Synthesis of α-galactosyl ceramide analogues with an α-triazole at the anomeric carbon

Article abstract of DOI:10.1016/j.tet.2014.03.029

The synthesis of 1,2,3-triazole containing analogues of α-GalCer and galacturonic acid containing Sphingomonous cell wall antigens is described. Anomerisation was used to provide the required α-glycosyl azide precursor. Copper azide-alkyne cycloaddition (

Full text of DOI:10.1016/j.tet.2014.03.029

Tetrahedron 70 (2014) 3191e3196
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Tetrahedron
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Synthesis of a-galactosyl ceramide analogues with an a-triazole
at the anomeric carbon
*
Anthony W. McDonagh, Paul V. Murphy
School of Chemistry, National University of Ireland Galway, University Road, Galway, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of 1,2,3-triazole containing analogues of
Sphingomonous cell wall antigens is described. Anomerisation was used to provide the required
cosyl azide precursor. Copper azideealkyne cycloaddition (CuAAC) generated the -triazole linkage.
a
-GalCer and galacturonic acid containing
Received 31 December 2013
Received in revised form 25 February 2014
Accepted 11 March 2014
a-gly-
a
Ó 2014 Elsevier Ltd. All rights reserved.
Available online 16 March 2014
Keywords:
Glycolipid
Anomerisation
Glycosyl azide
CuAAC
1. Introduction
assist with the alleviation of autoimmune diseases. The Th1 and
Th2 cytokines tend to inhibit each other’s biological functions and
The
a
-galactosyl ceramide (
a
-GalCer, KRN7000) 1 and several
a
-GalCer stimulates the production of high levels of these cyto-
kines. However, there is a lack of discrepancy between the Th1 and
Th2 response to -GalCer and many glycolipid antigens have been
other structurally related bacterial glycolipids, such as the glucur-
onic acid containing 2 interact with natural killer T (NKT) cells
when bound to the glycoprotein CD1d (Fig. 1).1,2 This recognition
event promotes an immune response leading to the production of T
a
synthesised in efforts to generate bias. Structural modifications
investigated to date have included varying of the sugar moiety, as
well as the polar portion of the ceramide, the lipid chain and the
nature and configuration of the anomeric linkage. Some analogues
have shown promising results. Wong and co-workers have in-
troduced a fluorinated biaryl ether derivative 3, which showed
enhanced Th1 cytokine production.4 Glycosidic bond modifications
have been investigated for reasons, which include limiting the
degradation of glycolipid antigens by glycosidases, and with a view
to investigating whether such derivatives can display bias towards
the production of the Th1 or Th2 cytokines. Modifications at the
anomeric position have included synthesis of S-, and C-glycolipids
and oxime derivatives. There is continuing interest in the synthesis
of analogues.5
helper 1 (Th1) and T helper 2 (Th2) cytokines, such as interferon-
g
(IFN-g
) and interleukin 4 (IL-4).3 The production of Th1 cytokines
assists against various types of infection, whereas Th2 cytokines
Glycosyl triazoles have been of increased interest in recent years
with such neoglycoconjugates being evaluated as lectin binding
agents.6 Despite this research, variants of the glycosphingolipids,
which have an
a-1,2,3-triazole linkage at the anomeric position
(glycosyl triazole) have not been synthesised to date and they
would be of interest to prepare. While glycosyl azides have been
used as intermediates in preparation of carbohydrate derivatives,
Fig. 1. Glycosphingolipid antigens 1e3.
work has focused mostly on
vestigations using -glycosyl azides to date. In the case of these
immunostimulatory glycolipids, having the -configuration at the
b-azides with there being few in-
a
* Corresponding author. Fax: þ353 91 495576; e-mail address: paul.v.murphy@
a
nuigalway.ie (P.V. Murphy).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.029

3192
A.W. McDonagh, P.V. Murphy / Tetrahedron 70 (2014) 3191e3196
anomeric carbon seems to be very important. The insertion of
a triazole between the anomeric carbon and the carbon atom ad-
jacent to the lipid nitrogen atom alters the spatial orientation be-
tween the sphingolipid and the saccharide. A simple molecular
modelling comparison between 2 and 5 indicated that the distance
between the carbon adjacent to the carbon atom adjacent to the
ꢀ
lipid nitrogen and the anomeric carbon increases by w1.2 A. The
triazole atoms potentially have interactions with the CD1d re-
ceptor. We describe herein the preparation of the galacturonic acid
and galactose derivatives 4 and 5.
2. Results and discussion
2.1. Synthesis
The retrosynthetic analysis of 4 and 5 is shown in Scheme 1. It
was envisaged that the 1,4-triazole glycolipid 4 would be generated
by the copper azideealkyne cycloaddition reaction (CuAAC)7 be-
tween
be generated from aldehyde 9. We envisaged that the anomerisa-
tion of the -azide 8 to give the required -azide precursor 6.
a
-glycosyl azide 68 and alkyne 7. In turn, the alkyne 7 would
Scheme 2. Synthesis of alkyne 7.
b
a
Scheme 3. Synthesis of a-azides 6 and 17.
case the higher amount of SnCl4 was needed in order to ensure full
conversion of 16 to glycosyl azide. This glycosidation provided
a mixture of 4:1 mixture of anomers 6 and 8, which could not be
separated. Lewis acids such SnCl4 and TiCl4 have been shown to
promote chelate induced anomerisation in uronic acid O-, S- and N3
glycoside derivatives and these reactions can proceed in high yield
and selectivity for the a-anomer. Coordination of the pyranose ring
oxygen and the C-5 carbonyl to the Lewis acid increases the
anomerisation rate, promoting endocyclic cleavage leading to the
Scheme 1. Retrosynthetic analysis of glycolipids with an a-triazole.
The synthesis began with the preparation of 7 (Scheme 2). The
pseudoephedrine chiral auxiliary 10 was used as described pre-
viously for the preparation of the aldehyde 9.9 The Ohir-
aeBestmann modification of the SeyfertheGilbert homologation
has provided mild conditions for the preparation of terminal al-
kynes from aldehydes.10 Reaction of 9 with the OhiraeBestmann
reagent 11 provided the alkyne 12 in 87% yield. Treatment of 12
with formic acid11 for 2 h removed both the oxazolidine and Boc
protecting groups and gave the sphinganine 13, which was im-
mediately reacted with succinate 1412 to give the desired glycolipid
precursor 7. Overall the lipid 7 was obtained in nine steps from the
glycinamide 10.
more thermodynamically favoured
Hence the formation of the -azide as the major anomer is due to
Sn(IV) promoted anomerisation of the initially formed
-azide 8.8
-azide, the
ratio in
a-anomer in high selectivity.
a
b
In order to further increase the proportion of the
a
mixture was treated with TiCl4 (2.5 fold excess) as the
a:b
such anomerisation reactions can be influenced by the concentra-
tion of TiCl4. The effect of TiCl4 on anomerisation ratio can be
explained by coordination of this more active Lewis acid to the
anomeric azide, increasing the electron withdrawing nature of the
anomeric substituent and thus enhancing the anomeric effect. The
The synthesis of
a-glycosyl azide 6 was next carried out
(Scheme 3) by a procedure modified from that in the recent liter-
ature.8 Firstly, the methyl ester 16 was prepared in two steps from
galacturonic acid 15 as previously described.8 Next the introduction
of the azide at the anomeric centre using SnCl4 (3 equiv) and TMSN3
(2.5 equiv)13 was investigated in order to try to effect glycosidation
and anomerisation in one pot. The exchange of the acetate for azide
can usually be effected in the presence of 0.5 equiv of SnCl4. In this
a:b ratio was not just dependent on TiCl4 concentration but also on
temperature and the
a
-selectivity was found to be higher at ꢀ15 ꢁC
than at room temperature. Next, the selective cleavage of methyl
ester 6 to its carboxylic acid derivative was achieved by heating
with LiI in EtOAc at reflux.14 Chemoselective reduction of the acid

A.W. McDonagh, P.V. Murphy / Tetrahedron 70 (2014) 3191e3196
3193
with BH3$THF followed by acetylation successfully provided the
galactosyl azide 17.15
CDCl3 (
(CD3)2SO (
d
0.0) or CDCl3 (
d
d
77.0), pyridine-d5 (
d
150.0,136.0,124.0) and
39.5) for 13C. 1H NMR signals were assigned with the aid
With the glycosyl azides 6 and 17 in hand the synthesis of the
triazole linkage was then explored. The copper catalysed version of
the Huisgen azideealkyne cycloaddition has been an important
advance in the preparation of 1,2,3-triazoles and this reaction
usually provides the 1,4-isomer in a highly regioselective manner.
The glycolipid 18 was prepared as depicted in Scheme 4. On using
microwave conditions described by Opatz and co-workers, com-
pound 18 was obtained in 65% yield.16 The reaction was highly
selective, giving only the 1,4 isomer. Removal of the protecting
groups from 18 then gave target compound 4. As previously de-
scribed for the deprotection of uronic acid derivatives, the removal
of the protecting groups was achieved using hydroperoxide gen-
erated in n-propanol from sodium propoxide and hydrogen per-
oxide.17 The use of methoxide, which is more basic than peroxide,
can lead to the elimination of acetic acid and the formation of the
undesired saturated compound. The synthesis of the 1,4-triazole
galactose derivative 5 was achieved by a similar sequence from
the azide 17. The CuAAC reaction from 17 provided the triazole in
68% yield and subsequent removal of protecting groups gave 5 in
86% yield.
of COSY and 13C NMR signals were assigned with the aid of DEPT,
gHSQCAD and/or gHMBCAD. Coupling constants are reported in
Hertz. The IR spectra were recorded using thin film with an ATR
attachment. High resolution mass spectra were recorded using
ꢀ
electrospray TOF spectrometry. Silica gel used had a pore size 60 A,
particle size 40e60
methane, methanol, THF and DMF solvents were used as obtained
from a Pure SolvÔ Solvent Purification System. DMA, ethyl acetate
and acetone were used as obtained from commercial suppliers.
Reagents were used as obtained from commercial suppliers.
mm 230e400 mesh particle size. Dichloro-
4.2. (4S,5R)-tert-Butyl-5-heptadecyl-2,2-dimethyl-4-(prop-1-
eny-l)-oxazolidine-3-carboxylate
This alkene precursor to aldehyde 9 was synthesised according
to previously reported procedures detailed in Ref. 9. Analytical
data: IR (film) cmꢀ1: 2923, 2854, 1698, 1456, 1383, 1375, 1364, 1251,
1178, 1073; 1H NMR (500 MHz, CDCl3, 1:1 mixture of E & Z isomers)
d
5.57 (1H, dq, J 13.1, 6.3, H-2), 5.47 (1H, dq, J 13.1, 6.4), 5.26 (1H, dd, J
8.8, 1.7), 5.23 (1H, dd, J 8.8, 1.7), 4.17 (1H, t, J 6.9), 4.00 (1H, dd, J 9.1,
5.0), 3.89 (2H, q, J 6.2), 1.65 (3H, d, J 1.6, CH3), 1.64 (3H, d, J 1.7, CH3),
1.55 (2H, s), 1.50 (2H, s), 1.44 (5H, s), 1.41 (7H, s), 1.34 (9H, s), 1.18
(51H, s), 0.81 (6H, t, J 6.9, each CH3); 13C NMR (125 MHz, CDCl3)
d
151.9, 129.0, 128.8, 126.6, 126.3, 92.7, 92.3, 79.8, 79.1, 76.8, 62.6,
62.2, 56.6, 31.9, 29.7 (3s), 29.6 (2), 29.5, 29.4, 29.2, 28.5, 27.3, 25.8,
25.6, 24.9, 23.8, 22.7, 17.8, 17.7, 14.1; ESI-HRMS calcd for
C
30H57NO3Na 502.4236, found m/z 502.4235 [MþNa]þ.
4.3. (4S,5R)-tert-Butyl-5-heptadecyl-4-(formyl)-2,2-dimethy-
loxazolidine-3-carboxylate (9)
To a solution of alkene described above (194 mg, 0.41 mmol) in
10:1 acetone/water (3.9 mL) were added, 2,6-lutidine (0.1 mL,
0.82 mmol), 4-methylmorpholine-N-oxide (72 mg, 0.615 mmol) and
a catalytic amount of osmium tetroxide (0.1 mL of 2.5% in t-BuOH,
2 mol %). The solution was stirred vigorously for 2 days. Then
PhI(OAc)2 (264 mg, 0.82 mmol) was added and the mixture stirred
for a further 3 h. The reaction was quenched with aq sodium thio-
sulphate and then extracted into EtOAc (2ꢂ). The combined organic
portions were washed with water, brine, dried over Na2SO4 and the
solvent was removed under reduced pressure. Flash chromatogra-
phy of the residue (petroleum ether/EtOAc 30:1) provided 9 (117 mg,
61%) as a colourless oil; IR (film) cmꢀ1: 2923, 2854, 1738, 1712, 1466,
1366, 1256, 1176, 1112; 1H NMR (500 MHz, 3:2 mixture of rotamers,
Scheme 4. Synthesis of 1,4-triazoles.
the asterisk* denotes the signals of the minor rotamer, CDCl3) d 9.51*
3. Conclusion
(1H, d, J 3.0, H-1), 9.44 (1H, d, J 4.0, H-1), 4.19e4.11 (1H, m, H-3), 3.99
(1H, dd, J 6.6, 3.9, H-2),1.66 (3H, s, CH3),1.60* (3H, s, CH3),1.50 (5H, s,
overlapping signals, CH2 & CH3),1.46* (3H, s, CH3),1.43* (9H, s, t-Bu),
1.33 (9H, s, t-Bu),1.19 (48H, s, each CH2 & CH2*), 0.81 (5H, t, J 6.9, each
To conclude, the synthesis of a-glycolipids based on galactose
and galacturonic acid, and with a triazole at the anomeric position
has been achieved. The route included anomerisation to generate
CH3 & CH3*); 13C NMR (125 MHz, CDCl3)
d 200.2, 200.0* (C]O),
the
to the galactose derivative. Microwave assisted CuAAC from these
-azides led to the generation of the desired triazole linkage.
a-azide of galacturonic acid, which was subsequently converted
152.5*,151.4 (C]O), 94.4, 93.7* (each isopropyl C), 81.1*, 80.8 (each t-
Bu C), 77.2*, 76.4 (CHO), 67.6, 67.5* (CHN), 31.9, 29.8, 29.7 (3s), 29.6,
29.5, 29.4 (3s) (each CH2), 28.3*, 28.3, 27.5*, 26.7, 26.2*, 26.1, 24.8*,
23.8 (each CH3), 22.7 (CH2), 14.1 (CH3); ESI-HRMS calcd for
a
Consequently the evaluation of the immunostimulatory potential
of such glycolipids will be of interest.
C
28H53NO4Na 490.3872, found m/z 490.3889 [MþNa]þ.
4. Experimental section
4.1. General
4.4. (4S,5R)-tert-Butyl-5-heptadecyl-4-(ethynyl)-2,2-
dimethyloxazolidine-3-carboxylate (12)
Under an argon atmosphere, aldehyde 9 (111 mg, 0.24 mmol)
and the OhiraeBestmann reagent 11 (0.1 mL, 0.72 mmol) were
taken up in dry methanol (1.1 mL) and cooled to 0 ꢁC. Potassium
carbonate (133 mg, 0.96 mmol) was added and the reaction mix-
ture was stirred at 0 ꢁC for 1 h, warmed to room temperature and
Optical rotations were determined at the sodium D line at 20 ꢁC.
NMR spectra were recorded at 500 & 600 MHz. Chemical shifts are
reported relative to internal Me4Si in CDCl3 (
d 0.0) or CDCl3 (d 7.26),
pyridine-d5 ( 8.74, 7.58, 7.22), (CD3)2SO (
d
d
2.50) for 1H and Me4Si in

3194
A.W. McDonagh, P.V. Murphy / Tetrahedron 70 (2014) 3191e3196
stirred for a further 16 h. The reaction was diluted with satd NH4Cl
and then extracted into EtOAc (2ꢂ). The combined organic layers
were dried over Na2SO4 and the solvent removed under reduced
pressure. Flash chromatography of the residue (petroleum ether/
4.7. 1,2,3,4-Tetra-O-acetyl-a-D-galactopyranosiduronic acid,
methyl ester (16)
To a stirred solution of HClO4 (220
was added -galacturonic acid monohydrate 15 (10 g, 52 mmol) in
m
L) in Ac2O (57 mL) at 0 ꢁC
EtOAc 30:1) provided the title compound 12 (96 mg, 87%) as
D
20
a colourless oil; [
a
]
þ23 (c 1, CHCl3); IR (film) cmꢀ1: 3313, 2923,
one portion. The reaction was warmed to room temperature and
then stirred for 3 h. The reaction was then re-cooled to 0 ꢁC and
MeOH was added cautiously. After stirring for a further 30 min the
reaction was partitioned between EtOAc and H2O. The aq layer was
extracted into EtOAc (2ꢂ) and the combined organic layers were
washed with water, brine, dried over Na2SO4 and the solvent re-
moved under reduced pressure. The resulting residue was azeo-
troped several times with toluene to remove acetic acid. Once
removed the residue was taken up in DMF (58 mL). Sodium hy-
drogen carbonate (8.3 g, 100 mmol) and iodomethane (8.1 mL,
130 mmol) were added and the solution was stirred overnight. The
reaction was diluted with H2O and extracted into EtOAc. The
combined organic layers were washed with H2O, brine, dried over
NaSO4, filtered and solvent removed under reduced pressure. Flash
chromatography of the residue (petroleum ether/EtOAc 2:1) pro-
vided the title compound 16 (13.5 g, 69% over two steps) as a white
solid; NMR data (1H and 13C) were in good agreement with the
reported literature data;17 Rf 0.18 (petroleum ether/EtOAc 2:1); mp
135e145 ꢁC; IR (film) cmꢀ1: 2966, 1747, 1440, 1371, 1208, 1068, 942;
D
2854, 1704, 1457, 1375, 1365, 1246, 1176, 1142, 1089; 1H NMR
(500 MHz, 2.5:2 rotamer ratio, the asterisk denotes the signals of
the minor rotamer, CDCl3)
d 4.50* (1H, dd, J 5.1, 2.1, H-2), 4.35 (1H,
dd, J 5.1, 2.1, H-2), 3.91e3.86 (2H, m, overlapping signals, H-3* & H-
3), 2.24* (1H, d, J 2.2, H-1), 2.22 (1H, d, J 2.1, H-1), 1.77e1.64 (4H, m),
1.57 (3H, s, CH3), 1.53* (3H, s, CH3), 1.49* (3H, s, CH3), 1.44 (3H, s,
CH3), 1.43* (9H, s, t-Bu), 1.42 (9H, s, t-Bu), 1.19 (60H, s, each CH2
CH2*), 0.81 (6H, t, J 6.9, CH3 & CH3*); 13C NMR (125 MHz, CDCl3)
151.8*, 151.3 (C]O), 93.8, 93.3* (each isopropyl C), 80.8*, 80.2
&
d
(each t-Bu C), 79.9, 79.5* (eC^CH), 76.1, 75.8* (CHO), 72.8*, 72.3
(eC^CH), 52.2, 52.0* (CHN), 31.9, 30.3, 30.1, 29.7 (3s), 29.6, 29.5,
29.4 (2s) (each CH2), 28.4, 27.5*, 26.5, 25.6, 25.5*, 25.3*, 24.4 (each
CH3), 22.7 (CH2), 14.1 (CH3); ESI-HRMS calcd for C29H53NO3Na
486.3923, found m/z 486.3945 [MþNa]þ.
4.5. 2,5-Dioxopyrrolidin-1-yl nonadecanoate (14)
N-Hydroxy-succinimide (0.27 g, 2.34 mmol) and EDC (0.45 g,
2.34 mmol) were added to a solution of nonadecanoic acid (0.7 g,
2.34 mmol) in CH2Cl2 (46 mL). After stirring the mixture overnight,
the solvent was concentrated under reduced pressure and the
resulting residue dissolved in CH2Cl2. The solution was washed
with water, dried over Na2SO4 and solvent removed under reduced
pressure to provide the title compound 14 (0.84 g, 90%) as a white
solid. The compound was used without further purification; 1H
1H NMR (500 MHz, CDCl3)
d 6.52 (1H, d, J 2.6, H-1), 5.84e5.78 (1H,
m, H-4), 5.42e5.36 (2H, overlapping signals, H-2, H-3), 4.75 (1H, d, J
1.4, H-5), 3.77 (3H, s, OMe), 2.16 (3H, s), 2.12 (3H, s), 2.02 (6H, s)
(each OAc); 13C NMR (125 MHz, CDCl3)
d 170.0, 169.6 (2s), 168.4,
166.5 (each C]O), 89.6 (C-1), 70.7 (C-5), 68.6 (C-4), 66.9, 66.0 (C-2
and C-3), 52.8 (OMe), 20.8, 20.6, 20.5 (2s) (each OAc); ESI-HRMS
calcd for C15H20O10Na 399.0903, found m/z 399.0916 [MþNa]þ.
NMR (500 MHz, CDCl3) d 2.83 (4H, s, O]CCH2CH2C]O), 2.60 (2H, t,
J 7.5, CH2C]O), 1.78e1.69 (2H, m, CH2), 1.45e1.35 (2H, m, CH2), 1.25
4.8. 1-Azido-1-deoxy-2,3,4-tri-O-acetyl-D-galactopyranuronic
acid, methyl ester (6 & 8)
(28H, s, each CH2), 0.88 (3H, t, J 6.9, CH3); 13C NMR (125 MHz, CDCl3)
d
169.1, 168.7 (each C]O), 31.9, 31.0, 29.7 (2s), 29.6 (2s), 29.4, 29.1,
28.8, 25.6, 24.6, 22.7 (each CH2), 14.1 (CH3).
Methyl ester 16 (10 g, 26.6 mmol) and trimethylsilyl azide
(8.7 mL, 67 mmol) were taken up in dry CH2Cl2 (100 mL) and cooled
to 0 ꢁC. Tin (IV) chloride (9.4 mL, 80 mmol) was added dropwise.
The resulting solution was warmed to room temperature and stir-
red for 24 h. The mixture was diluted with CH2Cl2 washed with 1 M
KHSO4, satd NaHCO3, water and brine, dried over Na2SO4 and the
solvent was removed under reduced pressure. Flash chromatogra-
phy of the residue (cyclohexane/EtOAc 2:1) provided the title
4.6. N-((3S,4R)-4-Hydroxyhenicos-1-yn-3-yl)nonadecanamide
(7)
Alkyne 12 (90 mg, 0.19 mmol) was taken up in formic acid
(6 mL) and stirred vigorously for 2 h. Toluene (15 mL) was added
and the solvents were removed under reduced pressure. The
resulting residue was taken up in water and basified with solid
NaHCO3, extracted into CH2Cl2, dried over Na2SO4 and solvent re-
moved under reduced pressure to give intermediate amine 13. This
was taken up in CH2Cl2 (6 mL) and DIPEA (0.12 mL, 0.68 mmol) was
added. To this was added a solution of 14 (192 mg, 0.49 mmol) in
CH2Cl2 (3 mL) and the mixture stirred for 24 h. Upon completion
the reaction mixture was diluted with CH2Cl2, washed with satd aq
NaHCO3 and then extracted into CH2Cl2 (2ꢂ). The combined or-
ganic layers were washed with water, brine, dried over Na2SO4 and
the solvent was removed under reduced pressure. Flash chroma-
compound 8 (5.92 g, 62%) as a mixture of anomers (a:b, 4:1); NMR
data for both anomers (1H and 13C) were in good agreement with
the reported literature data;8 IR (film) cmꢀ1: 2959, 2119, 1744, 1439,
1371, 1207, 1129, 1063; 1H NMR (500 MHz, CDCl3)
d
5.76 (1H, d, J 3.9,
), 5.72 (1H, dd, J 3.4, 1.4, H-4 ),
), 5.24 (1H, dd, J 10.7, 3.9, H-2 ), 5.18
), 5.08 (1H, dd, J 10.2, 3.5, H-3 ), 4.76 (1H, d,
), 4.67 (1H, d, J 8.7, H-1 ), 4.39 (1H, d, J 1.4, H-5 ), 3.76
H-1
5.28 (1H, dd, J 10.9, 3.0, H-3
(1H, dd, J 10.4, 8.7, H-2
J 1.6, H-5
a
), 5.75 (1H, dd, J 3.1, 1.6, H-4
a
b
a
a
b
b
a
b
b
(3H, s, OMe), 3.75 (3H, s, OMe), 2.11 (6H, s), 2.10 (3H, s), 2.09 (3H, s),
2.08 (3H, s), 1.99 (3H, s, each OAc); 13C NMR (125 MHz, CDCl3)
tography of the residue (petroleum ether/EtOAc, 4:1) provided the
d
169.9, 169.8, 169.7, 169.6, 169.5, 169.1, 166.6, 165.8 (each C]O),
88.4 (C-1 ), 86.9 (C-1 ), 74.0 (C-5 ), 70.3 (C-3 ), 70.1 (C-5 ), 68.6
(C-4 ), 68.0 (C-4 ), 67.6 (C-2 ), 66.9, 66.7 (C-2 and C-3 ), 52.9
20
title compound 7 (83 mg, 71% over two steps) as a white solid; [
a
]
b
a
b
b
a
a
D
þ5.5 (c 0.8, CHCl3); Rf 0.3 (cyclohexane/EtOAc 3:1); mp 86e90 ꢁC;
a
b
b
a
IR (film) cmꢀ1: 3341 br, 3228, 2917, 2849, 1631, 1532, 1472; 1H NMR
(OMe), 52.8 (OMe), 20.6 (2s), 20.5 (3s), 20.4 (each OAc); ESI-HRMS
(500 MHz, CDCl3)
d
6.07 (1H, d, J 8.5, NH), 4.81 (1H, dt, J 8.5, 2.6, H-
calcd for C13H17N3O9Na 382.0862, found m/z 382.0869 [MþNa]þ.
3), 3.62 (1H, td, J 6.7, 2.8, H-4), 2.30 (1H, d, J 2.4, H-1), 2.20 (2H, t, J
7.7, CH2), 1.67e1.56 (4H, overlapping signals, CH2), 1.53e1.42 (1H,
m, CH(H)), 1.34e1.21 (59H, overlapping signals, CH2), 0.88 (6H, t, J
4.9. 1-Azido-1-deoxy-2,3,4-tri-O-acetyl-a-D-galactopyranur-
onic acid, methyl ester (6)
6.7, CH3); 13C NMR (125 MHz, CDCl3)
d 172.6 (C]O), 79.7 (C^CH),
73.8 (C-4), 73.3 (C^CH), 46.9 (C-3), 36.8, 34.5, 32.1, 29.9 (3s), 29.8,
29.7 (2s), 29.6, 29.5 (2s), 29.4, 25.7 (2s), 22.9 (each CH2), 14.3 (CH3);
ESI-HRMS calcd for C40H78NO2 604.6033, found m/z 604.6025
[MþH]þ.
To a stirred solution of the mixture of anomers 6 and 8 (1.2 g,
3.34 mmol) in dry CH2Cl2 (15 mL) at 0 ꢁC was added 1 M TiCl4 in
CH2Cl2, (8.35 mL) dropwise. The solution was stirred at 0 ꢁC for
10 min and then placed in a fridge freezer at ꢀ15 ꢁC for 48 h. The

A.W. McDonagh, P.V. Murphy / Tetrahedron 70 (2014) 3191e3196
3195
reaction mixture was then diluted with CH2Cl2, washed twice with
satd NaHCO3, water, brine, dried over NaSO4 and solvent removed
under reduced pressure. Flash chromatography of the residue
(petroleum ether/EtOAc 2:1) provided the title compound 6
(987 mg, 82%) as a white foam; NMR data (1H and 13C) were in good
agreement with the reported literature data;8 Rf 0.54 (cyclohexane/
EtOAc 1:1); mp 107e110 ꢁC; IR (film) cmꢀ1: 2959, 2114, 1768, 1744,
solution was diluted with EtOAc and washed with H2O (3ꢂ10 mL).
The organic layer was dried over Na2SO4 and solvent was removed
under reduced pressure. Flash chromatography of the residue (cy-
clohexane/EtOAc 2:1) provided the title compound 18 (15 mg, 65%)
as a white solid; [
a
]
20 þ58 (c 1.3, CHCl3); Rf 0.3 (cyclohexane/EtOAc
1:1); IR (film) cmꢀ1D: 3298 br, 2918, 2850, 1752, 1651, 1467, 1371,
1215, 1072, 720; 1H NMR (500 MHz, CDCl3)
d 7.68 (1H, br s, tri-
1441, 1368, 1250, 1213, 1057; 1H NMR (500 MHz, CDCl3)
d
5.78 (1H,
azoleeH), 6.65 (1H, d, J 7.9, NH), 6.54 (1H, d, J 5.9, H-1), 6.13 (1H, dd, J
10.6, 3.5, H-3), 5.97 (1H, dd, J 3.5, 1.6, H-4), 5.52 (1H, dd, J 10.5, 5.9,
H-2), 5.19 (1H, d, J 1.6, H-5), 5.09 (1H, dd, J 8.0, 3.1, H-10), 3.87 (1H, br
s, H-20), 3.74 (3H, s, OMe), 2.18 (2H, t, J 7.7, CH2), 2.15, 2.02 (3H, s)
(each OAc), 1.91 (1H, br s, OH), 1.84 (3H, s, OAc), 1.67e1.52 (2H,
overlapping signals, CH2), 1.51e1.44 (1H, overlapping signals, CH2),
1.37e1.16 (60H, overlapping signals, each CH2), 0.88 (6H, t, J 6.8,
d, J 3.9, H-1), 5.77 (1H, dd, J 3.0, 1.6, H-4), 5.30 (1H, dd, J 10.8, 3.1, H-
3), 5.26 (1H, dd, J 10.7, 3.9, H-2), 4.78 (1H, d, J 1.5, H-5), 3.77 (3H, s,
OMe), 2.12 (3H, s), 2.11 (3H, s), 2.01 (3H, s) (each OAc); 13C NMR
(125 MHz, CDCl3) d 170.0, 169.7, 169.6, 166.6 (each C]O), 86.0 (C-1),
70.1 (C-5), 68.7 (C-4), 66.9, 66.8 (C-2 and C-3), 52.9 (OMe), 20.6 (2s),
20.5 (each OAc); ESI-HRMS calcd for C15H17N3O9Na 382.0862,
found m/z 382.0864 [MþNa]þ.
each CH3); 13C NMR (125 MHz, CDCl3)
d 172.8, 169.2, 169.5, 169.4,
166.5 (each C]O), 145.0 (triazole, CH]C), 125.6 (triazole CH), 81.7
(C-1), 74.4 (C-20), 72.3 (C-5), 68.5 (C-4), 67.2 (C-3), 66.8 (C-2), 52.8
(OMe), 48.8 (C-10), 36.6, 34.6, 31.9, 29.7 (2s), 29.6 (3S), 29.5 (2s), 29.3
(2s), 25.8, 25.5, 22.7 (each CH2), 20.6, 20.5, 20.2,14.1 (each CH3); ESI-
HRMS calcd for C53H93N4O11 961.6841, found m/z 961.6847 [MꢀH]ꢀ.
4.10. 2,3,4,6-Tetra-O-acetyl-a-D-galactopyranosyl azide (17)
Lithium iodide (1.6 g, 8.3 mmol) was added to a solution of
methyl ester 6 in anhydrous EtOAc and the reaction mixture was
heated at reflux for 16 h. Upon cooling the reaction mixture was
quenched with 10% HCl and the aqueous layer extracted into EtOAc
(2ꢂ). The combined organic portions were washed with satd
Na2S2O3, dried over Na2SO4 and the solvent was removed under
reduced pressure to afford the carboxylic acid intermediate
(397 mg, 83%) as a yellow solid. This compound was used in the next
4.12. N-((1S,2R)-2-Hydroxy-1-(1-(5-(S)-hydroxycarbonyl-
arabinopyranosyl)-1H-1,2,3-triazol-4-yl)nonadecyl)non-
adecanamide (4)
b-L-
The protected lipid 18 (13.6 mg, 14
PrOH (3.4 mL) and H2O2 (0.34 mL of 30% aq solution). To this was
added n-PrONa/n-PrOH (850 L of a 0.1 M solution in n-PrOH,
85 mol) dropwise at a rate of 100 L/h. After addition was com-
mmol) was dissolved in n-
step without further purification; mp 171e173 ꢁC; IR (film) cmꢀ1
3484 (br), 2998, 2121, 1744, 1678, 1619, 1371, 1212, 1122; 1H NMR
(500 MHz, CDCl3) 5.85e5.76 (2H, overlapping signals, H-1 and H-
:
m
d
m
m
4), 5.39e5.10 (3H, overlapping signals, H-2, H-3 and OH), 4.82 (1H, s,
pleted the reaction was stirred for a further 1 h. Water (9 mL) was
added and the solution centrifuged at 15,000 rpm for 15 min. The
supernatant was removed and the precipitate treated a further two
times with water. The precipitate was lyophilised to provide the
title compound 4 (6.6 mg, 57%) as a white solid; 1H NMR (600 MHz,
H-5), 2.12 (6H, s each OAc), 2.00 (3H, s, OAc); 13C NMR (125 MHz,
CDCl3)
68.5 (C-4), 66.8 (C-2 or C-3), 66.7 (C-2 or C-3), 20.6, 20.5, 20.5 (each
OAc); ESI-HRMS calcd for 12H14N3O9 344.0730, found m/z
d 170.1, 169.8, 169.8, 168.8 (each C]O), 86.9 (C-1), 69.8 (C-5),
C
344.0733 [MꢀH]ꢀ. This acid intermediate (100 mg, 0.29 mmol) was
taken up in dry THF (3 mL) and cooled to 0 ꢁC. To this was added
BF3$THF complex (0.9 mL of a 1.0 M solution in THF, 0.9 mmol)
dropwise. The reaction was warmed to room temperature and
stirred overnight. Methanol was added and the solvents were re-
moved under reduced pressure. The crude residue was taken up in
Ac2O (2 mL) and pyridine (2 mL) and stirred for a further 4 h. The
reaction was diluted with EtOAc, washed with 1 M HCl, water, brine,
dried over Na2SO4 and solvent removed under reduced pressure.
Flash chromatography of the residue (petroleum ether/EtOAc 2:1)
provided the title compound 17 (70 mg, 65% over two steps) as
a crystalline solid; NMR data (1H and 13C) were in good agreement
CD3CO2D/DMSO-d6, 60 ꢁC)
d 7.92 (1H, s, triazoleeH), 6.22 (1H, d, J
5.2, H-1), 4.99 (1H, d, J 5.9, H-10), 4.51 (1H, d, J 2.3, H-5), 4.27e4.23
(2H, overlapping signals H-3 & H-4), 4.14 (1H, dd, J 8.7, 5.2, H-2),
3.70 (1H, p, J 4.4, 3.8, H-20), 2.14e2.05 (2H, overlapping signals,
CH2), 1.49e1.41 (2H, overlapping signals, CH2), 1.39e1.31 (1H,
overlapping signals, CH2), 1.16 (61H, s, each CH2), 0.76 (6H, t, J 6.9,
13
each CH3); C NMR (150 MHz, CD3CO2D/DMSO-d6, 60 ꢁC)
d 174.3,
170.9 (each C]O), 146.0 (triazole, CH]C), 126.3 (triazole, CH]C),
85.7 (C-1), 74.6 (C-5), 73.6 (C-20), 70.6 (C-3 or C-4), 70.2 (C-3 or C-4),
68.5 (C-2), 51.3 (C-10), 36.7, 34.4, 32.5, 30.2 (4s), 30.1, 26.5, 26.2, 23.2
(each CH2), 14.6 (CH3); ESI-HRMS calcd for C46H85N4O8 821.6367,
found m/z 821.6379 [MꢀH]ꢀ.
with the reported literature data;15
[a]
20 þ180 (c 1.0, CHCl3); Rf 0.3
D
(cyclohexane/EtOAc 2:1); mp 77e78 ꢁC; IR (film) cmꢀ1: 2981, 2118,
4.13. N-((1S,2R)-2-Hydroxy-1-(1-(a-D-galactopyranosyl)-1H-
1,2,3-triazol-4-yl)nonadecyl)nonadecanamide (5)
1744, 1373, 1207, 1122, 1064; 1H NMR (500 MHz, CDCl3)
d
5.66 (1H,
d, J 4.0, H-1), 5.46 (1H, dd, J 3.2, 1.3, H-4), 5.25 (1H, dd, J 10.8, 3.1, H-
3), 5.20 (1H, dd, J 10.7, 4.1, H-2), 4.36 (1H, td, J 6.9, 1.2, H-5),
4.16e4.09 (2H, overlapping signals, H-6a & H-6b), 2.14 (3H, s), 2.11
(3H, s), 2.06 (3H, s), 1.99 (3H, s) (each OAc); 13C NMR (125 MHz,
Alkyne 7 (10 mg, 0.017 mmol) was dissolved in N,N-dime-
thylformamide (0.5 mL). After addition of azide 17 (9.3 mg,
0.025 mmol), copper(I) iodide (1 mg, 0.005 mmol) and N,N-diiso-
CDCl3)
d
170.4, 170.1, 170.0, 169.8 (each C]O), 86.7 (C-1), 68.5 (C-5),
propyl-ethylamine (9 mL), the reaction mixture was placed in
67.6 (C-4), 67.4, 67.2 (C-3 & C-2), 20.6 (4s, each OAc); ESI-HRMS
a microwave reactor for 60 min, at 80 ꢁC and 120 W. The resulting
solution was diluted with EtOAc and washed with H2O (3ꢂ10 mL).
The organic layer was dried over Na2SO4 and solvent removed
under reduced pressure. Flash chromatography of the residue (cy-
clohexane/EtOAc 2:1) provided the protected glycolipid (11 mg,
calcd for C14H19N3O9Na 396.1019, found m/z 396.1036 [MþNa]þ.
4.11. N-((1S,2R)-2-Hydroxy-1-(1-(5-(S)-methoxycarbonyl-
2,3,4-tri-O-acetyl-b-L-arabinopyranosyl)-1H-1,2,3-triazol-4-yl)
nonadecyl)nonadecanamide (18)
68%) as a white solid; [
a
]
20 þ45 (c 0.9, CHCl3); Rf 0.4 (cyclohexane/
D
EtOAc 1:1); IR (film) cmꢀ1: 3337 br, 2917, 2850, 1747, 1631, 1530,
Alkyne 7 (15 mg, 0.025 mmol) was dissolved in N,N-dime-
1371, 1217, 1070, 915, 729; 1H NMR (500 MHz, CDCl3)
d 7.65 (1H, s,
thylformamide (1.5 mL). After addition of azide
0.038 mmol), copper(I) iodide (1 mg, 0.005 mmol) and N,N-diiso-
propyl-ethylamine (9 L), the reaction mixture was placed in a mi-
crowave reactor for 60 min, at 80 ꢁC and 120 W. The resulting
6
(14 mg,
triazoleeH), 6.67 (1H, d, J 8.0, NH), 6.38 (1H, d, J 6.0, H-1), 6.10 (1H,
dd, J 10.7, 3.5, H-3), 5.66 (1H, dd, J 3.4, 1.2, H-4), 5.48 (1H, dd, J 10.7,
6.0, H-2), 5.08 (1H, dd, J 8.0, 3.2, H-10), 4.69 (1H, td, J 6.6, 1.3, H-5),
4.11 (1H, dd, J 11.4, 6.8, H-6a), 4.05 (1H, dd, J 11.4, 6.4, H-6b), 3.87
m

3196
A.W. McDonagh, P.V. Murphy / Tetrahedron 70 (2014) 3191e3196
(1H, ddt, J 9.8, 7.1, 4.1, H-20), 3.49 (1H, d, J 10.1, OH), 2.20e2.16 (5H,
overlapping signals, CH2 & OAc), 2.01 (3H, s), 2.00 (3H, s), 1.83 (3H,
s, each OAc), 1.59 (2H, s, CH2), 1.51e1.45 (1H, m, CH(H)), 1.33e1.18
References and notes
1. Mattner, J.; DeBord, K. L.; Ismail, N.; Goff, R. D.; Cantu, C.; Zhou, D.; Saint-Me-
zard, P.; Wang, V.; Gao, Y.; Hoebe, K.; Schneewind, O.; Walker, D.; Beutler, B.;
Teyton, L.; Savage, P.; Bendelac, A. Nature 2005, 434, 525e529.
2. Kinjo, Y.; Wu, D.; Kim, G.; Xing, G. W.; Poles, M. A.; Ho, D. D.; Tsuji, M.; Ka-
wahara, K.; Wong, C. H.; Kronenberg, M. Nature 2005, 434, 520e525.
3. Kronenberg, M. Annu. Rev. Immunol. 2005, 23, 877e900.
(61H, overlapping signals, each CH2), 0.88 (6H, t, J 6.9, 2ꢂ CH3); 13
C
NMR (125 MHz, CDCl3)
d
172.9,170.3,170.1,170.0,169.5 (each C]O),
144.8 (triazole, CH]C), 125.5 (triazole, CH]C), 81.9 (C-1), 74.4 (C-
20), 70.7 (C-5), 67.6 (C-3), 67.4 (C-4), 67.2 (C-2), 61.1 (C-6), 48.7 (C-
10), 36.6, 34.6, 31.9, 29.7 (3s), 29.6 (3s), 29.5, 29.4, 29.3 (2s), 25.8,
25.5, 22.7 (each CH2), 20.6 (3s), 20.2, 14.1 (each CH3); ESI-HRMS
calcd for C54H95N4O11 975.6997, found m/z 975.7020 [MꢀH]ꢀ. The
4. (a) Lin, K. H.; Liang, J. J.; Huang, W. I.; Lin-Chu, S. Y.; Su, C. Y.; Lee, Y. L.; Jan, J. T.;
Lin, Y. L.; Cheng, Y. S. E.; Wong, C. H. Antimicrob. Agents Chemother. 2010, 54,
4129e4136; (b) Lia, X.; Fujiob, M.; Imamurab, M.; Wub, D.; Vasana, S.; Wong, C.
H.; Hoa, D. D.; Tsujia, M. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 13010e13015.
5. (a) Dere, R. T.; Zhu, X. Org. Lett. 2008, 10, 4641e4644; (b) Blauvelt, M. L.; Khalili,
M.; Jaung, W.; Paulsen, J.; Anderson, A. C.; Wilson, S. B.; Howell, A. R. Bioorg.
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Wang, P. G. Bioorg. Med. Chem. Lett. 2010, 20, 3859e3862.
protected lipid (7 mg, 7.2
H2O2 (30%, 0.12 mL). To this was added n-PrONa (430
solution in n-PrOH, 43 mol) dropwise at a rate of 100
m
mol) was dissolved in n-PrOH (1 mL) and
L of a 0.1 M
L/h. After
m
m
m
the addition was completed the reaction was stirred for a further
1 h. Water (4 mL) was then added and the solution centrifuged at
15,000 rpm for 15 min. The supernatant was removed and the
precipitate treated a further two times with water. The precipitate
was lyophilised to provide the title compound 5 (5 mg, 86%) as
ꢁ
~
ꢁ
6. (a) Perez-Balderas, F.; Ortega-Munoz, M.; Morales-Sanfrutos, J.; Hernandez-
ꢁ
Mateo, F.; Calvo-Flores, F. G.; Calvo-Asín, J. A.; Isac-García, J.; Santoyo-Gonzalez,
F. Org. Lett. 2003, 5, 1951e1954; (b) Morvan, F.; Meyer, A.; Jochum, A.; Sabin, C.;
Chevolot, Y.; Imberty, A.; Praly, J.-P.; Vasseur, J.-J.; Souteyrand, E.; Vidal, S. Bi-
oconjugate Chem. 2007, 18, 1637e1643; (c) Wang, G.-N.; Andre, S.; Gabius, H.-J.;
Murphy, P. V. Org. Biomol. Chem. 2012, 10, 6893e6907; (d) Campo, V. L.; Car-
valho, I.; Da Silva, C. H. T. P.; Schenkman, S.; Hill, L.; Nepogodiev, S. A.; Field, R.
A. Chem. Sci. 2010, 1, 507e514; (e) Papadopoulos, A.; Shiao, T. C.; Roy, R. Mol.
Pharm. 2011, 9, 394e403; (f) Kuijpers, B. H. M.; Groothuys, S.; Keereweer, A. R.;
Quaedflieg, P. J. L. M.; Blaauw, R. H.; van Delft, F. L.; Rutjes, F. P. J. T. Org. Lett.
a white solid; 1H NMR (600 MHz, pyridine-d5)
d 9.01 (1H, d, J 8.9,
NH), 8.71 (1H, s, triazole H), 7.64 (1H, br s, OH), 6.99 (1H, br s, OH),
6.86 (1H, d, J 4.7, H-1), 6.80 (1H, d, J 4.2, OH), 6.54 (2H, br s, J 6.6,
each OH), 6.08 (1H, dd, J 8.8, 5.0, H-10), 5.24e5.14 (2H, m, over-
lapping signals, H-2 & H-3), 4.89 (1H, td, J 5.9, 1.5, H-5), 4.83 (1H, s,
H-4), 4.50 (1H, td, J 7.7, 5.9, 3.4, H-20), 4.47e4.43 (1H, m, H-6a), 4.37
(1H, dt, J 10.8, 5.0, H-6b), 2.50e2.38 (2H, m, CH2), 1.96e1.76 (5H,
overlapping signals, CH2), 1.59 (1H, tdd, J 13.1, 10.6, 9.2, 5.3, CH(H)),
1.33e1.23 (58H, overlapping signals, each CH2), 0.88 (6H, t, J 6.9, 2ꢂ
ꢁ
2004, 6, 3123e3126; (g) Andre, S.; Jarikote, D. V.; Yan, D.; Vincenz, L.; Wang, G.-
N.; Kaltner, H.; Murphy, P. V.; Gabius, H.-J. Bioorg. Med. Chem. Lett. 2012, 22,
313e318.
7. (a) Meldal, M.; Tornoe, C. M. Chem. Rev. 2008, 108, 2952e3015; (b) Kolb, H. C.;
Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004e2021; (c)
Dedola, S.; Nepogodiev, S. A.; Field, R. A. Org. Biomol. Chem. 2007, 5, 1006e1017.
8. Farrell, M.; Zhou, J.; Murphy, P. V. Chem.dEur. J. 2013, 19, 14836e14851.
9. O’Reilly, C.; Murphy, P. V. Org. Lett. 2011, 13, 5168e5171 Analytical data, pre-
viously not reported for 9 is provided in the Experimental section.
10. (a) Ohira, S. Synth. Commun. 1989, 19, 561e564; (b) Mueller, S.; Liepold, B.; Roth,
G. J.; Bestmann, H. J. Synlett 1996, 521e522.
11. Long, R. M.; Lagisetti, C.; Coates, R. M.; Croteau, R. B. Arch. Biochem. Biophys.
2008, 477, 384e389.
12. Howarth, N. M.; Lindsell, W. E.; Murray, E.; Preston, P. N. Tetrahedron 2005, 61,
8875e8887.
CH3); 13C NMR (150 MHz, pyridine-d5)
d 172.7 (C]O), 146.4 (tri-
azole C), 126.3 (triazole, CH), 87.5 (C-1), 77.2 (C-5), 73.8 (C-20), 71.6
(C-2 or C-3), 70.2 (C-4), 69.5 (C-2 or C-3), 62.0 (C-6), 51.8 (C-10),
36.8, 35.1, 32.3, 30.2 (2s), 30.1 (2s), 30.0, 29.9 (2s), 29.8, 26.8, 26.5,
23.1 (each CH2), 14.4 (CH3); ESI-HRMS calcd for C46H87N4O7
807.6575, found m/z 807.6579 [MꢀH]ꢀ.
13. Tosin, M.; Murphy, P. V. Org. Lett. 2002, 4, 3675e3678.
14. Mayato, C.; Dorta, R. L.; Vazquez, J. T. Tetrahedron Lett. 2008, 49, 1396e1398.
15. The spectra of 17 were in good agreement with previously reported data:
Acknowledgements
ꢁ
ꢁ
ꢁ
Capicciotti; Szilagyi, L.; Gyorgydeak, Z. Carbohydr. Res. 1985, 143, 21e41.
16. Wiebe, C.; Schlemmer, C.; Weck, S.; Opatz, T. Chem. Commun. 2011,
9212e9214.
The authors are grateful to NUI Galway (College Scholarship to
A.W.M.), the Irish Research Council (GOIPG/2013/1045 to A.W.M.)
and Science Foundation Ireland (12/IA/1398) for financial support.
17. Vogel, C.; Boye, H.; Kristen, H. J. Prakt. Chem. 1990, 332, 28e36.