Synthesis of Glucuronoxylan Hexasaccharides by Preactivation-Based Glycosylations

Article abstract of DOI:10.1002/ejoc.202000211

The synthesis of two glucuronoxylans is described, which both consist of a pentaxylan backbone and a glucuronic acid linked to the 2 position in the fourth xylose residue from the reducing end. The two target molecules differ in the 4 position of the glucuronic acid where one is unsubstituted while the other contains a methyl ether. The pentaxylan backbone is assembled in four glycosylation reactions with phenyl thioglycoside donors. The couplings are performed by preactivation of the donor with in-situ-generated p-nitrobenzenesulfenyl triflate prior to addition of the acceptor. The glucuronic acids are then attached by Koenigs-Knorr glycosylations followed by deprotections. The syntheses employ a total of 8 steps from monosaccharide building blocks and afford the two glucuronoxylans in 12 and 15 % overall yield. The hexasaccharide products are valuable substrates for investigating the activity and specificity of glucuronoxylan-degrading enzymes.

Full text of DOI:10.1002/ejoc.202000211

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Synthesis of Glucuronoxylan Hexasaccharides by Preactivation-
Based Glycosylations
Authors: Emilie N. Underlin, Clotilde d’Errico, Maximilian Böhm, and
Robert Madsen
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202000211
Link to VoR: https://doi.org/10.1002/ejoc.202000211
01/2020

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
Synthesis of Glucuronoxylan Hexasaccharides by Preactivation-
Based Glycosylations
Emilie N. Underlin,[a] Clotilde d’Errico,[a] Maximilian Böhm,[a] and Robert Madsen*[a]
[a]
Dr. E. N. Underlin, Dr. C. d’Errico, Dr. M. Böhm, Prof. Dr. R. Madsen
Department of Chemistry, Technical University of Denmark
2800 Kgs. Lyngby (Denmark)
E-mail: rm@kemi.dtu.dk
https://www.kemi.dtu.dk
Supporting information for this article is given via a link at the end of the document.
Abstract: The synthesis of two glucuronoxylans is described, which
both consist of a pentaxylan backbone and a glucuronic acid linked
to the 2 position in the fourth xylose residue from the reducing end.
The two target molecules differ in the 4 position of the glucuronic
acid where one is unsubstituted while the other contains a methyl
ether. The pentaxylan backbone is assembled in four glycosylation
reactions with phenyl thioglycoside donors. The couplings are
performed by preactivation of the donor with in situ-generated p-
nitrobenzenesulfenyl triflate prior to addition of the acceptor. The
glucuronic acids are then attached by Koenigs-Knorr glycosylations
followed by deprotections. The syntheses employ a total of 8 steps
from monosaccharide building blocks and afford the two
glucuronoxylans in 12 and 15% overall yield. The hexasaccharide
products are valuable substrates for investigating the activity and
specificity of glucuronoxylan-degrading enzymes.
glucuronoxylans where cleavage occurs at the second glycosidic
linkage towards the reducing end from the glucuronic acid-
bound xylose.[3] The chemically strong -linkage to glucuronic
acid can be hydrolyzed by GH67 and GH115 -glucuronidases
where the former only removes glucuronic acid from terminal
non-reducing end xylose residues while the latter can also
cleave internally bound substituents.[3] GH67 -glucuronidases
are selective for 4-O-methylglucuronic acid[4] while GH115 -
glucuronidases and GH30 xylananses are able to act on both
glucuronic acid- and 4-O-methylglucuronic acid-containing
substrates.[5] In principle, the combination of xylanases and -
glucuronidases should completely degrade glucuronoxylan
polysaccharides, but in reality this does often not occur.[3]
Instead, a variety of small glucuronoxylan oligosaccharides
remain after pretreatment, hydrolysis and fermentation of
lignocellulose and in some cases these recalcitrant
carbohydrates can be recovered in large amounts.[6]
A problem in the study of xylanases and -glucuronidases is
the lack of well-defined and pure substrates to investigate the
activity and the specificity. Mild acidic hydrolysis of
glucuronoxylan gives rise to a mixture of oligosaccharides,
which mostly contain two to eight xylose units and one
glucuronic acid per chain.[7] Enzymatic hydrolysis of
glucuronoxylans and glucuronoarabinoxylans followed by
extensive chromatographic purification makes it possible to
isolate pure oligosaccharides containing a tri- or a tetraxylan
backbone and a glucuronic acid bound to the third xylose
residue.[8] Only in one case has it been possible to isolate small
amounts of a pentaxylan with a glucuronic acid bound to xylose
number three.[9]
Chemical synthesis offers a solution to this supply problem,
but glucuronoxylans have so far received very little attention.[10]
In four cases, glucuronoxylan di- and trisaccharides have been
prepared by glycosylating a glucuronic acid donor onto a xylose
or a xylobiose acceptor.[11] The coupling with the uronic acid was
performed by using either the Koenigs-Knorr, the imidate or the
thioglyccoside glycosylation method.[11] Only in one case has a
pentasaccharide been prepared by glycosylating a glucuronosyl
chloride onto a branched tetraxylan.[12]
Introduction
Hemicellulose is composed of
a
diverse group of
polysaccharides where some of the most abundant oligomers
are (1→4)-linked xylans decorated with arabinose and
glucuronic acid substituents.[1] The hydroxy group at position 4
of the glucuronic acids may be methylated and the uronic acids
are attached by -linkages to the 2-position of the xylose
residues. In hardwoods, glucuronoxylans are the main
hemicellulosic polysaccharide accounting for 15 – 30% of the
total weight.[2] The ratio between the xylose and the glucuronic
acid residues is typically around 7:1 depending on the hardwood
source.[2] In softwoods, cereals and grasses, glucuronoxylans
are further decorated with arabinose substituents to form
glucuronoarabinoxylans
polysaccharide.[1]
as
the
major
hemicellulosic
The (1→4) xylose linkages in glucuronoxylans are
hydrolyzed by xylanases from glycoside hydrolase (GH) families
10, 11 and 30.[3] The substrate specificity for the three enzyme
classes differs depending on the position of the glucuronic acid.
GH10 xylanases require two consecutive unsubstituted xylose
residues and are able to cleave the linkage to the glucuronic
acid-bound xylose from the non-reducing end.[3] GH11
xylanases need three continuous unsubstituted xylose units and
can hydrolyze the xylan chain one linkage before the glucuronic
acid-containing xylose.[3] GH30 xylanases are specific for
We have recently presented a short synthetic strategy to
prepare arabinoxylans[13] where the xylan backbone is
assembled by a preactivation-based approach.[14] In this protocol
a protected phenyl 1-thioxylopyranoside is activated by in situ-
generated p-nitrobenzenesulfenyl triflate[15] and glycosylated
1
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
onto a partially protected phenyl 1-thioxylopyranoside acceptor.
The procedure is then repeated until the desired xylan is
prepared.[13] In this way, a linear xylan backbone is assembled
without using any deprotection step for each glycosylation
reaction.[13,16] We envisioned that the strategy could be extended
to the synthesis of glucuronoxylans by coupling a glucuronic
acid to the xylan backbone. Glycosylations with uronic acids,
although, are often a challenge due to their low reactivity as
donors.[17] Overall, two distinct approaches are often used, which
both start from the corresponding hexose.[17] In the first
approach, the hexose is protected and oxidized to the uronic
acid, which is then used for the coupling[17] as shown in the
above syntheses of glucuronoxylans.[11,12] In the second
approach, the coupling is carried out with the more reactive
hexose as the donor followed by oxidation of the product at C-
6.[17] We have previously used this latter approach in our
syntheses of pectic oligosaccharides for introducing galacturonic
acids.[18]
Benzoylated thioglycosides 3 and 4 were prepared in our
earlier work (Figure 2)[13] where the latter was synthesized from
phenyl 1-thio--D-xylopyranoside through 2,3-O-isopropylidene
and 4-O-p-methoxybenzyl (PMB) protection followed by
deprotection and benzoylation. The intermediate phenyl 4-O-(p-
methoxy)benzyl-1-thio--D-xylopyranoside (5)[13] was selected as
the starting material to prepare building block 6 with a levulinoyl
and a benzoyl group at position 2 and 3, respectively (Scheme
1). Attempts to perform a selective levulinoyl protection at the 2
position in 5 were unsuccessful.[20] Various conditions with
levulinoyl chloride, levulinic acid and levulinic anhydride were
investigated, but either led to very little conversion or a mixture
of the two levulinate regioisomers. Selective benzoylation of the
3 position in 5 with benzoyl chloride under different conditions
were also fruitless since the 2-O-benzoylated regioisomer was
obtained as the major product in all cases.[20] Instead, it was
decided to divert to a temporary silyl-protection of diol 5 based
on a report with the corresponding selenoglycoside, which was
Herein, we present the synthesis of glucuronoxylans 1 and 2, shown to undergo a highly regioselecive TBS-protection at
which both contain a pentaxylan backbone and a glucuronic acid
at xylose number four (Figure 1). The only difference is the
absence (as in 1) or presence (as in 2) of the 4-O-methyl group,
which renders the substrates suitable for investigating the
influence of this ether moiety. The position of the glucuronic acid
and the length of the xylan backbone are chosen to ensure
sufficient enzyme activities with xylanases and -
glucuronidases.[19]
position 3 with TBSOTf and lutidine in THF at –78 °C.[21] When
these conditions were applied to the sulfur analogue 5, the 3-O-
TBS-protected product was obtained in 84% yield as the sole
product. The 2-hydroxy group was then esterified with levulinic
acid, DMAP and DCC to afford fully protected xyloside 7. The
subsequent cleavage of the TBS group was first attempted with
TBAF, but in the absence of a stoichiometric acid, the TBS and
the levulinoyl groups were both cleaved while no reaction
occurred with TBAF in the presence of an excess of acetic acid.
Finally, the use of a 20% aqueous solution of HF in acetonitrile
affected a clean removal of the TBS ether to afford alcohol 8 in
91% yield. The hydroxy group was benzoylated and excess
benzoyl chloride removed with 3-(dimethylamino)-1-propylamine
(DMAPA).[22] Without further purification, the crude product was
submitted to PMB deprotection with DDQ to give building block 6.
Figure 1. Structure of target glucuronoxylans 1 and 2.
Results and Discussion
The pentaxylan backbone will be assembled from four different
xylose building blocks by the use of the preactivation-based
glycosylations. As demonstrated in our arabinoxylan
syntheses,[13] the benzoyl group will serve as a permanent
protecting group for xylose hydroxy groups not involved in the
glycosylations while the levulinoyl (Lev) group will function as a
temporary protecting group at the position where the glucuronic
acid will be installed. The benzoyl and levulinoyl groups are both
ester protecting groups and thus ensure neighboring group
participation in the glycosylations to form the -linkages.
Scheme 1. Synthesis of xylose building block 6.
It was decided to install a benzyl group at the anomeric
center in the xylose unit at the reducing end since a phenyl
thioglycoside may not be compatible with the glucuronic acid
glycosylations (vide infra). The necessary building block 9 was
prepared from phenyl 2,3-di-O-benzoyl-4-O-(p-methoxy)benzyl-
1-thio--D-xylopyranoside (10)[13] by glycosylation with benzyl
alcohol in the presence of NIS and triflic acid followed by PMB
removal with DDQ (Scheme 2).
Figure 2. Benzoylated xylose building blocks 3 and 4.
2
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
Scheme 2. Synthesis of xylose building block 9.
With the xylose building blocks in hand the stage was now
set to assemble the pentaxylan backbone by preactivation-
based
nitrobenzenesulfenyl triflate as the promoter. The coupling
between monosaccharides and gave exclusively
glycosylation
with
in
situ-generated
p-
3
6
disaccharide 11, which was isolated in 89% yield (Scheme 3).
As noted in our earlier study, it is important to keep the
temperature low during the glycosylation.[13] Therefore the
coupling reactions were carried out by first activating the donor
thioglycoside at a temperature below –60 °C for 10 min with p-
nitrobenzenesulfenyl chloride and silver triflate, which was
followed by addition of the acceptor thioglycoside and stirring at
a temperature around –55 °C until the glycosylation had gone to
completion according to TLC analysis. Using this protocol, the
following two consecutive glycosylations with acceptor
4
proceeded in 68 and 79% yield, respectively, to afford
trisaccharide 12 and tetrasaccharide 13. It should be noted that
the glycosylation with the 2-O-levulinoyl-protected donor 11
gave a slightly lower yield than when 2-O-benzoyl-protected
donors 3 and 12 were employed. The same observation was
made during our previous work where the highest yields were
obtained with 2-O-benzoyl-protected donors,[13] which may be
due to the higher stability of the activated intermediate (i.e. the
1,2-benzoxonium ion)[23] in this case. At last, tetrasaccharide 13
was coupled with the reducing end xylose building block 9 to
afford pentasaccharide 14 in 83% yield. Subsequent removal of
the levulinoyl group with hydrazine afforded the corresponding
alcohol 15 in near quantitative yield. The -linkages in 15 were
confirmed by measuring the JC1,H1 coupling constants, which
were located around 162 – 165 Hz and thus characteristic for -
xylopyranosides.[24]
Scheme 3. Synthesis of pentaxylan backbone 15.
To assemble glucuronoxylans 1 and 2 the next step will
involve a glycosylation between pentaxylan 15 and a glucose or
a glucuronic acid donor. It was decided to use the latter
approach, which has provided moderate-to-good yields and
selectivities in the coupling with different uronic acid donors to
xylose, xylobiose and xylotetraose acceptors.[11,12] The best
result was obtained by using an ethyl thioglycoside donor and
performing the coupling with dimethyl(methylthio)sulfonium
triflate (DMTST) as the promoter in diethyl ether.[11a,25] Since
thioglycosides can also be converted into other donors, it was
decided to use this building block for attaching the glucuronic
acid residue. An ether protecting group will be necessary at the
2 position to favor formation of the desired -linkage. Thus,
uronic acid building blocks 16[26] and 17[11a] were prepared from
ethyl 1-thio--D-glucopyranoside by slight modification of
literature protocols (Figure 3).[20]
Figure 3. Glucuronic acid donors 16 and 17.
The pivotal glycosylation with acceptor 15 was first
investigated with DMTST as the promoter (Table 1 and Scheme
4). Disappointingly, the reaction between 17 and 15 was very
slow and mainly led to decomposition of donor 17 (entry 1).
Changing the promoter to the more reactive combination of NIS
and TESOTf led to a faster conversion, but in this case only
decomposition of 17 was observed (entry 2). The promoter
system from Scheme 3 was then investigated and subjecting 17
3
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
and 15 to p-nitrobenzenesulfenyl chloride and silver triflate
actually produced the desired hexasaccharide 19 in 61% yield,
but unfortunately as an almost equal mixture of the - and the -
glucuronide (entry 3). Consequently, it appears that the direct
coupling with the ethyl thioglycosides of the uronic acids is very
challenging and it was therefore decided to convert 16 and 17
into another donor. An easy transformation is the titration of
thioglycosides with molecular bromine in dichloromethane to
form the corresponding -glycosyl bromides, which can then be
used directly in a Koenigs-Knorr glycosylation. Thus, titration of
17 followed by reaction with 15 and silver triflate afforded
hexasaccharide 19 in 42% yield as a 3:2 / mixture (entry 4).
Another silver salt, which often gives a better  selectivity in
Koenigs-Knorr glycosylations, is silver perchlorate and
especially when it is dissolved in ether.[27] Using this protocol
hexasaccharide 19 was isolated in 44% yield and with an
improved / selectivity of 5:2 (entry 5). When the same
sequence was applied to donor 16, the corresponding
hexasaccharide 18 was obtained in 45% yield with an / ratio
of 4:1 (entry 6). In both cases, a significant amount of unreacted
acceptor 15 was recovered and it was therefore decided to
continue the syntheses with these silver perchlorate
glycosylations. The  stereochemistry of the major isomer in 18
and 19 was established from the H-1 and C-1 chemical shifts of
the glucuronic acid moiety[28] as well as the measurement of the
JC1,H1 coupling constants, which in both cases were around 173
Hz.[29]
were removed by hydrogenolysis with Degussa-type palladium-
on-carbon to afford fully deprotected target structures 1 and 2
with the same / glucuronic acid ratio as in Table 1, entry 5 and
6. The minor amounts of the -glucuronides should not influence
the subsequent studies with the target molecules. An alternative
synthesis strategy would be to introduce the glucuronic acid
earlier on trisaccharide 12 instead of on pentasaccharide 14.
Although not attempted, it may have resulted in a more
straightforward purification of the glucuronides. The overall
yields of 1 and 2 from the monosaccharide building blocks were
15 and 12%, respectively, over a total of 8 steps.
Table 1. Glycosylation of Acceptor 15 with Donors 16 and 17.
Scheme 4. Synthesis of glucuronoxylans 1 and 2.
Entry
Donor
Conditions
Product
Yield
[%]
:
Conclusion
1
2
17
17
DMTST, Et2O, 0 °C, 20 h
[a]
[a]




In summary, we have described a concise synthetic route to
glucuronoxylans 1 and 2 by the use of preactivation-based
glycosylations to assemble the xylan backbone. The glucuronic
acids are introduced through Koenigs-Knorr glycosylations to
afford the  anomers as the major products. Hexasaccharides 1
and 2 constitute the largest glucuronoxylans synthesized to date
and are valuable substrates for studying the activity and the
specificity of hemicellulose-degrading enzymes.
NIS, TESOTf, CH2Cl2, Et2O,
10 °C, 1 h
3
4
5
6
17
17
17
16
pNO2PhSCl, AgOTf, CH2Cl2,
40 °C, 20 min
19
19
19
18
61
1:0.9
3:2
Br2, CH2Cl2, then 15, AgOTf,
30 °C, 1 h
42
Br2, CH2Cl2, then 15, AgClO4,
Et2O, 30 °C, 1.5 h
44[b]
45[c]
5:2
Br2, CH2Cl2, then 15, AgClO4,
Et2O, 30 °C, 2 h
4:1
Experimental Section
General Information: Starting materials, reagents, and solvents were
purchased from commercial suppliers and used without further
purification unless otherwise noted. All solvents used were of analytical
HPLC grade. Anhydrous solvents were obtained from an Innovative
Technology PS-MD-7 PureSolv solvent purification system except for
dichloromethane and toluene for glycosylations, which were dried over 3
[a] Decomposition of 17. [b] 17% of 15 recovered. [c] 23% of 15 recovered.
It was not possible to separate the - and the -glucuronide
in 18 and 19 by flash chromatography and the following
deprotections were therefore carried out on the mixtures. It was
first attempted to perform a Zemplén deprotection of the benzoyl
groups, but this transformation turned out to be rather slow and
led to partial epimerization at position 5 in the D-glucuronic acids
to give L-iduronic acid. To prevent this side reaction, the methyl
ester was first removed with lithium hydroxide and hydrogen
peroxide,[30] which was then followed by the Zemplén reaction to
cleave the benzoates (Scheme 4). The products were purified
through a short reverse-phase column, but the - and the -
glucuronide could not be separated. Finally, the benzyl groups
Å
molecular sieves. Air and moisture sensitive experiments were
conducted under inert atmosphere (N2) in dried glassware and
anhydrous solvents. The water content was checked on an 899
Coulometer from Metrohm. Crushed
3 Å molecular sieves for
glycosylations were stored in the oven at 110 °C before being activated
by heating under vacuum. Thin-layer chromatography (TLC) was carried
out using Merck Aluminium Sheets pre-coated with 0.25 mm silica gel, C-
60 F254 plates. Compounds were visualized under UV light or by charring
after dipping in
a
cerium ammonium sulfate solution (1%
cerium(IV)sulfate and 2.5% ammonium heptamolybdate in a 10% sulfuric
acid solution). Flash column chromatography was performed using Merck
4
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
Geduran silica gel 60 Å (40-63 m) as the stationary phase. NMR
spectra were recorded on a Bruker Ascend 400 or a Bruker Ascend 800
spectrometer. Chemical shifts are reported in part per million (ppm)
relative to the residual solvent peak in CDCl3 (H = 7.26 ppm, C = 77.16
ppm) and D2O (H = 4.79 ppm). Coupling constants (J) are reported in Hz.
Assignment of 1H and 13C resonances were based on APT, DQF-COSY,
HSQC, H2BC, HMBC, TOCSY, and HSQC-TOSCY experiments when
needed. Xylose residues are labelled A – E from the reducing end as
shown in Scheme 4. Optical rotation was measured on a Perkin Elmer
Model 341 Polarimeter. HRMS analysis was performed on either a
UHPLC-QTOF system (Dionex ultimate 3000 and Bruker MaXis) with an
electrospray ionization (ESI) source or a MALDI-TOF system (Bruker
Solarix XR 7T).
9.0 Hz, 1H, H2), 4.69 (d, J = 11.5 Hz, 1H, PMB), 4.60 (d, J1,2 = 9.8 Hz,
1H, H1), 4.58 (d, J = 11.4 Hz, 1H, PMB), 4.01 (dd, J5,5’ = 11.5 Hz, J5,4
5.2 Hz, 1H, H5eq), 3.80 (s, 3H, OMe), 3.75 (t, J = 8.9 Hz, 1H, H3), 3.53
(ddd, J4,5’ = 10.2 Hz, J3,4 = 8.9 Hz, J4,5 = 5.2 Hz, 1H, H4), 3.22 (dd, J5’,5
=
=
11.5 Hz, J5’,4 = 10.3 Hz, 1H, H5’ax), 2.94–2.76 (m, 2H), 2.69–2.56 (m,
2H), 2.20 (s, 3H). 13C NMR (101 MHz, CDCl3):  = 207.6, 172.1, 159.6,
132.9, 132.5 (×2), 130.2, 129.7 (×2), 129.1 (×2), 128.0, 114.1 (×2), 86.5
(C1), 76.6 (C4), 76.4 (C3), 73.2 (PMB), 72.8 (C2), 67.9 (C5), 55.4 (OMe),
38.5, 30.0, 28.4. HRMS: calcd. for C24H28O7SNa [M + Na]+ 483.1447;
found 483.1458.
Phenyl 3-O-benzoyl-2-O-levulinoyl-1-thio--D-xylopyranoside (6): To
alcohol 8 (0.893 g, 1.94 mmol) dissolved in dry pyridine (4.0 mL) was
added BzCl (0.34 mL, 2.91 mmol) and the solution was left to stir at r.t.
After 17 h TLC (heptane/EtOAc 1:1) showed full conversion. DMAPA
(0.37 mL, 2.91 mmol) was added to quench excess BzCl. After stirring for
1 h, CH2Cl2 was added and the mixture was washed with 1 M HCl and
brine, dried over MgSO4, filtered, and conc. in vacuo thereby providing
the crude product as a yellow oil (1.0053 g, 1.78 mmol). This material
was directly dissolved in a 10:1 mixture of CH2Cl2/H2O (11 mL) and DDQ
(0.566 g, 2.49 mmol) was added. The reaction was stirred vigorously at
r.t. in the dark overnight. TLC (heptane/EtOAc 1:1) showed full
conversion and the mixture was filtered through a thick pad of Celite. The
filtrate was washed with sat. aq. NaHCO3, brine, dried over MgSO4,
filtered, and conc. in vacuo. The residue was purified by flash column
chromatography (hexane/EtOAc 1:1) to obtain alcohol 6 as a white solid
Phenyl
3-O-tert-butyldimethylsilyl-2-O-levulinoyl-4-O-(p-
methoxy)benzyl-1-thio--D-xylopyranoside (7): Diol 5[13] (1.000 g, 2.76
mmol) was dissolved in dry THF (30.0 mL) and cooled to –78 °C. 2,6-
Lutidine (0.482 mL, 4.14 mmol) and TBSOTf (0.761 mL, 3.31 mmol) were
added followed by stirring for 20 min until TLC (heptane/EtOAc 1:1)
showed full conversion. The reaction was diluted with CH2Cl2 and
washed with H2O. The organic phase was dried over Na2SO4, filtered
and conc. in vacuo. The crude product was purified by flash column
chromatography (heptane/EtOAc 10:1) to obtain phenyl 3-O-tert-
butyldimethylsilyl-4-O-(p-methoxy)benzyl-1-thio--D-xylopyranoside as a
clear oil (1.110 g, 84%). Rf = 0.28 (heptane/EtOAc 9:1). []25
= –130.2 (c
D
0.083, CHCl3). 1H NMR (400 MHz, CDCl3):  = 7.49–7.47 (m, 1H), 7.30–
7.20 (m, 7H), 6.89–6.87 (m, 1H), 5.20 (d, J1,2 = 3.0 Hz, 1H, H1), 4.62 (d,
(0.696 g, 81%). Rf = 0.42 (hexane/EtOAc 2:1). []2D5
= +16.1 (c 0.6,
J = 11.5 Hz, 1H, PMB), 4.53 (d, J = 11.5 Hz, 1H, PMB), 4.40 (dd, J5,5’
=
CHCl3). 1H NMR (400 MHz, CDCl3):  = 8.08–8.05 (m, 2H), 7.62–7.58 (m,
1H), 7.53–7.51 (m, 2H), 7.48–7.45 (m, 2H), 7.36–7.31 (m, 3H), 5.19–5.15
(m, 2H, H2, H3), 4.96–4.91 (m, 1H, H1), 4.37 (dd, J5eq,5ax = 11.9 Hz, J5eq,4
= 4.4 Hz, 1H, H5eq), 3.93–3.88 (m, 1H, H4), 3.54 (dd, J5ax,5eq = 11.9 Hz,
J5ax,4 = 7.9 Hz, 1H, H5ax), 3.03 (bs, 1H, OH), 2.71–2.67 (m, 2H), 2.64–
2.50 (m, 2H), 2.09 (s, 3H). 13C NMR (101 MHz, CDCl3):  = 206.0, 171.4,
167.0, 133.9, 133.0, 132.7 (×2), 130.3 (×2), 129.2 (×2), 129.0, 128.7 (×2),
128.2, 86.5 (C1), 75.8, 69.8 (C2, C3), 68.3 (C4), 67.5 (C5), 38.0, 29.8,
12.4 Hz, J5,4 = 1.8 Hz, 1H, H5), 3.87 (t, J = 4.4 Hz, 1H, H3), 3.81 (s, 3H,
OCH3), 3.75 (d, J = 9.4 Hz, 1H, OH), 3.70 – 3.66 (m, 1H, H2), 3.62 (dd,
J5’,5 = 12.4 Hz, J5’,4 = 3.7 Hz, 1H, H5’), 3.34 (q, J = 5.4 Hz, 1H, H4), 0.93
(s, 9H), 0.12 (s, 3H), 0.05 (s, 3H). 13C NMR (101 MHz, CDCl3):  = 159.5,
136.6, 130.8 (×2), 129.5 (×2), 129.4, 128.8 (×2), 126.9, 114.0 (×2), 88.9
(C1), 76.0 (C4), 72.5 (C2), 71.4 (PMB), 69.5 (C3), 59.9 (C5), 55.3 (OMe),
25.8, 18.1, -4.8, -5.0. HRMS: calcd. for C25H36O5SSiNa [M + Na]+
499.1944; found 499.1956. The above alcohol (1.050 g, 2.21 mmol) was
dissolved in CH2Cl2 (45.0 mL) followed by addition of DCC (1.380 g, 6.63
mmol), DMAP (0.405 g, 3.32 mmol) and LevOH (0.340 g, 3.32 mmol).
The reaction was stirred for 2 h at r.t. where a white precipitate had
formed and full conversion was observed by TLC (heptane/EtOAc 1:1).
The mixture was filtered through a pad of Celite, the filtrate conc. in
vacuo, and the crude product purified by flash column chromatography
(heptane/EtOAc 7:1). The product 7 was obtained as a colorless oil
28.1. HRMS: calcd. for C23H24O7SNa [M
467.1146.
+
Na]+ 467.1134; found
Benzyl 2,3-di-O-benzoyl--D-xylopyranoside (9): Compound 10[13]
(0.200 g, 0.35 mmol) and benzyl alcohol (0.044 ml, 0.42 mmol) were
mixed in the reaction flask and dried overnight on the vacuum line. The
reactants were dissolved in CH2Cl2 (6 mL), cooled to –40 °C followed by
addition of NIS (0.094 mg, 0.42 mmol) and triflic acid (9 l, 0.11 mmol) to
the stirred mixture. Full conversion of the starting material was observed
via TLC analysis after 20 minutes and the reaction was neutralized with
Et3N (0.145 mL, 1.05 mmol). The resulting mixture was stirred with 1 M
Na2S2O3 (6 mL) until the yellow color disappeared. The organic phase
was diluted with CH2Cl2, washed with brine, dried over Na2SO4, filtered,
concentrated and purified with flash chromatography (heptane/ethyl
acetate 7:3) yielding benzyl 2,3-di-O-benzoyl-4-O-(p-methoxy)benzyl--D-
xylopyranoside (0.155 g, 78%) as a colorless oil. 1H NMR (400 MHz,
CDCl3):  = 7.96–7.93 (m, 4H), 7.55–7.50 (m, 2H), 7.39–7.35 (m, 5H),
7.25–7.21 (m, 4H), 7.16–7.14 (m, 2H) 6.76–6.72 (m, 2H), 5.56 (t, J = 8.1
Hz, 1H, H3), 5.35 (dd, J2,3 = 8.3 Hz, J1,2 = 6.5 Hz, 1H, H2), 4.87 (d, J =
12.3 Hz, 1H, Bn), 4.74 (d, J1,2 = 6.5 Hz, 1H, H1), 4.63 (d, J = 12.3 Hz, 1H,
Bn), 4.57 (d, J = 11.8 Hz, 1H, PMB), 4.54 (d, J = 11.8 Hz, 1H, PMB), 4.14
(dd, J5eq,5ax = 11.9 Hz, J5eq,4 = 4.6 Hz, 1H, H5eq), 3.83–3.77 (m, 1H, H4),
3.76 (s, 3H, OMe), 3.51 (dd, J5ax,5eq = 11.9 Hz, J5ax,4 = 8.5 Hz, 1H, H5ax).
13C NMR (101 MHz, CDCl3):  = 165.7, 165.4, 159.4, 141.1, 137.1, 133.2,
130.0, 129.9, 129.7, 129.6, 129.6, 129.5, 128.6, 128.4, 128.4, 128.4,
127.9, 127.8, 127.7, 127.1, 113.9, 99.4 (C1), 74.0 (C4), 72.6 (C3), 72.4
(PMB), 71.1 (C2), 70.4 (Bn), 63.1 (C5), 55.3 (OMe). The above glycoside
(0.155 g, 0.27 mmol) was dissolved in CH2Cl2/H2O 9:1 (3 mL) and DDQ
(0.093 g, 0.41 mmol) was added. The reaction was vigorously stirred for
4 h at r.t. and the remaining DDQ was quenched using a buffer solution
composed of ascorbic acid (0.7%, 0.072 g, 0.41 mmol), citric acid (1.5%)
and sodium hydroxide (1%). The mixture was diluted with CH2Cl2 and
washed with sat. aq. NaHCO3 and water. The organic phase was dried
with Na2SO4, filtered and conc. in vacuo affording alcohol 9 (0.113 g,
(1.210 g, 95%). Rf = 0.27 (heptane/EtOAc 3:2). []D25
= –33.2 (c 0.28,
CHCl3). 1H NMR (400 MHz, CDCl3):  = 7.46–7.44 (m, 2H), 7.30–7.23 (m,
5H), 6.87–6.85 (m, 2H), 4.89–4.85 (m, 2H, H1, H2), 4.58 (d, J = 11.6 Hz,
1H, PMB), 4.47 (d, J = 11.6 Hz, 1H, PMB), 4.13 (q, J = 7.0 Hz, 1H, H5),
3.80 (s, 3H, OCH3), 3.80–3.77 (m, 1H, H3), 3.39–3.33 (m, 2H, H4, H5’),
2.78–2.74 (m, 2H), 2.66–2.61 (m, 2H), 2.17 (s, 3H), 0.89 (s, 9H), 0.09 (s,
3H), 0.06 (s, 3H). 13C NMR (101 MHz, CDCl3):  = 206.2, 171.7, 159.3,
135.0, 131.2 (×2), 130.1, 129.5 (×2), 128.9 (×2), 127.3, 113.8 (×2), 86.7
(C1), 76.6 (C4), 72.8 (C2), 72.9 (PMB), 71.8 (C3), 64.4 (C5), 55.3 (OMe),
37.9, 29.9, 28.3, 25.7, 18.0, -4.5, -4.8. HRMS: calcd. for C30H42O7SSiNa
[M + Na]+ 597.2312; found 597.2325.
Phenyl
2-O-levulinoyl-4-O-(p-methoxy)benzyl-1-thio--D-
xylopyranoside (8): A mixture of the silylated xyloside 7 (0.100 g, 0.17
mmol) in CH3CN (5.0 mL) was cooled to 0 °C. A 20% HF solution (0.30
mL, 3.48 mmol) was added and the reaction was allowed to warm to r.t.
overnight. TLC (heptane/EtOAc 1:1) showed full conversion, and
afterwards the remaining HF was quenched by addition of
methoxytrimethylsilane (0.96 mL, 6.96 mmol) followed by stirring for 1 h.
The mixture was diluted with CH2Cl2 and washed with sat. aq. NaHCO3
and water. The organic phase was dried over Na2SO4, filtered, and the
solvent removed in vacuo. The crude mixture was purified by flash
column chromatography (heptane/EtOAc 4:3) yielding the product 8 as a
white amorphous solid (0.073 g, 91%). Rf = 0.24 (heptane/EtOAc 1:1). []
25 = –18.8 (c 0.47, CHCl3). 1H NMR (400 MHz, CDCl3):  = 7.47–7.45 (m,
D
2H), 7.32–7.24 (m, 5H), 6.89–6.83 (m, 2H), 4.83 (dd, J1,2 = 9.8 Hz, J2,3
=
5
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
93%) as
a
white amorphous solid after purification by column
crystals (0.611 g, 89%). Rf = 0.54 (hexane/toluene/EtOAc 3:1:2). []25
= –
D
chromatography (heptane/EtOAc 7:3). 1H NMR (400 MHz, CDCl3):  =
7.99–7.97 (m, 4H), 7.59–7.52 (m, 2H), 7.45–7.35 (m, 4H), 7.30–7.23 (m,
5H), 5.44 (dd, J2,3 = 7.8 Hz, J1,2 = 6.0 Hz, 1H, H2), 5.27 (t, J = 7.5 Hz, 1H,
H3), 4.90 (d, J = 12.2 Hz, 1H, Bn), 4.79 (d, J1,2 = 6.0 Hz, 1H, H1), 4.66 (d,
J = 12.2 Hz, 1H, Bn), 4.28 (dd, J5eq,5ax = 12.0 Hz, J5eq,4 = 4.4 Hz, 1H,
H5eq), 4.03 (td, J = 7.6 Hz, J4,5eq 4.5 Hz, 1H, H4), 3.55 (dd, J5ax,5eq = 12.0
Hz, J5ax,4 = 7.7 Hz, 1H, H5ax). 13C NMR (101 MHz, CDCl3):  = 167.2,
165.3, 137.0, 133.7, 133.5, 130.1, 130.0, 129.4, 129.0, 128.6, 128.5,
128.5, 128.0, 99.1 (C1), 75.4 (C3), 70.5 (C2), 70.4 (Bn), 68.7 (C4), 64.6
(C5). HRMS: calcd. for C26H24O7Na [M + Na]+ 471.1414; found 471.1450.
43.6 (c 0.38, CHCl3). 1H NMR (400 MHz, CDCl3):  = 8.06–8.04 (m, 2H),
7.97–7.91 (m, 6H), 7.58–7.28 (m, 17H), 5.64 (t, J = 6.6 Hz, 1H, H3B),
5.50 (t, J = 8.2 Hz, 1H, H3A), 5.22 (dd, J2B,3B = 6.6 Hz, J1B,2B = 4.9 Hz,
1H, H2B), 5.11–5.04 (m, 2H, H2A, H4B), 4.91 (d, J1B,2B = 4.8 Hz, 1H, H1B),
4.83 (d, J1A,2A = 8.6 Hz, 1H, H1A), 4.19 (dd, J5A,5A’ = 12.0 Hz, J5A,4A = 4.9
Hz, 1H, H5A), 4.08–4.00 (m, 2H, H4A, H5B), 3.48–3.40 (m, 2H, H5A’,
H5B’), 2.64–2.46 (m, 4H), 2.08 (s, 3H). 13C NMR (101 MHz, CDCl3):  =
205.9, 171.4, 165.6, 165.5, 165.3, 165.1, 133.5, 133.5, 133.5, 132.8,
132.5, 130.0, 130.0, 129.9, 129.9, 129.5, 129.3, 129.1, 129.0, 128.6,
128.6, 128.5, 128.5, 128.3, 99.8 (C1B), 86.5 (C1A), 75.3 (C4A), 73.5
(C3A), 70.4 (C2A), 70.2 (C2B), 69.6 (C3B), 68.6 (C4B), 66.1 (C5A), 60.9
(C5B), 37.9, 29.8, 28.1. HRMS: calcd. for C49H44O14SNa [M + Na]+
911.2343; found 911.2362.
Glycosylation with Thiophenyl Donor (General Procedure A):
Crushed molecular sieves (3 Å) was added to a 2-neck Schlenk flask,
where the middle neck was fitted with a glass stopper and the other with
a septum. The flask was then placed under vacuum and heated.
Afterwards an atm. of N2 was applied. The donor (1.0 equiv.) dissolved in
dry CH2Cl2 (c = 0.12 M) was added to the flask together with AgOTf (2.0
equiv.) dissolved in dry toluene (c = 0.36 M). Stirring of the reaction was
initiated and the glass stopper exchanged for a thermometer under N2
pressure, and the solution cooled to –65 °C. p-Nitrobenzenesulfenyl
chloride (1.0 equiv.) was dissolved in dry CH2Cl2 (c = 0.72 M) and slowly
added as to not raise the temperature above –60 °C. The mixture is left
to stir for approximately 10 min until the activation was completed. The
acceptor (0.9 equiv.) was dissolved in dry CH2Cl2 (c = 0.65 M) and added
quickly. The temperature was kept between –55 °C and –50 °C for the
reaction time indicated. Afterwards the mixture was allowed to warm to –
15 °C over 10 min at which point Et3N (3.0 equiv.) was added. The
solution was filtered through a pad of Celite and conc. in vacuo. The
residue was purified by flash column chromatography to afford the
product.
Phenyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-levulinoyl--D-xylopyranosyl-(1→4)-2,3-di-O-benzoyl-1-thio--D-
xylopyranoside (12): General procedure A: Crushed molecular sieves
(0.372 g). Donor 11 (1.131 g, 1.27 mmol). AgOTf (0.654 g, 2.55 mmol).
p-Nitrobenzenesulfenyl chloride (0.240 g, 1.27 mmol). Acceptor
4
(0.4158 g, 1.14 mmol). Reaction time 85 min. Et3N (0.53 mL, 3.81 mmol).
Eluent for flash column chromatography hexane/toluene/EtOAc 2:1:1.
The product was obtained as a white crystalline solid (0.768 g, 68%). Rf
= 0.46 (hexane/toluene/EtOAc 3:1:2). []D25
= –43.3 (c 0.24, CHCl3). 1H
NMR (400 MHz, CDCl3):  = 8.00–7.88 (m, 12H), 7.57–7.28 (m, 23H),
5.62–5.56 (m, 2H, H3A, H3C), 5.35 (t, J = 8.4 Hz, 1H, H3B), 5.32 (t, J1A,2A
= 7.7 Hz, 1H, H2A), 5.12 (dd, J2C,3C = 6.7 Hz, J1C,2C = 4.9 Hz, 1H, H2C),
5.06 (d, J1A,2A = 7.8 Hz, 1H, H1A), 5.06–5.02 (m, 1H, H4C), 4.90 (dd, J2B,3B
= 8.5 Hz, J1B,2B = 6.7 Hz, 1H, H2B), 4.68 (d, J1C,2C = 4.8 Hz, 1H, H1C),
4.59 (d, J1B,2B = 6.7 Hz, 1H, H1B), 4.36 (dd, J5Aeq,5Aax = 12.2 Hz, J5Aeq,4A
=
4.6 Hz, 1H, H5Aeq), 4.01–3.95 (m, 2H, H4A, H5C), 3.76 (td, J = 8.5 Hz,
J4B,5Beq = 5.0 Hz, 1H, H4B), 3.63 (dd, J5Aax,5Aeq = 12.1 Hz, J5Aax,4A = 8.3
Hz, 1H, H5Aax), 3.52 (dd, J5Beq,5Bax = 12.2 Hz, J5Beq,4B = 4.9 Hz, 1H,
H5Beq), 3.35 (dd, J = 12.3, 6.2 Hz, 1H, H5C’), 3.09 (dd, J5Bax,5Beq = 12.2
Hz, J5Bax,5B4A = 9.0 Hz, 1H, H5Bax), 2.65–2.36 (m, 4H), 2.07 (s, 3H). 13C
NMR (101 MHz, CDCl3):  = 206.0, 171.3, 165.6, 165.5 (×2), 165.4,
165.4, 165.3, 165.0, 133.6, 133.6, 133.5, 133.5, 133.3, 133.2, 133.0,
132.7, 130.1, 130.0, 130.0, 129.9, 129.9, 129.9, 129.7, 129.5, 129.3,
129.2, 129.1, 129.0, 128.6, 128.6, 128.6, 128.5, 128.5, 128.4, 128.1,
100.8 (C1B), 99.5 (C1C), 86.7 (C1A), 75.5 (C4A), 75.0 (C4B), 72.8 (C3A),
72.5 (C3B), 71.6 (C2B), 70.5 (C2A), 70.1 (C2C), 69.6 (C3C), 68.6 (C4C),
65.6 (C5A), 62.4 (C5B), 60.9 (C5C), 37.8, 29.8, 27.9. HRMS: calcd. for
C68H60O20SNa [M + Na]+ 1251.3290; found 1251.3311.
Glycosylation with Glucuronic Acid Donor (General Procedure B):
Crushed molecular sieves (3 Å) was added to a 2-neck Schlenk flask,
where the middle neck was fitted with a glass stopper and the other with
a septum. The flask was placed under vacuum and heated. Afterwards
an atm. of N2 was applied. The donor (4.0 equiv.) dissolved in dry CH2Cl2
(c = 0.2 M) was added to the flask. Stirring of the reaction was initiated
and the glass stopper exchanged for a thermometer under N2 pressure,
and the solution cooled to –30 °C. Br2 (1 M in CH2Cl2) was slowly added
until a yellow color persisted, and then the mixture was left to stir for 10
min. Acceptor (1 equiv.) dissolved in dry CH2Cl2 (c = 0.2 M) was added
alongside dry Et2O (23 vol.%). AgClO4 (4.8 equiv.) dissolved in dry
toluene (c = 3.0 M) was added. The reaction was stirred at –30 °C for 2 h,
at which point Et3N (5.0 equiv.) was added. The solution was allowed to
warm to r.t., filtered through a pad of Celite and conc. in vacuo. The
residue was purified by flash column chromatography to afford the
product.
Phenyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-levulinoyl--D-xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-
xylopyranosyl-(1→4)-2,3-di-O-benzoyl-1-thio--D-xylopyranoside
(13): General procedure A: Crushed molecular sieves (1.050 g). Donor
12 (0.550 g, 0.45 mmol). AgOTf (0.230 g, 0.90 mmol). p-
Nitrobenzenesulfenyl chloride (0.102 g, 0.54 mmol). Acceptor 4 (0.181 g,
0.40 mmol). Reaction time 60 min. Et3N (0.09 mL, 1.35 mmol). Eluent for
flash column chromatography hexane/toluene/EtOAc 2:1:1. The product
was obtained as a white crystalline solid (0.500 g, 79%). Rf = 0.38
Deprotection of methyl ester and benzoyl groups (General
Procedure C): The fully protected hexasaccharide (1.0 equiv.) was
dissolved in THF (c = 0.013 M) and the solution cooled to 0 °C under an
atm. of N2. A solution of 1 M aq. LiOH (50 equiv.) and H2O2 (100 equiv.)
was added and the reaction left to stir for the reaction time indicated. The
mixture was conc. in vacuo after which the intermediate was re-dissolved
in MeOH (c = 0.016 M) and 3 M NaOH was added until the solution was
basic and left to stir overnight. At completion of the reaction, the solution
was neutralized using 0.1 M HCl and then conc. in vacuo. The resulting
residue was purified through a SepPak C18 Classic cartridge (eluent H2O
– H2O and 40% acetonitrile).
(hexane/toluene/EtOAc 3:1:2). []2D5
= –42.1 (c 0.38, CHCl3). 1H NMR
(400 MHz, CDCl3):  = 8.01–7.86 (m, 16H), 7.57–7.50 (m, 6H), 7.45–7.25
(m, 22H), 7.18–7.13 (m, 1H), 5.63 (t, J = 7.9 Hz, 1H, H3A), 5.57 (t, J = 6.7
Hz, 1H, H3D), 5.46 (t, J = 7.7 Hz, 1H, H3B), 5.33–5.27 (m, 2H, H2A, H3C),
5.15 (dd, J2B,3B = 7.9 Hz, J1B,2B = 6.0 Hz, 1H, H2B), 5.11 (dd, J2D,3D = 6.4
Hz, J1D,2D = 4.7 Hz, 1H, H2D), 5.03 (td, J = 6.3, 4.1 Hz, 1H, H4D), 4.98 (d,
J1A,2A = 8.0 Hz, 1H, H1A), 4.83 (dd, J = 8.6 Hz, J1C,2C = 6.8 Hz, 1H, H2C),
4.78 (d, J1B,2B = 6.1 Hz, 1H, H1B), 4.66 (d, J1D,2D = 4.9 Hz, 1H, H1D), 4.35
(d, J1C,2C = 6.8 Hz, 1H, H1C), 4.18 (dd, J5A,5’A = 12.1 Hz, J5A,4A = 4.7 Hz,
1H, H5Aeq), 4.03 (td, J = 8.2 Hz, J4A,5A = 4.8 Hz, 1H, H4A), 3.97 (dd,
J5Deq,5Dax = 12.4 Hz, J5Deq,4D = 3.9 Hz, 1H, H5Deq), 3.78–3.65 (m, 2H, H4B,
H5B, H4C), 3.51–3.44 (m, 2H, H5’A, H5C), 3.33 (dd, J5Dax,5Deq = 12.4 Hz,
J5Dax,4D = 6.3 Hz, 1H, H5Dax), 3.28 (dd, J5Bax,5Beq = 11.7 Hz, J5Bax,4B = 7.9
Hz, 1H, H5Bax), 3.01 (dd, J5Cax,5Ceq = 12.2 Hz, J5Cax,4C = 9.1 Hz, 1H,
H5Cax), 2.61–2.46 (m, 2H), 2.44–2.30 (m, 2H), 2.06 (s, 3H). 13C NMR
(101 MHz, CDCl3):  = 205.8, 171.2, 165.6, 165.5 (×2), 165.4, 165.3,
Phenyl 2,3,4-tri-O-benzoyl-β-D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-levulinoyl-1-thio--D-xylopyranoside (11): General procedure A:
Crushed molecular sieves (1.004 g). Donor 3 (0.475 g, 0.86 mmol).
AgOTf (0.440 g, 1.71 mmol). p-Nitrobenzenesulfenyl chloride (0.178 g,
0.94 mmol). Acceptor 6 (0.034 g, 0.77 mmol). Reaction time 23 min. Et3N
(0.36 mL, 2.58 mmol). Eluent for flash column chromatography
heptane/toluene/EtOAc 6:2:2. The product was obtained as light yellow
6
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
165.3, 165.1, 165.0, 133.5, 133.5, 133.4, 133.4, 133.3, 133.1, 132.9,
132.6, 130.1, 130.0, 130.0, 129.9, 129.9, 129.9, 129.8, 129.8, 129.7,
129.6, 129.5, 129.5, 129.4, 129.3, 129.1, 129.1, 129.0, 128.6, 128.5,
128.5, 128.5, 128.4, 128.1, 100.8 (C1B), 100.6 (C1C), 99.5 (C1D), 86.7
(C1A), 75.4 (C4A), 75.3, 75.1 (C4B, C4C), 73.0 (C3A), 72.5 (C3C), 71.9
(C3B), 71.4, 71.3 (C2B, C2C), 70.5 (C2A), 70.1 (C2D), 69.6 (C3D), 68.6
(C4D), 65.7 (C5A), 62.4, 62.3 (C5B, C5C), 60.9 (C5D), 37.8, 29.8, 27.9.
HRMS: calcd. for C87H76O26SNa [M + Na]+ 1591.4237; found 1591.4254.
H2D, H5’E), 3.37 (td, J = 10.1, 3.5 Hz, 1H, H5’A), 3.14 (dd, J = 12.0, 7.7
Hz, 1H, H5’C), 3.12–3.03 (m, 2H, H5’B, H5’D). 13C NMR (101 MHz,
CDCl3):  = 166.1, 165.6, 165.5 (×2), 165.5, 165.4, 165.3, 165.3, 165.1,
165.0, 136.9, 133.6, 133.6, 133.5, 133.4, 133.4, 133.3, 133.3, 133.2,
133.1, 130.1, 130.0, 130.0, 129.9, 129.9, 129.8, 129.8, 129.8, 129.7,
129.6, 129.6, 129.6, 129.5, 129.4, 129.3, 129.2, 129.0, 128.6, 128.6,
128.5, 128.4, 128.4, 128.3, 127.9, 127.9, 101.7 (C1D, JC-H = 164 Hz),
101.2 (C1B, JC-H = 162 Hz), 100.6 (C1C, JC-H = 162 Hz), 99.4 (C1A, JC-H
=
163 Hz), 99.0 (C1E, JC-H = 165 Hz), 76.2 (C4A), 75.4 (C4B), 74.0 (C4C,
C4D), 73.2 (C3D), 72.3, 72.2 (C3A, C3B), 71.8 (C3C), 71.6 (C2B), 71.2,
71.1 (2C) (C2A, C2C, C2D), 70.4 (OCH2Ph), 70.2 (C2E), 69.5 (C3E), 68.6
(C4E), 62.7 (C5A), 62.4 (C5B), 62.0 (C5C), 61.3(C5D), 61.0 (C5E). HRMS:
calcd. for C102H88O31Na [M + Na]+ 1831.5202; found 1831.5112.
Benzyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-levulinoyl--D-xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-
xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-xylopyranoside-(1→4)-
2,3-di-O-benzoyl-β-D-xylopyranoside (14): General procedure A:
Crushed molecular sieves (0.754 g). Donor 13 (0.400 g, 0.26 mmol).
AgOTf (0.1317 g, 0.51 mmol). p-Nitrobenzenesulfenyl chloride (0.048 g,
0.26 mmol). Acceptor 9 (0.103 g, 0.23 mmol). Reaction time 90 min. Et3N
(0.11 mL, 0.77 mmol). Eluent for flash column chromatography
hexane/toluene/EtOAc 4:3:2. The product was obtained as a white
crystalline solid (0.364 g, 83%). Rf = 0.33 (hexane/toluene/EtOAc 3:3:2).
Benzyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-[methyl
2,3,4-tri-O-benzyl-D-glucopyranosyluronate]--D-
xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-xylopyranosyl-(1→4)-2,3-
di-O-benzoyl--D-xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-
xylopyranoside (18): General procedure B: Crushed molecular sieves
(0.395 g). Donor 16 (0.281 g, 0.54 mmol). Acceptor 15 (0.243 g, 0.13
mmol). AgClO4 (0.133 g, 0.64 mmol). Et3N (0.09 mL, 0.67 mmol). Eluent
for flash column chromatography heptane/toluene/acetone 4:1:1 (elution
of product) and heptane/toluene/acetone 2:1:1 (elution of acceptor). The
product was obtained as a white crystalline anomeric mixture (/ 4:1)
(0.138 g, 45%), and acceptor 15 was furthermore reisolated (0.057 g,
23%). Rf = 0.50 (heptane/toluene/acetone 2:1:2). For the -glucuronide
(including partial NMR data for the -isomer): 1H NMR (400 MHz, CDCl3):
 = 8.03–7.82 (m, 28H), 7.59–7.15 (m, 75H), 7.01–6.98 (m, 2H), 5.57–
5.24 (m, 9H, H2A, H3A, H2B, H3C, H3D, H3E, H1F), 5.12 (dd, J = 8.0, 6.4
Hz, 1H, H3B), 5.08 (dd, J = 6.8, 5.0 Hz, 1H, H2E), 4.97 (td, J = 6.4, 4.2 Hz,
1H, H4E), 4.92 (dd, J = 7.3, 5.5 Hz, 1H, H2C), 4.85–4.52 (m, 14H, H1A,
H1B, H1E, Bn), 4.44 (d, J = 3.4 Hz, 0.25H), 4.39 (d, J = 5.4 Hz, 0.25H),
4.34 (d, J = 11.2 Hz, 1H), 4.22 (d, J = 7.2 Hz, 1H, H1D), 4.17 (d, J = 5.4
Hz, 1H, H1C), 4.08 (d, J = 10.0 Hz, 1H), 4.01–3.93 (m, 2.5H, H4A, H5A,
Bn), 3.89–3.79 (m, 3H, H5E), 3.72–3.58 (m, 5.5H, H4B, H2D, H4D), 3.56–
3.44 (m, 7H, H5B, H4C, H5C, H5D), 3.40 (s, 3H, COOMe), 3.37–3.33 (m,
1H, H5’A), 3.26–3.20 (m, 2H, H5’E), 3.11–2.97 (m, 2H, H5’B, H5’C), 2.96–
2.91 (m, 1H, H5’D). 13C NMR (101 MHz, CDCl3):  = 170.2, 169.0 (Cβ),
165.7, 165.5, 165.4, 165.4, 165.4, 165.3, 165.1, 165.0, 165.0, 138.6,
138.4, 138.3, 136.9, 133.5, 133.5, 133.4, 133.3, 133.2, 133.2, 133.1,
133.1, 130.2, 130.1, 130.1, 130.0, 129.9, 129.9, 129.8, 129.8, 129.6,
129.4, 129.3, 129.2, 129.0, 128.6, 128.6, 128.5, 128.4, 128.4, 128.4,
128.3, 128.2, 128.1, 128.1, 128.0, 127.9, 127.9, 127.8, 127.5, 127.4,
102.2 (C1D), 101.0 (C1B), 99.8, 99.5, 99.3 (C1A, C1C, C1E), 97.3 (C1F,
JC-H = 173 Hz), 80.7 (C3F), 80.0 (C4F), 79.3 (C2F), 76.6 (C2D), 76.2, 76.1
(C4A, C4D), 75.8 (Bn), 74.5 (Bn), 74.1 (C4B), 73.7 (C3D), 73.5 (Bn), 73.4
(C4C), 72.4 (C3A), 71.8 (C3B), 71.4 (C2B), 71.2, 71.1, 70.8 (C2A, C2C,
C3C), 70.5 (C5F), 70.4 (Bn), 70.3 (C2E), 69.7 (C3E), 68.7 (C4E), 63.1, 62.8
(C5A, C5D), 61.9 (C5B), 61.4 (C5C), 60.9 (C5E), 52.6 (Cβ), 52.1 (COOMe).
HRMS: calcd. for C130H116O37Na [M + Na]+ 2291.7088; found 2291.7098.
[]D25
= –43.0 (c 0.10, CHCl3). 1H NMR (400 MHz, CDCl3):  = 7.98–7.85
(m, 20H), 7.57–7.49 (m, 6H), 7.45–7.16 (m, 29H), 5.57 (t, J = 6.7 Hz, 1H,
H3E), 5.55–5.51 (m, 1H, H3A), 5.49 (t, J = 8.0 Hz, 1H, H3B), 5.40 (t, J =
8.0 Hz, 1H, H3C), 5.31–5.27 (m, 2H, H2A, H3D), 5.15 (dd, J = 8.4, 6.6 Hz,
1H, H2B), 5.12 (dd, J = 6.9, 5.1 Hz, 1H, H2E), 5.08–5.01 (m, 2H, H2C,
H4E), 4.84–4.80 (m, 1H, H2D), 4.80 (d, J = 12.5 Hz, 1H, Bn), 4.70 (d, J =
6.3 Hz, 1H, H1B), 4.66 (d, J = 4.9 Hz, 1H, H1E), 4.64 (d, J = 6.6 Hz, 1H,
H1A), 4.55 (d, J = 12.4 Hz, 1H, Bn), 4.54 (d, J = 6.0 Hz, 1H, H1C) 4.33 (d,
J = 6.7 Hz, 1H, H1D), 3.99–3.94 (m, 3H, H4A, H5A, H5E), 3.80–3.73 (m,
2H, H4B, H4D), 3.69 (td, J = 8.0, 7.5, 4.4 Hz, 1H, H4C), 3.60 (dd, J = 12.1,
4.8 Hz, 1H, H5C), 3.48–3.43 (m, 2H, H5B, H5D), 3.40–3.31 (m, 2H, H5’A,
H5’E), 3.20 (dd, J = 12.2, 8.4 Hz, 1H, H5’C), 3.09 (dd, J = 12.2, 8.6 Hz, 1H,
H5’B), 3.00 (dd, J = 12.2, 9.0 Hz, 1H, H5’D), 2.53 (q, J = 6.7 Hz, 2H),
2.38–2.33 (m, 2H), 2.05 (s, 3H). 13C NMR (101 MHz, CDCl3):  = 205.7,
171.2, 165.6, 165.5, 165.4, 165.4, 165.4, 165.3 (×2), 165.1, 165.0, 165.0,
136.9, 133.5, 133.5, 133.4, 133.4, 133.3, 133.2, 133.1, 133.1, 130.0,
130.0, 130.0, 129.9, 129.8, 129.8, 129.7, 129.7, 129.7, 129.6, 129.6,
129.5, 129.4, 129.4, 129.3, 129.1, 129.0, 128.6, 128.6, 128.5, 128.5,
128.5, 128.4, 128.4, 128.4, 128.3, 127.9, 127.9, 101.1 (C1B), 100.6,
100.5 (C1C, C1D), 99.5, 99.4 (C1A, C1E), 76.1 (C4A), 75.3, 75.2, 75.0 (C4B,
C4C, C4D), 72.5 (C3D), 72.2, 72.1, 72.0 (C3A, C3B, C3E), 71.5, 71.4 (C2B,
C2D), 71.2 (C2C), 71.1 (C2A), 70.4 (Bn), 70.1 (C2E), 69.6 (C3E), 68.6
(C4E), 62.7 (C5A), 62.4, 62.3 (×2) (C5B, C5C, C5D), 60.9 (C5E), 37.8, 29.7,
27.9. HRMS: calcd. for C107H94O33Na [M + Na]+ 1930.5603; found
1930.5619.
Benzyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl--D-
xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-xylopyranosyl-(1→4)-2,3-
di-O-benzoyl--D-xylopyranoside-(1→4)-2,3-di-O-benzoyl--D-
xylopyranoside (15): Pentasaccharide 14 (1.740 g, 0.912 mmol) was
dissolved in pyridine/AcOH 2:1 (1.80 mL). A mixture of a 50% solution of
hydrazine hydrate (88 L, 1.82 mmol) dissolved in pyridine (c = 20 M)
was added at 0 °C. The reaction was left to stir at r.t. overnight, at which
point TLC showed consumption of the starting material and formation of
the product. The reaction was stopped by addition of acetone (34.0 mL,
456 mmol) and was left to stir at r.t. for 1 h. EtOAc was added, and the
mixture washed with 1 M HCl and brine, filtered, and conc. in vacuo. The
Benzyl 2,3,4-tri-O-benzoyl--D-xylopyranosyl-(1→4)-3-O-benzoyl-2-
O-[methyl 2,3-di-O-benzyl-4-O-methyl-D-glucopyranosyluronate]--D-
xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-xylopyranosyl-(1→4)-2,3-
di-O-benzoyl--D-xylopyranosyl-(1→4)-2,3-di-O-benzoyl--D-
xylopyranoside (19): General procedure B: Crushed molecular sieves
(0.372 g). Donor 17 (0.197 g, 0.44 mmol). Acceptor 15 (0.200 g, 0.11
mmol). AgClO4 (0.111 g, 0.53 mmol). Et3N (0.08 mL, 0.55 mmol). Eluent
for flash column chromatography heptane/toluene/acetone 6:3:2. The
product was obtained as a white crystalline anomeric mixture (/ 5:2)
(0.106 g, 44%), and acceptor 15 was furthermore reisolated (0.034 g,
17%). Rf = 0.45 (heptane/toluene/acetone 2:1:2). For the -glucuronide
(including partial NMR data for the -isomer): 1H NMR (400 MHz, CDCl3):
 = 8.04–7.83 (m, 33H), 7.59–7.11 (m, 79H), 5.58–5.24 (m, 10.7H, H2A,
H3A, H3B, H3C, H3D, H3E, H1F), 5.17–5.06 (m, 3H, H2B, H2E), 5.04 (dd, J
= 7.0, 5.1 Hz, 0.4H), 5.00–4.93 (m, 1.6H, H4E), 4.90 (dd, J = 7.5, 5.6 Hz,
1H, H2C), 4.83–4.82 (m, 2.8H, Bn), 4.79–4.73 (m, 2H), 4.71–4.68 (m,
2.4H, H1B, Bn), 4.66–4.60 (m, 3.7H, H1A, H1E, Bn), 4.57–4.52 (m, 3.3H,
Bn), 4.50 (d, J = 5.1 Hz, 0.4H), 4.45 (d, J = 11.5 Hz, 0.4H), 4.39 (d, J =
residue
was
purified
by
flash
column
chromatography
(hexane/toluene/EtOAc 3:3:2) affording the product as a white powder
(1.610 g, 97%). Rf = 0.34 (hexane/toluene/EtOAc 3:3:2). []25
= –38.3 (c 1,
D
CHCl3). 1H NMR (400 MHz, CDCl3):  = 8.02–7.84 (m, 20H), 7.59–7.30
(m, 30H), 7.22–7.16 (m, 5H), 5.64 (t, J = 6.7 Hz, 1H, H3E), 5.52 (t, J = 8.1
Hz, 1H, H3A), 5.49 (t, J = 8.1 Hz, 1H, H3B), 5.40 (t, J = 7.9 Hz, 1H, H3C),
5.29 (dd, J = 8.5, 6.7 Hz, 1H, H2A), 5.21 (t, J = 7.4 Hz, 1H, H3D), 5.18–
5.09 (m, 3H, H2B, H2E, H4E), 5.06 (dd, J = 8.1, 6.1 Hz, 1H, H2C), 4.80 (d,
J = 12.3 Hz, 1H, Bn), 4.72 (d, J = 4.9 Hz, 1H, H1E), 4.70 (d, J = 6.4 Hz,
1H, H1B), 4.63 (d, J = 6.6 Hz, 1H, H1A), 4.54 (d, J = 5.3 Hz, 1H, H1C),
4.55 (d, J = 12.5 Hz, 1H, Bn), 4.27 (d, J = 5.6 Hz, 1H, H1D), 4.15 (dd, J =
12.4, 3.9 Hz, 1H, H5E), 4.00–3.94 (m, 2H, H4A, H5A), 3.79–3.70 (m, 3H,
H4B, H4C, H4D), 3.63–3.57 (m, 2H, H5C, H5D), 3.47–3.43 (m, 3H, H5B,
7
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
5.4 Hz, 0.4H), 4.21 (d, J = 7.1 Hz, 1H, H1D), 4.13 (d, J = 5.6 Hz, 1H, H1C),
4.02–3.95 (m, 4H, H4A, H5A, H5F), 3.89–3.56 (m, 11.3H, H4B, H2D, H4D,
H5E, H3F), 3.53–3.34 (m, 14H, H5’A, H5B, H4C, H5C, H5D, H2F, COOMe),
3.29–3.18 (m, 7.4H, H5’E, H4F, OMe), 3.11–3.02 (m, 2H, H5’B), 2.99 (dd,
J = 11.4, 6.8 Hz, 1H, H5’C), 2.95–2.89 (m, 1H, H5’D). 13C NMR (101 MHz,
CDCl3):  = 170.3, 169.1, 165.7, 165.5, 165.4, 165.4, 165.4, 165.3, 165.3,
165.3 (Cβ), 165.2 (Cβ), 165.1, 165.0 (Cβ), 164.9, 164.9, 138.7, 138.6 (Cβ),
138.5, 136.9, 133.5, 133.5, 133.4, 133.3, 133.2, 133.2, 133.1, 133.0,
130.2, 130.1, 130.1, 130.1, 123.0, 129.9, 129.9, 129.8, 129.8, 129.7 (Cβ),
129.6 (Cβ), 129.6, 129.6, 129.5 (Cβ), 129.4 (Cβ), 129.4, 129.3, 129.3 (Cβ),
129.2, 129.0, 128.6, 128.5, 128.4, 128.4, 128.4, 128.3, 128.2, 128.2,
128.1, 128.0, 127.9, 127.9, 127.8, 127.7 (Cβ), 127.6 (Cβ), 127.4, 103.1
(Cβ), 102.0 (C1D), 101.1 (C1B), 100.9 (Cβ), 99.9 (C1E), 99.6 (Cβ), 99.5 (×2,
C1A, C1C), 99.4 (Cβ), 97.6 (C1F, JC-H = 173 Hz), 83.6 (Cβ), 81.7 (C4F),
80.6 (C3F), 79.1 (C2F), 76.8 (C2D), 76.6 (C4D), 76.1 (C4A), 76.1 (Cβ), 75.7
(Bn), 75.5 (Cβ), 75.4 (Cβ), 75.1 (Cβ), 75.1 (Cβ), 74.8 (Cβ), 74.5 (Cβ), 74.2
(C4B), 74.1 (Cβ), 73.7 (C3D), 73.5 (Bn), 73.5 (C4C), 72.6 (Cβ), 72.4 (C3A),
72.3 (Cβ), 71.8 (C3B), 71.5 (Cβ), 71.4, 71.2, 71.2 (C2A, C2B, C3C), 71.1
(Cβ), 70.6, 70.5 (C2C, C2E), 70.4 (Bn), 70.3 (C5F), 70.2 (Cβ), 69.8 (C3E),
68.7 (C4E), 62.9, 62.8 (C5A, C5D), 62.7 (Cβ), 62.0 (C5B), 61.5 (C5C), 60.9
(C5E), 60.7 (Cβ), 60.1 (OMe), 52.7 (Cβ), 52.2 (COOMe). HRMS: calcd. for
C124H112O37Na [M + Na]+ 2215.6775; found 2215.6758.
4H, H3D, H4E), 3.61–3.55 (m, 7H, H2αA, H3βA, H3B, H3C, H2F), 3.53 (dd, J
= 6.9, 2.6 Hz, 0.88H), 3.51–3.48 (m, 3H, H2D, H4F), 3.46–3.38 (m, 8H,
H5’βA, H5’B, H5’C, H5’D, H3E), 3.33–3.26 (m, 8H, H2βA, H2B, H2C, H2E,
H5’E). 13C NMR (201 MHz, D2O):  = 177.0, 102.0, 101.6 (×2) (C1B, C1C,
C1E), 101.3 (C1D), 97.6 (C1F), 96.5 (C1βA), 92.0 (C1αA), 76.8 (C4D), 76.5,
76.5, 76.4, 76.3 (C4αA, C4βA, C4B, C2D), 75.9 (C4C), 75.6 (C3E), 75.3 (C),
74.0 (C2βA), 73.9 (C3βA), 73.8 (C), 73.7, 73.6 (C3B, C3C), 73.6 (C), 72.8,
72.7 (C), 72.7, 72.6, 72.6 (C2B, C2C, C2E, C2F), 72.4 (C3D), 72.1, 72.0
(C4F, C5F), 71.3 (C2αA), 71.1 (C2F), 70.9 (C3αA), 69.2 (C4E), 62.9 (C),
65.2 (C5E), 63.0, 62.9, 62.8, 62.8 (C1βA, C5B, C5C, C5D), 58.8 (C5αA).
HRMS: calcd. for C31H50O27Na [M + Na]+ 877.2432; found 877.2443.
-D-Xylopyranosyl-(1→4)-[4-O-methyl-D-glucopyranosyluronic acid-
(1→2)]--D-xylopyranosyl-(1→4)--D-xylopyranosyl-(1→4)--D-
xylopyranosyl-(1→4)-D-xylopyranose (2): General procedure C: Fully
protected hexasaccharide 19 (17.9 mg, 0.008 mmol). Reaction time 4 h.
TLC eluent for deprotection of methyl ester heptane/toluene/acetone
2:1:2. Reaction time for deprotection of benzoyl groups overnight with
TLC eluent for EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2. The product
benzyl
glucopyranosyluronic
-D-xylopyranosyl-(1→4)-[2,3-di-O-benzyl-4-O-methyl-D-
acid-(1→2)]--D-xylopyranosyl-(1→4)--D-
xylopyranosyl-(1→4)--D-xylopyranosyl-(1→4)--D-xylopyranoside was
obtained as an inseparable / mixture (8.6 mg, 93%). Rf() = 0.42
-D-Xylopyranosyl-(1→4)-[D-glucopyranosyluronic acid-(1→2)]--D-
xylopyranosyl-(1→4)--D-xylopyranosyl-(1→4)--D-xylopyranosyl-
(1→4)-D-xylopyranose (1): General procedure C: Fully protected
hexasaccharide 18 (47.8 mg, 0.021 mmol). Reaction time 5.5 h. TLC
eluent for deprotection of methyl ester heptane/toluene/acetone 2:1:2.
Reaction time for deprotection of benzoyl groups overnight with TLC
eluent EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2. The product benzyl -D-
(EtOAc/MeOH/H2O/acetic
acid
6:3:0.8:0.2).
Rf()
=
0.55
(EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2). For the -glucuronide
(including partial NMR data for the -isomer): 1H NMR (800 MHz, D2O): 
= 7.50–7.39 (m, 30H), 5.48 (d, J = 3.5 Hz, 1H, H1F), 5.03 (d, J = 10.9 Hz,
0.5H), 4.92–4.90 (m, 2H, Bn), 4.90–4.82 (m, 5H, Bn), 4.77–4.74 (m, 3H,
Bn), 4.60 (d, J = 7.5 Hz, 1H, H1D), 4.54–4.52 (m, 2H, H1A), 4.51–4.45 (m,
4H, H1B, H1E), 4.41 (d, J = 9.9 Hz, 1H, H5F), 4.16–4.14 (m, 1H), 4.13–
4.11 (m, 3H, H5A, H5D), 4.04 (dd, J = 11.9, 5.0 Hz, 1H, H5B), 4.01 (d, J =
7.4 Hz, H1C), 3.99–3.97 (m, 2H, H5E, H3F), 3.91–3.87 (m, 2H, H5C),
3.84–3.79 (m, 4H, H4A, H4D), 3.75–3.71 (m, 3H, H4C, H2F), 3.70–3.67 (m,
2H, H3D), 3.66–3.63 (m, 2H, H4E), 3.62–3.51 (m, 14H, H3A, H3B, H4B,
H2D), 3.46–3.26 (m, 19H, H2A, H5’A, H2B, H5’B, H3C, H5’D, H2E, H3E, H5’E,
H4F, OMe), 3.32–3.19 (m, 2H, H2C), 3.02 (t, J = 11.1 Hz, 1H, H5’C). 13C
NMR (201 MHz, D2O):  = 176.6, 137.8, 137.4, 136.7, 129.1, 129.1,
129.0, 128.9, 128.9, 128.8, 128.8, 128.6, 128.4, 127.9, 102.9, 102.3,
102.1, 101.8 (C1A, C1B, C1E), 101.8, 101.7, 101.5 (C1C), 100.7 (C1D),
99.5, 96.2 (C1F), 83.1, 82.7 (C4F), 82.5, 81.3, 80.6 (C3F), 79.5, 79.3 (C2F),
77.0 (C4D), 76.7 (C2D), 76.6 (C4A), 76.5, 76.4, 76.2, 76.2 (C4B), 76.0,
76.0 (Bn), 75.8, 75.7 (C3E), 75.7, 75.6, 75.3, 74.9 (C4C), 74.1 (Bn), 74.0
(C3A), 73.9, 73.8, 73.8, 73.7 (C3C), 73.6 (C3B), 73.1, 73.0 (C2A, C2E),
72.9, 72.8, 72.8 (C2C), 72.7, 72.6, 72.6 (C2B, C3D, C5F), 71.8 (Bn), 69.3
(C4E), 69.2, 65.4 (C5E), 65.3, 63.1, 63.1, 63.0 (C5A, C5B, C5D), 62.8
(C5C), 60.3 (OMe), 60.3. HRMS: calcd. for C53H70O27Na [M + Na]+
1161.3997; found 1164.4005. The above glycoside (21.2 mg, 0.019
mmol) was dissolved in EtOAc/EtOH/H2O 1:1:1 (2.25 mL) and Pd/C
Degussa type (10.4 mg, 0.098 mmol) was added. The mixture was
stirred under an atm. of H2 overnight. The reaction was then filtered over
a syringe filter (0.45 m) and conc. in vacuo to afford product 2 (15.0 mg,
93%). Rf = 0.27 (EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2). : ratio
approximately 0.6:1. For the -glucuronide (including partial NMR data
for the -isomer): 1H NMR (800 MHz, D2O):  = 5.31 (d, J = 3.5 Hz, 0.18),
5.29 (d, J = 3.7 Hz, 1H, H1F), 5.19 (d, J = 3.5 Hz, 0.62H, H1αA), 4.68 (d, J
= 6.8 Hz, 0.22H), 4.63 (d, J = 7.6 Hz, 1H, H1D), 4.61 (d, J = 7.9 Hz,
0.38H), 4.59 (d, J = 7.9 Hz, 1H, H1βA), 4.49–4.46 (m, 5H, H1B, H1C, H1E),
4.33 (d, J = 10.1 Hz, 1H, H5F), 4.15 (dd, J = 11.9, 5.2 Hz, 1H, H5C),
4.12–4.10 (m, 4H, H5B, H5D), 4.06 (dd, J = 11.7, 5.2 Hz, 1H, H5βA), 3.99–
3.96 (m, 2H, H5E), 3.86–3.73 (m, 12H, H3αA, H4αA, H5αA, H5’αA, H4βA, H4B,
H4C, H4D, H3F), 3.67 (d, J = 9.7 Hz, 0.69H), 3.64–3.61 (m, 4H, H3D, H4E),
3.59–3.51 (m, 8H, H2αA, H3βA, H3B, H3C, H2F), 3.49–3.42 (m, 11H, H5’C,
H2D, H3E, OCH3), 3.40–3.36 (m, 5H, H5’βA, H5’B, H5’D), 3.33–3.21 (m,
10H, H2βA, H2B, H2C, H2E, H5’E, H4F). 13C NMR (201 MHz, D2O):  =
176.8, 103.5 (C), 102.0 (C1E), 101.9 (C), 101.6 (×2) (C1B, C1C), 101.5
(C), 101.3 (C1D), 99.8 (C), 97.5 (C1F), 96.5 (C1βA), 92.0 (C1αA), 82.4
(C4F), 82.2 (C), 81.7 (C), 76.8 (C4D), 76.5 (C), 76.5, 76.4, 76.4, 76.3
(C4αA, C4βA, C4B, C2D), 75.9 (C4C), 75.6 (C3E), 75.5 (C), 74.7 (C), 74.0,
73.9 (C2βA, C3βA), 73.8 (C), 73.6, 73.6 (C3B, C3C), 73.6 (C), 72.8 (C),
xylopyranosyl-(1→4)-[2,3,4-tri-O-benzyl-D-glucopyranosyluronic
acid-
(1→2)]--D-xylopyranosyl-(1→4)--D-xylopyranosyl-(1→4)--D-
xylopyranosyl-(1→4)--D-xylopyranoside (18.9 mg, 74%) was obtained
as an inseparable / mixture. Rf() = 0.50 (EtOAc/MeOH/H2O/acetic
acid 6:3:0.8:0.2). Rf() = 0.65 (EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2).
For the -glucuronide (including partial NMR data for the -isomer): 1H
NMR (800 MHz, D2O):  = 7.49–7.39 (m, 22H), 5.50 (d, J = 3.2 Hz, 1H,
H1F), 4.92–4.90 (m, 1H, Bn), 4.88–4.72 (m, 7H, Bn), 4.66 (d, J = 10.5 Hz,
1H), 4.60 (d, J = 7.4 Hz, 1H, H1D), 4.53 (d, J = 7.7 Hz, 1H, H1A), 4.49–
4.46 (m, 3H, H1B, H1E, H5F), 4.12 (dd, J = 11.8, 5.2 Hz, 2H, H5A, H5D),
4.03 (dd, J = 11.8, 5.2 Hz, 1H, H5B), 4.01–3.98 (m, 3H, H1C, H5E, H3F),
3.90 (dd, J = 11.7, 5.2 Hz, 1H, H5C), 3.85–3.80 (m, 3H, H4A, H4D), 3.76
(dd, J = 9.8, 3.3 Hz, 1H, H2F), 3.75–3.72 (m, 2H, H4C, H4F), 3.70 (d, J =
9.2 Hz, 1H, H3D), 3.65–3.62 (m, 2H, H4E), 3.59–3.52 (m, 5H, H3A, H3B,
H4B, H2D), 3.46–3.39 (m, 5H, H5’A, H3C, H5’D, H3E), 3.37–3.32 (m, 4H,
H2A, H5’B), 3.31–3.27 (m, 3H, H2B, H2E, H5’E), 3.21–3.19 (m, 1H, H2C),
3.03 (t, J = 11.2 Hz, 1H, H5’C). 13C NMR (201 MHz, D2O):  = 176.3,
137.6, 137.2, 137.0, 136.5, 129.0, 128.8, 128.7, 128.7, 128.7, 128.5,
128.4, 128.3, 128.2, 127.7, 102.0 (C1E), 101.9 (C1A), 101.7, 101.7 (C1B),
101.6, 101.3 (C1C), 100.5 (C1D), 96.1 (C1F), 80.5 (C4F), 80.4 (C3F), 79.5
(C2F), 76.8, 76.7 (C2D, C4D), 76.5, 76.4 (C4A), 76.4, 76.0, 75.9 (C4B, Bn),
75.6 (C3E), 74.9 (Bn), 74.8 (C4C), 73.9 (Bn), 73.8 (C3A), 73.5 (C3C), 73.4
(C3B), 72.9, 72.9 (C2A, C5F), 72.9, 72.8 (C2B, C2E), 72.6 (C2C), 72.4
(C3D), 71.6 (Bn), 69.2 (C4E), 65.2 (C5E), 62.9, 62.8, 62.8 (C5A, C5B, C5D),
62.7 (C5C). HRMS: calcd. for C59H74O27Na [M + Na]+ 1237.4310; found
1237.4318. The above benzyl glycoside (17.1 mg, 0.014 mmol) was
dissolved in EtOAc/EtOH/H2O 1:1:1 (2.25 mL) and Pd/C Degussa type
(8.3 mg, 0.077 mmol) was added. The mixture was stirred under an atm.
of H2 overnight. The reaction was then filtered over a syringe filter (0.45
m) and conc. in vacuo to afford product 1 (11.3 mg, 94%). Rf = 0.11
(EtOAc/MeOH/H2O/acetic acid 6:3:0.8:0.2). For the -glucuronide
(including partial NMR data for the -isomer): 1H NMR (800 MHz, D2O): 
= 5.32 (d, J = 3.9 Hz, 1H, H1F), 5.20 (d, J = 3.6 Hz, 0.62H, H1αA), 4.71 (d,
J = 6.8 Hz, 0.30H), 4.69 (d, J = 7.9 Hz, 0.33H), 4.66 (d, J = 7.5 Hz, 1H,
H1D), 4.60 (d, J = 7.9 Hz, 1H, H1βA), 4.50–4.47 (m, 5H, H1B, H1C, H1E),
4.38 (d, J = 10.2 Hz, 1H, H5F), 4.17 (dd, J = 11.8, 5.2 Hz, 1H, H5C),
4.15–4.10 (m, 4H, H5B, H5D), 4.07 (dd, J = 11.8, 5.3 Hz, 1H, H5βA), 3.99
A
(dd, J = 11.7, 5.5 Hz, 2H, H5E), 3.85–3.75 (m, 11H, H3αA, H4αA, H5α
,
H5’αA, H4βA, H4B, H4C, H4D, H3F), 3.71–3.70 (m, 0.48H), 3.66–3.62 (m,
8
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
72.8 (C2E), 72.7 (C), 72.7, 72.6 (C2B, C2C), 72.3 (C3D), 72.2, 72.1 (C3F,
C5F), 71.3 (C2αA), 71.2 (C2F), 70.9 (C3αA), 69.2 (C4E), 69.1 (C), 65.2
(C5E), 62.9, 62.9, 62.8 (×2) (C1βA, C5B, C5C, C5D), 59.8 (OMe), 58.8
(C5αA). HRMS: calcd. for C32H52O27Na [M + Na]+ 891.2588; found
891.2603.
3832; c) M. H. Clausen, M. R. Jørgensen, J. Thorsen, R. Madsen, J.
Chem. Soc., Perkin Trans. 1 2001, 543-551.
[19] a) K. Šuchová, S. Kozmon, V. Puchart, A. Malovíková, T. Hoff, K. B. R.
M. Krogh, P. Biely, Arch. Biochem. Biophys. 2018, 643, 42-49; b) F. J.
St. John, J. C. Hurlbert, J. D. Rice, J. F. Preston, E. Pozharski, J. Mol.
Biol. 2011, 407, 92-109; c) K. Kolenová, O. Ryabova, M. Vršanská, P.
Biely, FEBS Lett. 2010, 584, 4063-4068; d) K. Kolenová, M. Vršanska,
P. Biely, J. Biotechnol. 2006, 121, 338-345.
Acknowledgements
[20] See Supporting Information for details.
[21] K. C. Nicolaou, H. J. Mitchell, K. C. Fylaktakidou, R. M. Rodríguez, H.
Suzuki, Chem. Eur. J. 2000, 6, 3116-4148.
We thank the Danish Council for Strategic Research for financial
support (SET4Future project, grant 0603-00463B). In addition,
The NMR Center • DTU and the Villum Foundation are
acknowledged for access to the 800 MHz spectrometer.
[22] S. M. Andersen, M. Heuckendorff, H. H. Jensen, Org. Lett. 2015, 17,
944-947.
[23] D. Crich, Z. Dai, S. Gastaldi, J. Org. Chem. 1999, 64, 5224-5229.
[24] K. Bock, C. Pedersen, Acta Chem. Scand. 1975, B29, 258-264.
[25] See also: M. Alpe, S. Oscarson, Carbohydr. Res. 2003, 338, 2605-
2609.
Keywords: Glycosylation • Hemicellulose • Oligosaccharides •
Synthetic methods • Thioglycosides
[26] L. J. van den Bos, J. D. C. Codée, J. C. van der Toorn, T. J. Boltje, J. H.
van Boom, H. S. Overkleeft, G. A. van der Marel, Org. Lett. 2004, 6,
2165-2168.
[1]
[2]
H. V. Scheller, P. Ulvskov, Ann. Rev. Plant Biol. 2010, 61, 263-289.
Biermann’s Handbook of Pulp and Paper: Raw Material and Pulp
Making (Ed.: P. Bajpai), Elsevier, Amsterdam, 2018, pp. 19-74.
P. Biely, S. Singh, V. Puchart, Biotechnol. Adv. 2016, 34, 1260-1274.
H. Yagi, T. Maehara, T. Tanaka, R. Takehara, K. Teramoto, K. Yaoi, S.
Kaneko, J. Appl. Glycosci. 2017, 64, 115-121.
[27] K. Igarashi, J. Irisawa, T. Honma, Carbohydr. Res. 1975, 39, 213-225.
[28] T. Ishii, T. Konishi, T. Yamasaki, A. Enomoto, M. Yoshida, I. Maeda, K.
Shimizu, Carbohydr. Polym. 2010, 81, 964-968.
[3]
[4]
[29] K. Bock, C. Pedersen, J. Chem. Soc., Perkin Trans. 2 1974, 293-297.
[30] D. A. Evans, T. C. Britton, J. A. Ellman, Tetrahedron Lett. 1987, 28,
6141-6144.
[5]
a) T. Maehara, H. Yagi, T. Sato, M. Ohnishi-Kameyama, Z. Fujimoto, K.
Kamino, Y. Kitamura, F. St. John, K. Yaoi, S. Kaneko, Appl. Environ.
Microbiol. 2018, 84, e01850-17; b) R. Yan, T. V. Vuong, W. Wang, E. R.
Master, Enzyme Microb. Technol. 2017, 104, 22-28.
[6]
[7]
M. C. Jonathan, J. DeMartini, S. Van Stigt Thans, R. Hommes, M. A.
Kabel, Biotechnol. Biofuels 2017, 10, 112.
M. Chemin, A.-L. Wirotius, F. Ham-Pichavant, G. Chollet, D. Da Silva
Perez, M. Petit-Conil, H. Cramail, S. Grelier, Eur. Polym. J. 2015, 66,
190-197.
[8]
a) H. Togashi, A. Kato, K. Shimizu, Carbohydr. Polym. 2009, 78, 247-
252; b) M. K. Nacos, P. Katapodis, C. Pappas, D. Daferera, P. A.
Tarantilis, P. Christakopoulos, M. Polissiou, Carbohydr. Polym. 2006,
66, 126-134; c) P. Katapodis, S. Kintzios, J. Konstas, D. Kekos, B. J.
Macris, P. Christakopoulos, J. Biosci. Bioeng. 2003, 95, 630-632; d) M.
A. Verbruggen, B. A. Spronk, H. A. Schols, G. Beldman, A. G. J.
Voragen, J. R. Thomas, J. P. Kamerling, J. F. G. Vliegenthart,
Carbohydr. Res. 1998, 306, 265-274.
[9]
T. Yamasaki, A. Enomoto, A. Kato, T. Ishii, M. Kameyama, H. Anzai, K.
Shimizu, Carbohydr. Polym. 2012, 87, 1425-1432.
[10] C. Kinnaert, M. Daugaard, F. Nami, M. H. Clausen, Chem. Rev. 2017,
117, 11337-11405.
[11] a) S. Oscarson, P. Svahnberg, J. Chem. Soc., Perkin Trans. 1 2001,
873-879; b) Y. Kawabata, Y. Gama, I. Kusakabe, Biosci. Biotech.
Biochem. 1994, 58, 1463-1466; c) P. Kováč, E. Petráková, P. Kočiš,
Carbohydr. Res. 1981, 93, 144-147; d) J. Hirsch, P. Kováč, J. Alföldi, V.
Mihálov, Carbohydr. Res. 1981, 88, 146-152.
[12] P. Kováč, J. Hirsch, V. Kováčik, P. Kočiš, Carbohydr. Res. 1980, 85,
41-49.
[13] E. N. Underlin, M. Böhm, R. Madsen, J. Org. Chem. 2019, 84, 16036-
16054.
[14] a) B. Yang, W. Yang, S. Ramadan, X. Huang, Eur. J. Org. Chem. 2018,
1075-1096; b) W. Yang, B. Yang, S. Ramadan, X. Huang, Beilstein J.
Org. Chem. 2017, 13, 2094-2114.
[15] D. Crich, F. Cai, F. Yang, Carbohydr. Res. 2008, 343, 1858-1862.
[16] For an alternative approach to arabinoxylans by automated glycan
assembly, see: D. Senf, C. Ruprecht, G. H. M. de Kruijff, S. O.
Simonetti, F. Schuhmacher, P. H. Seeberger, F. Pfrengle, Chem. Eur. J.
2017, 23, 3197-3205.
[17] a) J. D. C. Codée, A. E. Christina, M. T. C. Walvoort, H. S. Overkleeft,
G. A. van der Marel, Top. Curr. Chem. 2011, 301, 253-289; b) L. J. van
den Bos, J. D. C. Codée, R. E. J. N. Litjens, J. Dinkelaar, H. S.
Overkleeft, G. A. van der Marel, Eur. J. Org. Chem. 2007, 3963-3976.
[18] a) A. N. Zakharova, R. Madsen, M. H. Clausen, Org. Lett. 2013, 15,
1826-1829; b) M. H. Clausen, R. Madsen, Chem. Eur. J. 2003, 9, 3821-
9
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202000211
European Journal of Organic Chemistry
FULL PAPER
Oligosaccharide Synthesis
Insert graphic for Table of Contents here.
Glucuronoxylans 1 and 2 have been prepared by a concise synthetic route where the pentaxylan backbone is assembled by
preactivation-based glycosylations with phenyl thioglycosides and the glucuronic acids are introduced by Koenigs-Knorr couplings
10
This article is protected by copyright. All rights reserved.