes after
which Pd(OH)2/C (60 mg, 20% wt loading) was added followed by
another purge with argon for 5 minutes. The solution was purged with
hydrogen for 5 minutes and kept under a hydrogen atmosphere overnight.
The mixture was filtered over a Whatmann filter, which was rinsed 3x
with the H2O/THF/tBuOH mixture. The solution was concentrated and
redissolved in 10 mL H2O. Triethylamine (0.5 mL) was added and the
reaction was stirred overnight. Purification using size exclusion
chromatography (sephadex LH20 9:1 MeOH/H2O) followed by two
lyophilizations yielded fully deprotected tetrasaccharide 10 in quantitave
yield (16.2 mg) as a white powder. 1H NMR (D2O, 500 MHz): δ 5.22 (s,
1H), 5.06 (s, 1H), 4.97 (s, 1H), 4.22 – 4.13 (m, 1H), 4.11 – 4.06 (m, 2H),
4.04 – 3.93 (m, 2H), 3.90 – 3.69 (m, 9H), 3.61 – 3.44 (m, 6H), 3.22 (q, 3H,
J = 7.3, 7.3, 7.3 Hz), 3.06 – 2.99 (m, 2H), 2.64 (s, 2H), 1.77 – 1.63 (m,
5H), 1.54 – 1.42 (m, 2H), 1.37 – 1.23 (m, 25H); 13C NMR (D2O, 126
MHz): δ 102.4, 102.1, 100.8, 99.7 (4x C-1), 78.1, 77.5, 72.2, 72.0, 71.8,
71.4, 70.2, 70.2, 70.0, 70.0, 69.9, 69.4, 69.3, 69.2, 68.7, 67.5, 46.8, 42.3,
39.4, 28.3, 28.1, 26.6, 25.8, 25.0, 22.5, 16.7, 16.7, 16.7, 16.6, 8.3. HRMS
calculated for [C29H53NO17 + H]+: 688.33865, found 688.33825.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(3,4-di-O-
benzyl-2-O-levulinoyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-
cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-4-O-benzyl-2-
O-(3-cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranoside
(30)
Acceptor 25 (0.204 g, 0.303 mmol, 1.1 equiv.) and donor 14 (0.232 g,
0.264 mmol, 1 equiv.) were coevaporated three times with anhydrous
toluene before being dissolved in distilled DCM (3.8 mL) under an argon
atmosphere and stirred at room temperature for 30 min over activated
molecular sieves (3Å). The reaction was cooled to 0 °C, followed by the
addition of NIS (0.073 g, 0.32 mmol, 1.2 equiv.) and a solution of
TMSOTf in distilled DCM (0.221 M, 0.12 mL, 0.027 mmol, 0.1 equiv.)
were added. After 100 min the reaction was quenched with 0.1 mL Et3N,
diluted with Et2O and the organic layer was washed with H2O (2x) and
brine (2x). The organic layer was dried over MgSO4 and concentrated in
vacuo. Purification by size exclusion (1:1 DCM/MeOH) and
coevaporation with CHCl3 resulted in the title compound as a yellow oil
(0.199 g, 0.138 mmol, 52%). Rf = 0.31 (2:1 PE/EtOAc). 1H NMR (400
MHz, CDCl3) δ: 7.38-7.24 (m, 29H, CHarom), 7.16 (m, 1H, CHarom), 5.36
(m, 1H, H-2’’), 5.17-5.13 (m, 3H, H-2’, CH2 Cbz), 5.06 (s, 1H, H-2), 4.98
(s, 2H, H-1’, H-1’’), 4.89 (d, 1H, J = 11.2 Hz, CH2 Bn), 4.82 (d, 1H, J =
10.8 Hz, CH2 Bn), 4.76 (d, 1H, J = 10.8 Hz, CH2 Bn), 4.62-4.56 (m, 5H,
H-1, 2x CH2 Bn), 4.46-4.43 (m, 3H, 2x CH2 Bn), 4.11 (d, 1H, J = 7.2 Hz,
H-3), 4.02 (dd, 1H, J = 9.6, 3.2 Hz, H-3’), 3.73 (dd, 1H, J = 9.2, 3.2 Hz, H-
3’’), 3.66-3.54 (m, 4H, H-5, H-5’, H-5’’’, CH2), 3.46-3.40 (m, 2H, H-4, H-4’),
3.35 (t, 1H, J = 9.2 Hz, H-4’’), 3.30-3.18 (m, 3H, CH2), 2.71-2.62 (m, 4H,
2x CH2 Lev), 2.59 (q, 2H, J = 9.6 Hz, CH2 CNPiv), 2.41 (q, 2H, J = 12.4
Hz, CH2 CNPiv), 2.15 (s, 3H, CH3 Lev), 1.52 – 1.14 (m, 25H); 13C NMR
(100 MHz, CDCl3) δ: 206.3 (C=O Lev ketone), 174.4, 173.9, 171.8 (C=O
CNPiv, CNPiv, Lev), 138.7, 138.0, 137.9, 137.9, 137.7 (Cq, Carom), 128.6,
128.5, 128.5, 128.4, 128.4, 128.2, 128.0, 128.0, 127.9, 127.8, 127.7,
127.6, 127.4 (CHarom), 117.5, 117.4 (CN), 99.9, 98.9 (C-1’, C-1’’), 96.7
(C-1), 80.4 (C-4), 79.7 (C-4’), 79.5 (C-4’’), 77.4 (C-3’’), 77.0 (C-3), 76.7
(C-3’), 75.7, 75.2. 74.9 (CH2 Bn), 73.2 (C-2), 73.0 (C-2’), 71.2 (CH2 Bn),
69.0 (C-2’’), 68.7, 68.5, 67.8, (C-5, C-5’, C-5’’), 67.7 (CH2), 67.2 (CH2
Cbz), 50.6, 50.2 (CH2 Bn), 47.1, 46.2 (CH2), 41.1, 40.9 (Cq CNPiv), 38.1
(CH2 Lev), 29.9 (CH3 Lev), 29.8, 29.1 (CH2), 28.1, 27.9, 27.7, 27.5 (2x
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(2-O-(4-O-
benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-3-O-levulinoyl-α-L-
rhamnopyranosyl)-3,4-di-O-benzyl-α-L-rhamnopyranosyl)-4-O-
benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-
4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-
rhamnopyranoside (32) Acceptor 31 (1.09 g, 0.81 mmol, 1.0 equiv.) and
donor 12 (0.68 g, 1.22 mmol, 1.5 equiv.) were coevaporated three times
with anhydrous toluene before being dissolved in dry DCM. The solution
was stirred at room temperature on activated molecular sieves after
which NIS (0.309 g, 1.377 mmol. 1.7 equiv.) was added. The reaction
mixture was cooled to -40 °C and treated with 1.4 mL of a freshly
prepared solution of TMSOTf in DCM (0.1 M, 1.4 mL, 0.17 equiv.). After
65 minutes, TLC analysis showed complete consumption of the acceptor,
and the reaction was quenched with 0.5 mL Et3N. The mixture was dilute
with EtOAc, washed with sat. aq. Na2S2O3, sat. aq. NaHCO3 and sat. aq.
NaCl, dried over MgSO4 and concentrated. Column purification
(hexanes/acetone 10:1  4:1) followed by size exclusion purification
(DCM/MeOH 1:1) yielded tetrasaccharide 32 as a yellow oil (1.087 g,
0.608 mmol, 75%). Rf 0.62 (PE/EtOAc, 1/1, v/v); IR (neat, cm-1): 698, 731,
979, 1074, 1128, 1454, 1697, 1737, 2245, 2877, 2935, 2976; 1H NMR
(CDCl3 400 MHz): δ 7.37 – 7.13 (m, 35H), 5.44 – 5.36 (m, 1H), 5.33 (dd,
1H, J = 9.5, 3.3 Hz), 5.19 – 5.10 (m, 3H), 5.01 – 4.77 (m, 5H), 4.77 –
4.66 (m, 3H), 4.61 (dd, 5H, J = 11.0, 5.4 Hz), 4.52 (dd, 3H, J = 11.8, 3.7
Hz), 4.48 (s, 1H), 3.91 – 3.76 (m, 2H), 3.70 – 3.64 (m, 2H), 3.64 – 3.54
(m, 2H), 3.47 (dp, 4H, J = 14.8, 5.1, 5.1, 4.9, 4.9 Hz), 3.42 – 3.11 (m, 5H),
2.81 – 2.34 (m, 13H), 2.20 – 2.09 (m, 3H), 1.58 – 1.07 (m, 34H) ppm 13
C
NMR (CDCl3, 101 MHz): δ 206.3, 174.3, 173.8, 173.7, 171.7, 138.8,
138.3, 138.0, 137.9, 137.8, 137.6, 128.5, 128.5, 128.4, 128.4, 128.3,
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
128.3, 128.2, 128.2, 128.1, 128.0, 127.9, 127.9, 127.8, 127.6, 127.6,
127.5, 127.4, 127.3, 117.5, 117.3, 117.3, 101.6, 98.7, 98.6, 96.6, 80.3,
79.7, 79.4, 79.0, 78.3, 77.7, 75.6, 75.3, 75.1, 74.9, 73.2, 73.1, 72.2, 72.0,
70.8, 68.8, 68.6, 68.1, 67.7, 67.6, 67.1, 41.1, 40.8, 37.8, 29.8, 29.1, 27.9,
27.9, 27.8, 27.6, 25.0, 24.9, 24.8, 24.8, 24.8, 24.6, 23.3, 18.0, 17.9, 17.8,
17.7; HRMS (MALDI-TOF): [M+Na]+ calculated for C102H122N4O24Na
1809,8341, found 1809.8353.
2.35 (m, 5H), 2.15 (s, 3H), 1.60 – 1.03 (m, 46H); 13C NMR (CDCl3, 101
MHz): δ 206.2, 174.3, 174.0, 173.9, 171.8, 138.7, 138.7, 138.3, 138.0,
137.9, 137.9, 137.7, 137.6, 128.7, 128.6, 128.5, 128.5, 128.4, 128.4,
128.3, 128.3, 128.1, 127.9, 127.9, 127.8, 127.7, 127.7, 127.7, 127.5,
127.3, 117.6, 117.4, 117.3, 100.0, 98.8, 98.5, 96.7, 80.6, 80.4, 79.6, 79.5,
77.0, 76.8, 75.6, 75.2, 74.9, 73.3, 73.2, 73.0, 72.8, 72.0, 71.2, 69.0, 68.8,
68.7, 68.5, 68.5, 67.2, 41.2, 41.1, 40.9, 40.9, 38.1, 29.9, 28.2, 27.9, 27.9,
27.7, 25.0, 24.8, 24.7, 24.7, 23.4, 18.1, 17.9, 17.9; HRMS (MALDI-TOF):
[M+Na]+ calculated for C141H167N5O33Na 2481,1436, found 2481.1436.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(2-O-(4-O-
benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-
3,4-di-O-benzyl-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-
2,2-dimethylpropanoyl)-α-L-rhamnopyranoside (33) A solution of 32
(0.492 g, 0.275 mmol, 1.0 equiv.) in pyridine/AcOH (2.9 mL:0.75 mL) was
cooled to 0 °C and treated with H2NNH2·AcOH (0.124 g, 1.35 mmol, 5
equiv.). After 90 minutes the reaction was quenched with acetone, diluted
with EtOAc, washed with H2O (2x) and sat. aq. NaCl, dried over MgSO4
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(3,4-di-O-
benzyl-2-O-(3-O-(3-O-(3,4-di-O-benzyl-α-L-rhamnopyranosyl)-4-O-
benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-
4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-
rhamnopyranosyl)-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-
2,2-dimethylpropanoyl)-α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-
cyano-2,2-dimethylpropanoyl)-α-L-rhamnopyranoside
(35)
and
concentrated.
Purification
by
column
chromatography
Compound 34 (0.133 g, 0.054 mmol) was dissolved in 0.8 mL pyridine
and 0.2 mL AcOH. The solution was cooled to 0 °C followed by addition
of H2NNH2·AcOH (0.025 g, 0.27 mmol, 5 equiv.) and stirred for 10
minutes at 0 °C. After stirring at rt for 160 minutes, TLC and TLC/MS
analysis showed complete conversion of the starting material and the
reaction was quenched by addition of acetone. The mixture was diluted
with EtOAc, washed with H2O and sat. aq. NaCl, dried over MgSO4 and
concentrated. Column purification (hexanes/acetone) followed by size
exclusion purification (DCM:MeOH 1/1) yielded the title hexasaccharide
as a yellow glass-like solid (0.124 g, 0.052 mmol, 96%). Rf 0.68
(PE/EtOAc, 1/1, v/v); IR (neat, cm-1): 698, 734, 983, 1028, 1041, 1454,
1697, 1735, 2247, 2875, 2933, 2974; 1H NMR (400 MHz, CDCl3): δ 7.40
– 7.12 (m, 50H), 5.26 – 4.97 (m, 5H), 4.99 – 4.72 (m, 9H), 4.72 – 4.45 (m,
17H), 4.17 (dd, 1H, J = 9.5, 3.1 Hz), 4.13 – 4.05 (m, 1H), 3.99 (ddd, 2H, J
= 21.0, 9.5, 3.1 Hz), 3.85 – 3.53 (m, 10H), 3.49 – 3.29 (m, 8H), 2.61 –
2.32 (m, 10H), 1.49 – 1.03 (m, 46H); 13C NMR (101 MHz, CDCl3): δ
174.4, 174.0, 174.0, 173.9, 138.8, 138.7, 138.3, 138.1, 138.1, 138.0,
137.9, 137.8, 137.7, 128.6, 128.6, 128.5, 128.5, 128.4, 128.3, 128.1,
128.0, 128.0, 128.0, 127.9, 127.9, 127.8, 127.7, 127.7, 127.6, 127.4,
117.5, 117.4, 117.4, 117.4, 101.8, 101.7, 98.8, 98.6, 98.5, 96.7, 80.6,
80.4, 80.1, 79.9, 79.6, 79.1, 78.8, 77.8, 76.9, 75.7, 75.5, 75.4, 75.3, 75.2,
75.0, 74.9, 74.7, 73.3, 73.2, 72.8, 72.0, 71.8, 68.9, 68.7, 68.6, 68.2, 67.8,
67.8, 67.3, 50.7, 46.2, 41.2, 40.9, 40.9, 29.2, 28.0, 27.9, 27.8, 27.8, 25.1,
25.0, 24.9, 24.9, 24.9, 24.8, 24.7, 23.4, 18.1, 17.9; HRMS (MALDI-TOF):
[M+Na]+ calculated for C136H161N5O31Na 2383.1068, found 2383.1064.
(hexanes/acetone 9:1  4:1) yielded the title compound 33 as a
colorless oil (0.306 g, 0.18 mmol, 67%). Rf 0.74 (PE/EtOAc, 1/1, v/v); IR
(neat, cm-1): 696, 732, 979, 1028, 1055, 1128, 1454, 1697, 1735, 2245,
2933, 2974, 3030; 1H NMR (500 MHz, CDCl3) δ 7.37 – 7.18 (m, 35H),
5.26 (dd, J = 3.1, 1.7 Hz, 1H), 5.19 – 5.13 (m, 3H), 5.13 – 5.02 (m, 3H),
5.00 – 4.93 (m, 3H), 4.90 – 4.79 (m, 4H), 4.78 – 4.62 (m, 5H), 4.62 –
4.59 (m, 2H), 4.59 – 4.42 (m, 8H), 4.11 (dt, J = 9.1, 4.6 Hz, 2H), 3.98 (dd,
J = 9.5, 3.1 Hz, 1H), 3.85 – 3.72 (m, 3H), 3.67 (dd, J = 9.0, 2.8 Hz, 2H),
3.65 – 3.48 (m, 4H), 3.48 – 3.12 (m, 11H), 2.66 – 2.38 (m, 9H), 1.64 –
0.94 (m, 34H); 13C NMR (126 MHz, CDCl3) δ 174.4, 174.2, 174.0, 138.8,
138.7, 138.3, 138.1, 138.1, 138.0, 137.9, 137.7, 137.0, 132.3, 129.3,
128.7, 128.7, 128.6, 128.6, 128.5, 128.5, 128.4, 128.4, 128.3, 128.3,
128.2, 128.1, 128.0, 127.9, 127.9, 127.9, 127.8, 127.7, 127.7, 127.6,
127.6, 127.6, 127.3, 117.9, 117.4, 117.4, 101.7, 98.8, 96.7, 92.6, 91.9,
81.4, 81.3, 81.1, 80.4, 80.1, 79.8, 79.6, 79.5, 79.1, 78.9, 77.9, 76.8, 75.6,
75.3, 75.2, 75.2, 75.1, 74.9, 74.9, 73.8, 73.3, 73.3, 73.2, 73.0, 72.3, 72.1,
71.8, 70.2, 69.8, 68.7, 68.2, 68.2, 67.8, 67.8, 67.6, 67.2, 50.7, 50.3, 47.2,
46.2, 41.2, 41.2, 40.9, 29.2, 28.1, 28.0, 27.9, 27.8, 27.6, 25.1, 25.0, 24.9,
24.9, 24.8, 24.7, 23.4, 18.3, 18.1, 17.9; HRMS (MALDI-TOF): [M+Na]+
calculated for C97H116N4O22Na 1711,7973, found 1711.7979.
N-benzyl-N-benzyloxycarbonyl-5-aminopentanyl-3-O-(3-O-(3,4-di-O-
benzyl-2-O-(3-O-(3-O-(3,4-di-O-benzyl-2-O-levulinoyl-α-L-
rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-
α-L-rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-
dimethylpropanoyl)-α-L-rhamnopyranosyl)-α-L-rhamnopyranosyl)-4-
O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-α-L-
5-aminopentanyl-3-O-(3-O-(2-O-(3-O-(3-O-(α-L-rhamnopyranosyl)-α-
L-rhamnopyranosyl)-α-L-rhamnopyranosyl)-α-L-rhamnopyranosyl)-
α-L-rhamnopyranosyl)-α-L-rhamnopyranoside (11) Compound 35
(0.069 g, 0.029 mmol) was dissolved in a mixture H2O/THF/tBuOH (3
mL:1.3 mL: 1.3 mL) followed by addition of several drops of acetic acid.
The solution was purged for 5 minutes with argon. Pd(OH)2/C (60 mg,
20% wt loading) was added and the solution was purged for another 5
minutes with argon. The solution was then purged with hydrogen for 5
minutes and kept under a hydrogen atmosphere overnight. The mixture
was filtered over a Whatmann filter and concentrated. This procedure
was repeated two times after which the residue was dissolved in 10 mL
H2O, followed by addition of 0.5 mL Et3N. The mixture was stirred for 150
minutes and concentrated. Purification using size exclusion
chromatography (sephadex LH20 9:1 MeOH/H2O) followed by three
rhamnopyranosyl)-4-O-benzyl-2-O-(3-cyano-2,2-dimethylpropanoyl)-
α-L-rhamnopyranoside (34) Donor 14 (0.15 g, 0.17 mmol, 1.5 equiv.)
and acceptor 33 (0.19 g, 0.11 mmol, 1.0 equiv.) were coevaporated three
times with anhydrous toluene and kept under argon, after which they
were dissolved in anhydrous DCM. Activated molecular sieves were
added and the mixture was stirred for 30 minutes at room temperature.
After addition of NIS (0.042 g, 0.19 mmol, 1.7 equiv.), the solution was
cooled to -40 °C, followed by addition of a freshly prepared DCM solution
of TMSOTf (0.1 M, 0.18 mL, 0.018 mmol, 0.17 equiv.). After TLC and
TLC/MS analysis showed complete consumption of the acceptor, the
reaction was quenched by addition of 0.3 mL Et3N and allowed to warm
up to room temperature. The mixture was diluted with EtOAc, washed
with sat Na2S2O3 (aq), dried over MgSO4 and concentrated. Column
purification (Hexanes/EtOAc) followed by size exclusion (1:1
DCM/MeOH) yielded fully protected hexasaccharide 34 as yellow glass
like solid (0.237 g, 0.096 mmol, 88%). Rf 0.74 (PE/EtOAc, 1/1, v/v); IR
(neat, cm-1): 698, 734, 981, 1028, 1043, 1201, 1454, 1697, 1737, 2247,
2875, 2933, 2972; 1H NMR (400 MHz, CDCl3): δ 7.36 – 7.13 (m, 50H),
5.43 – 5.30 (m, 1H), 5.29 – 5.08 (m, 5H), 5.08 – 4.92 (m, 5H), 4.92 –
4.75 (m, 6H), 4.75 – 4.41 (m, 16H), 4.20 – 4.06 (m, 2H), 3.99 (ddd, 2H, J
= 22.7, 9.5, 3.0 Hz), 3.85 – 3.11 (m, 20H), 2.74 – 2.48 (m, 8H), 2.48 –
lyophilizations yielded fully deprotected hexasaccharide as
a white
powder (23.8 mg, 24.4 mmol, 84%). 1H NMR (D2O, 600 MHz): δ 5.18 (s,
1H, H-1), 5.06 - 4.96 (m, 3H, 3x H-1), 4.92 (d, 1H, J = 4.8 Hz, H-1), 4.73
(s, 1H, H-1), 4.15 - 4.08 (m, 2H, 2 x H-2), 4.04 (s, 2H, 2 x H-2), 3.98 (s,
1H, H-2), 3.91 (m, 1H), 3.89 - 3.83 (m, 3H), 3.83 - 3.78 (m, 4H), 3.78 -
3.62 (m, 8H), 3.59 - 3.35 (m, 8H), 3.00 - 2.94 (m, 2H), 1.65 (m, 4H, CH2),
1.45 (m, 2H, CH2), 1.41 - 1.31 (m, 2H, CH2), 1.25 (m, 18H, 6x CH3-6);
13C NMR (D2O, 151 MHz): δ 121.8, 103.4, 103.4, 103.2, 103.0, 101.8,
100.5 (6x C-1), 79.3, 79.2, 79.1, 79.0, 78.7 (6x C-2), 73.1, 73.0, 72.9,
This article is protected by copyright. All rights reserved

European Journal of Organic Chemistry
10.1002/ejoc.201600956
FULL PAPER
Davies, G. Dougan, F. Zhang, S. Dahesh, L. Shaw, J. Gin,
M. Cunningham, J. A. Merriman, J. Hütter, B. Lepenies, S.
H. M. Rooijakkers, R. Malley, M. J. Walker, S. J. Shattil, P.
M. Schlievert, B. Choudhury, V. Nizet, Cell Host Microbe
2014, 15, 729–740.
72.6, 72.3, 72.2, 72.2 , 71.1, 71.0, 71.0, 70.9, 70.8, 70.7, 70.3, 70.2, 70.2,
70.2, 70.1, 70.0, 69.7, 68.4 (6x C-3, 6x C-4, 6x C-5), 67.5, 47.6, 43.2,
40.4, 40.3 (CH2), 29.2 (CH2), 29.0, 27.5 (CH2), 25.9, 23.4 (CH2), 17.6,
17.6, 17.5 (6x CH3), 9.2. HRMS (MALDI-TOF): [M+Na]+ calculated for
C41H73NO25Na 1002.4364, found 1002.4359.
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Acknowledgements
This work was supported by The Netherlands Organization of
Scientific Research (NWO Vidi grant to J.D.C.C.). We thank C.
Erkelens, F. Lefeber, and K. Babu for their assistance with the
NMR experiments. Dr. Nina van Sorge and Prof. J. Huebner are
kindly acknowledged for helpful discussions.
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Keywords: Carbohydrate Synthesis – Protecting Groups –
Glycosylation – Rhamnan - Pivaloyl
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European Journal of Organic Chemistry
10.1002/ejoc.201600956
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Entry for the Table of Contents (Please choose one layout)
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Key Topic* Oligosaccharide
Synthesis
Anne Geert Volbeda, Niels R.M.
Reintjens, Herman S. Overkleeft,
Gijsbert A. van der Marel, and Jeroen D.
C. Codée*
Text for Table of Contents
Page No. – Page No.
The Cyanopivaloyl Ester: A New
Protecting Group in the Assembly of
Oligorhamnans
*Carbohydrate synthesis – protecting groups
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