Stereoselective α-glycosylation of C(6)-hydroxyl myo-inositols via nickel catalysis - Application to the synthesis of GPI anchor pseudo-oligosaccharides

Article abstract of DOI:10.1016/j.carres.2013.09.006

Glycosylphosphatidyl inositol (GPI) anchors play a key role in many eukaryotic biological pathways. Stereoselective synthesis of GPI anchor analogues have proven to be critical for probing the biosynthesis, structure, and biological properties of these co

Full text of DOI:10.1016/j.carres.2013.09.006

Accepted Manuscript
Note
Stereoselective α-glycosylation of C(6)-hydroxyl myo-inositols via nickel cat‐
alysis – application to the synthesis of GPI anchor pseudo-oligosaccharides
Matthew S. McConnell, Enoch A. Mensah, Hien M. Nguyen
PII:
S0008-6215(13)00357-1
DOI:
http://dx.doi.org/10.1016/j.carres.2013.09.006
CAR 6576
Reference:
To appear in:
Carbohydrate Research
Received Date:
Revised Date:
Accepted Date:
29 July 2013
6 September 2013
14 September 2013
Please cite this article as: McConnell, M.S., Mensah, E.A., Nguyen, H.M., Stereoselective α-glycosylation of C(6)-
hydroxyl myo-inositols via nickel catalysis – application to the synthesis of GPI anchor pseudo-oligosaccharides,
Carbohydrate Research (2013), doi: http://dx.doi.org/10.1016/j.carres.2013.09.006
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Stereoselective α-glycosylation of C(6)-hydroxyl myo-
inositols via nickel catalysis – application to the
synthesis of GPI anchor pseudo-oligosaccharides
Matthew S. McConnell, Enoch A. Mensah, and Hien M. Nguyen*
Department of Chemistry, University of Iowa, Iowa City, IA 52242
Email: hien-nguyen@uiowa.edu
Abstract
Glycosylphosphatidyl inositol (GPI) anchors play a key role in many eukaryotic biological pathways.
Stereoselective synthesis of GPI anchor analogues have proven to be critical for probing the
biosynthesis, structure, and biological properties of these compounds. Challenges that have emerged
from these efforts include the preparation of the selectively protected myo-inositol building blocks and
the stereoselective construction of glucosamine α−linked myo-inositol containing pseudodisaccharide
units. Herein, we describe the effectiveness of the cationic nickel(II) catalyst, Ni(4-F-PhCN)4(OTf)2, at
promoting selective formation of 1,2-cis-2-amino glycosidic bonds between the C(2)-N-substituted
benzylideneamino trihaloacetimidate donors and C(6)-hydroxyl myo-inositol acceptors. This catalytic
coupling process allows rapid access to pseudosaccharides of GPI anchors in good yields and with
excellent levels of α-selectivity (α:β = 10:1 – 20:1). In stark contrast, activation of trichloroacetimidate
.
donors containing the C(2)-N-substituted benzylidene group with TMSOTf and BF3 OEt2 provided the
desired pseudodisaccharides as a 1:1 mixture of α- and β-isomers.

Keywords:
• Pseudosaccharides
• 1,2-Cis-2-Amino Glycosidic Bonds
• Nickel Catalysis
• N-Substituted Benzylidene Groups
• Inositols
1. Introduction
The GPI anchor (1, Figure 1) is a glycophospholipid which is post-translationally tethered to a
protein for attachment to a cell membrane.1 Proteins containing GPI anchor are functionally diverse and
play a pivotal role in biochemical processes such as signal transduction, prion disease pathogenesis,
immune response, the pathobiology of trypanosomal parasites, and cancer metastasis.2 All GPI
structures share the basic core that includes a phosphoethanolamine linker, a tetrasaccharide attached to
the C(6)-position of myo-inositol, and phospholipid tail.3 The glycan core of the GPI anchor family can
be further modified with specific sugar, lipid, and phosphoethanolamine groups. While studies have
shown that the main function of the GPI anchor is to bind proteins to a cell surface, the relationship
between structural diversity and biological function is poorly understood.4 Synthetic analogues of the
GPI anchor could provide useful insight into this relationship.5
Despite remarkable advances in the syntheses of GPI anchors,6,7 their analogues,5 and other
bioactive compounds containing myo-inositol unit,8 there are several key challenges that remain. First
is the stereoselective construction of the 1,2-cis-2-amino glycosidic bond between the glucosamine unit
and myo-inositol moiety.6-8 Current approaches provide this type of pseudodisaccharide with modest to
excellent α-selectivity. Another challenge involves the synthesis of myo-inositol moiety with
differential protecting groups at C(6)-hydroxyl centers. Several approaches toward the synthesis of
C(6)-hydroxyl myo-inositols have been reported in an effort to generate GPI anchor.9 For GPI anchor

synthesis, the second challenge involves formation of the α-glycosidic linkages which connect the
mannose units without the use of C(2)-acyl neighboring group participation in the glycosyl donor unit.
This is essential, as the basic conditions employed to remove the acyl groups could potentially cleave
the ester bonds of the lipid chains attached to the myo-inositol.
Figure 1. Structure of GPI anchor
Our goal is to develop a reliable and operationally simple glycosylation procedure that provides
alternative approaches to a variety of pseudosaccharides of GPI anchors and their analogues. Herein, we
present a cationic nickel (II) catalyst, Ni(4-F-PhCN)4(OTf)2, that efficiently promotes the α-selective
pseudosaccharide formation from the C(2)-N-benzylideneamino trihaloacetimidate donors and C(6)-
hydroxyl myo-inositols.
2. Results and discussion
We previously reported a suitable model system to screen a number of C(2)-N-substituted
benzylidene D-glucosamine donors 2-5 with the sterically hindered inositol acceptor 611b (Figure 2a)
under cationic nickel conditions. The most promising substrate identified was the N-para-
fluorobenzylideneamino donor 4, which underwent glycosylation to provide the desired

pseudodisaccharide 9 in 72% yield and solely as the α-isomer. Here, we further investigate the ability of
Ni(4-F-PhCN)4(OTf)2 as the effective catalyst to promote the glycosylation of C(6)-hydroxyl inositol
acceptors 129a,9d (Figure 2b) with trihaloacetimidate donors 11. The purpose of the current studies is to
explore the reaction on inositol substrates that could be further functionalized so that the fatty acid and
phospholipid tail can be selectively installed at both the C(1)- and C(2)-position of the inositol unit of
pseudodisaccharides 13 (Figure 2b)
Figure 2. Previous work vs. Current work
Given our previous studies with nickel-catalyzed glycosylations,11 it was prudent to investigate
the electronic properties of the C(2)-N-substituted benzylidene group and the effects on yield and α-
selectivity in D-glucosamine trichloroacetimidate donors. Our studies have shown that electron-
withdrawing substituents on the benzylidene group increase the yield and α-selectivity of the coupling
products.11c To simplify our investigations, we initially tested the efficacy of the cationic nickel catalyst,
Ni(4-F-PhCN)4(OTf)2, in promoting the coupling of C(6)-hydroxyl perbenzylated myo-inositol 1412,13

(Table 1) with four different C(2)-benzylidene D-glucosamine trichloroacetimidate donors 15–18 at
varying donor/acceptor ratios. Overall, the desired pseudodisaccharides 19–22 were isolated in good
yield (65–79%) and with high α-selectivity (α:β = 10:1–15:1). The 2-trifluoromethyl-N-benzylidene 18
showed the highest reactivity and α-selectivity (entry 6), affording pseudodisaccharide 22 in 79% yield
as a 15:1 α:β ratio. The 2-fluoro-N-benzylidene substrate 17 (entry 5) showed similar α-selectivity
(α:β = 15:1) but with decreased yield (66%). While not ideal, the 4-substituted benzylidene donors 15
and 16 (entries 1 and 2) reacted with C(6)-hydroxyl myo-inositol acceptor 14 to provide the coupling
products 19 and 20 in good yield (72– 78%) and with high α-selectivity (α:β =11:1). Use of excess
donor 16 relative to acceptor 14 (entry 4) was shown to increase α-selectivity (11:1→13:1) but
decreased yield (72 → 65%). On the other hand, excess equivalents of donor 15 (entry 3) only led to a
decrease in both α-selectivity (11:1 → 10:1) and yield (78 → 67%).
Table 1. Studies with C(6)-hydroxyl perbenzylated myo-inositola
AcO
AcO
AcO
AcO
AcO
AcO
10 mol %
O
O
Ni(4-F-PhCN)4(OTf)2,
CH2Cl2, 25 oC, 3 h
BnO
OBn
N
N
O
CCl3
NH
OBn
O
OBn
BnO
BnO
OBn
X
X
HO
OBn
OBn
BnO
19 - 22
14
________________________________________________
c
yield (%)b
:
donor/acceptor
entry
donors
products
________________________________________________
1
2
3
4
5
6
1/1.3
1/1.3
1.3/1
1.3/1
1/1.3
1/1.3
19
20
19
20
72
78
67
65
66
79
11:1
11:1
10:1
13:1
15:1
15:1
15: X = 4-F
16: X = 4-CF3
15: X = 4-F
16: X = 4-CF3
17: X = 2-F
21
22
18: X = 2-CF3
a All reactions were run at 0.2 M with 10 mol% catalyst at 35 oC. b Isolated Yield. c 1H NMR ratio.
Since the 2-trifluoromethyl-benzylidene donor 18 (Table 1, entry 6) showed the highest α-
anomeric selectivity and yield, it seemed practical to use this glycosyl donor for further studies.
Unfortunately, the α-trichloroacetimidate of 18 is the minor product from the reaction of hemiacetal and

trichloroacetonitrile (α:β = 1:3). Since the β-isomer of 18 is unreactive under nickel conditions,11b we
looked into utilizing N-phenyl trifluoroacetimidate donors.14 We have established that a mixture of α-
and β-isomer of 2-substituted benzylidene N-phenyl trifluoroacetimidate donors effectively reacts with a
wide variety of glycosyl acceptors under our nickel conditions.11c Unfortunately, the glycosylation of
inositol 14 with N-phenyl trifluoroacetimidate 23 (Scheme 1) did not proceed, even at elevated
temperature, increased catalyst loading, and extended reaction times. We hypothesized that this may be
due to steric encumbrance surrounding the C(6)-hydroxyl group in perbenzylated myo-inositol 14.
Scheme 1. Attempted cupling with N-phenyl trifluoroacetimidate 23
Since the 4-trifluoromethyl benzylidene 16 gave the next highest α-selectivity (Table 1, entry 4),
this directing group was employed to examine the substrate scope of various donors reacting with other
myo-inositols 25 and 26 (Table 2). When the C(6)-hydroxyl tetrabenzylated myo-inositol 25 bearing a
C(1)-p-methoxybenzyl ether (Table 2, entry 1) was glycosylated with trichloroacetimidate 16, a similar
yield (71%) and α-selectivity (α:β = 10:1) was observed when compared with the coupling of C(6)-
hydroxyl perbenzylated inositol 14 with donor 16 (Table 1, entry 2). Given this result we infer that
inositol 25 would react in a similar manner as acceptor 14; both too sterically hindered to undergo
glycosylation with N-phenyl trifluoroacetimidate substrates. Gratifyingly, myo-inositol 26 (Table 2,
entry 2) showed an improvement in yield (71 → 79%) and α-selectivity (10:1 → 12:1) when coupled
with glycosyl donor 16. We hypothesize that this improvement may be due to a reduction in steric
crowding around the C(6)-hydroxyl group of myo-inositol resulting from the acetyl groups incorporated
at the C(1)- and C(2)-positions in inositol 26 in lieu of the C(1)-PMB ether and C(2)-benzyl ether in

inositol 25. With that in mind, we decided to attempt coupling of inositol 26 with a α/β-mixture of the
N-phenyl trifluoracetimidate donor 23 (entry 3). To our excitement, after 18 h of reaction time, the
desired pseudodisaccharide 29 was isolated in 72% yield and with α:β = 10:1.
Table 2. Substrate Scopea
AcO
AcO
AcO
AcO
O
O
RO
10 mol % Catalyst,
CH2Cl2, 25 - 35oC
R2O OBn
AcO
N
N
OBn
O
O
CCl3
NH
R1O
OBn
R2O
OBn
F3C
F3C
HO
R1O
OBn
OBn
27 - 30
16, 23, 24
25: R1 = PMB, R2 = Bn,
26: R1
2 = Ac
__________________________=_R___________________________________
c
yieldb
(%)
:
acceptors
catalyst
entry
donors
products
time
(h)
______________________________________________________________
AcO
O
AcO
10:1
Ni(4-F-PhCN)4(OTf)2
25
4
27
71
1
AcO
N
O
CCl3
NH
16
F3C
28
29
Ni(4-F-PhCN)4(OTf)2
Ni(4-F-PhCN)4(OTf)2
4
79
72
12:1
10:1
2
3
26
26
16
AcO
AcO
AcO
O
18
N
O
CF3
NPh
CF3
23
BF3. OEt2
TMSOTf
4
4
40
55
1:1
1:1
4
5
26
26
16
28
28
16
OAc
O
AcO
AcO
AcO
AcO
AcO
26
30
Ni(4-F-PhCN)4(OTf)2
4
40
11:1
O
6
O
N
O
CCl3
24
F3C
NH
a All reactions were run at 0.2 M with 10 mol% catalyst. All trichloroacetimidate donors were conducted at 25 oC, except for
N-phenyl trifluoroacetimidate 23 which was performed at 35 oC. b Isolated Yield. c 1H NMR ratio.

To evaluate the unique properties of the cationic nickel catalyst, Ni(4-F-PhCN)4(OTf)2, to
efficiently promote the α-selective glycosylation with myo-inositol acceptors, control experiments were
performed with traditional Lewis acids, BF3.OEt215 and TMSOTf16 (Table 2, entries 4 and 5). In these
reactions, the desired pseudodisaccharide 28 (entries 4 and 5) was obtained in much lower yield
(79→55%) and α-selectivity (12:1→1:1) when compared to the glycosylation performed with the nickel
catalyst (entry 2), Ni(4-F-PhCN)4(OTf)2. Pseudotrisaccharide 30 obtained in entry 6 highlights the
efficacy of the nickel-catalyzed glycosylation method. Accordingly, Ni(4-F-PhCN)4(OTf)2 was applied
to the more challenging mannose-α(1,4)-glucosamine disaccharide trichloroacetimidate 24, chosen for
its similar connectivity to that found in GPI anchor 1 (Figure 1). Although the glycosylation provided
the corresponding pseudotrisaccharide 30 in only moderate yield (40%), a high α-selectivity (11:1) was
still observed in the coupling process.
10 mol %
AcO
AcO
TESO
AcO
O
Ni(4-F-PhCN)4(OTf)2,
O
TESO
CH2Cl2, 25 - 35oC
AcO
AcO
OBn
N
N
O
CF3
NPh
O
OBn
AcO
OBn
OBn
AcO
CF3
HO
AcO
OBn
OBn
32
61% ( : = 11:1)
CF3
31
26
TBAF, AcOH/THF,
pH = 7
OBn
O
BnO
BnO
BnO
AcO
20 mol% TMSOTf,
CH2Cl2, 0 oC, 3 h
O
HO
AcO
AcO
AcO
O
N
AcO
OBn
N
O
OBn
BnO
O
OBn
AcO
OBn
OBn
AcO
O
BnO
O
OBn
BnO
OBn
AcO
33
(84%)
CF3
O
CCl3
NH
34
35
(56%)
CF3
Scheme 2. Another approach to GPI anchor pseudotrisaccharide
To validate the ability of the C(2)-N-substituted benzylidene to serve as effective protecting
group in oligosaccharide synthesis and to demonstrate the utility of our pseudodisaccharides as valuable
building blocks in GPI anchor synthesis, N-phenyl trifluoroacetimidate 31 (Scheme 2), with labile TES

protecting group at the C(4) position, was investigated in the glycosylation of C(6)-hydroxyl myo-
inositol 26. The coupling process proceeded smoothly, providing pseudodisaccharide 32 in 61% yield
and with 11:1 α:β selectivity. The TES group in 32 was subsequently removed using TBAF (Scheme 2)
to reveal the free C(4)-hydroxyl group of pseudodisaccharide 33. This acceptor 33 was then used in a
glycosylation with tetrabenzylated D-mannose trichloroacetimidate 34 in the presence of TMSOTf as a
catalyst to afford α-pseudotrisaccharide 35 exclusively in 47% yield over two steps, highlighting the
versatility of the N-substituted benzylidene protecting group under various coupling conditions. The
benzylidene group can be easily to removed in less than 5 min with HCl and acetone.11c
Overall, the results obtained in Table 2 and Scheme 2 demonstrate the efficacy of our nickel
catalyst, Ni(4-F-PhCN)4(OTf)2, to promote the high-yielding and α-selective coupling of a number of
C(6)-hydroxyl myo-inositols with monosaccharide and disaccharide trihaloacetimidate donors bearing
the C(2)-N-substituted benzylidene groups. To further explore the scope and limitation under nickel
catalysis, the coupling of inositol acceptor 36 bearing the C(1)-allyl and C(2)-PMB groups with both
donors 16 and 23 (Scheme 3) was examined. Unfortunately, inositol 36 did not perform well with Ni(4-
F-PhCN)4(OTf)2. Pseudodisaccharides 37 and 38 were obtained in very poor yield and selectivity along
with other byproducts. In fact, we were unable to fully analyze and characterize compounds 37 and 38.
Scheme 3. Attempted glycosylation of myo-inositol 36

We have established that β-isomer of C(2)-N-substituted-benzylideneamino trichloroacetimidate
donor would not react with alcohol acceptor in the presence of Ni(4-F-PhCN)4(OTf)2,11b and the α-
orientation of the trichloroacetimidate leaving group is important for the ionization and subsequent
glycosylation to occur. Based on these previous studies, we performed a control experiment containing a
mixture of β-isomer of N-phenyl trifluoroacetimidate (23β) and 10 mol% of Ni(4-F-PhCN)4(OTf)2
(Scheme 3) in CH2Cl2 in the absence of an inositol acceptor to determine whether 23β undergoes
isomerization to its corresponding α-isomer (23α) prior to the coupling event. The reaction mixture was
1
monitored by H NMR at 10-minute intervals. The β-isomer 23β, whose anomeric proton resonance
resided at δ 6.05 pm, did not convert to the corresponding α-isomer 23α (anomeric proton resonance at
δ 6.74).17 As the reaction progressed, the β-isomer 23β transformed into the undesired glycal product 39
(anomeric proton resonance at δ 7.28). This appeared to be the major product after 80 min. These
results suggest that N-phenyl trifluoroacetimidate substrates may react via a different pathway compared
to trichloroacetimidate donors under nickel conditions.
Scheme 4. Attempted isomerization of β-isomer to α-isomer.
3. Conclusion
In summary, we have developed an efficient strategy for the preparation of pseudodisaccharides
that are applicable to the synthesis of GPI anchor analogues. We have addressed a major hurdle that is
commonly encountered in the synthesis of these compounds by achieving high α-selectivity in the
glycosylation step to form the major pseudosaccharide moieties. The cationic nickel catalyst, Ni(4-F-

PhCN)4(OTf)2, acts as an effective activating reagent for promoting the coupling of myo-inositols with a
variety of trichloroacetimidate and N-phenyl trifluoroacetimidate donors bearing the C(2)-N-substituted
benzylidene group. The desired 1,2-cis-2-amino pseudosaccharides were obtained in moderate to good
yields and excellent α-selectivity where the best results were obtained from less sterically encumbered
inositols. In addition, both α- and β-isomers of N-phenyl trifluoroacetimidates are viable glycosyl
donors in the nickel-catalyzed reaction, an important finding for increasing the overall efficiency. In
.
contrast, TMSOTf and BF3 OEt2 coupling of myo-inositols with the N-substituted benzylidene donors
provided pseudodisaccharides as a 1:1 mixture of α- and β-isomers. Lastly, the synthesis of the GPI
anchor pseudotrisaccharides highlights the utility of the C(2)-N-benzylidine functionality to serve not
only as a directing group in nickel-catalyzed glycosylation, but also as a stable protecting group under
various conditions.
4. Experimental section
4.1 General Methods
All reactions were performed in oven-dried Schlenk flasks fitted with glass stoppers under a positive
o
pressure of argon. Organic solutions were concentrated by rotary evaporation below 40 C at 25 torr.
Analytical thin-layer chromatography (TLC) was routinely used to monitor the progress of the reactions
and performed using pre-coated glass plates with 230-400 mesh silica gel impregnated with a
fluorescent indicator (250 nm). Visualization was achieved using UV light, iodine, or ceric ammonium
molybdate. Flash chromatography was performed and employed 230-400 mesh silica gel.
Dichloromethane were distilled from calcium hydride under an argon atmosphere at 760 torr. All of the
nickel catalysts were prepared according to our procedure.11b All other chemicals were obtained from
commercial vendors and used without further purification. All proton (1H) nuclear magnetic resonance
spectra were recorded on 400 MHz spectrometer. All carbon (13C) nuclear magnetic resonance spectra

were recorded on 100 MHz NMR spectrometer. Chemical shifts are expressed in parts per million (δ
scale) downfield from tetramethylsilane and are referenced to the residual proton in the NMR solvent
(CDCl3: δ 7.26 ppm, δ 77.00 ppm). Data are presented as follows: chemical shift, multiplicity (s =
singlet, d = doublet, t = triplet, q = quartet, m = multiplet, and brs = broad singlet), integration, and
coupling constant in hertz (Hz). Infrared (IR) spectra were reported in cm-1. High resolution TOF mass
spectrometry utilizing electrospray ionization in positive mode or electron ionization was performed to
confirm the identity of the compounds.
4.2 General Glycosylation with Trichloroacetimidate Donors Using Ni(4-F-PhCN)4(OTf)2
4.21. 3,4,6-Tri-O-Acetyl-2-Deoxy-2-p-Fluorobenzylidene-amino-α-D-Glucopyranosyl-(1→6)-1,2,3,4,5-
Penta-O-Benzyl-myo-Inositol (19).
An oven dried, argon flushed 10 mL Schlenk flask was charged with 15 (83.4 mg, 0.15 mmol,
1.0 equiv), 14 (123 mg, 0.195 mmol, 1.3 equiv), and dichloromethane (1 mL). A preformed solution
of Ni(4-F-PhCN)4(OTf)2, which was generated in situ from Ni(4-F-PhCN)4Cl2 (9.22 mg, 0.015 mmol,
10 mol%) and AgOTf (7.70 mg, 0.03 mmol, 20 mol%) in dichloromethane (0.5 mL) was then added to
the solution.The reaction mixture was stirred at room temperature. When the reaction was complete as
monitored by TLC (hexane/ethyl acetate = 3/1), the reaction mixture was filtered, evaporated, and
purified by flash chromatography on silica gel (hexane/ethyl acetate = 3/1 → 3/2 with 1% Et3N) to give
19 as a yellow semisolid: 104 mg, 78%, 11:1 α:β; [α]24D = 36.7 (c = 1.0, CHCl3); 1H NMR (CDCl3, 400
MHz): δ = 7.93 (s, 1H, N=CH), 7.78 – 7.74 (m, 0.2H, Ar), 7.55 – 7.52 (m, 2H, Ar), 7.43 – 7.27 (m,
16H, Ar), 7.23 – 7.13 (m, 9H, Ar), 7.03 (t, J = 11.0 Hz, 2H, Ar), 6.87 (d, J = 8.5 Hz, 2H, Ar), 5.72 –
5.68 (m, 2H, H-1’, H-4’), 5.24 (d, J = 14.5 Hz, 1H, CH2), 5.04 – 4.99 (m, 2H, CH2), 4.88 (dd, J = 14.5,
5.0 Hz, 2H, CH2), 4.80 (d, J = 8.5 Hz, 2H, CH2), 4.64 (d, J = 8.5 Hz, 2H, CH2), 4.46 (d, J = 13.0 Hz,
1H, CH2), 4.39 – 4.34 (m, 2H, H-3’, H-6a’), 4.24 – 4.18 (m, 2H, H-6b’, H-6), 4.00 (t, J = 3.0 Hz, 1H, H-
2), 3.65 – 3.59 (m, 3H, H-5’, H-1, H-5), 3.51 – 3.42 (m, 3H, H-2’, H-3, H-4), 2.04 (s, 3H, CH3), 1.90 (s,

3H, CH3), 1.84 (s, 3H, CH3). 13C NMR (CDCl3, 100 MHz): δ = 170.6, 169.8, 169.7 (C=O), 162.5
(N=C), 138.7, 138.6, 138.5, 138.3, 137.8, 131.8, 131.8, 130.4, 130.3, 129.1, 128.4, 128.4, 128.3, 128.3,
128.2, 128.1, 128.0, 127.8, 127.7, 127.6, 127.4, 127.0, 126.0, 125.4, 125.3, 115.6, 115.4 (Ar), 99.0 (C-
1’), 82.1 (C-4’), 82.0 (C-3’), 81.2 (C-6’), 80.9 (C-6), 75.9, 75.6, 75.4, 74.3, 73.4 (CH2), 72.9 (C-1), 72.7
(C-5), 71.7 (C-5’), 71.5 (C-2), 68.3 (C-4), 67.1 (C-3), 61.4 (C-2’), 20.8 (CH3), 20.7 (CH3). IR (film, cm-
1): ν = 3063, 3030, 2869, 1744, 1644, 1601, 1508, 1454, 1363, 1227, 1125, 1048, 1021. HRMS (ESI):
calc. for C60H63 NO13F (M+H): 1024.4283; found: 1024.4290.
4.3. General Glycosylation with N-Phenyl Trifluoroacetimidate Donors Using Ni(4-F-PhCN)4(OTf)2
4.31 3,4,6-Tri-O-Acetyl-2-Deoxy-2-o-Trifluoromethylbenzylideneamino-α-D-Glucopyranosyl-(1→6)-1,2-O-
Di-Acetyl-3,4,5-Tri-O-Benzyl-myo-Inositol (29).
A 10 mL oven-dried Schlenk flask was charged with donor 23 (53.1 mg, 0.084 mmol, 1.5 equiv),
inositol acceptor 26 (30.0 mg, 0.056 mmol, 1.0 equiv), and CH2Cl2 (0.5 mL). Then 0.5 mL of preformed
solution of Ni(4-F-PhCN)4(OTf)2, which was generated in situ from a reaction of Ni(4-F-PhCN)4Cl2
(3.4 mg, 0.00561 mmol, 10 mol%) and AgOTf (2.9 mg, 0.0112 mmol, 20 mol%) in CH2Cl2 for 30 min,
o
was added to the solution. The resulting mixture was stirred at 35 C overnight. When the reaction was
complete as monitored by TLC (toluene/acetonitrile = 4/1), the mixture was purified by silica gel flash
chromatography (hexane/ethyl acetate = 5/1 → 3/1 → 3/2 → 1/1 with 1% Et3N) to afford disaccharide
29 as a semisolid. 72%, 10:1 α:β; [α]24D = 67.4 (c = 1.0, CHCl3); 1H NMR (CDCl3, 500 MHz): δ = 8.69
(d, J = 2 Hz, 1H, N=CH), 8.59 (d, J = 8.0 Hz, 1H, Ar), 7.66 (d, J = 7.5 Hz, 1H, Ar), 7.60 (t, J = 7.5 Hz,
1H, Ar), 7.51 (t, J = 7.5 Hz, 1H, Ar) 7.40 – 7.30 (m, 15H, Ar), 5.75 (t, J = 10.0 Hz, 1H, H4’), 5.64 (t, J =
10.0 Hz, 1H, H3’), 5.58 (t, J = 10.0 Hz, 0.1H, H4’), 5.16 – 5.11 (m, 2H, H1’, H1), 5.04 (d, J = 11.0 Hz,
1H, CH2), 4.96 (d, J = 10.5 Hz, 1H, CH2), 4.92-4.88 (m, 2H, CH2), 4.83 (d, J = 12.0 Hz, 1H, CH2),
4.74 (d, J = 12.0 Hz, 1H, CH2), 4.67 (d, J = 11.0, 1H, H6’), 4.63 (dt, J = 10.5, 2.5 Hz, 1H, H6’), 4.41 (t, J
= 2.5 Hz, 1H, H2), 4.30 (t, J = 10.0 Hz, 1H, H6), 3.93 (dd, J = 12.5, 3.0 Hz, 1H, H5), 3.70 (dd, J = 10.0,
3.5 Hz, 1H, H5’), 3.64 (dd, J = 12.5, 2.0 Hz, 1H, H3), 3.57 – 3.55 (m, 2H, H4, H2’), 2.06 (s, 3H, CH3),

2.04 (s, 3H, CH3), 1.91 (s, 3H, CH3), 1.86 (s, 3H, CH3), 1.76 (s, 3H, CH3). 13C NMR (CDCl3, 125
MHz): δ = 170.6, 170.0, 169.9, 169.7, 169.1 (C=O), 160.8 (N=C), 132.7, 130.5, 130.2, 128.6, 128.5,
128.4, 128.2, 128.1, 128.0, 127.9, 127.9, 127.7, 127.6, 127.4, 127.2 (Ar), 125.1, 125.0 (CF3), 99.5 (C-
1’), 81.7 (C-4’), 80.7 (C-3’), 78.6 (C-1), 75.9 (C-2), 75.4 (C-6’), 73.6, 73.5, 72.8 (CH2), 72.1 (C-6), 72.0
(C-5’), 70.8 (C-5), 68.6 (C-4), 67.7 (C-3), 61.4 (C-2’), 29.7, 20.8, 20.4 (CH3). IR (film, cm-1): ν = 3032,
2952, 2926, 2859, 1753, 1643, 1455, 1367, 1315, 1239, 1123, 1044. HRMS (ESI): calc. for C51H55
NO15F3 (M+H): 978.3524; found: 978.3549.
4.4. Preparation of 2,3,4,6-Tetra-O-Benzyl-α-D-Mannopyranosyl-(1→4)-3,6-Di-O-Acetyl-2-Deoxy-2-o-
Trifluoromethylbenzylideneamino-α-D-Glucopyranosyl-(1→6)-1,2-O-Di-Acetyl-3,4,5-Tri-O-Benzyl-myo-
Inositol (35).
A 10 mL oven-dried Schlenk flask was charged with donor 34 (10.0 mg, 0.015 mmol, 2.0 equiv),
pseudodisaccharide acceptor 33 (7.0 mg, 0.0075 mmol, 1.0 equiv), crushed 4 Å molecular sieves (10
mg), and CH2Cl2 (0.5 mL). The reaction mixture was stirred for 1 h at room temperature. The mixture
o
was cooled to 0 C and TMSOTf (0.27 μL, 0.0075 mmol, 0.2 equiv.) was added. The reaction was
stirred at 0 oC for 4 h. Triethylamine (0.5mL) was added to quench the reaction. The reaction mixture
was filtered and concentrated. The crude product was purified by flash chromatography on silica gel
(hexane/ethyl acetate = 5/1 → 3/1 → 1/1 with 1% Et3N) to afford pseudotrisaccharide 35 (6.1 mg, 56%)
1
as a yellow oil. H NMR (CDCl3, 500 MHz): δ = 8.64 (d, J = 2.5 Hz, 1H, N=CH), 8.57 (d, J = 8.0 Hz,
1H, Ar), 7.65 (d, J = 7.5 Hz, 1H, Ar), 7.59 (t, 7.5 Hz, 1H, Ar), 7.51 (t, J = 8.0 Hz, 1H, Ar), 7.37 – 7.24
(m, 40H, Ar), 5.74 – 5.69 (m, 2H, H-1’, H-3’), 5.11 (d, J = 2.0 Hz, 1H, CH2), 5.08 (d, J = 4.0 Hz, 1H,
CH2) 5.05 – 4.86 (m, 6H, CH2), 4.78 – 4.77 (m, 3H, CH2, H-1”), 4.70 – 4.64 (m, 5H, CH2, H-1), 4.51 –
4.46 (m, 3H, CH2, H-6’), 4.38 (t, J = 2.0 Hz, 1H, H-2), 4.30 (t, J = 9.5 Hz, 1H, H-4’), 4.15 (t, J = 9.5
Hz, 1H, H-6), 4.02 (dd, J = 12.5, 2.0 Hz, 1H, H6’), 3.91 (t, J = 9.5 Hz, 1H, H4”), 3.87 – 3.85 (m, 2H, H6’,
H3”), 3.65 (d, J = 7.5 Hz, 1H, H5), 3.58 – 3.53 (m, 4H, H2”, H3, H4, H6” ), 3.46 – 3.43 (m, 2H, H2’, H5’),
2.02 (s, 3H, CH3), 1.83 (s, 3H, CH3), 1.75 (s, 3H, CH3), 1.72 (s, 3H, CH3). 13C NMR (CDCl3, 125

MHz): δ = 170.5, 169.9, 169.1, 169.0 (C=O), 160.1 (N=C), 138.6, 138.5, 138.5, 138.5, 138.4, 138.3,
137.4, 133.1, 132.8, 130.9, 130.5, 130.3, 128.8, 128.7, 128.4, 128.4, 128.3, 128.3, 128.3, 128.2, 128.0,
128.0, 127.9, 127.8, 127.8, 127.7, 127.6, 127.5, 127.5, 127.4, 127.4, 127.4, 127.3 (Ar), 125.0, 125.0
(CF3), 100.9 (C-1’), 99.4 (C-1”), 81.5 (C-3’), 80.6 (C-1), 79.5 (C-2), 78.6 (C-4’), 76.2 (C-6’), 75.9 (C-
6), 75.7, 75.3, 74.4, 73.5, 73.4, 73.2, 73.2 (CH2), 73.0 (C-5’), 72.8 (C-2”), 72.1 (C-3), 72.0 (C-3”), 71.9
(C-5), 70.6 (C-4”), 68.7 (C-5”), 68.6 (C-4), 68.2 (C-6”), 62.8 (C-2’), 38.7, 30.4, 29.7, 28.9, 26.5, 23.8,
23.0, 22.7, 20.9, 20.8, 20.6, 20.4 (CH3). IR (film, cm-1): ν = 3088, 3066, 3033, 2928, 2854, 1752, 1497,
1455, 1367, 1315, 1238, 1224, 1163, 1038. HRMS (ESI): calc. for C83H87NO19F3 (M+H) 1458.5824;
found: 1458.5841.
Acknowledgements
We would like to thank Ms. Kathleen White for preparation of imidate donor 24 and inositol 25. M.S.M
thanks the Graduate College for a Summer Research Fellowship. Funding of this work by the University
of Iowa and National Science Foundation (CHEM 1106082) is gratefully acknowledged.
Supporting data
Supplementary data associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/
References
1 Goel, M.; Azev, V. N.; d’Alarcao, M. Future Med. Chem. 2010, 23, 95.
2
(a) Nosjean, O.; Briolay A.; Roux B. Biochim. Biophys. Acta. 1997, 1331, 153. (b) Chesebro, B.;
Trifilo, M.; Race, R.; Meade-White, K.; Teng, C.; LaCasse, R.; Raymond, L.; Favara, C.; Baron, G.;
Priola, S.; Caughey, B.; Masliah, E.; Oldstone, M. Science, 2005, 308, 1435.
3 M. Low, D. C. Hoessli and S. Ilangumaran, Eds; 1999, pp1-14, Landes Company, Austin, TX.
4 (a) van den Berg, C. W.; Cinek, T.; Hallett, M. B.; Horejsi, V.; Morgan, B. P. J. Cell Biol. 1995, 131,
669. (b) Zhang, F.; Schmidt, W. G.; Hou, T.; Williams, A. F.; Jacobson, K. Proc. Natl. Acad. Sci.
U.S.A., 1992, 89, 5231.

5 Representative examples of GPI analogues: (a) Paulick, M. G.; Wise, A. R.; Forstner, M. B.; Groves,
J. T.; Bertozzi, C. R. J. Am. Chem. Soc. 2007, 129, 11543. (b) Paulick, M. G.; Forstner, M. B.; Groves J.
T.; Bertozzi, C. R. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 20332. (c) Swarts, B. M.; Guo, Z. Chem.
Sci., 2011, 2, 342. (d) Tsai, Y-H.; Liu X.; Seeberger, P. H. Angew. Chem. Int. Ed., 2012, 51, 11438.
6
Representative examples of the syntheses of GPI anchors: (a) Murakata, C.; Ogawa, T. Carb. Res.
1992, 235, 95. (b) Mayer, T. G.; Kratzer, B.; Schmidt, R. R. Angew. Chem. Int. Ed. 1994, 33, 2177. (c)
Lu, J.; Jayaprakash, K. N.; Schlueter, U.; Fraser-Reid, B. J. Am. Chem. Soc. 2004, 126, 7540. (d)
Baeschlin, D. K.; Chaperon, A. R.; Green, L. G.; Hahn, M. G.; Ince, S. J.; Ley, S. V. Chem. Eur. J.
2000, 6, 172. (e) Schofield, L.; Hewitt, M. C.; Evans, K.; Siomos, M-A.; Seeberger, P. H. Nature 2002,
418, 785. (f) Liu, X.; Kwon, Y-U.; Seeberger, P. H. J. Am. Chem. Soc. 2005, 127, 5004. (g). Xue, J.;
Guo, Z. J. Am. Chem. Soc. 2003, 125, 16334. (h) Xue, J.; Shao, N.; Guo, Z. J. Org. Chem. 2003, 68,
4020. (i) Wu, X.; Guo, Z. Org. Lett. 2007, 9, 4311. (j) Swarts, B. M.; Guo, Z. J. Am. Chem. Soc. 2010,
132, 6648. (l) Srinivas, B.; Swarts, B. M. Chem. Eur. J. 2012, 18, 1194. (m) Tsai, Y.-H.; Goetze, S.;
Vilotijevic, I.; Grube, M.; Silva, D. V.; Seeberger, P. H. Chem. Sci., 2013, 4, 468. (n) Yashunsky, D. V.,
Borodkin, V. S., Ferguson, M. A. J., Nikolaev, A.V. Angew Chem Int Ed. 2006, 45, 468–474.
7 For review of the syntheses and characterizations of GPI anchors, see: (a) Guo, Z.; Bishop, L. Eur. J.
Org. Chem. 2004, 3585. (b). Swarts, B. M.; Guo, Z. Adv. Carbohydr. Chem. Biochem. 2012, 67, 137.
(c) Homans, S. W.; Ferguson, M. A. J.; Dwek, R. A.; Rademacher, T. W.; Anand, R.; Williams, A. F.
Nature, 1988, 333, 269.
8 (a) Knapp, S.; Gonzalez, S.; Myers, D. S.; Eckman, L. L.; Bewley, C. A. Org. Lett. 2002, 4, 4337. (b)
Nicholas, G. M.; Eckman, L. L.; Kovac, P.; Otero-Quintero, S.; Bewley, C. A. Bioorg. Med. Chem.
2003, 11, 2641. (c) Knapp, S.; Amorelli, B.; Darout, E.; Ventocilla, C. C.; Goldman, L. M.; Huhn, R.
A.; Minnihan, E. C. J. Carbohydr. Chem. 2005, 24, 103. (d) Metaferia, B. B.; Fetterolf, B. J.; Shazad-ul-
Hussan, S.; Moravec, M.; Smith, J. A.; Ray, S.; Gutierrez-Lugo, M.-T.; Bewley, C. A.; J. Med. Chem.
2007, 50, 6326. (e) Rawat, M.; Johnson, C.; Cadiz, V.; Av-Gay, Y. Biochem. Biophys. Res. Commun.

2007, 63, 71. (f) Slattegard, R.; Gammon, D. W.; Oscarson, S. Carbohydr. Res. 2007, 342, 1943. (g)
Metaferia, B. B.; Ray, S.; Smith, J. A.; Bewley, C. A. Bioorg. Med. Chem. Lett. 2007, 17, 444. (h)
Stewart, M. J. G.; Jothivasan, V. K.; Rowan, A. S.; Wagg, J.; Hamilton, C. J. Org. Biomol. Chem. 2008,
6, 385. (i) Lamprecht, D. A.; Muneri, N. O.; Eastwood, H.; Naidoo, K. J.; Strauss, E.; Jardine, A. Org.
Biomol. Chem. 2012, 10, 5278,
9
(a) Guo, Z.; Bishop, L. Eur. J. Org. Chem. 2004, 3585. (b) Lopez-Prados, J.; Martin-Lomas, M. J.
Carbohydr. Chem. 2005, 24, 393. (c) Conrad, R. M.; Grogan, M. J.; Bertozzi, C. R. Org. Lett. 2002, 4,
1359. (d) Yu, F.; Guo, Z. Bioorg. Med. Chem. Lett. 2009, 3852.
10 Ferrier, R. J.; Middleton, S. Chem. Rev. 1993, 93, 2779.
11
(a) Mensah, E. N.; Nguyen, H. M. J. Am. Chem. Soc. 2009, 131, 8778. (b) Mensah, E. N.; Yu, F.;
Nguyen, H. M. J. Am. Chem. Soc. 2010, 132, 14288. (c) Yu, F.; H. M. Nguyen, J. Org. Chem. 2012,
77, 7330. (d) McConnell, M. S.; Yu, F.; Nguyen, H. M. Chem. Comm. 2013, 49, 4313.
12 (a) Cottaz, S.; Brimacombe, J. S.; Ferguson, M. A. J. J. Chem. Soc., Perkin. Trans. 1, 1993, 2945. (b)
Martin, S. F.; Josey, J. A.; Wong, Y.-L.; Dean, D. W. J. Org. Chem. 1994, 59, 4805. (c) Roemer, S.;
Stadler, C.; Rudolf, M. T.; Jastorff, B.; Schultz, C. J. Chem. Soc., Perkin. Trans. 1, 1996, 1683.
13 (a) Kornienko, A.; Turner, D. I.; Jaworek, C. H.; d’Alarcao, M. Tetrahedron: Asymmetry, 1998, 9,
2783. (b) Anikumar, G. N.; Jia, Z. J.; Kraehmer, R.; Fraser-Reid, B. J. Chem. Soc., Perkin. Trans. 1,
1999, 3591. (c) Saikam, V.; Raghupathy, R.; Yadav, M.; Gannedi, V.; Singh, P. P.; Qazi, N. A.; Sawant,
S. D.; Vishwakarma, R. A. Tetrahedron Lett. 2011, 52, 4277.
14
Representative examples of glycosyl N-phenyl trifluoroacetimidate donors: (a) Yu, B.; Tao, H.
Tetrahedron. Lett. 2001, 42, 2405. (b) Cai, S.; Yu, B. Org. Lett. 2003, 5, 3827. (c) Huchel, U.; Tiwari,
P.; Schmidt, R. R. J. Carbohydr. Chem. 2010, 29, 61.
15 (a) Schmidt, R. R.; Michel, J. Angew. Chem. Int. Ed. 1980, 19, 731. (b) Schmidt, R. R.; Michel, J. J.
Carbohydr. Chem. 1985, 4, 141. (c) Zimmermann, P.; Bommer, R.; Bär, T.; Schmidt, R. R. J.
Carbohydr. Chem. 1988, 7, 435.

16 (a) Schmidt, R. R. Angew. Chem. Int. Ed. 1986, 25, 212. (b) Schmidt, R. R.; Behrendt, M.; Toepfer,
A. Synlett 1990, 694. (c) Schaubach, R.; Hemberger, J.; Kinzy, W. Liebigs. Ann. Chem. 1991, 607. (d)
Paulsen, H.; Wilkens, R.; Reck, F.; Brockhausen, I. Liebigs. Ann. Chem. 1992, 1303. (e) Kulkarni, S. S.;
Hung, S.-C. Lett. Org. Chem. 2005, 2, 670.
17 See the supporting information for 1H NM spectral analysis.

Research highlights
• Ni(4-F-PhCN)4(OTf)2 is an effective catalyst in forming α-linked glycosidic bonds.
• A comparison of Lewis acids with the Ni catalyst is discussed.
• The scope and limitations of Ni(4-F-PhCN)4(OTf)2 are examined.
• Two routes for the stereoselective synthesis of GPI anchor analogs are provided.