A Streamlined Regenerative Glycosylation Reaction: Direct, Acid-Free Activation of Thioglycosides

Article abstract of DOI:10.1002/chem.202003479

Our group has previously reported that 3,3-difluoroxindole (HOFox) is able to mediate glycosylations via intermediacy of OFox imidates. Thioglycoside precursors were first converted into the corresponding glycosyl bromides that were then converted into the OFox imidates in the presence of Ag₂O followed by the activation with catalytic Lewis acid in a regenerative fashion. Reported herein is a direct conversion of thioglycosides via the regenerative approach that bypasses the intermediacy of bromides and eliminates the need for heavy-metal-based promoters. The direct regenerative activation of thioglycosides is achieved under neutral reaction conditions using only 1 equiv. NIS and catalytic HOFox without the acidic additives.

Full text of DOI:10.1002/chem.202003479

Accepted Article
Accepted Article
Title: A Streamlined Regenerative Glycosylation Reaction: Direct, Acid-
Free Activation of Thioglycosides
Authors: Samira Escopy, Yashapal Singh, Keith Stine, and Alexei V.
Demchenko
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: Chem. Eur. J. 10.1002/chem.202003479
Link to VoR: https://doi.org/10.1002/chem.202003479
01/2020

10.1002/chem.202003479
Chemistry - A European Journal
A Streamlined Regenerative Glycosylation Reaction: Direct, Acid-
Free Activation of Thioglycosides
Samira Escopy, Yashapal Singh, Keith J. Stine, and Alexei V. Demchenko*
Department of Chemistry and Biochemistry, University of Missouri – St. Louis, One University Boulevard, St. Louis, Mis-
souri 63121, USA
Supporting Information Placeholder
ABSTRACT: Our group has previously reported that 3,3-difluoroxindole (HOFox) is able to mediate glycosylations via intermedia-
cy of OFox imidates. Thioglycoside precursors were first converted into the corresponding glycosyl bromides that were then con-
verted into the OFox imidates in the presence of Ag2O followed by the activation with catalytic Lewis acid in a regenerative fash-
ion. Reported herein is a direct conversion of thioglycosides via the regenerative approach that bypasses the intermediacy of bro-
mides and eliminates the need for heavy metal-based promoters. The direct regenerative activation of thioglycosides is achieved
under neutral reaction conditions using only
1 equiv NIS and catalytic HOFox without the acidic additives.
From their ubiquitous presence in nature to vital roles in biol-
ogy, complex carbohydrates are essential molecules made by
every living organism. The structure diversity and complexity
of carbohydrates have intrigued glycoscientists for decades.[1]
Given that glycosylation is one of the most fundamental modi-
fications of carbohydrates, enzymatic and chemical synthesis
of glycosidic linkages remains a focus of many research pro-
grams around the world. Among significant advances made in
the area, automated synthesis using polymer supports has
come to the fore as a powerful means to synthesize glycans.[2]
Many glycosylations in solution make use of thioglycosides,[3]
but glycosylations on solid supports commonly demand highly
reactive imidates[4] or phosphates[5] as glycosyl donors to offset
challenges related to the mismatch between reactive solution-
based vs. their unreactive solid-phase-immobilized counter-
parts. The use of thioglycosides as glycosyl donors for auto-
mated solid-phase synthesis has also been reported,[6] and a
recent Glyconeer procedure comprises the treatment of a sup-
ported acceptor with 2 x 5.0 equiv thioglycoside donor in the
presence of 2 x 5.5 equiv of NIS and 2 x 0.2 equiv of TfOH for 2
x 30 min.[7] With the critical issue of making common glycosyl
donors commercially available, the use of thioglycosides is
attractive due to their superior stability, but a fairly low reac-
tivity profile and the requirement for stoichiometric promot-
ers leaves ample room for improvement.
As a part of the program to develop new methods and strate-
gies for chemical glycosylation, we reported a regenerative
glycosylation reaction concept.[8] In accordance with this con-
cept, 3,3-difluoroxindole (HOFox) reacts with a stable precur-
sor to form a highly reactive OFox imidate (Scheme 1).[9] The
latter will then react with the glycosyl acceptor while regener-
ating HOFox aglycone. The released HOFox will mediate the
next catalytic cycle to obtain a new OFox donor, etc. In our
original study, we reacted S-ethyl glycoside with Br2 to form
glycosyl bromide. The latter reacts very slowly in the presence
of Ag2O, but in the presence of HOFox gives reasonable reac-
tion rates (2-3 h) with only 10 mol % of HOFox and a catalytic
Lewis acid (BF3-Et2O or TMSOTf). The concentration of reac-
tive glycosyl donor can be controlled by the amount of HOFox
added. This regenerative concept differs from the two-step
activation[10] and Huang’s preactivation strategy[11] in the way
that the reactive donor is generated in only small amounts.
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10.1002/chem.202003479
Chemistry - A European Journal
This approach was successfully applied in oligosaccharide syn-
thesis.[12] However, the two-step conversion, a stoichiometric
generation of the glycosyl bromide from the thioglycoside
precursor, followed by the heterogeneous activation of the
bromide intermediate in the presence of Ag2O, remained a
drawback of this approach. Ultimately, this hampers its appli-
cation in polymer supported or flow-through approaches. Re-
ported herein is a direct conversion of thioglycosides via the
regenerative approach that bypasses the intermediacy of gly-
cosyl bromides and eliminates the need for heavy metal-based
promoters.
time and yield was observed (entry 3). Increasing the amount
of HOFox to 0.20 equiv decreased the reaction time to 3.5 h,
and disaccharide 3 was obtained in 92% yield (entry 4). Realiz-
ing the effect of catalyst loading, we increased the amount of
HOFox to 0.30 and 0.50 equiv. These adjustments led to a de-
creased reaction time to 3 and 1.5 h (entries 5 and 6). Based on
these results, we chose to perform all subsequent experimen-
tation using 20 mol % of HOFox. In our opinion, these reac-
tion conditions offer the best balance between the amount of
catalyst, reaction times, and product yields. While TMSOTf
(or TfOH) is not required in these reactions, adding as little as
0.05 equiv TMSOTf reduces the reaction time and expedites
both the generation of the OFox imidate and its activation.
Thus, glycosylation in the presence of HOFox and 0.05 equiv
of TMSOTf produced disaccharide 3 in 15 min in 72% yield
(entry 7).
Scheme 1. Regenerative glycosylation approach.
Table 1. NIS/HOFox mediated glycosidations of donor 1 with
acceptor 2.
When activated with N-iodosuccinimide (NIS) only, many
thioglycosides react slowly or do not react at all, even in the
presence of an excess of NIS (2-3 equiv). This is typically im-
proved by using strong Lewis (TMSOTf) or protic acids
(TfOH) as co-promoters. Our preliminary experimentation
showed that some reactive thioglycosides can be converted to
OFox imidates using 1 equiv NIS and catalytic HOFox without
the acidic additives. The formation of OFox intermediates can
easily be monitored by TLC and NMR (see the SI for details).
Once formed, the OFox imidates rapidly react with the accep-
tor while liberating HOFox aglycone. In our opinion, the ob-
servation that 1 equiv NIS and catalytic HOFox can activate
thioglycosides in a regenerative fashion offers a promising
venue for developing a new glycosylation reaction. This dis-
covery also hints on feasibility of the activation of thioglyco-
sides under neutral conditions offering a broader functional
and protecting group compatibility.
HOFox
(equiv)
TMSOTf
(equiv)
Entry
Time
Yield of 3
1
--
--
--
--
--
--
3.5-12 h
6 h
6 h
3.5 h
3 h
1.5 h
15 min
74%
91%
90%
92%
90%
91%
72%
2
3
4
5
6
7
0.05
0.10
0.20
0.30
0.50
0.20
--
0.05
After optimization of the basic reaction conditions, we inves-
tigated glycosidation of glycosyl donor 1 with other glycosyl
acceptors that differ in their reactivity. The key results of this
study are summarized in Table 2. Glycosidations of donor 1
were first conducted with hindered secondary glycosyl accep-
tors 4, 6 and 8.[14] The respective disaccharides 5, 7 and 9[15]
were obtained within 3-4 h in yields of 42-71% (entries 1-3).
Glycosidation with partially benzoylated deactivated primary
6-OH acceptor 10[16] was also performed. This reaction gave
the corresponding disaccharide 11 in 58% yield within 4 h (en-
try 4). The reactive 6-OH galactosyl acceptor 12 was glycosyl-
ated, and disaccharide 13[17] was obtained in 76% yield (entry
5). Glycosylation of reactive aliphatic acceptors such as prima-
ry acceptor n-butanol 14 and more sterically hindered tertiary
acceptor 1-adamantanol 16 proceeded smoothly and produced
glycosides 15 and 17 nearly quantitatively (99%) in 30 min and
45 min (entries 6 and 7).
Therefore, we endeavored to optimize these reaction condi-
tions. We began these studies by investigating a highly reac-
tive thiogalactoside donor 1[13] in reactions with partially ben-
zylated primary glycosyl acceptor 2.[14] These results are sum-
marized in Table 1. These reactive substrates were able react in
the presence of only 1.0 equiv NIS, even in the absence of the
acidic additive, producing disaccharide 3[15] in 74% yield (entry
1). However, this reaction slowed down after 3.5 h, and was
incomplete even after 12 h indicating that these reaction con-
ditions are insufficient for effective glycosylation. When glyco-
sidation of thiogalactoside 1 with glycosyl acceptor 2 was re-
peated in the presence of NIS (1.0 equiv) and catalytic HOFox
aglycone (0.05 equiv) the reaction was smoothly driven to
completion in 6 h, and disaccharide 3 was obtained in an ex-
cellent yield of 91% (entry 2). Upon increasing the amount of
HOFox to 0.10 equiv, no significant change in the reaction
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10.1002/chem.202003479
Chemistry - A European Journal
Table 2. HOFox-catalyzed glycosidation of thiogalactoside
donor 1 with various glycosyl acceptors.
we first proceeded with glycosidation of per-benzylated thio-
galactoside donor 18[13] with acceptor 2 under standard reac-
tion conditions. This glycosylation afforded disaccharide 19[18]
in a good yield of 80% in 2 h, albeit with no stereoselectivity
(α/β = 1.2/1, entry 1, Table 3). Glycosylation of the secondary 3-
OH glycosyl acceptor 6 produced the corresponding disaccha-
ride 20[15] in a lower yield of 58% in 4 h (α/β = 1.2/1, entry 2).
Glycosidations of less reactive mannosyl donor 21[19] under
identical reaction conditions were slower. Thus, glycosylation
of 6-OH acceptor 2 produced α-linked disaccharide 22[20] in
50% yield after 12 h (entry 3). Glycosylation of n-butanol 14
afforded α-linked glycoside 23[21] in 51% yield in 10 h (entry 4).
Some of the glycosylation reactions were repeated with in-
creased amount of promoter system (NIS/HOFox), however
no significant improvement was noticed (see the SI for further
details). We then moved on to investigate glycosyl donors
with the D-gluco configuration. Glycosylation of glucosyl do-
nor 24[22] proceeded smoothly and afforded disaccharide 25[18]
in 87% in 4 h (entry 5). Glycosidation of benzylated glucosyl
donor 26[23] with acceptor 2 produced disaccharide 27[18] in
67% yield in 6 h (α/β = 2.0/1, entry 6).
Entry
1
ROH
Time
3 h
Products, Yield
4
5, 53%
BnO
BnO
OBn
OBn
O
O
BnO
O
2
3
4 h
3 h
BzO
BnO
OMe
6
8
After investigating the activation of various ethylthio glyco-
sides, we were curious to see whether other thioglycoside leav-
ing groups would act accordingly. For this study we selected
the S-tolyl (STol) leaving group because STol glycosides are
better suited for large-scale preparations,[24] can be readily
pre-activated,[25] and a comprehensive reactivity database
compiled by Wong specifically for STol glycosides is availa-
ble.[26] Glycosidation of tolylthio glucosyl donor 28[27] with
acceptor 2 proceeded smoothly and afforded disaccharide 27
in an excellent yield of 97% in 6 h (α/β = 1.1/1, entry 7). Glyco-
sidation of glucosyl donor 28 with galactosyl acceptor 12 was
somewhat slower, which was reflected in a lower yield (72%)
of disaccharide 29[28] obtained in 8 h (α/β = 1.0/1, entry 8). Gly-
cosylation with less reactive secondary 4-OH acceptor 8 pro-
ceeded even slower, and the corresponding disaccharide 30[29]
was obtained in 40% yield in 10 h (α/β = 1/1.1, entry 9). Glyco-
sylation of donor 28 with 1-adamantanol 16 gave the corre-
sponding glycoside 31[30] in an excellent yield of 91% yield in 4
h (α/β = 1.0/1, entry 10).
7, 71%
9, 42%
4
4 h
10
11, 58%
5
4 h
In further expansion of the approach, we investigated confor-
mationally super-armed donor 32[31] equipped with silyl pro-
tecting groups. Glycosidation of glucosyl donor 32 with accep-
tor 2 smoothly afforded the desired disaccharide 33[31] in an
excellent yield of 93% with predominant α-stereoselectivity
(α/β = 5.0/1, entry 11). No loss of TBS protecting groups, which
was noted as a major side reaction in our previous unrelated
study,[31] was noted in NIS/HOFox-promoted reactions. Glyco-
sidation of relatively unreactive 2-phthalimido-protected ami-
nosugar donor 34[32] with electronically deactivated glycosyl
acceptor 10 was also proven feasible. However, for the best
results, 2.0 equiv NIS was necessary, and even then, the reac-
tion required 24 h and disaccharide 35 was obtained in 40%
yield. To demonstrate the efficacy of the new reaction, we at-
tempted selective activation of the SEt leaving group in donor
1 over the S-thiazolinyl (STaz) anomeric group of acceptor 36.
To obtain a better outcome, we used increased amounts of the
promoters, 1,2 equiv NIS and 0.5 equiv HOFox. Under these
12
14
13, 76%
15, 99%
30
min
6
7
45
min
16
17, 99%
After constructing different types of β-galactosidic linkages,
we moved on to expand this acid-free glycosylation method to
glycosidations of thioglycosides of other sugar series. For that,
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10.1002/chem.202003479
Chemistry - A European Journal
reaction conditions, disaccharide 37 equipped with the ano-
meric STaz leaving group was obtained in 65% in 16 h (entry
13).
Table 3. Expanding the scope of HOFox-catalyzed
glycosylation with various donors and acceptors of other
sugar series.
8
28
12
29, 8 h, 72%, 1.0/1.0
30, 10 h, 40%, 1.0/1.1
9
28
28
8
Product, time
Yield, ratio α/β
Entry
Donor
ROH
10
16
1
2
31, 4 h, 91%, 1.0/1.0
33, 6 h, 93%, 5.0/1.0
35, 24 h, 40%, β only
18
18
19, 2 h, 80%, 1.2/1.0
20, 4 h, 58%, 1.2/1.0
11
2
2
3
6
2
32
12a
10
21
21
34
22, 12 h, 50%, α only
23, 10 h, 51%, α only
13b
1
4
5
14
36
37, 16 h, 65%, β only
NIS 1.2 equiv, HOFox 0.5 equiv.
a
b
NIS 2.0 equiv;
In conclusion, presented herein the discovery of the direct
activation of thioglycosides in the regenerative fashion. We
demonstrated that in most cases, only 1 equiv NIS and catalyt-
ic HOFox (0.2 equiv) are needed to promote glycosidation of
various thioglycosides. One advantage of this approach is that
it does not require a strong acid as a co-promoter, which al-
lows to maintain neutral reaction conditions during glycosyla-
tion. One potential disadvantage of this approach is that it is
much less efficient with poorly reactive substrates, glycosyla-
tion of which would require the use of additional quantities of
HOFox and/or Lewis acid additives. We believe that this ap-
proach would be particularly advantageous with the HPLC
pump-based reagent delivery automated set-up that is being
developed in our labs.
2
24
25, 4 h, 87%, β only
6
7
2
2
26
28
27, 6 h, 67%, 2.0/1.0
27, 6 h, 97%, 1.1/1.0
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A 1 M solution of BH3 in THF (3.0 mL) was added dropwise to
a solution of 39 (290 mg, 0.51 mmol) in CH2Cl2 (9 mL). The
resulting solution was cooled to 0 °C, TMSOTf (4.6 µL, 0.025
mmol) was added dropwise, and the resulting mixture was
stirred for 1 h at 0 °C. The reaction mixture was then allowed
to warm to rt and stirred for additional 1 h. After that, the re-
action was quenched with NaHCO3 (~2 mL), diluted with
CH2Cl2 (100 mL), and washed with sat. aq. NaHCO3 (50 mL)
and water (2 × 50 mL). The organic phase was separated, dried
over MgSO4, and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel
(ethyl acetate-hexane gradient elution) to afford the title
compound as a white amorphous solid in 53% yield (150 mg,
0.27 mmol). Analytical data for 36: Rf = 0.30 (ethyl ace-
EXPERIMENTAL SECTION
General Experimental. The reactions were performed using
commercial reagents, and the ACS grade solvents used for
reactions were purified and dried in accordance with standard
procedures. Column chromatography was performed on silica
gel 60 (70−230 mesh); reactions were monitored by TLC on
Kieselgel 60 F254. The compounds were detected by examina-
tion under UV light and by charring with 10% sulfuric acid in
methanol. Solvents were removed under reduced pressure at
<40 °C. CH2Cl2 was distilled from CaH2 directly prior to the
application. Molecular sieves (3 Å), used for reactions, were
crushed, and activated in vacuo at 390 °C for 8 h in the first
instance and then for 2−3 h at 390 °C directly prior to applica-
tion. Optical rotations were measured at “JASCO P-2000” po-
20
1
tate/hexane, 2/3, v/v); [α]D +117.8 (c = 1.0, CHCl3); H NMR
(300 MHz, CDCl3): δ 3.22-3.26 (m, 2H, CH2N), 3.61-3.70 (m, 2H,
H-5, 6a), 3.81 (m, 1H, H-6b), 3.89 (dd, 1H, J3,4 = 2.5 Hz, H-3),
3.97 (d, 1H, J4,5 = 2.0 Hz, H-4), 4.16-4.34 (m, 2H, CH2S), 4.59-
1
larimeter. H NMR spectra were recorded at 300 MHz, 13C
1
NMR spectra were recorded at 75 MHz. The H NMR chemical
shifts are referenced to tetramethylsilane (TMS, δC = 0 ppm)
for 1H NMR spectra for solutions in CDCl3. The 13C NMR chem-
ical shifts are referenced to the central signal of CDCl3 (δC =
77.00 ppm) for solutions in CDCl3. HRMS analysis was per-
formed using Agilent 6230 ESI TOF LC/MS mass spectrome-
ter.
2
4.72 (m, 3H, CH2Ph, CHPh), 5.02 (d, 1H, J = 11.7 Hz, CHPh),
5.30 (s, 1H, OH), 5.76 (dd, 1H, J2,3 = 9.6 Hz, H-2), 6.11 (d, 1H, J1,2
= 9.2 Hz, H-1), 7.21-7.26 (m, 4H, aromatic), 7.37-7.59 (m, 9H,
aromatic), 7.99 (d, 2H, J = 7.7 Hz, aromatic) ppm; 13C NMR (75
MHz, CDCl3): δ 28.5, 51.4, 61.8, 69.5, 72.5 (×2), 74.4, 77.1, 77.3,
80.1, 83.1, 127.7 (×3), 127.9, 128.1, 128.4 (×4), 128.5 (×2), 129.1,
129.9 (×3), 133.4, 137.2, 137.9, 166.0 ppm; HR-FAB MS [M+Na]+
calcd for C30H31NO6S2Na 588.1490, found 588.1501.
Synthesis of Reagents and Building Blocks
3,3-Difluoroxindole (HOFox) was obtained from Isatin and
DAST as previously described, and its analytical data were in
accordance with that previously reported.[8, 33]
Synthesis of Glycosides
2-Thiazolinyl
2-O-benzoyl-3,4-di-O-benzyl-1-thio-ꞵ-D-
Typical Glycosylation Procedure. A mixture of thioglycoside
precursor (30.0 mg, 0.03−0.05 mmol), glycosyl acceptor
(0.02−0.04 mmol), and freshly activated molecular sieves (3 Å,
90 mg) in dry CH2Cl2 (1.0 mL) was stirred under argon for 1 h
at rt. After that, N-iodosuccinimide (NIS, 0.03−0.05 mmol)
and HOFox (0.005−0.02 mmol) were added and the reaction
mixture was stirred for the time specified in Tables 1-3. The
solids were filtered off through a pad of Celite and rinsed suc-
cessively with CH2Cl2. The combined filtrate (~20 mL) was
washed with sat. aq. Na2S2O3 (5 mL), sat. aq. NaHCO3 (5 mL)
and brine (2 × 5 mL). The organic phase was separated, dried
with MgSO4, and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel
(ethyl acetate–hexanes gradient elution) to afford a glycoside
product in yields listed in Tables 1-3 and below. Anomeric ra-
tios (if applicable) were determined by comparison of the in-
tegral intensities of relevant signals in 1H NMR spectra.
galactopyranoside (36). A solution of ethyl 2-O-benzoyl-3-O-
benzyl-4,6-O-benzylidene-1-thio-β-D-galactopyranoside (38,[34]
590 mg, 1.16 mmol) and activated molecular sieves 3Å (885
mg) in dry CH2Cl2 (20 mL) was stirred under argon for 1 h at
rt. The mixture was cooled to 0 °C, Br2 (0.077 mL, 1.51 mmol)
was added, and the resulting mixture was kept for 15 min at 0
°C. After that, the volatiles were removed under reduced pres-
sure at rt. The crude residue was dissolved in dry MeCN (10
mL), NaSTaz[35] (650 mg, 4.6 mmol) was added, and the result-
ing mixture was stirred under argon for 2 h at rt. After that,
the solid was filtered-off and rinsed successively with toluene.
The combined filtrate (~35 mL) was washed with 1% aq. NaOH
(~15 mL) and water (3 x 15 mL). The organic phase was sepa-
rated, dried over MgSO4, and concentrated under reduced
pressure. The residue was purified by column chromatography
on silica gel (ethyl acetate-hexane gradient elution) to afford
2-thiazolinyl
2-O-benzoyl-3-O-benzyl-4,6-O-benzylidene-1-
Methyl
6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
thio-β-D-galactopyranoside (39) as a clear film in 51% yield
galactopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(3) was obtained from thioglycoside 1[13] and glycosyl acceptor
2[14] by the general glycosylation method as a clear film in 92%
yield. Analytical data for 3 was in accordance with that report-
ed previously.[15]
over two steps (330 mg). Analytical data for 39: Rf = 0.50 (ethyl
acetate/hexane, 2/3, v/v); [α]D +6.9 (c = 1.0, CHCl3); 1H NMR
20
(300 MHz, CDCl3): δ 3.22-3.29 (m, 2H, CH2N), 3.63 (s, 1H, H-5),
3.93 (dd, 1H, J3,4 = 3.3 Hz, H-3), 4.06 (d, 1H, J6a,6b = 12.2 Hz, 6a),
4.28-4.47 (m, 4H, H-4, 6b, CH2S), 4.68 (dd, 2H, CH2Ph), 5.54
Methyl
2-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
(s, 1H, CHPh), 5.75 (dd, 1H, J2,3 = 9.5 Hz, H-2), 6.18 (d, 1H, J1,2
=
galactopyranosyl)-3,4,6-tri-O-benzyl-α-D-glucopyranoside
(5) was obtained from thioglycoside 1 and glycosyl acceptor
4[14] by the general glycosylation method as a clear film in 53%
yield. Analytical data for 5: Rf = 0.60 (ethyl acetate/hexane,
2/3, v/v); [α]D +62.9 (c = 1.0, CHCl3); H NMR (300 MHz,
CDCl3): δ 3.34 (s, 3H, OCH3), 3.55-3.72 (m, 9H, H-3, 5, 6a, 6b,
2ʹ, 4ʹ, 5ʹ, 6aʹ, 6bʹ), 3.87 (dd, 1H, J3ʹ,4ʹ = 9.2 Hz, H-3ʹ), 4.01 (d, 1H,
9.3 Hz, H-1), 7.24-7.26 (m, 4H, aromatic), 7.40-7.61 (m, 9H,
aromatic), 7.99 (d, 2H, J = 7.2 Hz, aromatic) ppm; 13C NMR (75
MHz, CDCl3): δ, 28.6, 51.3, 68.4, 68.5 (×2), 69.0, 71.4, 73.0, 77.2,
82.8, 101.1, 126.2 (×2), 127.7 (×2), 127.9, 128.3 (×2), 128.4 (×5),
129.2, 130.0 (×2), 133.4, 137.4, 137.5, 165.9 ppm; HR-FAB MS
[M+Na]+ calcd for C30H29NO6S2Na 586.1334, found 586.1339.
21
1
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10.1002/chem.202003479
Chemistry - A European Journal
2
J4,5 = 2.7 Hz, H-4), 4.32 (d, 1H, J = 10.9 Hz, CHPh), 4.40-4.47
(m, 5H, 5 x CHPh), 4.57-4.63 (m, 5H, 5 x CHPh), 4.81 (d, 1H, J1,2
1.49 (m, 4H, 2 x CH2), 3.43 (m, 1H, OCHa), 3.62-3.73 (m, 4H, H-
3, 5, 6a, 6b), 3.85 (m, 1H, OCHb), 4.01 (d, 1H, J4,5 = 2.7 Hz, H-4),
4.41-4.46 (m, 4H, J1,2 = 9.1 Hz, H-1, 3 x CHPh), 4.65 (dd, 2H,
2
= 7.8 Hz, H-1), 4.91 (d, 1H, J1ʹ,2ʹ = 3.0 Hz, H-1ʹ), 4.98 (d, 1H, J =
2
11.8 Hz, CHPh), 5.75 (dd, 1H, J2,3 = 9.1 Hz, H-2), 6.94-6.99 (m,
4H, aromatic), 7.06-7.45 (m, 29H, aromatic), 7.81 (d, 2H, J =
7.8 Hz, aromatic) ppm; 13C NMR (75 MHz, CDCl3): δ, 55.2,
68.4, 69.6, 71.6, 71.7, 72.3, 73.4, 73.5, 74.4, 74.8, 75.0, 76.5, 80.1,
80.4, 81.0, 99.5, 102.5, 126.9, 127.1 (×2), 127.4, 127.6 (×6), 127.7
(×4), 127.9 (×6), 128.1 (×5), 128.2 (×5), 128.3 (×2), 128.5 (×2),
129.8 (×3), 132.6, 137.3, 137.6, 137.9, 138.1, 138.4, 138.7, 165.1 ppm;
HR-FAB MS [M+Na]+ calcd for C62H64O12Na 1023.4295, found
1023.4312.
CH2Ph), 4.99 (d, 1H, J = 11.7 Hz, CHPh), 5.63 (dd, 1H, H-2),
7.14-7.60 (m, 18H, aromatic), 8.03 (d, 2H, J = 7.5 Hz, aromatic)
ppm; 13C NMR (75 MHz, CDCl3): δ 13.5, 18.8, 29.6, 31.3, 68.6,
69.3, 71.5, 71.9, 72.3, 73.5, 74.3, 79.8, 101.5, 127.4, 127.5, 127.6
(×2), 127.8, 127.9 (×2), 128.1 (×2), 128.2 (×3), 128.3 (×2), 128.4
(×2), 129.7 (×2), 130.3, 132.8 (×2), 137.6, 137.8, 138.4, 165.3 ppm;
HR-FAB MS [M+Na]+ calcd for C38H42O7Na 633.2828, found
633.2870.
1-Adamantyl
2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
Methyl
3-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
galactopyranoside (17) was obtained from thioglycoside 1
and 1-adamantanol 16 by the general glycosylation method as
a white amorphous solid in 99% yield. Analytical data for 17: Rf
galactopyranosyl)-2,4,6-tri-O-benzyl-α-D-glucopyranoside
(7) was obtained from thioglycoside 1 and glycosyl acceptor
6[14] by the general glycosylation method as a clear film in 71%
yield. Analytical data for 7 was in accordance with that report-
ed previously.[15]
21
= 0.70 (ethyl acetate/hexane, 2/3, v/v); [α]D +24.7 (c = 1.0,
CHCl3); 1H NMR (300 MHz, CDCl3): δ 1.45-1.78 (m, 12H, Ada),
2.02 (s, 3H, Ada), 3.56-3.69 (m, 4H, H-3, 5, 6a, 6b), 3.98 (d, 1H,
J4,5 = 2.6 Hz, H-4), 4.40-4.52 (m, 3H, 3 x CHPh), 4.62 (dd, 2H,
Methyl
4-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
2
CH2Ph), 4.75 (d, 1H, J1,2 = 7.9 Hz, H-1), 4.98 (d, 1H, J = 11.7 Hz,
galactopyranosyl)-2,4,6-tri-O-benzyl-α-D-glucopyranoside
(9) was obtained from thioglycoside 1 and glycosyl acceptor
8[14] by the general glycosylation method as a clear film in 42%
yield. Analytical data for 9 was in accordance with that report-
ed previously.[15]
CHPh) 5.58 (dd, 1H, J2,3 = 9.8 Hz, H-2), 7.11-7.60 (m, 18H, aro-
matic), 8.01 (d, 2H, J = 7.7 Hz, aromatic) ppm; 13C NMR (75
MHz, CDCl3): δ 30.7 (×5), 36.3 (×3), 42.4 (×4), 69.3, 71.6, 72.3,
73.6, 73.7, 74.5, 75.0, 80.3, 94.5, 127.7 (×2), 127.8 (×2), 127.9,
128.0 (×2), 128.3 (×2), 128.4 (×3), 128.6 (×2), 129.9 (×3), 130.6,
132.9, 137.9, 138.1, 138.7, 165.3 ppm; HR-FAB MS [M+Na]+ calcd
for C44H48O7Na 711.3298, found 711.3307.
Methyl
6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
galactopyranosyl)-2,3,4-tri-O-benzoyl-α-D-
glucopyranoside (11) was obtained from thioglycoside 1 and
glycosyl acceptor 10[16] by the general glycosylation method as
a white amorphous solid in 58% yield. Analytical data for 11: Rf
Methyl
6-O-(2,3,4,6-tetra-O-benzyl-α/β-D-
galactopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(19) was obtained from thioglycoside 18[13] and glycosyl accep-
tor 2 by the general glycosylation method as a clear film in
80% yield (α/β = 1.2/1). Analytical data for 19 was in accord-
ance with that reported previously.[18]
21
= 0.50 (ethyl acetate/hexane, 2/3, v/v); []D +28.5 (c = 1,
CHCl3); 1H NMR (300 MHz, CDCl3): δ 3.00.(s, 3H, OCH3), 3.53-
3.65 (m, 5H, H-3, 5, 6a, 6aʹ, 6b), 3.98-4.04 (m, 2H, J4,5 = 2.2 Hz,
J6aʹ,6bʹ = 11.1 Hz, H-4, 6bʹ), 4.16 (dd, 1H, J5ʹ,6aʹ = 8.7 Hz, J5ʹ,6bʹ = 9.7
Methyl
3-O-(2,3,4,6-tetra-O-benzyl-α/β-D-
Hz, H-5ʹ), 4.32-4.61 (m, 6H, H-1, 5 x CHPh), 4.80 (d, 1H, J1ʹ,2ʹ
=
2
galactopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(20) was obtained from thioglycoside 18 and glycosyl acceptor
6 by the general glycosylation method as a clear film in 58%
yield (α/β = 1.2/1). Analytical data for 20 was in accordance
with that reported previously.[15]
3.6 Hz, H-1ʹ), 4.95 (d, 1H, J = 11.6 Hz, CHPh), 5.06 (dd, 1H, J2ʹ,3ʹ
= 10.2 Hz, H-2ʹ), 5.27 (dd, 1H, J4ʹ,5ʹ = 9.7 Hz, H-4ʹ), 5.66 (dd, 1H,
J2,3 = 8.7 Hz, H-2), 6.03 (dd, 1H, J3ʹ,4ʹ = 9.8 Hz, H-3ʹ), 7.17-7.59
(m, 27H, aromatic), 7.78 (d, 2H, J = 7.8 Hz, aromatic) 7.85 (d,
2H, J = 7.9 Hz, aromatic), 7.90 (d, 2H, J = 7.7 Hz, aromatic),
8.01 (d, 2H, J = 7.8 Hz, aromatic) ppm; 13C NMR (75 MHz,
CDCl3): δ 30.9, 54.8, 68.2, 68.5, 69.5, 70.4, 71.6, 71.7, 72.0, 72.2,
73.5, 74.4, 76.5, 79.6, 96.1, 101.9, 127.5, 127.6 (×4), 127.8 (×2),
127.9 (×3), 128.1 (×4), 128.2 (×4), 128.3 (×6), 128.4 (×2), 128.7,
129.0, 129.2, 129.6 (×2), 129.8 (×4), 130.2, 132.9, 133.2, 133.3, 137.6,
137.7, 138.3, 165.3, 165.4, 165.6, 165.7 ppm; HR-FAB MS
[M+Na]+calcd for C62H58O15Na 1065.3673, found 1065.3691.
Methyl
6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-α-D-
mannopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(22) was obtained from thioglycoside 21[19] and glycosyl accep-
tor 2 by the general glycosylation method as a colorless syrup
in 50% yield. Analytical data for 22 was in accordance with
that reported previously.[20]
n-Butyl
2-O-benzoyl-3,4,6-tri-O-benzyl-α-D-
6-O-(2-O-Benzoyl-3,4,6-tri-O-benzyl-β-D-
mannopyranoside (23) was obtained from thioglycoside 21
and n-butanol 14 by the general glycosylation method as a
colorless syrup in 51% yield. Analytical data for 23 was in ac-
cordance with that reported previously.[21]
galactopyranosyl)-1,2:3,4-di-O-isopropylidene-α-D-
galactopyranose (13) was obtained from thioglycoside 1 and
glycosyl acceptor 12 by the general glycosylation method as a
clear film in 76% yield. Analytical data for 12 was in accord-
ance with that reported previously.[17]
Methyl
6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
glucopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
(25) was obtained from thioglycoside 24[22] and glycosyl accep-
tor 2 by the general glycosylation method as a clear film in
87% yield. Analytical data for 25 was in accordance with that
reported previously.[18]
n-Butyl
2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-
galactopyranoside (15) was obtained from thioglycoside 1
and n-butanol 14 by the general glycosylation method as a
white amorphous solid in 99% yield. Analytical data for 15: Rf
21
= 0.70 (ethyl acetate/hexane, 2/3, v/v); [α]D +3.6 (c = 1.0,
Methyl
6-O-(2,3,4,6-tetra-O-benzyl-α/β-D-
CHCl3); 1H NMR (300 MHz, CDCl3): δ 0.69 (t, 3H, CH3), 1.18-
glucopyranosyl)-2,3,4-tri-O-benzyl-α-D-glucopyranoside
This article is protected by copyright. All rights reserved.

10.1002/chem.202003479
Chemistry - A European Journal
2
(27) was obtained from thioglycoside 26[36] and glycosyl accep-
tor 2 by the general glycosylation method as a clear film in
97% yield (α/β = 1.1/1). Analytical data for 27 was in accordance
with that reported previously.[18]
4ʹ), 3.99-4.03 (m, 3H, H-4, 6bʹ, SCHa), 4.18 (d, 1H, J = 12.4 Hz,
CHPh), 4.26 (m, 1H, SCHb), 4.34 (d, 1H, J = 12.1 Hz, CHPh),
2
4.42 (s, 2H, CH2Ph), 4.56 (d, 1H, J1,2 = 7.9 Hz, H-1), 4.61-6.71 (m,
4H, 2x CH2Ph), 4.84 (d, 1H, 2J = 11.2 Hz, CHPh), 5.01 (d, 1H, 2J =
11.9 Hz, CHPh), 5.57-5.68 (m, 2H, J2ʹ,3ʹ = 9.6 Hz, J2,3 = 9.6 Hz, H-
2, 2ʹ), 5.95 (d, 1H, J1ʹ,2ʹ = 9.3 Hz, H-1ʹ), 7.01-7.57 (m, 31H, aro-
matic), 7.91 (d, 2H, J = 7.5 Hz, aromatic), 8.04 (d, 2H, J = 7.5
Hz, aromatic) ppm; 13C NMR (75 MHz, CDCl3): δ 29.7 (×2),
30.9, 71.5 (×2), 71.6, 71.7, 71.8, 72.1, 72.4, 73.5, 73.6, 74.6, 74.8,
75.3, 79.6, 79.8, 83.0, 101.1, 113.8, 127.4 (×4), 127.5 (×2), 127.6,
127.7 (×3), 127.9 (×3), 128.1 (×6), 128.2 (×5), 128.3, 128.4 (×2),
128.5 (×2), 129.2, 129.8 (×2), 129.9 (×4), 133.2, 137.4, 137.5, 137.7,
138.4 (×2), 165.2, 165.9 ppm; HR-FAB MS [M+Na]+ calcd for
C64H63NO12S2Na 1124.3684, found 1124.3717.
6-O-(2,3,4,6-Tetra-O-benzyl-α/β-D-glucopyranosyl)-1,2:3,4-di-O-
isopropylidene-α-D-galactopyranose (29) was obtained from
thioglycoside 28[27] and glycosyl acceptor 12 by the general
glycosylation method as a clear film in 72% yield (α/β = 1.0/1).
Analytical data for 29 was in accordance with that reported
previously. [28]
Methyl
4-O-(2,3,4,6-tetra-O-benzyl-α/β-D-
glucopyranosyl)-2,4,6-tri-O-benzyl-α-D-glucopyranoside
(30) was obtained from thioglycoside 28 and glycosyl acceptor
8 by the general glycosylation method as a clear film in 40%
yield (α/β = 1/1.1). Analytical data for 30 was in accordance
with that reported previously.[29]
ASSOCIATED CONTENT
Supporting Information
1-Adamantyl
2,3,4,6-tetra-O-benzyl-α/β-D-
glucopyranoside (31) was obtained from thioglycoside 28 and
1-adamantanol 16 by the general glycosylation method as a
white amorphous solid in 91% yield (α/β = 1.0/1). Analytical
data for 31 was in accordance with that reported previously.[30]
Additional experimental details and NMR spectra for all com-
pounds. This material is available free of charge via the Internet at
AUTHOR INFORMATION
Corresponding Author
*demchenkoa@umsl.edu (Word Style
“FA_Corresponding_Author_Footnote”). Give contact information
for the author(s) to whom correspondence should be addressed.
Methyl
6-O-(6-O-benzoyl-2-O-benzyl-3,4-di-O-tert-
butyldimethylsilyl-α/β-D-glucopyranosyl)-2,3,4-tri-O-
benzyl-α-D-glucopyranoside (33) was obtained from thio-
glycoside 32[31] and glycosyl acceptor 2 by the general glycosyl-
ation method as a colorless syrup in 93% yield (α/β = 5.0/1).
Analytical data for 33 was in accordance with that reported
previously.[31]
ACKNOWLEDGMENT
This work was supported by grants from the NIGMS (GM111835
and GM120673). SE is indebtful to the SACM for profiding her
with the graduate fellowship.
Methyl
6-O-(4,6-di-O-benzyl-2-deoxy-3-O-
fluorenylmethoxycarbonyl-2-phthalimido-β-D-
glucopyranosyl)-2,3,4-tri-O-benzoyl-α-D-glucopyranoside
(35) was obtained from thioglycoside 34[32] and glycosyl accep-
tor 10 by the general glycosylation method as a clear film in
40% yield. Analytical data for 35: Rf = 0.60 (ethyl ace-
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